1、AASHTO TITLE SLWD 91 = Ob39804 0012510 548 W Published by the American Association of State April 1991 Highway and Transportation Officia.; 444 North Capitol Street, N.W., Suite 225 Washington, D.C. 20001 COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Informatio
2、n Handling Servicese . a a AASHTO TITLE SLWD 91 m Ob39804 OOL25LL 484 m Published by the American Association of State Highway and Transportation Offcials 444 North Capitol Street, N.W., Suite 225 Washington, D.C. 20001 April 1991 Copyright, 1991, by the American Association of State Highway and Tra
3、nsportation Officials, Inc. Alf rights reserved. Printed in the United States of America. This book, or parts thereof, may not be reproduced in any form without permission of the publishers. COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling Ser
4、vicesAASHTO TITLE SLWD 91 m Ob39804 0012512 310 m American Association of State Highway and Transportation Officials Executive Committee 1991 President: Hal Rives, Georgia Vice President: SecretarylTreasurer : Immediate Past President: A. Ray Chamberlain, Colorado Clyde E. Pyers, Maryland Kermit Jus
5、tice, Deleware Elected Regional Members: Region I Region II Region III Region IV Howard Yerusalim, Pennsylvania, 1991 Thomas Downs, New Jersey, 1991 Jimmy Evans, Tennessee, 1991 Thomas Harrelson, North Carolina, 1992 Darrel Rensink, Iowa, 1991 Christine Letts, Indiana, 1992 Eugene Findlay, Utah, 199
6、1 Richard Howard, South Dakota, 1992 Chairpersons of Standing Committees: John R. Tabb, Mississippi, Washington, Administration Ray Pethtel, Virginia, Planning Arnold Oliver, Texas, Highways Ronald Fieldler, Wisconsin, Highway Traffic Safety Franklin E. White, New York, Water Transportation Ben G. W
7、atts, Fiorida, Aviation Duane Berentson, Washington, Public Transportation Darrel Rensink, Iowa, Railway Conference Robert N. Bothman, Oregon, Research Bobby Hopper, Arkansas, Special Committee of Commissioners and Boards Ex Officio Members: Past President: John R. Tabb, Mississippi Secretary of Tra
8、nsportation: Samuel K. Skinner Executive Director: Francis B. Francois ii COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SLWD 91 = Ob39804 0012513 257 HIGHWAY SUBCOMMITTEE ON BRIDGES AND STRUCTURES 1990 CLELLON LOVEALL,
9、TENNESSEE, Chairman THEODORE H. KARASOPOULOS, MAINE, Vice Chairman STANLEY GORDON, Federal Highway Administration, Secretary ALABAMA, Fred Conway, C. H. McPherson ALASKA, Karl Mielke ARIZONA, Dennis Grigg ARKANSAS, Veral Pinkerton CALIFORNIA, James E. Roberts COLORADO, A. J. Siccardi CONNECTICUT, Cl
10、ement Zawodniak, Daniel Coffey DELAWARE, Chao Hu D.C., Gary Burch FLORIDA, Tony Garcia GEORGIA, Paul Liles HAWAII, Donald C. Ornellas IDAHO, Richard Jobes ILLINOIS, Ralph E. Anderson INDIANA, Jack White IOWA, William A. Lundquist KANSAS, Kenneth F. Hurst KENTUCKY, Glen Kelly, Arthur W. Duncan LOUISI
11、ANA, Norval Knapp MANE, James Chandler, Theodore H. Karasopoulos MARYLAND, Earle S. Freedman, James K. Gatley MASSACHSEITS, Paul J. Sullivan MICHIGAN, (vacant) MINNESOTA, D. J. Flemming MISSISSIPPI, Bennie D. Verell MISSOURI, AI Laffoon MONTANA, James C. Hill NEBRASKA, Lyman D. Freemon NEVADA, Rod J
12、ohnson NEW HAMPSHIRE, James F. Marshall NEW JERSEY, Kenneth Afferton, Robert Pcge NEW MEXICO, Martin A. Gavumick NEW YORK, Arun Shirole, Michael J. Cuddy, NORTH CAROLINA, James D. Lee, John L. Smith NORTH DAKOTA, Forest Durow OHIO, G. David Hanhiammi John M. Robb OKLAHOMA, Veldo M. Goins OREGON, Tom
13、 Lulay PENNSYLVANIA, Mahendra G. Patcl PUERTO RICO, Jorge L. Acevedo RHODE ISLAND, Richard Kalunian, Richard P. Snow SOUTH CAROLINA, Ben Meetzc, Jr., SOUTH DAKOTA, Clyde H. Jundt TENNESSEE, Clellon Loveall, Ed Wasserman EXAS, Luis Ybanez U.S. DOT, Stanley Gordon, (FHWA), Nick E. Mpras (USCG) UTAH, D
14、ave Christensen VERMONT, Warren P. Tripp VIRGINIA, Fred G. Sutherland WASHINGTON, Allan H. Wailey WEST VIRGINIA, James Sothen WISCONSIN, Stanley W. Woods WYOMING, David Pope ALBERTA, R.W. Komelsen MANITOBA, W. Saltzberg MARIANA ISLANDS, Nick C. Sablan NEW BRUNSWICK, G. A. Rushton NEWFOUNDLAND, Peter
15、 Lester NORTHWEST TERRITORIES, Jivko Jivkov NOVA SCOTIA, R. Shaffelburg ONTARIO, Roger A. Dorton SASKATCHEWAN, Lome J. Hamblin MASS. METRO. DIST. COMM., David Lenhardt N. J. TURNPIKE AUTHORITY, Paul M. Weckesser PORT AUTH. OF NY = deck thickness in inches. VT = - P (l0.4 -;) (13-24) lo00 The moment
16、MT shall be taken as: where: for one-lane bridges: VT = transverse shear in Ibs./inch; P = maximum single wheel load in lbs. hfT = (1 3-2 1) 13.11.1.3 The initial prestress applied to the deck shall compensate for losses due to creer) and relaxation. The decklshall be laminated with an initial minim
17、um compressive prestress (pi) calculated as follows: for two-lane bridges with spans less than 50 feet: ( 13-22) where: MT = the transverse moment in inch-lbs/inch; Mx = the longitudinal moment caused by a single wheel line in inch-lbs.; b = half of the deck width in inches; L = the span length of t
