Abstract:
An isolated span of the decommissioned SH 20 Puhinui Stream Bridge in Manakau, New Zealand was subjected to forced vibration testing in order to determine the dynamic response of the span. The bridge span was four traffic lanes wide, with seven precast concrete columns per pier and supported on precast concrete pile foundations. The span was excited along the longitudinal axis using a large eccentric mass shaker, and a benchmark system identification of the unaltered state was carried out using a MATLAB based GUI system identification toolbox (SIT) developed at the University of Auckland. Soil was then removed from around the base of selected columns with a new system identification performed after the alteration to capture the change in mode shapes and natural periods. Forced vibration testing of the bridge was able to capture a 5% increase in natural period for both modes as well as a noticeable reduction in the torsional component of both mode shapes.