Close
About
FAQ
Home
Collections
Login
USC Login
Register
0
Selected
Invert selection
Deselect all
Deselect all
Click here to refresh results
Click here to refresh results
USC
/
Digital Library
/
University of Southern California Dissertations and Theses
/
Lateral design analysis: Web application. Design for wind and seismic forces in buildings
(USC Thesis Other)
Lateral design analysis: Web application. Design for wind and seismic forces in buildings
PDF
Download
Share
Open document
Flip pages
Contact Us
Contact Us
Copy asset link
Request this asset
Transcript (if available)
Content
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 of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, 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. UMI A Bell & Howell Information Company 300 North Zeeb Road, Ann Arbor MI 48106-1346 USA" 313/761-4700 800/521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LATERAL DESIGN ANALYSIS: WEB APPLICATION: DESIGN FOR WIND AND SEISMIC FORCES IN BUILDINGS. By Manasi Sham Khopkar A Thesis Presented To The FACULTY OF THE SCHOOL OF ARCHITECTURE UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment o f the Requirements for the Degree MASTER OF BUILDING SCIENCE MAY 1999 Copyright, Manasi Khopkar 1999 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1395131 UMI Microform 1395131 Copyright 1999, 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 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UNIVERSITY OF SOUTHERN CALIFORNIA SCHOOL OF ARCHITECTURE UNIVERSITY PARK LOS ANGELES, CA 90089-0291 ‘ This thesis, unitten G y M a m a s i - __________________ under the direction o f h -Cy ‘ Thesis Committee, and approved G y aid its m em G ers, has G een presented to and accepted G y the (Dean o f The SchooC o f Architecture in partiaCfuCfittment o f the requirements fo r the degree of M A S T E R £>P ■&UILDIM6 (Dean mate o g /1 a/9 9 THESIS COMMITTEE Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS I would like to recognize and thank the following people without whose help and encouragement this thesis would have never seen the light of the day. Prof. G G Schierle, Professor at the University of Southern California and the chairperson of my committee for his constant guidance, encouragement and patience and most importantly for considering me capable o f using his application as a precursor to my program. I would also like to thank him for having me as his Teaching Assistant and later Research Assistant, which aided me in supporting myself through this program. Prof. Marc Schiler, Director of the Master o f Building Science Program and Associate professor at the University of Southern California for his advice and encouragement and support without which I would not have been in this program. Prof. Doug Noble and Karen Kensek, Members of my Committee and professors at the University of Southern California. It was through them that I was exposed to the Virtual World and could develop this interest further. Thank you Karen for pushing me through ARCH 407, if it wasn’t for that I would not be here today. The Dean and the Staff at The School of Architecture, If it wasn’t for the constant encouragement that I received from them in form of Scholarships and Teaching Assistantship, I would not have been here at all. With special thanks to Enrique Barajas, for answering my endless questions about computers. And last but not the least, my colleagues who put up with my moods during the critical times. With special thanks to Vagish Narang, without whom this program would have never happened. ii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT A Computer program that allows the user to analyze specific architectural profiles and presents the result in a graphic form. This thesis is a web application for preliminary analysis of wind and seismic forces on buildings. The first objective was to identify a data input system that would be simple and intuitive, yet at the same time fairly comprehensive in nature. All phases of data input are aided with relevant theoretical/ practical examples to make the interface user friendly. The second and by far more important objective was to device an output system that would go beyond display of numbers. From background studies of similar concepts, such as LDG, the Graphic Display System was considered to be most effective and user friendly. The program is intended to be a Teaching Tool that analyses lateral forces in buildings, explains the concepts involved in the process, and displaces results in visually simple and comprehendible format. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Introduction 1 Part One: Background Research. 1.0 Sources and effect of lateral loads 1.1 What are Lateral Loads? 3 1.2 Sources of Lateral Loads (Wind and Seismic) 3 1.3 Effects of Lateral Loads 4 1.4 Application of Lateral Loads 8 2.0 Types of Lateral Resistive Systems 2.1 Shear wall 11 2.2 Cantilever 13 2.3 Moment frame 14 2.4 Internally Braced Frame 16 2.5 Externally Braced Frame 17 2.6 Eccentrically braced frame 18 3.0 Early Design Considerations 3.1 General Considerations for Wind forces 20 3.2 General Considerations for Earthquake forces 22 4.0 LDG: Lateral Design Graphs 29 5.0 Numerical Data for Analysis 5.1 Tables for Wind Analysis 32 5.2 Tables for Seismic Analysis 35 iv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Part Two: Lateral Design Analysis. 6.1 What is extracted from LDG? 3 8 6.2 What is the Application about? 39 6.3 Description of Data Input 40 6.3.1 Building geometry 42 6.3.2 Structure type 45 6.3.3 Wind factors 47 6.3.4 Seismic factors 48 6.4 Description of Data Output 50 6.5 Conclusion 55 6.6 Recommendation for future research 56 Bibliography 57 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES Figure 1.1 General Effects of Wind Figure 1.2 Motion of Tall Buildings during Earthquake Figure 1.3 Fundamental Seismic Response of Building Figure 1.4 Propagation of Wind Forces and Basic Functions of Elements System Figure 1.5 Seismic Loads Caused by Wall Weight Figure 2.1 Functions of Shear Wall Figure 2.2 Response to Lateral Forces by Cantilever Structures Figure 2.3 Behavior of Moment Frames Figure 2.4 Types of Lateral Bracing and Forces in Members Figure 2.5 Forms of Eccentric Bracing Figure 2.6 Knee-Braced Bent Figure 3.1 Forces in L-Shaped Building Figure 3.2 Damage to Roof Diaphragm Figure 3.2(a) Damage to Shear Walls Figure 3.3 Location of Possible Failures in Shear Wall Design Figure 3.4 Basic Shear Wall Yield Behavior Figure 3.5 Soft Story Failure Figure 3.6 Soft Story Failure Figure 4.1 Input Screen from LDG Figure 4.2 Output Screen from LDG Figure 6.1 Screen Images From LDA Figure 6.2 Building Geometry Input Screen Figure 6.3 Structure Type Selection Screen Figure 6.4 Wind Factor Selection Screen Figure 6.5 Seismic Factor Selection Screen Figure 6.6 Wind Analysis Checklist Figure 6.7 Seismic Analysis Checklist Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF UBC TABLES Table 1. Wind Stagnation Pressure (Qs)(16-F) 32 Table 2. Combined Height, Exposure And Gust Factor Coefficients (Ce) (16-G) 32 Table 3. Pressure Coefficients (Cq) (16-H) 33 Table 4. Occupancy Category (16-K) 34 Table 5. Seismic Zone Factor (Z) (16-1) 35 Table 6. Soil Profile Type (16-J) 35 Table 7. Seismic Coefficients (Ca) (16-J) 35 Table 8. Seismic Coefficients (Cv) (16-R) 36 Table 9. Near-Source Factor (Na) (16-S) 36 Table 10. Near-Source Factor (Nv) (16-T) 36 Table 11. Structural Systems 37 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. INTRODUCTION With the occurrences of major earthquakes and hurricanes/tornadoes the study of lateral design is now a major international concern. The loss of life due to failure of the buildings is raising the level of professional responsibility and the expanded knowledge of which the professional had to be cognizant. With this change in the range of knowledge has come a revised conception of professional responsibility and liability that is affecting all design areas. If protection from the effect such natural disasters like earthquakes and hurricanes could be segregated and left to the engineer, there would be little cause for the architect to show concern for the failure of the buildings. However this is not the case, the question then is what does the architect do that influences the performance of the building against lateral wind and seismic forces that is expressed as a concern by engineers? The answer to that is that the architect conceives and controls the configuration of the building, which includes the nature, size and position of the structural and non-structural elements that may affect the structural stability of the building. In conceiving the building configuration the architect influences, or even determines the kinds of resistive systems that can be used or even to the extent to which they will be, in the broadest sense, be effective. This is not to suggest that configuration is primary, and detailed engineering design and construction techniques secondary or of no consequence. But it does mean that the designer’s first ideas on configuration are very important, because at the conceptual stage, perhaps even before there is any engineering discussion, he is making decisions of great significance to the later engineering analysis and detail design. l Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Earthquakes and hurricanes attack the building as a whole and do not distinguish between elements designed by the architect and the engineers and thus, the architect is full participant in the lateral design. A great deal o f a building’ s inherent resistance to lateral forces is determined by its basic plan layout... Engineers are learning that the building’ s shape, symmetry, and its general layout developed in the conceptual stage are more important, or make fo r greater differences than the accurate determination of the code prescribedforces... Structural Engineer William Holmes, 1976 (Arnold, 1982) Thus the importance of preliminary lateral analysis by designers during the conceptual stage of the design is very critical. This awareness among the professionals is leading to the development of programs to aid the designers in designing for lateral resistance. Such analytical applications help the designer have a rough idea of what forces/factors they are dealing with. