ARCHITECTURAL ANDSTRUCTURAL TOPICS WOOD-STEEL-CONCRETE THE NEW LADDER TYPECURRICULUM GEORGE SALINDA SAtVAN... fuap ASSISTANT PROFESSOR College of Engineering andArchitecture Baguio Colleges Foundation 1980-1988 First and lone graduate of B.S. Architecture,1963 North of Manna,St. Louis University, Baguio City Former instructor 1965-1969 at St.louis University Recipient of various ACE certificates,Architects ContinuingEducation Program A licensed Architect,active practitioner and a licensed building constructor, inventor and a board topnotcher Past president of United Architects Phils. Baguio Chapter 1982 and1983 Elected National Director; UAP. Regional District I for the year 1987 Conferred thetitle of "Fellow United Architects Phils. College of Fellows, October,1988 JOSELITO F.BUHANGIN Bachelor of Science inCivil Engineering1987, St.Louis University, Baguio City Associate Professor, Civil Engineering1980 to Date Expertise: Structural Desig11,Construction Management Member:PICE- Phil. Institute of Civil Engrs. ACI - American Concrete Engineers Institute '. JMC PRESS, INC. 388 Quezon Avenue, Quezon City Copyright 1996 by: JMC PRESS, INC. and GEORGE S. SAL VAN JOSELITO F. BUHANGIN All rights reserved. No part of !his book may be reproduced in any manner without permission of the publisher. FIRST EDITION ISBN: 971 -1,-0987-5 Published and Printed by: JMC PRESS, INC. 388 Quezon Avenue, Quezon City Distributed by: GOODWILL BOOKSTORE Main Office: Rizal Avenue, Manila P.O.Box2942, Manila Dedicated to all future Architects and Engineers The hope for a functional, comfortable And convenient designs for better living. ACKNOWLEDGMENTS Theauthorswishtoacknowledgethehelpfulcommentsandreviewsofa rumber of individuals and organizations during its writing. Our sincere thanks to friends, colleagues and reviewers for their suggestions for improvement, discussions of general approach, and other assistance. In particular, we wish to thank Mr. Arnel Astudillo, Mr. Frede lito Alvarado, Miss MymaAquinoand Miss Agnes Arceo, all graduates of St. Louis University class '94 and '95, for their fine and clear drafting of all the illustrations throughout the various chapters. likewise to Engr. Anastacio D. AngNay Jr. class 1995, Civil Engineering BCF for his untiring and patient editing the original manuscripts and proofreading the galley proofs, with the help of Mr. Sudhir Thapa, an architect from Nepal, and a graduate of B.S.Arch. Baguio Colleges Foundation, class 1993, who made some must rations on Chapter 1 and likewise to Mr. Arthur B. Managdag Jr. a graduate of B.S. Civil Engineering, St.Louis University class 1995. ToMr. luis V. Canave who guided me on the complete process of publishing from pasted-up dummy, to final page proofs and up to the final printing, together with the patient laser typesetting of Mrs. Tess Espinoza Dulatre and Mr. Joseph P. Reate. Finally, to Mr. Roy Pagador, an AR student of Baguio Colleges Foundation, for developing and designing the chapter pages and the simple yet attractive cover design. PREFACE The purpose of this book is to introduce architects and engineers to the structural design of concrete, wood and steel structures in one volume. It's production was undertaken because it was felt that much of the three structural topics has become too specialist and detailed in nature and does not offer an easily understood introduction to the subject. Simplified in its approach, this book is a useful and practical guide and reference volume in design offices and a suitable text for senior architectural and engineering students. Particular emphasis has been placed on the logical order and completeness of the design examples. The examples are done in a step-by-step order and every step is worked out completely from first principles, at least once. This book deals principally in the practical application of engineering principles and forrrulas and in the design of structural members. The derivations of the most commonly used formulas are given in order that thereader may comprehend fully why certain formulas are appropriate in the solution of specifk: problems. This text pulls together the design of the variousinto single reference. A large number of practical design examples are provided throughout the text. Because of their wide usage, buildings naturally form the basis of the majority of these examples. The main reason, however, for writing this book was the observation made by the authors during many years of practical work and university teaching,that most so-called design books are still basically concerned with analysis. ttis the Author's conviction that a proper text must. demonstrate to the reader how to make his first assumptions, how toselect initial sections, and what procedure to follow after making a first choice so as to arrive at a final design. Part of this emphasis on an aspects of design hashere in the discussion of several modern automatic design techniques as well as design optimization procedures. Chapter 1 sets the stages for the volume by providing definitions, structural and engineering concepts for Architecture and giving illustrations of the various types and methods of construction. Chapter 2 continuestheintroductory material witha discussion of thegoals of structural design based,inpart,onthelimitstatesdesign concept.Itdealscomprehensivelyontheselection of structural system whether for wood, steel or concrete. Determiningtheloadsactingonbuildingsisbasictostructuralanalysisanddesign. Theseare presented in Chapter 3 asa basis for developing the flexural theory discussing time-dependent deflections, and so on. There are many types of loads on buildings. This chapter provides an overview of what the different types are, how they are determined and their effects on buildings and Architectural design. Chapter 4 deals with structural fundamentals like the of force, stress, the properties of cross-sections (centroid, moment of inertia, static moment of .area) and free body diagrams. Chapter 5 discusses theanalysisof beamsand columns. The corf1>lete analysis of beams would requirethesolutionfor shear andmomentdiagrams,whiletheprinciples ofcolumnanalysisand require an understanding of radius of gyration and slendernessratio as properties of the column. v Chapter 6 centers on truss analysis by the Methods of Joints, Sections, or by Maxwell's diagram. Chapter 7 is an introduction to soil mechanics with discussions on foundation systems and retaining wall structures. Chapter 8givesa description ofthedifferenttypesofconnectionsandtheir uses.Amajority of structural failures occur in the connection of members and not in the members themselves, and may be caused by either of the following (a) the incorrect type of connector is used, (b) the connector is undersized, (c) too few in number, or (d)improperly installed. Chapter 9discusses how buildingcodeprovisions relate tostructuraldesign,how loads must be determined,whatstressesareallowedinstructuralmembers,formulasfor designing members of various materials, and miscellaneous requirements for construction. Chapter 10 focuses on the basic concepts of Structural Timber Design. Chapter 11is an overview of the principles of Structural Steel Design. Chapter 12 discusses the basic principles of Structural reinforced concrete design and show how to make some common, fairly simple design calculations. Chapter 13. Although the primary focus of.this chapter is the structural design of walls, there are other considerations,inselectingtheoptimumwaHfora particular circumstance.Thedesignermust exercise judgement in selecting the wall system to best satisfy all the requirements of the project. Chapter 14 is a discussion of wind forces and their effects on building. Chapter 15 discusses the basic principles of earthquakes and primary design and planning guidelines to make a structure earthquake-resistant. In addition, a basic review of the static analysis method is presented withsome simplified problems to help explain the design concepts. vi TABLEOF CONTENTS Chapter1STRUCTURAL AND ENGINEERING CONCEPTS FOR ARCHITECTURE ..................................................................1 1.Overall Approach to Structural Education, 1 2.Structure and Other Subsystems, 3 3.Construction Methods and Structures as Expression of Architectural Design, 13 A.Building, 13 B.Form, Shape and Appearance, 13 C.Structural Forms, 13 D.Concrete, 15 Chapter2SELECTION OF STRUCTURAL SYSTEMS .........................37 1.Standard Structural Systems, 38 A.Wood, 38 B.Steel, 40 C.Concrete, 41 D.Masonry, 45 E.Composite Construction, 46 F.Walls and the Building Envelope, 47 2.Complex Structural Systems, 47 A.Trusses, 47 B.Arches, 48 c.Rigid Frames, 49 D.Space Frames, 50 E.Folded Pl ates. 51 F.Thin Shell Structures, 51 G.Stressed-Skin Structures, 51 H.Suspension Structures, 52 I.Inflatable Structures, 53 3.Structural System Selection Criteria, 53 A.Resistance toLoads,53 B.Building Use and Function, 54 C.Integration with Other Building Systems, 54 D.Cost Influences, 54 E.Fire Resistance, 55 F.Construction Limitations, 55 G.Style, 55 H.Socialand Cultural Influences, 56 Chapter3LOADS ON BUILDING ..........................................................57 1.Gravity Loads, 58 A.Dead Loads, 58 B.Live Loads, 60 C.Combination Loads, 63 vii 2.Lateral Loads, 63 A.Wind,63 B.Earthquake, 65 3.Miscellaneous Loads. 65 A.Dynamic Loads, 65 B.Temperature-Induced Loads, 67 C.Soil loads, 67 D.Water, 68 Chapter4STRUCTURAL FUNDAMENTALS ........................................69 . 1.Statics andForces, 70 A.Statics. 70 B.Forces, 70 C.Stresses, 72 D.Thermal Stresses, 72 E:Strain and Deformation, 73 F . .Moment, 75 2.Properties of Sections, 76 A.Centroid, 76 B.Statical Moment of Area, 76 C.Moment of lneryia, 79 3.Structural Analysis,61 A.Resultant Forces, 61 B.Components of a Force, 82 c. Free B_ody Diagrams, 63 Chapter5BEAMS AND COLUMNS ......................................................85 1.Beams,86 A.Basic Principles. 86 B.Types of Beams, 89 C.Shear Diagrams, 91 D.Moment Diagrams, 94 2.Columns. 96 . A.Basic Principles, 96 Chapter6TRUSSES ... . ... ... .. .. . . .. .. .. .. ... .. .. . .... .. .. . .. .. .... . .. . .... .. .. . . ........... ...99 1.Basic Principles, 100 2.Truss Analysis, 102 A.Method of Joints, 103 B.Method of Sections, 106 C.Graphic Method,108 Chapter7sOILS AND FOUNDATIONS ................................................111 1.Soil Properties, 112 A.Subsurface Exploration, 113 B.Soil Types and Bearing Capacities, 113 C.Water in Soil; 113 viii Chapter Chapter D.Soil Treatment, 114 E.Other Considerations, 118 2.Foundation Systems,119 A.Spread Footings, 119 B.Pile Foundations,120 C.Designing Footings,121 3.Retaining Walls, 123 A.Types of Retaining Walls, 123 B.Forces on Retaining Wall s,124 C.Design Considerations, 124 8CONNECTIONS ............................. .. ......... .... ........ ...... ..........125 1.Wood Connections. 126 AGeneral, 126 B.Type of Load,126 C.Condition of Wood,126 ;Q,Service Conditions,127 E.Fire-Retardant Treatment,127 F.AngleofLoad,127 G.Critical Net Section, 127 H.Type of Shear,128 I.Spacing Connectors, 128 J.End andEdge Distances to Connectors. 128 K.Nails,128 L.Screws,129 M.Lag Screws,130 N.Bolts. 