The estimation of free natural frequency of continuous bridges with variable cross-section

This study numerically investigates the natural frequencies of composite steel I-girder continuous-span bridges with straight haunched sections. In this context, three dimensional finite element analysis is performed to model dynamic behaviour of bridges by using CSIBridge package. Structural elements of bridge load-bearing system have been designed according to AASHTO LRFD Standards (2014). Effect of various parameters such as span length, the depth ratios between haunched cross-section to mid-span cross-section (r), the length ratio between haunched section to span (α), span configuration and steel girder arrangement on natural frequencies have been investigated numerically with one hundred fifty three bridge models. "r" and "α" values are set to be 0.5 - 2.0 and 0.1 - 0.5. The analysis results have been given and discussed for the natural frequency of continuous-span composite steel bridges with straight haunched section. Finally, non-linear regression analysis has been conducted to predict the first natural flexural frequency of composite steel I-girder continuous-span bridges with straight haunched sections. Based on regression analysis, a practical equation is also proposed.