Research On Key Technology Of Reinforced Plastic Buried Structure Based On Finite Element

Effective underground pipe network system is the premise of urban development. However, the traditional brick and cement buried structures no longer apply to the pace of the time because of the disadvantages such as high cost, inconvenient maintenance, short life and so on. With the development of plastic industry, plastic is widely used in various fields with its excellent chemical stability, corrosion resistance and electrical insulativity. New reinforced plastic buried structures not only solve the problems existing in the traditional structures, but also can well meet the requirements of energy conservation and sustainable development. Therefore, the new reinforced plastic buried structure will take the place of traditional structure.For plastic buried structures are non-standard parts, the structure design often relys on experience which makes the design cycle longer and the cost higher. With the rapid development of computer aided design, the design and optimization of the reinforced plastic buried structure increasingly tend to use the finite element analysis software to simulate the working conditions, structure tests and other extreme loading conditions which is more efficient and cost lower.In engineering, the key technology of plastic buried structures is to make the structures’ strength, stiffness and stability achieve the requirements through material modification and structural optimization. In this paper, selecting reinforced thermosetting (SMC) and thermoplastic (LLDPE) plastic buried structures as the research objects.First, take SMC valve inspection well, for example. Optimazing design for the structure was made with two enhanced forms; And the mechanical properties of materials were tested respectively. In order to determine the stress and deformation of the structures under different buried depth, the finite element software was used to simulate different working conditions. The results showed that the maximum deformation of glass fiber enhanced SMC valve well reduced 49.39% compared to steel wire enhanced SMC valve well. Then electrical measuring method was applied to backfill test of valve well, and the results of test were consistent with the FEM results which verify the correctness of the finite element model. It could provide the basis for the subsequent analysis and optimization. Considering the SMC structure characteristics of high strength, thin wall and light weight, the stability study must be carried out. The analysis of buckling and post-buckling showed that there was no negative stiffness appeared in the buckling curve and the post-buckling behavior was not sensitive to initial defects.As a typical form of thermoplastic, LLDPE has an excellent plasticity. So these ways could be used in the process of structural optimization for LLDPE sewage inspection well, such as adjusting the thickness of the structure, the size of the well’s mouth or change the location and the shape of the stiffeners. And the material nonlinearity and geometrical nonlinearity also be considered during the finite element analysis. According to the result, the LLDPE inspection well should not be used more than 6m. Then negative pressure test and simulation analysis were carried out on the structure which material is nonlinear. And the deformation got from the test can be used to verify the correctness of the finite element model, that meant negative pressure test of the structure which material is nonlinear is feasible.