2019 CSCE Annual Conference - Laval (Greater Montreal) Conference
Mr. Sriram Narasimhan, University of Waterloo
Dr. Scott Walbridge, University of Waterloo
The rapid advancement in material technology has paved the way for various lightweight yet highly durable materials such as aluminum with low maintenance cost, providing the construction industry with a fascinating opportunity to build lightweight and architecturally appealing pedestrian bridges. Nevertheless, this has resulted in lively bridges, which often suffer excessive vibrations leading to serviceability problems under pedestrian-induced walking loads. Various design standards have been developed for serviceability design of these structures, however primarily based on observations from low frequency bridges. These standards have neglected the altered mass-stiffness relationship for structures with lightweight material, which causes higher frequency but large amount of vibration magnitude. Hence, it is imperative to evaluate the existing design standards for lightweight bridges, especially using experimental observations. Another central issue in the design process by these standards is proper consideration and treatment of the large uncertainty in the loadings and the complex behavior of the pedestrians to bridge response. This study has underscored these discrepancies in the bridge standards through a coupled experimental and analytical investigation on aluminum pedestrian bridges under walking loads. The experimental results from two full-scale aluminum bridges show significant differences in the predicted responses by the design load models as compared to the measurements. The key parameters employed in the design equations, such as dynamic load factors, walking speed, and multiplication factors, are identified as primary reasons for this disagreement. Accordingly, modifications have been recommended to better align the predictions with experimental test results, which also harmonize these standards amongst each other. In addition, a reliability-based evaluation is carried out on code-compliant bridges by incorporating the uncertainties associated with various parameters in the design process. Based on the evaluation results, the design equations are calibrated for higher reliability indices and partial factors for the calibrated design equation are estimated. For economic designs, user’s comfort limits based on the frequency of occurrence of the traffic event and the class of pedestrian bridge are adopted during the calibration process. The calibrated design standards ensure acceptable performance during both design and non-frequent heavy traffic loading events, while at the same time yielding economic designs.