The manufacture and use of substandard, mismatched or bogus bolts have been, and continue to be, a major concern to bridge owners inthe u.s. based on fhwa-sponsored research at the university of texas, supplemental specifications were developed and issued modifying fastener manufacturing, testing and installation procedures. nearly all bridge bolts ae designed for dynamic loading. they are designed to resist either tension forces and/or shear forces. fatigue concernsgovern bolts designed for cyclic tension forces. cyclic shear forces require slip critical connections. both loading conditions requirebolts to be installed to a minimum preload. the fhwa recommendations were developed in order to assure the ability of bolts to achieve this preload. minimum nut strength is increased, maximum bolt strength is reduced, thread fit tolerance is reduced, additional rotational-capacity testing is required, and additional testing, documentation, handling and shipping requirements are imposed. the rationale forthese new fhwa provisions are discussed. finally, slip critical joints depend upon friction between faying surfaces to develop strength. values of slip resistance or coefficient of friction for various paints and coatings must be determined by testing. bolt design parameters depend upon minimum values of tested coatings. this paper appears in transportation research record no. 1290, third bridge engineering conference, march 10-13, 1991, denver, colorado, volume 1.
Samenvatting