130 0 .Timber Connectors,136 P.Miscellaneous Connection Hardware, 136 2.Steel Connections, 136 A.Bolts,137 B.Welds, 143 3.Concrete Connections,146 A.Rebars andKeyed Sections, 146 B.WeldPlates, 147 C.Shear Connectors,147 9BUI LDING CODEREQUIREMENTS ON STRUCTURAL DESIGN ........ .............................. .................149 1.Loading,150 A.LiveLoads, 151 B.Dead Loads,151 C.Lateral Loads,151 2.AllowableStresses, 152 A.Wood, 152 B.Steel. 153 C.Concrete, 154 ix 3.Construction Requirements, 154 A.Wood,154 B.Steel, 155 C.Concrete, 155 4.Fireproofing, 155 Chapter1 0WOOD CONSTRUCTION .....................................................157 1.Properties of Structural Lumber, 158 A.Sizes. 158 B.Grading, 158 C.Design Values, 160 D.Moisture Content. 160 2.Wood Beams, 162 A.Design for Bending, 162 B.Design for Horizontal Shear, 163 c. Design for Deflection, 163 3.Miscellaneous Provisions, 165 A.Notched Beams, 165 B.Size Factor, 166 C.Lateral Support, 166 D.Bearing, 166 4.Wood Columns,167 5.Joists, 170 6.Glued Laminated Construction, 171 7.Planking,172 Chapter11STEEL CONSTRUCTION .....................................................173 1.Properties of ~ t r u c t u r a lSteel,174 A.Types and Composition of Steel, 175 B.Shapes and-Sizes of Structural Steel, 175 C.AllowableStresses,177 2.Steel Beams, 178 A.Lateral Support and Compact Sections, 178 B.Design for Bending, 179 C.Design for Shear, 162 D.Design for Deflection, 186 3.Steel Columns,188 A.EndConditions. 188 B.Design for Axial Compression, 189 4.Built-Up Sections, 191 5.Open-Web Steel Joists,191 Chapter12CONCRETE CONSTRUCTION .......................................... ;.193 1.Concrete Materials and Placement,195 A.Composition of Concrete, 195 B.Admixtures, 196 C.Reinforcing Steel, 196 X D.Placing and Curing, 196 E.Testing Concrete, 198 2.Safety Factors, 199 3.Concrete Beams,199 ABasic Concepts of Design, 199 B.Design for Flexure,202 C.Shear, 206 D.Compression Steel, 207 E.Development Length and Reinforcement Anchorage, 207 F.Deflections, 208 G.Continuity, 208 H.T-Beams, 211 4.Concrete Slabs, 212 5.Concrete Columns. 212 A.Tied Columns, 2 ~3 8 .Spiral Columns,2 ~ 3 6.Prestressed Concrete,214 A.Precast, Pretensioned, 214 B.Post-Tensioned, 214 Chapter13WALL CONSTRUCTION.................... ..................................215 1.Masonry Walls, 216 A.Single Wythe Walls, 218 8 .Reinforced Hollow Unit Masonry, 2 ~ 8 C.Cavity Walls, 219 D.Reinforced Grouted Masonry, 2 ~ 9 E.Openings,221 2.Stud Walls, 221 A.Wood Studs, 222 B.Metal Studs. 223 C.Openings, 223 3.Concrete Walls,224 A.Cast-in Place, 224 8.Precast Concrete Walls, 225 4.Building Envelope, 226 AAttachment toStructural Members, 226 B.Movement, 227 Chapter14LATERAL FORCES- WIND ................. ................................229 1 .The Effect of Wind on Buildings, 230 B.Wind Measurement , 231 C.Variables Affecting WindLoading, 232 2.Analysis of Wind Loading, 233 A.Ce Factor, 234 B.Cq Factor. 236 C.qs Factor, 236 D.Importance Factor,237 xi E.Load Combinations Required, 239 F.Special Areas and Components, 239 3.Design of Wind-Resisting Structures. 240 A.Lateral Force Distribution,240 B.Building Shape and Framing Methods, 243 C.Diaphragm Design, 246 D.Chord Force,246 E.Shear Walls and Overturning, 247 F.Drift, 249 G.Connections, 249 Chapter15LATERAL FORCES-EARTHQUAKES .................................251 1.Basic Principles, 253 A.Characteristics of Earthquakes, 253 B.Measurement of Earthquakes, 254 C.Seismic Zones, 254 D.The Effect of Earthquakes on Buildings, 255 2.Structural Systems to Resist Lateral Loads, 256 A.Bearing Wall Systems, 257 B.Building Frame Systems, 259 C.Moment-Resisting Frame Systems, 260 D.Dual Systems, 260 E.Horizontal Elements, 260 3.Building Configuration, 261 A.Torsion, 263 B.Plan Shape, 264 C.Elevation Design, 266 4.Analysis of Earthquake Loading,268 A.ZFactor, 268 B.1 Factor, 269 c.c Factor.270 D.RwFactor, 271 E.w Factor,271 F.Distribution of Base Shear, 271 G.Parts of Buildings, 274 H.Load Combinations Required, 274 5.Additional Considerations, 274 A.Overturning Moment, 274 B.Drift, 274 C.The Rise and Fall of Buildings, 276 D.How Floors Damage Property, 278 Bibliography...........................................................................279 Index ......................................................................................280 xii I STRUCTURALandENGINEERING CONCEPTSforARCHITECTURE STRUCTURAL AND ENGINEERING CONCEPTS FORARCHITECTURES 1.OVERALL APPROACH TO STRUCTURAL EDUCATION The objective of architecturalis to create en effective environmental whole, a total system of interacting environmental subsystem.Since the architectural challenge is to deal ina coherent way,with organiZational,symbolic, a.nd complextty, fragmenta-tionof techntca!knowledge doesnot contributeto a creative by designers. This leads to an educational conclusion that the Ieamer must never be anowed to forget that his ability to conCeptualize overall space-form interactions will allow him to control the need for details, and not vice veBB. It a.tso suggests that a common educational strategy for stu-dents of both engineering and architecture would be to move deductively; from an.introduc-tion to structures that cOnsiden. the schematic implications of buildings viewed as space-fonn CENTRE GEORGES POMPIDOV- PARIS SYDNEY OPERA HOUSE: AUSTRALIA MUNICH ClYMPIC STADIUM 2 to a logical elaboration of this basic undemanding. The basic understanding focus-sesonconsiderationofmajor structuralsubsystemsanddiscriminationofkeyelements, whereas, the act of elaboration involves attention to the details required to realize the whole. The good senseof suchanoverallapproacl')to educationcanbe vividlycharacterized by consideringwhat we often termedthe nonstructuralspace enclosureandsubdivisionas-pects of architectural design. The spatial organization and'8rticulation of the various proper-tiesof activity spacescallsfor controlof theexternalandintemal adjacency and interface potentials.Horizontal and vertical surfaces in the form of floors,walls,roofs,and penetra-tions through these surfaces must be provided to establishvaryingdegrees of spatial diffe-rentiation,access,and geometric definition. Imagine that the physical components of a spatial organization scheme were designed with thought for tt)eir structuralimplications. The probability for major revision of earlycon-cepts due to structural requirements will be high. Now, in contrast, imagine that these com-ponents of spatial organization were organized from the beginning with overall structural im-piicationsof the schematic spaee-form systeminmind. Theprobability for major revision wouldbe minimized,andthesymbolicand physicalintegration of thestructure withthe overallarchitecturalschemewould beinsured. It became apparent that an ability for overall thinking can make it possible to apply structural knowledge to the'total designeffort fromthe very beginning and with a mini-mum of distraction by lower-level details.It alone canenable the architect to think of the physicat issues of a space-structureina c.ontext that is inherently compatible with his mode of dealing with the many organizational and symbolic issues of space-forming.it can assurethatthe emphasisoncomponentsconceivedasactingtogetherastotalsystems rather thanseparately,anindependentparts.It isalsoapparentthatmuchcanbe gained from applying this overall-to-specific model of educational management to a reconsideration of teaching andwriting strategies in many specialized fieldof deaign-releted knowledge. 2.STRUCTURE AND OTHER SUBSYSTEMS Thereareotherimportantreasonsforsuggestingthat structuralthinking should be intro-duced at the very earliest stages of the design process. These derive from the need to pro-vide buildings with mechanical and other environmental seNice subsystems that support ho-rizontal and vertical movement of men and materials as well as provide for heating, ventila-tion, air-conditioning, power, water, and waste disposal.ln addition, provision for acoustical andlighting needsisofteninfluencedbystructural VERTICALCIRCULATIONTOWERS ALSORESISTHORIZONTALFORCES \ (a) VERTICALMOVEMENT SU8S'(STEMSCANPLAY BASICSTROCTURALROLeS '-.,.,c.-- SLENDERCOLUMNSNOTREQUIRED TORESISTHORIZONTALFORCES 3 Vente:.!mowment ofthrougha building- requireerath largethafbl,end overetl thlndng c.n rMUtt in the uae of thele leMce components asma;or structural The requirements for proviaions of heating, ventilation, air-conditioning, power, water, and weste services can be viauatized In the form of a Tree diagram. TheM services usually origin-lite at a centralized location and must trace their way horizontatly and vertically throughout the ibucture in order to eerve the activity spaces.Largetrunk-chaeespaces rr.aybe. re-quired,W1dtheir structural implications thoukj be considered early in the design procea. US!U E CENTRALMECHANICAL ANDOTHERSERVICES In term1 of acoustics, it;. cleaF that the structural shape of a spatial organization can dtrectty inftuence ecou8tiCIIIIn addition,if a apetia) organization calls for heevy equip-ment to be located IUch that it !mpinges on a flexibte structure vibnltiorJand acoustical dia-turbanceeC8flbe transmittedthroughout the spacebecause ofanincompatibleinterfaCe between machines all(f stt.Ucture. DOMEROOF CONCENTRATES DISHROOFDISBURSES SOUNDDISTRIBUTION1S INFLUENCEDBYTHE OVERALLSHAPEOF SPACE Mechaf'Hcal Soundistransmittedthrough structure.When the structUre is flexibfe,vibrations are atao tran.mltted. The raqtjirernent for artificial and naturallight:t>rings. up other considerations. Artificial light-ing often calla for integrating conlideration of structural subsystems with considerations of the spatial qualmes of light and of the spatial requirements for housing and the lighting fix-tures. Thtt implications of naturalligthing are evenmore obvious. 4 ARTIFICIAL UGHT AND STRUCTURE INTERACT AT SUBSYSTEMLEVEL GOODINTERFACEMINIMIZESSTRUCTURALDEPTH l -.-1 """ POORI N T E R ~ C EMAXIMIZESSTRUCTURALDEPTH J DtPT......... Lighting systems should be made tointerfacewellwithstructural sub-systems LIGHTiNO I'ION.I Nill.L'fPINNED SUPPORT FRANKLlOYDWRIGHT'SJOHNSONWAXBUILDING For example, consider a fully enclosed space-form with all lighting provided artificially. Then cons!der anopen-top Spatial organization with a heavy reliance on natural lighting through-out the space. NATURAL LIGHT AND STRUCTURE INTERACT AT OVERALL LEVEL a)Fully enclosed box represents simple structural problems but provides no natural light. b)Fully transparent roof provides natural light but posesmorecomplexstructuraldesignprob-lems. 5 c)Bearingandshear wall designwithfew wind-ows is simple but admits little light. d)Frame design is more complex but allows up to ~ % o fthe wall to be transparent for light and view. BUILDING FORMSCONCEIVEDAS SPACE-STRUCTURES 4THiNVERTICALPLANES JOINEDTOFORMOPENTOP TABLE " 6 IFPLANESARETOOiHIN, THEYWILLBUCKLEANDTHE FORMWILLCOLLAPSE TUBE ACTIONCANBEACHIEVEDFORAVARIETYOFSECTIONALSHAPESANDBY MEANSOFSTRUCTURAL COREDESIGNS HORIZONTAL SUB-SYSTEM BALANCEDFRAME ACTIONREQUIRESTHAT INTERIORCOLUMNSBEABOUT TWO TIMES SiiFFER THANEXTERIORCOLUMNS -,- -r-e-~ - . - - e , - -'II IIII IIIIJ --1-- +-- ..J - -- ---1II1 1rIII -L8 -L . ._.L ..l_ v\7\T\1\ IIIIIIII 7 ()' ,-... ----! I I I ,I I I I I .I I ONECONNECTION INCREASED USEMORETHAN . ONECONNECTION The overat 8tfffnea and EfflciMay of aBaalc Frame Ia improvw by acombit'Nrtlon of more columna and Connector. 