EXPANSION JOINTS: WHERE, WHEN AND HOW JAMES M. FISHER
James M. Fisher
Biography James M. Fisher is vice president of Computerized Structural Design (CSD), a Milwaukee, Wisconsin, consulting engineering firm. He received a Bachelor of Science degree in civil engineering from the University of Wisconsin in 1962. After serving two years as a Lieutenant in the United States Army Corps of Engineers, he continued his formal education. He received his Master of Science and Ph.D. degree in structural engineering from the University of Illinois in 1965 and 1968 respectively. Prior to joining CSD, he was an assistant professor of structural engineering at the University of Wisconsin at Milwaukee. He is a registered structural engineer in several states. Fisher has specialized in structural steel research and development. He has spent a large part of his career investigating building systems and the study of economical structural framing systems. He was a former chairman of the American Society of Civil Engineers Committee on the Design of Steel Building Structures. Fisher is a member of the American Iron and Steel Institute (AISI) Committee on Specifications, and a member of the AISC Specification Committee for the Design Fabrication and Erection of Structural Steel Buildings. Fisher is the coauthor of seven books, as well as the author of many technical publications in the field of structural engineering. He is a member of the American Society of Civil Engineers and honorary fraternities Tau Beta Pi, Sigma Xi, Chi Epsilon and Phi Kappa Phi. Fisher received the 1984 T.R. Higgins Lectureship Award presented by the American Institute of Steel Construction. Abstract This presentation will address means of determining where building expansion joints should be located within a structure. When expansion joints are required, and how to proportion and design appropriate joints. Expansion joints for commercial as well as industrial facilities will be discussed. Details of various types of joints will be presented.
EXPANSION JOINTS: WHERE WHEN AND HOW JAMES M. FISHER1
Introduction In the most basic sense the need for an expansion joint in a structure depends on the consequence of not having an expansion joint. Will the lack of an expansion joint hamper or destroy the function of the facility, or cause damage to the structural or architectural components? The number and location of building expansion joints is a design issue not fully treated in technical literature. The LRFD Specification (AISC, 1999) lists expansion and contraction as a serviceability issue and provides the statement in Section L2, “Adequate provision shall be made for expansion and contraction appropriate to the service conditions of the structure.” ASCE 7-02 “Minimum Design Loads for Buildings and Other Structures” (ASCE, 2002) states, “Dimensional changes in a structure and its elements due to variations in temperature, relative humidity, or other effects shall not impair the serviceability of the structure.” This paper will focus on the basic requirements used to determine if an expansion joint is required at a given location, or locations within a structure. Requirements of expansion joints as they pertain to commercial, industrial and long span structures are discussed. Area dividers as provided in roof membranes to control the effects of thermal loads for roofing are not discussed, as they are relief joints in the membrane and do not require a joint in the roof structure below.
General Requirements Although buildings are often constructed using flexible materials, roof and structural expansion joints are required when plan dimensions are large. It is not possible to state exact requirements relative to distances between expansion joints because of the many variables involved, such as, ambient temperatures during construction and the expected temperature range during the life of a building. The National Roofing Contractors Association (NRCA, 2001) gives the following recommendations for the location of roof expansion joints: • • • • • •
Where steel framing, structural steel, or decking change direction. Where separate wings of L, U, T shaped buildings or similar configurations exist. Where the type of decking changes, for example, where a precast concrete deck and a steel deck abut. Where additions are connected to existing buildings. At junctions where interior heating conditions change, such as a heated office abutting unheated warehouse, canopies, etc. Where movement between walls and the roof deck may occur.
