Flexural Performance Of Plastic-Steel Fiber Reinforced Lightweight Aggregate Concrete Beams Strengthened In Compression Zone

Compared with ordinary concrete beam,plastic-steel fiber lightweight aggregate concrete beam has high bearing capacity and good deformation performance.However,when the ratio of reinforcement is relatively large,the compressive strength of concrete in compression zone is insufficient,and the concrete in compression zone will still be damaged before the steel bar yields.Such a brittle failure mechanism limits the use range of lightweight aggregate concrete beams.Improve the compression performance of concrete in the compression zone of lightweight aggregate concrete beams with plastic-steel fiber,so as to guarantee the bearing capacity and obtain good ductility.This research is of great significance to widening the application range of lightweight aggregate concrete.In this study,nine reinforced plastic-steel fiber lightweight aggregate concrete beams were designed by improving the strength of concrete in the compression zone,using steel fiber locally in the compression zone,and using rectangular stirrup and spiral stirrup to constrain the concrete of compression zone.Based on the analysis of concrete ultimate compressive strain,relative compression zone height,bending moment characteristic value,ductility coefficient and other indexes of SFRC beam,the influence of concrete strength,strengthening mode and reinforcement ratio on bending mechanical properties of SFRC beam was studied.Based on the failure characteristics of SFRC beams and the strengthening mechanism of compression zone,a formula for calculating the flexural bearing capacity of SFRC beams in compression zone is established.The results showed that all the nine reinforced plastic-fiber lightweight aggregate concrete beams in the compression zone are damaged by the failure of the appropriate reinforcement after the compression zone and the failure of the tensile longitudinal reinforcement.By changing the restraint mode of compression zone and the strength of concrete,the original 1.95% limit reinforcement and 2.52% excess reinforcement both showed good ductility.Using steel fiber locally in compression zone and stirrup concrete in compression zone can improve the bearing capacity and ductility of the beam.Although increasing the strength of concrete in compression zone can improve the bearing capacity of the specimen,the brittleness and ductility of the specimen are obvious when it is damaged.Because the section size of the specimen is small,the form of stirrup has little influence on the bearing capacity and ductility of the beam.It is suggested that steel fiber reinforced plastic-steel fiber lightweight aggregate concrete beam be used in the compression zone of actual project.The results calculated by the two methods of strengthening concrete in compression zone and using stirrup to restrain concrete in compression zone are in good agreement with the experimental values.The results of this paper can provide a basis for the calculation of flexural bearing capacity of reinforced plastic-steel fiber lightweight aggregate concrete beams in compression zone.Although increasing the strength of concrete in compression zone can improve the bearing capacity of the specimen,the brittleness and ductility of the specimen are obvious when it is damaged.