Tohru MATSUOKA
Experimental study on flexural strength of friction-type high-strength bolt connection in composite girder bridges
Masatugu NAGAIĄ¤Eiji IWASAKI
For the connection of members in steel and steel-concrete composite bridges, in most cases, welding and friction-type high-strength bolt have been used. In Japan, mainly from economical viewpoint, bolt connection has been preferably employed. At the design of high-strength bolts, the number of bolt has been determined based on Allowable Stress Design (ASD) Method. At ultimate or safety limit state, the required performance is defined to prevent the slipping of bolts or yielding of the steel plates. This means, based on ASD, that both phenomena have been judged to be collapse of the bridge system, and that the increase of bolt strength or friction factor is a key factor to obtain higher strength of bolt connection. So far, a lot of studies have been carried out in order to decrease the required number of bolt. Due to the delayed failure of high-strength bolt occurred, the maximum strength of bolt has limitation. Hence, the increase of friction factor has been drawn attention by many researchers, and as a result, friction factor of 0.5, instead of 0.4 stipulated in JHBS, has been proposed. By employing the coefficient of friction factor of 0.5, it is easy to understand that around 20% bolt number can be reduced. In Euro countries and USA, LSD has been used and the number of bolt is considerably smaller compared to the number determined based on ASD.
In this study, we carried out the experiment using two composite girder models with different bolt number in the lower flange, and the flexural strength of bolt connection has been checked. From this experimental study, we confirmed the increase of flexural strength exceeding yield moment, and that its degree depends on the number of bolts. Unfortunately, in this study, we failed to derive the formula for the exact evaluation of flexural strength of connection, we showed both slipping of bolts and yielding of the steel plates should not be defined to be collapse of the bridge.
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