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER ONE SOURCES AND EFFECTS OF LATERAL LOADS 1.1 What are lateral forces? The term refers to the horizontal forces on buildings, which means sideways. This identifies these forces in relation to the major orientation of the effect of gravity as a vertical force. Conceptually, therefore, designing of lateral forces is typically viewed in terms of bracing a building against bending, shear, drift and overturning. 1.2 Sources o f lateralforces The two main sources of lateral loads on buildings are wind and earthquake. Wind is basically moving air, and thus understanding the various effects of wind on buildings would require some knowledge of fluid mechanics. However from the designer and engineers viewpoint the wind pressure on a building and its effect on the lateral bracing system is most critical. Earthquakes or seismic forces have various disastrous effects on buildings, including acceleration, displacement, tidal waves and massive ruptures along earth faults and violent vibratory motions. It is for these effects that we design the lateral bracing systems for buildings, dealing mostly with the horizontal aspect of ground motion. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.3 Effects of lateral loads. Critical Wind Effects On Buildings The major effect of wind on buildings can be generalized to some degree because we know a bracketed range of characteristics that cover most of the conditions. Some of the general assumptions made are: • Most buildings are bulky in shape, resulting in a typical aerodynamic response • Most buildings provide closed, fairly smooth surfaces for wind • Most buildings are fit snuggly to the ground, presenting a particular situation for the drag effect of the ground surface • Most buildings have relatively stiff structures, resulting in fairly limited range of variation to the natural period of vibration of the structure The primary effect of wind is visualized in the form of pressures normal to the building’s exterior surfaces. The pressure however does not represent the actual effect on a single building surface, but the entire effect of all the surface pressures visualized as a single pressure on the windward side of the building. The various effects are as follows: 1. Inward direct pressure on the windward side exterior wall 2. Suction on the leeward exterior walls 3. Uplift pressure on the roof surfaces 4. Horizontal sliding of the building off its foundation 5. Overturning or toppling of the building 6. Torsion or twisting due to asymmetrical wind silhouette or lateral resistive systems 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Drag D ire ct p ressu re; S u c t i o n str e a m lin in g e f f e c t o f r o u n d e d b u ild in g fo r m s la r g e d r if t - f t — v ir t u a lly no d e fo r m a t io n 4- uplift r e s i s t a n c e r e q u ir ed v no u p lift overturn an d drift r e l a t e d to th e b u ild in g p rofile w in d c u p p in g e f f e c t o f o p e n s i d e s an d r e c e s s e s i n c r e o s e d f o r c e o n p r o j e c t i n g e l e m e n t s Figure 1.1 General Effects of Wind (Source: Ambrose, 1995) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Critical Earthquake Effects on Buildings The ground movements caused by earthquakes can have several types of damaging effects, and the one that is directly correlated with the lateral system design is the Direct Movement of the Structure. Direct Movement of the Structure is the motion of the structure caused by its attachment to the ground. The two primary effects of this motion are a general destabilizing effect due to the shaking and to the impelling force caused by the inertia of the structure’s mass. The force effect caused by the motion is generally directly proportional to the dead weight of the structure — or more precisely to the dead weight bome by the structure. The other major influences on the structure response are its fundamental period of vibration and its efficiency in energy absorption. The mass, the stiffness and the size of the structure basically determine the vibration period. Energy efficiency is determined by the elasticity of the structure and factors like, stiffness of supports, rigidity of connections and number of independently moving parts. A relationship of major concern is that which occurs between period of structure and that of the earthquake. For very large, flexible structures, such as tall towers and high-rise buildings, the fundamental period may be so long that the structure develops a w'hiplash effect, with different parts of the structure moving in opposite directions at the same time, as shown in the figure 1.2. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. g r o u n d m o tio n Figure 1.2 Motion of tall buildings during earthquakes (Source: Ambrose, 1995) The three general cases of structural response are illustrated by the three cases shown in the figure below. For period below 0.3 sec, the response of rigid structures is virtually no deformation or flexing. For buildings with a slightly higher period, there is some reduction in the force effect caused by the slight “giving” of the building and its using up some energy of the motion-induced force in its own motion. As the building period increases, the behavior approaches that of a slender tower as discussed earlier. r ig id s t r u c t u r e v ir t u a l ly n o d e f o r m a t i o n T = 0 . 3 s e c s e m i - r i g i d s t r u c t u r e s o m e d e f o r m a t io n 0 .3 s e c < T < 1.0 s e c f le x ib le s t r u c t u r e c o n s i d e r a b l e d e f o r m a t io n T > 1 0 s e c Figure 1.3 Fundamental seismic response of buildings (Source: Ambrose, 1995) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1.4 Application o f lateral loads To understand how a building resists the lateral load, effects o f wind and seismic force it is necessary to consider the manner of application of these forces and then to visualize how these forces are transferred through the lateral resistive structural systems and into the ground. Wind Forces: The application of wind forces to a closed building is in the form of pressure applied normal to the exterior surfaces of the building. The figure below shows a simple rectangular building under the effect of wind normal to one o f its flat sides. The lateral resistive structure that responds to this loading consists of the following: • Wall surface elements on the windward side — are assumed to take the total wind pressure and are typically designed to span vertically between the roof and the floor structures. It is loaded with uniformly distributed pressure and delivers reaction force to its supports. Even though the wall is continuous over a number of stories it is considered as a simple span over each story level and thus delivers half of its load to each supports. • Roof and floor decks — are considered as rigid planes (diaphragms), receiving the edge loading from the windward wall and distributing the load to the vertical bracing elements. While transferring forces between the end shear walls they produce bending that develops tension on the leeward edge and compression on the windward edge. It also produces shear in the plane of the diaphragm that becomes maximum at the end 8 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. shear walls. The shear is taken by the diaphragm, but the bending tension and compression is transferred to the framing at the edge of the diaphragm. • Vertical frames or shear walls — acting as vertical cantilevers receive the loads from the horizontal diaphragms and transfer them to the building foundation. These can develop shear as well as bending. The total shear force in the wall is delivered at its base in form of a sliding friction between the wall and its support. The bending caused by the lateral loads produces the overturning effect at the base of the wall and bending tension and compression at the edges of the walls. The overturn effect is resisted by the stabilizing effect of the dead load on the wall. • Foundation -anchors the vertical bracing system and transfers the load to the ground. Spon Figure 1.4 Propagation o f wind forces and basic functions of elements in a box system (Source: Ambrose, 1995) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Seismic Forces: Seismic loads are actually generated by the dead weight of the building construction. In visualizing the application of seismic forces, we look at each part o f the building and consider its weight as a horizontal force. The weight of the horizontal structure, although actually distributed throughout its plane, may usually be dealt with in a similar manner as the edge loading caused by wind. In the direction normal to their planes, vertical walls will be loaded and will function structurally in a manner similar to that of direct wind pressure, as indicated in figure 1. 