Study On The Seismic Performance Of The Railway Bridge Pier With Low Reinforcement Ratio

China's railway bridge piers basically use a few-reinforced concrete gravity bridge piers.This is because China's railways have very high requirements for the displacement control of the running beam.In order to limit the displacement caused by the operation and the earthquake,the pier of the railway bridge needs a lot of rigidity.In the earthquakes hitherto,a few domestic railway bridge piers showed obvious brittle failure characteristics.In response to this,this paper has carried out related research.(1)Using ANSYS finite element software,a refined solid model of the low-reinforced bridge pier was established,and a numerical pseudo-static analysis was carried out in the form of low frequency cyclic loading on the top of the pier.Difference between the results of the quasi-static test in the existing research and numerical pseudo-static analysis were studied.The results show that the refined solid model of the less-reinforced bridge pier is in good agreement with the results of the quasi-static test,which verifies the rationality of the established numerical model.(2)Taking the less-reinforced pier in the general drawing of the railway bridge design as the research object,based on the established refined model of the less-reinforced pier,the low frequency cyclic loading form is used to perform pseudo-static analysis on the top of the pier.The longitudinal and transverse displacement ductility coefficient,failure form,energy dissipation capacity and stiffness degradation characteristics of bridge piers with various reinforcement forms,shear span ratios and reinforcement ratio levels were deeply studied from 3 aspects: concrete craecking situation,hysteretic curve and skeleton curve;Results show that the failure modes under the pseudo-static action are similar in both directions.With the increase of the reinforcement ratio,the performance of the pier gradually exhibits plastic failure characteristics from brittle failure,and plastic hinges appear at the bottom of the pier.Because the lateral bearing capacity of the pier is greater,the pier ductility design should use the longitudinal bridge ductility parameter as the control index.(3)The effects of different reinforcement ratios,stirrup ratios and shear-span ratios on the pier ductility performance have been studied.The hoop ratio has basically no influence on the ductility of the pier.(4)Taking the bridges with less-reinforced piers in the general drawing of the railway bridge design as the research object,based on the nonlinear dynamic finite element analysis platform OpenSEES(Open System for Earthquake Engineering Simulation),a refined model of the whole bridge was established,and the influence of longitudinal reinforcement ratio,pier height and main beam span length on the dynamic characteristics of railway bridges with less-reinforced piers.The results show that as the longitudinal reinforcement ratio increases,the period of each order of the whole bridge decreases slightly,but the natural vibration mode of the whole bridge is basically unchanged;with the increment of the pier height,the period of each order of the whole bridge increases significantly,the order of the first transverse vibration mode is advanced,effectively avoiding the platform section of the code design acceleration spectrum;with the increase of the main beam span length,the period of each order of the whole bridge increases,but the natural vibration form of the whole bridge is basically unchanged.(5)Based on the established refined model of the whole bridge,seven far-field seismic records in accordance with the design spectrum of the "Code for Seismic Design of Railway Engineering" were selected as input,the influences of longitudinal reinforcement ratio,pier height and span length of simply supported beams on the seismic response characteristics bridges less-reinforced piers under multi-strength earthquakes(frequent earthquakes,design earthquakes and rare occurrence earthquakes)were deeply studied in two aspects: the dynamic response(pier bottom bending moment,shear force and pier top displacement)and energy consumption.The results show that the nonlinear state of the less-reinforced bridge pier bottom under longitudinal earthquake is more significant than that under horizontal earthquakes.With the increment of longitudinal reinforcement ratio,the pinch effect of the bending moment-curvature hysteresis curve and nonlinear state of the pier bottom can be notably weaken,and the energy dissipation capacity of bridge piers can be effectively improved;Due to the small shear span of the pier with a low height(such as 5m)and long vibration period of the pier with a high height(such as 30m)which avoids the platform section of the code design spectrum,these two kinds of piers has a small seismic bending moment response under multi-intensity earthquakes,the hysteresis relationship at the bottom of the pier presents a linear or weakly nonlinear state,and the bottom of piers with a height of 10 ~ 25 m presents relatively strong non-linear state;the bridge piers with larger spans of main beams under multi-intensity earthquakes all produce greater seismic response.