Study On The Flexural Behavior Of ECC-concrete Composite Beam Reinforced With Steel Bars

Although concrete is widely used,it often shows some shortcomings like low tensile strength,obvious brittle failure,low reliability and difficult control of cracking cracks and so on.These potential disadvantages have been the key factors restricting the durability and long-life of concrete.In order to effectively improve the durability of concrete,the new type of engineering cement matrix composites(Engineered Cementitious Composite,ECC for short)has been gradually applied to a large number of engineering solid structure.ECC has the characteristics of pseudo strain hardening and fine crack mode,and it can still maintain good integral synergistic force under the condition of structural cracking.The use of high strength steel bars has achieved the purpose of saving steel to some extent.In order to improve the durability of ordinary reinforced concrete beams,it will be an effective method to limit the number and width of cracks.Crack is the first factor to reduce the durability of ordinary reinforced concrete beams.This paper has designed 20 groups of specimens with 4 working conditions by changing the replacement height rate of ECC,the number,the grade and the diameter of steel bars.the bearing capacity,deflection,average strain along the beam height,reinforcement strain,and number and width of cracks can be measured by carrying out a two-point symmetrical bending test,then the deflection curve,the strain curve,the average strain curve along the height direction and the crack width curve can be drawing.Finally,the optimum design form and deformation characteristics of the specimen can be obtained based on the above analysis results.The results show that the bending cracking mode of composite beams is a fine crack mode,and the failure has certain ductility.The higher the ECC replacement height ratio is,the more the number of cracks and the finer the crack width of the composite beams are.When the replacement height ratio of ECC is changed,the bending moment-deflection curve of composite beam with two longitudinal steel bars has the same development trend,while the bending effect of composite beam with one longitudinal steel bar is not good.For this experiment,the optimum replacement height ratio of ECC is between 0.5 and 0.75.The bending moment-strain curve for longitudinally loaded steel bar and bending moment-deflection curve are in good agreement with the development trend,it shows that the connection has better bearing effect.The strain distribution of longitudinal steel bar in a certain span tends to be uniform by replacing ordinary concrete with ECC.The use of ECC replacing concrete can avoid or limit the occurrence of large cracks.The cross section strain of composite beam accords with the assumption of plane section.Increasing load can cause the natural axis to move upward and decrease the height of compression zone of concrete.The ECC replacement layer can significantly limit the width of cracks and reduce the average spacing of the cracks.The ductility of the test beam varies with the change of replacement height.However,the ductility ratio of ordinary reinforced concrete beams is not different from that of ECC-concrete composite beams.The ductility ratio is less affected by the change of ECC replacement height ratio.The finite element simulation values of composite beams agree well with the experimental values,and the material parameters and constitutive models can better reflect the bending process of composite beams.