1、 AASHTO TITLE SDTB-1 85 m Ob39804 0012400 718 m GUIDE SPECIFICATIONS for STRENGTH DESIGN OF TRUSS BRIDGES (Load Factor Design) 1985 DEVELOPED BY THE AASHTO SUBCOMMITTEE ON BRIDGES AND STRUCTURES Published by American Association of State Highway and Transportation Officials, Inc. COPYRIGHT American
2、Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SDTB-L 85 m 0639804 0032403 654 m GUIDE SPECIFICATIONS for STRENGTH DESIGN OF TRUSS BRIDGES (Load Factor Design) 1985 Published by the American Association of State Highway and Transportation
3、Officials, Inc., Executive Off ice located at 444 North Capitol Street, N.W., Suite 225 Washington, D.C. 20001 O Copyright 1986, by the American Association of State Highway and Transportation Officials, Inc. All Rights Reserved. Printed in the United States of America. This book, or parts thereof,
4、may not be reproduced in any form without written permission of the publishers. COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SDTB-L 85 0639804 0012402 590 HIGHWAY SUBCOMMITTEE ON BRIDGES AND STRUCTURES 1985 ROBERT C. C
5、ASSANO, CALIFORNIA, Chairman VELD0 M. GOINS, OKLAHOMA, Vice Chairman STANLEY GORDON, Federal Highway Administration, Secretary ALABAMA, Charlie H. Cook, B. A. Riddle ALASKA, Donald Halsted ARIZONA, Ron Brechler ARKANSAS, Vera1 Pinkerton CALIFORNIA, James E. Roberts, Robert C. Cassano COLORADO, Harol
6、d Henson CONNECTICUT, John Cavanaugh, Milton Q. Johnson, DELAWARE, Chao Hu D.C., Harry Moy, Gary Burch, Horace Jones FLORIDA, Henry T. Bollmann GEORGIA, Charles Lewis HAWAII, Clarence R. Yamamoto IDAHO, Richard Jobes ILLINOIS, James Raybum INDIANA, William B. Abbott IOWA, William Lundquist KANSAS, K
7、enneth F. Hurst KENTUCKY, Glen Kelly, Tom Layman LOUISIANA, Louis A. Garrido MAINE, James Chandler MARYLAND, Earle S. Freedman, James K. Gatley MASSACHUSETS, Robert Costello MICHIGAN, Ho Lum Wong MINNESOTA, Keith V. Benthin MISSISSIPPI, Bennie D. Verell MISSOURI, W. D. Carney MONTANA, Norman Rognlie
8、 NEBRASKA, James R. Holmes NEVADA, James Dodson, Ron Hill NEW HAMPSHIRE, Andrew J. Lane NEW JERSEY, Jack Freidenrich, Warren J. Sunderland NEW MEXICO, Martin A. Gavurnick NEW YORK, E. V. Hourigan Earle R. Munroe NORTH CAROLINA, James D. Lee, John L. Smith NORTH DAKOTA, Keith McLean OHIO, Walter J. J
9、estings OKLAHOMA, Veldo M. Goins OREGON, Walter J. Hart PENNSYLVANIA, Stephen R. Simco PUERTO RICO, Jorge L. Acevedo RHODE ISLAND, Richard Kalunian SOUTH CAROLINA, W. A. Boleman, J. R. Coleman SOUTH DAKOTA, K. C. Wilson TENNESSEE, R. L. Iddins, Jr., Clellon Loveall TEXAS, Wayne Henneberger U.S. DOT,
10、 Frank Sears (FHWA), Alfred T. Meschter UTAH, Dave Christensen VERMONT, Warren B. Tipp VIRGINIA, Fred G. Sutherland WASHINGTON, C. S. Gloyd WEST VIRGINIA, William D. Domico WISCONSIN, Stan Woods WYOMING, Charles H. Wilson ALBERTA, R. L. Foster GUAM, Casiano M. Bostre MANITOBA, G. A. DePauw MARIANA I
11、SLANDS, David M. Sablan NEW BRUNSWICK, G. A. Rushton NORTHWEST TERRITORIES, R. Ho NOVA SCOTIA, R. Shaffelburg ONTARIO, R. A. Dorton SASKATCHEWAN, L. J. Hamblin MASS. METRO. DIST. COMM., David Lenhardt N.J. TURNPIKE AUTHORITY, Paul M. Weckesser PORT AUTH. OF NY irw Wind“. for wind foticcs. nie number
12、 of fastcnen in a fiction splice or coa- nectionshaibedernrmned . baJed on the following over- Id provision for Group I Load Combinarion, ami by xrvi# loxi pnxxduns for ortier load combinations. D+f513XL+DsCl +(2n)RFvMA ForD5.m (2) GroupIIAisforthemmkndesionly D+L+ISF,MA ForD.m Wk R = (Live Load For
13、ce + ImpactMToral Force) F, = Pewissible Sms From Tables 10.323B and 10.32.3c M - Number of Bolts A = Am Per Boit 1.3 TRUSSMEMBERS The provisions of Artide 10.16.2 shaU apply, encqt th?t the i0,W pound aowaace for adjustable counien si About ttre Axis Pdic- 4 UktotbeBeadingAxis ing Axis L =LgthofMcm