4. If the wall is reasonably rigid in its own plane, it tends to act as a vertical cantilever for seismic load in the direction parallel to its surface. Thus the seismic load for the roof diaphragm would usually be considered to be caused by the weight of the roof and ceiling construction plus only those walls whose planes are normal to the direction being considered. These different functions of the walls are illustrated in figure 1.5. 1/2 o f lo a d t o r o o f 1/2 o f lo o d to fo u n d a t io n ( b ) L o a d p e r p e n d i c u l a r t o p l a n e o f w all Minor load to r o o f d u e to re la tiv e s t i f f n e s s o f w alI I M a jo r lo o d d ir e c t to f o u n d a t i o n I I Figure 1.5 Seismic loads caused by wall weight (Source: Ambrose, 1993) 1 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 2 TYPES OF LATERAL RESISTIVE SYSTEMS In this chapter the basic forms of lateral bracing systems, as presently used for most buildings are discussed. 2.1 Shear walls The box system most often uses sets consisting of horizontal planar construction (called horizontal diaphragms) and vertical planar construction (called vertical diaphragms or shear walls). The most common shear wall constructions are those of poured concrete, masonry and wood frames studs with surfacing elements. Some of the structural functions usually required o f vertical diaphragms are the following, refer figure 2.1 1. Direct Shear Resistance: This usually consists of the transfer of a lateral force in the plane of the wall from some upper level of the wall to a lower level or bottom of the wall. This results in a typical situation of shear stress and the accompanying diagonal tension and compression stresses. 2. Cantilever Moment Resistance: Shear walls generally work like vertical cantilevers, developing compression on one edge and tension on the opposite edge, and transferring an overturning moment (M) to the base of the wall. 3. Horizontal Sliding Resistance: The direct transfer of the lateral loads at the base of the wall produces the tendency for the wall to slip horizontally off its supports. 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Basic Shear Wall Configuration. (Source: Arnold, 1982) Inertial forces, diaphragm . • - » S h e a r forces G ro u n d m o t io n D ir e c t s h e e r r e s is ta n c e d ia g o n a l t e n s io n \ \ - 7 i r f r s h e a r ^ ^ \ d ia g o n a l com pression co m p ressio n t e n s on M om en t r e s i s t a n c e S lid in g r e s i s t a n c e Figure 2.1 Functions of a shear wall (Source: Ambrose, 1995) 1 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.2 Cantilever This type o f lateral system is classified into special systems. These types of systems are analogous to a nail that sustains lateral force, it is inserted in the ground and the combination of the surrounding earth and the bending capacity of the cantilever produces the lateral resistance. Fenceposts, driven piles and other structures function in this manner. ( a ) Figure 2.2 Response to lateral forces in cantilever structures: (a) Column-frame construction, columns cantilever downwards; (b) Column-platform construction, columns cantilever upward. (Source: Ambrose, 1993) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.3 Moment Resistive Frames In rigid frames with moment resistive connections, both gravity and lateral loads produce interactive moments between the members. In most cases rigid frames are the most flexible of that basic types of lateral load resistive systems. 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 Most moment-resistive frames consist of either steel or concrete. Steel frames have either welded or bolted connections between the linear members to develop the necessary moment transfers. Frames of concrete achieve moment connections through the monolithic concrete and continuity and anchorage of the steel reinforcing. Because concrete is basically brittle and not ductile, the ductile character is essentially produced by the ductility of the steel. In general the rigid frames offers the advantage of a high degree of freedom in architectural terms. Walls and interior spaces are freed of the necessity for solid diaphragms or diagonal members. For buildings planning as a whole, this is a principle asset. Unlike shear walls or X-bracing, moment frames are not generally used for lateral bracing alone. Thus their structural actions induced by the lateral loads must always be combined with the effects of gravity loads. These combined loading conditions may be studied separately in order to simplify the work of visualizing and quantifying the structural behavior, but it should be borne in mind that they do not occur independently. 14 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. m om ent in b eam m om ent in column Figure 2.3 Behavior of moment frames: (a) under gravity load; (b) under lateral load; (c) under combined gravity and lateral load; (d) lateral load on a multistory bent; (e) effect of single gravity load in a multiunit bent; (f) effects of rapid reversal of lateral loads. (Source: Ambrose, 1993) 15 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.4 Braced Frame Although there are actually several ways to brace a frame against lateral loads, the term “ braced frame” is used to refer to frames that utilize trussing as the primary bracing technique. 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. The trussing, or triangulation, is usually formed by the insertion of diagonal members in the rectangular bays of the frame. If single diagonals are used, they must serve dual function: acting in tension in one direction and in compression when the load is reversed. Because long tension members are more efficient that long compression members, frames are often braced with crisscrossed set of diagonals called X-bracing to eliminate the need for compression members. Braced frames are generally stiffer for both static and dynamic loading, having less deformation than the rigid frame. There are two basic types o f braced frames: Internal brace frames and External braced frames. _ £ ___ dual - fun ctio n in g bracing k - b ra c in g versus Figure 2.4 Types of Lateral Bracing and the forces in members. (Source: Ambrose, 1995) 16 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Internal braced frame: In this type of system the bracing is designed in the interior bays of the building as shown in Figure 2.5 below. Generally this is the type of bracing that is used for most commercial buildings. However there is one drawback of this system, when there is an eccentric load (wind or seismic) applied on the exterior surface due to the shorter length of the lever arm between the braces there is torsion or turning of the building thus making it unstable. Braces in the interior bay Figure 2.5 Internal Braced Frame External braced frame: In this type of system the braces are in the outer bay of the building, as shown in Figure 2.6 below. In this case even if there is an eccentric force because of the larger length of the lever arm between the braces, there is a greater resistive moment and thus no torsion in the building. Braces in external bays Figure 2.6 External Braced Frame 17 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2.5 Eccentrically Braced Frames A trussed structure ordinary uses member arrangements that consist of linear truss members all connected at their ends. Truss joints are therefore collections of concentric forces and the forces in members are simple axial tension or compression. A special type of trussing consists of attaching one or both ends of a member at other that the common truss joint, that is, at some point along the length of another member. The reference word eccentric is used to differentiate the structural action from that which is maintained when all members connect at common end points, thus developing what is called a concentric force system. By not connecting at the ends o f a member, the eccentric bracing induces shear and bending in the member which it connects, thus typically producing some form of rigid frame action in addition to the truss action. Shown in figure 2.5 are some types or eccentric bracing systems. These forms are used for various structural purposes and to accommodate some architectural planning. The knee-brace and the K-brace both induce bending in columns, which may be accepted in tall buildings with large columns. However, in low-rise buildings the V-bracing is sometimes preferred, as it induces bending only in the girders-which are already designed for bending. V-bracing may be installed in two positions, upright or inverted. The inverted V-bracing leaves the center portion of the rectilinear beam/column bay open, which can be used to design a hallway at that location. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. knee - bracing K -b racin g V - b ra cin g inverted V * b r a c in g Figure 2.5 Forms of Eccentric Bracing (Source: Ambrose, 1995) A . Figure 2.6 Combined form of truss and moment frame action in Knee-Braced Bent. (Source: Ambrose, 1995) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER THREE EARLY DESIGN CONSIDERATIONS 3.1 General Design Considerations for Wind The importance of design of wind as an influence on the general building design varies considerably among buildings. The location of the building is a major factor, it has been noted that the basic design pressure varies by a factor of 2.4 from the lowest wind speed are to the highest according to the UBC map. The other important factors would be the dead weight on the building, the height of the building, the type of lateral resistive system, the aerodynamic shape of the building and the exposed parts, and the large opening and recess in the surface. The following are the most essential criteria in the design of the building: 1. Dead Load Of The Building: The dead load on the building is generally advantageous in case of the wind design as it acts as a stabilizing factor against resisting uplift, overturn, and sliding and tends to reduce the vibration and flutter. However the stresses that result from the various loads may offset this gain when the dead load is excessive. 