COMNIIl'11E OF CALFORNIA

TECHNICAL INFORMATION & PRODUCT SERVICE

SEPTEMBER 1985

FIREPROOFING

OPEN-WEB JOISTS & GIRDERS

Due to the increased usage of open-web joists andtruss girders in the design of larger, taller buildings,their fireproofing requirement data is increasinglysought by the architect and engineer. This paperoutlines a few of the major points the designer shouldconsider when fireproofing of these members isrequired.

Use of a fire-rated ceiling will generally give aneconomical solution if the requirement is just for aprotective envelope.1 But since each penetration ofthe ceiling must take extra protection, such as firedampers, this Iow first-cost is often offset by theadded cost of the dampers.

Occupancy will influence the decision on whetherto use a fire-rated ceiling. For example, offices havemany penetrations for H.V.A.C., whereas residen-tial has relatively few requirements for ceilingpenetrations.

Spray-on fireproofing of open-web joists and trussgirders is done with the same crews and equipmentemployed in fireproofing wide flange structuralshapes. However, some variations in methods andtechniques must be used.

"LH" Series joists and "G" Series girders aregenerally made of angles with flat surfaces. Thefireproofing is sprayed on directly in the same man-ner as with structural steel beams. While it is gener-ally preferred that the joists or truss girders not bepainted when they are to be fireproofed, this is notas critical as for wide flange shapes since there areno large flat areas to create adhesion problems. Theindividual members are small, and as applied thefireproofing actually wraps the member and createsits own adherence. Generally it is the adherence ofthe paint to the steel that governs not the adherenceof the fireproofing to the paint, therefore, do notspecify paint where fireproofing is required.

For the minimum insulating material thickness re-quirement for a particular fire-resistive period (hour-rating) contact the fireproofing manufacturer2 or con-sult the latest issue of the U.L. Fire ResistanceDirectory.3 The thickness required for wide flangestructural shapes cannot be used in every case asa direct comparison to joists and truss girder con-struction. Consideration must be given as to whetherthe member is a primary or secondary structuralmember. Requirements for roofs are different thanfor floors.1,4

For members of equal vertical load carrying capac-ity, an open-web joist or truss girder will generallybe deeper than a wide flange structural shape.However, since the joist or truss girder has verylittle web surface there is a tendency to over-spray.The total effect is that the cost per square foot offloor area for spray-on fireproofing of joists andtruss girders will be approximately the same as withwide flange structural shapes.

Due to the thickness of the fireproofing there issome reduction in the available open space withinthe webs for utility ducts and pipes, and should betaken into consideration by the design engineer.

Another fireproofing option is intumescent mastic(swells or expands with heat). Required thick-nesses range up to 1/2". Generally, the greater costof this type fireproofing tends to limit its use.

References: Uniform Building Code (1982 Edition), Chapter 43, Fire-ResistantStandards, Table No. 43-C.

2 Most manufacturers have a research report or product evalua-tion for their fireproofing material on file with a City or the Interna-tional Conference of Building Officials, Whittier, California.

3 Underwriters Laboratories, Inc., 333 Pfingsten Rd., Northbrook,IL 60062

4 Designing Fire Protection for Steel Trusses, Second Edition, 1981,American Iron & Steel Institute, Washington, D.C.

STRUCTURAL STEEL EDUCATIONAL COUNCIL

TECHNICAL INFORMATION & PRODUCT SERVICE

JANUARY 1992'

STEEL DECK CONSTRUCTIONResum of Frequently Asked Questions on Formed Steel Floor and Roof Decksc 0 ` 0 ' 4 . o . Io . .

Figure I

, II I

I I

I [I I

Metal Cover PlateScrew Or TackWeld To Deck Units

fI

Square Cut Ends' T - - - -

I

..J Support Beam

warping required to achieve roof drainage. When highlydifferential warped surfaces are required, the lightergauge single sheet units are more adaptable than thedouble plated sections. The designer should investigatethe alignment of supports to be certain of the deck'sability to conform to differential elevations for multiplespans, otherwise the deck should be single span.

What's the proper way to frame a wedge-shapedbay?

It is usually desirable to let the deck ribs run as a tangentof thearc as this entails a minimum of-cutting--and,consequently, reduces waste and cost. When theflanges of the radial beams are wide enough to supportthe deck panels without bevel cutting, the panels areinstalled as a "stair-step" condition. The stair-step gapsare closed (capped) over with a flat plate on the top of thedecking surface to support insulation. See Fig. 1.

Should decking units be continuous over a ridge orvalley?Steel roof deck units have little bending resistance(dependent upon gauge) normal to the ribs, but greatstrength in the direction of the ribs. For changes in pitchparallel to the ribs, the deck units can be stepped downto conform to the change in pitch. When the sheets arerequired to span over a ridge or valley, the ability of theunit to conform is dependent upon its moment of inertia.Gradual changes in pitch can usually be accommo-dated using a man's weight to step it flat to the support.For abrupt changes, however, the sheet should bediscontinued at the ridge or valley and a 20 gauge or 18gauge flat cap sheet bent to the angle of the pitchfastened to the deck sheets. Its purpose is to provide

2 Steel Tips January 1992

diaphragm continuity and support for insulation androofing membranes. The designer should be certain toprovide structural support either at or close to ridge andvalley lines.

Should the structural member's supporting flangesurface be flat to the deck surface?It is not necessary for full surface bearing on the support-ing flange provided any wedge-shaped gap is small.Since the majority of steel deck is installed by welding,a gap less than 1/4" can be filled with weld metal toprovide a satisfactory installation. If there are heavyapplied loads or if the deck units are fastened by screws,the usual practice is to use a 14 gauge strip bent to anL-shaped profile and welded to the supporting beam.The slope of the strip after installation should provide abearing surface for the deck unit. The designer iscautioned that decking support members at a hip orridge condition should be reviewed to provide a smoothtransition and continuity at the supporting system for theadjoining decking sheets.

What kind of closures are available to close gapsb e t w e e n supports and deck units?Three types of closures are available: close cell neo-prene rubber, sheet metal and a combination metal andneoprene. Neoprene closures are oversize to fit eitherrib openings (top side) or void (underside) openings.Glue or friction fit ensures tight closing of the opening tostop light, heat and wind penetration. Notched sheetmetal closures are loose fitting and are used to stopsight view (as behind flashing) and as bird or large insect

F i g u r e 2

.(,

fL_/

1

Continuous Sheet Metal____ Closure and Fire Stop Support

J

/I III I Closure

PerpendicularoT ] I

Parallel To Deck Condition

stoppers For very large void or nb openings and undersevere pressure condlhons, combination metal/neo-prene rubber closures are recommended

Should I use closures m steel roof deck construc-tion?Use closures whenever an exposed deck overhangs anexterior wall with no soffit cover on the exterior, whensound control s necessary for interior partitions reach-mg the deck units, and over exterior exposed supportsto prevent bird roosting and to present a more finishedappearance

Are there special considerations for cantileveredroof deck units?Usual engmeenng calculations are sufficient The de-signer should be certain to show a heavy gauge angleor cap channel welded to the outboard end of a cantile-ver to tie adlacent deck sheets together for unity andsupport architectural facsas, dnp flashing, or gutters

Can steel deck panels be used as draft curtains?Yes, steel deck panels are often used to parhton largeareas for fire safety, building code and insurance ratingreasons They can be installed vertically on the face ofa truss or with a suspended vertical frame An importantdetail to incorporate into the design is the flashing at thetop to inexpensively separate and seal off adjacentareas Corrugated decks 1/2" to 1-5/16' deep are oftenused as draft curtains See Fig 2 (bottom of page 2)

Openings

How large a hole may be cut in steel roof deckwithout supplementary framing?Any hole which does not intersect a vertical web of thedeck may be cut. When holes intersect a deckingvertical web, some general rules will assmt the designerto make a decision, i e

I With 6" or 8" spaced nbs, one web may be cut2 With 12" or greater spaced ribs, avoid any web

removal3 The number of holes within any span of the deck

units should be limited to avoid cutting adjacent ribswithin the span

4 Holes In the high moment areas of the deck unitsmay be more restrictive than those located in theshear area

What kind of reinforcing is suggested for medium-sized opening?It Is preferred to use steel reinforcement angles, tubes,or plates which are applied from the top side It iscustomary to install reinforcement prior to cutting the

hole The reinforcing members should run at rightangles to the direction of the deck and be approximatelythree times the width of opening Designers are cau-honed to place the narrow dimension of the openingnormal to the deck ribs to minimize the structural impactto the deck. In all cases, the ablhty of the deck unitsadjacent to the hole to carry transferred loading shouldbe evaluated.

When are frames for holes required to be part of thestructural frame system?If an opening exceeds the width of the deck sheet or over24 inches (for long span 12" cover width sheets),supplementary framing should be attached to the struc-tural framing by struts or beams to create a framedopening Such openings are usually shown and dimen-sioned on the structural drawings.

Who pays for openings?Other than holes shown and dimensioned on the struc-tural drawings, the trade requinng the penetration isresponsible for approval, reinforcement and cutting Ifthe steel deck installer is still on the job, he can do thework on a mutually negohated fee basis

Diaphragms & Connections

How strong are steel deck diaphragms?Steel roof decks have a wide range of design values asdiaphragmsto resist honzontal loads Because of Codeapprovals, varying profiles, different fastener types andspacing, individual producers of steel roof decks shouldbe contacted for recommendations

Do lightweight concrete fills have diaphragm val-ues?Yes, the designer may secure the vanous code anddesign values for this type of construction by contactingthe steel deck manufacturer or the producers of hght-weight concrete

When are welding washers used?For corrugated decks hghter than 22 gauge, 14 gaugeweld washers are used when plug welding deck to thesupport

Is it necessary to touch up the welds on steel deckunits?Touch up by the deck erector is limited to top side of theunits only. However, if the deck is covered by concretefill, touch up of welds is not necessary as the concreteoffers adequate protection against corrosion Scorchmarks caused by welding attachments on the undersideof supports or deck unts should be touched up and

Steel Tips January 1992 3

painted by the painting subcontractor as part of thiswork Assignment of thru work by proper notation tn theproject speclhcatons s important

How are welds protected?

