Stochastic Theory Of Dynamics Of Structural Applications To Bridge Earthquake Engineering

As the important communal constructions, security of the long-span bridges is very crucial to their builders. How to make them have the enough aseismatic ability and the reasonable traffic safety during their constructional period is the important problems paid a lot of attention to by the domestic and the oversea scholars and engineers all the while. In the few past decades, researches for bridges' seismic responses have obtained a large number of achievements. But because of the variety and the complexity of the bridges' seismic problems, there are a lot of problems need farther investigations yet. In all the problems, the stochastic theory of dynamics of structural applications to bridge earthquake engineering is the hotspot recently in bridge's constructions. Therefore, the problem is studied in this doctoral dissertation and the main research works are as follows:(1) The equation 13 used to solve the integral of absolute values of the response variance of accelerations in spectral parameters of Kanai-Yajimi spectrum in accordance with response spectral method of code written by Sun Jing-jiang and Jiang Jin-ren is corrected. The analytical expression of the response standard deviation of acceleration was developed on condition that the seismic excitation was the white sound.(2) Using mass-spring-damp model to simulate the dynamic interactions of the pile-base-structure in seismic analysis of bridge, the impacts on seismic response of bridge, whether or not take the pile-base co-action into account, were studied.(3) Based on theory of random vibration and response spectral method, the wave propagation effect, the coherence loss, and the site conditions of the bases of the long-span bridges are investigated. The conclusions show that: analysis of random vibration is in accord with the response spectrum method excluding the spatial variation effect of the seismic action; second, the wave propagation effect and the coherence loss would surely change the internal forces of the continuous rigid frame-beam bridges and the computed conclusions by random vibration are greater than by response spectrum in most circumstance; third, the large differences of the site conditions of the bases significantly change the response of the continuous rigid frame-beam bridges, which should be included in the seismic design of the bridges.(4) Random of the structural parameters and seismic excitation is very important to the seismic design of the bridge. The perturbation equations were developed by combining the SFEM with the pseudo-excitation method. Based on theory of local average random fields and spatial structure member model, the FEM model of the long-span bridge with random parameters and subjected to random seismic excitation was meshed. In order to improve the computed speed, the matrices orthogonal transform technique was applied. The means with second-order precision and the variances with first-order precision of the structural responses could be obtained by solving the zeroth-order, first-order and second-order perturbation equations. A computer program is developed by C++builder, and its correctness and validity is verified by Monte Carlo method. As a sample, the dynamic response of a high-piers and long-span rigid frame bridge and a new type basket-handle arch with random parameters and subjected to random seismic excitation is computed.(5) Employing basic theory of elastic-plastic FEM under cyclic loading and incremental prestressed method, the iterative formulas of elastoplastic FEM under random loading method were deduced. According to theory of random fatigue life, local stress-strain method, Palmgren-Miner's rule for fatigue damage accumulation and the elastoplastic FEM under random loading, an algorithm for bridge component's stochastic fatigue life was proposed. The low-cycle fatigue life of the component of the long-span steel bridge which has hole or across section is weakened under seismic excitation was studied.(6) Dynamic reliability of the structures with random parameters is very important to the anti-seismic design of the bridge. Based on theory of the response surface of random vibration and response spectral method, an algorithm for the seismic reliability analysis of the structure with random parameters is proposed in this paper. The response surfaces generally take a approximate polynomial form to replace the function which denotes the relationships of the input random parameters and the output parameters. The reliabilities are studied according to structural failure criterions and the equations under their limit states. The anti-seismic reliabilities of the high-piers and long-span rigid frame subjected to seismic excitation in its design basic period are studied by this method. The random of the structure parameters and the site condition of this bridge are taken into account when it's failure seismic reliabilities are computed respectively at the low-level earthquake, design earthquake and high-level earthquake. According to the "three-level seismic fortification criterion" in the code for seismic design of bridge, the seismic reliabilities of the bridge are calculated in their design basic period. The conclusion shows that the design of this bridge meets the demands of the seismic code.