8 c INHERENTLYEFFICIENT COMBINATIONISEFFICi ENT Horizontalmay H. combinedInmany wavetoprovide overall atructurallntegrlty. EXTERIORSHEAR WALL(FRAMES) CORETUBE. 8 INTERIORSHEARWALL tORfRAMES) BRACEDTUBE TUBEINTUBE CLUSTEREDTUBES(FRAMES) COREANDSUSPENSION MACROFRAME 9 At conceptualstages,thedesignerneedonly keepinmind the fourbasicsub-system interactions that must in order to achieveoverall integrity in the struc-turalaction of a building form: DEADL.OAD ,------.... I I I I I I I 1.Horizontalsubsystemsm.ustpickupandtransfervertical lo_ads intheverticalsubsystems. 2.Horizontal subsystems must also pick up horizontal-loads ac-cumulated along tt')eheight of a building and distribute them totheverticalshear-resisting3Alloftheverticalsubsystemsmustcarrytheaccumulated dead load and live loads, and some must be capable of trans-ferringshearfromtheupper portionsof abuildingtothe foundation. 4.Keyverticalsubsystems that canresist bending and/or axial forces due to overturning moments must be provided. Wh.ere possible, shouldbeinteractedbyhorizontalsubsys-tems. -10 BYKEYINGBYFRICTION - KNIGHTOFCOLUMBUS BUILDINGFOURCORNER SHAFTSCARRYBOTH VERTICAL.ANDHORIZONTAL LOADS HighRiseBuilding -Steel Framing ~ WINOCONNECTIONK-BRACINGK-BRACINGSTAGGEREDTRUSS SHEARCONNECTiONSMOMENTCONNECTIONS TAPEREDF ~ M E v "' / ['._ / !/ "\.. / ' v v "'\ / .. [\ k:'1 TRUSSEDFRAMING ""' ~ - ~ CIRCULAR FRAMING ,. K 1\ 11 ~~IJW.VJI ~/ 1'\ / - ~ v ~ ~ \v \v '\ / I'\ v 1\ v 1/\ COREondSUSPENDED FRAMING SQUARECOLUMN PATTERN COHllttUOUSWALLFOOT\HG ISOLATEDFOOTJMG DIRECTBEARING SHEAR LEDGER NOTCH STRADDLEHOLE CONNECTORCONTINUOUS 12 3.CONSTRUCTION METHODS AND STRUCTURES AS EXPRESSION OF ARCHITECTURAL DESIGN A.BUILD_ING The purpose of abuilding is to provide ashelter for the performance of human activities. from the time.of the cave dwellers to the'present, one of the first needs of man has been a shelter from the elements.In a more general sense,the art of building encompasses all of man's efforts to control his environment and direct natural forceS to his own needs. This art includes,inaddition to buildings allthecivilengineeringstructuressuchasdams,canals, tunnels,aqueducts and bridges. The form of abuilding is anoutgrowth of its function,its environment and various soci9-economic factors. An apartment building, an office buiiding, and a school differ in term be-cause of the difference in function they fulfill. In an apartment building every habitable space such as living rooms and bedrooms, must have natural light from windows while bathrooms andkitchenscanhave artificial light therefore canbe in theinterior of the building. Inoffice buildings,on the other hand,artificialligt}t is accepted for more uniform illumina-tion,and therefore the depth of such buildings is not limited by need for natural light. B.FORM, SHAPE AND APPEARANCE: Environment may affect boththe shape and appearanceof the building.An urba11school may create its ow.nenvironme.nt by using blank walls to seal out the city completely,and a country school may develop as anintegral part of the land scape even though both schools futfillthe same function. The form of abuilding is affected by avarietyof socio-economic factors,including land, costs, tenancy building budget, and zoning restrictions. High land costs in urban areas result in high buildings.Ahousing project for the richwiil take adifferent form than a low cost housing project. A prestige office building will be more generously budgeted for than other office buildings.Buildings withsimilar functions thereforetakeondifferent forms. C.STRUCTURAL FORMS: The beam or arch have developed through the ages in relation to the availability of materials andthe technology of thetime.The archdevelopedon aresultof the availability of the brick.In theof buildings, every structure must work against the gravity, which tends to pulleverything downto the ground. Abalancethereforemust be attainedbetween the force of gravity,the shape of the struc-ture, and the strength of material used. To provide a cover over a sheltered space and permit openings in the walls that surround it.Builders have developed fourconsistent with these balance between gravity.form and material. WALLa.Post and Lintel /, I OPENJNG A HORIZONTAL BEAMBETWEEN TWOVERTICAL SUPPORTS 13 14 b.Arch Construction coveringanopenspacebyplacing wedge-shapedunitstOgetherwith their thick ends outward. c.Corbel or Cantilever a projection.from the face of a wall fixed in position to support a weight. d.TrussConstruction allowingfortheuseofapotnted roof. d D.CONCRETE Concrete is a conglomerate artifiCial stone. It is made by mixing a paste of cement and water -Mth$8ndandcrushedstone,gravel,or otherinertmaterial.Thechemicallyactivesub-stance in the mixture is the cement that unites physically and chemically with the water and, upon hardenirfg,binds the aggregates together to form a solidmass resemblingstone. A particular inherent property is that concrete may be made in any desired shape. "The wet mixture is placed in wood, plastic, cardboard or' metal forms in which it hardens or sets. Pro-perly proportioned concrete is hard anddurable materials.It is strong in compressionbut brittle and almost uselessin resisting tensile stresses. MASS or PLAIN is used .in members in which the stresses are almost entirely com-p1818ivesuch asdams.piers.andcertaintypesof footing. MASSCONCRETEBEAM -0 AtOYE IT8HOitTII!R WllGHT ATENOS +-lUISIONATCIHTIRlUKE THEEMOSLONGERAHO TEARSTHIl.OW!Itct!NTI!!R c In order to avoid compression and tension. Teinforcement made of billet steel and rail steel, usually intermediate grade is introduced. This.. is calledREINFORCEDCONCRETE. t,,. - r,-+----------"1 1 L L/4 L./!5 --, '/ '/ '- -- -------- - ----/ OLDMETHOD ICOfiiTtNUOUSBAA) CON PRESSIONBAR -

l -%::':::. ..-= I TENSIONEXTRABAR 1 L. CO""EaSIO"SPLICE -toOWFORIIIIO404PlAIN TUSIO.SPLICt!-24 4..4PLAI" NEWMETHOD 15 I L/4 L ---...c: ':..- .=:'\..... . L/5 I REINFORCED CONCRETE is produced in differentways: THEFORMOF THESIDESOF BEAMSCANBE REMOVEDEARUER . SLUMPTEST 1.CASTINPLACE - when: aconcreteIs pouredat the jobsite beams,slabs and columns aresetin forms onscaffold-ings and later on removed after !the concrete is hard.Usually the minimum length of time f or is12daysandforbeams and col-umns;7,to 11days. Arule of thumb is to re-tainthe bottom forms 2daysfor eachinch of thickness of concrete. For a3,000 lb. concrete aratioof 6gallons of WATER per sack of cement will produce a watertight concrete. 6l/2 gallonsshould be the maximum. Two Types of Mixture Tests: Someti mes,the mixtureof concreteis too much cement sandmortar causedby water, an(j sometimes insufficient cement-sandmortarwhichproduceshoneycombedS\Jf-faces.To test the consistency of mixes _of have the SLUMP TEST and to test the strength of the con-crete,we have t heCOMPRESSIONCYLINDERTEST. 10 L 2 0+ n 0::3 With an truncated cooe made of sheet metal, with dimensions shown as above,leave the top and bottom op8n.Freshiv mixed concrete is placed infhe mold in three layers, each being rodded separately 25 times with a 5/ 8"(16mm) diameter rod. When the mold is filf-edandroddedthe top is levelledoff,andthe moldisliftedat once.Immediately the slumping action of the concrete ismeasured by taking the difference in height between the top of the mold and the top of the slumped mass ofconcrete. 16 RECOMMENDED SLUMPS -- ---rPLAIH '-../' CYLIHDI'R TYPESOF CONSTRucnON ReinforcedFoundation walla andFooting Plain substructure waU8 Slabs,beams, reinforced walts Columns Pavements Heavy Mass ConstructiQn COMPRESSION TEST SLUMP METRIC MIN. 0.126 0.100.025 0.150.075 0.150.075 0.750.05 0.750.025 This is the test given to concrete for strength. The specimens to b4 testedare cylindricalin shapeandhave alengthtwice the diametet'.The standard is 6 inch 10.15) in. diameter and 12 inch (0.30inheight. Freshly made concrete is then placed into the mold in these se-paratelayers,eachaboutone-thirdthevolumeofthemokt. Roddedwitha16 mm,bullet-pointedrod.Afterthetoplayer hasbeenrodded,thesurfacesis levetedwithaTroweland covered with glass or planed metal. After 2 to 4 hours, when the concrete has ceased settlirig,the specimens are capped with a th!n layer of neat cement paste and covered with glass or metal. It is customary to keep the specimens at the siteof 24 hours. After which they are taken to the laboratory' and cured in a moist atmosphereat 70F.Testsareusualtymadeat7and liday periods. .In makingextreme care should be taken to see that theendsareplane-parallelsurfaces.Afterthespe.cimenis placed in the testing machine, a compressive load is applied until the specimen fails.The load causing the failure is recorded,and this load divided by the cross-sectional area of the cylinder gives the ultimate compressiveunit;stressusually inpsi. 2.PRECAST CONCRETE Prefabricatedreinforcedconcretewhichhavebeencast and curedinafactory rather than in place on the site. Then delivered by long trailer trucks and installed by welding to-gether all the components. These include floor and roof slabs, columns,girders,beams and joists, wall panels and stairs.Whole wall sections are precast and later raised to po-sition in what to be called TILT-UP Construction. 17 1 Advantages: 1.CaSting and curing conditions, as well as concrete design, can be rigidly controlled re-sutting in consistently high .quality2.The cost of forms and scaffolding is reduced since they can be placed on ground rather than havingto be suspended or supported inposition. 3 .. Where mass production of a unit is possible, forms can be made precisely of steel en- longuseand very smooth surfaces. 4.Structural members can be mass-produced in a plant while excavations and founda-tion work are taking place atthe site. 5.Pre-cast concrete members arethendelivered as. called for inwork schedules and in most cases erected directly from truck bed to the structure without rehandling at the site. 6.Close supervision and control of materials and a specialized work'force in a centralized plant resultin a high-quality product. 7.Finishing workconcrete surface$ can be done more easily in the plant than in posi-tion on the site. 8.Because of superior reinforcing techniques the dead load of the structural members themselves can be reduced. 9.Plant prqduction isnot normally subject to delays due to adverse weather conditions as so often happens to jobsiteoperations. Two GeneralClassifications of PRECAST Structural Members. 