Experimental Study On Shear Behavior Of Reinforced Concrete Beams With "Thin" Stirrups

The "thin" steel bar refer to straightened stress hardening bars,which is fine-drawn,leading to increased yield strength while brittle mechanical properties and its elongation does not meet the specification requirements.It is often used as beam and column stirrups and in floor.As can be seen from the online reports that once "thin" steel bar occurs,often involves a large amount of building and the social influence is more widely.At present,there is short of a guiding principle on treatment of "thin" stirrup construction,and there is little related research data,make appraisal of structural security and seismic strengthening with great blindness.Therefore,it is necessary to carry out the study on the influence of "thin" stirrups on the shear behavior of concrete beams.12 reinforced concrete simple-supported beam were tested,6 specimens disposed normal HPB300 stirrups at one end,and the other end disposed HPB300 "thin" stirrups with a 17.6% average weight-loss rate respectively.Crack development is certainly unsynchronized due to the asymmetry of stirrups configuration.The test apparatus was improved to get the full load-deflection curve,double electric cylinder was used for loading.The smaller shear force is expected to be distributed to one side,due to the rapid development of the crack,the stiffness decreases;While larger shear force is assigned to the other side which crack development slower.The experimental results show that:(1)The ultimate shear strength of simple beam with two points loads and the same shear span ratio,stirrup spacing was compared.It finds that although the area decreased,its strength is improved,makes the shear capacity of one side with HPB300 "thin" stirrups is higher than the other side with normal HPB300 stirrups,and slightly lower than configuration of the normal HRB400 stirrups side.(2)For the specimens with failure at both sides,the displacement ductility ratio is calculated by energy principle when the load is decreased to 85% and 70% of the ultimate strength.Compared with the displacement ductility of normal stirrups and "thin" stirrups on a specimen.It can be fond that the displacement ductility ratio at both sides are similar,there was not obviously different in shear ductility for concrete beams deployed "thin" stirrups.(3)Compared with the full shear-maximum crack width curve of normal stirrups and "thin" stirrups on a specimen.It shows that the maximum crack width of the concrete beam on the side of the "thin" stirrups is slightly larger than that of the normal stirrups in the same shear.(4)The deformation in the direction of principal tensile stress measured by the displacemeter,which is arranged in the shear span and vertical to the crack development direction.A comparison of deformation was made between the "thin" stirrups and the normal stirrups,It indicates that no obvious difference between them.(5)According to the test results,it can be seen that the maximum strain of the stirrup is 1.5% when the load is decreased to about 85% of the ultimate strength.No stirrups were found be ruptured in the whole test process.This shows that although the material ductility(elongation)of the "thin" stirrups is poor,it can basically meet the requirement of shear deformation.(6)ABAQUS finite element software is used to analyze the test beams,the total load-deflection curves achieved from calculation coincides well with the experimental results.It illustrate that concrete damage-plasticity model can accurately simulate the elastoplastic deformation of simple beam.(7)The finite element simulation reflected the elastoplastic uniform deformation of simple beam with a concentrated load.However,in the course of the experiment,the appearance of cracks is non-uniform,discreteness and discontinuity.The strain at the crack location is different from that in the other locations,and the position of strain gauge has a great influence on the monitoring data.So,it is very difficult to simulate the stirrup strain.In contrast,the maximum strain of longitudinal reinforcement always at mid-span,and the actual deformation is more uniform,so the simulation of longitudinal reinforcement strain is close to the measured.