Study On Flexural Behavior And Stability Performance Of High-strength Reinforced Reactive Powder Concrete Members

As a new kind of cementitious composites,reactive powder concrete(RPC)is becoming a very popular material in civil engineering.By eliminating coarse aggregate,optimizing the particle size distribution,mixing the steel fiber and the steam curing materials to reduce internal micro cracks and gaps,reactive powder concrete has high mechanical properties and toughness as well as durability.HRB500 bar is a type of high-strength hot-rolled ribbed bar,and its application can reduce the amount of steel reinforcement and easy the reinforcement layout due to its high strength,good ductility,low consumption of energy and material.The combination of reactive powder concrete and HRB500 makes it possible to optimize their properties.It is greatly necessary to carry out experimental and theoretical research on the combined application of HRB500 reinforcement and reactive powder concrete.In this paper a series of experimental researches and theoretical analyses on reactive powder concrete components were carried out.The main contentes are as follows:(1)The axial compression strength,axial tensile strength,flexural strength,compression stress-strain ascending-curve and tensile stress-strain full-curves of reactive powder concrete were determined through the compression tests,tensile tests and flexural tests.The constitutive model of compression and tensile stress-strain curves fitted the test ones.A simplified constitutive model of tensile stress-strain curves was also established,which could provide a theoretical basis for the whole process mechanical analysis of reactive powder concrete members.(2)A series pull-out tests were conducted on cubic specimens to investigate the bonding mechnism,bond stress-slip process and failure mode between high strength rebar and concrete.The influence laws of bond length of reinforcement,concrete protection layer thickness,standard curing age of reactive powder concrete,steel yield strength,rebar diameter and stirrup on bond properties were discussed.Based on the experimental results,equations for calculating the ultimate bond strength and critical anchorage length were derived respectively.And bond stress-slip constitutive model was established.(3)Experimental and theoretical research on high-strength reinforced reactive powder concrete subjected to bending was carried out.The detailed analyses on the process of flexural behaviors,crack distribution,the characteristics of the load-deflection curves and the failure modes were analyzed.Given that the contribution of the tensile stress in tension zone had caused by steel fibers,the computing formula for calculate ultimate bending moment,the cracking moment,crack width and stiffness of high-strength reinforced reactive powder concrete beam were proposed.The theoretical calculation values match well with the test results.(4)The elastic buckling coefficient and elastic buckling load formula of reactive powder concrete plates with simply supported on four sides,simply supported on three edges and simply supported on two edges under uniform pressure were derived.The buckling tests on reactive powder concrete plates were conducted to investigate the buckling mode,buckling load and failure mode.The influences of depth-thickness ratio,width-thickness ratio,boundary conditions on the buckling performance were discussed.The geometric initial defect effecting coefficient was introduced to modify the elastic load,the elastic-plastic buckling load and the post buckling load formula of the plates with four edges simple supported.The calculated values by the suggested formulas agreed well with the test results.The elastic buckling coefficient formula of reactive powder concrete plates with simply supported on four sides under pure bending was derived by theoretical derivation.The elastic buckling analysis of rectangular plates under pure bending was also carried out by numerical method.(5)The elastic buckling load formulas were derived for the longitudinal stiffened and transverse stiffened reactive powder concrete plates with simple supported on four edges,simple supported on three edges and simple supported on two edges.The influences of stiffness and the distance between ribs on the buckling behavior of plate were discussed.Then,the optimized stiffness ratio was derived.The elastic buckling analysis of stiffened rectangular plates and box girder webs under pure bending were also carried out by numerical method.A simple and accurate formula for buckling coefficients of web plates restrained by both upper and lower plates of the box girder were presented by numerical method.The influences of the distance and stiffness of the diaphragm,the height-to-thickness ratio of the web,the width-to-thickness of the upper plate on the stability of reactive powder concrete box girder were analyzed.