Experimental Study On Shear Properties Of Reinforced Concrete Beams Strengthened By Direct-Shear-Bolted Side-Plates

Bolting steel plate to the substrate of the concrete beam provides a practicable solution for improving the service performance of existing structure.When the steel sideplate is bolted to the beam web,the great shear bearing capacity can be achieved.Due to the clearance between anchor shaft and the wall of clearance hole in the steel plate,there is a deformation discrepancy between steel side-plate and relating concrete substrate in traditional bolted steel-side plate beam.In this way,the traditional bolted steel plate beam cannot effectively play the working performance of the anchor bolt group.In order to improve this phenomenon,the team independently developed the direct-shear-bolted side-plates technique(DBSP),which can eliminate the clearance between bolted steel side-plate and relating concrete substrate so as to minimize the extent of deformation discrepancy.This strengthening technique can utilize the bearing capacity of the material,while improving the stiffness of the specimen,the development of cracks on the part of the component is limited,and the limit of the increase in bearing capacity is broken.Based on the previous experimental results of the team,three groups of reinforced concrete simply supported beams with shear span ratios of 1.0,2.1 and 3.1 are designed in this paper.Each beam was subjected to two shear tests.The effectiveness of the shear strengthening technique applied to beams with different shear span ratio was explored,and the strengthening mechanism of steel side-plate in the loading process of the test beam was analyzed.This paper completed the specimen design,strengthening programme design,measurement programme design,shear test of three test beam,and completed the analysis of test results.The main research results in this paper are as flows:(1)Using measured data of this paper,the reliability of deformation decomposition approach for prismatic beam proposed by our team is verified.Through this approach,flexural deflection of the test region,shear deflection of the test region,and the rotational deflection of the load point can be calculated dependently.The fore mentioned flexural deflection,shear deflection,and deflection caused by measured target section rotation add up to estimated deflection of target section The test results show that the estimated deflection curve agrees well with directly measured deflection.The reliability of this deformation decomposition approach is demonstrated.(2)The comparative study on the un-strengthened and strengthened region of three groups of test beams shows that the shear strength,stiffness and ductility of test beam had a great improvement after strengthened.The strengthening technique of direct-shear bolted side-plate can be suitable for the shear bearing capacity of deep beams and slender beams.(3)Through the analysis of the stress and strain distribution of steel side-plate,it is found that during the shear force process of the test beam,the oblique compressive stress field from the load point to the support can be formed on the steel side-plate,which is consistent with the stress distribution state on the concrete beam in the truss theory,indicating that the steel side-plate can form composite mechanism with concrete beam.(4)Combine with the shear transmission mechanism of reinforced concrete beam and the stress and strain state on the steel side-plate,the strengthening mechanism of the steel side-plate is analyzed.There are two main situations,one is that the steel side-plate can form a composite action with the concrete beam,and the steel plate directly bears part of the shear force and transmits the shear force to the support.the other is the aggregate interlock mechanism in crack section was retained by limiting the crack width of concrete,so that the part of the concrete can continuously transfer the shear force.Specially,in deep beam,shear stress can be directly transmitted to the support by concrete strut,and the shear bearing capacity is mainly related to the compressive strength and the effectiveness of the concrete strut.Direct-shear-bolted side-pale can improve the effectiveness of the force transmission of the concrete strut by forming a constraint on the inclined compressive strut.