A method for damage detection of a simply supported concrete bridge structure in time domain is presented using the interaction forces from the moving vehicles as excitation. The vehicular loads are modeled as a group of vehicle-bridge interaction forces moving at a prescribed velocity, and the bridge is modeled as an Euler-Bernoulli beam simply supported at both ends. A damage function is used to simulate the crack damage in the reinforced concrete beam. The vehicle-bridge interaction forces and the structural damage in the bridge deck are identified from the measured responses in sequence of iteration without prior knowledge of the moving loads. The effects of parameters of the vehicle-bridge system and measurement noise on the damage detection result are studied. Simulation results show that the method is effective and noise insensitive to damage detection in the concrete bridge structure under moving vehicular loads.