Vulnerability of RC hammer head type bridge piers under seismic inducedP-delta effect and simultaneously strength and stiffness degrading hystereticbehaviour

摘要

Current philosophy of seismic design is performance based seismic design, where some degree of inelastic behaviouris permitted due to inherent redundancy and reserve strength present in a structure. Reinforced concrete hammer headbridge piers represents inverted pendulum category of structure. On virtue of their structural configuration such structu-res are more vulnerable to topple down under earthquake induced strong ground acceleration. Plasticization of structuralmaterials may take place at critical junctions like hammer head portion and the relatively slender stalk portion underconsecutive yield excursions. Lateral deflection of the slender stalk portion of the pier is increased causing time pro-gressive P-Δ effect, over each cycle. As such lateral deflection gets increased progressively and overturning tendency isaggravated continually until the structure topples down. This study is an attempt to demonstrate through an exampleproblem, the judicious range upto which inelastic behaviour may be permitted in case of performance based design ofhammer head type of bridge piers subjected to seismic activity. As such this work may serve as a guidance for strikinga critical balance between safety and economy for practicing designers in case of performance based seismic design ofstructures such as bridge piers.