Seismic Performance Analysis And Design Optimization Of Curved Continuous Rigid Frame Bridge Considering Material Deterioration

Seismic analysis of bridge structures considering deterioration of reinforced concrete is of great significance for seismic analysis and the related design optimization of existing bridges in China.Based on the relevant theories of reinforced concrete material deterioration and the engineering background of Wujiawan Bridge in Guizhou Province,this thesis compared and analyzed the dynamic characteristics of the structure under different degrees of deterioration of materials.Based on the site condition of the bridge,the SIMQKE program was used to fit the artificial seismic wave,and the displacement response,bending moment response and shear response of the high and low piers were discussed.The Mander model and Menegotto-Pinto model were used to simulate the constitutive relationship of concrete and steel bar respectively,and the moment curvature curve of main pier was studied.Then,in order to analyze the optimization of seismic parameters of curved continuous rigid frame bridges under various deterioration conditions,based on the deterioration regular pattern of reinforced concrete,a concept of average deterioration strength is put forward in this study.Based on this concept and the seismic regional conditions of the bridge site and the maintenance expectation of the bridge,the material deterioration time parameters for the bridge seismic resistance optimizing were selected.By considering the material deterioration,the design parameters of the crossbeams of the original bridge(the number,location,stiffness and pier-beam stiffness ratio)are discussed.Finally,based on well consideration of material deterioration,the seismic response of curved continuous rigid frame bridge under different site conditions was analyzed in this thesis.Based on the analysis of dynamic characteristics,typical section displacement and internal force seismic response of long-span rigid frame bridge with high and low piers under different site types,the seismic design suggestions considering site variability were obtained.Based on the analysis and research,the following results are obtained:(1)The foundation frequency of curved continuous rigid frame bridges is relatively low,and the first-order frequencies of the longitudinal,transverse and vertical orientations are all less than 1.5Hz,the structural flexibility is relatively large and is susceptible under dynamic loads.Compared with the deterioration of the main beam material,the deterioration of the main pier material has more obvious influence on the dynamic characteristics of the structure.The vibration mode,period and frequency of the whole bridge are mostly determined by the stiffness of the pier structure.In the seismic analysis of bridge structure,if the material deterioration is not considered but the damage of structure due to material deterioration occurs in actual operation,unsafe design state would appear.(2)Compared with the condition of non-deterioration,once the material deteriorates,the displacement of pier top increases obviously.By comparing and analyzing the moment response of the main pier at different deterioration time,it is found that the longitudinal moment of the main pier first decreases and then increases with the increase of material deterioration time.While the transverse bending moment of main pier increases first and then decreases in the meanwhile.The material deterioration has a negative impact on the shear force of the structure.(3)Both the longitudinal yield moment and the transverse yield moment of the cross-section decrease with the increase of deterioration time.This is mainly due to the deterioration of structural performance caused by deterioration of materials,which further leads to insufficient structural resistance.Under different degradation time,the degradation of structure is more obvious.(4)Longitudinal tie beams have obvious influence on the internal forces at the bottom of low piers and transition piers.With the increase of the number of transverse tied beams,the bending moment of thin-walled pier loaded with larger force decreases significantly,thus,the pier structure bear uniform force and the distribution of internal force tends to be reasonable.Adding more transverse tied beams can also reduce the displacement of pier top and the longitudinal displacement of the whole bridge.Considering from the aspects of the mechanics,economy and aesthetics,the setting of the three crossbeams is more reasonable.Based on comparative analysis,when the ratio of low pier height to high pier height is 0.75,the optimal combination of three crossbeams(upper,middle,lower)is 0.3H/0.5H/0.7H(H is pier height).When the stiffness ratio of the tied beam to the thin-walled pier is between 0.9 and 1.6,the force acting on the pier structure is reasonable.(5)The difference of local site conditions determines the changes of displacement of between adjacent piers.In the case of local site changes,attention should be paid to the limited design of piers and columns in the surrounding area.In seismic analysis,if local site changes occur,non-uniform excitation analysis should be carried out,and seismic design should be performed according to site changes to ensure structural safety.Meanwhile,in the seismic design of high pier continuous rigid frame,different site conditions and the ratio of high pier to low pier should be combined to control the seismic fortification measures of different pier columns.