Risk-based Optimal Parameters Selection Of Isolation Devices For Ordinary Bridges In Near-fault Regions

Near-fault pulse-like ground motions could enlarge seismic response of structures significantly due to the existence of high-amplitude and long-duration velocity pulse,which could increase the seismic risk obviously.As a dominant part of domestic transportation network,short-and medium-span bridges generally have low seismic design standards and are vulnerable to seismic damage,which makes them become a weak link of the network.How to assess the near-fault short-and medium-span bridges rapidly and propose effective seismic design and retrofitting measures have become the key of the earthquake resistance of near-fault bridges.Consequently,this paper proposes a novel probabilistic seismic risk analysis methodlogy incorporating the significant pulse effect.Different from the existing seismic risk analysis method,this method consider the pulse effect on the seismic response and assess the near-fault seismic risk through total probability theory.Based on this method,this paper investigates the influence law of bridge parameters on near-fault seismic risk and develops an optimization method of isolation devices parameters.The main research work of this paper are as follows:1.Develop the near-fault seismic risk anlysis method of near-fault ordinary bridges incorporating the pulse effect.As the conventional seismic risk analysis framework ignores the pulse effect,this paper establishes the near-fault seismic vulnerability curves with the vulnerability functions of pulse-like ground motions and far-field ground motions employing the pulse probability.Then the near-fault seismic vulnerability funtions are convolved with the near-field seismic hazard funtions to obtain the near-field seismic risk result.For illustration purpose,a simply supported bridge is selected to introduce the calculation process and main conclusions of this analysis method.2.Investigate the influence law of key bridge parameters on the near-fault seismic risk.With the near-fault bridges seismic risk analysis methodology,the influence law of several key bridge parameters on the seismic risk is investigated detailedly in this paper.Among the numerous factors,the source-to-site distance,the structues period and the bridge type are selected as the research objects and establish the functions of the nearfault seismic risk versus these parameters.Based on the functions,the influence law of the parameters is investigated systematically and some reasonable advice about bridge seismic design and retrofitting is given.3.Propose the parameter optimization methodlogy of isolation devices of near-fault bridges.This paper promotes the near-fault seismic risk anlysis method to the parameter optimization and proposes a novel parameter optimization method based on Kriging model.Different from the response-based parameter optimization methods of isolation devices,this method selects the near-fault seismic risk as the optimization index and establishes the seismic risk surfaces with Kriging interpolation method.And the optimal parameters of isolation devices are determined by searching the global optimal points of the surfaces.This paper reveals the influence law of pulse effect on the seismic damage of structures and provides a viable solution for quantifying the impact of pulse effect on the seismic risk.A systematic calculation framework of the near-field seismic risk is proposed,which is of great significance to the seismic design and retrofitting of near-fault bridges.On the basis of the calculation methodology,a risk-based optimization method is proposed,which can assess the performance of the bearing from the perspective of probability and identify the optimal parameters to guarantee that the the structure has the minimum near-field seismic risk.