It should be noted that the NRCA standard details show that the roof structure under roof expansion joints is intended to be discontinuous. The Building Research Advisory Board of the National Academy of Sciences (NAS, 1974) published Federal Construction Council Technical Report No. 65 “Expansion Joints in Buildings” (No longer in print). The report presents the graph shown in Figure 1 as a guide for spacing expansion joints in beam and column frame buildings as a function of design temperature change. The graph is directly applicable to buildings of beam and column construction, hinged at the base, and with heated interiors. When other conditions prevail, the following rules are applicable: 1. 2. 3. 1
If the building will be heated only and will have hinged-column bases, use the allowable length as specified; If the building will be air conditioned as well as heated, increase the allowable length by 15 percent (provided the environmental control system will run continuously); If the building will be unheated, decrease the allowable length by 33 percent;
James M. Fisher is Vice President Computerized Structural Design, S.C., Milwaukee, WI
4. 5.
If the building will have fixed column bases, decrease the allowable length by 15 percent; If the building will have substantially greater stiffness against lateral displacement at one end of the plan dimension, decrease the allowable length by 25 percent.
When more than one of these design conditions prevails in a building, the percentile factor to be applied should be the algebraic sum of the adjustment factors of all the various applicable conditions. The report also includes temperature data for numerous cities. This data is reprinted in Appendix B of this paper. Tw, is the temperature exceeded only 1% of the time during summer months, Tm, the mean temperature during the normal construction season and Tc, the temperature exceeded 99% of the time during winter months. The design temperature change is the larger of the two temperatures differences either (Tw-Tm) or (Tm-Tc).
Fig. 1 Expansion Joint Spacing Graph [Taken from F.C.C. Tech. Report No. 65, Expansion Joints in Buildings] Rather than consulting the above values, many engineers use a temperature change of 50 to 70 degrees for enclosed heated / air-conditioned buildings. In equation form the NAS requirements given above can be shown as follows: L max = Lallow + ( R1 − R2 − R3 − R4 ) Lallow
(Eq. 1)
where: Lmax = Maximum length of a building with no expansion joints or between expansion joints. R1 = 0.15, if the building is heated and air-conditioned. R2 = 0.33, if the building is unheated.
R3 = 0.25, if columns are fixed base. R4 = 0.25, if the building has substantially greater stiffness at one end. Lallow = Allowable length from Fig. 1 As a general rule expansion joints should always be carried through the roofing membrane. Regarding the type of structural expansion joint, most engineers agree that the best expansion joint (and generally the most expensive) is to use a line of double columns to provide a complete separation in the building frame at the joints. When joints other than the double column type are employed, low friction sliding elements, such as Teflon pads are used between the faying surfaces. It should be remembered that slip connections are not totally frictionless. In addition, they may induce some level of restraint to movement due to binding or debris build-up. Very often buildings may be required to have fire walls in specific locations. Fire walls may be required to extend above the roof or they may be allowed to terminate at the underside of the roof. Such fire walls become locations for expansion joints. In such cases the detailing of joints can be difficult because the fire wall must be supported laterally. Figure 2 depicts typical details to permit limited expansion. Additional details are given in various architectural texts. Not shown in the joist details is the OSHA bolting requirements that may be necessary. The designer is also cautioned that when roof diaphragm forces are to be transferred into shear walls or vertical Xbracing systems the transfer should be accomplished mid-way between expansion joints allowing edge members to expand and contract freely away from the fixed point of resistance. Expansion Joint Size The width of an expansion joint is determined from the basic thermal expression for the material used for the frames in the structure, ∆ = αL∆T. Where α =0.0000065 for steel structures, L is the length subject to the temperature change, and ∆T is the temperature change. ∆T is based on the design temperature change, (Tw-Tm) or (Tm-Tc). The change during the construction cycle, (Tm-Tc), is usually the largest.
