| In recent years,with the development of traffic construction in western mountainous areas,there are more and more long-span and high pier bridges crossing deep mountain canyons.Because the western areas are mostly high intensity seismic areas,the seismic problems of high pier bridges are more prominent.For the seismic response of high pier cable-stayed bridges,there are few studies at present.In order to understand the seismic response characteristics of high pier cable-stayed bridges,this paper is based on Lixianjiang bridge in Yunnan Province Engineering research.The main bridge of the bridge is a steel-concrete composite cable stayed bridge with(62.4 +127.6 + 420 + 127.6 + 62.4)m.The total height of two pylons is 210 m and 250 m respectively,and the height below the deck is 102 m and 142 m respectively.Combined with the bridge,the main research work and conclusions are as follows:(1)Firstly,the difference between the dynamic characteristics of high pier cable-stayed bridge and general cable-stayed bridge is studied.It is found that the stiffness of the high pier cable-stayed bridge is significantly smaller than that of the general cable-stayed bridge with the same span,and its first-order period is significantly larger than that of the cable-stayed bridge with the same span.The influence of the change of the main tower pier height and the connection mode of the tower beam and pier beam on the dynamic characteristics of the high pier cable-stayed bridge is analyzed.The calculation shows that within a certain range of parameters,when the height of the main tower pier decreases,the first-order longitudinal drift period and the first-order transverse vibration period of the whole bridge decrease approximately linearly with the pier height.By changing the connection mode of tower beam and pier,the first-order longitudinal drift period can be significantly changed,with a reduction of nearly 50%,but the influence on the transverse natural vibration period is very small.(2)Through the dynamic time history analysis,the seismic response characteristics of the high pier cable-stayed bridge are calculated and analyzed,and the influence of the bridge tower crossbeam on the seismic response of the bridge tower is studied.Due to the high pier body and large period of the supporting project,the displacement response of the tower top and the main beam along the bridge direction is large.The displacement of the tower top along the bridge direction is nearly 50 cm,and the displacement of the main beam along the bridge direction is nearly 40 cm.It is worth noting that the displacement response along the bridge direction of the bridge is relatively large after the end of the earthquake,the attenuation speed is slow,and the reset time is long.The seismic response of the cable tower shows that the seismic response changes greatly at the sudden change of the section of the tower pier.The transverse seismic response of the bridge tower is greatly influenced by the beam.The transverse seismic capacity of the bridge tower can be improved by reasonably setting the number,size and position of the beam.Although the two pylons are different in height,the superstructure of the bridge is generally symmetrical,so the seismic response of the two pylons is basically the same,and there is no significant difference due to the different height of the two main pylons.The transition pier and auxiliary pier at the same cross section of the supporting project are two separate piers,and there is no beam on the top of the two piers.In this case,the arrangement form of the supports on the top of the left and right piers should be the same,which is conducive to the distribution of seismic force,and the arrangement form of the supports in the original design is not conducive to seismic resistance.(3)Finally,the influence of geometric nonlinearity on the seismic response of high pier cable-stayed bridge is discussed,and the influence of cable sag effect and geometric stiffness on the dynamic characteristics of the whole bridge is analyzed.It is found that the change of cable stiffness mainly affects the vibration mode of main girder,and the vibration mode of main tower is mainly affected by the change of stiffness caused by dead load.The results show that the maximum values of seismic response such as displacement,shear force and axial force of cable tower and pier change little when geometric nonlinearity is considered,but the bending moment of two cable towers changes a lot,which increases by 10%-15% when geometric nonlinearity is considered.According to other data analysis,the main reason for the increase in bending moment is caused by the P-δ effect.The displacement response of the transverse bridge at the top of the tower is smaller than that in the forward direction,so when considering the geometric nonlinearity,the increase in the transverse moment in the transverse direction is not as large as that in the forward direction.Although the maximum displacement and shear response do not change much,the difference between the seismic time-history response curves when considering and not considering the geometric nonlinearity is more obvious. |
