8/10/2019 Serviceability AISC ASCE

1/3November 2004 Modern Steel Construction

Serviceability is defined in theAISC Specification as a state in

which the function of a build-ing, its appearance, maintain-ability, durability, and comfort

of its occupants are preserved under nor-mal usage. Although serviceabilityissues have always been a design consid-eration, changes in codes and materialshave added importance to these matters.

The shift to a limit-states basis fordesign is one example. Since 1986, boththe AISC LRFD and AISC ASD specifica-tions have been based upon the limitstates design approach in which two cat-

egories of limit states are recognized:strength limit states and serviceabilitylimit states. Strength limit states controlthe safety of the structure and must bemet. Serviceability limit states define thefunctional performance of the structureand should be met.

The distinction between the two cate-gories centers on the consequences ofexceeding the limit state. The conse-quences of exceeding a strength limitmay be buckling, instability, yielding,fracture, etc. These consequences are thedirect response of the structure or ele-ment to load. In general, serviceabilityissues are different in that they involvethe response of people and objects to the

behavior of the structure under load. Forexample, the occupants may feel uncom-fortable if there are unacceptable defor-mations, drifts, or vibrations.

Whether or not a structure or elementhas passed a limit state is a matter of

judgment. In the case of strength limits,the judgment is technical and the rulesare established by building codes anddesign specifications. In the case of ser-

viceability limits, the judgments are fre-quently non-technical. They involve the

perceptions and expectations of buildingowners and occupants. Serviceabilitylimits have, in general, not been codified,in part because the appropriate or desir-able limits often vary from application toapplication. As such, they are more a partof the contractual agreements with theowner than life-safety related. Thus, it isproper that they remain a matter of con-tractual agreement and not specified inthe building codes.

Ideally, the distinction betweenstrength and serviceability would disap-

pear, and problems or failures of anykind would not occur. In reality, alldesign methods are based upon a finite,

but very small probability of exceedance.Because of the non-catastrophic conse-quences of exceeding a serviceabilitylimit state, a higher probability ofexceedance is allowed by current practicethan for strength limit states.

The foregoing is not intended to saythat serviceability concerns are unimpor-tant. In fact, the opposite is true. By hav-ing few codified standards, the designeris left to resolve these issues in consulta-tion with the owner to determine theappropriate or desired requirements.

Serviceability problems cost moremoney to correct than would be spentpreventing the problem in the designphase. Perhaps serviceability discussionswith the owner should address the trade-off between the initial cost of the poten-tial level of design vs. the potential miti-gation costs associated with a morerelaxed design. Such a comparison isonly possible because serviceabilityevents are, by definition, not safety-

related. The customer or his or her agentmust identify the needed criteria for theengineer. Nevertheless, the engineermust foster the active involvement of thecustomer in the design stage of a struc-ture and address the need for informeddiscussion of standards and levels of

building performance.Numerous serviceability design crite-

ria exist, but they are spread diversely

Serviceability

By Charles J. Carter, P.E., S.E.

SteelWise

Updated in 2003, this AISC design guide now provides more extensive coverage for serviceability

considerations in steel building structures.

Updated Design Guide 3offers Guidance

Serviceability involves the

response of people and

objects to the behavior of the

structure under load.

8/10/2019 Serviceability AISC ASCE

2/3

8/10/2019 Serviceability AISC ASCE

3/3

requirements supersede the recommenda-tions of this design guide.

Structures framed in structural steelaccommodate numerous occupanciesand building types. The design guideaddresses ten occupancy types and thespecific serviceability design considera-tions associated with these occupancies

as follows: Storage/Warehouses Manufacturing Heavy Industrial/Mill Buildings Mercantile/Shopping Malls Health Care and Laboratory Facilities Educational Office Buildings Parking Structures Residential/Apartments/Hotels Assembly/Arenas Seismic Applications

Additionally, the design guide pro-

vides in-depth coverage of the followingspecific areas of serviceability: Design considerations relative to roof-

ing, including ponding stability, roof-ing, membrane roofs, and metal roofs.

Design considerations relative to sky-lights.

Design considerations relative to

cladding, frame deformation, anddrift, including cladding-structureinteraction, foundation-supportedcladding for gravity loads, frame-sup-ported cladding at columns, frame-supported cladding for gravity loadsalong spandrels, and special consider-ations for tall buildings.

Design considerations relative to inte-rior partitions and ceilings, includingsupport deflection, flat and levelfloors, specifying camber and cambertolerances, and maintaining floor ele-

vation.

Design considerations relative tovibration/acceleration, including

basic discussions of human responseto vibration, machines and vibration,tall building accelerationmotionperception, and reference to the AISCfloor vibration design guide for moredetailed information.

Design considerations relative to equip-ment, including elevators, conveyors,cranes, and mechanical equipment.

Design Guide 3: Serviceability DesignConsiderations for Steel Buildings, 2nded., is available online through AISCs ePubsmembership area at www.aisc.org/ePubs.

AISC gratefully acknowledges the efforts ofthe three authors of the design guide: JamesFisher and Michael West, both of Computer-ized Structural Design, Inc., and LawrenceG. Griffis, of Walter P. Moore Engineers and

Consultants.

November 2004 Modern Steel Construction