18、he deck in inches; Cbj = the butt joint factor from Article 3.25.5.4. ( 13-25) where: p = required minimum prestress in psi; pi = required initial minimum prestress during prestressing in psi. And, the deck shall be restressed to the same level during the second and again between the fifth and eight
19、h weeks after the first laminating. 13.11.2 Prestressing 13.11.1.2 Case B -Transverse shear: 13.11.2.1 Prestressing Steel The minimum prestress between laminae required to resist transverse shear through friction shallbecalculated as: 1.5V-r p=- ptd where: p = prestressinpsi; b = deck thickness in i
20、nches; p = 0.35 for surfaced wood or p = 0.45 for rough sawn wood, and VT shall be taken as follows: (13-23) Prestressing steel shall be as required in Article 9.3.1 of the Standards. All prestressing steel shall be provided with corrosion protection. In the case of high strength steel threadbar the
21、 protection of bars, anchor nuts, and couplers may be obtained through hot-dip galvanizing as specified in AASHTO Mlll and care may need to be taken with regard to reduction of strength or brittleness as specified in ASTM A143. Wire or strand, provided with corrosion protection, as specified in Arti
22、cle 9.3.1 of the Standards may be used to replace threaded bars after the final restressing but shall not be restressed unless threaded type anchors are used. 13.11.2.2 Prestress Spacing The maximum spacing of prestressing elements shall not exceed 60 inches. Spacing will be determined with consider
23、ation of the type of prestressing system utilized and requirements of Article 13.11.2.3. COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SLWD 91 = Ob39804 0012519 775 4 I DESIGN OF STRESS-LAMINATED WOOD DECKS 13.11.2.3 Pr
24、estress Element Sizing - where: Stresses in the prestressing materials shall be limited to the levels specified in Article 9.151 of the Standards. The required minimum prestressing element area shall be determined to provide the required initial prestress with the steel at the selected spacing. (13-
25、26) where: As = required minimum area of the prestressing pi = the required minimum initial prestress s = the spacing of prestressing elements in td = the deck thickness in inches; fs = the maximum allowed stress in the element in square inches; in psi; inches; prestressing element as spe pi = requi
26、red minimum initial prestress in psi; s = spacing of prestressing elements in inches; = deck thickness in inches; Fc = allowable compression perpendicular to grain in psi. . When plates are used the minimum plate thickness shall be calculated from the following: (1 3-29) where: tp = minimum required
27、 bearing plate thickness fbp = the actual bearing stress under the phte Fs = the allowable bending stress in the plate in inches; selected in psi; steel as specified in Table 10.32.1A of the Standards; and, the factor “k“ in inches depends on the shape of the bearing plate and anchorage plate (if us
28、ed) and is taken as the greater of (WP-WA)/2 or (L-LA)/ as shown in Figure 13.1 1.2.4A, where: W, Lp are bearing plate dimensions in inches, WA, LA are anchorage plate dimensions in inches (if used). t COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information H
29、andling ServicesAASHTO TITLE SLWD 93 m Ob39804 0032520 497 m GUIDE SPECIFICATIONS 5 Figure 13.11.2.4A Bearing plate f ,Anchorage plate 13.11.3 Deflections 13.113.2 Long-term deflections shall be assumed equal to three times the instantaneous deflection caused by the dead load. Sufficient camber shal
30、l be provided, when feasible, to compensate for long-term sustained load deflections. 13.113.1 Deflection computations shall be based on assumed beam action with the cross-section properties specified in Article 3.25.5 under the appropriate loadings unless a more exact method is used. Service load d
31、eflec- tions shall be limited to L/5OO. COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SLWD w, m o34 OOLSL 323 m 6 I DESIGN OF STRESS-LAMINATED WOOD DECKS This page left intentionally blank COPYRIGHT American Association
32、 Of State Highway and Transportation OfficeLicensed by Information Handling Servicesc3.25.5 AASHTO TITLE SLWD 91 = Ob39804 0032522 2bT M COMMENTARY 7 COMMENTARY ON DESIGN PROCEDURES Stress-laminated timber decks are essentially large orthotropic wood plates setting on two or more linear supports. Th
33、eir practical design, however, is basedon the assumption that a portion of a deck directly under a line of wheels loads acts as a kam spanning between sup- ports. This simplification can only be made if the deck configuration meets spccific criteria which were as- sumed in developing the simplified
