Polymer Matrix Composite Manhole Covers Finite Element Numerical Analysis

The manhole lid is a seal which leads to the top of underground facility, anywhere needs to install the running water, electric power, fuel gas, thermal energy, fire prevention, environmental sanitation and so on the public facility will be installed manholes. As a result of recycling value, the traditional cast iron manhole lid is often be stolen by some person, thus may cause serious traffic accident. Moreover, the metal manhole lid is easily rusted which made the worker open the manhole lid difficult when they overhaul underground facility. this papers which studies polymer matrix composites manhole lid is belonged to the type of compound material manhole lid .Because material itself is of 100% rejection, having no recycling value to other industries, it is not only one fundamental means which prevent manhole lid to be stolen, but also may save the massive cast iron resources, it is one idea substitute of cast iron manhole lid.The industrial standard of polymer matrix composites manhole lid is formulated according to the same standard of cast iron manhole. Because this type of material intensity is very low, if we want to achieve the same bearing capacity as cast iron manhole, we must make the manhole lid very thick, which causes the well lid to be opened not easily. Therefore, carrying on the structure of the manhole lid to be optimized, both can reduce thickness of the manhole lid and to be able to achieve the mechanics performance of manhole lid structure to be balanced, has the extremely vital significance.This paper use the finite element of ANSYS analysis software to establish 3D FEA model, firstly, we make the static field of force analysis to the manhole. It can be shown from the results that under the function of static load the stress peak value of manhole lid have been shifted. The biggest tensile stress of radial direction of the manhole lid has been transferred from the center of its upper surface to its edge,the upper surface of stiffer of the manhole lid is its major field of stress concentration, the rib which is connected to the stiffener mainly withstands tensile stress, it's another end connected to the lap mainly withstands compressed stress. Secondly, we analyze the effects of temperature load when the manhole lid works; altogether three kinds of situations are considered respectively, the effects of cold contraction, heat expansion, the heat transfer in steady state. The analysis indicates that under a smaller temperature difference, the temperature load has little influence on the stress field of the manhole lid and can be ignored. The effects of heat expansion and the heat conduction are equal to be exerted a small compressed stress on the upper surface of the manhole lid and the cold contraction is equal to tensile stress, if we must consider the effects of temperature load we can use the equivalent stress to carry on the computation. Finally, considered each kind of the effects of the load exert on the manhole lid, we make the structure optimization analysis to the manhole lid. In this case, the influence of thickness of the lap, the altitude of the stiffer on the mechanics performance of the manhole lid is considered. The analysis result indicates that reduces the thickness of the lap has little influence on the uniformity of the stress field distribution to the manhole lid. Therefore, the thickness of the lap may be attenuated some, but stiffener is the major component which the manhole resists to tensile stress, reduced the thickness of the stiffener may cause the manhole lid appear to the bigger stress peak value, so the altitude of the stiffer is not suitable to excessively be revised. When thickness of the stiffener and altitude of the stiffer are changed simultaneously, we may obtain a more reasonable plan. This paper also discussed other plan of the optimizations to the manhole lid, such as changed the altitude of the stiffer, increased its thickness, changed the of thickness of the lap and increased the altitude of the stiffer and so on, covered on the structure optimization to the manhole lid and to draw some beneficial conclusions.