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A statical analysis and structural performance of commercial buildings in the Northridge earthquake

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A statical analysis and structural performance of commercial buildings in the Northridge earthquake

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Content A STATICAL ANALYSIS AND STRUCTURAL PERFORMANCE OF COMMERCIAL BUILDINGS IN THE NORTHRIDGE EARTHQUAKE fey Mansour Farazmand A Thesis Presented to the FACULTY OF THE SCHOOL OF ARCHITECTURE UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF BUILDING SCIENCE May 1995 Copyright 1995 Mansour Farazmand UNIVERSITY OF SOUTHERN CALIFORNIA THE SCHOOL OF ARCHITECTURE UNIVERSITY PARK LOS ANGELES, CALIFORNIA 90069-0291 This thesis, written by . ' m P. M j /%■... r. f; < \ m s . under the direction of h Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The School of Architecture, in partial fulfillment of the require ments for the degree of Date Dean syio/^c,- THESiS COMMITTEE 'T’ jCa Z-, ACKNOW LEDGM ENTS I would like to express my deepest appreciation to my thesis advisor, Mr. Goetz Schierle, Professor of Master of Building Science at U.S.C. His strong support and clear guidance for the development of my thesis would not have originated without his interest and ideas in my work. Marc Schiler, Professor and Director of Master of Building Science at U.S.C. I am grateful for his precious instructions and encouragement throughout the development of my thesis. Dimitry Vergun, Professor of Architecture at U.S.C., for his plentiful experiences to lead me throughout the entire experiment. Sincere thanks to Mr. Carl Deppe and Karan Panera of the Department of Building and Safety, Los Angeles for their help and patience in providing valuable information. Sincere thanks to Mr. Richard Quacqarini of the Assessors office, Los Angeles for providing valuable information. Finally, many thanks to Mr. James Chin for his patience and providing information on seismology. HYPOTHESIS and ABSTRACT A statical analysis and performance of commercial buildings, in earthquakes, will provide data for selecting location and structural systems in the design process. A case study will be made on the Northridge earthquake based on the geological and statical conditions. This work will represent part of a continuing study on structural behavior and their damage pattern in earthquakes. As a result parts of the study on the Northridge earthquake will include the damage rates and the causes due to its surroundings. These conditions will include the geotechnical data, ground motion, age of the damaged buildings and the percent in building damage. In addition to the statical data, informative maps and graphs will give the relations and overview of the overall damage. From this the data collected and studied will provide future predictions and approximate conclusions of further preventions on building damage caused by the Nothridge earthquake. TABLE OF CONTENTS PAGE Acknowledgments ii Hypothesis and Thesis iii List of Figures vi List of Tables viii Chapter 1: CAUSES FOR EARTHQUAKES Introduction 1 Earthquakes at and within plate boundaries 2 Fault Lines 2 Earthquake waves 5 Body waves 6 Surface waves 7 Measurement of earthquake strength 7 The Magnitude scale 8 The Intensity scale 9 Chapter 2: SEISMIC DESIGN AND FORCES INDUCED ON BUILDINGS Introduction 11 Ground motion 12 Time Period 13 Loads Induced on Structures 16 Special Building Designs to Resist Lateral Forces 19 Moment Resi sting Frames 19 Braced Frames 20 Shear Walls 22 Base Isolation 23 Design for Seismic Forces 24 Chapter 3: BUILDING FORMS AND CONFIGURATIONS Introduction 28 General Building Forms 29 Building With Irregular Configurations 29 Vertical Massing in Buildings 30 Multi Mass Buildings 31 Common Configuration Problems 32 Re-entrant Comers 32 Soft Stories 37 Strength and Stiffiiess Variations in Building Perimeters 39 PAGE Chapter 4: EARTHQUAKES IN CALIFORNIA Introduction 41 Energy dissipated in earthquakes 44 Los Angeles City 45 Soil content 46 Water table 48 Northridge Earthquake 49 Location of the fault 50 Ground motion and displacement 52 Ground failure 59 Chapter 5: RESULTS FOR THE STATICAL ANALYSIS ON THE NORTHRIDGE EARTHQUAKE Introduction 60 Source of data for commercial buildings 61 Records for Damaged Buildings 61 Existing commercial buildings 64 Construction type for damaged buildings 66 Types of software used 68 Basic Layout for Mapping 69 Results of Damaged Buildings 71 A Summarized Overview of Results 95 Results for Different Occupancies 108 Damaged Buildings vs. Number of Floors 112 Damage Buildings by Distance From the River 114 CONCLUSION 116 RECOMMENDATION FOR FUTURE STUDIES 119 BIBLIOGRAPHY 120 V List of Figures: Figure 1-1 Creep movement Figure 1-2 Types of fault movement Figure 1-3 Body and surface waves Figure 1-4 Time measurement taken by a seismogram Figure 1-5 Surface wave Figure 2-1 Building under resonance Figure 2-2 Building collapse due to resonance Figure 2-3 Horizontal and vertical loads Figure 2-4 U.S. seismic risk map Figure 2-6 Braced frames Figure 2-7 Shear walls Figure 2-8 Base isolator Figure 3-1 Irregular plan configurations Figure 3-2 Stability in a building Figure 3-3 Multi mass building Figure 3-4 Lateral movement for an L-shaped building Figure 3-5 Collapse of re-entrant building L-shaped building Figure 3-6 Independent movement for L-shaped building Figure 3-7 Pounding damage Figure 3-8 Failure mode for a soft story building Figure 3-9 Discontinuous shear walls Figure 310 Tortional movement in a building Figure 4-1 San Andreas fault Figure 4-2 30 year probability for upcoming earthquakes Figure 4-3 Active faults in Southern California Figure 4-4 Measures in force and energy dissipated in an earthquake Figure 4-5 Los Angeles Metropolitan/Urban and urbanizing regions. Figure 4-6 Geological soil maps Figure 4-7 Potential liquifiable regions Figure 4-8 Geological model of the Northridge earthquake Figure 4-9 Aftershocks rates Figure 4-10 Horizontal ground displacement Figure 4-11 Vertical ground displacement Figure 4-12 Horizontal ground acceleration Figure 4-13 Horizontal ground acceleration on soil sites Figure 4-14 Horizontal ground acceleration on rock sites Figure 5-1 Basic layout of Los Angeles map Figure 5-2 Damaged buildings related to existing buildings Figure 5-3 Total damage pattern Figure 5-4 25-100% in building damage Figure 5-5 Categorized Percentage in building damage Figure 5-6 Tag posted buildings Figure 5-7 Red tagged buildings Figure 5-8 Graph for tag posted and percent in damage buildings Figure 5-9 Year built ranges for damaged buildings Figure 5-10 Tag posted and percent in buildings categorized by their year built Figure 5-11 Building’s specified structural frames Figure 5-12 Wood and steel or wood frame buildings Figure 5-13 Masonry or poured in place concrete structures Figure 5-14 Percent in building damage for structural frames Figure 5-15 Graphs for % in building damage and posted tags for all structural frames Figure 5-16 Graphs for % in number of red tagged buildings Figure 5-17 Graphs for 25-50% in building damage Figure 5-18 Graphs for 76-100% in building damage Figure 5-19 Graphs for masonry/concrete damaged buildings Figure 5-20 Graphs for wood/steel damaged buildings Figure 5-21 Graph for number of damage for all conditions Figure 2-22 Graph on damage for all conditions separated by their year ranges Figure 5-23 Graph for percent in total damage for maximum number in building damage Figure 5-24 Steel frame structures Figure 5-25 Reinforced concrete structures Figure 5-26 Masonry of concrete structures Figure 5-27 Wood and steel or wood structures Figure 5-28 25-50% in building damage for all structural type buildings Figure 5-29 51-75% in building damage for all structural type buildings Figure 5-30 76-100% in building damage for all structural type buildings Figure 5-31 Graphs for different occupant buildings Figure 5-32 Percent for occupant buildings related to existing buildings Figure 5-33 Red tags for different story buildings Figure 5-34 Number of floors for damaged buildings Figure 5-35 Distance for damaged buildings from the river lines List of Tables: Table Table Table Table Table Table Table Table Table 5-1 Sample records for damaged commercial buildings 5-2 Occupancy codes 5-3 Number of existing buildings 5-4 Percent in total damage 5-5 Percent in building damage 5-6 Tag posted buildings 5-7 Structural type buildings 5-8 Percentage in all types of damage separated by year ranges 5-9 Percentage in all types o f damage separated by total damage Chapter 1 CAUSES FOR EARTHQUAKES IN T R O D U C T IO N : The subject of seismic safety should always be discussed with clients. Typical questions often asked by clients are, “What are the causes o f earthquakes?”, “How often do they occur?” and “What will they do to my building?” Answers to these questions are not easy, since new scientific data, which modify previous opinions, becomes available after each major damaging earthquake. Causes for earthquakes initially begins with the theory of plate tectonics, introduced in 1967. The theory is that the mantle, or upper crust, o f the earth is in constant motion as segments o f its lithosphere, technically referred to as “plates,” slowly, continuously, and individually slide over the earth’s interior. Originally, the crust of the earth was believed to be held by a single mass, without the existence of ocean basins. Alfred Wegener, a young German Scientist, developed the theory o f continental drift. He recognized that the jigsaw-like puzzle of the earth’s crust was held by a single mass. Approximately 200 million years ago, this supercontinent started to gradually spilt apart and break into segments, known as plates. A total of six major plates and over six minor plates are said to make up this system o f the upper mantle. Today, evidence supports the theory of continental drift. Alfred Wegener managed to demonstrate his theory based on 1 fossils found on both sides o f the world, which suggests that land on the earth’s surface started as one joined mass. E A R T H Q U A K E S A T A N D W IT H IN P L A T E B O U N D A R IE S: Plate movements create earthquakes, as the respective plates slide about one another and/or subduct one another. Due to the plate movement, pushing into each other or sliding beneath one another, ninety percent of all earthquakes occur in the vicinity of boundaries. The motion creates shallow to deep-seated earthquakes, unlike deep-seated earthquakes, which are very uncommon. The other 10 percent o f earthquakes occur at faults located within the plates, where their occurrence is much less frequent. F A U L T LIN ES: Fault lines are known as fractures in rocks along which movement occurs. In most cases earthquakes tend to start on faults that have moved in the past and will continue to move again in the future. The reason for this behavior is that it is easier for rocks to move along pre-existing zones of weakness then to create new ones. Once an earthquake does occur within a fault chances are earthquakes will occur again in the same place and along the same fault. However if new stresses develop along the rocks, new faults will form and earthquake could occur in areas that were originally known to be earthquake free. The earth contains countless faults. The faults separates the seven major tectonic plates, along which the moving plates rub and grind against one another. The San Andreas fault, a well known fault line, runs approximately parallel to the coast of California. This large and dangerous fault line is the boundary between two plates that 2 slide horizontally past each other at a rate of approximately five centimeters per year. Due to the size and location of this fault, this snail like pace has left many Californians wondering when the fault will rupture, thus causing an earthquake, known as ‘the big one’. The dangers of San Andreas fault is its location, since California is a heavily populated area, its fault movement and the given rock strength that holds the two horizontal plates together. This fault movement is known as creep movement. Creep movement can be clearly observed in areas where movement of the earth’s crust occurs. Figure 1-1 shows examples of the gradual process of creep movement at a road side. They are particularly noticeable on locations where structures are built on top of the crust. Figure 1-1 Creep movement occurring at a road side. 3 The gradual accumulation of stress in the rock is known to be dangerous. When a portion of the fault is ‘locked in place’ so that the creep is not allowed to occur along that portion of the fault zone, it is believed that an accumulation of stress builds up until it exceeds the strength holding the locked portion in place, causing a rupture that produces the intense vibration associated with an earthquake. In the case of the San Andreas fault the parallel plates are at a constant rate of movement, hence stress within the rock is building up. The magnitude of an earthquake greatly depends on the duration of slippage, since deformation is dependent on time. Once the fault ruptures, the two appeasing plates start to slide against on another. Figure 1-2 shows the four major types of earthquake fault movements. With the most common being the strike-slip movement. 2. Normal fault movement 1. Strike- slip fault movement 3. Thrust (reverse) fault movement 4. Lateral strike-slip reverse (thrust) fault movement. Figure 1-2 Four different types of fault movements, 1 being the most common and 3 and 4 the least common. 