34、approach. The con- struction requirements which are noted must be followed. It is particularly necessary to control the skew at the deck supports. Decks with skewed ends can exhibit substantially different load carrying behavior from that found in rectiingular decks. While normal deck design assumes
35、 that loads arc carried longitudinally by a portion of the deck under the wheels, a skewed deck tends to have load carried along diagonals toward the corners of the supports or abutments. If the skew is less than 15 degrecs then this variation is small and can be neglected. c3.25.5.2 Actual orthotro
36、pic plate analyses (Batchelor 1981, Dimakis 1987:) prove that significant distribution widths can be obtained in stress-laminated decks. The simplified provisions included in this section arc conservative es- timates of the width. c3.25.5.4 The stress laminating procedure can effectively splice lami
37、nae which are butt jointed. This is accomplished by transferring the moment and shear from the butt end into adjacent laminae and carrying forces around the splice. Obviously there must be limitations on the number of laminae which are spliced in this fashion at any section. Furthermore, the butt jo
38、inting results in a reduced cross section afecting strength and stiffness. Thus, the effec- tive cross section to be used in structurai calculations must reflect the reduction in section area by using the butt joint factor Cbj. C13.2.7 The values for allowable strcss for wood, as tabulated in AASHTO
39、, were established for single nieniber use. The values are set at a level which should insure that 95 percent of the material will have a strength greater than the limiting value. When multiple members are com- bined together, as in glue-laminated material, the strengths of the assemblages have less
40、 variation than apparent in individual pieces. The assemblage strength more often reaches the average strength of the wood since all the pieces in the assemblage have to fail before the assemblage fails. As the assemblage strength ap- proaches the average material strength there is less variability
41、in the failure level. Since less variability ex- ists, a higher allowable strength may be used. Research at Forintek (Sexsmith, 1979) involving morc than 100 tests of members and stress-laminated assemblages indi- cated that 95 percent of the assemblrige test strengths were 83 percent stronger than
42、the fifth percentilemember strength for #1 and #2 white pine. The assemblage test strengths were 50 percent higher for #1 and #2 Hem-Fir. Similar studies on glue-laminated material (Wolfe, 1979) showed equal or greater increases in reliability of assemblage capacity. The increase in strength of the
43、assemblage is in reverse proportion to the quality, and hence low variability, of the individual material pieces. The suggested stress increases of 30 percent for high grade material and SO percent for low grade material is based on the results obtained by Sexsmith. C13.11 The provisions for design
44、of stress-laminated decks are based on completed research and prototype studies. The provisions are not applicable to material for which COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SLWD 91 Ob39804 0012523 1Tb W 8 / DE
45、SIGN OF STRESS-LAMINATED WOOD DECKS stress-laminating has not been proven. Identification of characteristics of behavior of stress-laminated decks has been accomplished for a limited number of wood species: Douglas fi-larch, Hem-Fir (north), Red pine, and Eastern White pine through research in Ontar
46、io (Batchelor) and the United States (Dimakis, Oliva). Other types of materials are currently being investigated. The individual properties of different wood species may have a strong impact on the loss of prestress over time, loss of prestress due to humidity or moisture content variations, and the
47、 friction between laminae. Oil-borne preservatives should be used in stress- laminated construction to protect the material from mois- ture and possible moisture content changes. Moisture content variation is accompanied by swelling and shrinkage which can change the prestress level. To avoid substa
48、ntial loss of prestress as the timber ries, the mois- ture content of the material at the time of stress-laminat- ing should approximate the likely long-term moisture content in the bridge environment. Research (Mc- Cutcheon, 1986) has shown that a moisture content of 18 to 19 percent might be typic
49、al for in-service bridges. C13.11.1 The level of prestress in the deck must be sufficient to resist internal transverse shear and flexural forces caused by a vehicle wheel load. Transverse shear and transverse bending moments are induced between the laminae in the deck. The laminae are prevented from slipping vertically with respect to each other by the high friction force which results from the laminae beingcom- pressed together. Since the laminae are not glued together flexural tension stresses cannot possibly develop; this shortcoming is overcome by inducing precompression