2. Anchorage For Uplift, Sliding And Overturn: Ordinary connections between parts of the building may provide adequately for various transfers of wind force. However in some cases of lightweight construction, wind anchorage may be a major consideration. 20 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3. Critical Shape Consideration: Various aspects of the building form can cause increase or reduction in wind effects. Some potential critical situations are as follows - • Flat versus curved forms. Buildings with rounded forms, rather that rectangular forms with flat surfaces offer less wind resistance. • Tall buildings that are short in horizontal dimension are more critical for overturn and possibly for the total horizontal deflection at their tops • Open-sided buildings or buildings with forms that cup the wind tend to catch the wind, resulting in more wind force than what is assumed for the wind design. Open structure must also be investigated for major outward force on internal surfaces. • Projections from building. Tall parapets, solid railings etc. catch considerable wind and add to the overall drag effect on the building. 4. Relative Stiffness O f The Structural Members: The manner in which the horizontal members of the laterals system distribute the force and the manner in which the vertical members share the force is critical in wind design. The relative stiffness of the individual members is the major property that affects these relationships 5. Allowance For Movement Of The Structure: All structures deform when loaded, the actual dimension of deformation may be insignificant in case of a concrete structure or may be considerable in case of a slender steel frame. The effect of this movement on other elements of the building construction must be given due consideration. A critical example would be in the case of doors and windows. Glazing must be installed so as to allow for some movement 2 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the glass with respect to the frame. The frame must be installed so as to allow for some movement of the structure of the building without the load being transferred to the window frame. All these considerations should be kept in mind in developing the general design of the building. If the building form and details are determined and the material is made before any consideration is given to the structural design, then it is most likely that the building may not have an intelligent design. This is not to suggest that structural concerns are the most important but just to make sure that they are not an afterthought. 3.2 General Design Considerations for Earthquake Forces The influence of earthquake considerations on the design of building structures tends to be greatest in the zones of highest probability of quakes. This fact is directly reflected in the UBC by the Z factor or seismic factor, which varies in the ratio of 1:5. Some of the considerations are: 1. Influence Of Dead Weight: Dead load in general is a disadvantage in earthquakes because the lateral forces are directly proportional to it. Choice o f material and construction details is very important in keeping the dead load to the minimum, especially at the upper levels of the buildings. Dead load is useful for the overturn resistance and the foundation anchorage. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2. Simple form and Symmetry: Buildings with relatively simple forms and with some degree of symmetry usually have the lowest requirements for elaborate bracing or complex connections. When the building is not architecturally symmetrical, the lateral bracing system must either be adjusted so that its center of stiffness is close to the centroid of the mass or must be designed for major twisting effects on the building. Many buildings are multimassed rather than consisting o a single geometrical form. If the elements of a tower building shown in Figure 3.1, are actually separated the independent movements of the separated elements will be different due to the difference in stiffness. Because of the differing orientation there will be damage to the junction. If the wings were separated they would move independently. ! " 7 . / A jj : j j j * Figure 3.1 Forces on L-shaped building. (Source: Arnold, 1982) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.2 Damage to roof diaphragm near junction of two wings, West Anchorage High School, 1964 Alaska Earthquake (Source: Arnold, 1982) Another classic problem of jointed elements is that of coupled shear walls. These are shear walls that occur in sets in a single wall plane and are connected by continuous construction of the wall, and the connecting links are wracked by the vertical shearing. As the building rocks back and forth, this effect is rapidly reversed, developing the diagonal cracking. This results in X-shaped crack patterns, which may be observed on walls of many masonry, concrete and stucco-surfaced buildings in regions of frequent seismic activity. Figure 3.2 (a) Damage to shear walls at intersections of the building wings. Note the weakening of these highly stressed walls. (Source: Arnold, 1982) 24 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3. F olio wing Through With Load T ransfer It is critical in the design for lateral loads that force the force paths be complete. Forces must travel from their points of origin through the whole system and into the ground. Where there are interruptions in the normal flow of the forces, problems will occur. In multistoried building the resolution of gravity forces requires a smooth, vertical path; thus the columns and the bearing walls must be stacked on top of each other. If a column is removed in a lower story, a major problem is created, requiring the use of heavy transfer girder to deal with the discontinuity. A common discontinuity is that of openings in horizontal and vertical diaphragms. These can be a problem because of their size, location and shape. In figure 3.3 we see the ways in which the shear wall is penetrated or reduced to a frame may cause localized areas of weakness and possible failure. Condition 5 is that of weak column strong beam, depending on the strength and stiffness of the walls and the short columns. Wm m 1. Random 2. Transfer May be interior or exterior shear walls ;Qyvg^P;: i — h r"— t.r—\ i-Xj; a± 3;f=ri J U . 4. Uniform Exterior shear walls only 5. Uniform 3 . C oupled a 6. Nonuniform Figure 3.3 Location of possible failure in shear wall design, caused by size and placement of opening. (Source: Arnold, 1982) 2 5 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The yield behavior of typical shear wall is shown in Figure 3.4. From this diagram it is seen that three types of behavior must be contained. The wall must have the capacity to resist shear forces introduced into each of its diaphragm connections, to deal with the flexure created by overturning moments and the wall frame relationship must be able to deal with the transfer o f forces. (Arnold, 1982) CofC’gypc»*l Ciaociiy ccrw alM fey * J O K O ty Figure 3.4 Basic shear wall yield behavior. (Source: Arnold, 1982) Discontinuities are usually inevitable in multistory and multimassed buildings. They add to the usual problem of dissymmetry to create many difficult situations for analysis and design and require careful study for the proper assumption for the study and the special needs of the construction. 26 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4. Soft Story Any discontinuity that constitutes an abrupt change in the structure is usually a source of some exceptional distress. Any increase or decrease in stiffness will result in some magnification of deformation and stress in a structure subjected to energy loading. Openings, notches, necking-down points and other form variation produce these abrupt changes in either the horizontal or vertical structure. A specially critical situation is the “Soft Story” effect. The soft story is most common at the ground-floor level between the rigid foundation and the relatively much stiffer upper level system, however it is also possible at some upper level. This condition is essentially one of change of mass or relative stiffness. A classic case is a very open, lightly structured space beneath a solid form of construction, a typical example would be of an apartment building with parking below created by merely lifting the apartment up and providing light columns for support. Figure 3.5 Soft story failure in a large apartment complex. Individual units extended on the rear of the apartment block had open parking at ground level with only steel pipe column support. These units were wagged like the tail of a dog until the columns failed and the rear end of the units dropped. (Source: Ambrose, 1999) 27 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3.6 The second-floor columns in this five story concrete structure collapsed, dropping the upper portion. The open first story was the potential soft story but