The top side of the weld is painted wth a rust inhibitivepaint Weld cleaning and etching Is not required Forgalvamzed surfaces, a zmc-rmh paint may be specified.Flux-type zinc repair compounds cannot be success-fully apphed to metal decks due to rapid dlsslpahon ofheat required for application

Roofing and Insulation

Do steel roof decks always require a built-up roof?

No, and by followmg a few general rules, many deckprofiles may be used exposed (without roofing)

1 Roof slopes at least 1" to 12"2 Fasten with gasketed screws at supports and shtch

the side joints with screws3 Overlap end iomts a minimum of 6"4 Use a full bed of caulking at sde and end joints5 Install deck units in a posihon to minimize

of side joint, i e, install deck with the side lap on thetop, not on the bottom of the flute

What is the correct thickness of insulation oversteel roof deck?

Aside from thermal requirements, the minimum thick-ness is based on the width of the nb opening related tothe density of the msulabon and Its shear capacity tobndge the openmg In general, a rule of thumb is 1" thickfor 0 to 1" openings, 1-1/2" for 2-1/2" openings Becausethe quahty of the waterproohng membrane s dependentupon proper support, roofing product manufacturersshould be consulted for their specffmatlons

Can lightweight concrete insulating fills be usedover steel roof deck?

Yes, but some confusion results from "hghtweght" ter-minology It Is necessary to differenhate between light-weight insulating concrete hll which ts approximately 30pcf density and hghtweight structural grade concrete of100 pcf or greater density Either type can be used

What are insulation mechanical fasteners?

Rigid insulabon is usually mechanically fastened tosteel deck by insulation chps There are many varietiesand methods of fastening these chps whmh penetratethe steel deck They are used to wmthstand wind uphftand Factory Mutual regulations These fasteners aresupphed and installed by the roohng contractor

4 Steel T/ps January 1992

What is the purpose of a vapor barrier?It prevents the absorption of moisture into insulationmaterials When moisture Is absorbed, the thermal Ufactor of the msulabon is adversely affected

What are effective vapor barriers?Steel decks with caulked side seams are somehmesused as a vapor barrier Other types of vapor barriersare asphalt impregnated paper or mcombusbble plasbcfilms above the deck units Mechamcal msulahon chps,if specified, should be consistent with the type of vaporbarrier suggested

Where are vapor barriers used most often?

Usually m cold chmates and on those facilities whoseoccupancy tends to generate moisture and humidity,such as swimming pools or laundnes, etc

Drainage

What is an adequate roof pitch for drainage?

For steel decking roofs, many designers prefer a minm-mum slope of 1/8" per foot when built up roof mem-branes are used For exposed steel roofs, 1" per foot isa usual minimum with 2" per foot preferred

What is an easy way to get roof pitch?

Shortening alternate columns s a good method on largeroofs to create sump areas, which can be connected tothe storm dram system

What are sump pans?

Standard sump pans are 14 gauge steel, approximately30" square, and of three general types flat, recessed flator recessed sloped Sump pans are flat or recessed flatfor Iow pitch roof surfaces and recessed sloped forsteeper pitch roofs Recessed pans prowde largerdrainage basins than do flat pans See Fig. 3 Sumppans are not used when concrete fill Is placed over thesteel deck m roof construchon

Who supplies the sump pans?

Sump pans are supphed and welded to the deck units bythe roof deck subcontractor The hole for the drain is cutin the plate by the plumbing contractor who also installsthe roof drain and connechons to the drainage system

What is the proper treatment of parapet conditions?

The designer can show either standard cant strips(minimum 20 gauge steel) or tapered steel cants whichvary the daagonal dimension to create a swale leading toa sump area For very wide tapered cant conditions, asloping shelf angle is used at the parapet and steeldecking of varying lengths is used to create a swale

Figure 3

F eld Cut

I I

Flat Sump Plate\ i I I /

Recessed Sump Pan -- Flat

----%--- /

Recessed Sump Pan -- Ptched

Figure 4 Wide Tapered CantSlolngSupportAngle

I / Pos,bo

LowPosrhon

Tapered Cant

spanning from the shelf angle to the metal deckingalready in place It is good pracbce to place scuppersthrough the parapet to reheve abnormal water heightsSee Fig 4

F L O O R DECK

General

What are the general types of floor deck panels?Steel floor deck panels fall into two general categonescellular and non-cellular Cellular panels are producedby spot welding a nbbed panel to a flat panel to createa void whtch ns usable as a raceway for in-floor power,hghtmg, electrJcal and communJcatJon dJstrJbutJon Non-cellular panels are simply fluted (ribbed) panels

Is concrete always used over floor deck?Concrete is usually used over steel floor deck In thiscapacJty, Jt fumJshes a smooth surface covering the

ribbed deck and the accessones It acts as part or all ofthe steel panel hreproohng and can be destgned to workcompositely to increase structural capacity without anincrease tn steel wetght There are structural uses offloor panels such as servtce catwalks, package convey-ors, shelving or temporary floormg where concrete ns notordinanly used

Is concrete over the steel deck units required to bestructural grade?Only tf compostte achon between the deck umts and theconcrete hll is required to provtde the design require-ments

Some temperature control mesh is required and theusual value Js 00083 times the area of concrete abovethe steel deck.

What causes concrete surface cracking?Concrete slabs that are poured on imperwous surfacessuch as steel deck or Vtsqueen can cause the topsurface to dry relatively quickly whde the lower portion ofthe slab remaJns wet The water bleeds to the top

Steel T/ps January 1992 5

surface and evaporates, causing cracks to open abovethe top surface of the rebars or mesh, whmh thenpropagate to the surface. Troweling closes the cracksonly at the surface and they tend to reopen m a matterof days.

How can surface cracking be prevented?A good way to reduce slab cracking Is to have a light fogwater spray applied to the slab during the finishingoperations. The concrete will have a sheen while it iswet. When this sheen starts to disappear, the fog sprayshould be applied to maintain the sheen Care should betaken not to get excess water on the slab Venting of thedeck may help to reduce cracking in the concrete.

How should the concrete be cured?There are several ways of curing the concrete Productsthat are sprayed on have ether a wax or a resin base.Ether one may impair the application of a sealant orhardener later It is recommended that the surface becovered with craft paper, Visqueen or polyethylene

Are additives to the concrete fill recommended?

No Corrosive salts should not be allowed as they canreact adversely with the steel deck units, especially withgalvanized decking

Framing

Is it necessary to put in additional support atcolumns or other areas of deck interruptions?Steel deck support angles are used If the nbs of thedeck units are left unsupported at the columns. SeeFig. 5. The project specifications should call for thesupport angles to be supplied by the structural steelsuppher. They can be installed by the metal deckerector. Voads mn the metal deck units may need to beclosed wth sheet metal or other closures to preventconcrete leakage.

Are cover plates or splice plates on structural steelmembers a problem?Any projection above the steel support sunace canimpose a hardship on the steel deck erector. If the topflange of the steel beam supporting the deck is notlevel, Jt may be difficult to achieve adequate bearing forthe steel deck units.

Are concrete closures necessary?

The designer should show a concrete closure wher-ever there is a concrete leak possible as at changes ofdlrecbon and ends of decking runs, at columns, duct orshaft openings, building perimeters, etc The closuredoes not have to match the profile of the deck. Whenshown on the drawing, a concrete slab edge form isprovided to retain the concrete slab at its approximateheight above the deck. Since concrete edge forms arenot intended to be screeds, they are not adjustable to

Figure 5

Deck {Direction "A" -

ColuOmmnlt at Exterior -] / ' % - Typ2" Max.

L2'x2`''x3/'6

NoteOmit Angles InDeck DIr "A" WhenM1 6" or in DeckDir "S" When M2 6"

- f ' r S e a m ,

Ii I / ; . I C o l u m n:- - '--V

- , _! /

I , . , .,-- Outhne of--_'"'_. _ ' _ . Deck Cutout

. . . . . . . !_ I I t

I* i t ' 1I On Top of Metal Deck

Angle t o - J - j IConnectTwo Full Deck --P'-

Iof FluteScutoutEach Side - I Om t Angles

= When DLmenslonC3 Between Edge of

Floor Support and Edge of Column

Q s Less than 6"

6 Steel T/ps January 1992

elevahon to meet the varying needs of the budding.The typical concrete edge form s a galvamzed sheetmetal angle, with a thickness to meet required needs

Openings

What is the proper treatment for holes ortions through a steel floor deck?

Large holes (over 24" wide) should be en-cased by structural frames connected to themare framing members Smaller holes arecreated by block-outs an the concrete (such asstyrofoam or wood forms) Either angles orrebar are used as headers in the slab, with thearea of the reinforcing equal to or greater thanthe area of the steel to be cut out. The headerbars should be installed on the dagonal at thecorner of the opening After the concrete hascured, the block-out can be removed and thesteel deck an the area of the hole removed witha cutting torch

Diaphragms and Connections

penetra-

Figure 6

Are there any precautions advised when using steeldecks in either roof or floor over open web steeljoists?Yes, at end laps of the deck for roof deck, the lap shouldbe over one angle See Fig. 6 If the deck is butted onroof decks, there should be a continuous plate added totransfer the shear from one angle to the other See Rg7 For decks wth structural concrete, the plate is notnecessary if the concrete does not have a joint over theJoist

/- typical support weld

//

I Open web steel joist

Suggested Detail at Deck Lapon Open Web Steel Joist

How effective are steel floor panels as ahorizontal diaphragm?Combined wath concrete the assemblies offergreat ngidity and strength without greatly add-ing to the diaphragm wetght. Values aredependent upon deck profile, weld patternsand spans In concept, the steel deck can actas the shear transfer device between the con-crete fill and the perimeter (shear collector)framing member Shearconnectorsordowelscan also be used for shear transfer

How are steel floor units attached?By welding through the deck umts (arc-spotweld) to the steel supports Side laps arebutton punched, welded or screwed to meet eitherstructural requirements or the specification of Under-writers Laboratories

How are diaphragm values of steel floor or roofdecks determined?Values are based on full-scale tests and on formulasdeveloped in the Se/stoic Design for Buildings (TnService Manual, Army TM 5-809-10) Each quahfieddeck manufacturer has on file with ICBO or vartouscities an Evaluation Report for approved welding pat-terns and decking profiles

Figure 7 typical support weld

IAdd mm 1/8' P. con t

Detail at Deck Butt Joint

See Fig. 8 (top of next page), which dlustrates a potentialproblem when an open web joist IS poslboned close toa wall The joist has camber and unlessthe ledger angleis placed with the same camber, it is difficult to bend thedeck down to the ledger angle The solution is to eitherpoSlbOn the joist far enough from the wall to allow thedeck to bend, or to camber the ledger angle the same asthe joist

Electrification

In in-floor wiring systems using cellular panels,how are the systems carried normal to the deckrun?Through the use of cross ducts above the top of the

Steel T/ps January 1992 7

Figure 8

._1

...I

Joist too close to wall to allow deck to bend

--i'I

Detail to Avoid

!