4 EARTHQUAKE W AVES: Energy is transmitted by waves. There are many types of waves, such as sound and radiation waves. Waves caused by earthquakes, travel through rocks and are called seismic waves. Several different types of seismic waves are generated from an earthquake such as Body waves and Surface waves. The initial rupture point of an earthquake, called the focus, radiates body waves outward in concentric spheres, as shown in Figure 1-3. The point directly above the focus is called the epicenter, where surface waves radiate away from the epicenter along the surface of the earth like waves generated when a rock is thrown into the lake. Surface wave [ Epicentel oci wave Figure 1-3 Showing the focus generating body waves initiated by an earthquake within a fault line, with the epicenter being the center of the surface wave. 5 Body W aves: There are two main types of body waves that travel through the earth’s interior, Primary waves and secondary waves. Primary waves known as P-waves are waves formed by alternate compression and expansion of the rock. Secondary waves or S-waves, move perpendicular to the advancing wave. Thus S waves form when shearing forces are transmitted. P waves travel at speeds of 5 to 7 km/s in the earth’s crust and about 8 km/s in the upper mantle. S waves are slower than P waves, traveling at speeds of 3 to 4 km/s in the crust. As a result S waves tend to arrive after the P waves and are the secondary waves to reach an observer on the earth. Figure 1-4 shows the time relations for waves to reach a recording station. The seismogram in Figure 1-4 shows that the time difference can be measured between the P and S waves. This type o f information is important to Geologists. It allows them to pin point the epicenter, hence locating the origin o f the earthquake. Seismogram Recording station Epicenter P, S waves Focus Figure 1-4 Time measurements taken by a seismogram at a recording station. 6 Surface waves: Surface waves cause the most property damage because they cause more ground movement than body waves. Surface waves, called Long waves or L waves, travel at a slower speed than the S waves. There are two types of motions within this wave. One is an up and down motion and the other is the side to side motion. Figure 1-5 shows the types of motions caused by surface waves at a road side. Direction of wave travel Direction of ground movement Figure 1-5 Surface waves. Surface motion includes up and down movement like that of an ocean wave and side to side sway. M EA SU R EM EN TS O F EA R TH Q UAK E STRENGTH: (L Agorio, 1990) Measuring the size and effects of an earthquake accurately has been attempted but has not yet been perfected. Many attempts have been made to develop methods to measure magnitude and intensity of an earthquake. O f all those developed, only two 7 methods have been generally accepted and are still in use today, the Magnitude Scale by Richter and the Mercalli Intensity Scale. The M agnitude Scale: This scale gives the magnitude of an earthquake based on measurements made by a seismographs. The scale was first developed by Professor Charles Richter in 1935, and today the Richter scale is used by most seismologists. It is simply used for measuring the size (magnitude) and to pinpoint the location (focus) of an earthquake. The Richter scale determines the magnitude of an earthquake by measuring the amplitude of the largest wave recorded by a seismograph. A correlation between the Richter scale and the amount of total energy released has been derived. A two-unit increase in magnitude, from 6 to 8 for example, renders approximately a 30 x 30, or 900 fold, increase in energy released. The amplitude of an earthquake increases by a factor of 10 for each unit in the Richter scale, for example a Richter magnitude of 6 records 10 times the amplitude of a Richter 5 and a Richter of 7 records 100 times that of the Richter 5. There are down sides of using the Richter scale. Independent of its place of observation, the Richter scale is said to be an abstract number because it has no direct physical meaning. The scale has no upper limit. Its Arabic numerals and decimals gives us an idea of how large the earthquake is. The largest known earthquakes had about a Richter scale of 9.0. 8 It is important to: (1) remember when using the Richter scale that it is simply intended to give a numerical rating of a specific earthquake event and location in comparison to another, and (2) understand which magnitude scale is being used as a measure of the event. Geological conditions of the location affect the magnitude of the Richter scale. Earthquakes of similar magnitude may differ greatly from each other due to their locations. Besides the immense variety of local geological conditions that affect the waves traveling through the earth, the Richter scale does not differentiate between deep-focused and shallow-focused earthquakes. The amount of damage from earthquakes depend on the depths at which the waves initially fan out in all directions and the geological characteristics. The Intensity Scale: The Mercalli scale devised in 1902 gives the intensity of an earthquake and measures the amount of destruction of an earthquake at a particular place, unlike the Richter scale which does not give an idea of the physical effects of an earthquake on buildings. Earthquakes vary from gentle tremors that can not be detected without sensitive seismographs to destructive giants that may cause large-scale destruction and loss of lives. Before seismographs were in common use, the evaluation of earthquake strength was based on human experience and structural damage. 9 The Mercalli scale uses Roman numerals ranging from I to XII with XU being the strongest. The Mercalli scale I represents very gentle shaking with no structural damage. XU on the other hand represents total destruction throughout the site. Although useful, the Mercalli scale is qualitative, not quantitative, and assignment of values is subjective. For example after an earthquake people’s view towards the earthquake intensity may vary. Some people may exaggerate their experience, while others underestimate them. Therefore it may be difficult to decide whether an earthquake could have been a level V or VI, for example. While the Richter scale is open ended, the Mercalli scale has a maximum value which allows for measurements in the worst case, and unlike the Richter scale, the magnitude of the Mercalli scale varies with distance from the epicenter. As a result, isoseismal maps may be produced by drawing equal intensity of damaged buildings and facilities located in the effected area. Overall both methods are useful with each having their advantages, possible ways. The important thing to remember is that both scales are needed, one to determine an event’s magnitude and epicenter and another to indicate its intensity. Both scales will provide a complete picture of an earthquake’s magnitude, location, and physical impact on buildings and facilities in the stricken area. 10 Chapter 2 SEISMIC DESIGN AND FORCES INDUCED ON BUILDINGS INTRO DUCTIO N: In designing a building, a designer must distinguish between two types of loads: 1) Vertical loads (gravity) 2) Lateral loads In areas of high seismicity lateral seismic toads, usually govern over wind. The governing lateral load depends on the location and type of structure material. Given the probabilistic uncertainties involved in seismic design it is essential that the designer act prudently with the client by clearly defining the limits of earthquake-resistant design before any preliminary drawings are initiated. For a successful design, the effects of the earthquake on the buildings and its uncertainties have to initially be taken into account. The following factors must be considered: 1) Location o f building I) period of ground motion according to the soil type. II) potential magnitude of the earthquake. III) Location of focal points from previous earthquake. IV) Duration of ground shaking. 1 1 2) Quality and type of building construction I) wood: platform framing II) wood: heavy timber framing III) steel: braced frames and moment resisting frames IV) concrete: shear walls or moment frame V) reinforced masonry VI) a mixture of any o f the above 3) Latest code provision. G R O U N D M O TIO N: During an earthquake, waves travel both along the surface of the earth and through subterranean rock. The ground undulates: buildings and bridges may topple and roadways fracture. A point to remember is earthquake damage depends not only on the magnitude of the quake and its proximity to population centers, but also on soil types. There are two general types of soils, sedimentary fill and rock. The ground motion in sedimentary soil depends on the depth of the fill and the type of soil that it consists of. On the other hand the rock’s ground motion depends only its rock type. In most cases sedimentary fills are known to have a larger ground motion than rocks, since rocks are a much harder soil and would require a larger force to cause the same ground motion as sedimentary soil. When severe ground vibrations occur during major earthquakes, literally everything placed on the ground vibrates in response. The foundation of a building in 12 Marina districts, for example, are built on soft wet unstable soil. Once the ground is under motion the wet unstable fill may settle and shift, causing heavy damage to properties. Another example is moist clay. Once the ground is shaken, rigid soil converts to liquid soil due to the change in position o f the water molecules. Overall soil content does effect the ground motion and may cause destruction to properties. It is important for the' designer to check with a soils engineer before the foundation and the structure is designed. After all careless mistakes are very easy to occur and recent earthquakes have proven the heavy price paid for such mistakes. T IM E PE R IO D : (L. Agorio, 1990) The time period depends on the depth of the focal point and the soil type. Most damaging earthquakes throughout the world are associated with a relatively shallow depth o f focus of less than 20 miles deep. Shallow-focused earthquakes produce a short-period where the energy released may be spread over a small area. With this kind of focal depth the ground motion do tend to die out more rapidly. Unlike deep-focal points, the earthquake will travel over a greater distance and be felt over a larger area as a longer- period undulating motion. Generally, long-period motions are defined as those with cycles o f 0.5 to 1 second or longer time periods. Earthquakes can be very destructive if the period of the building matches the period o f the ground. The period depends on building height and stiffness. For frame buildings, the period is approximately 1/10 second per story of height. A ten story building has a period of about 1 second. Hence the danger o f destruction, besides quality 13 construction, is a building’s resonance. Once the period of the building matches the period o f the ground, resonance may occur with each successive cycle, causing larger and larger displacements at the upper stories of the buildings. When this happens it may be detrimental to the structure absorbing the dynamic forces. Figure 2-1 shows a typical building reaching resonance. If the frequency of the building matches the frequency o f the ground, the building displacement begins to build up, causing the building to collapse. B uilding displacem ent building up due to resonance Initial Initial start o f resonance resonance < — i — > < — i — > Figure 2-1 Diagram showing the steps for a building to approach resonance. Low-rise buildings have short periods of vibrations and therefore do not tend to go into resonance with long-period waves but with short time period waves. Ground motion caused by earthquakes can be destructive. They can be even more deadly once the period o f the building matches the period of the ground. Figure 2-2 shows an example of a tall collapsed building in 1985 Mexico City earthquake. The displacement of the tall structure matched the long-period ground motion hence resulting in total collapse. This type of (- t ■ ) G round tim e period ( i- ) . B uilding displacem ent 14 destruction has been observed repeatedly in the past earthquakes. The solution to such a problem is to design buildings with periods that are different from expected, or probable ground periods. Figure 2-2 Building collapse due to resonance with long-period ground motion, Mexico City, 1985 earthquake. (Pepper, 1987, p. 46) 15 LOADS INDUCED ON STRUCTURES: (L. Agorio, 1990) As mentioned before, any structure must be designed for two types of forces, gravitational and lateral forces. Gravitational loads are induced simply by the weight o f the building, including its dead and live load. The dead load accounts for assumed permanent loads, such as air- conditioning and the structure itself. Live loads are moving and temporary loads, such as people within the building and movable objects such as furniture. Dead and live loads are calculated in terms of gravity (lg) and are applied vertically to the building. Lateral loads are forces induced on a building through seismic or wind loads. In other words earthquakes or wind loads are dynamic and are applied laterally (horizontally) to a building system. Figure 2-3 shows the horizontal (gravity) and vertical (seismic) loads acting on a building JL < 7 JU V Gravity load, produced by the weight of the building Lateral load ( seismic load) acting on the building c# Base shear produced by the earthquake Figure 2-3 Building under horizontal (seismic) and vertical (gravity) load. 16 The design of a structure must be based on the maximum lateral loads, which may be either seismic or wind. Figure 2-4 shows the seismic risk map for the United States. Each region has a given seismic zone number. Generally speaking, this map has been drawn on the basis of the location of historic earthquakes, their magnitude and intensity, their probability of recurrences, and the frequency of the events in a region. Regions are distinguished by designated numbers with 1 as being the least seismic hazard region and 4 the most hazardous. Southern California, with its history of earthquakes has been designed as seismic zone 4. 