GUIDE FOR HEAT-STRAIGHTENING OF DAMAGED STEEL BRIDGE MEMBERS 1. INTRODUCTION Damage caused by overload, vehicle impact, handling, earthquake, or fire is a perennial problem associated with steel bridge struc- tures. For almost half a century, heat- straightening techniques have been applied to bends and distortions in order to restore the original shape of steel elements. A few craftsmen, who have years of experience with heat straightening, perform the tech- nique in the field with varying degrees of success. Some of these experts have mas- tered heat straightening, but the process is still considered more of an art than a sci- ence. The ability to repair damaged struc- tural steel members in place, often without the need for temporary shoring, has gener- ated interest in heat straightening from the engineering profession. However, engineers have had to rely primarily on their own judgment and the advice of experienced technicians in applying heat-straightening techniques. Two key questions have often been raised: Do heat-straightening proce- dures exist which do not compromise the structural integrity of the steel? And if so, how can such repairs be engineered to en- sure adequate safety of the repaired struc- ture, both during and after repair? The pri- mary goal of this guide is to answer these two questions. This guide is intended for a general audience ranging from heat-straightening practitioner, to contractor, to inspector, and to bridge engineer. 1.1 History of Heat Straightening The origins of heat straightening can be traced to the early days of welding. Steel fabricators observed how the heat from welding caused distortion in regular pat- terns. Some of these individuals began to experiment with ways to reverse this distor- tion by heating the steel in specific patterns to counteract the initial distortion. With ex- perience, some of these technicians devel- oped skills at not only removing weld distor- tion, but repairing other damage as well. These heating procedures developed as an art form passed from one practitioner to the next. During this period, the use of curved steel members gained popularity for both practical and aesthetic reasons. Primary ex- amples include horizontally curved bridge girders and camber to compensate for verti- cal curve and dead load deflections. Heat curving techniques were developed for these applications. While many of the heating techniques are similar to those used in heat straightening, there are distinctions between the two. Heat curving is typically per- formed on undamaged steel, usually in the controlled environment of the fabrication shop, and the typical radius of curvature for heat-curved members is quite large, mean- ing that the curvature is usually very grad- ual. On the other hand, heat straightening is used on damaged steel in which the yield stress has been exceeded, and often exces- sively, well into the strain-hardening range. Most heat straightening is conducted in the field, under highly variable weather condi- This document was superseded in March 2023 by Manual for Heat Straightening, Heat Curving and Cold Bending of Bridge Components. Superseded
GUIDE FOR HEAT-STRAIGHTENING OF DAMAGED STEEL BRIDGE MEMBERS
Jun 27, 2023
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