..Q

EO

cellular unats Cross ducts are of two types, header ductand trench header. See Fig. 9

Figure 9

J;' i : ' :'' ',:1' Te'e0hnelPwer F,,'. . ;'..

Steel Deck

, ,,.

s tTrench Header

l-v .. .., ,.,,o. '.,i ......

o , < 3 .

Steel Deck '

) o

i t m'

Header Duct

potenhal common problem areas are resolved prior tobid time

Is header duct still used?Originally the only method to dlstnbute wire, it stdl hashmated use For example, header duct does not dasturbeither the daphragm action of the assembly or thevertical load capacity of the composite deck In addition,it is often used as a jack header to carry dlstnbution tocells interrupted by columns, openings and changes mdeck layout direction

Composite Construction

What consideration should I give trench headers?Since trench headers interrupt vertical composite de-signed loading, the deck unts must carry the total deadand live loads non-compositely Moment analysas at themost critical area of the trench dact will determine thestructural requirements of the deck units Trench head-ers should occur in areas of Iow diaphragm values orthedeck reinforced to carry the diaphragm without con-crete It is desirable to locate the trench duct outside ofthe effective beam flange area in composite beamconstrucbon. If this is not possible, design the beams asslab one side or non-composately Also rewewthe effectof the trench headers crossing the girder d that memberis designed on a composite basis, as wide trenchheaders can ehmmate both studs and concrete Closecoordinahon is required between the structural designerand the electrical designer so that rewew and solution of

8 Steel T/ps January 1992

Can steel deck units be used with composite beamconstruction?Yes, stud welding is a relahvely simple process whichprowdes high quahty welded connecbons The headedshear connectors may be apphed to the beam flangedirectly through the steel decking sheets Arc spot weldsmay be eliminated where they coincide wrth shear studplacement

Are all steel floor panels composite construction?Since the introduction of composite type floor construc-tion 25 to 30 years ago, nearly all floor assembhes nowtake advantage of the economies gamed by reduction ofweight of the steel, be t the frame or the deck panel Incomposite construcbon, steel floor panels hrst act tosupport wet concrete and temporary construchon loads,and upon curing of the slab act as the poshve steelreinforcement of the concrete slab by bonding to the

concrete Embossed ridges (in a variety of patternsdependent upon the producer) assist the bonding func-tion Steel studs complete the composite action byassisting the floor slab and steel beam to act as a singlecomposite unit

Can I use composite steel floor decks in everyapplication?Basically the answer Is yes, but some cautEons arenecessary Since a composite steel floor slab is essen-tially a one-way reinforced slab, it ts designed for officebuilding type installations When subjected to movingloads such as fork lift trucks In Industrial applications orheavy concentrated loads, special considerations suchas posdve or negative moment reinforcement are oftenrequired. It is recommended that a deck manufacturerbe consulted for special applications

How are section properties of a composite floordeck developed?Producers of composite floor decking material publishdata based upon full-scale tests Designers shouldreview individual manufacturers' building code approv-als

What are the design specifications for compositebeam/steel deck construction?AISC recognizes this form of construction with designcriteria given in the AISC Manual of Steel Construct/on,9th Edition, using ether ASD or LRFD In addition, theInternational Conference of Building Officials (ICBO)issues Evaluahon Reports listing approved use anddesign load values for individual stud manufacturers

Is there a maximum thickness of metal decking forthrough-deck stud welding?The maximum deck thickness is 16 gauge with lightcommercial (6 oz) galvamzed coating For doubleplated decks, I e, cellular panels, 18/18 is the maxi-mum

What are the usual size studs permitted for through-deck welding?The usual size is either 5/8" diameter or the widely used3/4" diameter. Studs larger than 3/4" are not presentlyapproved under AISC specifications Standard studsizes are stocked and should be specified wheneverpractical. Lead times are excessive for special lengthsand alloys on headed products

Does the design specify extra stud length to ac-count for burnoff?Studs from 1/4" through 1/2" diameter lose 1/8" in lengthduring the welding process, 5/8" through 7/8" diameterslose 3/16" However, when welding 3/4" inch shearconnectors through metal deck, 3/8" to 1/2" is burnedoff. Most manufacturers offer (stock) studs that accom-modate commonly specified after-weld lengths

When studs are used in through-deck welding, whatare the requirements for the top flange of the sup-porting steel beam?The top flange of the beam should be free of deleteriousmatenal which includes paint, rust and debris However,small amounts of mill scale and rust can be toleratedprovided the metal deck fits tightly to the steel beamsurface. Mimimum flange width of 4-1/2" is suggestedfor a single row of studs. For two rows of studs, theminimum flange width suggested is 5-1/2" Flange thick-ness should always be at least 1/3 of the stud diameterto ensure complete development of fastener strength

Who installs shear connectors in through-deck ap-plications?The shear connector studs act as a structural weldbetween the metal deck and the steel beam and areinstalled by the metal deck installer. The shear connec-tors cannot be placed in the shop because of field safetyregulations.

How is the soundness of arc spot welds (puddlewelds) determined?By assessing the ability of the welder to make an arc-spot weld as specified in AWS D1 3 Specification forWelding Sheet Steel /n Structures and by visual inspec-tion.

How are shear studs inspected in the field?Inspection, testing and operator qualification are out-lined in the Structural Welding Code, ANSI/AWS D1 1and the budding code governing the project.

CODE REQUIREMENTS

General

What agencies approve steel floor deck?Local, regional and state code authorities issue evalua-tion reports including seismic shear allowable and ver-tical load limits for each manufacturer's product. Inaddition, national codes and review bodies such asUnderwriters Laboratories (UL) conduct electrical andfire tested assemblies evaluations

What label service does Underwriters Laboratoriesoffer?UL authorizes the use of labels on products for fireresistance and for use as electrical raceways. They alsomaintain a follow-up service

Are steel floor units fire safe?Yes, steel floor decks are part of fire-resistant assem-blies Contact the deck manufacturer and review theFire ResJstance Directory handbook of UnderwritersLaboratories, Inc., for one of many assembhes bestsuited to your needs

Steel T/ps January 1992 9

STEEL COMMITTEE OF CALIFORNIA

T E C H N I C A L I N F O R M A T I O N & P R O D U C T S E R V I C E

JANUARY 1987

COMPOSITE BEAM DESIGN WITH METAL DECK

INTRODUCTION

The American Institute of Steel Construction(AISC) Specification has long recognized the use ofcomposite construction. In the Third Edition of theManual, 1936, steel beams were entirely encased inconcrete for composite development. The 1963AISC Specification contained provisions for both en-cased beams and beams with only a concrete slab onthe top flange. The entire horizontal shear betweenthe slab and steel beam was assumed to be trans-ferred by shear connectors welded to the top flangeof the beam.

The composite design provisions of the 1969AISC Specifications contained provisions forcomplete and incomplete (or partial) compositedevelopment. The 1978 AISC Specification wasexpanded to include design provisions for compositeconstruction with formed metal deck. Since moststeel framed buildings use metal decking as part ofthe floor system, it was only natural that thespecification recognize this type of construction.

This paper will present typical composite designexamples using metal deck. Both partial andcomplete development will be considered. It is well-known that composite design can reduce the size ofthe supporting steel beam and/or keep deflectionswithin acceptable limits. Realistic savings can oftenbe made with the use of partial composite action.

AISC Specification

Section 1.11.5. Composite Beams or Girders withFormed Steel Deck

Composite construction of concrete slabs onformed steel deck connected to steel beams orgirders shall be designed by the applicable portionsof Sects. 1.11.1 through 1.11.4, with the followingmodifications.

1.11.5.1 General

.

.

Section 1.11.5 is applicable to decks withnominal rib height not greater than 3 inches.

The average width of concrete rib or haunch,wr, shall not be less than 2 inches, but shallnot be taken in calculations as more than theminimum clearwidth near the top of the steeldeck. See Sect. 1.11.5.3, subparagraphs 2and 3, for additional provisions.

. The concrete slab shall be connected to thesteel beam or girder with welded stud shearconnectors 3/4-inch or less in diameter(AWS D1.1-77, Section 4, Part F). Studsmay be welded through the deck or directlyto the steel member.

. Stud shear connectors shall extend not less than I 1/2 inches above the top of the steeldeck after installation.

Sections 1.11.5 and 1.11.5.1 of the AISCSpecification pertaining to composite design withmetal deck have been included for a quick reference.The deck ribs can be oriented perpendicular orparallel to the steel beam or girder. Design rules forthe deck orientation are summarized in Table 1 (seepage 2, top).

,

6.

Total slab thickness, including ribs, shall beused in determining the effective width ofconcrete flange. ,

The slab thickness above the steel deck shallnot be less than 2 inches.

TABLE 1

AISC RULES - FORMED METAL DECK

ITEM RIBS PERPENDICULAR RIBS PARALLEL

1. Concrete Area BelowTop of Deck

2. Stud Reduction Factor

3 Maximum Stud Spacing

4 Deck Welding

5 Minimum Width of Rb

NEGLECT INCLUDE

0 85 Wr Hs Wr

(Nr)l/2 ( - r ) ( - r -1) 06 (-r-r)(rS-1)

32 in NOT SPECIFIED

16 m NOT SPECIFIED

2 m. DEPENDS ON Nr

Typical Design Problems

Example 1. Design a composite interior floor beam(no cover plate) for an office building See beam A inFigure 1.