1.Normally reinforced 2.Prestressed a.Pre-tensioned b.Post-tensioned Normally reinforced precast concrete are deSigned according to accepted reinforced-con-crete practice prestressedconcrete unit isone in which engineeredstresses have been placed before it has been subjected to a load. WhenPRE-TENSIONINGisemployed,thereinforcement,Intheformof high-tensile steel strands,is first stretchedthroughthe form or casting bedbetweentwo endabut rnents or anchorages.Concrete is then poured into the form, encasing the strands.As theconcretesets,it bondstothetensionedsteel;whenit hasreachedaspecified strength,.the ends.of the are released. These prestresses the concrete, put-ting it under compression and creating built-in tensile atrongttl having beenprestressed. Members hllve a.slight arch or camber. ---- - CAMBE'R STRt:CWED PLAINCONCftETElEAN 1 1 UNLOADED 1 18 LOAD LOADED LOADED POST TENSIONING involves placing and curing aprecaat member which contains nor-mal reinforcing and in addition, a number of ctlann* through which poststressing c8btes or rods (tendons) may be passed.Sometimes the tendons are wrapped in oiled paper for easy sliding.Oneside isanchored~ u r e l yat the findandone-sideisheldby acone. After concrete has hardened tothe desired suet lgth. The cone is fitted to a hydraulic jack and is pulled to the allowable strength then a amall steel plate is wedge so as the tendons will not go back to its normal posttion.Post tensioningis usually carried out when the member is very large or when only one or a very few of one particular kind of unit are to be made. In general, post-tensioning will be used if the unit is CNer 46 feet (14 mllong or over 7 tons is weight. tri)(U)PLATE CHANNEL$L.AI BUM . . THISPLAT!:18INIIIRTEDWHf:N PULLIDTORQUUtl!ITRENGnt t ORPit. 80 THATTtll!TI:NDON8 18PI!RIIIANI!MTLYITRI!CHI!O. BEAM,COLUMNS, "'OtSTS, FLOORING L. IN T DOUIIl.E- T- ROOf"SLAB 19 .. ---"SERIESf1FPR - CAST '...._CURTAIHWAI.LftLDED 'TOTHESTRUCTURAL...MS f'- ......_ WILLHASTENCONSTRUCTION 1......_TilliEANDLlii1HATESIIIIOST l'-. ......_ OFTHEI'ORNWORICS 1' I 1 I l WALLPANELS- AREPRECASTEDCUSTOM -DESIGNEDARCHITECTURALPANELS WITHSPECIALLYDESIGNEDWATERPROOfJOINTS THISISALSO USEDFORINDIVIDUALHOUSINGUNITS 3.LIFT SLAB BUILPING SYSTEMS lift slab is a systems approachto construction based on advanced Technology.But un-like some competitive systems, lift slab is deSigned to fit your requirements instead of try-ing to make you fit its requirements. In lift slab Building systems, floor and roof slabs are cast one on top of the other. After a short curing time, they are lifted_to their final positions by hydraOiic jacks and securedvertical supports. The result efficient utilization of man-poWer and desing versatility. No large expenditure is. requjred on the part of the general contractor who uses lift slab. Nor does thearchitect or engineerneedto limit hisdesigncreativityto fit arestrictive system. How Uft Stab lowers Costa a)FORMSARE REQUIREDONLY ONTHE OUTSIDE EDGE OF THE SLABS.Lift stab eliminates 90 percent ofthe formwork for acast-in-place concrete buikiing and reduces the number of carpenters to a minimum. With very littfe waste and trash, costlycleanup is eliminated.Irregularly shaped floorplans are easily formed. - ltl!AOYYIXl!:OCOI'ICRt:T! b)SLABS ARE CAST ONEATOP THE OTHER. After the first slab is laid out, it serves as a template for su.bsequent slabs. This elimi-nateslayout onall but the initial slab, and cuts mistakesto a minimum.EJectrical, plumbing, and mechanical work is fast and accurate; craftsmen are able to work more Elfficientty. 20 CONCitETt: COl.UMN - SPACALLOWANCE POSTTt:HSIOHINGTtNOONS FORMS lllll. - - 1!'. SLA8'.: \______ TENnOftS SLEI!:VIS (P"OAELECTRICAL ANOPLUM81HOPlf>IS) Here Pest-Tensioning Tendons, mild steel reinforcement rods and forms to block Ol openings in the slab are all in place,ready for next slab to be poured. There is no wait for erection of complex. elevated formworic. This shonens the timeinterval between pouring one slab and the next. The bottom of each slab is exceptionally smooth (just like the top); it is ready for finish paint or spraying without additional c.Two CastingSystems are Available .. . , . .QPEHSf'I'CE 21 Allslabsarecastandcuredonthe ground and then raised into position and secured.Theground-levetcastingme-thod is used for structural frame lift slab building systems up to twelve flooa and bearingwall lift stabbuilding systemup to four floors E - ~ oa'tO Powerfulhydraulic lifting tacks provide the muscle to lift up to 160,000 pounds (72, mkg. l per tack at rates of eight to twelve feet (2.40-3.60 ml per hour or more. As many as 48 lifting jackscanbe usedat the same time. First the designed footing is laid out and poured then the reinforced concrete column is enclosed in a form and poured. Up to a height of3 1/ 2 floors.When all slabs had been lifted. The top of the col-umns is againsmashedto expose the steel bars and another one and one half floors height of column is'connected by welding and pouredto asmoothenedtop finish.Thiswillaccomodateallthe t)ydrauli.c jacks in one horizontal elevation. 22 STEEL.ENI!II! OPEDTO COL.UMNAHDSl.A8 FOfltWELDINGPURPOSES ! I R-., .... -lltiRDCOLUNN RStMe 7-..., !S--!J--5Eif:D COUINN

.n-+- 4 n R 7 -INITI.4L TOI'OLLOWTHI!CAlLEPROFILE 32 tTtCAlLESARI!THEN L"AIOONA,_"RRWHICH THI'INALGROUTING ISAPPLIEDUPTOTHE I.EWLOPTHIEWAI"I'Lt: 8U81 7.SLIPFORMMETHOD This. method has been utilized extensively in agricultural and industrial com-plexes.In particular the silos, either cylindrical or straight-sided have found the most practicalapplications. Lately,however, this has been applied to elevator coreconstructions and evenmulti.-storey hotel buildings.It canbe applied to any construction in-cluding multi-storeybuildings. Advantages: a}short constructiontime b)low labor cost clsmall timber requirement d) smoothconcretesurface e)minimum of constructionjoints The conventional conrete construction which was earlier discussed .utilize a Jot of bracings and scaffoldings for the forms,are fixed and after pouring concrete cannot be removeduntil after15 days. SLIPFORMmodifiesthemethod offormingintheconventionalconcrete construction.It utilizes very much less framework,n,o scaffolding at all and some braces.The whole form systemis distributed over severalhydraulic jacks. The hydraulic jack system is the heart of the slipform method of con-struction. .. .... t ..,.'0 . ~. :. .. 33 ' JSl I I f~. I I I I .... '.. . . . ... . ..;. I 2 4 . 3 8.COMPOSITE FLOOR CONSTRUCTIONSYSTEM The COli_. aysam of the sttuct\Jre .te fonned about meter and hatf in height. When wery!hing Ia fbcedto the faob and me hYdraulic tiY$t8m IM8d to good workingcon system incorporatesaspecial Z-shaped cold-rolled steel top chord (the top member of aconventional'open web joist) wr.:ch is automatically"locked" to the concrete floor on hardening. In addition, the top chord is slotted to permit the inser-tionof "roUbars" between joists. These bars provide support for plyWood sheets laid over them. Reinforcing mesh is then drapedoverthe joist and theconcrete floor poured. Once the conrete has set, it is asimple matter to unlock the "roll bars" and remove the plywood for use again. 34 Butts, Magwood & Hall. Ltd., also cOMUfting engfneeFS'inoriginated the concept as a cost-control building system in 1967. To bring the invention to the marketing stage, the aid of local bui lders was enlisted and Hambro Structural Systemsltd. wasformed. In 1970,Minto ConstructionLtd.;Canada, used the system for eight-storey apartment building, and had since used it in four other buildings. Minto'sarchitect,JohnRussell,likesthesystembecauseofitsflexibilityandcost. savings.These result from dispensing with propping for short to medium spans.It also enables !subcontractors to move in quickly after the floor has been poured . . In one of Minto's recent projects, in which concrete had been poured the day before for th'e eighth floor,plumbing and elec.trical wiring had stanedon the seventh,wiring wai complete and plumbing was complete at the sixth floor, and the ceiling on the fifth f!oor. In fQr conventional poured-in-place conrete construction the building has to ad-vance through six floors beforethe subcontractorS can even get started. Such acceleration of other subcontractors leads to obvious savings in time. In additiOI) to the capital cost savings arising from the use of theD-500floor, it has been estab-lished by Hambro _that thereare significant savings:in electrical subcontraetons alone over the conventional eoncrete construction. . 35 Rollarerotated forrelff(Ni3/ of9.FLOORDECKING- madeofhighstrengthzinc-coatedsteeldeckingwhichactsasboth permanent formwor1:.;. . ~w-rise construction where over-all depth of the floor/ceiling system is not critiCal. They can span long distances and are noncombustible. Because the webs are open, mechanical and electrical service pipes and ducts can easily be run between the web members. KAMANDGIRDER SYSTEM C.Concrete (a) OHN Wll8ITIIL .IOIIT' SYSTIM (b) Figure 2.2 There are many variations of concrete structural systems, but the two primary types are cast-in-place andprecast.Cast-in-placestructuresrequireformwoiXandgenerallytakelonger tobuild than precast buildings, but can conform to an almost unlimited variety of shapes, siZes, destgn intentions andstructuralrequirements.Precastcomponentsareusuallyformedina plantunderstructJy controlledconditionssoquality_controlisbetteranderecttonproceedsquickly, especiallyifthe structure Is composed of a lirrited number of repetitive members. Themajorityofcast-in-placeconcretesystemsutmzeonly mildsteelreinforcing,butinsome Instances post-tensioning steel is used. Precast concrete systems, on the other hand, are usually prestressed, although sometimes only mild reinforcing steel is used. Sometimes concrete is precast on the site, but this iS usually limited to wall panels of moderate size. Lift slab construction is still used as ~ a l l .In this procedure, floor slabs of a rrultistory building are cast one on top of the next on the ground around the columns and then jacked into place and attached to the cok.Jmns. Cast-in-place concrete structural systems can be dassified into two general types, depending on how the floors are analyzed: one-way systems and two-way systems. In one-way systems the slabs and beams are designed to transfer loads In one directlon only. For example, a slab will transfer floor loads to an lntennediate beam which then trarl$mits the load to a larger girder supported by columns. 