Chief Structural Engineer

This paper presents the rationale for, and results of, structural monitoring of two steel basket-handle arch pedestrian bridges which were constructed in stages to minimize traffic disruptions. These bridges utilize a hanger system consisting of high-strength threaded steel rods to support the precast, post-tensioned concrete deck system. The research team used externally-mounted accelerometers to monitor the free vibration of each hanger during all incremental construction stages as well as one year after completion. The acceleration records for each hanger were analyzed using a fast fourier transform (FFT) to calculate the natural frequency of several modes of vibration. These natural frequencies were then used to estimate the tensile force in each hanger considering both taut-string theory and the flexural stiffness of the steel hanger rod. The results of this work show the value of structural monitoring during construction and indicat