40' BA IA_ 30'

B

Figure 1

Given: Span length, L = 30 ft.Beam Spacing, s = 10 ft.Slab thickness, t = 5.5 m.Concrete: f'c -- 3 0 ksiConcrete Weight = 145 pcf (n = 9)Steel: Fy = 50 ksi3 inch rfietal deck, ribs perpendicularto beamNo shoring permitted

Loads: Concrete slab including reinforcingsteel and metal deck . . . . . . . . 54 Ibs/ft2Mechanical ...................... 4 "Ceiling ....................... 6 "Partition ........................ 2 0 "Live ............................... 1 0 0 "

Page 2 Steel Tips January 1987

Solution.

1. Bending Moments:

a Construction loads:f

Slab = 054 kEps/ft2Steelbeam(assumed) = 003 "

Total = 057 "

MD-- 2/w____(.057x10x30) (30x12) =770k]pm8 8

b Loads applied after concrete has hardened.

wL2 (.13x10x30)(30x12)ML = 8 - 8 =175Skip-in

(Due to possible actual loading, no reducbon in hveloads were considered for these beams )

c. Mmax = MD + ML= 770 + 1755 = 2525 kip-in.

2 Maximum shear.

V = 10( 057 + .13) (30/2) = 28 1 kips

3. Effective width of concrete slab (AISC, para. 1 11 1)

b = L/4 = (30 x 12)/4 = 90 inches

b = s = 10 x 12 = 120 inches

b = 16t + bf = (16 x 5 5) + 6 0 in (assumed) = 94 in.

The 90 inch width governs.

4. Required section moduti:

5

For MD + ML, Str= 2525 = 76 5 in 333

For MD, Ss - 770 _233m333

From the "Composite Beam Selection Table"1for plain slabs:

Select W18x35, Str = 97 3 m 3 > 76 5 m 3(required) o k

AWl 6x31 beam satisfies the required sectionmodulus but does not meet the desired depthto span ratio of Fy/800. (See Commentary -Sect 1.13.1)

Sectton properties of W18x35Ss = 57 6 in 2 A sTM 10 3 n.2 tf = 425 m.Is=510m.4 d=177m, tw= 30m.

6. Calculate composite design sechon properties:

a. Moment of InertIa.

Ac= b(tc) = 90 x 2 5 = 225 in 2A'c = Ac/n = 225/9 = 25 0 m. 2Ys = d/2 = 17 7/2 = 8 85 nYc = d + hr + tc/2 = 17 7 + 3 0 + 2 5/2=21 95 in

bb .!

F '1

c

Figure 2

Flguro 3

1AISC Manual 8th Edit{on, page 2-109

Section A Y AYW18x35 10 3 8 85 91.2Concrete 25 0 21 95 548 8

353 18.13 6400

b

Yb =18.13in,ds=18 13 -8 85 =9 28mdc=21 95- 18.13 =3 82in.Io (For transformed concrete slab) = bh3/12n

Io = (90) (2 5)3/(12)(9) = 130 m.4Io [for steel beam) = 510 in '+

Itr = T Ad2 + T. Io

Sectton AW18x35 10 3Concrete 25 0

Itr = 1775 m.4

Section Moduh'

1775Str - 18 13

d Ad2 Io928 8870 5103 82 364 8 13

1251.8 + 523 = 17748

- 97 9 In.3

St = 1775 = 350 in.3(3 82 + 1 25)

7 Check concrete stress'

1755 0 557 ksl < 1 35 ksi o kfc = (350)(9) -

8. Check steel stress:

Total load Str = 97 9 in 3 > 76 5 In.3 o k

Dead Load Ss --576m3>233m.3 ok

28 1 = 5 29 ksz < 20 ks o kWeb shear, fy - (17 7) (0 30)

9. Check deflectEons

5wL4 ML2 -- - -

384EI 1920 I

(770) (30)2 = 0 71 m < 1 00 in o k.AD- (1920)(510)

(1755)(30)2 = 0 464 in. < 3'0 o.k 2AL= (1920)(1775)

10. Check to determine if shores are required:(AISC 1.11-2)

Str max ( 1.35 + 0.35 1 755

=_ 7--/ (57.6) =124 m.3

124 in.3> 979 in.3

No shores are required.

2Long term deflection due to creep is not consideredsignificant.

Steel Tips January 1987 Page 3

11. Calculate the number of shear connectorsrequired for full composite action.

Assume 3/4-nch diameter by 41/2 inch long studs.Maximum stud diameter unless located drectly overthe web s 2 5tI = 2.5 x 0 425 =1 06 m > 0 75 m o k

a Total horizontal shear:

Concrete Vh = 0 85f'c = .85 x 3 x - = 287 kips

(AISC 1.11-3)

Steel. =258k, ps

(AISC 1.11-4)Since the shear due to the steel area is less andgoverns, the number of studs will be based on 258 kips.

b. Calculate the stud reduction factor forthe deck nbsperpend,cular to the beam.

Reduct'on Factor - 0 85 (W-r) r )(Nr) l/2 -1 _< 1.0

(AISC 1.11-8)

Assume. Nr = 1, Hs = 4.5 in., wr = 4 m.Given: hr= 3 m.

Reduction Factor = 0 -1) = 0 565(1)1/2 k3/k3

q = (11 5) (.565) = 6 5 kips per stud

N1 = Vh/q= 258/6 5 = 39.7

Use 80 - 3/4 in. diameter by 41/2 tach studs (40 oneach side of mid-span).

Example 2. Design a composite intenor grder (nocover plate) for an office building. See gmrder B inFigure 1. The 3-inch deck nbs are onented parallel tothe girder. Grder is assumed loaded as shown inRgure 4.

[

P P P

4 e 10 = 40'

w,/ft./

Ftguro 4

Loads: Concrete slab including reinforcingsteel and metal deck .. . . . 54 Ibs/ft2Mechanical 4 "Ceiling 6 "Partition- 2 0 "IJve-- 100"

td

d,

Yb

b/nI_

-- m m

t Y s F'"'

.I

Figure 5 ,

Soluhon:

1. Bending Moments.

a. Construction loads.

Slab = .054 kps/ft2Steel beam (assumed) -- 0 0 3 "

Total = . 0 5 7 "

Assume steel girder weighs 100 lbs/ft = .1 kap/ft.(Approx. 3 Ibs./ft2)

PD = 0.057 kips/ft2 (10) (30) = 17 1 kps

wL2 PL _-1(40)2(12) (17 1)(40)(12)MD- 8 + 8 + 2

MD = 240 + 4104 = 4344 kip-in.

b. Loads applied afterconstruction:

Reduce live load for large area supported by girder.Total dead load = 57 + 3 = 60

Given:

Page4

Span length, L = 40 ft.Beam spacing, s = 30 ft.Slab thickness, t = 5.5 m.Concrete: f'c = 3.0 ksiConcrete weight = 145 pcf (n = 9)Steel: Fy = 50 ksi3 inch rfietal deck, ribs are parallel to girderNo shoring permitted

Steel T/ps January 1987

R = 23.1 (1 + D/L) = 23 1 (1 + 60/130) = 34%(UBC-1985)Live load reduction factor = 34%

P = 0.13 x 10 x 30 x 0.66 = 25.7 kips.

ML = PL = 25.7x40x12 =6168kip-in.2 2

c. Mmax= MD + ML=4344+6168 = 10512 kp-m.

2. Maximum Shear.

V = [(.13 x 66) + (.057 + .003)]30 x 40/2 = 87 5 kips

3. Effecbvewdth of concrete slab' (AISC, para. 1.11.1)

b = L/4 = (40 x 12)/4 = 120 hnches

b = s = 30 x 12 = 360 inches

b = 16t + bf = (16 x 5.5) + 10.0 in. (assumed) = 98 in.

The 98 tach width governs.

4. Requ:red secbon moduli.

FOrMD+ML' Str _ 10,51233

- 319 m.3

FOrMD, Ss - 4344 =132in.333

5. From the "Composite Beam Selectton Table"3 forplain slabs:

Select W27x94, Str = 342 in.3 > 319 m.3 (Requtred)

Section properties of W27x94'

Ss =243in3 A=27.71n2 tf =.745m.Is = 3270 m.4 d = 26.92 m. tw = .490 in.

6 Calculate composate design section properties

a. Moment of Inertia

Ac = Concrete above deck (88x2 5) = 220 m 2Concrete tn deck area (3x44) = 132 m.2Concrete over girder (10x5 5) = 55 in,2

Total = 407 m.2

AC' = Ac/n = (98 x 2.5)/9 = 27.2 m.2.Ys = d/2 = 26 92/2 = 13.46 in.Yc =d + hr + tc/2 = 26.92 + 3.0 + 2.5/2 =31.17 in.

Section A Y AYW27x94 27 7 13.46 372 8Concrete 27 2 31.17 847.8

54.9 22.23 1220.6

3AISC MANUAL, 8th Edbon, page 2-108.

"--" 4 Deflection due to long term creep is not consideredsignhcant.

Yb=22 23 m.,ds = 22.23 - 13 46=8 77mc = 31.1 7 - 22.23 = 8.94 in,!o (For transformed concrete slab) = bh3/12n

Io = (98)(2.5)3/(12)(9) = 14.2 m.4Io (For steel beam) = 3270 m.4

Itr = [ Ad2 + T Io

Sechon A dW27x94 27.7 877Concrete 27.2 8.94

Itr = 7588 in. 4

Ad2 Io2130 32702174 144304 + 3284 = 7588

*NOTE. Only the area above the metal deck has beenused to calculate the transformed section propertiesA more refined method of using all of the concretearea is usually not warranted. Neglecting the concretein the nb area is slightly conservabve. For thzsexample, takmg all of the concrete into accountdecreased the deflection about 5% and the concretestress about 15%

b. Sechon Moduli

7588 - 341m3Str = 2223

7588St= (8 94+1.25) = 745m'3

7 Check concrete stress:

fc- 6 1 =092ksl

10 Check to determine f shores are required.(ALSO 111-2)

6168 (243) = 449 m.3Str max = 1.35 + 0 35 4344!

