Sho HIROSE

Effect of evaluation of ultimate strength on dimension of composite girder bridges

Masatsugu NAGAI, Eiji IWASAKI


In order to reduce the bridge construction cost, Japan Highway Public Corporation has developed composite two-I-girder bridges with very simple stiffening systems. It has been reported that the construction cost of the developed bridge system is around 10% cheaper than that of conventional bridge system. Now, further reduction of the cost has been requested. However, the above-developed system is too simple to further simplify, facing difficulty in developing more economical system by removing the structural members.
Based on current Japan Highway Bridge Specifications, the maximum bending strength is defined to be yield moment. However, it has been commonly accepted, in European countries and USA, that the ultimate bending strength of the composite girder under sagging bending moment is plastic moment which is normally around 25% higher than the eyield moment. Based on this fact, the girder was designed using two ultimate strengths and compared the dimension. It was concluded that around from 20 to 25% reduction of the steel weight was obtained.