14、bcT S, = Gross Effcctivc scctioa Modulus About Btnd- (B) For H-Shcrpcd Members Betu About Their Minor Axis: M, = 1.5 Fy S, (C) For H-Shclped Members, and Members with Chun- nei FIanges and a Web Plate. Bent Abou Their Major Axis: where: S, = Gross Effective Section Modulus About Bend- ing Axis COPYR
15、IGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SDTB-3 85 m Ob39804 0032406 336 m 1.8 STRENGTH DESIGN OF TRUSS BRIDGES 3 J = St. Venant Torsional Constant, Approximately Z bt3/3 h = Depth of Web Plate Plus Flange Thickness G =
16、 Shear Modulus K = Effective Length Factor for Column Buckling I, = Moment of Inertia About the Axis Perpendic- E = Youngs Modulus u, = Critical Elastic Lateral-Torsional Buckling About Weak Axis ular to the Bending Axis stress 1.9 COMPRESSION MEMBERS-THICKNESS OF METAL The center of gravity of a bu
17、ilt-up section shall co- incide as nearly as practicable with the center of the section. Preferably, segments shall be connected by solid webs or perforated cover plates. Plates supported on one side, outstanding legs of an- gles and perforated plates-For outstanding plates, the outstanding legs of
18、angles and perforated plates at the perforations, the b/t ratio of the plates or angle segments, when used in compression, shall not be greater than the value obtained by use of the formula: b 2200 / 182.6 _- - t - fia or where: fa = The Calculated Compressive Stress b = The Width (Defined as Indica
19、ted for Each t = The Plate or Web Thickness Expression) but in no case shall b/t be greater than 12 for main members and 16 for secondary members. (Note: b is the distance from the edge of the plate or edge of perforation to the point of support by weld or line of connections.) When the compressive
20、stress equals the limiting factor 0.85Fy, the b/t ratio of the segments indicated above shall not be greater than the ratios shown for the following grades of steel: 36,000 psi (248.211 MPa) Y.P. Min. b/t= 12 50,000 psi (344.737 MPa) Y.P. Min. b/t= 10 90,000 psi (620.527 MPa) Y.P. Min. b/t = 8.0 100
21、,000 psi (689.470 MPa) Y .P. Min. b/t= 7.5 Plates supported on two edges or webs of main com- ponent segments-For members of box shape, consisting of main plates, rolled sections, or made up component segments, with cover plates, the b/t ratio of the main plates or webs of the segments, when used in
22、 compres- sion shall not be greater than the value obtained by use of the formula: b 5700 or ( ) t fia fia (in ma) 473.1 - but in no case shall b/t be greater than 45. (Note: b is the distance between points of support for the plate and between roots of flanges for the webs of rolled segments.) When
23、 the compressive stresses equal the limiting fac- tor 0.85Fy, the b/t ratio of the plates and segments in- dicated above shall not be greater than the ratios shown for the following grades of steel: 36,000 psi (248.211 MPa) Y.P. Min. b/t=32 50,000 psi (344.737 MPa) Y.P. Min. b/t = 27 90,000 psi (620
24、.527 MPa) Y.P. Min. b/t=20 100,000 psi (689.470 MPa) Y.P. Min. b/t= 19 Solid cover plates supported on two edges or webs connecting main members or segments-For members of H or box shape consisting of solid cover plates or solid webs connecting main plates or segments, the b/t ratio of the solid cov
25、er plates or webs when used in compression shall not be greater than the value obtained by use of the formula: b - EOr ( ) t fia fl (in MPa) 560.3 but in no case shail b/t be greater than 50. (Nore: b is the unsupported distance between points of When the compressive stresses equal the limiting fac-