Structural Roof Systems Metal roofs are of two types: Through Fastener Roofs (TFR) and Standing Seam Roofs (SSR). Standing Seam Roofs for the purpose of this discussion include only those of the floating type. Standing seam roofs without the floating feature should be treated as Through Fastener Roofs. Through fastener roofs rely on purlin roll to prevent slotting of the roof panels and to relieve thermal force build-up. Because of their greater lateral seat stiffness steel joists should not be used with through fastener roofs, except in rare instances such as small roofs. A practical limit between expansion joints for TFR is in the range of 100 to 200 feet, when these roofs are attached to light gage cold-formed purlins. Standing seam roofs are limited by the range of the sliding clips. Depending on the manufacturer, it is in the range of 150 to 200 feet. Standing seam roofs are more flexible in the direction perpendicular to the ribs, as compared to the direction of the ribs, thus expansion joints can be spaced at greater distances than those perpendicular to the ribs. The roof manufacturer’s recommendations should be consulted and followed relative to the distances between expansion joints.
Overhead Crane Buildings Vertical Bracing Vertical bracing for wind, seismic, or crane longitudinal runway forces should be located at or near the center of the runway length. Expansion and contraction can then occur away from the brace location. This will help prevent the permanent elongation of the vertical bracing due to temperature changes. The disadvantage of the center placement of the bracing is that bumper forces has to be transferred a greater distance to get to the bracing as compared to braces that are located near the crane stops. Crane Runway Beams Only as a last resort should expansion joints are provided for runway beams. By providing oversize holes at the beam ends expansion and contraction can be allowed in each beam segment, so that an expansion joint is not necessary. If an expansion joint is provided in the runway system, careful consideration must be given as to how the lateral crane forces are transferred across the joint. Special details are required to prevent high shears in the crane rail, and large forces in the rail clamps. Crane Rails Expansion joints should never be provided in the crane rails. Such joints often lead to rail cracking. In lieu of such joints, the rail should be allowed to expand toward the stops. Adequate space must be allowed between the end of the rail and the face of the crane stops. In addition, a rail clamping system which allows longitudinal expansion and contraction of the rail must be provided, particularly in runway systems which exceed 400 ft. in length. Large Clear Span Structures Long span structures and components often require special expansion joint hardware. The majority of bearings only have expansion and contraction capabilities of plus or minus one inch. Bearings which have smooth stainless steel surfaces can be specified for much grater expansion and contraction amounts. Slide bearings generally have a coefficient of frictions from 0.04 to 0.08. The bearings can accommodate pressures from 2000 to 4000 psi. Manufactures of slide bearings can be found on the web. The manufacturer should be consulted for proper ordering and installation procedures. Special Details On occasion special expansion joint details are required to transfer shear across the expansion joint, two such details are shown in Figures 3 and 4. In Figure 3 the strapping is relatively flexible thus allowing expansion and contraction across the joint, and yet is stiff in the direction perpendicular to the joint thus allowing shear transfer. The joint shown in Figure 4 allows shear transfer through bearing. Construction Concerns The author has experienced several issues relative to construction difficulties associated with expansion joints. The first is that temperature changes to which an unenclosed unheated structure is subjected to during construction may exceed the design temperature changes after completion of the structure. These increased temperature changes should be considered by the designer. The temperature to be considered during construction, of course, varies depending upon building location. Engineers often use a maximum value of 70 degrees for calculation purposes. A more accurate value to use is the Tm-Tc value from the NAS Report. Sometimes it is very difficult for the steel erector to adjust the expansion joint at the desired location as normal erection tolerances may force the expansion joint to one end of its travel. This problem can be eliminated if the designer considers a detail at the far end of the member to which the expansion joint is located, as a means of adjustment. In this way the construction tolerance can be compensated.
Sheet Metal Cap Batt Insulation 2 x 10 Continuous Wood Cant
Joist
Wood NailerScrew to Deck Built-up Roofing Steel Deck Insulation
Sheet Metal Cap Batt Insulation 2 x 10 Continuous
Wood Nailer Bolt or Screw to Joist or Deck
Wood Cant
Do Not Weld This Side
Do Not Weld This Side
"A"
Bent Bar Do Not Weld
Typ.