449 m.3 > 341 m.3 No shores are required

11. Calculate the numberof shear connectorsrequired for full composite action.

Assume 3/4 inch dameter by 41/2 inch long studs

a Total horizontal shear:,%. - 407Concrete. Vh = 0.85f'c -- = .85 x ; x -2- = 519 kps

(AISC 1.11-3)

Steel Vh = As __FY = 27.7 x -- = 693 kips2

(ALSO 1.11-4)

Since the shear due to the concrete area s less andgoverns, the number of studs wdl be based on519 kips.

b. Calculate the stud reducbon factor forthe decknbs oriented parallel to the girder.

Reduction Factor= 0 6 ( r/hrWr'- -1.0) < 1 0(AISC 1.11-9)

(wr) 9

(hr) 3- 3>1.5

Since this rabo s larger than 1.5 no reduction in studshearvalue is necessary. (wr was assumed 9 roches,the actual wdth will probably be closer to the flangewdth or 10 roches.)

Allowable Icad per stud = 11.5 kips.

NI= 519/11 5 = 45.1 Use 92 studs per girder, 46 oneach sde of mid-span.

c. Due to concentrated loads check stud spacing:

Mrnax = 6168 in.-kips at md- span

Moment at concentrated Icad 10 feet from support:

M = 3PLJ8 = (3 x 25.7 x 40 x 12)/8 = 4626 in. leps

Check for N2 (the number of studs required betweenthe concentrated Icad and the point of zero moment):(AISC 1 11-7)

N1 x -1)N2= 13 - I ; 13= Str/Ss =341/243=1 4

46[(4626 X 1 4/6168) -1] =5 75N2= I 4-1

Since 6 studs is less than the numberrequired for N1, formula 1.11-7 does not apply

of studs

Partial Composite Construction

Example 3 Design beam A, Example 1, using partialcomposite action.

Given. Same data as Example 1.

Soluhon: Steps 1 through 6 are the same as Example1. The maximum calculated shear due to dead and IweIcad is 28.1 kips Full composite acbon was based onthe steel area, and therefore the honzontal shear s258 Ips as determined by AISC formula 1 11-4

In order to dlustrate the reduchon in the number ofshear studs required, partal composite acbon wdl beconsidered 75%, 50%, and 25% development f ap-propnate. It should be noted that 25% s the minimumlevel permitted by AISC

a. 75% development

Serf = Ss + [V'h/Vh]l/2 (Str- Ss)

V'hNh = 0 75

Serf = 57.6 + [.7511/2(97.9 - 57.6) = 92 5 m.3

92.5 m. 3 > 76.5 m.3 o.k.

( AISC 1 11-1)

N =V'h/q = (.75 x 258)/6 5 = 29 8

Use 60 - 3/4 inch diameter by 41/2 tach long studs(30 on each side of md-span).

Check Deflection.

left = !s + [V'h/Vh]l/2(Itr - Is) (AISC 1 11-6)

left = 510 +[.75)1/2(1775-510) = 1606 m.4

'L = (1775/1606)(0 464) = 0 513 m.

0 5131n

b. 50% development:

V'h/Vh = 0.50

Serf = 57.6 + [.5011/2(97.9-57.6) = 86.1 in.3

86.1 in.3 > 76.5 in.3 o.k.

N = V'h/q = (.50 x 258)/6.5 = 19.8

Use 40 - 3/4 inch diameter by 41/2 inch long studs(20 on each side of mid-span).

Check Deflection:

left = 510 + [.5011/2(1775-510) = 1404 in.4

AL = (1775/1404)(0.464) = 0.587 in.

0.587 in. < L/360 = 1.00 in, o.k.

c. 25% development

V'h/Vh = 0.25

Serf = 57.6 + [.2511/2(97,9 -57.6) = 77.7 in.3

77.7 in. 3 76.5 in.3 o.k.

N = V'h/q = (.25 x 258)/6.5 = 9.9

Use 20 - 3/4 inch diameter by 41/2 inch long studs(10 on each side of mid-span).

Check Deflection:

left = 510 + [.25]1/2 (1775-510) = 1143 in.4

AL = (1775/1143)(0.464) = 0.721 in.

0.721 in. < L/360 = 1.00 in. o.k.

Example 4. Check girder B to determine if partialcomposite action would decrease the number ofshear studs.

Given: Same data as Example 2.

Solution: From AISC Formula 1.11-1 - (Assume Serf =required Sir); rearrange Formula 1.11-1 and solve forV'h.

Vh (Serf-Ss)2V'h=

(sir' Ss)2

519(319 -243)2V 'h = (341 -243)2 = 312 kips

V 'h 312

Vh 519- .60 or 60% development

N = (312)/(11.5) =' 27,1 or 28'studs on each side ofmid-span

Check Deflection:

left = 3270 + [.6011/2(7588 - 3270) = 6615 in.4

'L = .0639(7588/6615) = 0.733 in.

0,733 in < L/360 = 1.33 in. o.k.5

5Deflection due to long term creep is not consideredsignificant.

T A B L E 2

S U M M A R Y OF STUD REQUIREMENTS

Composite Construction

Beam ATotal StudsRequired

LL Def. in.

Full Vh100%

80

0.464

Partial Vh75% 60% 50% 25%

60 48 40 20

0.513 0.553 0.587 0.721

Girder BTotal StudsRequired

LL Def.in.

92

0.639

68 56

0.692 0.733

Will not developrequired shear transfer

SteelTips January 1987 Page 7

GENERAL DISCUSSION

Composite construcbon on medium to long spans canbe used to reduce construction costs Where appro-pnate the use of parbal composite acbon wdl generate ad-ditional savings As noted in Table 2, 40 to 60% of theshear studs mght be ehmmated when only the studs re-quired for the assumed loading condibons are consid-ered

Following are some general observations that shouldbe cons;tiered when using composite construction.

1 In most cases, composite construcbon should beconstdered for spans 25 feet and longer

2 It s more economical to use a rolled beam on shorterspans than a rolled beam with a cover plate Long spanbeams or girders fabricated from three plates may havethe bottom flange smaller than the top flange. Be surethe top flange is large enough to support all constructzonloads unbl the concrete has obtained its requiredstrength

3. The composite design tables in AISC for plato slabscan be used for preliminary estimates of required trans-formed sechon modulus when using metal deck.

4 For most condbons in steel framed bufidngs, onlythe concrete above the metal deck need be consJderedwhen determining the section properbes Ths assump-hon is slightly conservatwe However concrete belowthe top of the metal deck s to be included an calculatingthe concrete area for honzontal shear (AISC FormulaI 11-3)

5 References 2 and 3 point out addrt,onal refinementsthat can be made to gve a more accurate ndicaton ofthe deflections and stress levels

6 Composite beams should be designed as selfsupporting for most bufiding construcbon Except forunusual condJbons shonng should not be required as ftis too expensive The shonng may cost more than thesawngs generated by composite construction

On long spans, consideration must be given to theweight of additonal concrete' due to deflectEon of thegtrder when no shores are used Girders or beams onlong spans should be cambered to reduce the extraconcrete and dead load due to the members deflection

GENERAL NOMENCLATURE

Ac

Ac'

Actual area of effective concrete flange incomposite design (square inches)

Effecbve area of concrete diwded by modularrabo (in 2)

As Area of steel beam in composite design On 2)

MD Moment produced by dead load

ML Moment produced bylve load

Nr Number of stud shear connectors on a beam Enone nb of metal deck, not to exceed 3 ncalculations

E Modulus of eiasbcity of steel (29,000 kps persquare inch)

Fy Specified minimum yield stress of the type ofsteel being used (kips per square inch)

Hs

left

lo

Itr

Length of a stud shear connector after welding(inches)

Effective moment of inertia of composite secbonsfor deflection computations (inches4)

Moment of inertia of steel beam or concrete fill forits effectwe flange width (inches4)

Moment of inertia of transformed compositesection (in.4)

N1

N2

Number of shear connectors required betweenpoint of maximum moment and point of zeromoment

Number of shear connectors required betweenconcentrated load and point of zero moment

Serf Effectwe section modulus corresnding topartial composite action (inches')

Ss Section modulus of steel beam used incomposite design, referred to the bottom flange(inches3)

t Section modulus of transformed composrte crosssection, referred to the top of concrete (inches3)

Page 8 Steel Tips January 1987

G E N E R A L N O M E N C L A T U R E (cont/nued)

Str

Vh

V'h

b

bf

SectIon modulus of transformed compositecross section, referred to the bottom flange;based upon maximum permitted effecbve widthof concrete flange (inches3)

Total honzontal shear to be resisted byconnectors under full compos;te action (kips)

Total horizontal shear provided by theconnectors mn prowding parhal composIte action(kips)

Effectwe width of concrete flange

Flange wdth of rolled beam or plate girder(Inches)

fc Concrete compression working stress (kzps persquare inch)

f'c Specified compressive strength of concrete(kps per in.2)

fv Computed shear stress (kxps per square tach)

hr Nominal nb height for steel deck (roches)

n Modular ratio (BE c)

q Allowable horizontal shear to be resisted by ashear connector (kps)

tf Flange thtckness (inches)

tw 'V thfckness (inches)

wr Average wdth of nb or haunch of concrete slab onformed steel deck 0nches)

8 Rabo Str/Ss or Serf/Ss

A Displacement of the neutral axis of a loadedmember from ts posaton when the member snot loaded (inches)

REFERENCES

1 Manual of Steel Construction, EJghth EdJtlon, AISC,Chicago, 1980

2 Effectwe Width Criteria for Composite Beams -Vallemlla and Bjorhovde, AISC EngmeenngJournal, 4th Quarter, 1985, Vol. 22, No. 4.

3. Concrete Slab Stresses in Partml CompositeBeams and Grders - Lorenz and Stockwell, AISCEngmeenng Journal, 3rd Quarter, 1984, Vol 21,No 3.

4 Compomte Beams with Formed Steel Deck - Grant,Slutter and Fsher, AISC Engineenng Journal, 1 stQuarter, 1977, Vol 14, No. 1.

5 Comparative Tests on Composite Beams wrthFormed Metal Deck - Allan, Yen, Slutter, and Fisher,Fntz Engineering Laboratory Report No.200.76 456.1, Lehigh University, Bethlehem, Pa.,Dec. 1976.

