Study On Transverse Asymmetric Seismic Constraint System Of Wide Cable-stayed Bridge With Single Tower Based On Dampers

Single-pylon cable-stayed bridge is widely used in municipal bridge field because of its large span capacity and good landscape effect.In order to alleviate the increasing traffic volume,many newly-built municipal bridges are becoming wider and wider.One-pylon cable-stayed bridges with wide,multi-cable planes and mixed beams are typical examples.Mixed beams are used to solve the contradiction between the proportion of side and mid-span.In general,lighter steel beams are used in the main span and concrete beams are used in the side span.Compared with traditional cable-stayed bridges,the stiffness and mass distribution of single-tower and wide-span hybrid girder cable-stayed bridges are quite different,and the main span and side span are asymmetrical.Therefore,the problem of earthquake prevention and disaster reduction has become the focus of Engineering circles.Lateral seismic performance of cable-stayed bridges has always been a weak link,because the lateral stiffness of cable-stayed bridges is generally large,and the transition piers and auxiliary piers often become seismic vulnerable parts because they share a large proportion of lateral inertial force.In order to study the design of transverse asymmetric seismic system of single-tower and wide-span cable-stayed bridge based on dampers,a two-degree-of-freedom dynamic analysis model with non-linear viscous dampers is firstly taken as the research object.By solving the dynamic equation of the two-degree-of-freedom model,the mechanical properties of the non-linear viscous dampers and the influencing factors of energy dissipation are discussed.Then,the reasonable lateral seismic restraint system of a newly built single tower and wide cable-stayed bridge is studied.The main work includes the following aspects:(1)A two-degree-of-freedom analysis model with a non-linear viscous damper is constructed,and the motion equation of the model under sinusoidal excitation is established by using the d'Alambert principle.Based on the principle of energy conservation,the non-linear viscous damper is equivalent to a linear damper with the same energy dissipation effect,and the motion equation is decoupled for linear solution.On this basis,an accurate equivalent linearization iteration method is proposed.In the process of equivalent linearization,the maximum displacement at both ends of the damper is solved by the iteration method,and the corresponding linear modal damping coefficients of the non-linear viscous damper can be accurately solved.(2)Based on the results of the above equations of motion,the mechanical properties and energy dissipation characteristics of the nonlinear viscous dampers are studied.And the effects of relative dynamic characteristics of structures,frequency spectrum characteristics of ground motion and parameters of dampers on energy dissipation and seismic reduction of viscous dampers are analyzed.Research suggests:(1)With the increase of relative stiffness,the energy dissipation of non-linear viscous dampers increases,the displacement of particles and the shear response of supports decrease,but the relative additional force between particles is affected by the damping force and increases with the increase of relative stiffness.(2)The energy dissipation effect of viscous dampers is greatly influenced by the sinusoidal frequency.When the load/structure frequency ratio is less than 1.0,the energy dissipation effect increases with the increase of the load frequency;when the load/structure frequency ratio is more than 1.0,the energy dissipation effect decreases with the increase of the value.(3)When the damping index is constant,the effect of damper on structural displacement and bearing shear increases with the increase of damping coefficient,and the relative additional force increases first and then decreases with the increase of damping coefficient.When the damping coefficient is constant,the effect of damper on structural displacement and bearing shear decreases with the increase of damping index,and the relative additional force decreases first and then increases with the increase of damping coefficient.(3)Taking a newly-built single-tower and wide-span cable-stayed bridge as the research object,using structural analysis soft SAP2000 and non-linear time history analysis method,the asymmetric seismic response of the bridge is studied,and the two-level seismic performance of the bridge is evaluated by C/D method(capacity/demand ratio).The research shows that under the E1 earthquake,the damage status and seismic safety reserve of transition piers show obvious asymmetry,and some pier top,pier bottom section and fixed support do not meet the requirements of seismic fortification grade of E1;under E2 earthquake,the damage state and seismic safety reserve of the transition pier also show obvious asymmetry.The transition pier and its pile foundation do not meet the requirements of E2 earthquake fortification grade.Therefore,it is necessary to design reasonable seismic mitigation measures to ensure the seismic safety of the structure.(4)On the basis of the above aseismic performance evaluation and based on the asymmetric seismic response characteristics,four restraint systems,i.e.fixed in the transverse,sliding in the transverse,seismic mitigation system A and seismic mitigation system B are proposed.Nonlinear time history analysis method is used to cross-analyze the damping coefficient and damping exponent parameters of the nonlinear viscous dampers in seismic mitigation system A and B,and the optimal parameters of the dampers in the two systems are obtained.Then,by comparing the different arrangements of the optimal parameters of dampers in the two systems,the most reasonable combination of the optimal parameters of dampers in the two systems is obtained.It is found that the most reasonable arrangement of parameters for shock absorption system A and B are as follows:for the former,the dampers parameters in pier 1#is C(28)7000kN(7)m s(8)~???=0.5 and the dampers parameters in pier 3#is C(28)7000kN(7)m s(8)~???=0.3;for the latter,the dampers parameters in pier 1#is C(28)7000kN(7)m s(8)~???=0.5 and the dampers parameters in pier3#is C(28)5000kN(7)m s(8)~???=0.5.By using these optimal parameters combination,the seismic response control effect of the key components of the whole bridge in the two seismic mitigation systems can be optimized simultaneously.