Click for next page ( 2


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 1
STEEL BRIDGE ERECTION PRACTICES SUMMARY The erection of steel bridges, depending on the complexity of the structure, may pose critical issues for owners. Given such complexity, plus the great variety of practices being used today, there are often concerns with the integrity, speed, safety, quality, delays, and claims related to steel bridge erection. The number of curved structures and structures with complex geometry that are being constructed adds considerably to the type of steel erection issues that owners, designers, fabricators, erectors, and contractors are faced with at one time or another. A com- pilation of the methods employed by agencies or firms involved in all phases of a project, from design through construction, may be informative and may minimize these difficulties. This synthesis reports the results of and analyzes questionnaires, telephone conversations, specification reviews, and research reports solicited from states, Canadian provinces, fabrica- tors, and erector and contractors. A total of 111 questionnaires were distributed, with responses received from 30 states, 2 provinces, 15 fabricators, and 4 erector/contractors. The report concentrates on girder bridges--both I-girders and box girders. The erection of steel girder bridges is both craft and science. Erection practices are based on experience, rules of thumb, and intuition. Successful erection demands both an effective implementation of these practices, the craft, and a design that has appropriately considered principles of stability, the science. This synthesis addresses the craft. Most of the common problems that occur during erection can be prevented by taking the following measures: Verifying horizontal and vertical alignment before and during erection; Installing enough crossframes to maintain geometry and girder stability during erection; Properly using temporary falsework or additional cranes; and Rigorously following pinning, bolting, and tightening procedures. It is important to recognize that many erection problems can be attributed to a lack of understanding of girder behavior during erection. Therefore, when dealing with the erection problems, it is important to ask the question, "Is corrective action needed?" Furthermore, establishing acceptable tolerances of deviation from the intended vertical or horizontal align- ment of the superstructure would aid owners in knowing whether a true concern exists and save valuable construction time, while precluding frustration on the part of fabricators and erectors. Although erection problems were reported by all parties, the findings do not suggest that the problems are endemic. Rigorous erection analyses, including the prediction and reporting of intermediate deflections (deflections before the final erected condition), which could antic- ipate the reported problems, are not made before erection. Before more rigorous incremental analysis is routinely instituted, the issue to be considered is whether the potential field costs to solve unanticipated problems exceed any proposed rigorous pre-erection analysis costs.