41 One of common types of one-way systems is thesystem. See Figure 2.3 (a). This functions in a manner similar to a steel system in which the slab is supported by intermediate beams which are carried by larger girders. Typical spans are in the range of 4.5 m to 9 m.This system is economical for most applications, relatively easy to form, and allows penetrations and openings to be made in the slab. A concrete joist system,Figure 2.3(b), is composed of concrete members usually spaced 650 mm or 900mm apart,running in one direction, which frame into larger beams.Most spans range from 6 m to 9 m with joist depths ranging from 300 mm to 600 mm. A concrete joist system is easy to form since prefabricated metal pan forms are used. This system is good for light or medium loads where moderate distances must be spanned. There are three principal two-way concrete systems: the flat plate, flat slab, and waffle slab. In most cases, all of these are designed for use in rectangular bays, where the distance between columns is the same, or close to the same, in both directions. The flat plate is the simplest. SeeFigure2.3 (c).Here, the slab is designed and reinforced to span in both directions directly into the columns. Because loads increase near the columns and there is no provision to increase the thickness of the concrete or the reinforcing at the columns, this system is limited to light loads and short spans, up to about 7.5 m with slabs ranging from 150 mm to 300 mm. It is very useful in situations where the floor-to-floor height must be keptto a minimum or an uncluttered underfloor appearance is desired. When the span of flat plates is large,or the liv.e loads areheavier,flat plates require drop panels (increased slab thickness around the columns) to provide greater resistance against punching shear failures. Column capitals (truncated pyramids or cones) are sometimes also used to handle punching shear as well as large bending moments in the slab in the vicinity of the columns. This type of flat plate (a)BEAMANDGIRDER (c)ONE WAY PAN JOISTS Figure 2.3 42 (b)FLATPLATE {a)FLAT SlAB (b)WAFFLESLAB Figure 2.3 is usually referred toas a flat slab. See Figure2.3(d) . This system can accommodate fairly heavy loads with economical spans up to 9 m. T h ~waffle slab system Figure 2.3 (c), can provide support for heavier loads at slightly longer spans than the flat slab system. Spans up to 12m can be accomplished economically. Like the one-way joist system, waffleslabs areformed ofprefabricated, reusablemetal or fiberglass forms whichallow construction to proceed faster than with custom wood forms. Waffle slabs are often left unexposed with lighting intergrated irrto the coffers . ECTANGULARBEAMINVERTEDTEEBEAML SHAP0BEAM IIN8lETEE Figure 2.4 43 I ... TO11 THIC HOlLOW COM ILAa Figure 2.4 Precast structural mempers come in .a variety of forms for diffenMlt uaes. Figure 2.4 ilklstrlllll tome of themore common ones.They caneither be used for structural members such as beama .nd columns, or for enclosing elements such as wall panels. Concrete for wall panels can be call In an almost infinite variety of forms to provide the required size, shape, architectural finish, and opening configuration needed for the job. Precast concrete members are connected kl the field using welding plates that are cast into the mei'T'Der at the plant. When used for structure, precast concrete is typtcally prestressed; that is, high-strength steel cables are stretched in the precasting forms before the concrete is poured. After the concrete attains a certam minimum strength, the cables are released and they transfer conlpf'essive stresses to the concrete. When cured, the concrete memeer has a built-i n compressive stress which resists the tension fofces c ~ s e dby themember's own weight plus the tive loads acting on the mermer. Stngle tee or double tee beams are a popular form of precast concrete construction because thty can simultaneously serve as structural supports as well as floor or roof decking, and they are easy and fast to erect. A topping of concrete(usuaUy about 50 nvn thick) is placed over the tees to provide a uniform, smOOth floor surface, and also to provide increased strength when the tees are designed to act as composite beams. Becauseof thecompressivestressintheconcretecausedby the prestressing forces,unaoaded beams from the prestressing plant have a camber built into them. This is the upward curvature of the structuralment>er.Thestressingin thecables is calculatedto provide the correct camber and strength for the anticipated loading so that when the member is in place, and live and dead loads are placed onit, the cant>er disappears or is greatly reduced. Post-tensioned concreteis yet another structural system that takesadvantage of the. qualities of concrete and steel. In this system, the post-tensioning steel (sometimes called tendons) is stressed after the concrete has been poured and cured. Post-tensioning tendons can be small high-strength wires, sever-wire strands, or solid bars. They are stressed with hydraulic jacks pulling on one or both ends of the tendon with pressure about 0.70 mPa to 1.75 mPa of concrete area for slabs and 1.40 mPa to 3.50 mPa for beams. Post-tensioned structural systems are useful where high strength is required and where it may be too difficult to transport precast members to the job site. 44 D.Masonry A a structural system in conteff1)0rary construction, masonry is generalty limited to bearing wals. It has a high compressive strength but is unitized nature makes It inherently weak in tension and bending.There are three basic types of masonry bearing wall construction:single wythe,doubte wythe, and cavity (see Figure2.5). Both of the layers in double wythe construction may be of the same materialor differentmaterials.Cavitywaltsanddoublewythewallsmaybeeithergroutedand relnloreed or ungrouted. Single wythe walls have no provisions for reinforcing or grouting. Unh masonry bearing walls offer the advantages of strength, design flexibility, appearance, to weathering, fire resistance, and sound insulation. In addition, their mass makes them Ideal for any passive solar energy applications. IINeUWYTHfCONSTRUCTION HONZCWTAL IVERTICAL IU'INFORCEM.ENT CAVITYFULLY GROUTED TIS DOUILIWYTHICONSTRUCTION CAVITYWALL Figure 2.5 ThejointsofmasonryunitsmustbereinforcedhOrizontallyatregularintervals.Thisnotonly strengthens the walt, but also controls shrinkage cracks, ties ITlJitiwythe walls together, and provides a way to anchor veneer facing to a structural backup wall . Horizontal joint reinforcement comes in a variety of forms and is generally placed 400mm on center. 45 Vertical reinforcement is accomplished with standard reinforcing bars sized and spacedin.accordance with thestructural requirements of the wall. Typically, horizontal bars are also used and tied tothe vertical bars with the entire assembly being set in a grouted cavity space. In a single wythe concrete block wall, only venical reinforcing is used with fully grouted wall cavities. One if1l>Ortant consideration in utilizing masonry wall is the thickness of the wall, which determines three important properties; the slenderness ratio, the flexural strength, and the fire resistance. The ~ J e n d e r n e s sratio is the ratio of the wall unsupported height to its thickness and is an indication of the ability of the wall toresistbuckling whena compressiveloadisapplied fromabove.The flexural strength is important when the wall is subjected to lateral forces such as from wind. Finally, the fire rating depends on both the material of the wall and its thickness. These topics will be discussed in more detail in Chapter 12. HEADED STUD ANCHORS COMPOSITESTEELDECI< ANDBEAMSYSTEM. E.Composite Construction HEADED STUD ANCHORS OPENW8STEEL..JOISTSAND \11000CHClftDS Figure 2.6 CONCRETE - - CAST CONCRETESLAB AND STEEL BEAM CWFORMS Composite oonstruction is any structural system consisting of two or more materials designed to act together to resist loads. Composite construction is employed to utilize the best characteristics of each of the individUC\1 materials. Reinforcedconcreteconstructionisthemosttypicalcompositeconstruction, but othersinclude composite steel deck and concrete, concrete slab and steel beam systems, and open-web steel joists with wood chords. See Figure2.6. In composite construction with concrete and steel beams, headed stud anchors are used to transfer load between the concrete and steel, making them act as one unit. Composite steel deck is designed with deformations or wires welded to the deck to serve the same purpose. Composite open-web joists are used to provide a nailable surface for the floor and ceiling while using the high strength-to-weight ratio of steel for the web members. There are many_other types of composite constructions that are less frequently used. These include trusses with wood for compression mermers and _steelllbds for tensiOn members, and concrete-filed steel tube sectiOns. F.Walls and the Building Envelope Nonbearing walls are generally not considered part of the structural system of a building, but there are two important structural considerations when deciding how to atach the exterior, non-structural envelope to the structural frame. The first ishow the weight of the envelope itself will be supported, and the second is how exterior loads, primarily wind, will be transferred tot he structural frame without damaging the facing. How anexterior facingisattached depends,of course,onthespecific materialandthe typeof structuralframe.Paneland curtainwallsystemsareattachedwHhclipson themullionsatthe structural frame. The size and spacing of the clips is determined by the structural capabilities of the curtain wall or panel system. Stone and masonry facings are attached with clip angles. Continuous angles, or special fastenings to the structural frame at the floor lines. If additional attachment is required, a grid of secondary steel framing Is attached to the primary structure and then serves as a framework for the facing. Lightweight facings such as wood siding, shingles, and stucco need to be applied over continuous sheathing firmly secured to the structural wall framing. One of the most important considerations in attaching exterior facing to the structural frame is to allow for expansion and contraction due to the temperature changes and slight movement of the structural frame.Materials with a high coefficient of thermal expansion, such as aluminum, require space for movement withineach panel,at the perimeter of largesections of the facing.Movement canbe provided for by using clip angles with slotted holes, slip joints, and flexible sealants. Materials with a low coefficient of expansion, such as masonry, still require expansion joints at regular intervals and at changes in the plane of the wall. If these arenot provide, the joints or masonry may crack or the facing itself may break away during extreme temperature changes. Usually, steel-framed buildings do not present many problems with movement of the structuralframe. but concrete and wood structures will move enoughto present problems. Concrete structures are especially subject to creep, a slight deformation of the concrete over time under continuous dead load. This condition must be accounted for when designing and detailing connections.Wood structures alsodeform over timedue to shrinkage of the woodandlong-term deflection. Sjnce most wood buildingsare relativelysmall, this is notalwaysa problem, butshould be consideredinattaching exterior facings.-2.COMPLEX STRUCTURAL SYSTEMS A.Trusses Trussesarestructurescomprisedofstraightmembersforminganumber of triangleswiththe connectionsarrangedso that the stresses in themer)'lbersare either in tensionor compression. Trusses can be used horizontally. vertically, or diagonally to support various types of loads when it would beimpossible tofabricate a single structural member tospan a large distance. Although trusses are primarily tension/compression structural systems, some amount of bending is present in many otthe members. This is due to loads applied between the connections and secondary bending and shear stresses at the connections themselves caused by minor eccentric loading. Trusses can be field-fabricated or assembled in the factory as is the case with open-web steel joists and wood trussed rafters. The primary limiting factor is theto transport them from the factory to the job Trusses are discussed in more detail in Chapter 5. 