Expansion Joints: Where, When and How - AISC

1 Expansion Joints: Where, When and HowBy James M. Fisher, the most basic sense, the need for anexpansion joint in a structure dependson the consequence of not having anexpansion joint. Will the lack of anexpansion joint hamper or destroy thefunction of the facility, or cause damageto the structural or architectural compo-nents? The number and location of build-ing Expansion joints is a design issue notfully treated in technical literature. TheLRFD Specification(AISC, 1999) listsexpansion and contraction as a service-ability issue and provides the statementin Section L2, Adequate provision shallbe made for Expansion and contractionappropriate to the service conditions ofthe structure. ASCE 7-02 Minimum Design Loads forBuildings and Other Structures (ASCE,2002) states, Dimensional changes in astructure and its elements due to varia-tions in temperature, relative humidity,or other effects shall not impair the ser-viceability of the structure.

2 This paper will focus on the basicrequirements used to determine whetheran Expansion joint is required at a givenlocation, or locations within a of Expansion joints as theypertain to commercial, industrial, andlong span structures are discussed. Areadividers as provided in roof membranesto control the effects of thermal loads forroofing are not discussed, as they arerelief joints in the membrane and do notrequire a joint in the roof structure RequirementsAlthough buildings are often con-structed using flexible materials, roof andstructural Expansion joints are requiredwhen plan dimensions are large. It is notpossible to state exact requirements rela-tive to distances between expansionjoints because of the many variablesinvolved, such as ambient temperaturesduring construction and the expectedtemperature range during the life of abuilding.

3 The National Roofing Contrac-tors Association (NRCA, 2001) gives thefollowing recommendations for the loca-tion of roof Expansion joints: Where steel framing, structural steel ,or decking change direction. Where separate wings of L, U, and Tshaped buildings or similar configura-tions exist. Where the type of decking changes;for example, where a precast concretedeck and a steel deck abut. Where additions are connected toexisting buildings. At junctions where interior heatingconditions change, such as a heatedoffice abutting an unheated ware-house, canopies, etc. Where movement between walls andthe roof deck may should be noted that the NRCA standard details show that the roof struc-ture under roof Expansion joints isintended to be Building Research AdvisoryBoard of the National Academy of Sci-ences (NAS, 1974) published Federal Con-struction Council Technical Report No.

4 65: Expansion Joints in Buildings (no longer inprint). When other conditions prevail, thefollowing rules are the building will be heated only andwill have hinged-column bases, usethe allowable length as the building will be air conditionedas well as heated, increase the allow-able length by 15% (provided theenvironmental control system will runcontinuously). the building will be unheated,decrease the allowable length by 33%; the building will have fixed columnbases, decrease the allowable lengthby 15%. the building will have substantiallygreater stiffness against lateral dis-placement at one end of the plandimension, decrease the allowablelength by 25%.When more than one of these designconditions prevail in a building, the per-centile factor to be applied should be thealgebraic sum of the adjustment factorsof all the various applicable should Expansion joints go?

5 Where are they needed? How are they sizedand designed? Here are some basic STEELCONFERENCEJ ames M. Fisher is vice president of Com-puterized structural Design (CSD), a Mil-waukee, WI consulting engineering 2005 Modern steel ConstructionThe report also includes temperaturedata for numerous cities. (This data isreprinted in Appendix B of the completepaper. For the complete paper, please the 2005 NASCC Proceedings at )Tw is the temperature exceeded only 1%of the time during summer months; Tm,the mean temperature during the normalconstruction season; and Tc, the tempera-ture exceeded 99% of the time duringwinter months. The design temperaturechange is the larger of the two tempera-tures differences either (Tw-Tm) or (Tm-Tc).Rather than consulting the above val-ues, many engineers use a temperaturechange of 50 F to 70 F for enclosedheated/air-conditioned equation form, the NAS require-ments given above can be shown in Eq.

