Earthquake Response Analysis Of Glass Fiber Reinforced Plastics Pipes

Glass fiber reinforced plastics pipes are widely used in urban water supply,petroleum,chemical industry,metallurgy and other industries for their advantages of lightweight,high strength,strong corrosion resistance,smooth inner wall,low transportation energy consumption and easy production and installation.With the rapid development of the national economy,composite structures including glass fiber reinforced plastics pipes play a more important role in structural engineering.Many cities of China are located in earthquake-prone zones.It is necessary to study the seismic response and seismic performance of buried pipes.In this paper,the response of buried Glass fiber reinforced plastics pipes under seismic induced transient soil deformations and permanent soil deformations is analyzed.The main works of this paper are as follows.(1)Based on a series of assumptions,an ideal model for the free field of soil under the transverse shear wave is established,and the stress solution is derived from the basic theory of elasticity.Then a finite element model of pipe-soil under the effect of transverse shear waves is established and the free field stress caused by the earthquake is applied as the external force on the boundary of this model.Based on the above model,the mechanical response of the glass fiber reinforced plastic buried tube under the action of the transverse shear wave is analyzed.Some important factors such as the material,the diameter,the ring stiffness,the depth of the GFRP pipes and the pressure grade are studied and discussed.The results show that the hoop safety factor of the GFRP pipes is much higher than that of the steel pipes and the ductile cast iron pipes under the transverse shear wave;the higher the elastic modulus of the soil,the more safe the pipe is under the transient soil deformation;with the increase of the pipe ring stiffness,the strength ratio will be reduced;With the increase of buried depth,the cyclic stress of the pipeline increases rapidly because of the increase of the seismic load and earth pressure,which indicates that the buried depth is an important factor in the seismic performance of the pipeline;with the increase of the pressure grade,the stress caused by the internal pressure gradually exceeds the stress caused by the seismic load,and when the pressure grade is higher than the 0.6MPa,the seismic load is much higher than that of the earthquake load and the stress caused by the earthquake is small relative to the that caused by internal pressure,so the pipe with lower pressure level,such as the pipe under the pressure level of below 0.6MPa must be calculated under the action of the seismic load.(2)For the response of pipeline under earthquake induced permanent ground deformations,another pipe-soil model is established and eleven different models are calculated to study the influence of some important factors such as fault angle,elastic modulus of soil and buried depth etc.The results show that the smaller the fault angle,the more dangerous the pipes are;the lower the elastic modulus of the soil,the safer the pipes are;the greater the buried depth,the greater the axial stress of the pipes and the decrease of friction coefficient will increase the axial stress of the pipes.In addition,the calculation of the pipe under the action of the fault shows that the stress of the glass fiber reinforced plastic pipe is close to the strength limit under the fault of 0.3m,indicating that the pipe is easily damaged under the action of the fault.In order to prevent the damage of the fault,the pipe should not be installed in the area where the fault is likely to occur.When it is impossible to avoid installing the pipe in the area where the fault is likely to occur,we can increasing the number of flexible joints to reduce the axial stress or reducing the lost caused by the fault damage by changing the lining material to the thermoplastic.