일반교량의 내진설계

Abstract

The purpose of earthquake resistant design for bridges is to secure the "No Collapse Requirement" and to shut down the delivery of seismic force to superstructure, which is possible by bridge mechanism design. For typical bridges, damage of superstructure or foundations leads to the bridge collapse and therefore bridge mechanism design is to be carried out with the connection and substructure. Bridge mechanism with substructure yielding is ductile mechanism, which requires plastic hinge formation at pier ends. On the contrary, bridge mechanism with connection failure is brittle mechanism, which requires shear keys. Such ductile or brittle mechanism is to be proved with section forces obtained from the spectrum analysis method based on elastic behavior. Because seismic forces are delivered to the superstructure through the pier, piers are essential structural members in the earthquake resistant design. For typical bridges with reinforcement concrete piers as substructure, the "Roadway Bridge Design Code" provides the application of flexural/yield stiffness according to the yielding of axial reinforcement for calculating the section forces. Because different column stiffness provides different section forces, from which the yielding of connection or substructure is determined. The ductility design determines the transverse reinforcement ratio and ductility with the required response modification factor but ductile or brittle mechanism is not verified therefrom. Because the seismic behavior of piers is determined by the flexural/shear performance curve, the possibility of ductile or brittle mechanism design can be confirmed with those performance curves. In this study, a bridge with steel bearing and T-type circular RC piers is selected, and section forces are obtained with the flexural/yield stiffness of piers. Base on these two different section forces, bridge mechanism design is carried out and the safety of the "No Collapse Requirement" is reviewed. Also, for circular RC piers, influence of design factors such as height, diameter and transverse reinforcement ratio on the flexural/shear performance curves are analysed, and conditions are proposed for ductile mechanism design.