Study On The Method Of Probability Limit State Design For Tunnel Portal

As one of the part of the railway tunnel structures, the tunnel portal plays an important role for safe construction and normal operation of the tunnel. The safety factor method can’t embody the discreteness when designing and judging the carrying capacity of the tunnel portal because of the uncertainty of the matters. However, the probability limit states method is up to the requirement of the structures which is on the basis of researching for the probability of the structures that complete predetermined function during the providing time and condition. Now, with a lot of high-speed and double track railway tunnel portals having been built, it is necessary to put forward new limit state design expression combining the standard drawing of pre-existing portals. The contents of this thesis are as follows:(1) Make a taxonomic revision of the different tunnel portals through reviewing literature. Confirm the way of dividing the portal’s end wall into strips when calculating. This part is the basis of the study on the method of probability limit state design for tunnel portal.(2) Establish set of limit state equations according to force analysis and then make sure the statistical characteristics of the random variable in the equations.(3) Compare and select the most appropriate way of calculating the reliability index of probability limit condition design methods among several different reliability methods. Make sure the target reliability index in different limit state of tunnel portal structures using calibration method combining the current codes.(4) Found the limit state expression for design. Calculate the partial coefficient of action effect and resistance in the limit state expression. When considering the load combination, the coefficient will be optimized and tested to make sure the result can be used in the design of the tunnel portal.