because of the stiffness it remained intact and the real base for the seismic force was shifted to the second floor. (Source: Ambrose, 1999) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER FOUR LATERAL DESIGN GRAPHS (LDG) Lateral Design Graphs (LDG) is a precursor program to this application. It was developed by G Schierle, professor at USC and by thesis chairperson. The LDG project was funded by a grant from NSF and developed in 1991 based on the earlier building code (UBC, ICBO, 1991). LDG is a computer aided design for wind and seismic forces in early design stages. The program has a modular structure, with modules for Input, Analysis, Graph and Data results. It had been designed as an interactive tutorial program. While LDG is intended as a design and teaching tool, a basic understanding of lateral forces is required; and it can be taught while the program is being introduced. Once a building is defined, any parameters can be altered to examine its impact on the building. The input is of two types Basic and Supplementary input in which the user can stack floors with constant or variable areas, story heights and dead weight. A 1 ... li 1 1 Jl Figure 4.1 Input screen from LDG. (Source: Schierle, 1992) 29 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The analysis module computes seismic and wind values by UBC equation which substitute dynamic forces by an equivalent static method, that is limited to buildings with relative regular form and mass distribution as defined by UBC tables. The analysis results are displayed in numeric tables and graphs. The graphs display information in a consistent manner, some are line graphs and some are bar charts depending on the output type. The following type of results are displayed: Force at each level Base shear at each level Overturn Moment at each level Length of Shear Wall at each level depending on the strength Pressure at each level (Wind Analysis) ! CONCRETE 9 £ A f l m i l 6 U IL D I IG SCIS-IC • 0 ° C I O t a t r i D w t t o n e n r O u l i O i n g e a r f lo o r - °______ *00_______ *00 i o o *00 fo rc e F t (K) 195.6 176.0 160.2 142.* 124.6 106.6 69.0 71.2 32.0 16.0 0 .0 O v e r t u r n M o v n t K x ( k ' ) 0 .0 1.958.1 5.696.3 11.036.6 17,600.9 25.611.3 34,689.8 44.656.3 55.536.6 72,040.2 66,782.0 Shear Vi (k ) 0 .0 195.8 373.6 534.0 676.4 801.0 907.8 996.9 1,066.1 1.100.1 1,116.1 Figure 4.2 Output Screens from LDG. (Source: Schierle, 1992) 30 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LDG as a teaching tool The author has used the LDG program in large undergraduate classes, as well as graduate seminar. Students like the LDG approach. They find the LDG program to be fun to use and, thus, develop a positive attitude, which is so vital to comprehend any complex subject. Student evaluated the effectiveness with an average score of 4.5, on a scale of 1 to 5 (Schierle, 1992). It is hoped that this program gets similar review from the students. In many ways, there has been an effort to understand some of the difficulties that the students had and those issues have been simplified or presented in more intuitive manner. Being a Teaching Assistant for the Structures class where this program is taught gave the author a better insight on what the students felt and how they reacted to certain functions. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER FIVE NUMERIC DATA FOR ANALYSIS Tables from Uniform Building Code 5.1 Tables for Wind Analysis: Table 1 Wind Stagnation Pressure (Source: UBC 1994) Basic wind speed (m ph)' C X 1-61 Tor km/h) 70 80 90 100 110 120 130 Pressure qs (psf) ( x 0.0479 for kN/m2) IZ6 16.4 20.8 25.6 31.0 36.9 43 J * Wind speed from Section 1615. Table 2 Combined Height, Exposure and Gust Factor Coefficients. (Source: UBC 1994) HEIGHT ABOVE AVERAGE LEVEL OF ADJOINING GROUND (Im Q EXPOSURE D EXPOSURE C EXPOSURE B - x 30a.8 for nun 0-15 1-39 1.06 0.62 20 1.45 1.13 0.67 25 1.50 1.19 _ 0.72 30 1.54 1.23 0.76 40 1.62 1.31 0.84 60 1.73 1.43 0.95 80 1.81 1.53 1.04 100 1.88 1.61 1.13 120 1.93 1.67 1.20 ! 160 2.02 1.79 1.31 200 2.10 1.87 1.42 300 2.23 2.05 1.63 | 400 2.34 2.19 1.80 1 'Values for intermediate heights above 15 feel (4572 mm) may be interpolated. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 3 Pressure Coefficients (Source: UBC 1994) STRUCTURE OR PACT THEREOF o e s c m p t io n I. Primary frames and systems / M ethod 1 (Normal force method) Walls; Windward wall Leeward wall Roofs1 : Wind perpendicular to ridge Leeward roof or flat roof Windward roof less than 2:12 (16.7%) Slope 2:12 (16.7%) to less than 9:12 (73%) Slope 9:12 (75%) to 1312 (100%) Slope > 12:12 (100%) Wind parallel to ridge and flat roofs 0.8 inward 0.5 outward 0.7 outward 0.7 outward 0.9 outward o r 0.3 inward 0.4 inward 0.7 inward 0.7 outward - M etbod 2 (Projected area method) On vertical projected area Structures 40 feet (12 192 mm) or less in height Structures over 40 feet (12 192 mm) in height On horizontal projected area1 13 horizontal any direction 1.4 horizontal any direction 0.7 upward 2. D em ents and compooents not in areas _ o f discontinuity1 Wall elements All structures Enclosed and unenclosed structures Partially enclosed structures Parapets walls 1 3 inward 13 outward 1.6 outward 13 inward o r outward Roof elements^ Enclosed and unenclosed structures Slope < 7:12 (58.3%) Slope7:12(58.3% ) to 12:12(100%) Partially enclosed structures Slope < 2:12 (16.7%) Slope 2:12 (16.7%) to 7 :12 (583% ) Slope> 7 :1 2 (5 8 3 % ) to 12:12(100%) 1 3 outward 13 outward or inward 1.7 outward 1.6 outward or 0.8 inward 1.7 outward o r inward 3. D em ents and components in areas o f discontinuities1* 4-5 Wall comers6 Roof caves, rakes or ridges without overhangs6 Slope < 2:12 (16.7%) Slope 2:12 ( 16.7%) to 7:12 (58.3%) Slope > 7:12 (583% ) to 12:12(100%) For slopes less than 2 :12 (16.7%) Overhangs at roof eaves, rakes or ridges, and canopies 1 3 outward o r 13 inward 2 3 upward 3 6 outward 1.6 outward 0 3 added to values above 4. Chimneys, tanks and solid towers Square or rectangular Hexagonal or octagonal Round or elliptical 1.4 any direction 1.1 any direction 0.8 any direction 5. Open-frame towers7* 8 Square and rectangular Diagonal Normal Triangular 4.0 3.6 3.2 6. Tower accessories (such as ladders, conduit, lights and elevators) Cylindrical members 2 inches (51 mm) or less in diameter Over 2 inches l5 1 mm) in diameter Flat or angular members 1.0 0.8 13 7. Signs, flagpoles, lightpoles. minor structures* 1.4 any direction 33 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 4 Occupancy Category (Source: UBC 1994) OCCUPANCY CATEGORY OCCUPANCY OR FUNCTIONS OF STRUCTURE s e s M C M POR- TANCE FACTOR./ 8 B S M C M PO ft- TANCE1 FACTOR, t NMD WPOR- TAHCE FACTOR, t r 1. Essential facilities- Group I. Division ! Occupancies having surgery and emergency treatment areas Ftre and police stations Garages and shelters for emergency vehicles and emergency aircraft Structures and shelters in emergency-preparedness centers Aviation control towers Structures and equipment in government communication centers and other facilities required for emergency response Standby power-generating equipment for Category I facilities Tanks or other structures containing housing or supporting water or other fire-suppression material or equipment required for the protection of Category L II or III structures 1.25 1.50 1.15 i i i | i i 2. Hazardous facilities Group H. Divisions 1.2 .6 and 7 Occupancies and structures therein housing or supporting toxic or explosive chemicals or substances Nonbuiiding structures housing, supporting or containing quantities of toxic or explosive substances which, if contained within a building, would cause that building to be classified as a Group H. Division 1.2 or 7 Occupancy 1.25 1.50 1.15 i | 3. Special occupancy structures-' Group A. Divisions 1. 2 and 2.1 Occupancies Buildings housing Group E. Divisions I and 3 Occupancies with a capacity greater than 3(X) students Buildings housing Group B Occupancies used for college or adult education with a capacity greater than 5(X) students Group I. Divisions 1 and 2 Occupancies with 50 or more resident incapacitated patients, but not included in Category 1 Group 1 . Division 3 Occupancies All structures with an occupancy greater than 5.1X X ) persons Structures and equipment in power-generating stations: and other public utility (aciliues not included in Category 1 or Categor) II above, and required lor continued operation 1.00 1.00 1.00 4. Standard occupancy structures'* All structures housing occupancies or Imving (unctions not listed hi Category I. II or III and Group l ! Occupants lowers I.(XI I_ (X 1 l.(X) 3 Miscella neous structures Group I Ov cup.ui;. ics cvccpt tor timers 1 (X ) 1 (X I I. (X I ‘T he lim itatio n ol lf, lo r p;m cl l o n r i a t i u i ^ in S ectio n 1031 2 4 shall t v 1.0 lor th e e n tire c o n n e cto r. ‘ S tructural o b se rv a tio n req u irem en ts a rc g iven in S ection* ICIK. 17(11 and 1702. 