26、 tor 0.85Fy, the b/t ratio of the cover plate and webs indicated above shall not be greater than the ratios shown for the following grades of steel: support .) 36,000 psi (248.211 MPa) Y.P. Min. b/t=38 50,000 psi (344.737 MPa) Y.P. Min. b/t=32 90,000 psi (620.527 MPa) Y.P. Min. b/t=24 100,000 psi (6
27、89.470 MPa) Y.P. Min. b/t=23 Perforated cover plates supported on two edges-For members of box shape consisting of perforated cover plates connecting main plates or segments, the b/t ratio of the perforated cover plates when used in compression COPYRIGHT American Association Of State Highway and Tra
28、nsportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SDTB-L 5 m 0639804 0032407 072 m 4 STRENGTH DESIGN OF TRUSS BRIDGES 1.9 shall not be greater than the value obtained by use of the formula: b=80000r( 664.3 t fia fia (in MPa) ) - but in no case shall b/t be greater than 55. (Not
29、e: b is the distance between points of support. At- tention is directed to requirements for plate thick- ness at perforations, namely plate supported on one side, which also shall be satisfied.) When the compressive stresses equal the limiting fac- tor 0.85Fy, the b/t ratio of the perforated cover p
30、lates shall not be greater than the ratios shown for the following grades of steel: 36,000 psi (248.211 MPa) Y.P. Min. b/t=45 50,000 psi (344.737 MPa) Y.P. Min. b/t = 38 90,000 psi (620.527 MPa) Y .P. Min. b/t = 29 100,000 psi (689.470 MPa) Y.P. Min. b/t=27 The point of support shall be the linear l
31、ine of fasteners or fillet welds connecting the plate to the main segment. For plates butt welded to the flange edge of rolled seg- ments, the point of support may be taken as the weld whenever the ratio of outstanding flange-width-to-flange- thickness of the rolled segment is less than seven. Oth-
32、erwise, point of support shall be the root of flange of rolled segment. Terminations of the butt welds are to be ground smooth. 1.10 EYEBAR PINS The maximum bearing stress on eyebar pins shall be 1.35 F,. Eyebar pins shall be proportioned for shear and bend- ing to satisfy the following interaction
33、equation and all other provisions of the Standard Specijcations for High- way Bridges not related to shear, bending and bearing. 3 D3 Fy + (E) 4 0.95 where: D = Diameter of Pin M = Factored Moment V = Factored Shear The applied bending moment and shear shall act si- multaneously on the design sectio
34、n of the pin. 1.11 GUSSET PLATES Gusset plates shall be designed for shear, bending and axial load by the conventional “Method-of-Section” pro- cedures used for service load design. The maximum stress from combined factored bending and axial loads shall be the yield stress based on the actual area,
35、Le., no “plastic shape factors” or other parameters which imply plastification of the cross-section shall be used. The maximum shear stress on a section shall be Fy/fl for uniform shear and 0.74 F,/fi for bending shear computed as shear force divided by area. Design checks of gusset edges (stiffened
36、 and unstif- fenedj shall be performed on the same idealized column section as currently used in service load design. The load factor capacity of the column is evaluated using the strenth design procedures described herein. If the length of unsupported edge of a gusset plate exceeds the value of the
37、 expression 11,OOO/fl or (913/* (in MPa) times its thickness, the edge shall be stiffened. Listed below are the values of the expression 11 ,OW/ fl or (913/* (in MPa) for the following grades of steel: 36,000 psi (248.211 MPa) Y.P. Min. b/t=58 50,000 psi (344.737 MPa) Y.P. Min. b/t=49 90,000 psi (62
38、0.527 MPa) Y.P: Min. b/t = 37 100,000 psi (689.470 MPa) Y.P. Min. b/t = 35 COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling Servicese -. . c. AASHTO TITLE SDTB-3 85 m 0639804 0032408 TO9 m STRENGTH DESIGN OF TRUSS MEMBERS: COMMENTARY (Load Fac
