| With the vigorous development of cable-stayed bridges,the bridge type with shorter side piers is derived under certain terrain conditions,which puts forward higher requirements for the lateral seismic design of cable-stayed bridges.In order to solve the transverse seismic problem of cable-stayed bridge with low side piers,the seismic vulnerability analysis method is firstly used to comprehensively evaluate the seismic performance of all key components of transition piers,auxiliary piers,cable towers,stay cables and support systems,and the damage transcendence probability of each key component under the design earthquake is obtained.At the same time,the vulnerability curve of the bridge structure system is obtained based on the first-order limit estimation method and the second-order limit estimation method;Then,in order to solve the damage problem of cable-stayed bridge with low side piers,eight kinds of seismic measures were constructed by using two construction methods,namely,optimizing pier section form and setting anti-buckling bracing(BRB)elements.The shock absorption effect of each measure was verified and compared based on capacity demand ratio method.Finally,in view of the shortcomings of the previous seismic measures,a total of 8 new seismic measures including the new BRB side pier structure and the new quasi seismic isolation concept were constructed,and the best seismic measures were determined through comparison and verification.The main research work and conclusions are as follows:(1)Based on the vulnerability analysis method,the damage transcendental probability of each key component of the whole bridge under the design earthquake was obtained.Through comparison,the transition pier,auxiliary pier,cable tower and cable,the transition pier has the highest probability of three kinds of damage,up to26.40%(E1 earthquake)and 38.70%(E2 earthquake).The probability of medium damage in the unidirectional support of the transition pier in the bearing system is the highest,which can reach 34.40%(E1 earthquake)and 50.00%(E2 earthquake).The transition pier and its support are the weak link in the seismic resistance of this bridge.(2)Based on the first-order bound estimation method and the second-order bound estimation method,the vulnerability curves of the structural system of cable-stayed Bridges with low side piers are obtained.Through comparative analysis,the second-order bound method is more accurate than the first-order bound method in describing the damage of the system,in which the damage probability of the system under the E1 design earthquake is between 36.20 and 72.60%.The damage probability of the system under the design earthquake of E2 is 52.50～85.20%,but the probability of serious damage of the structural system is less than 40.00%.(3)By comparing and verifying the two kinds of seismic measures constructed,in the first kind of measures,the I-2 has the best damping effect,and the transition pier has the most obvious damping effect,and the damping amplitude can reach 84.85%.The shock absorption effect of the second type of seismic measures is better than that of the first type of measures.Among them,the shock absorption effect of the second type of seismic measures is the best,and the shock absorption effect of the transition pier is the most prominent,with the maximum reduction range up to 94.30%.(4)Optimizing the pier section form can effectively improve the problem of large lateral stiffness of cable-stayed bridge with low side piers,while setting BRB energy dissipation element dissipates some seismic energy through its own buckling deformation.Both of the two construction methods are worthy of recommendation,but the yield problem of support system is still not solved completely.(5)By comparing and verifying the two kinds of new seismic measures constructed,the new quasi-seismic isolation concept has little influence on the seismic performance of the main tower and stay cables,while the damping effect of the support system is the most obvious,and the maximum damping effect can reach78.33%.Compared with the previous measures,the seismic performance of the key components of the first type of new measures has been improved to a certain extent,while the second type of new measures have been reduced to a certain extent,among which the transition pier has the most obvious decline,up to 54.32%.Compared with the original bridge,Measure II-6 has the best damping effect and is the recommended seismic measure in this paper.(6)The new quasi-isolation design can effectively solve the damage problem of the original bridge support system,and greatly improve the seismic performance of the support,up to more than 7 times.BRB energy dissipating element,X-shaped soft steel damper and isolation steel bearing reduce the damping effect of each other,and make the bridge structure in a safe balance state at the same time.The new concept of quasi-isolation and the application of three kinds of isolation devices have great prospect and value for improving the seismic performance of Bridges. |