47 B.ARCHES Archesmaybe hinged or fixedsupports.Ahingedarchisa structuralshape whiChis primarily .subjected to compressive forces. For a given set of loads the shope of an arch to resist the loads only in compression is its funicular shape. This shape can be found by suspending the anticipated loads from a flexible cable and then turning the shape upside down, as Antonio Gandi did in many of his structural studies.For ahingedarchsupportinga unifonnloadacrossitsspanthisshapeisa parabola. However, no arch is subjected to just one set of loads, so there is always a combination of compression andsome bending stresses. At thesupports ofa hinged archthere are two reactions: the vertical reactionsand the horizontal reactions, or thrust, as shown in Figur9j 2.7. Since the loads on the arch tend to force it to spread out, the thrust- must be resisted either with tie rods which hold the two tower portions of the arch together or with foundations which prevent the spread. For a givenspan, the thrust isinversely proportional to the rise, or height, of the arch; if the rise is reduced by one-half, the thrust doubles. Arches can be constructed of any material : steel, concrete, wood, or stone, ahhough each has its inherent limitations. Arches canalso take a variety of shapes, fromthe classic half-roundarch of theRomans, to the pointed Gothic arch, to the more decorate Arabic arches, to the functional parabolic shapes. Since the shape of a building arch is often selected tor its aesthetic appeal, it is not always the ideal shape and must be designed for the variety of loads it must carry in addition to simple compression. Wood arches typically span from15m to 72 m, concrete arches from 6 m to 96 m, and stee I arches from 15 m to 150m. Althougharches may' have fixedsupports, theyareusuallyhinged. Thisallows the arch to remain flexibteandavoidsdevelopinghighbendingstressesunderliveloadingandl o ~ d i n gdueto temperature changes and foundation settlement . Occasionally, an arch will have an additional hinge connection at the apex and iscalled a three-hinged arch. The addition of the third hinge makes the structure statically determinate whereas two hinged or fixed arches are statically indeterminate. REACTIONSOFA HINGEDARCH Figure 2.7 48 C.Rigid Frames In contrast to a simple post-and-beam system, a rigid frame is constructed so that the vertical and horizontal members wo!'1( as a single structural unit. This makes for a more efficient structure because au three members resist vertical and lateral loads together rather than singly. The beam portion is partially restrained by the columns and becomes more rigid tovertical bending forces,and both the columns can resist lateral forces because they are tied together by the beam.See Figure2.8. Because the three members are rigidly attached, there are forces and reactions in a rigid frame unlike those in gjmpie post-and-beam system. This is shown in Figure 2.8 (b anc c) and results in the columns being subjected to both COI11lressive and bending forces and a thrust, or outwa(d force,induced by . the action of the vertical loads on the beam transferred tothe columns.As with an arch, this thrust must be resisted with tie rods as with appropriate foundations. The attachment of the columns to the foundationsmay be rigid or hinged.This resultsinslightly different loads on the columns. Thefixed frame as showninFigure 2.8- (c)is s t i f f ~ rthat thehinged frame and the thrust in the fixed frameis also greater. When a horizontal beam is not required, such as in a single-story structure. a rigid frame often takes on the appearance of a gabled frame a showninFigure2.9. Thisshapedecreases the bending stressesin the twoinclinedmernbers andincreases the compression, making theconfiguration a moreefficientstructure.Becauserigidframesdevelop ahighmoment(seeChapter3)atthe connections between horizontal and vertical members, the amount of material is often increased near these points as shown in the tapered columflS and roof members inFigure2.9. IIlj IIIlIII (a) SIN PLPOSTANDBEAM RIGIDFRAMEWITHFlXDCONNECTIONCot.UAT8AS!S I!IIIlI Figure 2.8 49 GABLEDRIGIOFRAME Figure 2.9 D.Space Frames In simplest terms,a space frameis a structural system consisting of trussesin two directions rigidly connected at their intersections. With this definition it is possible to have a rectangular space frame where the top and bottom chords of the trusses are directly above and below one another. The bays createdby the intersection of the twosets of trusses then form squares or rectangles. Themore common type of space frame is a triangulated space frame where the bottom chord is offset from the top chord by onehalf bay, and each is connected with inclined web members.See Figure 2.1 0. Space frames are very efficient structures for enclosing large rectangular areas because of the two-way action of the components acting as asingle unit. This results in a very stiff structure that may span up to105m.Span-to-depth ratios of space framesmay be from20:1to30:1. Other advantages include light weight andthe repetitive nature of connectors and struts so that fabrication and erection time is minimized. The structural design of a space frame is complex because they are statically indetermine s!ructures withnumerous intersections. A computer isneeded for analysis anddesign. TYPICALSPACEFRAME Figure 2.10 50 E.Folded Plates A folded plate structure is one in which the loads are carried in two directions, first in the tansverse direction through each plate supported by adjacent plates and secondly in the longitudinal direction with eachplate actingasa girder spanningbetween vertical supports. SeeF:igure2.11.Since the plates act as beams between supports, there are compressive stresses above the neutral axis and tensile stresses below. Folded plates are usually constructed of reinforced concrete from 75 mm to 150 mm thick although structures made of wood or steel are possible. Typical longitudinal spansare9 m to30 mwith longer spans possible using reinforced concrete. FOLDEDPlATECONSTRUCTfON Figure 2.11 F.Thin Shell Structures A thin shell structure is one with a curved surface that resists loads through tension. compression, and shear in the plane of the shell only. Theoretically, there are no bending or moment stresses in a thin shell structure. These structures derive part of their name (thin} because of the method of resisting loads; a thick structure is not necessary since there are no bending stresses. Since thinshellsarecomposed of curvedsurfaces,thematerialispractically alwaysreinforced concrete from about 75 mm to 150 mm. The forms can be domes, parabolas, barrel vaults, and the more complex shape of the saddle-shaped hyperbolic paraboloid. Thin shell domes can span from 12m to over 60 m while hyperbolic paraboloids may span from 9 m to 48 m. G.Stressed-Skin Structures These structures comprise panelsmade of a sheathing material attached on one or both sides of intermediate web members in such a way that the panel acts as a series of !-beams with the sheathing being the flange and the intermediate members being the webs. Since the panel is constructed of two or more pieces, the connection between the skin and the interior web members must transfer all the horizontal stress developed. Stressed-skin panels are typically made of wood as shown in Figure 2.1 (g), but are also fabricated of steel and other composite mate rials. Although long-span steel stressed-skin panels are possible, most panels of this type span intermediate distances from 3.6 m to 10.5 m. 51 H.Suspension Structures Suspension structures are most commonly seen in suspension bridges, but their use is increasing in buildings, most notably in large stadiums with suspended roofs. The suspension system was boldly used in the Federal Reserve Bank in Minneapolis where two sets of cables were draped from towers at the ends of the building. These, in turn, support the floors and walls, leaving the space on the grade level of columns. Cable suspension structures are similar to arches in that the loads they support must be resisted by both vertical reactions and horizontal thrust reactions. The difference is that the vertical reaction is outward since the sag tends to pull the ends together.Asshown inFigure.2.12 (a),the horizontal reaction is dependent on the amount of sag in the cable. Shallow sags resuh in high reactions while deep sags result in lower reactions. Since suspension structures can only resist loads with the shape of the cable used changes as the load changes. No bending stresses are possible.With a single. concentratedload, the cable assumes the shape of two straight lines (not counting the intermediate sag due to the weight ot.the cable).With two concentrated loads, the shape is three straight lines. and so on. If the cable is uniformly loaded horizontal, theshape of the curve is a parabola. If the cable is loaded along its length uniformly (such as supporting its own weight) the shape will be a catenary curve. See Figure 2.12 (b} and (c). (a)tfORIZONTALREACTIOHDPDl8ONSAt (b) HONZONTAL LOAD ft!SULTIWPMAIMlLICCUAVE (c)YI'IFOIUILOADONCAlLa ..IULTS INCATINAitY CUIWI Figure2.12 52 The fact that a suspension structure can only resist loads in tension creates one of its disadvantages: instability due to wind and other types of loading. Suspension structures must be stabilized or stiffened with a heavy infill material, with cables attached to the ground or with a secondary grid of cables either above or below the primary set. I.Inflatable Structures Inflatable structures are similar to suspension structures in that they can only resist loads in tensiOn. They are held in place with constant air pressure which is greater than the outside air pressure.The simplestinflatablestructureisthesinglemembraneanchoredcontinuouslyatgroundleveland inflated. A variation of this is the double-skin inflatable structure in which the structure is created by inflation of a series of voids, much like an air mattress. With this system, the need for an "air-lock" for entry andexitiseliminated.Another variation is a double-skinstructurewithonly one large air pocket supported on the bottom by a cable suspension system and with the top supported by air pressure. Like cable suspension buildings, inflatable structures are inherently unstable in the wind and cannot support concentrated loads. They are often stabilized with a network of cables over the top of the membrane.Inflatablestructuresareusedfortemporaryenclosuresandfor large,single-space buildings such as spons arenas. 