39、tor Design) 1.2 LOAD FACTORS The Group I load factors currently in the AASHTO Specifications are: Maximum Design Load = 1.3D + (513) (L + i) This is shown as Curve “A” on Figure 1 which relates factor of safety for bending and tension members to the percent of total load which is either dead load (u
40、pper scale), or live load plus impact (lower scale). The con- ventional factor of safety against first yield in the service load method is 1.82 and this is shown as Curve “B”. It has not been uncommon in long span bridge design to ailow 10 percent overstress in members carrying mostly dead load. Thi
41、s corresponds to a factor of safety of 1.65. The transition to the 10 percent allowable overstress has often occurred when the dead load is more than 75 percent of the total load. This is shown as Curve “C”. The Group I load factors originally proposed herein were de- veloped by starting with a line
42、 which would intercept, (1) the point corresponding to a factor of safety of 1.65 at 75 percent dead load and, (2) the point at which the AASHTO service load and load factor design methods have the same factor of safety, i.e., 40 percent dead load. However, in lieu of the proceeding discussion, the
43、load factor relation for Group I, as determined by Committee action will be: 1.3 D + (513) (L + 111 $. 1.5 D + L + 11 The second relationship provides a minimum factor of safety of 1.5. It will control for those members where dead constitutes 77 percent or more of the total load. These load factors
44、are shown as the heavy curve on Figure 1. The proposed load factors for groups other than Group I have been selected to yield essentially the same results as service load design. Group UA is specifically intended for lateral truss members. 5 1.8 COMPUTATION OF MEMBER CAPACITY The interaction equatio
45、n for tension members contains two simplifying assumptions. The first is that the shape of the interaction equation is a straight line joining the points (P = P, M = O) and (P = O, M = Mp). This is known to be a conservative assumption for wide flange shapes bent about their major axis and rectangul
46、ar shapes. All shapes under consideration can be considered in this range. The second assumption is that the plastic shape factor for net section is the same as the plastic shape factor for gross effective sections. These are reasonable assumptions, especially considering that the moment por- tion o
47、f the interaction curve is usually less than 5 percent of the total. Two interaction equations for compression members are basically as discussed in AASHTO Article 10.54.2.1. Typical box-shaped truss members have such high lat- eral-torsional stiffness that the reduction in bending strength arising
48、from lack of lateral support is minimal. The re- duction in bending capacity computed by the recom- mended equation is usually small for truss box members of usual proportions. The recommended equations for H-shaped members bent about their major axis are the equations from which the bending allowab
49、le stresses in Table 10.32.1A were developed. The more rigorous solution is required for truss members because of their long unbraced lengths. 1.9 COMPRESSION MEMBERS-THICKNESS OF METAL Critical elastic buckling stress for plates can be written as: K IT E = 12(1 - p2) (b/t)2 Substituting E = 29,000,000 psi and p = 0.3, and solving for b/t yields: COPYRIGHT American Association Of State Highway and Transportation OfficeLicensed by Information Handling ServicesAASHTO TITLE SDTB-1 5 W 0639804 0012409 945 6 STRENGTH DESIGN OF TRUSS BRIDGES 1.9 I FAASHTO SERVICE LOA
