1、 To recipients of the Guide Design Specifications for Bridge Temporary Works, First Edition (1995): Instructions Interim revisions have been made to the Guide Design Specifications for Bridge Temporary Works, First Edition (1995). They have been designed to replace the corresponding pages in the boo
2、k and are numbered accordingly. Underlined copy indicates revisions that were approved in 2007 by the AASHTO Highways Subcommittee on Bridges and Structures. A listing of newly changed and deleted articles is included with these interim revisions as an addendum to the preface of the book. All revise
3、d pages also display a box in the lower outside corner indicating the interim publication year. Any non-technical changes in page appearance will be indicated by this revision box alone to differentiate such changes from those which have been approved by the AASHTO Highways Subcommittee on Bridges a
4、nd Structures. To keep your Specifications correct and up-to-date, please replace the appropriate pages in the book with the pages in this packet. ii American Association of State Highway and Transportation Officials Executive Committee 19941995 Voting Members Officers: President: Wayne Shackelford,
5、 Georgia Vice President: Bill Burnett, Texas Secretary/Treasurer: Clyde E. Pyers, Maryland Regional Representatives: Region I Patrick Garahan, Vermont Region II Ben Watts, Florida Region III Darrel Rensick, Iowa Region IV Larry Bonine, Arizona Non-Voting Members Executive Director: Francis B. Franco
6、is, Washington, D.C. 2008 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.1 Interim2008 Section 1 INTRODUCTION 1.1 SCOPE This guide design specification has been developed for use by State agencies to include
7、 in their existing standard specifications for falsework, formwork, and related temporary construction used to construct highway bridge structures. The specification should also be useful to bridge engineers, falsework designers, contractors, and inspectors. Sections within this specification addres
8、s falsework, formwork, and temporary retaining structures. Reference standards, related publications, and definitions are identified below. 1.2 REFERENCES 1.2.1 Codes and Standards Standard Specifications for Highway Bridges, 17th Edition, American Association of State Highway and Transportation Off
9、icials, Washington, DC. Errata to the Standard Specifications for Highway Bridges, 2003, American Association of State Highway and Transportation Officials, Washington, DC. Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-03), Federal Highway Administrati
10、on, Washington, DC. American National Standard for Construction and Demolition Operations: Concrete and Masonry Work-Safety Requirements (ANSI A10.9-1997), American National Standards Institute, New York, NY. American National Standard for Construction and Demolition Operations: Safety and Health Pr
11、ogram Requirements for Multi-Employer Projects (ANSI A 10.33-1998), American National Standards Institute, New York, NY. Manual of Steel Construction, Thirteenth Edition, American Institute of Steel Construction, Chicago, IL. Structural Welding Code-Steel (AWS D1.1/D1.1M-06), American Welding Societ
12、y, Miami, FL. National Design Specification for Wood Construction, 2005 Edition, National Forest Products Association, Washington, DC. NDS Supplement-Design Values for Wood Construction, National Forest Products Association, Washington, DC. Building Code Requirements for Reinforced Concrete (ACI 318
13、-05) and Commentary (ACI 318R-05), American Concrete Institute, Detroit, MI. Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-05), American Society of Civil Engineers, New York, NY. Uniform Building Code, 1997 Edition, International Conference of Building Officials, Whittier, CA.