7 Analyszs of Tests of Composite Steel andConcrete Beams with Mahon Steel Decking -Errera, Structural Engineenng Department,Cornell Umversty, Ithaca, New York, Dec 1967

8 Tests of Laghtweght Concrete Members wth MetalDecking - Slutter, Fritz Engmeenng LaboratoryReport No 200 68 458 1, LehJgh UnJversty,Bethlehem, Pa, March 1969

9

10

11

Composite Beam Incorporating Cellular SteelDecking - Robinson, Journal of the StructuralDwsson, Amencan Society of Ctvd Engineers, Vol95, No ST3, March 1969

Flexural Strength of Steel-Concrete ComposrteBeams - Slutter and Dnscoll, Journal of theStructural Division, American Society of CwdEngineers, Vol. 91, No ST2, April 1965.

Design of Composite Beams with Formed MetalDeck - Fisher, AISC Engineering Journal, AmericanInsbtute of Steel Construcbon, Vol. 7, No 3, July1970.

6. Partal-lnteraction Design of Composite Beams -Johnson and May, The Structural Engineer, Vol.53, No 8, Aug 1975.

12 Tests of Composite Beams with Cellular Deck -Robinson, Journal of the Structural Dwsion,American Society of Clwl Engineers, Vol. 93, No.ST4, Aug. 1967.

Steel T/ps January 1987 Page 9

MARCH 1991

by Ron Vogel, Computers and Structures, Inc.

March, 1991

LRFD-COMPOSITE BEAM DESIGN

WITH METAL DECK

INTRODUCTION

This is the companion paper to the "STEEL TIPS" dated January 1987 entitled "CompositeBeam Design with Metal Deck". The original paper used allowable stress design (ASD). This"STEEL TIPS" utilizes the same three original examples but designed by the Load andResistance Factor Design (LRFD) Method. The purpose is to show the design procedure, theadvantages of the method, and the ease of using the AISC First Edition (LRFD) for design.

Three main areas have been revised from the ASD Approach:

1. Determination of effective slab width2. Shored and unshored construction requirements3. Lower bound moment of inertia may be utilized.

A number of papers have been written about these differences and the economies of the LRFDmethod. The reader is referred to the list of references included.

Table 1

S U M M A R Y OF AISC-LRFD SPECIFICATION SECTIONS I3 & I5

SECTION ITEM SUMMARY

I3.1 Effective Width, b = Beam Length/8 (L/8)on each side of beam = Beam Spacing/2 (s/2)(lesser of the 3 values) = Distance to Edge of Slab

I3.5a General hr < 3.0 in. (Height of Rib)Wr > 2. 0 in. (Width of Rib)ds < 3/4 in. (Welded Stud Diameter)Hs = hr + 1 1/2 in. (Minimum Stud Height)

= hr + 3 in. (Maximum Stud Height value for computations)tc > 2.0 in. (Minimum concrete above deck)

15.1 Material Hs > 4ds

I5.2 Horizontal = 0.85f'cAcShear Force = AsFy(lesser of the 3 values) -- Qn

I5.3 Strength of Stud Qn = 0.5 Asc (f'c Ec) (but not more than Asc Fu)= 0.5 Asc (f'c wc)3/4 (using E = wcl'5 fxc in above formula)

I5.6 Shear Connector = 6 ds LongitudinalPlacement and Spacing = 4 ds Transverse (See LRFD Manual Fig. C-I5.1, pg. 6-177)

AISC-LRFD

Table 2

RULES - F O R M E D M E T A L DECK

(Sections I3.5b and I3.5c)

ITEM RIBS PERPENDICULAR RIBS PARALLEL

1. Concrete Area Below Top of Deck NEGLECT INCLUDE

06wrl, 1} 1.02. Stud Reduction Factor (N0'85 [rrjWrl{SrS- 1}-< 1'0 ' [hrrJ [ h r - - 1224 kip--ft O.K

or from Table page 4-33 for Y2 = 3.5 and TFLOMn = 1230 kip-ft

c. Design for deflection

Initial deflection during construction

19PL3 (19)[(10)(30)(54 + 6)](480)3A=

384Eis (384)(29,000,000)(2100)

= 1.62 in.

Camber 1 1/2 inches.

Composite deflection using Lower Bound Itr (Ilb).

From Table on page 4-46 of LRFD Manual,

with Y2 = 3.5 D.L. = 90 psfPNA = TFL . Construction D.L. = 60 psfIlb = 4780 in4 L.L. = 60 psf

19PL3 (19)[(10)(30)(90 - 60 + 60)1(480)3ATL- 384EI- (384)(29,000,000)(4780)

= 1.07 inches or L/450

ALL= (60/90)(1.07)= 0.71 in. or L/673 O.K.

NOTE: The mooment of inertia using the gross areaequals 5510 in.

Page 8 Steel Tips March 1991

d. Shear Connectors

= AsFy For full composite action

= 1120 kips

( ' " ' 1 [ ]Reduction Factor = 0.6 [hr J[ 1 _< 1.0% /

= 0.6 -1 = 0.8

Use 0.8 for stud reduction factor.

Qn = (0.8)(21.1) = 16.9 kips (See Example 1)

1120No.- - - - - - - 67 StudsQn 16.9

67 Studs are required from Zero to Maximum Moment.

Total = 134 $uds,

Use equal spacing for full length.

e. Check Shear

Vu --- 1.5 (Pu) = 1.5 (61.2) = 92 kips Vn = (0.6 Fy) d tw = (0.9) (0.6) (50) (23.92) (.44)

= 284 kips > 92 kips Q.K.

NOTE: The original Steel Tips design, based upon ASD,used a W27X94 with 92 studs.

Partial Composite Action

Example 3

Design Beam in Example 1 for pfial composite action.

SOLUTION:

a. Determine required shear studs

Estimate number of shear studs for partial composite actionusing the following approximate equation

Mu - Mp ' ,QnNo. [Mn - *Mp ) Qn

Where Mu = Moment demand Mp = Steel Beam Capacity with ) = 0.85 Mn = Full Composite Beam Capacity

Mu = 297 kip-ft{Mp = Fy Z = (0.85) (36) (66.5)/12 = 170 kip-ft{Mn = 356 kip-ft

= AsFy = 371 kips

Qn = 21.1 kips

= [356-170) ,21.1) 0.47 (17.6)= 8.2

Try 9 studs on each 1/2 beam.

Total = 18 studs.

b. Check flexural strength

Qn = (9)(21.1) = 190 kips

From Eq. C-I3-4 in commentary of LRFD Manual

190a = 0.85f'cb- (.85)(3.0)(90)- 0.83 in.

Y2= Yc-a/2= 5.5-0.41 = 5.09

From Table on page 4-23 of the LRFD Manual

for W18X35Y2 = 5.0 - 5.09 in.

Qn = 187 - 190 kips ( PNA = BFL approx.)

) Mn = 296 kip-ft (approx. equal 297 kip-ft required) O.K.

Therefore, partial composite action with 18 total studs isadequate for the required moment.

Steel Tips March 1991 Page 9

c. Check deflection

For deflection computation use the lower bound value givenin the Table on page 4-49 of the LRFD Manual.

For W18x35PNA = BFL +Y2 = 5.0 +_

4Ilb = 1170 in.

A TOTAL = (1775/1170) 0.46 = 0.70 in.ADL = 0.16 in.ALL = 0.54 in. or L/667 O.K.

Obviously any number of studs from 9 (47%) to that for fullcomposite action may be used (per 1/2 Beam Span) with theassociated increase in moment capacity and decrease in de-flection.

Location of. a/2 . effec'ive concreteb

Y2{ m. t 1). . - ' - ' T I ' - - : t (pt s)

...[.. ( Y1(varies - Sgure below)

I I

Y1 = Distance from top of steel flange to any of the seventabulated PNA locations.

qn (@ point 5) + qn (@ point 7) qn (@ point 6) =

2

qn (@ point 7) = .25AsFy

Bo$/l{Top Flange

4equ spaces

I 1 ,, BFLPNA Flange Locations

Figure 10

DISCUSSION

With the use of the First Edition AISC-LRFD manual,composite beam design can be simplified, particularywith partial composite action. As in the past, AISChas tried to incorporate enough tables and charts tomake repetitive design computations easier. Deter-mining preliminary beam sizes, number of weldedstuds and composite beam deflections is now verystraight forward. With a minimum of assumptions (i.e.location to the compressive force, Y2) preliminarycomparative designs can be done in minutes with theuse of the tables.

The reader is encouraged to read the LRFD ManualPART 4 (Composite Design), PART 6 (Specificationsand Commentary), especially Section I on CompositeMembers, and the other references listed. The numberof articles dealing with LRFD composite membersdesign is growing as designers are becoming morefamiliar with the method and the AISC-LRFD manual.

Page 10 Steel Tips March 1991

NOMENCLATURE

AcA'cAsAsc

BFL

CD.L.E

EcFyFu

HsIIbIoItrLL.L.

MnMpMuNr

PPNAQ.

Area of concrete (in.2)Area of concrete modified by modular ratio (in.2)Area of steel (in.2)Area of welded stud (in.2)Bottom of flange locationCompressive force (kips)Dead load (psf)Modulus of elasticity of steel (29,000,00 psi)Modulus of elasticity of concrete (ksi)Minimum yield strength of steel (ksi)Minimum tensile strength of steel (ksi)Welded stud height (in.)Lower bound moment of inertia (in.4)Moment of inertia (in.Transformed moment of inertia (in.4)Span length (ft)Live load (psf)Nominal flexural strength 0dp-ft)Plastic bending moment (kip-fOFactored Moment (Required flexural strength) (kip-ft)Number of stud connectors in one rib at a beamintersection

Factored point load (kips)Plastic neutral axisWelded stud shear capacity (kips)

S.R.F.