17 2A Figure 2-4 U.S. seismic risk map, 1988 U.B.C. Source International Conference of Building Officials. 00 SPECIAL BUILDING DESIGNS TO RESIST LATERAL FORCES: (L. Agorio, 1990) Based on traditional approach to seismic safety, three systems are most commonly used in structural design of earthquakes-resistant buildings today. 1) Moment resisting frames (rigid frames) 2) Braced frames. 3) Shear walls Each of the systems above have different approaches of resisting the seismic forces that are induced on them. The following will explain each system in details. 1) Moment Resisting Frames Generally, steel frames can be designed as rigid-frames or more commonly known as moment resisting frames. Moment resisting frames (MRF) in most cases are actually the most flexible o f the basic type of lateral bracing systems, meaning that the structure has a tendency to move more freely during an earthquake. This deformation character, together with the required ductility, makes the rigid frame a structure that absorbs energy loading through deformation as well as through its sheer brute strength. The base o f a moment resisting frame is fixed into the ground, as shown in Figure 2-5. The limit of motion of the column allows minimum movement. In other words, the column is resisting a moment and the strength of that moment to be resisted is calculated from the lateral load. The beam-column joint connection is the second part of the frame that goes into making a moment resisting frame. The joint for a moment 19 resisting frame, for example, can be either bolted or welded, or both in some special cases (Figure 2-5). The uniqueness of the moment joint is the stiffener plates welded between column flanges to form a continuation of the beam across the column. This type of joint system forces the beam and the column to act together in resisting lateral loads induced in the frame, making the frame more stable during an earthquake. Deformation Stiffener pj&es Bolts Welding Beam Column Column fixed at the base Figure 2-5 Lateral deformation of a moment resisting frame and joint details. 2) Braced Frame: Post and beam systems, consisting of separate vertical and horizontal members, may be inherently stable for gravity loading, but they must be braced in some manner for lateral loads. For example pin-connected square or rectangular shapes are not stable in their ability to resist horizontal forces unless bracing elements are added to their configurations, in order to form triangular panels, which are stable to resist lateral loads. 2 0 There are several types of bracings, X-bracing, K-bracing, eccentric bracing. These types of bracings will allow the frame to resist lateral load in truss action with less deformation than rigid frames. Figure 2-6 shows the common types of bracing frames used in structures. Framing system with no bracing (unstable) Tension bracing Compression bracing X-bracing K-bracing Eccentric bracing Figure 2-6 Braced frames. 21 3) Shear Walls: Shear walls have two purposes: they support the gravity loads and transfer lateral loads down into the foundation. As its name implies the basic way to resist lateral loads is shear. Acceptable materials used for shear walls are wood, masonry and concrete. Each material has different strength limits in resisting lateral forces. In the U.S. the most common material for general residential structures is wood. Plywood, nailed to wood studs, make up shear walls. This type of shear wall provides an economic way of transferring lateral loads (Figure 2-7). Essentially a shear wall cantilevers from the foundation as it is subjected to one or more lateral loads. I) Unit shear through a shear wall II) Chosen shear walls on four walls Figure 2-7 I) Building with shear walls placed around the perimeter. II) Unit shear shown through a shear wall. 2 2 BASE ISOLATION: Base Isolation pads, which started to be utilized about 10 years ago, are a new way of reducing earthquake forces induced on the building. This recent development is becoming increasingly viable as a method used in the seismic rehabilitation of older buildings. It has been known to be more effective than some of the traditional approaches to strengthen buildings. As its name implies, Base Isolators are placed at the base of the building, some cases under columns. Its use is limited to low-and mid sized buildings but has no limits regarding type of construction. Unfortunately Base Isolators can not be used on high rise structures because building excitation problems may produce excessive deformation. Base Isolator pads are composed of layers of steel and special rubber surrounding a steel rod (Figure 2-8). The layers are designed to dampen the horizontal forces caused by an earthquake, where the flexible rubber absorbs the induced energy. The horizontal motion of the building is dampened by absorbing the kinetic energy induced by the earthquake. 23 j — Plastic layer Steel layer Grace beam Figure 2-8 Base isolator DESIGN FOR SEISMIC FORCES: The ground motions of an earthquake tends to push the mass which lay on top. All structures are in motion due to the acceleration produced by the earthquake. As the base of the building responds to the ground motions produced by an earthquake, the bottom of the structure moves immediately, while the upper portion tends to lag behind due to its mass of inertia. With rapid motion caused by the ground the building’s inertia tends to resist the movement and thus causes seismic forces within the structure. The building’s size, dimension and structure type effect the amount of seismic force. The greater the mass of a building the greater the seismic force. All buildings undergo an acceleration. The acceleration is effected by the building height, mass, and structural stiffness. For example, seismic forces of wood buildings tend to have smaller acceleration than concrete buildings, due to less mass and structural stiffness. Seismic forces of 24 buildings with concrete shear walls (which are very stiff) are three times greater than of buildings with more flexible moment resisting frames, due to its stiffness. Earthquake may cause vertical ground movement that can create vertical loads in addition to horizontal loads. However the vertical components are usually smaller than the horizontal components, and most the structures have more inherent strength vertically than horizontally. For this reason, normal design practice for earthquakes considers horizontal forces only. The total horizontal force acting at the base of the building is known as the base shear, V. This total horizontal base shear is equal to the mass of the building, M, multiplied by the acceleration produced by the earthquake motions, A. Based on Newton’s first law of motion a basic equation may be written as: V = M A Since the motion of an earthquake causes dynamic forces on the building, a more refined equation is required. The Uniform Building Code (UBC) has come up with a way of calculating dynamic forces using an equivalent static method. V = W 2 1 (C / Rw) The base shear of the building is simply the product of W, Z, I and C divided by the structure coefficient Rw. Each coefficient will effect the size of the base shear depending on the structure type and location of the building. This simplified equation will allow the engineer to get an estimate of the amount of shear acting on the building. The steps for finding the base shear is described in the following steps: 25 I) Weight of structure W, the total dead load of the structure. II) Height of the building, forces increase linearly with building height due to increasing moment lever arm from the ground. III) Building time period T, the time for one complete cycle of oscillation. The building time period is computed as: T = Ct ( h ) ^ ^ h = height of building above ground Ct = 0.035 steel moment resisting frame Ct = 0.03 concrete moment resisting frame and eccentricity braced frames Ct = 0.02 all other buildings IV) Site coefficient S, soil type conditions on which the building sits on. S = Site coefficient S = 1.0 for rock-like material and stiff dense soil < 200 feet deep S = 1.2 for dense or stiff soil > 200 feet deep S = 1.5 for soft to medium stiff soil > 20 feet deep S = 2.0 soft clay > 40 feet deep S = 1.5 is used for no geological report V) Seismic factor C The seismic coefficient is computed as: C = 1.25 (S) / ^ . 6 6 6 Cmax = 2.75 VI) Seismic zone factor Z, where the coefficient accounts for relative seismic risk of various areas in the country. Z = 0.075 for seismic zone 1 Z = 0.15 for seismic zone 2a Z = 0.2 for seismic zone 2b Z = 0.3 for seismic zone 3 Z = 0.4 for seismic zone 4 26 VII) Occupancy importance coefficient I, a coefficient that provides certain essential facilities to be designed for higher seismic forces than other types of structures. I = 1.25 for essential facilities such as hospitals, police and fire stations and any building with an occupancy rate greater than 300. I = 1.0 for all other structures Vni) Structure coefficient Rw, takes in to account the building material and seismic design (minimum of 4, for concrete structures and maximum of 12, for special moment resisting frames). IX) Base shear V, total horizontal force at the base acting on the building. 27 Chapter 3 BUILDING CONFIGURATIONS INTRODUCTION: Great precautions need to be taken in a seismic zone region. The buildings configuration is a great concern regarding its safety. Besides the building’s natural period/resonance potential which may effect its seismic performance, the configuration of the building is also a concern. Architects know that it is next to impossible to satisfy all outside constraints placed on the design of a building. Yet with all precautions, buildings are still being designed without the considerations of form. Past major earthquakes have proven the poor behavior of buildings with problem configurations. Such buildings tend to experience severe twisting as well as the usual rocking back and forth. Yet many buildings have problem configurations. Buildings are meant to be safe, and to provide seismic safety, two steps need to be considered in designing. 1) Does the building have structural symmetry? In other words, is the center of gravity aligned with the center of stifihess of the lateral resistive system. 2) If the Architectural design can not achieve symmetry, then does the building provide safe resistance against torsional moments? Since earthquake ground waves may arrive from any direction, the building system must be able to resist lateral loads from any direction. Therefore, the design of a structure 28 must be able to withstand forces from any direction, taking into account the shape and form of the building. GENERAL BUILDING FORMS: Buildings come in numerous shapes and sizes. Therefore it is the Architects responsibility to study such forms under seismic forces. Buildings With Irregular Configurations: (L. Agorio, 1990) Regular buildings configurations and symmetrical buildings are seismically optimal. They provide an equal share of stress and strain on all sides with optimum lateral resistive systems. Un-symmetrical buildings tend to experience twisting. This twisting action often has its greatest effects on the joints between elements of the bracing system. The stresses are even more effected at the comers of the building. Figure 3-1 shows irregular buildings, illustrating the stress build up at the comers. Stresses tend to be focused at the intersection o f building parts with different stiffeners. ^ 'S . Stress F ig u re 3-1 Irregular plan configurations showing stress concentrated at intersections. 29 Vertical Massing in Buildings: (J. Ambrose, 1988) In addition to planning concerns the vertical massing of a building has various implications on its seismic response. The position of the center o f gravity and the base width of a building effects the building’s stability. For example, Figure 3-2 (b) shows that a triangular formed shaped structure is stable once it is laid flat on its side but once the triangle is turned upside down (Figure 3-2 (a)) the narrow base forms an unstable structure. Triangular shaped building a) unstable b) stable Figure 3-2 Center of gravity of a) is unstable, hence making it an unstable structure, unlike b) which has a low center of gravity. 30 Multi-Mass Buildings: (J. Ambrose, 1988) When a building is not architecturally symmetrical, the lateral bracing system must either be adjusted so that its center of stiffness is close to the centriod of mass (center of gravity) or it must be designed for major twisting effects. Multi-mass buildings with numerous shapes (Figure 3-3) experience different lateral movement within each shape due to their lateral stiffness. F ig u r e 3 -3 Multi-mass building (numerous shapes), can experience severe damage. If a multi-mass building was designed as a single system, the building movements will be very complex, with extreme twisting effects and considerable stress at points of connection of the discrete parts of the mass. The Architect’s key concern should be to 31 design a multi-massed building as independent units, separated by seismic joints. Thus each unit will create its own forces independent of the others with no stress or strain at the intersecting joints. COMM ON CONFIGURATION PROBLEMS: (A1A/ACSA1994, J. Ambrose 1988) Past earthquake studies indicate the adverse affects of irregular configurations in building plan and section performance. Some of the major damages are caused by irregular shaped buildings. Such torsions are produced when the center of mass does not coincide with the center of rigidity, causing potential torsion to occur about its center of rigidity hence causing larger lateral forces on structural components. Re-entrant Corners: L,T,H,U plans or similar shaped buildings contain re-entrant comers. The advantages to these configurations are their relatively compact form with a high percentage of perimeter rooms with access to air and light. Never the less, they have problems created by their irregular shapes due to their diverse variations of rigidity. For example an L-shaped building will experience diverse deformations in direct correlation to its respective position relative to the incoming direction of the earthquake forces. Earthquake forces coming in from the direction shown in the plan view (Figure 3-4) will move one wing more than the other. The wing which is perpendicular to the direction of the earthquake force is less rigid hence more flexible and 32 weaker to resist seismic forces. In addition, this type of configuration sets up an undesirable torsion causing rotation and undesirable stress concentration at the connection of the wings. The picture in Figure 3-5 is a common and familiar damage for an L-shaped building Direction of seismic force I _ I 1= 1 CD Horizontal wing Stress concentration Vertical wing Torsion Figure 3-4 Plan view showing the direction o f the earthquake movement effecting two wings differently. 