Artificial Synthesis Of Near-Fault Pulse-Type Ground Motion And Its Influence On The Responses Of Long-Span Cable-Stayed Bridge

Near-fault pulse-type ground motions often possess distinct characteristics, such as long period and high amplitude, that make them different from those recorded in far-fault regions and can have strong influences on the long period structural response, especially for long-period structures. The lack of observed near-fault pulse-type ground motions has been restricting the study on seismic response of structures subjected to the ground motions. In order to analyze the influence of near-fault pulse-type ground motions on long-span cable-stayed bridge systematically, a new method called "record decomposition incorporation" (RDI) has been proposed to synthesize the artificial near-fault pulse-type ground motions. The Sutong Cable-stayed Bridge is taken as an example to establish a numerical analysis model considering soil structure effect (SSI effect). The effect of pulse type and pulse parameter of near-fault grounds on the seismic response of bridge are investigated. The main tower of the cable-stayed bridge may be into plastic or even damaged because of the devastating of near-fault pulse-type ground motions. The plastic-elastic performance of main tower subjected to near-fault pulse-type ground motions has been studied. The main research content is as follows:(1) Artificial synthesis method of near-fault pulse-type ground motionIn order to make up for the inadequate of observed near-fault pulse-type ground motions, The Butterworth filter is used to decompose velocity pulse component and the high frequency component of near-fault pulse-type ground motions. The appropriate equivalent pulse model has been chosen to simulate the velocity pulse component. A new method called "record decomposition incorporation" has been proposed. The study shows that "record decomposition incorporation" method has certain rationality and accuracy. It can be obtained to adjust the pulse parameters to meet the design requirements of the ground motions.(2) The influence of soil-structure interaction effect in long-span cable-stayed bridgeSoil structure interaction effect is very important factors which affect the structural seismic response. Systematic lumped-parameter models are utilized to represent the dynamic behavior of the foundation supported on soil. The vibration modes and structural response of the consolidation model and considering SSI model are coMPared. It shows that SSI effect will change the dynamic characteristics of structure. The displacement response of the main tower is increased and the internal force responses of the main tower and main girder are reduced. SSI effect should be payed attention to analyze the seismic response of long-span cable-stayed bridge. The effective simulation of soil structure effect is the foundation for accurately evaluating the seismic response of long-span cable-stayed bridges under near-fault pulse-type ground motion.(3) Effects of near-fault pulse-type ground motions on long-span cable-stayed bridgeIn order to study the effect of near-fault pulse-type ground motions on long-span cable-stayed bridge, the observed near-fault pulse-type ground motion records and synthetic near-fault pulse-type ground motions are used to analyze the pulse type and pulse parameters on seismic response of long span cable-stayed bridge respectivelyFristly, the near-fault ground motions are divided into three groups as seismic inputs. The effects of SSI and pulse-type on the seismic response of the tower and deck are investigated. The results reveal that the seismic response of the cable-stayed bridge under pulse-type ground motions is significantly higher than non-pulse ground motions. Fling-effect ground motions amplify the response of tower under longitudinal excitation and the response of girder under longitudinal or horizontal excitation. Forward-directivity effect ground motions amplify the response of tower under horizontal excitation.Secondly, based on the above-mentioned RDI method, artificial near-fault pulse-type ground motions can be generated to facilitate the investigation of the effects of pulse parameters associated with near-fault pulse-type ground motion, such as the pulse period, velocity amplitude and numbers of pulse-like wave peaks, on the response of the long-span cable-stayed bridge. The results show that the deformation and internal force of the tower increase with the PGV of the near-fault pulse-type records. The fling-step records with different pulse periods impose a larger deformation and increase demands on the bridge coMPared to forward-directivity records. When the arrival times of the peak velocities of forward-directivity pulses are close to those of fling-step pulses, the seismic responses of the tower are significantly amplified.(4) Elastic-plastic seismic performance of main tower for cable-stayed bridge subjected to near-fault pulse-type ground motionsIn order to study elastic-plastic seismic performance of main tower for cable-stayed bridge subjected to near-fault pulse-type ground motions, based on Opensees nonlinear finite element platform, a nonlinear finite bridge model, considering the main tower's elastic-plastic performance, was established. Dynamic incremental analysis (IDA) is used to analyze the plastic development process of the main tower and elastic-plastic dynamic time history response of critical states. On the basis of the above, the influence of the pulse parameters (velocity amplitude, pulse period) on the plastic performance of the main tower is studied. The results show that the near-fault pulse-type ground motion makes the concrete main tower more likely to yield and failure coMPared with the non-pulse ground motions. Seismic design of long span cable-stayed bridge can consider the use of elastic plastic properties of main tower to be yield and dissipate energy to reduce seismic response of tower. The key parameters of velocity pulse can affect long-span cable-stayed bridge elastoplastic seismic performance significantly. It is worth to pay attention to that the influence of fling-step effect and forward-directivity effect on the plastic behavior of long-span cable-stayed bridge are different.The research results could be used to synthesis near-fault pulse-type ground motion and provide reference for the near-fault seismic design of long-span cable-stayed bridge.