Study On Flexural Behavior Of SMA-CFRP Composite Strengthened Flawed Steel Beams

Carbon fiber reinforced polymer(CFRP)can improve the bearing capacity of steel beam,but it is difficult to restrain the development of existing cracks at the initial stage of stress.If prestressed CFRP is used for strengthening,mechanical support is needed,which restricts its application.Shape memory alloy(SMA)can recovery to its original state after thermal excitation with both ends anchored,which can produce prestress to inhibit crack development.The use of SMA and CFRP composite can play the advantages of the two materials and get better reinforcement effect.In this paper,the reinforcement of flawed steel beams with SMA-CFRP composite was experimentally studied.The reinforcement effect of SMA,CFRP and SMA-CFRP composite on flawed steel beams was compared and analyzed.Meanwhile the anchorage performance of SMA embedded in CFRP was discussed.The main research contents and conclusions are as follows:(1)The main properties of NiTiNb shape memory alloy,which include mechanical properties,heating efficiency under electrification and optimal prestrain.The method to improve the mechanical properties and shape memory effect of SMA and the temperature change when heating up with electricity were clarified and the optimal prestrain ratio of SMA was obtained.The maximum recovery force of SMA was 273.86MPa,when the SMA was prestrain at 12%.(2)The anchoring performance of SMA embedded in CFRP was studied,and the influences of different anchoring lengths,anchoring quantities and anchoring spacing on the anchoring ability of SMA were considered.The results show that the anchoring length changes the anchoring force,the anchoring number determines the failure mode of the specimen,and the anchoring distance has little effect on the anchoring performance.(3)The reinforcement effects of CFRP reinforcement,SMA reinforcement and SMA-CFRP composite reinforcement methods on flawed steel beams were compared and analyzed.The bearing capacity of SMA reinforced beams is similar to that of CFRP reinforced beams,while the increase ratio of SMA-CFRP composite reinforcement is about the sum of the two reinforcement effects alone.Compared with CFRP reinforcement,SMA reinforcement can better limit the development of flaw and increase the yield load at the flaw tip.SMA-CFRP composite reinforcement can further improve the stress condition at the flaw tip,and the effect of restraining the development of flaw is better than the sum of the two reinforcement alone,and the yield load at the flaw tip increases by 230.6%after composite reinforcement.(4)The theoretical calculation of flawed steel beams under various working conditions are carried out.The active constraint of SMA and the passive constraint of CFRP are considered in the calculation.The error between the theoretical value and the experimental value is less than 14%.