33 Ir-K * j , Figure 3-5 Collapse of re-entrant comer o f the L-shaped San Marco Building, 1925 Santa Barbara, California Earthquake. (A1A/ACSA, 1994, p. 33) Stress concentrations and torsional effects are interrelated. The magnitude of forces depend on: 1) Mass of building 2) Structural system 3) Length of wings and their aspect ratio, and 4) Height of the wings and their height/depth ratios 34 It is possible to overcome configuration problems by separating the building into simpler shapes or tying the building wings together, assuring strong connection. Figure 3-6 shows independent movement o f an L-shaped building. Separation between the two buildings [ Figure 3-6 Independent movement for an L-shaped building. One approach that must be considered is its maximum allowable drift of adjacent units. Figure 3-7 the partial collapse of the adjacent building due to pounding of both buildings A calculated drift allows the two independent structures to lean towards each other simultaneously. Hence the sum of the dimension of the separation space must allow for the sum o f building drift for both wings. .few * ■ m a IBtfe Figure 3-7 Adjacent structures suffered pounding damages during the 1985 Mexico City earthquake. (A1A/ACSA, 1994, p.20) W Q \ Soft Stories: Discontinuity of the strength and stiffness between a building is defined as soft story. Buildings with stiff, rigid superstructures placed on top of an open, flexible first floor with relatively unbraced vertical supports between large openings experience a large deflection at the first floor during an earthquake. Figure 3-8 shows a typical soft story failure. § 1 Failure at the columns Open space Figure 3-8 Failure mode of a soft story building. A soft story may be located at any floor depending on the weakness in the structural design. But since the forces are generally greatest at the ground floor, a stiffness discontinuity between the first and second floors tends to be most frequent. 37 Discontinuity of shear walls also are a common soft story problem. Shear walls are designed to resist lateral loads. If these walls do not line up in plan from one floor to the next the forces can not flow directly down through the walls from roof to the foundation. This may causes over-stressing at the points of discontinuity in the vertical stiffness and strength leading to concentration of stresses and ultimately to damage or collapse of the building. Picture in Figure 3-9 shows The Olive View Hospital with a discontinuous shear wall problem damaged in the 1971 San Fernando, California earthquake. The vertical configuration of this building was a “soft” two-story layer of rigid frames on which was supported a four story stiff, shear wall-plus-frame structure. Figure 3-9 Failure in the ground floor due to discontinuous shear walls. (AIA/ACSA, 1994, p.31) 38 If the Architectural designs permits, soft stories can be eliminated by stiffening and bracing the respective floor, or increasing the number of columns at the respective floor. The next best step would be to avoid and discontinuity of the framing system. Strength and Stiffness Variations in Building Perimeters: This type of problem occurs on symmetrical and un-symmetrical buildings. The perimeter stiffness plays an important part in the building’s seismic behavior. If there is a wide variation in strength and stiffness around the perimeter, the center of mass will not coincide with the center of resistance, and torsional forces will cause the building to rotate around the center of resistance. Figure 3-10 shows a typical store with an open front. Glass windows Solid wall Glass door Torsional force Glass wall - Figure 3-10 Shopping store with an open front end undergoing torsional forces due to variations in perimeter strength and stiffness. 39 The seismic force induced on a building, with imbalanced in perimeter strength and stiffness can cause large torsional forces. Several alternative strategies can be used in the design of the building perimeter to reduce the possibility of torsion. The first approach would be to increase the stiffness in the open facade by adding shear walls at or near the open face. A second approach would be to use moment resisting frames at the open front end. If the Architectural design does not permit the addition of structural components, then stiffening the floor/roof diaphragm would be the next approach. If the configuration is good, the seismic design should be simple and economical with more assurance in performance. If the configuration is bad, the seismic design will be expensive and performance will be uncertain. The Architect should pay careful attention to the perimeter of the building, taking into account the size of openings around the perimeter. This is not to say that all buildings should be symmetrical cubes, but to understand the problems involved with building configurations. 40 Chapter 4 EARTHQUAKES IN CALIFORNIA California, known as a land of vast opportunities, is one of most highly populated states in America. In addition to its great powers in industry and marketing, California has life threatening earthquakes. Rated as a number four in the seismic risk zone map, California suffers greatly from earthquakes. Past major earthquakes within the state have caused great amounts of money in damages and grievous loss of lives. Earthquakes initially start from plate tectonics, a process that has developed for millions of years. California is separated into two plates, Pacific and North American plates. The San Andreas fault marks the boundary between the two plates. The plates are in constant motion, approximately five centimeters a year, if continued, it will bring Los Angeles abreast of San Francisco in about 10 million years. Figure 4-1 shows the San Andreas fault cutting California, passing through Los Angeles. Hence Figure 4-2 shows an estimate in a 30 year probability for future earthquakes caused by the San Andreas fault. 41 Cape M endocino 1906 break San ^ Francisco H o llis te r P ark fie Id 1857 break .Angeles .El Centro* 0 100 200 300 KILOMETERS Figure 4-1 Approximate location of the San Andrea’s fault in California. (Pepper, 1987) C VHULA TI V[ JO TEAR PftOSASlLITr £ 0 V . CQ9DA BA5|H 2 0 V . SHIZM > b ALL OTHER FAULTS OtEHA M e -FARK FtEL O n t 2 0 0 KtlOHETEAS Figure 4-2 30 year probability for upcoming earthquakes. (Pepper, 1987) The threat for major earthquakes caused by the San Andreas fault, arises from the fact that some portions of the fault are locked in place, hence building large stresses within the rock. The Los Angeles area is within one of those portions. In addition to the main fault line, California contains smaller active fault lines. Figure 4-3 shows the vast number of faults spotted around the Southern California region. The number of faults is still unknown, since new faults are always being discovered. M J- - 'cLoe AngtJes ,U 4 ' 1 2 2 ' EX P LA N A TI O N fauJi segment* wit h surface or postulated ft&njmse siip dtmng historical earth- quakes or with contiftuou^ or intermittent as«nuc fault slippage 114 116' 118 ' 1 2 0 ' Figure 4-3 Major historically and geological recent active faults in Southern California. (L. Agorio 1990) 43 ENERG Y D ISSIPA TED IN EARTH QUAK ES: (Pepper, 1987) Once an earthquake occurs, large amounts of energy are released to the surface. The Energy realized by a nuclear bomb is usually used to illustrate the vast amount of energy released by E m earthquake. Figure 4-4 shows a dramatic demonstration of the vast differences in force or energy released between moderate earthquakes, such as San Fernando and great earthquakes, such as Alaska’s earthquake in 1964. E arthquake M agnitudes - S e le c te d Earthquakes «- 8 .9 L A R G E S T O N R E C O R D 1 2 5 120 50 1 9 5 2 K E R N C O U N T Y . C A . I- u- 1 9 4 0 EL C E N T R O 1 9 5 9 H E B G E N LAK CO 4 0 1 9 7 1 S A N F E R N A N D ' .1954 A L A S K A 3 0 H IR O S H IM A A T O M IC BOM i- 1 9 3 3 L O N G B E A C H 1 9 2 5 S A N T A B A R B A R A L U 20 1 9 0 6 S A N F R A N C IS C O 1 9 5 7 S A N F R A N C 1 S O 6 10 n: UJ A V E R A G E T O R N A D O UJ io M A G N IT U D E Figure 4-4 Dramatic difference in force or energy between moderate and large earthquakes. (Pepper, 1987) 44 LOS ANGELES CITY: irbank ■'--v > i /Long EteadvLakewood Los Angeles shown in the grey area. Los Angeles, a heavily populated city, is built over active faults. With the population and urban development on the rise, see Figure 4-5, the city’s past seismic activities places many lives and properties in jeopardy. Past major earthquakes such as Wittier, Lomar, El-Central and Sylmar earthquakes, shock the city and brought fear and anxiety through the region. As a result earthquake preparation has become a big issue among the residents. Similarly, the Los Angeles City Code (the code deals with the design 45 and safety of structures) is constantly being upgraded to decrease the damage of upcoming earthquakes. COUNTY BOUNDARY SUBREGIONAL AREAS H i g h ly U r b a n i z e d U rb a n iz in g M t . / D e s e r t Figure 4-5 Los Angeles Metropolitan area/Urban and urbanizing areas. (Pepper, 1987) Soil Contents: The city of Los Angeles sits on moderate soft soil in which the soil varies in age and contents throughout the city. Figure 4-6 provides a simplified map for the city with only three generic soil types, Holocene sediments, Pleistocene alluvium, considered as soft soils, and rock. The purpose for the simplification of mapping the Los Angeles soil 46 content was to provide an easier way of identifying the soil content as rock and soft soil for comparitive studies. Rock | I I Pleistocene alluvial and ! i ____| marine terrace deposits ! I Holocene sediments Figure 4-6 Simplified geological soil map for Los Angeles City. Redrawn from UBC/EERC-94/08 47 W ater Table: (UBC/EERC/75-17) Areas underlain by granular sediments which are water-saturated at depths of less than 30 feet are subject to potential liquefaction during an earthquake. Saturation may occur in soft soils if there is an existence of underground water. Liquefaction is caused by hydrostatic pressure in soft soils saturated with water. Los Angeles city sits on vast area of potential liquefaction zones ( Figure 4-7). Chances for liquefaction during an earthquake exist since large areas within the city have a water table with depths of less than 30 feet. Figure 4-7 Areas of potentially liquefiable deposits within Los Angeles city limit. Redrawn from UBC/EERC-94/08 48 NORTHRIDGE EARTHQUAKE: (Preliminary report from UBC/EERC-94/08) On the night of January 17, 1994 at 4:30 AM, Los Angeles city was awakened by a major earthquake. With the epicenter located in the heart of Northridge city and measured as a 6.8 magnitude on the Richter scale, this earthquake was the most costly natural disaster in U.S. history. In addition to collapsed highway structures, up to 140,000 buildings were damaged or destroyed, as well as a wide spread of utilities and other lifelines and numerous landslides. A total of 61 deaths resulted from this tragic disaster, many of them around the Northridge area. Fortunately, due to the time of the earthquake, the number of deaths was not greater. The epicenter was located at the intersection of Reseda and Devonshire Boulevard, in the north side of Northridge. Although much of the damage was in the highly developed epicentral area where intense shaking was felt, additional concentrated damages were found outside of the San Fernando Valley region. These concentrated damages were located at areas such as Hollywood, Central Los Angeles and areas outside of the Los Angeles city such as Santa Monica. 49 Location of the Earthquake: The Northridge earthquake epicenter location determined by the U.S. Geological Survey is 34.213N and 118.537W with a focal depth of 18.4 km which propagated up to a depth of about 5 km, (Figure 4-8) with a 6.7 magnitude Richter scale. Although the location of the earthquake was determined, understanding the rupture of the fault was not exact. S a n a o Bridge failures p e r s p e c t iv e o f t h e N o r th r id g e E a rth q u a k e Patrick Williams Preston Holland Lawrence Berkeley Latjoratoty Bertetey California Figure 4-8 Geological model of the Northridge Earthquake. (UCB/EERC-94/08) The following example from the University of California Berkeley preliminary report of Northridge Earthquake, will describe the reason for the rupture of the fault: 50 The Northridge earthquake took place in a complex, transitional region ofpredominant south dipping reverse faults to the west (Yeats, 1994) and north dipping structures to the east (Heaton, 1982; Haukkson and Jones. 