Investigation On Fatigue Behavior Of RPC And Impact Behavior Of CFRP Cables

To essentially overcome the corrosion and fatigue problem of conventional steel cable,and to improve the applicable span of the cable-stayed bridge,the scheme of high-performance materials based concrete cable-stayed bridge was proposed to be composed of Reactive-Powder-Concrete(RPC)girder and Carbon-Fiber-Reinfoced-Plastics/Polymers(CFRP)cable with properties of high strength,light weight and superior corrosion resistance.With respect to the reasonability of the novel bridge scheme,the structural static and dynamic behavior,as well as the economical efficiency have been discussed extensively in literatures.However,due to the disadvantages of RPC and CFRP,the high-performance materials based concrete cable-stayed bridge will encounter two problems,the first,since the RPC has a high compressive strength to weight ratio,fatigue problem will become obvious as the cross-section of the girder becomes slim and the proportion of the live load increases;the second,CFRP cables are threatened by possible vehicle collisions because of their vulnerability to lateral shear.At present,little reseach has been done on the fatigue property of RPC and impact performance of CFRP cable.Therefore,to solve the two key problems of the high-performance materials based concrete cable-stayed bridge,this paper conducted investigations on the fatigue property of RPC and impact performance of CFRP cable under the under the financial support of Program "Research on the impact performance of CFRP cable and anchor system(National Natural Science Foundation of China,No.51478177)" and Program "Structural behaviors of super-long span cable-stayed based on high performance materials(National Natural Science Foundation of China,No.51078134)".The research manily includes following studies and draws conclusions as follows:(1)Proposed a continuous fatigue strain prediction equation based on a visco-elastic-plastic model.This paper reviewed the existing fatigue strain prediction model and discussed the similarities between fatigue and creep processes.Based on a visco-elastic-plastic model,a fatigue strain prediction equation was proposed.The parameters in the proposed equation,which all vary with the concrete compressive strength,were determined using test results from the literature using least-squares and global optimisation methods.The accuracy of the proposed model was verified with results different from those used to calibrate the model parameters and good agreement was observed.Further applications of the proposed model,including simulation of secant modulus degradation and the damage development of concrete,were performed and the predicted results were compared with test results.The results showed that the three-stage development of fatigue strain,the secant modulus and the damage parameter of concrete at high cyclic stress can be described well by the proposed model.(2)Conducted uniaxial compressive fatigue tests on RPC prism specimens.The fatigue properties of RPC with three different steel fiber ratios of 0%,1.5%and 3%in volume were investigated using uniaxial compressive fatigue tests.Typical failure patterns of RPC under compressive fatigue,fatigue strain development were discussed.The S-N curve and fatigue strength of RPC were established for the prediction of fatigue life.The proposed model was applied to predict the fatigue strain of RPC,the model parameters were identified in accordance with test results.Finally,a fatigue prediction model for RPC was developed.(3)Conducted static tensile test and transverse loading tests on CFRP cables.The failure patterns and mechanical properties of CFRP cables under static loading were investigated by tensile test and transverse loading tests.A total of 14 specimens,including senve single CFRP strands and seven single CFRP rods were tested.These specimens were anchored by the RPC grouted bond-type anchor.Test parameters include the type of the CFRP cable,the pretension,the anchor length.The ultimate transverse bearing capacity,ultimate longitudinal cable tension,and ultimate transverse deflection were determined in accordance with the test results.(4)Conducted transverse impact tests on CFRP cables.Drop-weight impact tests were conducted on 16 CFRP cable specimens,these specimens include single CFRP strand and single CFRP rod anchored by RPC grouted bond-type anchors.Time histories for impact force,cable tension,tranveverse deflection and longitudinal deformation of the CFRP cable were measured.Influence of anchor length,pretension,impact energy,and numer of repeated impacts on the impact behavior of the CFRP cable were investigated.Besides,the failure mechanism of the CFRP cable under transverse impact was discussed.(5)Conducted transverse impact tests on CFRP cables with protective sheath.Feasible protections of CFRP cable for transverse impact were investigated based on traditional protections that applied in traditional steel cables.A total of 14 CFRP cable specimens with different protective sheath were tested under drop-weight impact experiments.These speicmens include single CFRP strand and single CFRP rod.The external protive layer for each specimen was the PVC tube.Three kinds of internal protive layers,including PU,PE,and EP,were tested in present study.The effect of different protections,types of CFRP cable,as well as the number of repeated impacts on the transverse impact resistance,deformation,and energy dissipation capacity of the CFRP cable were investigated.(6)Analysis of the impact behavior of the CFRP cable.Proposed a modified SDOF model for the preidiction of impact response of CFRP cable.The modified SDOF was establied based on the classic SDOF model with consideration of geometrical nonlinearity and available energy.With regard to the CFRP rod,for which slip occured in the impact process,the changes in pretension and available energy before and after the slip shoule be considered when using the modified SDOF model.The impact force and deflection of the CFRP strand and CFRP rod were accurately predicted by the model.The modified SDOF model provided a simplified tool for the evaluation of a real CFRP cable under transverse impact.At last,the mechanical and deformation behavior of the CFRP cable under transverse static load and impact load were compared and analyzed.