Study Of Underground Structural Stochastic Seismic Response And Dynamic Reliability

The stochastic design methods based on reliability theory will no doubt be increasingly applied in underground structural design. Based on the theory of random vibration, the stochastic earthquake responses and dynamic reliability of underground structures under the condition of the linear elastic states were studied by using the method of probability analysis in this thesis. The contents of this thesis include:1. By using the current aseismatic computation theory of the underground structures and the principles of impulse-response function, a method of acceleration impulse function applied in computing the seismic responses of the underground structures was proposed, the formulas for calculating the stochastic characteristics of the underground structural seismic responses were derived and an analytic method for this purpose was put forward. The examples show that this method has the characteristics of high precision and simplicity.2. Based on the mathematical model for analyzing the seismic responses of submerged tunnels proposed by Choshiro Tamura and Shunzo Okamoto, the analytical model for calculating the stochastic earthquake responses of the whole underground structure was proposed and the formulas for evaluating the stochastic characteristics of the underground structural seismic responses were derived. The dynamical mean-square responses of the Nanjing Changjiang Tunnel under Gauss Stationary Random Process were calculated.3. The statistical parameters of the underground structural maximum responses for three earthquake input model by using the formulas proposed by Davenport were calculated. The longitudinal stresses in the tunnel structure calculated by using the model of Tamura & Okamoto are obviously greater than the stresses in transverse direction obtained by using two dimensional finite element analysis. It is proposed that the axial and bending stresses should not be ignoredfor the underground structural design.4. The seismic dynamic reliabilities of the Nanjing Changjiang Tunnel were analyzed, and its dynamic reliable and disable probabilities under the 7 degree earthquake were obtained, by using the maximum stochastic responses and the first overstress mechanism. In the other hand, the probability of serious seismic intensity and its probability distribution function were calculated by analyzing the seismic degree, and the seismic dynamic reliable and disable probabilities of the tunnel in its design reference period were calculated by using the maximum stochastic responses and the first overstress mechanism. The calculation shows that axial and bending tensile safeties are obviously insufficient, so the problem of arranging the longitudinal reinforcing steel bar should be fully considered.5. The influence of the joint form was analyzed, and the damping effects of the elastic joint were studied. In the other hand, the structural maximum responses for the three earthquake input model were computed. The computation shows that the structural reliabilities is improved by use of the elastic joint. The calculation obtained from the seismic input model proposed by Oujinping is more closed to the analysis calculation from fixed value, and the calculating results from the other two seismic input models are larger.6. Based on the basic principles of dynamical analysis by using finite element method, formulas for back-evaluating the stochastic seismic characteristics of the bedrock from the stochastic seismic characteristics of the ground surface were derived by using the impulse-response function and the principles of Fourier transform. A method of back analysis for this purpose is put forward. The example shows that the ground has an obviously amplifying effect for seismic motion.