1989). It occurred on a south dipping fault, adjacent to the north dipping structures involved in the 1971 San Fernando Earthquake (Mw=6.6). The Aftershock distribution clearly defines this structure at depths greater than 5 to 10 km. It remains unclear whether this earthquake occurred on an eastward extension o f the Oak Ridge Fault (Yeats, 1994; Williams et ah, 1994), a previously unknown “ blind thrust" which is truncated at a depth by the north dipping SierraM adre fa u lt system (Haukkson et ah, 1994) or a “blind" back thrust o f the Elysian Park system (Davis and Namson, 1994). After the main earthquake, many aftershocks started to occurred but nothing unusual was found about their time sequence. Six of the shocks had a magnitude greater than 5.0, the largest of which was 6.0, with a similar mechanism as the main shock. Figure 4-9 shows a graph made for the number of aftershocks greater than 3.0 magnitude. 51 50 m i mi m i ii 1111 1 i n n I't1 1 mini n rn 11 n 1 1 in i n m 1111 1 1 ifii rn i n ii i nn 0 II III H I I .1 .. I IH T I lifit » r - — 1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 Days after Northridge mainshock Figure 4-9 Aftershock rate of January 17, 1994 Northridge Earthquake. (UBC/EERC-94/08) Ground Motion and Displacement: The U.S. Geological Survey (USGS) obtained ground displacement data from numerous recording stations after the Northridge earthquake. Figures 4-10 and 4-11 show the horizontal and vertical ground displacements in the Los Angeles County region. Maximum displacements occurred close to the epicenter, as expected. In some cases, the displacement was so great that measurements were visible to the eye. Ground acceleration created by the earthquake generated a large number of strong motion recordings from stations throughout the Los Angeles area. The strong motion 52 stations recorded horizontal accelerations of up to 0.01 g at distances of about 250 km from the fault plane. The largest horizontal acceleration of 1.829 was reported at the Tarzana-Cedar Hill Nursery approximately 5 km from the epicenter. The Uniform Building Code requires a 0.186g lateral load (18.6 %) for low rise type V buildings. The acceleration recorded was approximately 10 times greater. Figure 4-12 shows contour lines drawn to develop the regions of identical horizontal accelerations in the Los Angeles County area. The 1.82g and 1.58g recorded at the Tarzana and Pacoima Dam were removed so as to lessen the distortion of the contours. These ground accelerations were measured at rock and soil sites, hence interpretation has to be made with caution. Rock sites are composed of hard material, have smaller accelerations than soft soil sites. Figures 4-13 and 4-14 shows the contrast between the sedimentary soil and rock sites. Due to the angle of the rupture and the type of fault, major vertical accelerations were recorded. In general maximum vertical accelerations recorded were typically less than or equal to two-thirds of the maximum horizontal accelerations. Largest vertical accelerations, as expected, occurred near the epicenter. 53 < s > . SURFACE PROJECTION OF APPROXIM ATE FAULT RUPTURE PLANE Scole • * < B > .. N o te : S c a l e o f d is p la c e m e n t v e c t o r s is 1 c m = 5 c m . Figure 4-10 Approximate horizontal ground displacements (data courtesy of California Department of Transportation). (UBC/EERC-94/08) 54 SURFACE PROTECTION OF APPROXIMATE FAULT RUPTURE PUNE E P K ■ <3 > ‘ N o t e : Scale of displacement vectors is 1 cm = 5 cm. Figure 4-11 Approximate vertical ground displacements (data courtesy of California Department of Transportation). (UBC/EERC-94/08) 55 ■ 0.6- SUSFACE PROJECTION OF APPROXIMATE. FAULT RUPTURE PLANE. Scoie Note: Site classification was provided by the owner/agency orcept lor USGS stations a s rfecussed in Section 3.3.1. Sites were typically classified by surficial geology: however, USC stations were classified b ased on S eed et. al. (1976) in which suifidai materials with Vs > B O O m/s are designated a s ■rodr sites. Figure 4-12 Contours of maximum horizontal acceleration based on recording at the rock and soil sites. (UBC/EERC-94/08) 56 „ SURFACE PROJECTION OF APPROXIMATE FAULT RUPTURE PU N E1 Scofe lJ? ....U ■ Nats: Site classification w as provided by the owner/agency except for USGS stations a s discussed in Section 3,3.1. Sites were typically classified by surficia] geology; however, USC stations were classified based on S e ed et. ai. (1976) i t which surfidal materials with Vs > 600 m/s a re designated a s "rode sites. Figure 4-13 Contours of maximum horizontal acceleration based on recordings at soil sites. (UBC/EERC-94/08) 57 E P I C E N T E R V SURFACE PROJECTION OF APPROXIMATE FAULT RUPTURE PUNE gj_ Scale Nets: She classification was provided by the owner/agency except for USGS stations a s discussed in Season 3.3.1. Sites were typically classified by surfidal geology: tvMever. USC stations were classified based on S eed et. aJ. (1976) in which surfidal materials with V s > 800 m/s are designated as 'rock* sites. Figure 4-14 Contours of maximum horizontal acceleration based on recordings at rock sites. (UBC/EERC-94/08) 58 Ground Failure: Ground failure resulting from the Northridge earthquake caused by dynamic ground shaking over a widespread area effected sites as far as 36 miles away from the epicenter. In addition to the widespread ground shaking, the region most heavily impacted by ground failure was within the epicentral region, where most of the damages included pipe breakage, pavement disruption and structural distress. Furthermore, ground failure by soil liquefaction or partial liquefaction occurred to the west in the Simi Valley, to the north at a number of locations near the Santa Clarita River, and to the south in several coastal areas. The damages caused by soil liquefaction resulted in broken utility pipes, disruption of pavements, and moderate distress to structures. Overall, ground failure was the least of the problems since only moderate damages were reported. Fortunately much of the soil liquefaction took place at deserted areas were no structures or lives were in any danger. 59 Chapter 5 STATICAL ANALYSIS FOR COMMERCIAL BUILDING PERFORMANCE ON NORTHRIDGE EARTHQUAKE INTRODUCTION: The Northridge Earthquake, centered in a heavily populated city, brought great fear into the heart o f residents. As a result everyone shared the loss of some personal belongings and even up to this day suffering from the damages and bitter memories still exists. Immediately after the earthquake, many were shocked by the large ground displacement and acceleration. Even though the building code was designed to resist the lateral forces, the code was nowhere near the ground accelerations caused by the Northridge earthquake. Hence it was to no surprise that the amount of damage was so vast. The damage resulting from such an earthquake started intense research on the cause and effects of the earthquake activity by Engineers, Architects, Geologists and Universities. Studies covered areas such as faults, ground motions, building design and quality in construction. As a result the Los Angeles city code changed the lateral force design, raising it from 18.6% to 30% for low rise type V buildings. Also, the quality of construction was questioned and more strict regulations were implemented. Some change was needed, since many structures were not as safe and as well constructed as they were expected it to be. 6 0 SOURCE OF DATA FOR COMMERCIAL BUILDINGS: Records for Damaged Buildings: The data for building damage was provided by the Building and Safety Department in the city ofLos Angeles. This reports was collected by building inspectors and volunteer Engineers and Architects. Buildings damage were recorded in a compatible file in a standard layout. On September 27, 1994 the revised file contained a total o f 140,000 records o f damaged commercial, residential and mixed buildings within the Los Angeles county area. The revised file, named as Earthquake Damage Assessment file, contained approximately 19 million bytes in its exploded form. The information o f the revised file was placed on two diskettes, the first diskette had approximately 12MB and the second diskette had around 7MB. In addition to the 140,000 records, the file still continues to grow at a rate of approximately lOOkb (100,000) per day. Each record gives information about the damaged building. The final record layout for each damaged building is follows: 1. Street Number Location o f the building on the road. 2. Street Fraction Building having the same street number but separated by a fraction number. 3. Street direction Given direction such as North, East, South or West. 4. Street Name Name of the street the building is located on. 5. Street Type Type of street such as Avenue, Boulevard etc.. 6. Unit number The location may have more than one building such as Apartment complexes and Condominiums. 61 7. Building Use 8. Occupancy 9. Estimated Total Dwelling Units 10. Estimated Number of Units Vacated 11. Estimated Percent Damage 12. Estimated Repair Cost 13. Posted 14. Number of Stories 15. Construction Type 16. Building Size 17. Zip Code 18. Year Built Uses are either Residential, Commercial or Mixed. The usage of the Building Number of units within the same building Vacated units before the earthquake. The percent of the buildings overall damage. Cost of repairing the damaged building. Damaged buildings will be rated as to the amount of damage with red , yellow and green tags. Red being the worst case, unsafe building, and green being safe case. Number of floors in the building. Construction types range from I to V and un-reinforced masonry, each describing the type of material the building is made of. The width and length of the approximate building size. Zip code for the building. The year the building was built. The dates ranged from the 1900 up to existing day, which was before the Northridge earthquake. Table 5-1 shows an example of records for some damaged commercial buildings. Lc 0L1___________________ lUnitNum IConDI |BLD |Oc|DwUn |VaUn~|Dam% [CostRcp |PostCon iN um S IConTylBLDslze IzipCOde |YearBlt ~| 4914 W ADAMS BL 10 C 16 0 0 9 20000 RED 1 URM 70 X 40 90016 24 5000 W ADAMS BL 2 C 13 0 0 20 100000 YELLOW 2 URM 50X105 90016 25 9225 ALABAMA AV 12 C 13 1 0 2 9450 YELLOW 1 TLTUF 90X210 91311 81 2021 S ALAMEDA ST 14 c 12 0 0 10 160000 YELLOW 2 URM 200 X 200 90058 25 2140 ALTA ST 14 c 5 12 0 15 30000 GREEN 3 V 45X120 90031 62 20750 LASSEN ST 12 c 12 0 0 5 1000 GREEN 1 III 91311 77 21350 LASSEN ST 12 c 22 0 0 5 50000 YELLOW 1 TLTUF 500 X 350 91311 68 4705 LAUREL CYN BL 5 c 13 0 0 7 15000 GREEN 5 I I 140X 90 91607 07 19901 NORDHOFF ST 12 c 12 0 0 10 5000 GREEN 2 V 600 X 500 0 58 20500 NORDHOFF ST 12 c 22 0 0 1 1000 GREEN 1 TLTUF 150X100 91311 80 20550 NORDHOFF ST 12 c 22 0 0 1 5000 GREEN 1 TLTUF 150X100 91311 78 19631 PRAIRIE ST 12 c 22 0 0 15 90000 YELLOW 1 III 110X 65 91324 68 20257 PRAIRIE ST 12 c 12 0 0 15 150000 RED 1 III 80 X 80 91311 70 1913 PURDUE AV 11 c 6 0 0 4 10000 YELLOW 2 V BOX 80 90025 34 6020 RADFORD AV 2 c 6 0 0 5 30000 YELLOW 2 III 100 X 200 91606 64 5525 SEPULVEDA BL 2 c 11 184 0 1 12000 2 V 425 X 232 91411 73 5650 SEPULVEDA BL 11 c 13 0 0 15 100000 YELLOW 3 V 60X150 91411 89 7101 SEPULVEDA BL 2 c 18 0 0 5 40000 YELLOW 5 1 1 1 100X100 91405 62 17732 SHERMAN WY 3 c 13 0 0 1 25000 GREEN 1 1 1 1 60 X 30 91335 65 18115 SHERMAN WY 11 c 6 0 0 2 50000 RED 1 V 60X130 91335 64 12050 VENTURA BL 2 c 16 0 0 5 250000 GREEN 2 V 200 X 200 91604 76 12124 VENTURA BL 5 c 16 0 0 1 10000 GREEN 1 V 120X 25 91604 56 12345 VENTURA BL 5 c 13 0 0 2 30000 GREEN 1 V 5GX 60 91604 77 12420 VENTURA BL 4 c 16 0 0 10 11000 YELLOW 2 V 70 X 60 0 47 6815 WILLOUGHBY AV 5 c 13 0 0 2 1000 GREEN 2 V 100X 50 90038 29 11859 WILSHIRE BL 11 c 13 0 0 5 5000 GREEN 6 II 200 X 200 90025 86 6530 WJNNETKA AV 3 c 18 0 0 1 2000 GREEN 0 V 100X100 91367 87 7435 WINNETKA AV 3 c 11 47 0 1 10000 GREEN 2 V 90X210 91306 63 Table 5-1 Sample records for damaged commercial buildings. The Occupancy types comes in numeric codes describing functional use for the building (Table 5-2). 00 - Vacant Lot 01 - Single Family Res. 02 - Duplex 03 - Airport 04 - Amusement 05 - Apartment 06 - Church 07 - Private Garage 08 - Public Garage 09 - Gas Service Station 10 - Hospital 11 - Hotel 12 - Manufacturing 13 - Office 14 - Public Administration 15 - Public Utilities 16-Retail 17 - Restaurant 18 - School 21 - Theater 22 - Warehouse 24 - Mobil Home 35 - Condominium 99 - Other Table 5-2 Occupancy Codes. Existing Commercial Buildings: The number of existing commercial buildings were obtained from the City Planning Department. Information such as the total number of existing buildings for a particular occupancy could be extracted from by a software. Further more, the software gave the year in which the commercial buildings were built ranging from 1900 to the 1995. As a result, this allowed the buildings to be categorized by type of occupancy and the year in which it was built. The city records the number of buildings in form of parcels. Each parcel covers a certain plan area. For example one whole street block could be designated to one parcel, or that same block could be separated by four parcels. Within each parcel there can be a certain number of commercial buildings hence this type of layout brings some uncertainties as to the number of existing buildings. But the uncertainty is reduced dramatically by grouping the existing building in to its type of occupancy and the year in which it was built in, hence chances for identical buildings being in the same parcel was reduced. The date of year built for the buildings have been categorized into three groups according to the dates for the change in the Los Angeles City Code. The year ranges are as follows: Prior to 1934 1934 to 1976 After 1976 Table 5-3 gives the number of existing commercial buildings for each occupancy. Furthermore the City Planning occupancy code of Table 5-3 was matched with the Los Angeles Building and Safety Department occupancy code (Table 5-2). 