'F o r an c h o ra g e ol m a ch in ery and e q u ip m e n t required lor life v dctx sy stem s th e v alu e o f sh all he ta k e n as 1.3 3 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5.2 Tables for Seismic Analysis Table 5 Seismic Zone Factor (Z) (Source: UBC 1997) TABLE 164—SEISMIC ZONE FACTOR Z ZONE r * - 2A 2B 3 4 z 0.075 0.15 0.20 0 3 0 0.40 Table 6 Soil Profile Type (Source: UBC 1997) TABLE 16-J— SO IL PROFILE TY PES AVERAGE SOIL PROPERTIES FOR TOP 100 FEET (30 480 mm) OF SOIL PROFILE SOIL PROFILE TYPE SOIL PROFILE NAME/GENERIC DESCRIPTION Shear Wave Velocity. feevsecond (m/s) Standard Penetration Test. H [or for cohesionless coil layers] (blows/toot) Undralned Shear Strength, s.. Dst (kPa) * • uP*> $4 Hard Rock >5.000 (1300) Sb Rock 2300 to 5.000 (760 to 1300) Sc Very Dense Soil and Soft Rock 1.200 to 2300 (360 to 760) > 5 0 >2.000 (100) So Stiff Soil Profile 600 to 1.200 (180 to 360) 15 to 50 1,000 to 2.000 (50 to 100) Se 1 Soft Soil Profile <600 (ISO) < 15 < 1.000 (50) Sf Soil Requiring Site-specific Evaluation. See Section 1629.3.1. Table 7 Seismic Coefficient (Ca) (Source: UBC 1997) TABLE 16-Q— SEISMIC COEFFICIENT Ca SEISMIC ZONE FACTOR. Z SOIL PROFILE TYPE Z = 0.07S Z=0.1S | Z * 0 .2 Z = 0 J Z = 0 .4 $4 0.06 0.12 | 0.16 0.24 0.3 2V„ Sb 0.08 0.15 ( 0.20 03 0 0.40.V„ Sc 0.09 0.18 1 0.24 0.33 0.40A'„ So 0.12 0.22 j 0.2S 0.36 0.44.V„ Se 0.19 0.30 | 034 0.36 0.36A’ „ Sf Sec Footnote I Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 8 Seismic Coefficient (Cv) (Source: UBC 1997) TABLE 16-R— SEISM IC COEFFICIENT Cy, SBSMIC ZONE FACTOR. Z SOIL PROFILE TYPE z * o s m Z*0.15 Z e 0 2 Z - a s Z-O A • S a 0.06 0.12 0.16 0 5 4 0 3 2 K Sb 0.08 0.15 0 3 0 0 3 0 0.40Ny Sc 0.13 0.25 0 3 2 0.45 056Jfv Sd 0.18 03 2 0.40 0 5 4 0.64Ar v Se 0.26 050 0.64 0.84 0.96NV Sf See Footnote 1 Table 9 Near-Source Factor (Na) (Source: UBC 1997) TABLE 16-S— NEAR-SOURCE FACTOR Na ' CLOSEST DISTANCE TO KNOWN SEISMIC SOURCE2-3 SEISMIC SOURCE TYPE s 2km 5 km 2 10 km A 15 1 5 1.0 B 13 1.0 1.0 C 1.0 1.0 1.0 Table 10 Near-Source Factor (Nv) (Source: UBC 1997) TABLE 16-T—NEAR-SOURCE FACTOR Nv ' CLOSEST DISTANCE TO KNOWN SEISMIC SOURCE2* 9 SBSMIC SOURCE TYPE | s 2 km | S km 10 km 2 15 km A I 2.0 | 1.6 1.2 1.0 B I 1.6 | 1.2 1.0 1.0 C ! 1.0 1 1.0 1.0 1.0 36 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 11 Structural Systems (Sources: UBC 1997) BASIC STRUCTURAL SYSTEM' M* LATERAL-EORCE-RESg'nHG SYSTEM— OESCHPnOX X 10«A lor X U S 1. Bearing wall I. Light-framed walls with shear panels system a. "Wood struct oral panel walls for structures three stories o r less g 65 b. All other light-framed walls 6 65 ■ 2. Shear walls a. Concrete 6 160 b. Masonry 6 160 3. Light steel-framed bearing walls with tension-only bracing 4 65 4. Braced frames w here bracing carries gravity loads a. Steel 6 160 b. Concrete4 4 _ c. Heavy timber 4 65 2- Building 1. Steel eccentrically braced frame (EBF) 10 240 frame 2. Light-framed walls with shear panels system a. Wood structural panel walls for structures three stories or less 9 65 b. All other light-framed walls 7 65 3. Shear walls a. Concrete 8 240 b. Masonry 8 160 4. Ordinary braced fram es a. Steel 8 160 b. Concrete4 8 _ c. Heavy timber 8 65 5. Special concentrically braced frames a. Steel 9 240 3. Moment- 1. Special moment-resisting frames (SMRF) resisting a. Steel 12 N.L. frame b. Concrete 12 N.L. system 2. Masonry moment-resisting wall frame 9 160 3. Concrete intermediate moment-resisting frames (IMRF)-' 8 _ 4. Ordinary moment-resisting frames (OMRF) a. Steel'’ 6 160 b. Concrete7-" 5 — 4. Dual 1. Shear walls systems a. Concrete with SM R F 12 N.L. b. Concrete with steel O M RF 6 160 c. Concrete with concrete !M RF-s 9 160 d. Masonry with SM R F X 160 c. Masonry with steel OM RF ft 160 I. Masonrv with concrete IMRF4 7 _ 2. Steel EBF ' a. With steel SM R F 12 N.L. b. With steel O M RF 6 160 3. Ordinary braced Iramcs a. Steel with steel SM RF 10 N.L. h. Steel with steel O M RF G 160 c. Concrete w-ith concrete SMRF4 9 _ d. Concrete w-uh concrete IMRF4 6 _ 4. Special concentrically braced frames a. Steel with steel SM RF 1 1 N.L. b. Steel with steel O M RF G 160 5. Undefined Sec Sections lti27X.3 and Ih2?.9.2 _ _ systems N .L — N o lim n *BaMC stru ctu ral sy stem s j t c ilclm cvi m S e c tio n 1 (0 7 .0 •S e e S ectio n 162X 3 lo r co m b in atio n ot s tru c tu ra l s y ste m . / / — H cipltt lim it a p p licab le to S ctsiu ii /.o n e s * .irul 4 S e e S ection 1(0 7 7 P ro h ib ited in S eism ic / o n e s ^ am ! 4 P to h ih itcd m Seism iv Z one* * .uul 4 e w c p t j ' (v rm itte tl in S ection l(i^2 2. ^ O rJ m a r) m o m en t-rcsistm j: Irjm c'* m S eism ic / o n e I m e etin g the r e q u ir e m e n t o f S e c tio n 22 11 6 m a y u s e an value of 12 P ro h ib ited in S eism ic Z o n e s 2. ' j n J 4 “ P ro h ib ited in S e ism ic Z o n e s 2A . 2B . * am ! 4 S e e S e c tio n I6 M .2 7 3 7 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LATERAL DESIGN ANALYSIS 6.1 What is extracted from LDG 96? As mentioned in Part One, Chapter Five this application is based on the framework of Lateral Design Graphs (LDG 96). LDG is an application that computes Wind and Seismic loads in structures and displays the result graphically and numerically. LDG was designed to be used on the DOS platform and is based on the 1994 Uniform Building Code. Lateral Design Analysis (LDA 99) has extracted its foundation from LDG, it computes wind and seismic loads in buildings and displays the results in numeric tables and graphs. It had the same fields of input but the user interface is designed differently. The output is identical in nature, such that it calculates and displays the same graphs but it has a different look because of the difference in the operating system. The author of LDG had recommended that the interface should more flexible as far as the geometrical input of the structure is concerned. LDA has attempted to do so by incorporating ten different layouts, which the user selects from and they also have a choice of stacking different profiles on one another to make a composite structure. The profiles are grouped according to seismic design considerations and the concepts are explained with the help of some theory at that point. Another feature that is added is the checklist before the analysis, which indicated if all the required input fields are filled. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. In this application there has been an attempt to make the program more user friendly and has features which will make it a better teaching tool. Thus LDA is a step forward, it takes on some of the recommendations of the earlier application and updates the same idea for the present and near future. 6.2 What is the application about and whom is it intended for? A Computer application that allows the user to analyze specific architectural profiles and presents the result in a graphic form. It does preliminary analysis of wind and seismic forces on buildings. In its most basic form architects and designers can use it to do preliminary lateral analysis in the conceptual stages of the design. This kind of analysis can avoid some basic design geometry errors. Another consideration was to design it as a teaching tool at the undergraduate level for architecture students. LDG has been effectively used as a part of the coursework in Structures class. Some of the student opinions were reviewed and an attempt has been made to make it easier to understand and work with. Theory related to lateral design has been integrated into the computation process at various points. Hence this application is targeted for the professional in the field for conceptual analysis and for the students to learn and understand the concepts and analysis of lateral designing. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.3 Description on Data Input The program has a modular structure with modules for Building Input, Wind Factor Input, Seismic Factor Input and Graphs and Results. Since it is a Web based application written in JavaScript and it is both IBM and Mac compatible. At the launch of the application the user has a choice of going through the How to Use section that is recommended for beginners, advanced or frequent users can directly launch the program without going through the beginner procedures. The beginners’ section has an outline of every module and what the user needs to input at every level and what the expected results would be. The user can launch the application from this level without having to go back to the main frame. There is a help module on the left navigation bar which is accusable at all time and this section opens another window to view the theory or working procedures, so that the user can work through the application and refer to the theory along side. The user manual is also a part of the help section along with the formulae and important UBC tables used to derive the various constants and variables. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Lateral u e s i g n A n a ly s is Design for',Vinci a n d Seism ic F o r c e s tn buildings D iv d o p e d in Ja /a S c x ip l Click on one of th e buttons below to procee-d. H o .'i t o L _ r— Start - I • R ecom m ended fo r beginers. F requent Users Start here > -.1 <T B u it c n > 1 L J L -<jic >J uT f* furtl^u'uf*: ■ ■ 9 9 9 9 9 9 THE STRUCTURE OF THE APPLICATION The navigation bar to tire left defines the structure application at various levels jf th is BUILDING INPUT Building G eom etry Structural T ype Building G eo m etry T he u s e r selects- an architectural profile from th e d a t a b a s e T here are two ty p e s of profiles to c h o o s e from The P ro b le m a tic Profile and The N o n P ro b le m a tic Profile T he P ro b le m a tic Profile's are t h o s e that are m o s t likely to fail during tec to n ic activity W h e n the u s e r s e l e c t s o n e s u c h profile a w indow p u p s up. d iag ra m a tic a lly indicating the point of p o s s ib le failure and •what n e e d s to b e d o n e to prevent it T h e Non P r o b e lm a tic Profile; are the c o m m o n ly u s e d profiles w hich have no specific failure m e c h a n i s m d u e to its g e o m e try T he u s e r th e n g o e s on th e define th e planer g e o m e try , the n u m b e r of levels and th e h eig h t of e a c h level T he gravitational load is also defined at this s ta g e The u s e r th e n h a s a c h o ic e to s e e th e elveation or go on to s e le c t an o th e r profile to c re a te a s ta c k S tructural T ypes T he u se r s e l e c t s from th e four m ain stru ctu ral ty p e s a s defined in the Uniform Building C ode(U B C ) T h e s e c a te g o r ie s have s u b -c a ta g o r ie s to c h o o s e from T he Help s e c t i o n d efin es e a c h of t h e s e c a te g o r ie s and s u b - c a t a g o n e s Figure 6.1 Screen Images from LDA. Top — Main Page, Bottom - User Guide. