The use of substandard and mismatched bolts continues to
be a major concern to bridge owners in the United States.
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 are designed for dynamic loading.
They are designed to resist either tension forces and/or shear
forces. Fatigue concerns govern bolts designed for cyclic ten-
sion forces. Cyclic shear forces require slip critical connec-
tions. Both loading conditions require bolts 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 ration-
ale for these 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.
Download File
Tidak ada komentar:
Posting Komentar