65 Occupancy codes Prior 1934 1934- 1976 After 1976 03-Airport 32 0 0 04-Amusement 152 183 22 06-Church 655 816 98 08-Public / Private Garage 75 2121 603 09-Gas Service Station 113 676 116 10-Hospital 24 113 9 11-Hotel 187 465 96 12-Manufacturing 2041 6706 1039 13-Office 3938 5004 930 16-Retail 2225 3270 770 17-Restaurant 253 915 184 18-School 124 304 55 21-Theater 152 183 22 22-Warehouse 2027 6942 1344 Table 5-3 Number of existing buildings in Los Angeles city. Construction Type for Damaged Buildings: In an earthquake a building’s type of construction is vital to its performance. Hence all buildings are categorized by construction type. The Uniform Building Code (U.B.C.) identifies the buildings as type I through type V. A summarized description of construction type is as follows: 66 Type I Fire resistant buildings. Type II Fire resistant buildings and combustible partitions. Type I and II are mostly steel and concrete structures. Type III Heavy timber (perform well in fires). Type IV Wood frame, high fire resistant. Type V Wood frame buildings. According to the Uniform Building Code, a building can be of more than one type. Hence a building’s construction type code can be uncertain. The Los Angeles County Assessor Department provides a more precise way of identifying the building construction, designating buildings as a certain class. Since the class codes are confidential, the following will not include the codes assigned to each class. There are a total of five different classes as follows: Class 1 Buildings having fireproofed structural steel frames carrying all wall, floor and roof loads. Wall, floor and roof structures are built of non-combustible materials. Class 2 Buildings having fireproofed reinforced concrete frames carrying all wall, floor and roof loads. Wall, roof and floor structures are built of non-combustible materials. Class 3 Buildings having exterior walls built of a noncombustable material such as brick, concrete block or poured in place concrete. Interior partitions and roof structure are built of combustible materials. Floor may be concrete or wood. Class 4 Buildings having wood and steel or wood frames. Class 5 Specialized buildings that do not fit in any of the above classes. 67 Types of Software Used: The records collected from Los Angeles Building and Safety Department and Los Angeles County Assessors Department are mapped using Mapinfo, version 3.0 . Mapinfo, a computer program, performs geographic analysis with visual maps and graphs a powerful tool to analyze statical data. Hence patterns and trends which are difficult to detect in lists of data become obvious when displayed on a map. Quattropro, is a computer program used to graph data. The software allows statical data to be graphed in a 2D and 3D view, hence the visual effects o f the graphs allows an overall view of the data in graph mode. 68 BASIC LAYOUT FOR MAPPING: The of commercial building damage recorded by the Los Angeles Building and Safety Department totaled 2531 buildings. Unfortunately some of the records in the file were not complete since some vital data were missing. For example, some records did not contain the percent damage or the year in which the buildings were built, even in some cases the given address for the buildings were wrong. Those buildings were not included.. As a result this brought down the record numbers to 1708 damaged commercial buildings within the Los Angeles city limits. The 1708 records included of 245 buildings with 25% or greater building damage. The results for the records and data are given graphically in form of maps and graphs. Figure 5-1 shows the typical layout for each map. The white portions of the map represents areas outside of the Los Angeles city limits, for example, the Santa Monica and Pasadena area. Ground motion is presented inform of bar charts. The bar charts shown include the period, horizontal and vertical ground accelerations, and displacements at 15 different seismic measuring stations. Furthermore the maps show location o f the epicenter with a black star at the cross street of Devonshire and Reseda Boulevard in Northridge. The areas for liquefaction are shown on the upper north side of Los Angeles right across the 210 freeway. Finally, the lakes and rivers are shown in a shades of black. 69 HR DG FERN Pacific Ocean E £ D 1 O T i / 1 (j y iO -T H — I — I — I — rso j Freeways I Lakes City Boundaries Note: Predominant period 1n 0 1 2 I N e ★ Epicenter Pleistocene alluvial and marine terrace deposits lllll R °ck □ Molocene sediments Liquefaction Figure 5-1 Basic map of Los Angeles city. 70 RESULTS OF DAM AGED BUILDINGS: The number of existing commercial buildings were retrieved from the Los Angeles Planning Department. There numbers are given in terms of parcels where each parcel may contain more than one commercial building. The search for existing buildings was broken down into types of occupancy. Hence chances for the same occupant building to be in the same parcel would be dramatically reduced. Finally we can assume that each parcel accounts for one existing building. According to Table 5-4, o f27,698 commercial buildings built between 1934 to 1976, where 110 buildings were reported damaged. Roughly half the number of damage reported in the Northridge earthquake. Out of the 27,698 existing buildings 0.4% were damaged. The 5,288 existing buildings built after 1976, 0.98% were reported damaged. Hence buildings built after 1976 were more liable to be damaged. Prior 1934 From 1934 to 1976 After 1976 Existing buildings (45,000 total) 11,998 27,698 5,288 Damaged buildings (245 total) 83 110 52 Percent damaged 0.69% 0.40% 0.98% Table 5-4 Percent in damages related to the existing building categorized by their year ranges. 71 Figure 5-2 shows the total existing buildings separated by the year built, according to the Los Angeles City Code. Graph 1 on Figure 5-2 shows the building numbers for existing buildings and percent in building damage greater and less than 25%. Hence the highest numbers for both existing and damaged buildings are within the 1934-1976 categorized year range. On the other hand, Graph 2 on Figure 5-2 shows the percent in number of damage related to the total existing buildings. As a result, buildings built after 1976 have a higher percent in number of damage related to the existing buildings. In other words in relation to the total existing buildings within their categorized year range, buildings built after 1976 had a higher number of damage related to its total existing buildings. These numbers refer to both above and below 25% in building damage. Finally buildings built before 1934 have a surprisingly low percent in number of building damage. 72 Total Existing Buildings Related to D am aged Buildings — / TOTAL BUILDINGS y < 2 5 % DAMAGE > = 2 5 % DAMAGE . PRIOR 1934 1934-1976 AFTER 1976 YEAR BUILT Percent D a m a g es vs. Total Existing Buildings < < 25% DAM. BUILDING > = 2 5 % DAM. BUILDING PRIOR 1934 1934-1976 AFTER 1976 YEAR BUILT Figure 5-2 Graph 1: Total existing buildings related to total damaged buildings. Graph 2: Percent in damages taken from total existing buildings. 73 Figure 5-3 shows a total of 1708 commercial buildings with damages ranging from 0-100%. From this point on all buildings with less than 25% in damage are ignored since a majority of the buildings with low percent in damage have non-structural failure. Building with failure greater than or equal to 25% damage will be used, unless it is specified. Hence a total of 245 buildings have been recorded with percent in damage ranging from 25 to 100%. Figure 5-4 shows a total o f245 damaged commercial buildings. Surprisingly the map shows no concentrated number of damage around the epicenter in the two to three mile radius. The damages are found to be concentrated at further distances away from the epicenter. The map shows a mixture of concentrated and random distribution of damages within the city limits. The majority o f damages are located on soft soil areas. Some buildings lay on the boundary between the rock and soft soil. In addition to the location of the damage, Figure 5-5 shows that some buildings located on the soil boundary line have a high percentage of damage. Furthermore areas such as Hollywood, Sherman Oaks and Van Nuys, where the ground accelerations are small, have a high concentration of building damage. These areas are particularly noticeable because a majority of the buildings have high percent in building damage. A summarized statical data is given in Table 5-5 in which the outcome for the number of damage are given for the conditions explained in Figures 5-4 and 5-5. 74 Prior 1934 From 1934 to 1976 After 1976 Existing buildings 11,998 27,698 5,288 Damaged buildings 83 110 52 25-50% Damage 44 79 39 51-75% Damage 10 13 4 76-100% Damage 28 18 9 Table 5-5 Number o f percent in building damage categorized by their year ranges. Eyy] sf8 Pacific Ocean ★ Epicenter D am ag ed building Rock n Holocene sediments Liquefaction Lakes Pleistocene alluvial and marine terrace deposits City B oundaries No(e: Prcdortsarl period Figure 5-3 Damage pattern for 1994 Northridge earthquake in Los Angeles city . Percent of damage range from 0-100% for all buildings. 76 m Pacific Ocean * o o -c H .H T O T O Q ) T 3 T J x > & > X Note: Predonwunt ptriod J Freeways I Lakes . City Boundaries o 1 z e ★ Epicenter Rock □ marine terrace deposits Pleistocene alluvial and □ Holocene sediments liiH I U S I Liquefaction @ D am aged building Figure 5-4 Damage pattern for buildings with percent damages ranging from 25-100% in Los Angeles city. 77 g g ^ i i f i 3 5 2 . 5 S M o lt PrM om rtan p*n« J Freeways i Lakes - City Boundaries Epicenter Rock □ Pleistocene alluvial and marine terrace deposits □ Holocene sediments W H ittl Liquefaction Building Damage ® 76% -100% O 5 1 % -7 5 % O 2 5 % -5 0 % Figure 5-5 Categorized percent in damage for all commercial buildings. Of the 245 damaged buildings, approximately 195 buildings are on soft soil and the rest on rock. The maximum acceleration occurred on the rock at a distance of 7.1 miles away from the epicenter with horizontal and vertical accelerations were recorded as 1.82g and 1.18g. Maximum displacement occurred approximately 3.6 miles from the epicenter on soft soil with horizontal and vertical displacements of 1.2 and 2.12 cm. The research report of U.C. Berkeley on relationships between maximum acceleration and distance from the epicenter and local sites conditions for moderately strong earthquakes points out the following: Studies fou n d that fo r distances near the source o f energy (epicenter) release within 40 to 60 Kilometers, maximum accelerations on rock were somewhat higher than those recorded on soil while the reverse was true fo r higher distances from the energy center. (UBC/EERC/75-17) Such conditions described also relate for to ground accelerations found for the Northridge earthquake where the maximum accelerations occurred on rock at a distance of less 40 to 60 Kilometers from the epicenter. 79 Each building that was inspected after the earthquake was labeled with a tag by the building inspector. The posting of the tag states the damage condition of the building but is not directly related to the building’s percent damage. The identity for the tags are as follows: Red tag: Building severely damaged, causing the building to be closed for use. Yellow tag: Building damaged but may be eligible for use, depending on the damage rate. Green tag: The damage to the building is minor hence the building is safe for use. It is the building inspector’s responsibility to decide if the building is safe, Figure 5-6 shows all the different tagged commercial buildings. The Figure shows that concentrations of red tags are found in the Hollywood, Sherman Oaks, Van Nuys and along the 10 freeway regions where there are a high concentration of damaged buildings. Furthermore red tags are also located on the boundary between the rock and soft soil parallel to the 101 freeway. Figure 5-7 gives a clearer view of the red tagged commercial buildings. In addition to the red tags, green and yellow tagged buildings are found to be generally located around the epicenter mostly in the San Fernando area where the ground displacements and accelerations are high. Table 5-6 gives a summarized outcome for the number of damages for all tagged buildings. 8 0 Prior 1934 From 1934 to 1976 After 1976 Existing buildings 11,998 27,698 5,288 Damaged buildings 83 110 52 Red tag 47 70 24 Yellow tag 35 34 26 Green tag 1 6 2 T able 5-6 Number of tagged posted buildings categorized by their year ranges. As a result a total of 142 red tagged buildings are shown graphically in Graph 1 Figure 5-8, hence most of the damaged buildings are posted as unsafe. Graph 2 has a large number of buildings with low percent damage. Both graphs show that a building with a low percent in damage could still be unsafe. Pacific Ocean * e e C l O l (5 U l) 2 .0 -1 ■ r ~ i — i ---------r so u U t a .! C rt B a is tj X > D . > X Note: Prwtoninr* period J F re e w a y f L a k e s . City Boundaries 0 1 3 " ' f a W ★ Epicenter Pleistocene alluvial and marine terrace deposits | | | | | Rock □ □ Holocene sediments t t tttittt Liquefaction 0 Red tagged buildings □ Yellow tagged buildings /\, Green tagged buildings Figure 5-6 Tag posted commercial buildings. 82 m K -4 ' Pacific Ocean ^ , , ® E E Q > w « A U u 2 .0 - 1 — ^ — i — i — r r so m 8 S ! i f a to o v u X > IX > X Note: Prsdwrtrart period Freeways L akes - City Boundaries ★ Epicenter Pleistocene alluvial and marine terrace deposits llllfl Rock □ □ Holocene sediments | | | § | ! Liquefaction © Red tagged commercial buildings Figure 5-7 Red tagged commercial buildings. 