Ambient and forced vibration tests were carried out on a unique 177-m combined suspension and cable-stayed bridge near Montreal, Canada. A rehabilitation program was completed in 1989 on Beauharnois Bridge during which the deck was completely rebuilt with an orthotropic slab on two steel trusses. The rehabilitation program also included the addition of two pairs of stay cables on both towers therefore creating a hybrid suspension system. The experimental program, involved the measurement of vertical, transverse and longitudinal acceleration responses of the deck and tower under ambient and controlled traffic loads. Dynamic amplification factors were obtained for the bridge. Modal properties were evaluated and used to correlate a three dimensional finite element model for the bridge, including nonlinear analysis of the bridge, and were used in the modal analysis. The paper discusses the experimental setup as well as the techniques used to evaluate vibration frequencies and mode shapes. Numerical dynamic properties are compared with experimental results.
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