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.3.1 Building Input This module is further divided into two sections, Building Geometry and Structural System. When the user moves the cursor over the Building Input on the navigation bar this sub menu appears. Building Geometry In this module the user selects from ten predefined architectural profiles to make a building. These profiles are of two types in accordance to the lateral design considerations stated in the background research of Part One of this book. They are classified as Non-Problematic Profiles and Problematic Profiles in set of five. The user selects one of the profiles from the horizontal selection bar and the detail input required for that profile appear in the frame window below along with a larger image, which indicated the various input dimensions on the diagram. The typical inputs for any profile would be: • The length (L), or multiple lengths as per the profile. All subsequent lengths are indicated on the diagram and are typical denoted with a number suffix (LI, L 2 ,...... ), the dimensions are in feet. • The width (W), or multiple widths as per the profile. All subsequent widths are indicated on the diagram and are typical denoted with a number suffix (W l, W2, ), the dimensions are in feet • The Area ( A), this is computed by the program when the required dimension are entered in. The area is in square feet (sqft.) • The number of levels (N), the number of levels of this profile • The height of each level (h) in feet 42 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. • The dead load on each level(W) in pounds per square feet (psf) Each input has a reset and a show elevation button. The elevation appears in a new window. The user can add a couple of profiles on top of each other, but they have to be added in the order of bottom to top, like from the base to the top of the building. When the user selects a problematic profile there is an added feature which acts like a quite theory reference. The image in the input frame has a hyperlink to a new window, which diagrammatically represents why that particular profile is problematic, where the possible failure would occur and what would be the corrective measure. These samples of the profiles which open in new windows can be printed with the browsers print command. Once the user has inputted all the geometrical properties of the buildings, they have to proceed to the next sub section in building input, the Structural Systems. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sd) menu appears ivhen cursor is on this p art of the n arration h ar SELECTION BAR Non-Problematic Problematic Profiles A r e » W i Larger Image with Dimension Codes 6.2 The Building Geometry Input Screen CRITICAL PLANES FOR A L-3HAPPED FRCFUE Critical Panes for seismic tsar. Ws need to hare on expansion join tor steel relnforcementat those intersections CRITICAL PLANES FOR A U-SHAPPED PROFLE Crlttcai Pbnesfor seismic tear. We need to hare an etc pension jofntor steel relnforcementat those intersections The Pop up Window for Problematic Profiles 4 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.3.2 The Structure Type In this sub division of the Building Input Module, the user has to select a specific structural system for the building. These systems are as per the Uniform Building Code and are basically four types. The choice is in form of a drop down list from which the user selects the desired system and then detailed subsystem, which depends on the construction material. For details refer Table 11. • The Bearing Wall System: This is further divide into the following types as per UBC 1. Light -framed walls with shear panels 2. Shear walls. 3. Light steel -framed bearing walls with tension bracing 4. Braced frames where bracing carries gravity loads • Building Frame System This is further divided into the following types as per UBC 1. Steel eccentric braced frame 2. Light framed walls with shear walls 3. Shear walls 4. Ordinary braced frame 5. Special concentrically braced frame • Moment Resisting Frame System This is further divided into the following types as per UBC 1. Special moment resisting frame 45 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2. Masonry moment resisting wall frame 3. Concrete intermediate moment resisting frame 4. Ordinary moment resisting frame • Dual Systems This is further divided into the following types as per UBC 1. Shear walls 2. Steel eccentric braced frame 3. Ordinary braced frame 4. Special concentrically braced frames Once the user has inputted the type of system, the program will retrieve corresponding seismic factor (Rw) and it appears in the appropriate field. ijS id d tititi gf.tacfldur~khcpfca/ldg3SA)a_fnan.Hiri £l«s» c Ught-Framed Wood Structural panel Shear Walls c A d other Light-Framed Walls r Concrete Shear Walls c Masonry Shear Walls r Light SteeLFramed Beanng Wafls(tension bracing) c Steel Braced Frame c Concrete Braced Frame c Heavy Timber Braced Frame c steel Eccentncalty Braced Frame c Light-Framed Wood Structural S Y 9 A M SB E 1 1 c i cn g Figure 6.3 Structure Type Selection Screen Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.3.3 Wind factors In this module all the wind analysis variables are defined, some by the user and some the program determines. The first step when the user enters this module is the prompt to calculate the total height of the structure. This is required to find out the Pressure Coefficient (Cq), which then appears in the corresponding text field. The user is then required to select the wind speed, which they select from the drop list as per UBC. The Wind Stagnation Pressure (qs) depends on the speed and so it appears in its corresponding text field. The next input is that of the Exposure Factor, which again is a drop list to select from according to UBC. When this value is entered then the program will make an array/list of all the Gust Coefficients (Ce) which depend on the height at each level and the exposure factor. The final user input is the Importance Factor, which is required to calculate the Wind Pressure. After all the fields in this module are filled in the user is directed to go to the Graphs Module. Figure 6.4 Wind Factor Selection Screen 47 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6.3.4 Seismic Factors Like the wind factor input module, this module has some input by the user and the program computes some of the factors. These inputs by the user are in form of selection from the UBC tables: Seismic Zone, in which the structure is located, based on UBC. The seismic coefficients (Cv and Ca ) are based on this. Soil Profile Type, based on UBC. The seismic coefficients (Cv and Ca ) are based on this. Once this data is entered the values of Ca and Cv will appear in the corresponding text boxes. Seismic Source Type from the UBC, which depends on the capacity to produce large magnitude events. This is needed to compute the near source factors (Nv and Na). Closest distances to known seismic source, select from the range as defined in the UBC. Once the distance and the source type are entered than the values for the Near-Source factors will appear in the respected boxes. The broad category of the frame type to find the Numeric Coefficient (Ct) which is needed to compute the Time Period. The value for the Time Period (T) will appear in the corresponding text box. The formula for computation of period is, T = Ct (h)3 /4 The importance factor as per UBC will be used for computation of the base shear in the static analysis method. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. t v IN PU T B O ! N v ltc u p e SEISMIC ZONE | Please Select j*| SOIL PROFILE TYPE [Please Select SEISMIC SOURCE TYPE [Please Select CLOSEST DISTANCE TO KNOWN SEISM IC SOURCE | Please Select r i FRAME TYPE [Please Select IMPORTANCE FACTOR [ Please Select S| H M E PE R IO D fl) 1 SEISMIC C OEFFICIENT (Ca) 1 . - ............. -------------------- - Figure 6.5 Seismic Factors Selection Screen 6.4 Description of Output Like the Building Input module, this module is also subdivided into two sections, the Wind Graphs and the Seismic Graphs. When the user clicks on any one of the graphs, the first thing that appears before the computation is the Checklist. This checklist lets the user see if all the required fields have been entered in all the modules. There is a warning that tells the user to make sure that all the boxes next to the specific values are checked and then tells the user to proceed to the Results. 