TTFLVaVuY1Y2YcZa

b

ddsf'chrntc

tftwWc

Wr

wu

A

Stud reduction factorTensile force (kips)Top of flange locationShear capacity (kips)Shear demand (kips)Distance from top of beam flange (in.)Distance from top of beam to concrete flange force (in.)Total thickness of concrete fill and metal deck (in.)Plastic section modulus (in.3)Effective concrete flange thickness (in.)Effective concrete flange width (in.)Depth of steel beam (in.)Welded stud diameter (in.)Concrete compressive strength at 28 days. (ksi)Nominal rib height of metal deck (in.)Modular ratio (E/Ec)Thickness of concrete above metal deck (in.)Steel beam flange thickness (in.)Steel beam web thickness (in.)Unit weight of concrete (lbs./cu. ft)Average metal deck rib width (in.)Factored uniform load (kip/fODeflection (in.)Resistance factor

,

2.

3.

4.

5.

6.

7.

REFERENCES

"Manual of Steel Construction, "First Edition, AISC, Chicago, 1986.

STEEL TIPS, "Composite Beam Design with Metal Deck," Steel Committee of California, January 1987.

STEEL TIPS, "The Economies of LRFD in Composite Floor Beams," Steel Committee of California, May 1989.

Smith, J.C., "Structural Steel Design - LRFD Approach," John Wiley & Sons, Inc., N.Y., 1991.

Salmon, C. and Johnson, J., "Steel Structures," Third Edition, Harper & Row, N.Y., 1990.

McCormac, J., "Structural Steel Design - LRFD Method," Harper & Row, N.Y.,1989.

Vinnakota, S., et al., "Design of Partially or Fully Composite Beams, with Ribbed Metal Deck, Using LRFDSpecifications," AISC Engineering Journal, 2nd Quarter, 1988.

Steel Tips March 1991 Page 11

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 2

Seismic Behavior and Design of Composite Steel Plate Shear Walls By Abolhassan Astaneh-Asl This report presents information on cyclic behavior and seismic design of composite shear walls made of steel plate and reinforced concrete encasement walls connected to each other to act as a composite element. The cast-in-place composite shear walls have been used in a few structures in the United States and Japan. A hospital structure, where the composite shear walls are used is discussed and presented. Recently, the traditional and an innovative version of composite shear wall were studied and tested at the University of California at Berkeley by the author. The test results are summarized in this report. Using the available information, design guidelines for seismic design of composite shear walls made of steel plates connected to reinforced concrete walls were developed and are presented in this report. Finally, two configurations of composite shear walls that are believed to be efficient, economical and easy to fabricate are suggested at the end of the report. First Printing, May 2002 Figures by Abolhassan Astaneh-Asl unless otherwise indicated. COPYRIGHT 2002 by Abolhassan Astaneh-Asl. All rights reserved. _____________________________________________________________________________ Abolhassan Astaneh-Asl, Ph.D., P.E., Professor, 781 Davis Hall, University of California, Berkeley, CA 94720-1710, Campus Phone: (510) 642-4528, Home Office Phone and Fax: (925) 946-0903, E-mail: astaneh@ce.berkeley.edu, Web page: www.ce.berkeley.edu/~astaneh

Disclaimer: The information presented in this publication has been prepared in accordance with recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or relied upon for any specific application without competent professional examination and verification of its accuracy, suitability, and applicability by a licensed professional engineer, designer or architect. The publication of the material contained herein is not intended as a representation or warranty on the part of the Structural Steel Educational Council or of any other person named herein, that this information is suitable for any general or particular use or of freedom from infringement of any patent or patents. Anyone making use of this information assumes all liability arising from such use. Caution must be exercised when relying upon specifications and codes developed by others and incorporated by reference herein since such material may be modified or amended from time to time subsequent to the printing of this document. The Structural Steel Educational Council or the author bears no responsibility for such material other than to refer to it and incorporate it by reference at the time of the initial publication of this document.

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 3

ACKNOWLEDGMENTS The publication of this report was made possible in part by the support of the Structural Steel Educational Council (SSEC). The authors wish to thank all SSEC members for their valuable input and support. Particularly, special thanks are due to Brett Manning and James Putkey for their review comments.

The test summarized in Chapter 3 was part of a research project on Seismic Studies of

Innovative and Traditional Composite Shear Walls funded by the National Science Foundation, Directorate of Engineering, Civil and Mechanical Systems. The support and input received from Program Directors Dr. S. C. Liu and Dr. P. Chang at NSF were very valuable and greatly appreciated. Graduate student Qiuhong Zhao was the lead graduate student in conducting these tests. The efforts of Judy Liu, formerly graduate student at UC-Berkeley in developing and designing test set-up were very valuable and are sincerely appreciated. Ricky Hwa, undergraduate student research assistant participated in preparing specimens, instrumentation and testing and conducted material tests. His dedicated and valuable work was very helpful to success of the project. The author would like to thank James Malley of Degenkolb Engineers for providing information on the San Francisco hospital designed by Degenkolb Engineers with composite shear walls and for permission to include the design in this report. The opinions expressed in this report are solely those of the author and do not necessarily reflect the views of the National Science Foundation, the University of California, Berkeley, the Structural Steel Educational Council or other agencies and individuals whose names appear in this report.

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 4

SEISMIC BEHAVIOR AND DESIGN OF COMPOSITE STEEL PLATE SHEAR WALLS By Dr. ABOLHASSAN ASTANEH-ASL, P.E. Professor Department of Civil and Environmental Engineering University of California, Berkeley

_____________________________________________ CONTENTS

ACKNOWLEDGMENTS / Page 3 TABLE OF CONTENTS / Page 4 NOTATIONS AND GLOSSARY / Page 5 1. INTRODUCTION / Page 7 2. BEHAVIOR OF COMPOSITE SHEAR WALLS / Page 15

3. RELEVANT CODE PROVISIONS / Page 28 4. SEISMIC DESIGN OF COMPOSITE SHEAR WALLS/ Page 33 REFERENCES/ Page 41 APPENDIX - SUGGESTED COMPOSITE STEEL PLATE SHEAR WALLS SYSTEMS / Page 43 ABOUT THE AUTHOR / Page 45 LIST OF PUBLISHED STEEL TIPS REPORTS /Page 46

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 5

_________________________________________________________________________

Notations and Glossary _________________________________________________________________________

A. Notations In preparing the following notations, whenever possible, the definitions are taken with permission of the AISC, from the Seismic Provisions for Structural Steel Buildings (AISC, 1998). Such definitions are identified by (AISC, 1998) at the end of the definition. Asp Horizontal area of stiffened steel plate (AISC, 1997). a Height of story in tension field action equations (AISC, 1999). b Width of unstiffened element. Cd Deflection amplification factor . Cpr A factor to account for peak connection strength( FEMA, 2000). Cs Seismic coefficient given by IBC-2000. Cv Ratio of plate critical stress in shear buckling to shear yield stress( AISC, 1999). D The effect of dead load( IBC-2000). E Modulus of elasticity. E The combined effect of horizontal and vertical earthquake-induced forces (IBC-2000). Em The maximum seismic load effect (IBC-2000). Fy Specified minimum yield stress of the plate (AISC, 1997). Fye Expected yield Strength of steel to be used,(AISC, 1997). Fu Specified minimum tensile strength,(AISC, 1997) . IE The occupancy importance factor given by IBC-2000. kv Plate buckling coefficient (AISC, 1999). QE The effect of horizontal seismic forces (IBC-2000). R Response modification factor. Rn Nominal strength. (AISC, 1997). Ru Required strength. (AISC, 1997). RUS R-factor. Ry Ratio of the Expected Yield Strength Fye to the minimum specified yield strength Fy.

(AISC, 1998) .

maxr Maximum values of imaxr .

imaxr The ratio of the design story shear resisted by the most heavily loaded single element in the

story to the total story shear, for a given direction of loading. For shear walls see Section 1617.2.2 of IBC-2000.

S1 The maximum considered earthquake spectral response acceleration at 1-second period (IBC-2000).

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 6

SDS The design spectral response acceleration at short periods (IBC-2000). T The fundamental period. t Thickness of element. tf Thickness of flange. V Shear force, also base shear. Vns Nominal shear strength of a member or a plate. Vnse Expected shear capacity of a member or a plate. Vu Required shear strength on a member or a plate. Vy Shear yield capacity. W Weight of structure, IBC-2000. dy Yield displacement. f Resistance factor. r Reliability factor based on system redundancy (IBC-2000). ri Reliability factor for a given story (IBC-2000). s Normal stress. W o System over-strength factor. B. Glossary In preparing the following glossary, whenever possible, the definitions are taken with permission of the AISC, from the Seismic Provisions for Structural Steel Buildings (AISC, 1998). Shear Wall. A vertical plates system with boundary columns and horizontal beams at floor levels

that resists lateral forces on the structural system. Connection. A combination of joints used to transmit forces between two or more members.

Connections are categorized by the type and amount of force transferred (moment, shear, end reaction).

Design Strength. Resistance (force, moment, stress, as appropriate) provided by element or connection; the product of the nominal strength and the resistance factor.

Dual System. A Dual System is a structural system with the following features: (1) an essentially complete space frame that provides support for gravity loads; (2) resistance to lateral load provided by moment resisting frames (SMF, IMF or OMF) that are capable of resisting at least 25 percent of the base shear and concrete or steel shear walls or steel braced frames (EBF, SCBF or OCBF); and, (3) each system designed to resist the total lateral load in proportion to its relative rigidity.

Expected Yield Strength. The Expected Yield Strength of steel in structural members is related to the Specified Yield Strength by the multiplier Ry.

Slip-critical Joint. A bolted joint in which slip resistance on the faying surface(s) of the connection is required. Structural System. An assemblage of load-carrying components that are joined together to

provide interaction or interdependence.

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 7

1. INTRODUCTION 1.1. Introduction

The composite shear walls discussed in this report consist of a steel plate shear wall with reinforced concrete walls attached to one side or both sides of the steel plate using mechanical connectors such as shear studs or bolts. In the AISC Seismic Provisions (AISC, 1997) these systems are denoted as Composite Steel Plate Shear Walls, (C-SPW). In the remainder of this report, whenever composite shear wall is mentioned, it refers to this system. Examples of the composite shear wall configurations are shown in Figure 1.1. The composite shear walls have been used in buildings in recent years although not as frequently as the other lateral load resisting systems.