Low Friction Sliding Element (Optional)
Purlin Slotted Holes in P. L Tighten Bolts Finger Tight, Provide Jamb Nut or T.W. Bolt to Nut, Provide Washers
SECTION "A"
Fig. 2 Typical Expansion Joints
BRACING SAG SUPPORT CONNECT TO ONE SIDE ONLY
Fig. 3 Shear Across Expansion Joint
Fig. 4 Shear Across Expansion Joint Example 1: 400 Foot Long Braced Frame Determine whether a rectangular 400 ft. by 180 ft., unheated building with pinned base columns requires an expansion joint. The building has x-bracing at one end only in the two side walls along the 400 ft. direction. The building is located in Buffalo, New York. From the Appendix: For Buffalo, New York: Tw = 88, Tm = 59, Tc = 3 Design Temperature Change = Maximum of (Tw-Tm) or (Tm-Tc) = Maximum of (88-59) or (59-3) = 56 degrees From Equation (1): L max = Lallow + ( R1 − R2 − R3 − R4 ) Lallow Where: R1 = 0.15, the building is not heated and nor air-conditioned, N.A. R2 = 0.33 the building is unheated. R3 = 0.25 the columns are fixed base, N.A. R4 = 0.25 the building has substantially greater stiffness at one end. From Fig. 1: Lallow = 450 ft. L max = 450 + ( 0 − 0.33 − 0 − 0.25 )( 450 ) = 189 ft.
Therefore an expansion joint is required. Since the building is a braced frame and the bracing is at only one end of a typical frame additional bracing will be required on both sides of the expansion joint. Example 2: Expansion Joint Size Determine the size of the expansion joint required for the building in Example 1. The structure is braced at both ends away from the expansion joint. ∆ = 0.0000065L∆T = (2)(0.00065)(200)(56/100) = 0.146 ft. = 1.75 in., USE 2 in. total movement.
The above calculation assumes that the thermal movement for each segment occurs away from the x-braced bays. REFERENCES American Institute of Steel Construction, 1999, Load and Resistance Factor Design Specification for Structural Steel Buildings and Commentary, Chicago, IL. American Society of Civil Engineers, 2003, Minimum Design Loads for Buildings and Other Structures, ASCE 702, ASCE Reston, VA. Federal Construction Council, 1974, Technical Report No. 65, 1974, Expansion Joints in Buildings, National Research Council, Washington, D.C. (out of print)
APPENDIX B TEMPERATURE DATA The following tabulation presents mean construction season temperature (Tm) and extreme summer (Tw) and winter (Tc) temperature data for various localities in the United States. Most stations listed are located at airports; those identified as CO are city offices. Tm = the mean temperature during the normal construction season in the locality of the building. For the purpose of this report the normal construction season for a locality is defined as that contiguous period in a year during which the minimum daily temperature equals or exceed 32°F.* Tw = the temperature exceeded, on the average, only 1 percent of the time during the summer months of June through September in the locality of the building. (In a normal summer there would be approximately 30 hours at or above the design value.**) Tc = the temperature equaled or exceeded, on the average, 99 percent of the time during the winter months of December, January, and February in the locality of the building. (In a normal winter there would be approximately 22 hours at or below this design value.**)
*
These contiguous periods for each locality in the United States were obtained from the Decennial Census of United States Climate: Daily Normals of Temperature and Heating Degree Days (see reference on page 11) and the mean construction season temperature values Tm were computed (by Maj. T.E. Stanton of the USAF Environmental Technical Applications Center, Washington, D.C.) from the mean monthly temperatures extracted from the National Weather Services’ Local Climatological Data Summaries for the stations. In a few cases other sources also were used. **
The Tw and Tc values are extracted from the ASHRAE Handbook of Fundamentals (1972), published by the American Society of Heating, Refrigerating and Air Conditioning Engineers.
