A new time domain method is presented to identify moving loads on a bridge deck based on the measured responses. The bridge deck is modeled as an orthotropic plate and the loads are modeled as a group of four loads moving on top of the bridge deck at fixed distance apart. Dynamic behavior of the bridge deck is analyzed by the orthotropic plate theory and mode superposition technique. Like all inverse problems, this identification is an ill-conditioned problem, and a regularization technique is employed to stabilize the computations. The identified loads moving at different eccentricities are presented. Laboratory work on the force identification is also presented. The effect of incomplete measured modes in the responses is discussed, and an underestimation in the loads may result if the number of vibration mode for identification is larger than that in the responses. Computational simulations and laboratory tests show that the method is effective and practical for identification of individual wheel loads on bridge decks.

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