From: (AISC, 1997)

Shear Connectors

Steel Plate Concrete Wall

Reinforceme

(a)

(b)

(c)

(d)

Figure 1.1. Examples of Composite Shear Walls Discussed in This Report

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 8

This report attempts to provide information on the basic characteristics of composite shear walls, an example of their past applications, their actual seismic behavior, the current code provisions and additional recommendations on their design and a few examples of suggested configurations. The report is intended for the structural engineers, fabricators, architects and others involved in structural and earthquake engineering and construction of buildings.

1.2. Some Advantages of Composite Shear Walls

1. Compared to a reinforced concrete shear wall, a composite wall with the same shear

capacity, and most likely larger shear stiffness, will have smaller thickness and less weight. The smaller footprint of the composite shear wall is very advantageous from architectural point of view providing more useable floor space particularly in tall buildings. The lesser weight of composite shear wall will result in smaller foundations as well as smaller seismic forces.

2. A composite shear wall can have cast in place or pre-cast walls. Since steel plate shear walls can provide stiffness and stability during erection, the construction of reinforced concrete walls can be taken out of the critical path of field construction and done independent of fabrication and erection of steel structure. In particular, if pre-cast concrete walls are used, such walls can be bolted to the steel plate shear walls at any convenient time during construction.

3. In a steel shear wall, the story shear is carried by tension field action of the steel plate after buckling of diagonal compression. In a composite shear wall, the concrete wall restrains the steel plate and prevents its buckling before it yields. As a result, the steel plate resists the story shear by yielding in shears. The shear yield capacity of steel plate can be significantly greater than its capacity to resist shear in yielding of diagonal tension field. In addition, the reinforced concrete wall provides sound and temperature insulation as well as fire proofing to steel shear walls.

4. In the aftermath of a moderate and more frequent earthquake, steel shear walls develop buckling and reinforced concrete shear walls develop cracking, both needing some measure of repair. Such repairs can be costly not only because of the cost of construction, but also for disruption of functionality and occupancy use of the area to be repaired. However, as the tests summarized in Chapter 2 indicate, the damage to composite shear walls, particularly when the innovative system proposed herein is used, can be limited to shear yielding of steel plates with almost no cracks in the concrete wall or damage to other elements of the system. Such performance is very desirable since the building can continue its full functionality after such events.

1.3 Main Components of a Composite Shear Wall

Main components of composite shear walls shown in Figure 1.2 are steel wall, concrete wall; shear connectors, boundary columns, boundary beams, connection of steel wall to boundary

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 9

beams and columns, and beam-to-column connections. These components and their role in overall performance of composite shear walls are discussed in the following sections. 1.3.a. Steel plate shear wall

This element is usually a relatively thin steel plate. Plates thinner than 3/8 inch are not

recommended since such thin plates cannot be easy to handle during fabrication and erection. In addition, as later will be discussed, such thin plates may require a large number of shear connectors to postpone plate buckling until yielding of the plate, a desirable mechanism, occurs. A36 and high strength steel plates can be used although A36 steel plate due to its low yield point is preferred to encourage yielding of steel plate. The main role of the steel plate in a composite shear wall is to provide shear strength and stiffness as well as shear ductility. It also participates to some limited extent to resist overturning moment. Figure 1.3(a) shows forces resisted by steel plate. In a composite shear wall the steel plate resists story shear by shear yielding, an advantage over the steel plate shear walls where story shear is resisted through development of diagonal tension field action (Astaneh-Asl, 2001) as shown in Figure 1.3(b). The reason in composite shear walls steel plate is able to almost reach its yield point in shear is that the concrete wall provided bracing to steel plate and prevents its buckling prior to reaching yielding. In other words, the concrete wall acts as stiffeners and prevents buckling of plate. Of course, concrete wall itself also carries some of the story shear by developing compression diagonal field.

Concrete Wall

Shear Connectors

Steel Plate Wall

Boundary Column

Connections of Steel Wall

Boundary Beam

Figure 1.2. Main Components of a Typical Composite Shear Wall

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 10

1.3.b. Reinforced concrete (R/C) shear wall

Reinforced concrete walls can be connected to one side of a steel plate shear wall, Figure

1.1(a) or both sides of a steel plate shear wall, Figure 1.1(b and c) or the R/C wall can be sandwiched between two steel shear walls, Figure 1.1(d). In all of these cases, the R/C wall provides shear strength and stiffness, through its compression field as shown in Figure 1.4, and some ductility depending on the amount of reinforcement in the wall. The R/C wall also

a. Shear Wall Elements Under Pure Shear b. Shear Wall Elements Under Tension Field Action

Figure 1.3. Shear Resistance by Steel Plate in (a) Composite Shear Wall and (b) Steel Shear Wall

Figure 1.4. Shear Resisted by Diagonal Compression Field of Concrete

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 11

participates in resisting overturning moment. The R/C wall can be cast-in-place wall or pre-cast. One of the important roles of the R/C wall is to prevent buckling of steel plate wall. This is done by connecting the steel plate to the R/C wall using shear connectors. 1.3.c. Shear connectors

Shear connectors are used to connect steel elements of the composite wall to concrete. For cast-in-place concrete usually welded shear studs are used. Of course other shear connectors such as channels can also be used although they may not be as economical as welded shear studs. For pre-cast concrete walls, bolts can be used to connect the R/C walls to steel plate walls. Tests of composite shear walls (Zhao and Astaneh-Asl, 2002) have shown that in composite shear walls, in some cases, shear studs not only are subjected to shear but also to a considerable tension due to local buckling of the steel plate. 1.3.d. Boundary columns

In addition to gravity loads, the columns on the sides of a composite shear wall resist the bulk of overturning moments. The columns also provide an anchor point for tension field action of the steel plate and bearing element for compression diagonal element of the concrete wall. In structures with relatively large columns, the columns can also transfer a considerable amount of story shear. 1.3.e. Boundary beams

The top and bottom beams in a composite shear wall act as anchor for tension field action of the steel plate and as compression bearing element for compression diagonal of the concrete wall. In addition, the beam resists its tributary gravity load from the floor. Due to overturning moment, the beams are subjected to relatively large shear flow at their ends.

1.3.f. Connections of shear wall to boundary members

The steel shear wall should be connected to boundary columns and beams either by bolts or welds. The main role of these connections is to transfer shear and tension. The concrete wall can also be connected to the boundary walls using mechanical connectors. These connections transfer shear that is resisted by the reinforcement inside the wall. 1.3.g. Beam-to-column connections

These connections play a major role in performance of the walls. In a dual system, where

the steel frame is the back-up system for the composite shear wall, the connections should be moment connections. 1.4. Structural Systems Using Composite Walls

Figure 1.5 shows a typical steel structural system with composite shear walls. Like reinforced concrete and steel shear walls, the composite shear walls are used to provide resistance

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 12

to lateral loads. Figure 1.5(a) shows a composite shear wall used in a steel frame with simple supports. In this case, the composite wall is designed to carry the entire story shear. The wall provides the bulk of story shear and ductility through yielding of the steel shear wall and reinforcements inside the concrete wall as well as compressive crushing of concrete. The wall also acts as the web of the vertical cantilever beam that resists the overturning moment. The flanges of this cantilever beam are boundary columns.

The system shown in Figure 1.5(b) is a dual system where the shear wall is either inside a moment frame or is parallel to it. Although in reality, the shear wall and moment frame provide lateral load resistance together, in current practice, the shear wall is designed to resist total lateral load while the moment frame is designed as a back-up system to resist of the lateral load. More on design and code procedures are given in Chapter 3. The moment frame in this system does not have to be the Special ductile moment frame as defined by codes and FEMA 350 report. Based on test results, (see Chapter 2) it appears that because of the presence of shear wall the rotational demand on moment connections in this system is relatively small until the shear wall is severely damaged. Even after shear wall is heavily damaged, because of the presence of gusset like corner pieces of the steel plate above and below the moment connections, the connections are not subjected to large rotations.

The system in Figure 1.2(c) is also a dual system, which has two shear walls with a relatively short coupling beam between them. By adjusting bending and shear strength of the coupling beams, the designer can design the system such that the coupling beam acts as a ductile fuse and participates in not only providing strength and stiffness but also significant ductility and energy dissipation capability.

(b) Shear Wall Inside or in Parallel With a Moment Frame (Dual System)

(c) Coupled Shear Walls (a) Shear Wall Inside Simply-Supported Frame

Simple Supports

Moment Frame

Coupling Beams

Figure 1.5. Typical Steel Structure with Composite Shear Walls

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 13

1.5. An Example of Application of Composite Shear Walls Degenkolb Engineers have used composite shear walls in a hospital in San Francisco (Dean et al., 1977). A plan view of the structure is shown in Figure 1.6. This structure is a good example of the early use of composite shear walls in a hospital building in an area of very high seismicity such as California. A view of the structure and a close up of the shear walls in this building are shown in Figure 1.7. The steel shear walls in this structure were covered on both sides with reinforced concrete shear walls making the wall a composite steel concrete shear wall. For information on steel shear walls the reader is referred to a previous Steel TIPS report: Seismic Behavior and Design of Steel Shear Walls (Astaneh-Asl, 2001).

Composite Shear Walls

Plan

240 (73.2 m)

75 (22.9 m)

Figure 1.6. Plan view of 18-story hospital in San Francisco

(Photos: Courtesy of Degenkolb Engineers, San Francisco)

Figure 1.7. A view of 18-story hospital and close-up of a shear wall

Seismic Behavior and Design of Composite Steel Plate Shear Walls, by Abolhassan Astaneh-Asl 14

Because of this building being a hospital, the designers Dean et al., (1977) have used site-specific response spectra and dynamic analysis to establish seismic forces. The resulting seismic forces were relatively large. In selecting composite shear walls for this building, Dean et al, (1977) state that:

The combination of force level and allowable stresses would have required shear wall thicknesses of over 4 feet if walls were of reinforced concrete only. This would have been unacceptable architecturally and the added weight would have increased the design forces substantially. It was therefore, necessary to introduce solid structural steel plate into the principal walls to resist high shears. The plates are enclosed in concrete to provide stiffening against plate buckling.

The composite shear walls in this building consist of steel plates with concrete walls on