Study On Optimization Of Stiffness Distribution Of Continuous Rigid Frame Bridge Under Stationary Random Excitation

Continuous rigid frame bridge is a kind of medium and small span bridge which is widely used to span valleys,rivers and roads.At present,the structural optimization of continuous rigid frame bridges is usually limited to the optimization of structural internal force distribution under static external load,while the relevant research on structural optimization for improving the seismic performance of rigid frame bridges considering the seismic input is rare.Considering that the seismic input is a random process,this paper will study the optimization of the pier stiffness distribution of continuous rigid frame bridge under random seismic excitation and its influence on the seismic performance.The main contents are as follows:(1)Taking the three span continuous rigid frame as the research object,based on the existing modeling method of continuous beam bridge,the model of continuous rigid frame bridge is simplified.This paper defines the optimization objective expressed by the key response value of the structure,constructs the structural characteristic system and the corresponding structural response calculation program under the random load,and studies the optimization of pier stiffness distribution and seismic performance under the random excitation by using the global optimization algorithm.The influence of the change of characteristic parameters such as site soil and constraint conditions on the optimization of stiffness distribution and seismic performance is analyzed.The influence of the plastic parameters of the pier on the yield performance is studied when the pier enters into the plasticity.(2)Combined with the actual bridge engineering,the multi degree of freedom fine model of the continuous rigid frame bridge is established by using the concentrated mass method,and the effectiveness of the optimization of the pier stiffness distribution on the improvement of the actual bridge seismic performance is further studied.This paper studies the stiffness distribution of the bridge piers in the transverse and longitudinal directions respectively,points out that the stiffness distribution of the optimized bridge piers gradually decreases from the bottom of the pier to the top of the pier,and makes quantitative analysis and evaluation of the structural response before and after the optimization in the transverse and longitudinal directions.The optimization of stiffness distribution can significantly improve the seismic performance of the bridge.(3)Considering the influence of dynamic characteristics of continuous rigid frame bridge on the optimization of pier stiffness distribution and seismic performance,a fine model of three span continuous rigid frame bridge with different pier height and span is established.The stiffness optimization and aseismic analysis of bridge piers in transverse and longitudinal directions are carried out respectively.The relationship between the change rate of pier element stiffness and the change of span and pier height is studied,and the change rule of seismic performance with span and pier height after optimization is analyzed.The results show that the optimization of stiffness distribution of continuous rigid frame bridges with different dynamic characteristics under random excitation can improve the seismic performance of bridges,but with the increase of span and pier height,the improvement of seismic performance is relatively reduced.