Research Of Shear Behavior Of Plastic-Steel Fiber Reinforced Lightweight Aggregate Concrete Beams

Lightweight aggregate concrete has the advantages of light weight and high strength,but it is more brittle than ordinary concrete.The shear failure of beams is brittle failure,and the brittleness of shear failure of lightweight aggregate concrete beams is more obvious.Thus,how to overcome this defect has become the focus of current research.Compared with steel fiber,plastic-steel fiber has more stable chemical properties and better alkali resistance.When incorporated into lightweight aggregate concrete,it can prevent crack and increase toughness with no effect on the bulk density of lightweight aggregate concrete.Therefore,the shear performance of plastic-steel fiber reinforced lightweight aggregate concrete beams is studied in this paper.Shear test under symmetrical concentrated load on 11 plastic-steel fiber reinforced lightweight aggregate concrete beams and 3 lightweight aggregate concrete beams was carried out to research the influence of plastic-steel fiber content(0 kg/m~3、3 kg/m~3、6 kg/m~3、9 kg/m~3),the reinforcement ratio of stirrups(0%、0.19%、0.38%)and the shear span ratio(1、2、3)on shear performance of oblique section of plastic-steel fiber reinforced lightweight aggregate concrete beams.The effectiveness of plastic-steel fiber to replace the stirrups to bear shear force is discussed,and the formula of shear bearing capacity of plastic-steel fiber lightweight aggregate concrete beams is established.The results show that the failure mode of lightweight aggregate concrete beams changes with the incorporation of plastic-steel fibers.Among them,the failure mode of lightweight aggregate concrete beams without web reinforcement are transformed from diagonal tension failure to shear-compression,and the failure mode of the lightweight aggregate concrete beams with stirrup reinforcement ratio of 0.38%changes from brittle shear-compression failure to shear-bending failure with better ductility.The shear bearing capacity,ductility and initial crack load of shear span zone are increased by adding plastic-steel fiber into lightweight aggregate concrete beams,and the maximum width of diagonal crack in shear span zone decreases.The shear bearing capacity and ductility of lightweight aggregate concrete beams without stirrup and with stirrup reinforcement ratio of 0.19%are better than the lightweight aggregate concrete beams without plastic-steel fiber but with stirrup reinforcement ratio of 0.19%and the stirrup reinforcement ratio of 0.38%respectively.That is to say,plastic-steel fiber can replace the stirrups.Based on the analysis of the contribution of various factors to the shear bearing capacity,the formula of shear bearing capacity of oblique section of plastic-steel fiber reinforced lightweight aggregate concrete beams is derived.And the calculated results of bearing capacity agree well with the experimental results.It is indicated that the formula has certain applicability,which can provide reference for the engineering practice of plastic-steel fiber lightweight aggregate concrete.