Calculation Method And Experimental Verification Of Shear Capacity Of RC Beams With Circular Web Openings Reinforced By Encased Section Steel

With the rapid development of science and technology and the increasing population expansion,the function of buildings is increasing day by day,in order to facilitate the penetration of the pipeline,it is necessary to open holes in the web of the reinforced concrete beam.However,for reinforced concrete beams,the openings of the web will significantly weaken its shear bearing capacity,reduce the stiffness of the member,and cause the stress concentration in the corner of the opening to cause the crack to develop prematurely,resulting in a decrease in the bearing capacity of the beam and an increase in deflection and crack width.the bottom longitudinal rebar fails to yield,that is,shear failure occurs,which has a serious impact on safety and applicability of the structure.In order to improve the shear bearing capacity of reinforced concrete beams with circular web openings,a shear bearing capacity reinforcement method of encased section steel is proposed,the finite element analysis of the shear bearing capacity of the reinforced concrete beam with circular openings in the web is carried out,and the follow-up test verification is carried out.The following research work is mainly completed:(1)For reinforced concrete beams with circular openings reserved in the web,a shear bearing capacity reinforcement method of encased section steel is proposed.The method uses a hexagonal steel section welded by angle steel which is arranged around the circular openings.Based on the stress characteristics of the open-hole beam under the shear failure beside openings and shear failure of chords above and below openings,the calculation methods of shear capacity of reinforced concrete beams with circular web openings reinforced by encased section steel under these two failure modes are respectively proposed.(2)In order to verify the effectiveness of the reinforcement method and the accuracy of the calculation methods of shear bearing capacity,a simply supported reinforced concrete beam with solid web is designed firstly in this paper,and then its ultimate shear bearing capacity is calculated;two beams with circular web openings are designed by opening circular holes in the web of the solid web beams,then in order to achieve the same shear bearing capacity as the solid web beam,the cross-sectional area of the encased section steel and stirrups required of the beams with circular web openings is obtained by using the proposed shear bearing capacity calculation methods.(3)The finite element models of three simply supported reinforced concrete beams are established by Abaqus,and then the nonlinear analysis of shear bearing capacity is carried out.the crack development,the strain of the steel bar and the section steel of these three beams are preliminarily analyzed,and the finite element simulation values of the ultimate shear bearing capacity of the three beams are obtained.The result shows that the two beams with circular web openings reinforced by encased section steel can achieve the same shear bearing capacity as the solid web beam.(4)In order to verify the validity of the finite element analysis results,further static loading tests are carried out on the two beams with circular web openings mentioned above;The data such as cracks,steel bar strain and vertical deflection under various loads are studied,and the ultimate shear bearing capacity test values of these two beams are obtained;The finite element simulation value,experimental value and theoretical calculation value of the shear bearing capacity of these two beams are compared with each other,the result shows that the experimental value is close to the finite element simulation value,and the maximum error between the two is about 2.8%which indicates that the finite element model of the reinforced concrete beam with circular web openings reinforced by encased steel can better predict its actual shear bearing capacity;the experimental value is larger than the theoretical calculation value,and the two are in good agreement,the maximum error between the two is about 14.3%,the effect of the shear bearing capacity reinforcement method of encased section steel is remarkable,the proposed calculation methods of shear bearing capacity are accurate and have a certain safety reserve.