3.STRUCTURAL SYSTEM SELECTION CRITERIA The selection of an optimum structural system for a building can be a complex task. In addition to the wide varietyof structural systems available and their many variations and combination, thereare dozens of other considerations that must be factored into making the fullscope of the problem and find the best balance among often conflicting requirements. This section briefly outlines some of the major selection criteria youshould be familiar with whenanalyzing possible systems. A.Resistance toLoads Of course the primary consideration is the ability of the structural system to resist the anticipated and unanticipated loads that will be placed on it. These include the weight of the structure itself (dead load). loads caused by external factorssuch as wind and earthquakes,loads caused by the use of the building such as people, furniture, and equipment (live loads) , as well as others. These are discussed in more detail in Chapter 2. The anticipated loads can be calculated directly from known weights of and equipment and fromrequirements ofbuilding codes that set down what is statistically probable in a givensituation, the load caused by people in a church, for example.Unanticipated loadsare difficult to plan for but include such thingsas changesin the use ofabuilding,overloading causedby extra peopleor equipment, pending of water on a roof, and degradation of the structure itself. When decidingon whatmaterialor system touse, thereisalways theconsiderationof whatis reasonable for the particular circumstances. For example, wood can be made to support very heavy with long spans, but only at a very high cost with complex systems. A wood system doesn't make sense if other materials and systems such as steel and concrete are available. Often, very unusual loads will be the primary determinant of the structural system and its effect on the appearanceofthebuilding.Extremelytallhigh-risebuildingsliketheSearsTower or theJohn Hanrock Building in Chicago with its exterior diagonal framing are examples of load-driven structural solutions. 53 B.Building User and Functions The type of occupance is one o1the primary determinants of a structural system. A parking garage need spans long enough to allow the easy movement and storage of automobiles. An office building works well with spansin the 9 m to12m foot range. Sports arenas need quite large open areas. Some buildings have a fixed use over their l ~ espan and may work with fixed bearing walls while others must remain flexible and require small columns widely spaced. These are all examples of somewhat obvious determinates of building systems. However, there are many other needs that are not so apparent. For example, in a location where building height is limited, a client may want to squeeze as many floors into a multistory building as possible. This may require the use of concrete flat plate construction with closely spaced columns although another system is more economical. In another instance, a laboratory building may need large spaces between usable floors in which to run mechanical services. This may suggest the use of deep span, open-web trusses. If the ~ m e laboratoryweretohousedelicate,motionsensitiveequipment, then theuse ofarigid,massive concrete structure might be warranted. C.Integration With Other Building Systems Although a building's structure is an important element. it dOes not exist alone. Exterior cladding must be attached to it, ductwork and pipes run around and through it, electrical wires among it, and interior finishes must cover it. Somematerials and structural systems make it easy for other services to be integrated. For instance, a steel column-and-beam system with open-web steel joists and concrete floorsover metal deckingyieldsa fairly penetrablestructure tor pipes, ducts, and wiring while stiR allowing solid attachment of ceilings, walls, and exterior cladding. On theother hand, reinforced prestressed concrete buildings may require more consideration as to how mechanical services will be run so there is not an excess of dropped ceilings, furred-out columns, and structure-weakening penetrations. Exposed structural systems, such as glued-laminated beams and wood decking or architectural concrete, present particularly difficult integration problems. D.Cost Influences As with most contemporary construction, the concern over money drives many decisions. Structure is no exception. It is one portion of a building that is most susceptible to cost cutting because it quite often cannot be seen and the clien1 sees no reason to spend more on it than absolutely necessary. There are two primary elements of selecting a structural system based on cost. The first is selecting materials and systemsthataremostappropriatefor theanticipated loads,spans required,style desired,integrationneeded,fire-resistancecalledfor,andalltheotherfactorsthatmustbe considered. This generally leads to major decisions such as using a concrete flat slab construction instead of steel, or using a steelarchsystem instead of glued-laminated beams. The second part is refining the selected system so that the most economical arrangement and use ofmaterialsisselectedregardlessof the system used. Ina typical situation,for example,a steel system isselected butvarious framing options must be comparedand evaluated. Changing the directions of the beams and girders or slightly altering the spacing of beams may result in a savings in the weight of steel and therefore a savings In money. Or, a concrete frame may be needed, butthe one with the simplest forming will generally cost less. 54 E.Fire Resistance Building codes dictate the fire resistance of structural system as well asotherparts of a building. These range from one hour to four hours; the time is an indication of how long the member can withstand a standard fire test before becoming dangerously weakened. The structure is,of course, the most important part ofa building becauseitholds everything else up.As a consequence,required tire resistancesaregenerallygreater for structuralmembers than for other componentsin thesame occupancy type and building type. There are two-considerations in the fire resistance of a structural member. One is the combustibility of the framing itseH and the other is the loss of strength a merroer may experience w h ~ nsubjected to intense heat. Steel, for instance, will not burn but will bend and collapse when subjected to high temperature.It must, therefore be protected with other noncombustible materials. Heavy timber, on the other hand, will burn slightly and char, but still maintain much of its strength in a fire before it bums completely. Some materials, such as concrete and masonry, are inherently fire, resistant and are not substantially weakened when subjected to fire {assumingany steel reinforcingisadequately protected). Other materials, such as wood and steel, must be protected for the time period required by building codes. Since it costs money to protect structural members from fire this rrust be factored into the decision to use one material instead of another. Even though steel may be a less expensive structural material to use than concrete,it may bemoreexpensive to fireproofand in thelongrun cost more thana concrete-framed building. F.Construction Limitations The realities of construction often are a decisive factor in choosing a structural system. Some of these include construction time,material and labor availability, and equipment availability. Constructiontimeisalmostalwaysa factorduetofluctuationsinmaterialcoststypicalinthe Philippines. However, other things influence the need to shorten the construction period as much as possible. The cost of financing requires that the term of construction loans be as short as feasible. This may dictate the use of large, prefabricated structural elements instead of slow, labor-intensive systems such as unit masonry.Another factor can be climate and weather.In locations with short construction seasons,buildings need to be erected as fast as possible. Materialandlaborarethetwoprimaryvariablesinallconstructioncost.Sometimesbothare expensive, but usually one dominates the other. In the Philippines as in many developing countries, labor is extremely cheap while most modern materials are expensive or even unattainable. Related to the cost of labor are theskills of the work force.A sophisticated structural system may require a technically skilled workforce that is not available in a remote region. The cost to transport and house the needed workers could very well make such a system unfeasible. Finally,equipmentneededtoassemblea structuralsystemmaybeunavailableor prohibitively expensive. Thelack ofheavy cranesnear thejob location, for example couldsuggest thatlarge, prefabricated components not be used. G.Style Some structural systems are more appropriate as an expression of a particular style than others. One of the most obvious examples is the International Style, which could only be achieved with a steel post-andbeam system.Even when fireproofing requirementsmight have implied a concretestructure, steel was used. 55 The architect and client usually determine what style the building will be and then require thatany structuralsolutionadapt tothatneed.Insomeinstances,thestructuralengine_ermaydevise a struCtural solution that becomes the style itself. Once again, there should be a balance between what styte may be desired and what is practical and reasonable from a structural point of view. H.Social and Cultural Influences Relatedtothestyle ofa buildingare thesocialandculturalinfluences on thearchitectureof a geographical location and particular time period. The architect must be sensitive to these influences. For example, in a historic area where most buildings are constructed of brick, a masonsy bearing wall structuralsystemcertainlyshouldbeconsidered.Inanewlydevelopingindustrialpark,more contemporary and daring structural systems might be appropriate. 56 .....~.... LOADSONBUILDINGS LOADS ONBUILDINGS Nomenclature A D L p r R v area of floor or roof dead load live load direct wind pressure rate of reduction of liveloads allowable reduction ofliveload wind velocity M2 Pa Pa Pa kph Determining theloads actingon buildings isbasic to structuralanalysisand design.Anaccurate determination of loads is necessary to design a safe building and satisfy building code requirements while not requiring a more costly structure than necessary. The probable magnitudes building loads have been determined over a long period of time based on successful experience and the statistical probability that a particular situation will result in a given load. They are also based on the worst case situation. For example, the common liveload for residences of 2000Pa in a house, but provides an allowance for safety andunusual circumstances. Typically, loads are defined by building codes and by common practice. Codes, tor example, give live load requirements, wind values, and earthquake values. Standard published tables provide accepted weights of building materials for dead load calculations. Occasionally, special situations may require custom load determination such as when building models are tested in a wind tunnel. Most loads on buildings are static, and those that are dynamic, such as wind, are assumed to have a static effect on the building structure so calculations are easier. There are many types ~ floads on buildings. This chapter provides an overview of what thedifferent typesare,howtheyaredeterminedand theireffectsonbuildingsandarchitecturaldesign. More detailedinformation concerningbuildingcoderequirementsisgivenin Chapter 9, whilespeciiic calculation procedures for lateral loads due to wind and earthquake are described in Chapters 14 and 15, respectively. 