Station
Temperature (°F) Tm Tc Tw
Alabama Birmingham Huntsville Mobile (CO) Montgomery
97 97 96 98
63 61 68 66
19 13 28 22
Alaska Anchorage Barrow Fairbanks Juneau Nome
73 58 82 75 66
51 38 50 48 45
-25 -45 -53 -7 -32
Arizona Flagstaff Phoenix Prescott Tucson Winslow Yuma
84 108 96 105 97 111
58 70 64 67 67 72
0 31 15 29 9 37
Arkansas Ft. Smith Little Rock Texarkana
101 99 99
65 65 65
15 19 22
California Bakersfield Burbank Eureka/Arcata Fresno Long Beach Los Angeles Oakland Sacramento San Diego San Francisco Santa Maria Colorado Alamosa Colorado Springs Denver Grand Junction Pueblo
103 97 67 101 87 94 85 100 86 83 85 84 90 92 96 96
65 64 52 63 63 62 57 60 62 56 57 60 61 62 64 64
31 36 32 28 41 41 35 30 42 35 32 -17 -1 -2 8 -5
Connecticut Bridgeport Hartford New Haven
90 90 88
60 61 59
4 1 5
Delaware Wilmington
93
62
12
Station
Temperature (°F) Tw Tm Tc
Florida (Continued) Jacksonville Key West Lakeland (CO) Miami Miami Beach (CO) Orlando Pensacola (CO) Tallahassee Tampa West Palm Beach
96 90 95 92 91 96 92 96 92 92
68 77 72 75 75 72 68 68 72 75
29 55 35 44 45 33 29 25 36 40
Georgia Athens Atlanta Augusta Columbus Macon Rome Savannah/Travis
96 95 98 98 98 97 96
61 62 64 65 65 62 67
17 18 20 23 23 16 24
Hawaii Hilo Honolulu
85 87
73 76
59 60
Idaho Boise Idaho Falls Lewiston Pocatello
96 91 98 94
61 61 60 60
4 -12 6 -8
Illinois Chicago Moline Peoria Rockford Springfield
95 94 94 92 95
60 63 61 62 62
-3 -7 -2 -7 -1
Indiana Evansville Fort Wayne Indianapolis South Bend
96 93 93 92
65 62 63 61
6 0 0 -2
Iowa Burlington Des Moines Dubuque Sioux City Waterloo
95 95 62 96 91
64 64 63 64 63
-4 -7 -11 -10 -12
Kansas Dodge City Goodland
99 99
64 65
3 -2
Station
Temperature (°F) Tm Tc Tw
Florida Daytona Beach Ft. Myers Kentucky Covington Lexington Louisville
94 94
70 74
32 38
93 94 96
63 63 64
3 6 8
Louisiana Baton Rouge Lake Charles New Orleans Shreveport
96 95 93 99
68 68 69 66
25 29 32 22
Maine Caribou Portland
85 88
56 58
-18 -5
Maryland Baltimore Frederick
94 94
63 63
12 7
Massachusetts Boston Pittsfield Worcester
91 86 89
58 58 58
6 -5 -3
Michigan Alpena Detroit-Metropolitan Escanaba Flint Grand Rapids Lansing Marquette Muskegon Sault Ste Marie
87 92 82 89 91 89 88 87 83
57 58 55 60 62 59 55 59 55
-5 4 -7 -1 2 2 -8 4 -12
Minnesota Duluth International Falls Minneapolis/St. Paul Rochester St. Cloud
85 86 92 90 90
55 57 62 60 60
-19 -29 -14 -17 -20
Mississippi Jackson Meridian Vicksburg (CO)
98 97 97
66 65 66
21 20 23
Missouri Columbia Kansas City St. Joseph
97 100 97
65 65 66
2 4 -1
Station Topeka Wichita Montana Billings Glasgow Great Falls Havre Helena Kalispell Miles City Missoula
Temperature (°F) Tw Tm Tc 99 69 3 102 68 5 94 96 91 91 90 88 97 92
60 60 58 58 58 56 62 58