14、The BOCA National Building Code/1999, Building Officials d is the least dimension of rectangular columns, or the width of a square of equivalent cross-sectional area for round columns, or the depth of beams; b is the width and t is the thickness of the compression flange; and r is the radius of gyra
15、tion of the member. 2.1.2.3 Welding All provisions of the Structural Welding Code, AWS D1.1/D1.1M, of the American Welding Society, except 2.3.2.4, 2.5, 8.13.1.2, and Section 9, as appropriate, apply to work performed under this specification. 2.1.3 Timber 2.1.3.1 Allowable Stresses All species of w
16、ood to which allowable unit stresses have been assigned in the National Design Specification for Wood Construction (NDS) Supplement are acceptable for use in falsework. Design working stresses for new lumber shall not exceed the design values for visually graded dimension lumber and visually graded
17、timbers as tabulated in the National Design Specification for Wood Construction (NDS) Supplement. The listed values are for normal load duration and dry service conditions, and shall be modified as provided herein. 2.1.3.2 Modification Factors Modification factors for service conditions and duration
18、 of load shall be as prescribed by NDS except that the normal service condition for falsework members shall be considered to be dry and reduction for wet service conditions will not apply. All modification factors are cumulative. Load duration factors shall not apply to values for modulus of elastic
19、ity or compression perpendicular to the grain. 2008 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.7 Interim2008 2.2.4 Minimum Vertical Load The minimum total design vertical load for any falsework member sh
20、all be not less than 100 psf (4800 N/m2) for the combined dead and live load, exclusive of any increase for impact, regardless of slab thickness. 2.2.5 Environmental Loads 2.2.5.1 Wind For heavy duty shoring systems having a vertical load-carrying capacity exceeding 30 kips (130 N) per tower leg, th
21、e minimum horizontal load to be allowed for wind shall be determined in accordance with Chapter 23, Part II of the Uniform Building Code (reproduced in Appendix C). The wind impact area shall be the total projected area of all elements in the tower face normal to the applied wind. The basic wind pre
22、ssure for each height zone shall be increased by 5 psf (240 N/m2) for falsework members over or adjacent to traffic openings. The minimum horizontal load to be allowed for wind on all other types of falsework, including falsework supported on heavy duty steel shoring, shall be the sum of the product
23、s of the wind impact area and the applicable wind pressure value for each height zone listed on Table 2.2. The basic wind speed used in the determination of design wind loads shall be as given in Fig. 2.1. The wind impact area shall be the gross projected area of the falsework and any unrestrained p
24、ortion of the permanent structure, excluding the areas between falsework posts or towers where diagonal bracing is not used. The basic wind pressure for each height zone shall be increased by 5 psf (240 N/m2) for falsework members over or adjacent to traffic openings. 2.2.5.2 Stream Flow When falsew
25、ork supports are placed in flowing water, water pressure on the supports shall be determined by the following formula: 2wPKv.=(2-1) in the formula, Pwis the pressure in psf; v is the water velocity in fps; and K is a constant that shall take the following values: 1.375 for square faces 0.67 for circ
26、ular piers 0.5 for angular faces Where a significant amount of drift lodges against a pier is anticipated, the effects of this drift build-up shall be considered in the design. When it is anticipated that the flow area will be significantly blocked by drift build-up, increases in high water elevatio
27、ns, stream velocities, stream flow pressures, and the potential increases in scour depths shall be investigated. 2.2.5.3 Snow Where necessary, the effects of snow shall be considered, and determined in accordance with ASCE 7. Table 2.2 Wind Pressure Values (P = CeCqqsI)(a)Pressure, psf for Indicated
28、 Wind Velocity, mph Height Zone (ft above ground) 70 80 90 100 0 to 30 1.5 Q 2.0 Q 2.5 Q 3.0 Q 30 to 50 2.0 Q 2.5 Q 3.0 Q 3.5 Q 50 to 100 2.5 Q 3.0 Q 3.5 Q 4.0 Q over 100 3.0 Q 3.5 Q 4.0 Q 4.5 Q Notes: (a) Refer to Appendix C for specific information on variables. When using U.S. Customary Units, th
29、e value of Q in Table 2.2 shall be determined as follows: Q = 1 + 0.2 W, but not more than 10. In the preceding formula, W is the width of the falsework system, in ft, measured in the direction of the wind force being considered. (b) Conversion: 1 ft = 0.3048 m; 1 psf = 47.88 N/m2; 1 mph = 1.609 km/
30、hr 2008 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.8 Notes: (a) Values are fastest-mile speeds at 33 ft (10 m) above ground for exposure category C and are associated with an annual probability of 0.02.
