It is essential that the effect of individual member

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level, and line. It is essential that the effect of individual member tolerances on the overall structural steel frame be recognized and accounted for with practical detailing and fabrication techniques that permit compliance with overall tolerances. Other General Information How are tolerances determined if they are not addressed in the applicable standards ? The fabrication and erection tolerances in the AISC LRFD Specification for Structural Steel Buildings, the AISC Code of Standard Practice for Steel Buildings and Bridges , AWS D1.1, and other existing specifications and codes have evolved over nearly three-quarters of a century. Although these standards generally present a workable for- mat for the fabricator and erector, they tend to address individual members, rather than the role of individual members in the completed structure. Tolerances for assemblies, such as those on shop-assembled bents, frames, platforms, pairs of girders, etc., are not covered by any code or standard. AWS D1.1 Section 5.23.11.4 states that "... other dimensional tolerances
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APPENDIX PAGE 16 of members not covered by [Section] 5.23 shall be individually determined and mutually agreed upon by the con- tractor and the owner with proper regard for erection requirements." This practice is recommended in all cases. The agreed upon tolerances should account for the erection tolerances specified in the AISC Code of Standard Practice . If special or more restrictive tolerances are required for the overall structural steel frame, can they be met ? Possibly, but at a higher cost. Special clearances or tolerances may be difficult or impossible to achieve because of considerations such as temperature change, fabrication and construction procedures, and erection stresses. When specified, such requirements must be identified in the contract documents. The additional cost of special or more restrictive tolerance requirements should be justified. How can the accumulation of mill, fabrication, and erection tolerances be economically addressed ? While individual member tolerances are usually self-compensating and of minor significance in the overall struc- ture, the possibility exists that these tolerances may accumulate and lead to misalignments that are difficult to cor- rect in the field. As an example of the effect individual member tolerances may have on the total structure, con- sider the tolerances on columns and beams. Individual column and beam members are shown with their respec- tive permissible tolerances in Figure 2. These tolerances come from several sources: permissible camber and sweep are specified in ASTM A6/A6M and AWS D1.1; permissible variation from detailed length for members framed to other steel parts is specified in the AISC Code of Standard Practice ; mill tolerances on the cross-sec- Figure 2. Beam and column fabrication tolerances Figure 3. Possible (but unlikely) accumulation of tolerances when details are located from actual centerlines.
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PAGE 17 APPENDIX tion are illustrated in the 2000 AISC Code of Standard Practice Figure C-5.1. The foregoing example involves
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  • Structural steel

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