In order to reduce erection pieces at combined joints of steel bridges, we proposed a new connection method in which we use bolted joints of longitudinal ribs as restrainers by tightening the bolts before welding of webs and flanges. The bolted joints of the longitudinal ribs have mixed state of damaged and undamaged friction surfaces. To establish the execution procedure, we investigated slip coefficient of the mixed state friction surfaces by slip tests. As a result, we obtained the relationship between the ratio of damaged surface and the reduction ratio of slip strength. On the basis of the test results, we showed the detailed procedure and applicable conditions of the proposed connection method.