4 9 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. □ I o T T CHECK LIST f tfie boxes below are not checked it IncScates that there is no input in hat field Make sure all the boxes are checked before you proceed with the calculations. IT W ind S p eed C T Im portance F ac to r I” P re s su re CoefficientfCq) C Wind S tag n a tio n P re ssu re (q s) C A L C U L A T I O N S Figure 6.6 Wind Analysis Checklist as it appears on the Screen BBBB H T tSte b o x e s b e lo w an d oc c h e c k e d & n d c x c t th a t th e r e is o o s p o t n th a t £ e l d 4 & U sau* <d l t h 4 b c x * t e b sc M h fr v jrc u pr oc +*d w i sh th t ! c a U a U u e i t x . r S e is m ic Z m w < 2 !) r D e a d W e i j h u W ) P rfc s n e ric m l C o e £ C d r n t( R ] P T im e P e r io d f T ) P S e is m ic C o e f H r ie m lC a ) P S e t t m i r C c e flIc i« B t(C v ) P N > a r-> S o c re * F i t t a r ^ a ) r iftit-S tfiu tt F a r t o K N v j Figure 6.7 Seismic Analysis Checklist as it appears on the Screen 5 0 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Analysis Wind Analysis is based on the UBC Static Method. • The Wind pressure is calculated according to the UBC equation P = Ce * Cq * qs * I Where Ce = Height/Exposure /Gust Factor Cq = Pressure Coefficient qs = Wind Stagnation Pressure I = Importance Factor • Wind Forces per floor are computed as product o f pressure, floor height and width, integrated per foot according to the height intervals given in UBC tables Force = P * h * W • Shear per floor is computed as the sum of all the forces on each level above the level in question. Like Shear on level 8, of a 10 story building would be the sum of forces on level 10 + - level 9. n Vx = Sum of Fj i = x x = level of the floor i = total number of floors • Overturn Moment at any floor, is the cumulative of product of the force and the height of each level above the level in question. n Mx = Sum of Fj (hi -h x ) i = x+1 5 1 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Seismic Analysis by the Static Force Procedure • Design Base Shear. There is a different computation method for Seismic Zone 4 and the rest of the zones. The total design base shear in a given direction shall be determined from the following formula: V = Cv * I * W R * T Maximum base shear shall not be more than V= 2.5 * Ca * I * W ---------- K-------- Total base shear shall not be less than V=0.11 *Ca*I* W For Seismic zone 4, the minimum base shear shall not be less than V= 0.8 * Z * Nv * I * W R Where Cv — Seismic Coefficient I — Importance Factor W — Dead load on the building R- Numeric coefficient representative of the overstrength and global ductility T — Time Period Ca — Seismic Coefficient Nv - Near-Source Factor 5 2 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The Numeric and Graphic Output When the user clicks on the CALCULATIONS button then a window opens up which shows the numeric and the graphic output in the same window. The numeric output is in the form of tables and the graphics are bar charts, indicating Pressure, Force, Shear and Overturn Moment at each floor level. These graphs/tables can be printed by the browser’s print command. H tip h r ■ etd » fa/el Ore C m fflriaie O C t i W rid F r m s± e e fr«f) Fi*ce C fc O [10 1.39. 27.8 252980 Q O 1.45 29 263900 30 1.54 30.8 280280 40 1.62 32:4 294840 [50 1.71 34.2 [311220 £0 1.71 34.2 p i 1220 70 1.81 36.2 329420 30 1.81 36.2 329420 r 1.88 37.S 342160 llQ O 1.88 37.6 [342160 NUMERIC TABLE WIND PRESSURE AND FORCE AT EACH LEVEL Figure 6.8 Numeric Table Output Screen 53 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Seen here is a sample graphic output type, which shows the Wind pressure at each level. These graphs can then be printed with the help of the browser’s print command. ' 5 P ir x tv o n ji! tJilff-Jnni lc rv rls - H itm ic d l I n lr r n H F K p la n i C m c u & IQ 9 & 7 6 J 4 3 2 1 □ ■ ■ ■ ■ ■ 2 7 . 5 ■ ■ ■ ■ ■ 2 9 . 0 3 2 . 4 H H H H H H H p 42 3 6 2 f l H H B H H H I 362 3 7 . 6 3 7 . 6 P tcssnm C p sft WIND PRESSURE GRAPH F i g u r e 6 . 9 G r a p h O u t p u t S c r e e n 5 4 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CONCLUSION This application was to follow the format of its precursor application LDG. Along the time that it was being developed a lot of changes took place, but an attempt was made to implement the recommendations of LDG. This application had a lot of user-friendly features and a lot of flexibility in the design input, such that the user can select from a larger variety of profiles. An attempt has been made to include some teaching features like reference to some theory as and when possible. However due to time constraint and the limitation of programming ability all the set parameters were not done exactly as planned. The author had hoped to have students work on this application to get their reviews, but it wasn’t quite possible to do that, and so there is no statistical data of the success/failure of this as a teaching tool like the one presented by the author of LDG in his paper. Finally in conclusion, it would a great topic of study that could be pursued in the future by other graduates. I sincerely hope that somebody would work on this subject and continue where I left. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. RECOMMENDATIONS FOR FUTURE STUDY There are a lot of improvements that can be made to this application which were not possible due to time constraint. Some of the features that can be added to this application that would make it much better would be: • Incorporate a transfer from a CAD program like ACAD into this application so that the building description and layout could be done away with and will cater to more people than just students. • Have a built in drawing tool, using Java Applets so that the user can actually draw the building and not have to select from predefined profiles. This offers more flexibility to the user and could extend the range of the users. • This application uses the 1997 UBC for Seismic analysis, however it is a very complicated procedure to teach the students and so if a simpler way to do this analysis is figured out and used. • Include the shear wall lengths, as used by LDG for specific wall types. Theses are just some of the recommendation, I am sure many more will be applicable as there is progress in the technology and the user interfaces become more interactive. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. BIBLIOGRAPHY Ambrose, Vergun (1999) Ambrose, Vergun (1995) Ambrose, James (1993) Arnold, Reitherman (1982) Schierle G G (1992) Schierle G G (1994) Design for Earthquakes John Wiley & Sons, Inc. ISBN 0-471-24188-1 Simplified Building Design For Wind and Earthquake Forces Third Edition, John Wiley & Sons, Inc. ISBN 0-471-30958-3 Building Structures Second Edition, John Wiley & Sons, Inc. Building Configuration and Seismic Design John Wiley & Sons, Inc. ISBN 0-471-86138-3 Computer Aided Design for Wind and Seismic Forces Computer Aided Design in Architecture ACADIA Computer Aided Seismic Design Journal of Architecture and Planning Research, Vol. II, No-2 Loche Science Publication Company, Inc. ISSN 0738-0805 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IMAGE EVALUATION TEST TARGET (Q A --3) ✓ / ✓ & < V » * % S i v / , 1 . 0 l.l _ 1 » J 13.6 2* M2J5 2.2 2.0 1 . 8 1.25 1 .4 1 . 6 150mm I IV H G E .In c 1653 East Main Street Rochester, NY 14609 USA Phone: 716/482-0300 Fax: 716/288-5989 O 1993. Applied Image. Inc.. All Rights Reserved Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Linked assets
University of Southern California Dissertations and Theses
Conceptually similar
PDF
Lateral force design (LFD) software for wind and seismic loads per IBC 2003 and ASCE 7-02
PDF
Hebel design analysis program
PDF
Wind design of fabric structures: Determination of gust factors for fabric structures
PDF
Mahoney Tables plus a tool for sketch design recommendations for a building
PDF
Interactive C++ program to generate plank system lines for timber rib shell structures
PDF
WebArc: Control and monitoring of building systems over the Web
PDF
Thermbuilder: A Web-based teaching tool to study thermal processes in buildings
PDF
Comparison of lateral performance: Residential light wood framing versus cold-formed steel framing
PDF
Reinforced concrete structure design assistant tool for beginners
PDF
VRSolar: An exploration in Web based interactive architectural teaching
PDF
Natural ventilation in the high-rise buildings for Taipei
PDF
Bracing systems for tall buildings: A comparative study
PDF
Sustainable building materials adviser: A Web-based tool for architects
PDF
Guidelines for building bamboo-reinforced masonry in earthquake-prone areas in India
PDF
Maximizing natural ventilation by design in low-rise residential buildings using wind catchers in the hot arid climate of United Arab Emirates
PDF
Catalyst: A computer-aided teaching tool for stayed and suspended systems
PDF
Computer aided design and manufacture of membrane structures Fab-CAD
PDF
Eccentric braced frames: A new approach in steel and concrete
PDF
A visual and digital method for predicting discomfort glare
PDF
Lighting design assessment tool for an elderly living environment
Asset Metadata
Creator
Khopkar, Manasi Sham
(author)
Core Title
Lateral design analysis: Web application. Design for wind and seismic forces in buildings
Degree
Master of Building Science / Master in Biomedical Sciences
Degree Program
Building Science
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
Architecture,Computer Science,engineering, civil,OAI-PMH Harvest
Language
English
Contributor
Digitized by ProQuest
(provenance)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c16-30898
Unique identifier
UC11336930
Identifier
1395131.pdf (filename),usctheses-c16-30898 (legacy record id)
Legacy Identifier
1395131.pdf
Dmrecord
30898
Document Type
Thesis
Rights
Khopkar, Manasi Sham
Type
texts
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
Repository Location
USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA
Tags
engineering, civil