83 N U M B E R O F E .. S S N U M B E R O F B U ILD IN G S i ag Posted C om m ercial Buildings G REEN YELLOW R ED 180 160 140 1 20 100 80 60 40 20 0 'ercent Damaqes for All Z) C o m m ercia l Buildings 25-50% 51-75% 76-100% Figure 5-8 Graph 1: Tag posted commercial buildings. Graph 2: Percent of damage for commercial buildings. ^ The records retrieved from the Los Angeles Building and Safety Department contain the year in which the buildings were built. The damaged commercial buildings were grouped according to the code modifications. Figure 5-9 shows the year ranges of the Los Angeles City Code as being prior to 1934, 1934-1976 and after 1976. Figure 5-9 shows San Fernando Valley located between 101 and 5 interstate freeway, contains a large number o f damaged buildings built after 1934. Damaged buildings built before 1934 are mainly located on the south side of the city, with the majority of structures located in the Hollywood region. The graphs in Figure 5-10 show the different tags and percent in damages for the buildings. From the graph it can be seen that the highest rate in damage occurred for 1934 to 1976 year range. Furthermore majority of the percent in building damage for the 1934-1976 year on Graph 1 are in the 25-50% range. However Graph 2 shows that a majority of the buildings are posted as red tags. On the hand, damaged buildings built after 1976 have the lowest numbers in damage. Overall, both graphs show that buildings built during the years 1934 to 1976 suffered the most in the earthquake. 85 & SlM iD ), D O) I/) u y j Freeways I Lakes . C ity B o u n d a r ie s 0 ■ . ! u u o fir J? u o *c .2 .E re n »> T3 *o I > C L > X Note: PretfonMu nt period 1n 0 1 2 e ★ Epicenter Rock □ P leisto cen e alluvial and m arine te rra c e d ep o sits □ HolDcene sediments [ § § | § j Liquefaction After 1976 © During 1934 and 1976 O Before 1934 Figure 5-9 Year built ranges for damaged buildings, according to the Los Angeles City Code. 86 N U M B ER O F COMMERCIAL BUILDINGS Year Built vs. Percent Damage 1 2 0 - / V A / / . / A / / / _/ / / _/ / _/ / / / _/ / / A / ■ » I * £ r- ; S ;3 s ? * * $ ► ? 'F ~ v m ~-3. A V ( ;‘ ' ~ 7 . TOT. DAM . BUILDINGS 2 5 -5 0 % DAMAGE 5 1 -7 5 % DAMAGE J / 7 6 - 1 0 0 % DAMAGE PRIOR 1934 1934-1976 AFTER 1976 C / 1 o 120 1 0 0 ZD CD < < J Q C b J o o L i . o Q C L U C D 2 Z / / / / t o t a l Da m a g e RED TAGS YELLOW TAGS GREEN TAGS PRIOR 1934 1 9 3 4 - 1 9 7 6 AFTER 19 76 Figure 5-10 Graph 1 : Categorized year built damaged buildings separated by their percent in damage. Graph 2: Categorized year built damaged buildings separated by their posted tags. 87 A building’s construction type is vital to its performance in an earthquake. Furthermore the building’s performance is dependent on the size of the base shear induced by an earthquake. Hence the base shear is a combination o f the building’s mass and its structure type. Although identifying the structure type of a building is confidential, since private owners have the right not to give out that type o f information, the uniform building code gives out general codes for the building structure type. Unfortunately more than one code may apply to the building’s structure type. The Los Angeles Assessor’s office identifies the building’s structure type in a more precise way, but is also confidential. Hence Table 6-3 gives the number in damage for the different structural buildings of different structure types. Prior 1934 From 1934 to 1976 After 1976 Existing buildings 11,998 27,698 5,288 Damaged buildings 83 110 52 Steel frame 1 3 3 Reinforced concrete 2 3 1 Wood and/or steel 48 40 24 Masonry/Concrete 20 55 22 Table 5-7 Buildings by structural type vs. year ranges. Type of structures for all damaged buildings (from Assessor’s office) are shown in Figure 5-11. The majority of the buildings on the map are composed of Masonry/Concrete and Wood and/or Steel frame buildings. As a result damaged buildings in the San Fernando Valley area have an equal mixture of both. However the majority of 88 the buildings concentrated in the Hollywood region and along the 10 and 5 interstate freeways are composed o f Masonry/Concrete type structures. Nevertheless, by viewing the map, we can say that structure types such as Wood and/or Steel and Masonry/Concrete were effected the most by the earthquake, see Figure 5-12 and 5-13 for individual mapping of both structure types. The percent in structural damage on Figure 5-14 shows Masonry/Concrete type buildings as the worst effected in damaged in the earthquake. The worst effected areas for this type o f structures are in the Hollywood region and along freeway 10. In addition to the damage the percent damage for both regions are in the 76 to 100% range. The ground displacement and acceleration in the San Fernando Valley area was high, but the percent in building damage for all the buildings were in the low ranges. Graphs 1 and 2 on Figure 5- 15 will show the damage pattern for all the structure types. As a result, both graphs show Masonry/Concrete and Wood and/or Steel buildings contain the most damaged buildings. Both structure types range in the low percent damage and are posted with red tags. 89 O) cn irt o u U < J 'S ... . n ft d j < D V X > Q. > X tot#: Prodomrunt period Freeways Lakes ■ City Boundaries e i t Epicenter Pleistocene alluvial and marine terrace deposits lllflf Rock □ □ Holocene sediments milljiH Liquefaction A Steel frame V Reinforced concrete farme □ Masonary/Concrete O Wood and/or steel frame Figure 5-11 Building’s damaged by structural types. r ; \ Pacific Ocean < j r _ ® j E c 0 1 O in u o } F r e e w a y s I L a k e s . C ity B o u n d a r ie s ^ Epicenter Rock B § 1 £ .s x > a > 5 Noi«: Predominant period 1n o t 2 W □ P leisto cen e alluvial and m arine te rra c e d ep o sits □ H olocene s ed im en ts I I Liquefaction Wood and/or steel buildings Figure 5-12 Wood and steel or wood framed structures. 91 Mason ary/con crete buildings w \ Pacific Ocean S ee O ) D > V ) u u s 8 j ; a m 5 » * © x > a , > i Ntti P j* d c m n a * p # ftD d ^ F r e e w a y s I Lakes . C ity B o u n d a rie s 1" 0 * 2 e ^ Epicertef | | | | R o c k □ PWstoeene aliMal and r w r « terrace depotftt □ H o k K tn e s e g m e n t s ffHUfl Uquefacbon Steel frame A A A Masonary/ concrete n □ □ Reinforced concrete frame y 76-100% dam V 51-75% dam V 25-50% dam Wood and/or steel frame © 76-100% dam O 51-75% dam O 25-50% dam Figure 5-14 Percent damage by structure types. 93 NUMBER O F COMMERCIAL BUILDINGS . NUMBER O F COMMERCIAL BUILDINGS Percent Damages of A ll Structures W OOD AND/OR STEEL MASONARY/CONCRETE REINFORCED CONCRETE STEEL FRAM E 25-50% 51-75% 76-100% Tag Posted vs. Structural Type 70 60 50 40 30 20 10 0 . / _/ . / / / / / / / / / / / / / / / / / / / / / / / / _ /W O O D AND/OR STEEL /MASONARY/CONCRETE REINFORCED CONCRETE STEEL FRAM E RED YELLOW GREEN Figure 5-15 Graph 1 : Percent damage o f all structure types. Graph 2: Posted tags vs. structure types. 94 A Summarized Overview of the Results: Table 5-8 gives the percentages of damage related to the total number of damaged buildings within the given year ranges. Table 5-9 gives the percentages of damage related to the total number of damaged buildings. Damaged Buildings Prior 1934 From 1934 to 1976 After 1976 Total of 245 buildings 83 110 52 Red tags 56.6% 63.6% 46.0% Yellow tags 42.2% 30.9% 50.0% Green tags 1.2% 5.5% 4.0% 76-100% 33.7% 16.4% 17.3% 51-75% 12% 11.8% 7.7% 25-50% 53.0% 71.8% 75.0% Wood and/or steel 24% 50% 42% Masonry/Concrete 57.8% 36.4% 46% Table 5-8 Percentage o f damage o f year ranges. 95 Damaged buildings Prior 1934 From 1934 to 1976 After 1976 Red tags 19.2% 28.6% 9.8% Yellow tags 14.3% 13.9% 10.6% Green tags 0.41% 2.5% 0.82% 76-100% 11.4% 7.4% 3.7% 51-75% 4.1% 5.3% 1.6% 25-50% 18.0% 32.2% 15.9% Wood and/or steel 8.2% 22.5% 9.0% Masonry/Concrete 19.6% 16.3% 9.8% Table 5-9 Percent o f damage related to the total number o f damages (245 buildings). Out of the 245 damages, 141 buildings were reported as red tagged in which a total of 70 red tags were assigned to buildings built for the years 1934 to 1976. Consequently out of the 245 damages, 28.6% were reported as red tags within that year range, where 63.6% of the 110 buildings for that year range were red tags. The graph on Figure 5-16 will show the relations for all the categorized years. 96 P 70 47 Prior 1934 70 1 9 3 4 to 1976 24 After 1976 % within their catagorized year ranges % from 245 damaged buildings Figure 5-16 Percent o f red tagged buildings by: I) total number o f damaged buildings II) total number o f damaged buildings within their categorized year ranges. The majority of percent in building damage were in the 25-50% range. A total of 162 buildings had 25-50% in building damage. Buildings built between 1934 to 1976 ( a total of 79 buildings), 32.2%, had building damage in the 25-50% range. For the same year category out of the 110 damages, 71.8% were reported with damage in the low percent range. Buildings built prior to 1934 had the highest number of damages in the 76- 100% building damage. For instance a total of 55 buildings were reported in the high percent range. As a result up to 28 out of 245, 11.8%, buildings were reported with building damages in the 76-100% range for buildings built prior to 1934. Figure 5-17 and 5-18 will show summarized graphs for the percent in building damage for all the categorized year built building damages in the 25-50% and 76-100% range. 97 Buildings with Masonry/concrete and Wood and/or steel structural frames had the highest number of damage with a total of 112 and 97 damaged buildings reported. Within the year range of 1934 to 1976, a total of 55 out of 97 buildings with Wood and/or Steel structures were reported as damaged. On the other hand 48 out of 112 Masonry/Concrete structural frame buildings built prior to 1934 were reported as damaged. Figure 5-19 and 5-20 will show summarized graphs for the percentage in number of building damage for both structural types. LU O < < o o 100-r 90 80 70 60 50 44 Prior 193 4 79 1 934 to 1976 39 After 1976 % within their catagorized year ranges % from 245 damaged buildings Figure 5-17 Graph showing the percent in number o f 25-50% in building damage by: I) total number o f damaged buildings II) total number o f damaged buildings within their year ranges. 98 L d O < < Q O 44 Prior 19 3 4 79 193 4 to 1976 39 After 1 9 7 6 SSSSSi % within their catagorized year ranges 1-113 % from 245 damaged buildings Figure 5-18 Graph showing the percent in number of 76-100% in building damage by: I) total number of damaged buildings II) total number of damaged buildings within their year ranges. u 70 48 P rio r 1 9 3 4 40 1 9 3 4 to 1 9 7 6 24 A fter 1 9 7 6 1 ^ ^ % within their ca ta g o rized year ran ges % fro m 2 4 5 d a m a g ed buildings Figure 5-19 Percent of Masonry/Concrete damaged buildings by: I) total number of damaged buildings II) total number of damaged buildings within their year ranges. 99 4204 L l I O < < Q U - o B 20 Prior 1934 55 1934 io 1976 22 After 1976 % within their catagorized year ranges % from 245 damaged buildings Figure 5-20 Percent of Wood and/or Steel damaged buildings by: I) total number of damaged buildings II) total number of damaged buildings within their year ranges. The graphs on Figures 5-21 through 5-23 will give a summary for each of the conditions just explained in Figures 5-16 through 5-19. As a result these graphs will show a summary for the highest rates in damage for the given conditions and their relations in. too ? 6 0 S3 2 0 - RED TAGS 2 5 - 5 0 % DAMAGE 7 6 - 1 0 0 % DAMAGE MASONRY/CONCRETE { WOOD AND/OR STEEL Prior 1934 1934 to 1976 After 1976 Figure 5-21 A summary for the conditions with the highest rate in damage for the given year range. Aszz O 9 0 RED TAGS / 2 5 - 5 0 % DAMAGE 7 5 - 1 0 0 % DAMAGE MASONRY/CONCRETE WOOD AND/OR STEEL Prior 1934 1934 to 1976 After 1976 Figure 5-22 Summarized percent for the conditions with the highest rate in damage within their categorized year range. 101 tn o 3 m Q L d o < < O Wi RED TAGS 2 5 - 5 0 % DAMAGE 7 6 - 1 0 0 % DAMAGE Prior 1934 1934 to 1976 After 1976 - / MASONRY/CONCRETE { WOOD AND/OR STEEL Figure 5-23 Summarized percent for the conditions with the highest rate in damage by the total number of damaged buildings. The graph on Figures 5-21 show that 245 buildings damaged in the earthquake, those built prior to 1934 had the most damage for the Masonry/Concrete building and the 76-100% in building damage. Buildings built within the 1934 to 1976 year range had the highest damage for Wood and/or Steel frames, red tags and 25-50% in building damage. The percentages of total and in categorized year ranges for the damage are given in a summarized format in Figures 5-22 and 5-23. During an earthquake the structural frame of a building plays an important role in a buildings performance. In addition to the type of structure, four general structural frames 102 are considered for all damaged buildings. They are known steel frame, reinforced concrete, masonry or concrete and wood and/or steel framed structures. To illustrate the damage numbers for each structure type, Figures 5-24 through 5-27 give the following graphs with relations to the building’s posted tag and the year in which they were built. Consequently the number of damages for steel framed structures and reinforced concrete in Figures 5-24 and 5-25, are so small that they can be neglected. On the other hand the structures that received the highest number in damage are given in Figures 5-26 and 5-27. Looking back at Table 5-6, 141 red tags were reported. Out of the 141 damages 69 Masonry/Concrete structures were reported with red tags. Figure 5-26 shows that a high number, 31, of the red tagged Masonry/Concrete structures were for buildings built 1934-1976. Similarly, buildings built prior to 1934 had a total of 27 damaged Masonry/Concrete structures. Buildings of Wood and/or Steel structures have similar damage patterns as for Masonry/Concrete structures within the 1934-1976 range, where a total of 31 red tagged Wood and/or Steel buildings received damage. Unlike the Masonry/Concrete structures, large numbers of buildings, 55, were damaged in the 1934-1976 year range for all tagged buildings (see Figure 5-27). 