1. GRAVITY LOADS A.DeadLoads Dead loads are the vertical loads due to the weight of the building and any permanent structural and nonstructural components of a building. Theseinclude such things as beams, exterior andinterior walls, floors, and fixed service equipment. Dead loads of structural elements cannot always be readily determined because the weight depends onthesize,whichin turndepends on the weight to be supported. Initially, the weight of the structure must be assumed to make a preliminary calculation of the size of the structural member. Then the actual weight can be used for checking the calculation. Most deadloadsare easily calculated from publishedlists of weights of building materials found in standardreferencesources. Somec ~ m m o nweights are giveninTable3.1Inadditiontothis, the UniformBuildingCoderequiresthatfloorsinofficebuildingsandother buildingswherepartition locations are subject to change be designed to support an extra 1000 Pa ofdeadload. 58 TABLE3.1 WEIGHTS OF ASSEMBLED ELEMENTS OF CONTRUCTION Member or Element Wood Floor (20 mm) and wood joists Concrete Slab, per em thick Steel Decking Floor finishes Finish, 2-3 em {aver.) t ile &mortar, 3 ems.(aver.) Cement tile & mortar,4 ems Asphalt or Vinylon cement mortar base {min) Parquet floor oncement mortar base Granolithic or terrazo., casHn-place or terrazo tiles on mortar base 20 mmwood floor on sleepers wl cone.filler Partitions 6 mm plywood double wall on 50 x 100 studs 20 mm wood panels, double on SOx 100 studs Glass blocks,100 mm thick Brick,100 mm thick Brick,150 mm thick Brick, 200 mm thick Curtain wall. aluminum & glass, (aver.) Concrete Hollow Blocks {1/2 of cells filled) 100 mm, CHB, no plaster 100 mm, CHB, plastered one face 100 mm, CHB, plastered both faces 150 mm, CHB, no plast er 150 mm, CHB, plastered one face 150 mm, CHB, plastered both faces 200 mm, CHB, no plaster 200 mm, CHB, plastered one face 20 mm, CHB, pl asteredboth faces Ceilings,including joists and furrings 6 mm plywood 20 mm wood boards 12 mm insulation or acoustical boards Metal lath and plaster 4.5 mm asbestos cement sheets 6 mm asbestos cement sheets Root Covering (Excludes purlins and/or rafters) Galvanized Corrugated (includes laps & fastenings) 22 U.S. Std gage 24U.S. Std gage 26 U.S. Std gage Plain G. I. WI battens (includes sheathing boards) 22 U.S. Std gage 24 U.S. Std gage 26 U.S. Std gage Corrugated asbestos cement (includeslaps and fastenings} 3.75 mm thick 4.50 mm thick 6.00 mm thick Clay roofing tiles withsheathing, membrane waterproofingand fastenings, no mortar Metal roof tiles withsheathing, membrane water proofingand fastenings Asphalt shingles Built-up Roofing, 5 ply 59 Weight i Pa 526.90 239.50 143.70 718.50 718.50 958.00 574.80 622.70 1437.00 1676.50 1437.00 335.30 431. 10 862,20 1916.00 2874.00 3832.00 718.50 1532.80 1820.20 2107.60 2155.50 2442.90 2730.30 2730.30 3017.70 3305.10 239.50 383.20 31 1.35 862.20 335.30 383.20 114.96 95.80 76.64 335.30 325.72 316.14 153.28 182.02 239.50 1005.90 479.00 95.80 287.40 Example3.1 Find the uniform load on a typical interior beam supporting the floor shown in the diagram.Do not include the weight of the beam. 1 - - - - - - - - - - - ~ : ~.."-- . - - -- --l QUARRYTILE 2 .40 .. ~ O O N M soMN 2. BEAN i ACOUSTICALCEILING - ------__ _j PLAN SECTION From Table 3.1 determine the weight per square meter foot of the materials comprising the floor. Since the concrete is on fluted steel deck, take the average thickness of 125 mm. The total weight is therefore: cement tile and mortar concrete (239.50 Pax 125 mm x 1 mm/1 0 em) steel deck 6 mm plywood ceiling Total 958.00Pa 2993.75Pa 143.70Pa 239.50Pa 4334.95Pa The beam supports a portion of the floor half the distance of the beam spacing on either side of it, or 2.40meters.2.4 times 4334.95 is10403.88N/m. In practice, numbers such as 71.8 are rounded to the nearest whole number, so the weight in this case would be 72 pst and the load would be 576 plf. B.Live Loads live loads are those imposed on the building by its particular use and occupancy, and are generally considered movable or temporary such as people, furniture, movable equipmern, and snow. It does not include wind loading or earthquake loading. Live loads are established by building codes for different occupancies.Table 3.2gives the uniform live floor loads from the national structural code of the Philippines and Table 3.3.minimum roof live loads.Therequirementsforspecialconditionsascranes,elevators,andfiresprinkler structural support,among others. The code also requires that floors be designed to support concentrated loads if the specified load on an otherwise unloaded floor would produce stresses greater than those caused by the uniform load. The concentratedloadisassumedtobe located onanyspace750mmx750mmsquare. The concentrated load requirements are giveri in the last column in Table 3.2. 60 TABLE 3.2 UNIFORM AND CONCENTRATED LOADS Use of Occupancy CategoryDescription 1.Armories Fixed seating areas 2.Assembly areas andMovable seatingand other areas auditorium andStage areasand balconies therewi1h"enclosed platforms 3.Cornices, marquees and residential balconies 4.Exit facilities s 5.Garages General storage and/or repair Private pleasure car storage 6.Hospitals Wards and rooms 7.librariesReading rooms Stack rooms 8.ManufacturingLight Heavy 9.Offices 10.Prir.ting PlantsPress rooms Composing and linotype rooms 11.Residential6 12.Rest rooms 7 13.Reviewingstands, grandstands and bleachers 14.Roo1deckSame as area served or for the type of occupancy accommodated 15.SchoolsClassrooms 16.Sidewalks and drivewaysPublic access 17.StorageLight Heavv 18.StoresRetail 19.low cost housing unit111 See Section 3.1.4 for live load reductions. 2 See Section 3.1.2.3, first paragraph, for area of load application 3 See Section 3.1.2.3,second paragraph, for concentrated loads. UniformConcern-load1trated load PaN 72000 24000 48000 60000 3000 oe 48000 4800 :\ 2400 3 200045002 3000 450()2 600067002 360089002 6000134002 240089002 7200112002 480089002 2000 06 48000 200045002 12000 3 6000 12000 360089002 .48001344002 1500 oe Assembly are include such occupancies as dance halls. drill moms, gymnasiums, playgrounds, plazas, terraces and similar occupancies which are generally accessible to the public. 5 Exit facilities shall include such uses as corridors serving an occupant load of 10 or more persons, exterior exit balconies, stairways, fire escapes and similar uses. 6 Residential occupancies include private dwelling, apartment and hotel guest rooms. 7 Restroomloads shall benot less than the load for theoccupancy with which they are associated, but not to &xceed 2400 Pa. 8 Individual stair treads shall be designed to support a 1300 N c:oncentraled k>adplaced in position which would cause maximum stress, stair stringers may be designated for the uniform load set forth in the table. eTotal floor area ofa unit shall not exceed 60 .m2 61 RoofSlope 1.Flat or rise less than 1 verlical to 3 horizontal; Arch or dome with rise less1/8 ofspan 2.Rise1 vertical per 3 horizontal to less than 1 horizontal; Arch or dome with rise1/8 of span to less than 3/8 of span 3Ris.e1 vertical to1 horizontal ; Arch or dome with rise 3/8 of span or greater600 Pa TABLE3.3 MINIMUM ROOF LIVE LOADS TRIBUTARY LOADED AREA FOR ANY STRUCTURAL MEMBER 0 to 20 sq.m.21to 60 sq.m.Over 60 sq.m. 1000Pa800 Pa600Pa 800Pa700 Pa600Pa 600Pa600Pa 4Awning, except 5 cloth covered250Pa250Pa250 Pa Green Houses, lathhouses I and agricultural buildings I There are two instances when the national structural Code allows the live load to be reduced: when a structural member supports more than 14 sq meters (except for floors in places of public assembly) and for live loads greater than 4800Pa. The allowable reduction from theload values shown in Table 3.2is given bythe formula: A = r (A- 14)3:1 The rate of reduction, r, is equal to 0.08 for floors, 0.08 for roofs ranging from flat to less than4 inches rise per foot , and 0.06 for roof slopes ranging from 4/12 to12/12. There are a few limitations, however. The reduction cannot exceed 40 percent for members receiving loadfromonelevelonly, or60percentforothermembers,norcanthereductionexceedthe percentage determined by the formula: R "'23.1(1+ 0/L) Where R=Reductionin percent r= Ra1e of reduction equal to 0.86 percent for floors A=Area of floor supported by member in sq.m. D= Dead load per square meter of area supported by the members 3:2 L=Unitlive load per square meter of area supported by themembers 62 Example 3.2 What live load should be used to design a structural member thatsupportsan area of 20 square meters of single-level office space, a live load of 2800 Pa and a dead load of 3400 Pa? Since the live load Is less than 4800 Pa and it is not a public assembly place, a reduction is permitted. First, determine the reduction and then check against the other two limitations and select theleast one. A=r (A -150) = 0.86 (20- 14) =6% =40% for membersreceivingload from one floor Check againstformula 2.2 R"'23.1 (1+ D/L) = 23. 1 (1+ 3400/2800) R= 51.15%--------- (3) Of the three values, 5.16% is the least, so thereducedliveload will be2800- (5.16/ 1 00)(2800)or 2655.52 Pa C.Combination Loads It is generally agreed that when calculating all the loads on a building, all of them probably will not act at once.TheNationalStructural Coderecognizes thisandrequires thatseveral combinationsof loadsbecalculatedtofindthemostcriticalone(floorliveloadshallnotbeincludedwhereits inclusion result s in lower stresses in the under investigation) These combination ofloads are as follows: dead plus floor live plus roof live dead plus floor live dead plus floor liveplus seismic (or wind} dead plus seismic (or wind) 2.LATERAL LOADS A.Wind Wind loading on buildings is a dynamic process. That is, the pressures. directions. and timing are constantly changing. For purposes of calculation, however, wind is considered a static force. There areseveral variables that affect wind loading. The first is the wind velocityitself. The pressure on a building variesasthe square of the velocity according tothe following formula: p = 0.0000473V2 The second variable is the height of the wind above the ground. Since wind acts as any fluid where a surface causes friction and slows the fluid, wind velocity is lower near the ground and increases with height. Wind speed values are taken at a standard height of 10 meters (33 feet) above the ground, soadjustmentsmustbe made when calcul atingpressureatdifferent elevations. 63 WINODIRECTION " " ,_,./

' / ........ / / / / FORCESONABUILDINGDUETOWINO Figure 3.1 A third variableis the nature of the building's surroundings. Other buildings, trees, and topography affect how the wind will finally strike the structure under consideration. Buildings in large,areas are subject to more wind force than those in protected areas. The type of surrounds is taken in account with multiplying factors found in the building codes. Finally, there are things like the size, shape, and surface texture of the building. Some buildings allow the wind to flow around them while otherschannel or focus the wind. A building subjected to wind forces responds in several ways. These a