The Analysis On Stress Properties Of Support Structure System With Thermal Stress

This thesis adopted the spatial finite element method (FEM) to have a numerical simulation on the foundation pit excavation as well as the temperature stress of inner-supporting structure, systematically analyzed the impact of temperature change on the inner-supporting structure system. Based on this, this paper compared and analyzed the influence that the factors including soil parameter, brace’s length and different excavation seasons have on the inner-supporting structure temperature effect, and finally drew some reasonable conclusions that have certain reference value for the practical engineering and theoretical research.The main conclusion are as follows:1. The results of the finite element analysis indicate that the temperature change has a great influence on the brace axial force. When the brace is 20 metres long, the temperature rises by 20 degrees, the axial force of the middle brace will increase by 15.6 percent, at the same time, with the rising temperature, horizontal displacement of retaining structure will be of a linear change, but the soil pressure is not the case.According to the simulation result, it’s found that with the rising temperature, the variation range of the axial force of the middle brace is much less than that of the brace on the left and right. Combined with a simplified calculating method by Zheng Gang and Gu Xiaolu that is considering the interactions among brace, retaining wall and soil, this paper explained this result theoretically which conforms to the time-space effect of foundation pit and verified the rationality of the spatial finite element simulation on foundation pit engineering.2. The following conclusions can be reached with different changes on the compression modulus of soil mass. When compression modulus is 5MPa, 10MPa and 15MPa, with the same rising temperature, the variation range of brace axial force will increase accordingly, which is explained in this paper based on the proportionality coefficient of the ground coefficient(m-value) in theory. Meanwhile, according to the simulation result, we can find the change rule of axial force of the middle brace is slightly different from that of other two sides. From the simulations, it can be found that when the brace is short and it is on the top of soil, the compression modulus of soil mass will have a smaller impact on horizontal displacement of retaining structure after the rising temperature. When the temperature rises, with the increasing compression modulus of soil mass, the variation range of soil pressure will increase as well.3. The brace’s length has a great impact on its temperature effect. Under the same soil condition, when the temperature rises by 20℃, the braces are 40 metres long, the axial force of the middle brace will increase by 24.3 percent, which is 10 percent more than that of the braces of 20 metres long. And the variation of both the horizontal displacement of retaining structure and soil pressure will increase accordingly. It shows that the longer the brace is, the greater the temperature effect will be. Hence, during the designing of foundation pit, if the brace is longer, temperature effect needs to be paid close attention to, which should be considered during the construction process as well.Based on the analysis results of different changes on the compression modulus of soil mass, which means the situations of 5MPa and 15MPa, it can be found that with the change of brace’s length, the effect law of the compression modulus of soil mass on the brace axial force is almost the same before or after the rising temperature. Also, when the brace as well as the excavation’s length is longer, the change law of the axial force of the middle brace will continually reach that of the two sides. What’s more, in this case, the compression modulus of soil mass will have certain effects on the horizontal displacement of retaining structure especially near the pile bottom, while its effect on the horizontal displacement of retaining structure under the rising temperature will get greater slowly but limited.4. Considering foundation pit constructions in different seasons, so the temperature effect of the inner-supporting structure system is different accordingly. This paper respectively simulated all foundation pit excavations from the late winter to the early spring, the early summer to the early autumn and found that excavations in different seasons will have a great effect on the inner-supporting axial force and the deformation of retaining wall. Based on the finite element simulation, it is recommended that excavation can be carried out during the winter.5. At the end, combined with the actual project, this paper verified the rationality and applicability of calculation model based on the spatial finite element simulation.