Seismic Response And Damage Analysis Of Long-span Continuous Rigid Frame Bridge With High Piers Considering The Influence Of Construction Process

Continuous rigid frame bridges were very popular in medium and long span bridges due to its excellent mechanical performance.With the innovation of materials and construction technologies,continuous rigid frame bridges were developing towards higher piers and longer spans,and had become one of the commonest bridge types used to cross natural barriers like high mountains and deep rivers.However,because the structural system and construction method of continuous rigid frame bridges were different from other types of bridge such as simply supported beam bridges and continuous beam bridges,the construction period was generally longer and requires multiple system conversions.Factors such as concrete self-weight,bridge deck pavement,box girder prestressing,construction loads,shrinkage and creep of concrete had a great influence on internal force state of the bridge,leading to the internal force state of the continuous rigid frame bridges would be changed after the bridge was completed.Therefore,in the study of seismic performance of continuous rigid frame bridges,the influence of the construction phase on the internal force state of the bridge could not be ignored.To investigate the seismic responses and damage of continuous rigid frame bridges with high piers and long span under near-fault ground motions,the seismic responses and damage of the typical construction stages and overall bridge under actual internal force states were analyzed.And the seismic performance of the continuous rigid frame bridge with high piers and long span was also evaluated by using the endurance time method.The main work and results were summarized as follows:(1)The development and seismic damage characteristics of continuous rigid frame bridges were summarized.The seismic damage of Miaoziping Bridge during the Wenchuan earthquake was investigates.And the seismic response characteristics,damage analysis,damage control methods and seismic problems of continuous rigid frame bridges under the action of the near-fault ground motions were studied.(2)The construction phase model of a high-pier long-span continuous rigid frame bridges were established and analyzed using MIDAS/Civil,and the internal force state of the continuous rigid frame bridges at different construction stages and completion was obtained.Based on MIDAS / Civil and OpenSees platform,a dynamic analysis model of the bridge was established,and the correctness of the dynamic model was verified by dynamic characteristics analysis.(3)The problem that the structural system and dynamic characteristics of continuous rigid frame bridges with high piers and long span were different during the construction phase and the actual internal force state.Five typical T-shaped rigid frames during the construction phase were selected,the actual internal force of the bridge under different construction stages was obtained by the construction phase analysis based on MIDAS/Civil.A simplified method for simulating the actual internal force state of the key section of the main girder was proposed.Displacement,displacement ductility coefficient,Park-Ang damage index,main beam displacement,and steel bar strain were considered as indicators of analysis.The seismic response and damage of each indicator at different construction stages of the bridge were compared and analyzed.The results showed that the bridge piers in the typical construction stages would suffer severe earthquake damage under the near-fault ground motion,and the seismic damage of the pier will be more serious with the increase of the cantilever section of the main girder.Compared with the longitudinal direction,the damage of bridge in transverse direction was more serious.In addition,the damage of the piers was concentrated on the bottom rather than the column top.(4)A dynamic analysis model of the continuous rigid frame bridges including the main bridge and approach bridge was established.The influence of the internal force state on the pier and the main beam during the construction phase was considered,and chain impact effects between the adjacent components including the girders and the abutment back walls were considered.To obtain the seismic responses and damage status of the continuous rigid frame bridges,several near-fault ground motions were selected to carry out nonlinear time-history analysis.The results showed that the lateral “swing tail” and vertical “slap” phenomenon of the main girders at side span will occur under the ground motions,which confirmed the seismic damage characteristics of the Miaoziping Bridge during the Wenchuan Earthquake.The impact force of adjacent girders located at the expansion joint of the transition pier was largest and the damage of transition piers was more serious than other piers.The displacement of the end of the main girder increased with the increase of the initial gap,and the approach bridge was the opposite.The impact force and number of impact at the expansion joint decreased with the increase of the period ratio.(5)A method called endurance time method(ETM)was adopted to evaluate the seismic performance and damage of continuous rigid frame bridges.First,endurance time accelerogram(ETA)with increasing ground motion strength over time was synthesized based on the basic theory of the ET method.The seismic response and damage of a continuous rigid frame bridges were evaluated,and The applicability of the ET method was verified.The seismic response and damage of a continuous rigid frame bridges were evaluated.The results showed that the ET method could be applied to the seismic performance analysis and damage assessment of long-span continuous rigid frame bridge systems.The pier and beam of the main bridge and the approach bridge at the same seismic time correspond to different seismic responses,and the ET method could predict the time of the first collision and the magnitude of the collision force between adjacent beams at the expansion joint.The damage of the main bridge pier was less than that of the approach bridge pier under small earthquake(short earthquake-resistant time),while the damage of the main bridge pier under large earthquake(long earthquake-resistant time)was greater than that of the approach bridge pier.