Study On Shear Behavior Of Strengthening RC Beam By Bolting & Bonding Steel Box

Method of strengthening RC beams by externally bonded steel box is a new type of technology arouse in recent years.Instead of strengthening RC beams by externally bonded steel plate,bonding steel box will provide more bonding capacity and usually have a better torsional performance.Compared with the traditional strengthening method,the method of strengthening RC beams by externally bonded steel box has advantages of convenient construction,short construction period,lighter weight,less steel consuming,higher capacity and stiffness.However,at present the theorists still do not have an in-depth research on this strengthening method especially for its shear behavior as the appearance of the method is not very long up to now.Therefore,the experimental and theoretical research has been carry out under the support Optics Valley 3551 Talent Investment Fund.10 RC beams have been made and all of them were controlled to produce shear failure.9 of these beams are strengthened with externally bonded steel box.Test variables include concrete compressive strength,thickness of the steel web plate,shear-span ratio and the height of the box.Experimental results show that:(1)Strengthening RC beams by externally bonded steel box will obviously improve the shear capacity of the beam.The shear capacity of the reinforced beams are at least 100%better while the stiffness of the strengthened beam is also increased.At the same time,the ductility of strengthened beam is improved to a certain extent although all beams fail in shear.(2)The strength of bonding surface increased with the concrete compressive strength.Usually the separation of steel plates happened in the concrete.The concrete with higher strength will prevent the strengthened beams from premature buckling and provider higher capacity as well.(3)Height to thickness ratio of the steel plates should be controlled to ensure stability when bonding U-shaped steel box strengthening method is used.Hight and thickness are two factors.When the steel web is thickened,the stability of the steel web is enhanced,and the strength of the steel can be effectively utilized.The bearing capacity of the strengthened concrete beam is improved.When the height of the box is increased,the area of the oblique section increases and the shear capacity of the beam increases when the stability is guaranteed.(4)The steel web plates will effectively delay the emergence and development of the crack which also weaken the influence of the shear-span ratio on the strengthened beams.When the beam is strengthened with box steel,shear-span ratio has little influence on shear capacity.The shear mechanical behavior of strengthened is analyzed by the elastic theory and the section conversion method;The stability of the web plates of the steel box is analyzed by plate theory.The formula of the shear capacity of the beam strengthened by externally bonded U-shaped steel box is proposed base on the experiment.Finite element calculation model of beam strengthened by externally bonded U-shaped steel box has been made by Abaqus.The numerical calculation results show that the FEM can simulate the shear mechanism of the strengthened beam.