Analysis Of Experiment And Simulation For CFRP Renewal Of Prestressed Concrete Cylinder Pipe With Internal Pressure

Prestressed Concrete Cylinder Pipe is consisted of four materials:core concrete,prestressed wires,steel cylinder and mortar coating,which is widely available for water transfer projects,municipal and hydraulic projects.PCCP generally contains two types;,a steel cylinder lined with a concrete core which is called PCCP-Lined Cylinder Pipe(LCP)and a steel cylinder embedded in a concrete core which is called PCCP-Embedded Cylinder Pipe(ECP).The scope of this paper is limited to ECP.For PCCP,circumferential prestressing force that is derived from spiral wound prestressed wires makes concrete compression.It must offset this prestressing force firstly when the pipe is subjected to the internal pressure,then the concrete will be transferred to tension from compression.As is known to all,concrete owns a low tension strength,applying for prestressing force will partly compensate for tension stress that is produced by internal pressure,prestressed wires could relieve the extension of crack,improve the bearing capacity of defending internal pressure.On the other hand,the prestressed wires can play a role of reinforcement on the effect of exteral loads.Thus,wires is vital to PCCP.In fact,wires may break for the sake of corrosion and hydrogen embrittlement,little wires break have a limited effect on the safe serviceability of pipe.With the development of wires break,the pipe’s internal and enternal capacility will decrease constantly,servicing risk will in increase continuously,bringing a serious disaster.So,it’s necessary for utility to study the process of breaking wires and repair it after failure.At present,the method for repairing PCCP include replacement,inserting a smaller-diameter sleeve,reinforceing concrete again and attaching CFRP to the inner surface of pipe.Foremost,attaching CFRP owns many advantagements:never contain the necessitates removal of soil and earth,simpler craft,shorter time of construction,less impact on the environment.It’s not well known for us about the mechanism of strengthening theory,the corresponding craft is not wholly mature.This paper has acquired some achievements for the study of repairing PCCP:(1)Based on the design technique of PCCP,finite element theory and the structured type,we choose the appropriate element type and constitutive relation for numerical analysis.(2)Based on the failure pattern,we develop the limit state principal for PCCP with broken wires have three limit states:Serviceability Limit State,Damage Limit State and Strength Limit State.Those limit state is expressed by Number of Broken Wires-Intermal Pressure curves,we can devide pipes these pipes into different reapiring priority through these curves,which can provide some basis for the strengthening design scheme for PCCP.(3)We conduct the wire-breaking experiments,bond strength test and laboratory tests for PCCP with one longitudinal CFRP and one hoop CFRP.Through wire-breaking experiments,we analysis the mechanics behavior for the composite pipe of CFRP strength PCCP at different stages;Through bond strength test,we confirm the bonding quality;Through laboratory tests,we test the CFRP tension strength and CFRP Young modulus,which provide some basis for CFRP reapirs PCCP.(4)Combined with the structured characteristic of CFRP repaired PCCP,we develop the CFRP and CFRP-concrete interface numerical model and study the whole failure process of composite pipe.Compared the experiment results with the simulating results,we found these two resules are very close and vertified the correctness of research method.What’s more,we draw the Number of Broken Wires-Internal Pressure curves that judging the decreasement level of PCCP and determine the threshold value of broken wires for strengthened pipes with working pressure is 0.8MPa and design pressure is 1.12MPa.(5)We study the pipe with broken wires at the situation of pasting CFRP and the situation of no CFRP which used in South-to-North Water Transfer Project,analysis the mechanical behavior of all materials at crown,springline and invert for increasing pressure stage and breaking wires stages.As a result,we know the internal pressure bearing body at wires breaking stage for PCCP in actual state and the role of CFRP plays.