103 Number of Buildings 3 0 - ' T 3 2 5 - 2 0 - — / PRIOR TO 1 9 3 4 / FROM 1 9 3 4 TO 1 9 7 6 AFTER 1 9 7 6 R e d Yellow G r e e n Figure 5-24 D am age pattern for steel frame structures. PRIOR TO 1 9 3 4 FROM 1 9 3 4 TO 1 9 7 6 AFTER 1 9 7 6 Red Yellow G r e e n Figure 5-25 Damage pattern for reinforced concrete structures. 104 m s ?wmm “ \ s i t PRIOR TO 1 9 3 4 FROM 1 9 3 4 TO 1 9 7 6 AFTER 1 9 7 6 Red Yellow Green Figure 5-26 Damage pattern for masonry or concrete structures. n 10 :v:v;v>;v>:v:v; j \ ' , V \ y s V / k V A V / W A 'A 'iV A V A ' t o S ^ s ' ^ . '/ w W / A V s V 2 l PRIOR TO 1 9 3 4 FROM 1 9 3 4 TO 1 9 7 6 AFTER 1 9 7 6 Red Yellow Green Figure 5-27 Damage pattern for wood and/or steel structures. 105 The amount of damage for a building in an earthquake is rated by percent of building damage. Hence the percent of damage are categorized as 25-50%, 51-75% and 76-100%. The numbers for the damage given by their structure types and categorized year ranges are given in the following graphs on Figures 5-28 through 5-30. Figure 5-28 shows that the highest number of damage, 156 buildings, have building damage in the 25-50% range. As a result, buildings in that percent range contain the most number of damage. Masonry/Concrete and Wood and/or Steel structures had the highest damage where 69 buildings were reported for the 1934-1976 year range. Approximately 38 of those buildings were of Wood and/or Steel structural type. On the other hand Masonry/Concrete structures had the highest number of damage, 79, with an equal number o f damage, 31, for both 1934-1976 and prior to 1934 year ranges. A low number of buildings were damaged in the 51-75% range, see Figure 5-29. Once again the buildings effected the most were the Masonry/Concrete and Wood and/or Steel structures. Finally, buildings damaged in the 76-100% range had the second highest numbers. A total of 41 buildings were damaged, where 20 buildings were reported as Wood and/or Steel and 18 buildings as Masonry/Concrete structures. Hence both the 1934-1976 and prior to 1934 year ranges hold the majority of number in damages, see Figure 5-30. 1 0 6 UM&C fiM flJS L ta tJ B . m m m <J 3 0 WOOD AND/OR STEEL MASONARY/CONCRETE REINFORCED CONCRETE STEEL FRAME P r i o r 1 9 3 4 1 9 3 4 - 1 9 7 6 A f t e r 1 9 7 6 Figure 5-28 Damage pattern for 25-50% in building damage. in O ) _/ 5 3 ° - ‘d 00 25 2 0 - / . / o L . 1 5 (1 ) jD 10 < r c 5 - t D / / / / / / / / / / / / / / / / W OOD A N D /O R STEEL M A SO N R Y /C O N C R ET E REINFORCED CONCRETE STEEL FRAME Prior 1934 1 9 3 4 -1 9 7 6 After 1976 Figure 5-29 Damage pattern for 51-75% in building damage. 107 0 > / r 35^ Q D 25- WOOD A N D /O R STEEL M A SO N RY /CO N C RETE REINFORCED CONCRETE FRAME Prior 1 9 3 4 1 9 3 4 - 1 9 7 6 After 1976 Figure 5-30 Damage pattern for 76-100% in building damage. Results for Different Occupancies: Graph 1 of Figure 5-31 shows commercial buildings by occupancies types. The graph present damaged buildings with percent in building damage greater and less than 25%. The y-axis for the graph gives the number of buildings in thousands, hence Graph 2 on Figure 5-31 provides a more detailed view of the damages without the existing buildings. Overall there are 13 types of occupancies, in which offices, manufacturers and warehouses have the highest number of existing buildings. Graph 2 shows that offices and retail stores have the highest damage. Damage to warehouses compared to its high number of existing buildings were very low (see Graphs 1 and 2). 1 0 8 Figure 5-32 shows which building occupancy types suffered the most damage once compared to its total number of existing buildings. The Graph shows that schools suffered the most damage, in which case approximately 19.4% of the existing schools in Los Angeles city had less than 25% building damage. However gas stations, warehouses and manufacturers suffered the least number of damages with building damage greater and less than 25%. Finally, buildings such as churches, hospitals and retail stores suffered the greatest percent in building damage greater than or equal to 25%. 109 C O o z CD o o c 1 _ 1 _ J c n 10 o 2 - • CHURCH C A S STATIO N HOTEL OFFICE RESTAURANT THEATER AMUSEMENT g a r a g e h o s p i t a l m a n u f a c t o k - r e t a il s c h o o l w a r e h o u s e EXISTING BUILDINGS ; 2 5 % D A M A G ES > = 2 55? DA M AG ES 6 0 0 5 0 0 LO ^ 4 0 0 - Q Z D CCS oo - LU CO 200 1 OO C H U R C H C A S S T A T IO N H O T E L O F F IC E R E S T A U R A N T T H E A T E R A M U SE M E N T G A R A G E H O S P IT A L M A N U F A C T O R RETA IL S C H O O L W A R E H O U S E < 2 5 % D A M A G E S > = 2 5 % D A M A G E S Figure 5-31 Graph 1 : Types of building occupancies for damaged and existing buildings. Graph 2: Types of building occupancies for damaged buildings. 110 2 0 _I O f — yn x Li_l 10 o < o CHURCH GAS STATION HOTEL OFFICE RESTAURANT THEATER AMUSEMENT GARAGE HOSPITAL MANUFACTOR RETAIL SCHOOL WAREHOUSE + — < 2 5 % DAMAGES > = 2 5 % DAMAGES Figure 5-32 Percentage for different occupancies. Damaged Buildings vs. Number of Floors: One aspect of building’s performance in an earthquake is the number of floors or height. In other words the behavior of a buildings lateral motion is related to its period and the period is dependent on the structure type and height. Figure 5-33 shows the damaged and red tagged buildings by number of floors. The results show single story commercial buildings had the most damage where majority were assigned with red tags. I ll All Posted VS Red Posted Commercial Buildings 140 120 - -9 40 U P P ' A l l P o ste d Red ta g s Number of Floors Figure 5-33 Number of floors for damaged and red tagged buildings. Figure 5-34 shows the location of buildings by height. Number of floors ranging from 6 to 13 have been identified with the same symbol since the damage numbers are very low. As a result the map shows single story buildings concentrated in the San Fernando Valley region around the epicenter. Further away from the epicenter such as Sherman Oaks, Van Nuys, Hollywood and along the 10 freeway, two story buildings were effected the most. 112 Pacific Ocean o» o } Freeways ■ Lakes ■ City Boundaries 0 \ D g f t ’ s a a 8 8 -I .is .s n n a * T 3 3 X > CL > X Note: Predominant period 1n e 'it Epicenter HfHi Rock □ □ Holocene sediments tftfHtfi Liquefaction Pleistocene alluvial and marine terrace deposits Number of floors: One □ Two o Three A Four to five V Six to thirteen Figure 5-34 Damage by number of floors. 113 Damaged Buildings bv Distance From Rivers: The water table for soils close to rivers are usually high. Hence buildings built close to rivers are positioned over saturated soil. Los Angeles has many rivers. Figure 5-35 shows the rivers running across San Fernando Valley region. The distance for the damaged buildings from rivers range from one to three mile radius. The map shows that the majority of the red tagged buildings are located closest to the rivers. 114 Pacific Ocean @ Red tagged buildings □ Yellow tagged buildings Green tagged buildings Figure 5-35 Map showing relative distance of river from damaged buildings. 115 CONCLUSION The Northridge earthquake measured at 6.8 magnitude on the Richter scale lasted for approximately 30 seconds with strong motion of about 5 seconds. The time duration may have seemed like a short time, but to the victims in the Los Angeles area, 30 seconds felt like an endless horror. As a result, out of the 45,000 existing commercial buildings, 0.5% (245 in damage) exceeded 25% in building damage throughout the city. Buildings built of Masonry/Concrete and Wood and/or Steel framed structures suffered the most in the earthquake. Majority of the buildings built from these two structural frames had: a) Building damage in the 25-50% range b) Posted with red tags In addition, majority of the buildings built prior to 1934 had damage due to Masonry/Concrete structures. According to the Los Angeles City code, the categorized year built ranges were, prior to 1934, 1934-1976 and after 1976. Hence buildings built after 1976, being the most current upgrade in the code, had damage rate exceeding all of the categorized year ranges once related to the existing buildings. The geological site played a major role in the earthquake. The ground displacements for the different geological sites are as follows: a) Maximum displacements were located on soft soil, close to the epicenter with small acceleration. 116 b) Maximum accelerations were found to be located on rock with small displacements. Out o f 245 damaged buildings, 195 buildings were found to be on soft soil with large displacements and small accelerations. Buildings located close to the border line of rock and soft soil experienced severe damage. In which many of those buildings had high percent in building damage and were posted with red tags. The damage pattern in the city o f Los Angeles had an even spread on soft soil. In addition, concentrations of damage were found in areas such as: a) Hollywood b) Van Nuys c) Sherman Oaks d) along the Interstate 10 freeway Hollywood holds the most distinct features. Approximately 95% of the damage in the Hollywood region were mainly composed of unreinforced masonry buildings built before 1934 with 25-50% in building damage and posted with tags. Another important aspect that was noticed was in the San Fernando region. Distance for the damaged buildings from the rivers were noticed to be: a) within the one to three mile range, b) in which a majority o f the red tagged buildings were located close to the rivers. In order for a building to be built, a number o f points have to be taken into account. They are location in relation to the type of structure. These two points combine to give the safety o f the building. Another important aspect is quality in construction. 117 There has been too many flaws in the past, a point which was clearly pointed out by a report on ‘Quality Control in Seismic Resistant Construction’, by G.G. Schierle. 118 RECOMMENDATIONS FOR FUTURE STUDIES: Future studies can be done on ground motion such as displacement and acceleration and their relative distance from the epicenter. A further step in this could be to study the ground period related to the soil type. In addition the period for a soil o f the same station for different earthquakes could be taken into account. Another study could focus on building structure types and performance in an earthquake. Past earthquakes have shown that a building’s performance depends greatly on its structure. Hence not all structural frames perform as well as expected. Finally, quality in construction is another aspect. Many building fail in an earthquake due to flawed construction or flawed design. 119 BIBLIO G RAPH Y Lagorio, H. J., (1990) A n Architects Guide to Non Structural Seismic Hazards, Wiley, New York. Ambrose, J. (1988) B uilding Structures, Wiley, New York. Iacopi, R., (1964) Earthquake Country, Lane B ook Company, San Francisco. Spangle, W., (1987) Pre Earthquake Planning fo r Post Earthquake Reconstruction (PEPPER) Southern California Earthquake Preparedness Project (SCEPP), Sacramento. UBC/EERC (1994) 94/08 Preliminary Report on the Principle Geotechnical Aspects o f the January 17, 1994 Northridge Earthquake, U.C. Berkeley, San Francisco, C.A. UCB/EERC (1975) 75-17 Relationships Between M aximum Acceleration, M aximum Velocity, Distance fro m Source and Local Site Conditions fo r M oderately Strong Earthquakes, U.C. Berkeley, San Francisco, C.A. UCB/EERC (1975) 75-28 Evaluation o f Soil Liquefaction P otential D uring Earthquakes, U.C. Berkeley. C.A. Bolt, B.A., Horn, W.L., et al. (1977) Geological Hazards, Springer-Verlag, New York. Arnold, C. and Reitherman, R. (1982) B uilding Configuration and Seismic Design. Wiley, New York. ALA/ACS A (1994) B uilding at Risk, Council on Architectural Research, NHRP, Washington, D.C. Dept, of City Planning, L.A.., (1990) Socio Demographic Studies, City o f Los Angeles. LUPAMS, (1993) Report on Land Use Planning in L.A., Department o f City Planning, Los Angeles. Schierle, G.G., (1994) Architects and Earthquakes, Seminar Report, U.S.C. School o f Architecture, Los Angeles. 120 Schierle, G.G., (1993) Quality Control in Seismic Design, National Science Foundation Report, Washington D. C. Science, Vol. 266, The Magnitude 6.7 Northridge Earthquake, California, Earthquake o f 17 January 1994, Scientists o f the U.S. Geological Survey and the Southern California Earthquake Center. 121 INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality o f the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9 " black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. A Bell & Howell Information Company 300 North Zeeb Road. Ann Arbor. M l 48106-1346 USA 313/761-4700 800/521-0600 UMI Number: 1376451 UMI Microform 1376451 Copyright 1995, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103

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Asset Metadata

Creator Farazmand, Mansour (author)

Core Title A statical analysis and structural performance of commercial buildings in the Northridge earthquake

School School of Architecture

Degree Master of Building Science

Degree Program Building Science

Degree Conferral Date 1995-05

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag architecture,engineering, civil,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Schierle, Goetz (committee chair), Schiler, Marc (committee member), Vergun, Dimitry (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-1216

Unique identifier UC11356880

Identifier 1376451.pdf (filename),usctheses-c18-1216 (legacy record id)

Legacy Identifier 1376451-0.pdf

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Document Type Thesis

Rights Farazmand, Mansour

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Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

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