Numerical Analysis Of Shear Bearing Characteristics Of Steel Reinforced Concrete Underpinning Beams

With the rapid development of urbanization in our country,many large cities have faced the problem of shortage of construction land resources.At the same time,a large number of existing buildings that have been built for many years have difficulty parking due to unbuilt underground garages.This problem can be effectively solved by developing underground space through the technology of adding underground floors to existing buildings.At present,the key technology for underground increase in existing buildings is foundation underpinning.If the frame column is set between two adjacent underpinning piles and the load is transferred through the underpinning beam,the concentrated load of the superstructure will be applied to the underpinning beam.Therefore,higher requirements are put forward for the shear bearing capacity and mid-span deflection control of the underpinning beam.The steel reinforced concrete underpinning beam has the advantages of large bearing capacity,large rigidity,small cross-section and good structural ductility.It can be used in underground layer addition technology to obtain a larger headroom.Therefore,the relevant research on the shear bearing performance of steel reinforced concrete underpinning beams can provide technical support for the popularization and application of underground storey-added technology.Based on the existing underpinning beam tests in this research group,the finite element software ANSYS is used for numerical analysis,and the following research work is carried out:(1)The modeling method suitable for the finite element analysis of steel reinforced concrete underpinning beams is studied.And related parameters;(2)The effects of shear span ratio,hoop ratio,concrete strength,steel content of section steel and prestress on the shear bearing capacity of the inclined section of steel reinforced concrete underpinning beams are studied,and the underpinning beams for steel reinforced concrete are described.(3)Establish a calculation formula for shear capacity of steel reinforced concrete underpinning beams.The research results show that:(1)By comparing the finite element analysis and test results of the underpinning beam,it is proved that the numerical analysis of the steel-concrete underpinning beam considering the bond-slip between steel and concrete is feasible,and the bond-slip is considered The numerical analysis results of the underpinning beams are more consistent with the experimental results;(2)The shear bearing capacity of the steel reinforced concrete underpinning beams increases with the increase of the hoop ratio,the steel content,the concrete strength,and the effective prestress.The increase of the span ratio decreases;the cracking load increases with the increase of concrete strength and effective prestress;(3)The shear capacity of steel reinforced concrete underpinning beams calculated by the existing specifications is conservative,based on the truss-The calculated value of the shear capacity formula established by the arch model is in good agreement with the numerical analysis value(test value).