Study On The Interaction Between Arch And Spandrel Of Deck-Type Arch Bridges Under Earthquakes

Arch bridges have excellent mechanical performance,reasonable cost,and harmonious appearance,making them very suitable for mountainous and river valley areas with good foundations.They are one of the widely used bridge types in western China.The western region is a high incidence area of strong earthquakes in China.In recent years,there have been dozens of earthquakes,such as Wenchuan,Ya’an,Luding and other earthquakes,which have caused huge damage to transport infrastructure.Among them,the Wenchuan earthquake caused varying degrees of damage to dozens of arch bridges,while top arch bridges such as Jingtianba and Chenjiaba experienced extreme seismic damage of complete collapse.Arch bridges are usually considered one of the bridge types with good seismic resistance,but recent earthquake damage research has shown that arch bridges also have prominent seismic safety hazards.Unlike the simple and clear transmission path of beam bridges,the transmission path of deck arch bridges includes two links: the arch building and the main arch ring.In statics,the phenomenon that the buildings on the arch bear the load together with the main arch ring is called "joint action".This phenomenon is often more prominent under the seismic load,because the influence of the three-way vibration of the arch ring on the buildings on the arch is similar to the non-uniform dynamic excitation.The impact of dynamic joint action on the seismic performance of deck arch bridges is a rarely discussed aspect both domestically and internat ionally.In view of this,this article takes three typical deck reinforced concrete arch bridges in practical engineering as examples to specifically study the combined effect of arch buildings and main arch rings under earthquake action,in order to provi de reference for the seismic performance evaluation and design of deck arch bridges.The main research work is as follows:(1)Summarized and analyzed the connotation of "joint action" of deck arch bridges under static and dynamic actions,and proposed an analysis method for dynamic joint action;On this basis,three typical deck reinforced concrete arch bridges(with different main spans and arch building forms)were selected as examples.Based on the Open SEES open source platform,a full bridge finite element analysis model considering nonlinear factors such as material,geometry,and boundary was established,laying the foundation for subsequent nonlinear time history analysis.At the same time,the dynamic characteristics of the three bridge cases were compared and studied based on the corresponding linear elastic analysis model.Research has shown that the stiffness of the main arch ring of a deck arch bridge determines the main vibration mode and its natural vibration period,and the first few main vibr ation modes are not significantly affected by the building on the arch;For small and medium-sized span deck reinforced concrete arch bridges,the in-plane stiffness of the main arch ring is smaller than the out-of-plane stiffness,and the first mode of vibration is usually inplane vibration;The stiffness of the columns and supports at the junction pier will affect the high-order vibration mode of the entire bridge;An increase in the stiffness of the bridge deck system will slightly reduce the natural vibration period,without affecting the higher-order vibration mode,but will change the subsequent vibration mode of the pier at the junction.(2)According to the connotation of dynamic joint action,the arch building is equivalent to an additional distributed mass acting on the main arch ring.A bare arch analysis model is established considering nonlinear factors such as material and geometry of the main arch ring,and its analysis results are used as a benchmark.By comparing the results with the nonlinear analysis model of the entire bridge,the influence of joint action on the seismic response and seismic performance of the main arch ring is studied;Furthermore,the damage index of the main arch ring was used to determine the degree of influence of dynamic joint action,while changing the layout of the bridge beam(simple support,continuous,rigid structure).The influence of the arch building form(arch type,beam type),bridge beam layout,and main span span on the joint action was explored.Research has shown that the joint action between the arch foot of the main arch ring and the l/8 span area has a significant impact.The arch foot is a dangerous section,and the maximum parameter affected by the joint action can reach 10.85;The existence of the upper structure significantly reduces the axial force and in-plane bending moment of the main arch ring,and the larger the span,the more significant the reduction effect;The larger the span,the greater the influence of the stiffness of the bridge deck system on the combined dynamic action.(3)Further analyze the impact of joint action on the seismic response and seismic performance of arched buildings using two bridges with beam arched structures as examples,and determine the degree of influence of dynamic joint action based on the damage indicators of columns and supports on the arched structures;Considering the significant impact of the vibration mode and amplitude of the main arch ring on the arch building,the stiffness of the main arch ring of the above two bridge examples was scaled in different proportions(0.5,1.5,2.0 times the original stiffness and infinite stiffness,which is equivalent to all the column roots of the arch building being consolidated).Research has shown that the impact of dynamic joint action on the seismic performance of high columns is relatively small,while it has a significant impact on the seismic performance of low columns.However,as the ground motion increases,the impact of dynamic joint action gradually decreases;The transverse displacement of the mid span bridge deck and the longitudinal displacement response of the side span bridge deck are the largest,and the displacement of the mid span bridge deck decreases with the increase of the combined action;The sup port is a vulnerable component,and the response of the support at the junction pier is the highest.The seismic response is relatively small,and the influence of the combined dynamic action is greater.The response of the arch support is the lowest;Taki ng the acceleration time series at the bottom of the arch column as the research object,this study explores the filtering effect of the main arch ring.After the filtering effect of the main arch ring,the original seismic motion at the bottom of the high column has a significant reduction in the response spectrum values in the longitudinal and transverse directions,while the transverse and vertical response spectra of the low column have a very obvious amplification effect.The stiffness of the main arch ring has a certain impact on the filtering effect,and the filtering effect is more obvious when the stiffness is small.