31、(b) Linear interpolation between wind speed contours is acceptable. (c) Caution in the use of wind speed contours in mountainous regions of Alaska is advised. (d) Conversion: 1 mph = 1.609 km/hr; 1 mi = 1.61 km Figure 2.1 Basic Wind Speed (mph) 2.3 DESIGN 2.3.1 General The falsework design analysis
32、shall consider the effect of foundation settlement, interaction between elements of the falsework system and completed portions of the permanent structure, and load redistribution due to shrinkage and dead load deflection. The falsework design shall accommodate these factors if necessary. For cast-i
33、n-place prestressed construction, the falsework shall be designed to support any increased load resulting from load redistribution caused by the prestressing forces. The entire superstructure cross section, except railing, shall be considered to be placed at one time except as otherwise provided her
34、ein. Girder stems and connected bottom slabs, if placed more than 5 days prior to the top slab, may be considered to be self-supporting between falsework posts at the time the top slab is placed, provided that the distance between falsework posts does not exceed four times the depth of the portion o
35、f the girder placed in the first pour. The support system for form panels supporting concrete deck slabs and overhangs on girder bridges shall be considered to be falsework and 2008 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violat
36、ion of applicable law.9 shall meet all falsework design criteria and requirements. Additionally, such falsework shall be designed so not differential settlement will occur between the girders and the deck forms during placement of the deck concrete. 2.3.2 Load Combinations The groups given in Table
37、2.3 represent combinations of loads and forces to which the falsework may be subjected. All elements of the falsework, or the foundation upon which it rests, shall be designed to resist the Group I, II, III, and IV load combinations at the percentage of the basic allowable stress shown. 2.3.3 Stabil
38、ity Against Overturning The falsework system, including individual elements and units of the system that are subject to overturning forces, shall be analyzed for stability against overturning with the falsework in the loaded and unloaded condition; that is, with and without the dead load of the conc
39、rete. The ratio of the resisting moment to the overturning moment shall be equal to or greater than 1.2 for all load combinations. Except as otherwise provided in the following paragraph, if the ratio of the resisting to the overturning moments is less than 1.2, external bracing shall be provided to
40、 resist the full overturning moment. Except for bracing required to prevent overturning or collapse of the falsework system or any element of the system, the ability of falsework members to resist horizontal loads may include the contribution to stability provided by the supported structure. Bracing
41、 required to prevent overturning or collapse shall be designed to resist the full horizontal design load with the falsework in the unloaded (before the concrete is placed) condition, except for cable bracing used to externally brace heavy-duty shoring systems. Such cables may be designed to resist t
42、he difference between the overturning and resisting moments. 2.3.4 Combined Stresses The adequacy of falsework members subjected to both axial and bending stresses shall be determined by the following combined stress expression: ffab1.0,FFab+ (2-2) where, respectively, faand fbare the calculated axi
43、al and bending stresses and Faand Fbare the allowable axial and bending stresses. 2.3.5 Deflection The calculated vertical deflection for falsework members shall not exceed 1/240 of their span under the dead load of the concrete only, regardless of the fact that deflection may be compensated for by
44、camber strips. Table 2.3 Load Combinations Group Load Combinations Percentage of Basic Allowable Stress or Load Group I DL + DP + LL + I + H 100% Group II DL + DP + PS + H 100% Group III DL + DP + LL + I + W + ALL 133% Group IV DL + DP + LL + PS + W + ALL 133% where DL = design dead load; DP = dead
45、load of supported permanent structure; LL = construction live load; I = impact load; H = minimum horizontal design load; PS = redistributed prestress load; W = wind load; ALL = all other loads, including stream flow and snow. 2008 by the American Association of State Highway and Transportation Offic
46、ials.All rights reserved. Duplication is a violation of applicable law.10 Interim 2008 2.3.6 Slenderness For compression members, the slenderness ration, Kl/r, shall not exceed the following: (a) Main load-carrying members: (i) Steel180; (ii) Aluminum100. (b) Bracing members: (i) Steel200; (ii) Alum
47、inum150. The slenderness ration of a tension member, other than guy lines, cables, and rods, shall not exceed 240 for a main member nor 300 for a bracing member. These limits may be waived if other means are provided to control flexibility, sag, vibration, and slack in a manner commensurate with the
48、 service conditions of the structure, or if it can be shown that such factors are not detrimental to the performance of the structure or of the assembly of which the member is a part. 2.3.7 Steel Beam Grillages Webs and flanges of steel beams under concentrated loads shall satisfy the criteria speci
49、fied in Chapter K, AISC Specification for Structural Steel Buildings-Allowable Stress Design and Plastic Design, reproduced in Appendix B. 2.3.8 Proprietary Shoring Systems Differential leg loading of vertical shoring systems shall be minimized. In cases where differential leg loading cannot be avoided, the manufacturer of the shoring system shall furnish a letter of certification stating that the proposed loading differential will not overstress any tower component. 2.3.9 Traffic Openings The vertic