-10 -25 -20 -22 -17 -7 -19 -7
Nebraska Grand Island Lincoln (CO) Norfolk North Platte Omaha Scottsbluff
98 100 97 97 97 96
65 64 64 64 64 62
-6 -4 -11 -6 -5 -8
Nevada Elko Ely Las Vegas Reno Winnemucca
94 90 108 95 97
61 59 66 62 63
-13 -6 23 2 1
New Hampshire Concord
91
60
-11
New Jersey Atlantic City Newark Trenton (CO)
91 94 92
61 62 61
14 11 12
New Mexico Albuquerque Raton Roswell
96 92 101
64 64 70
14 -2 16
New York Albany Binghamton (CO) Buffalo New York Rochester Syracuse
91 91 88 94 91 90
61 67 59 59 59 59
-5 -2 3 11 2 -2
North Carolina Asheville Charlotte Greensboro Raleigh/Durham
91 96 94 95
60 60 64 62
13 18 14 16
Station St. Louis Springfield
Temperature (°F) Tm Tc Tw 98 65 4 97 64 5
North Dakota Bismarck Devils Lake Fargo Minot Williston
95 93 92 91 94
60 58 59 ? 59
-24 -23 -22 -24 -21
Ohio Akron/Canton Cincinnati (CO) Cleveland Columbus Dayton Mansfield Sandusky (CO) Toledo Youngstown
89 94 91 92 92 91 92 92 89
60 62 61 61 61 61 60 61 59
1 8 2 2 0 1 4 1 1
Oklahoma Oklahoma City Tulsa
100 102
64 65
11 12
Oregon Astoria Eugene Medford Pendleton Portland Roseburg Salem
79 91 98 97 91 93 92
50 52 56 58 52 54 52
27 22 21 3 21 25 21
Pennsylvania Allentown Erie Harrisburg Philadelphia Pittsburgh Reading (CO) Scranton/Wilkes-Barre Williamsport
92 88 92 93 90 92 89 91
61 59 61 63 63 61 61 61
3 7 9 11 5 6 2 1
Rhode Island Providence South Carolina Charleston Columbia Florence Greenville Spartanburg
89 95 98 96 95 95
60 66 64 64 61 60
Station Wilmington Winston/Salem
Temperature (°F) Tw Tm Tc 93 63 23 94 63 14
Tennessee Bristol/Tri City Chattanooga Knoxville Memphis Nashville
92 97 95 98 97
63 60 60 62 62
11 15 13 17 12
Texas Abilene Amarillo Austin Brownsville Corpus Christi Dallas El Paso Fort Worth Galveston Houston Laredo AFB Lubbock Midland Port Arthur San Angelo San Antonio Victoria Waco Wichita Falls
101 98 101 94 95 101 100 102 91 96 103 99 100 94 101 99 98 101 103
65 66 68 74 71 66 65 66 70 68 74 67 66 69 65 69 71 67 66
17 8 25 36 32 19 21 20 32 28 32 11 19 29 20 25 28 21 15
Utah Salt Lake City
97
63
5
Vermont Burlington
88
57
-12
Virginia Lynchburg Norfolk Richmond Roanoke
94 94 96 94
62 60 64 63
15 20 14 15
Washington, D.C. National Airport
94
63
16
Washington Olympia Seattle Spokane Walla Walla Yakima
85 85 93 98 94
51 51 58 57 62
21 20 -2 12 6
6 23 20 21 19 18
West Virginia
Station
Temperature (°F) Tm Tc Tw
South Dakota Huron Rapid City Sioux Falls
97 96 95
62 61 62
-16 -9 -14
Wisconsin Green Bay La Crosse Madison Milwaukee
88 90 92 90
59 62 61 60
-12 -12 -9 -6
Station Charleston Huntington (CO) Parkersburg (CO) Wyoming Casper Cheyenne Lander Sheridan
Temperature (°F) Tw Tm Tc 92 63 9 95 63 10 93 62 8
92 89 92 95
59 58 58 59
-11 -6 -16 -12
