Despite commonly used in highway bridge design in Japan, composite twin I-girder bridge system is currently classified as non-redundant mainly due to the oversimplified assumption in the current bridge design. In this study, two composite twin I-girder bridge models are tested to investigate the mechanical behavior and redundancy analyses of the composite twin I-girder bridge system in fractured condition. Numerical models were first validated based on the experimental results. Hereafter, numerical study was carried out to investigate the effect of fracture location and the effect of concrete slab on the redundancy level of the composite twin I-girder bridge system. Results show that the fracture at the mid-span section is the most critical damage condition comparing to other fracture locations. In addition, the concrete slab is found as the main structural component that ensures the survivability of the composite twin I-girder bridge system in fracture condition.