| The application of Carbon-Fiber-Reinforced-Polymers(CFRP)bar in civil engineering can essentially eliminate the premature failure of the structures caused by the steel corrosion,and meet the requirements of structural lightweight,owing to its lightweight,high strength and excellent durability.T he high performa nce CFRP bar is a kind of anisotropic and temperature dependent material,and it is necessary to investigate the longitudinal and transverse mechanical properties,as well as the temperature effect on the performance of CFRP bar,before its real applicatio n in engineering.However,the research on the mechanical properties,especially the mechanical performance of CFRP bar under variable temperature,is incomplete at present.T herefore,this paper conducted systematic investigations on the static and impact performance of CFRP bar with considering the temperature effect,which can provides theoretical references for the application of CFRP bars in real engineering.The present research was supported by the Program “Research on the impact performance of CFRP cable and anchor system(National Natural Science Foundation of China,Grant number: 51478177)” and Program “Integration and demonstration of key technologies in new type of fiber reinforced polymer structure(Ministry of Science and Technology of China,G rant number: 2017YFC0703008)”.The main conclusions are as follows:(1)Experimental research on the axial tensile properties of CFRP bars exposed to varied temperature.T he CFRP bars were exposed to a temperature of ambient temperature(30 °C),100 °C and 200 °C,and then anchored with two bond-type anchors grouted with a reactive powder concrete(RPC).Based on the results of the axial tensile tests on CFRP bar-RPC specimens,the reliability of the bond-type anchor system was verified,and the axial tensile properties,including elastic modulus,tensile strength,fracture strain and stress-strain relationship,of the bar was obtained.Additionally,the effect of exposed temperature on the performance of CFRP bar and its anchor system was revealed,and corr espondingly,a degradation function for the axial tensile property of CFRP bars exposed to varied temperature was proposed.By comparing the axial tensile properties of a CFRP strand and its single wire,the non-uniformity of load distribution among the st rand was determinded.(2)Experimental research on the transverse static properties of CFRP bar.T he failure pattern and mechanical properties of CFRP bar under pure bending load was obtained through three-point bending tests.Afterwards,the transverse st atic load tests were carried out on 9 groups of CFRP bar-RPC specimens under different pretension,to verify the reliability of the anchor system and clarify the effect of pretension ratio on the longitudinal and transverse ultimate load,transverse deform ation and energy absorption capacity of CFRP bar.Based on the test results,the response of CFRP bars subjected to combined tension and bending load was uncovered,and a failure criterion with a simply expression was established to evaluate the damage sta te of CFRP bar under such load case.(3)Experimental research on the transverse static properties of CFRP bar after high temperature treatment.T he three-point bending tests were conducted to obtain the bending performance of CFRP bar exposed to a tempera ture of 100 °C and 200 °C.Afterwards,the transverse static load tests were performed on CFRP bars exposed to a temperature of ambient temperature(30 °C),100 °C and 200 °C.According to the test results,the action mechanism and effect of experienced te mperature history on CFRP bar was revealed.A theoretical analysis model for CFRP bar subjected to a concentrated load in the mid-span was established,and prediction formulas to determine the transverse static response of the bar were provided.Additional ly,the applicability of the proposed failure criterion used for evaluating the failure state of CFRP bar after high temperature treatment was verified.(4)Experimental research on the transverse impact properties of CFRP bar.Based on Charpy pendulum impact test,the fracture toughness of CFRP rod and strand with rigid and soft protection was evaluated,and a reasonable protection pattern to enhance the impact performance of CFRP bar was proposed.The transverse low-velocity impact tests were conducted on 4 groups of CFRP bar-RPC specimens under different pretension ratio with a drop weight impact test system.Compared to the transverse static response of CFRP bar,a dynamic reduction factor(DRF)for a CFRP bar under impact event was determined to be 0.85.As well,formulas were proposed to accurately predict the impact resistance of a CFRP bar.(5)Experimental research on the transverse impact properties of CFRP bar under different temperature.Considering the temperature effect and possible vehicle impa ct on the cables of a bridge when in service,the transverse impact tests were performed on CFRP bar-RPC specimens under a temperature range from-40?80°C using a drop weight impact test system.During the tests,the impact force,cable tension,transverse deformation and absorbed energy were captured,and the impact resistance and energy absorption capacity of CFRP bar under varied temperature were evaluated.Based on the test results,a temperature effect function was proposed to quantify the influence of temperature on the impact performance of CFRP bar.Combined with the transverse impact response prediction model,formulas used for predicting the impact response of CFRP bars at different temperatures were proposed.(6)Numerical simulation analysis of C FRP bar subjected to transverse load.Based on ABAQUS finite element analysis(FEA)software,the numerical analysis model of CFRP bars under transverse static and dynamic load were established by using Hashin failure criterion.First,the feasibility and effectiveness of the FEA model was demonstrated by the test results,and then the stress and damage state of CFRP bar during the whole loading process were analyzed,which uncovered the failure mechanism of CFRP bar subjected to transverse load.Additional ly,the effect of load location,hammer size and impact velocity on the transverse static and impact response of CFRP bar was determined using the established FEA model. |
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