Probability Analysis Of Seismic Performance Of Long-span Special-type Suspension Bridge

Southwest China is a complex region of high-intensity earthquakes,its mountains are high,the valleys are deep,and the terrain is undulating,bridges often need to cross ultra-deep "V" shaped canyons.Affected by irregular terrain and site construction conditions,it is often possible to build bridges with large spans and special structural forms,such as long-span special-type suspension bridges.Compared with the traditional suspension bridge,the bridge type has only one tower,which is beautiful and novel in appearance,but it has strong spatiality,complex stress,and is easily damaged under the action of strong earthquakes.Once the bridge is damaged,the repairability is extremely poor,not only affect the ability of mountainous areas to rescue and disaster relief,but also cause serious loss of life and property.Due to the complexity and randomness of ground motions and the uncertainty of structural model parameters,the seismic requirements of bridge structures are more discrete,so,traditional deterministic analysis methods are difficult to effectively evaluate the seismic performance of structures.However,domestic scholars have relatively little research on this type of bridge from the perspective of performance-based seismic engineering.Therefore,it is very necessary to analyze beam end collision and seismic vulnerability analysis of suspension bridges from the perspective of probability.Taking the long-span special-type suspension bridge in a mountainous area as a research background,the nonlinear finite element analysis model was established based on the Open Sees software platform.Through nonlinear seismic response time history analysis,beam end collision probability analysis,and bridge system seismic vulnerability analysis Probability characteristics of seismic performance of bridges.The main contents are as follows:1、Summarizes the development status of domestic long-span suspension bridges,the research status of collision mechanism at the expansion joints at the beam ends,and the calculation method of bridge seismic vulnerability.2、Based on the Open Sees software platform,a nonlinear finite element model of a long-span special-type suspension bridge is established,and the dynamic p-y model is used to consider the soil-pile-structure interaction.The seismic response of a special-type suspension bridge under the action of pulsed ground motion or ordinary ground motion is compared and analyzed.The effects of velocity pulse effect and site soil effect on seismic response under four different probability levels of ground motion are discussed.The damping mechanism of nonlinear damper is studied.3、Considering the random ground motion and the random model parameters,the kernel density estimation method(KDE)was used to quickly establish the beam end collision probability curve,which was verified and compared with the results of the probabilistic seismic demand model.The effects of bridge structure parameters,expansion joint width values and nonlinear damper parameters on beam end collision probability are discussed.4、The basic theory of probabilistic seismic demand model is introduced,the damage index of bridge components is established,the Nataf transform is introduced to consider the correlation between structural random variables,and the distribution types and parameters of uncertain parameters of bridge structures are determined.Twenty-five measured ground motions under different site conditions were selected,and the fragility curves of bridge components were calculated using LHS and IDA methods.The effects of site soil condition types and structural random variables correlation on bridge vulnerability were investigated.5、Based on the basic theory of the reliability of the bridge system,the series model is used to analyze the vulnerability of the bridge system.The first-order bound method is used to estimate the upper and lower bounds of the vulnerability of the bridge system and the improved PCM method is used to quickly and accurately establish the vulnerability of the bridge system that can consider multiple failure modes,the comparative study is based on the accuracy of the calculation results of the above two calculation methods.