6 1as follows:Lmax= Lallow+ (R1 R2 R3 R4)Lallowwhere:Lmax= maximum length of a buildingwith no Expansion joints orbetween Expansion jointsR1= , if the building is heated andair-conditionedR2= , if the building is unheatedR3= , if columns are fixed baseR4= , if the building has substan-tially greater stiffness at one endLallow= allowable length from Fig. 1As a general rule, Expansion jointsshould always be carried through theroofing the type of structuralexpansion joint, most engineers agreethat the best Expansion joint (and gener-ally the most expensive) is to use a line ofdouble columns to provide a completeseparation in the building frame at thejoints. When joints other than the doublecolumn type are employed, low frictionsliding elements, such as Teflon pads, areused between the faying surfaces.

7 Itshould be remembered that slip connec-tions are not totally frictionless. In addi-tion, they may induce some level ofrestraint to movement due to binding ordebris often, buildings may be requiredto have fire walls in specific walls may be required to extendabove the roof or they may be allowed toterminate at the underside of the fire walls become locations forexpansion joints. In such cases, the detail-ing of joints can be difficult because thefire wall must be supported designer is also cautioned thatFig. 1 Expansion Joint Spacing Graph [taken from Tech. Report No. 65, Expansion Jointsin Buildings].Fig. 2 Typical Expansion steel Construction April 2005when roof diaphragm forces are to betransferred into shear walls or vertical X-bracing systems, the transfer should beaccomplished mid-way between expan-sion joints allowing edge members toexpand and contract freely away fromthe fixed point of Joint SizeThe width of an Expansion joint isdetermined from the basic thermalexpression for the material used for theframes in the structure, = L T.

8 Where = for steel structures, Lis thelength subject to the temperature change,and Tis the temperature change. Tis based on the design temperaturechange, (Tw-Tm) or (Tm-Tc). The changeduring the construction cycle, (Tm-Tc), isusually the largest. structural Roof SystemsMetal roofs are of two types: ThroughFastener Roofs (TFR) and Standing SeamRoofs (SSR). Standing seam roofs, for thepurpose of this discussion, include onlythose of the floating type. Standing seamroofs without the floating feature shouldbe treated as through fastener fastener roofsrely on purlinroll to prevent slotting of the roof panelsand to relieve thermal force of their greater lateral seat stiff-ness, steel joists should not be used withthrough fastener roofs, except in rareinstances such as small roofs. A practicallimit between Expansion joints for TFR isin the range of 100 to 200 , when theseroofs are attached to light gage cold-formed seam roofsare limited bythe range of the sliding clips.

9 Dependingon the manufacturer, it is in the range of150 to 200 .Standing seam roofs are more flexiblein the direction perpendicular to the ribs,as compared to the direction of the , Expansion joints can be spaced atgreater distances than those perpendicu-lar to the ribs. The roof manufacturer srecommendations should be consultedand followed relative to the distancesbetween Expansion Crane BuildingsVertical bracingfor wind, seismic, orcrane longitudinal runway forces shouldbe located at or near the center of the run-way length. Expansion and contractioncan then occur away from the brace loca-tion. This will help prevent the perma-nent elongation of the vertical bracingdue to temperature changes. The disad-vantage of the center placement of thebracing is that bumper forces have to betransferred a greater distance to get to thebracing as compared to braces that arelocated near the crane runway beams: Only as a lastresort should Expansion joints be pro-vided for runway beams.

10 By providingoversize holes at the beam ends, expan-sion and contraction can be allowed ineach beam segment so that an expansionjoint is not necessary. If an expansionjoint is provided in the runway system,careful consideration must be given as tohow the lateral crane forces are trans-ferred across the joint. Special details arerequired to prevent high shears in thecrane rail and large forces in the rails: Expansion joints shouldnever be provided in the crane rails. Suchjoints often lead to rail cracking. In lieu ofsuch joints, the rail should be allowed toexpand toward the stops. Adequatespace must be allowed between the endof the rail and the face of the crane addition, a rail clamping system whichallows longitudinal Expansion and con-traction of the rail must be provided, par-Fig.