Study On Flexural Performance Of The Strengthened Steel Beams With Precast Concrete Slabs

As one of the main building structures of prefabricated buildings,steel structure is widely used in civil buildings and industrial buildings.When the steel structure is corroded by the environment or the function of the building changed,it is easy to lead to insufficient bearing capacity,structural damage,casualties and economic property losses without strengthened and repaired in time.Under the implementation of the "dual carbon" goal,the reinforcement of the existing steel structure is not only conducive to extending the service life of the steel structure and improving the performance of the structure,but also can reduce construction waste and economic losses,which is in line with the green development strategy of China.Aiming at the shortcomings of the existing steel beam reinforcement methods,this paper proposes a new reinforcement method-precast concrete slabs to reinforce steel beams to form a Partially Encased Composite Beam(PEC beam),which not only gives full play to the mechanical properties of steel-concrete composite beams,but also improves the fire resistance and corrosion resistance of the structure.In order to study the flexural performance of strengthened steel beam specimens with precast concrete slabs,four groups of full-scale four-point bending tests were designed to carry out to study the failure mode,load-deflection curve,crack development,stress-strain relationship,etc.The number of precast concrete slabs and other parameters on the bending bearing capacity of the specimens were also studied.The test results show that the pulling bolts can ensure that the concrete and steel beams have a complete combination effect.Compared with the existing steel beams,the average ultimate bending bearing capacity of the strengthened steel beam specimens by precast concrete slabs is increased by 60%,indicating that the concrete on both sides of the steel beam web can effectively prevent the instability of the steel beam,and greatly improve the stiffness and bending bearing capacity of the specimens.The number of precast concrete slabs has little effect on the bending bearing capacity of the specimen,but when the splicing of the precast plate and the cast-in-situ section is set in the pure bending section,the cracks at the splicing develop more rapidly,which will make the deflection of the specimen reach the ultimate bearing capacity,and the concrete crushing will appear at the joints when the final failure occurs.The finite element software ABAQUS was used to simulate and analyze the strengthened steel beam specimens with precast concrete slabs,and the simulation results are in good agreement with the test results,which verified the accuracy of the finite element model established in this paper.By setting the parameters such as concrete strength and longitudinal rib diameter,the influence of different parameters on the strengthened steel beams with precast concrete slabs was further analyzed.The results show that with the increase of concrete strength and longitudinal rib diameter,the bending bearing capacity of the specimens continues to increase.Based on the Code for Design of Composite Structures,the calculation formula of bending stiffness of the strengthened steel beams with precast concrete slabs is obtained.Based on the local buckling criterion,the calculation formula of yield bending bearing capacity is proposed.Based on the full-section plasticity criterion,the calculation formula of ultimate bending bearing capacity in the plastic stage is proposed.The calculation results are similar to the test results,indicating that the theoretical calculation formula proposed in this paper is suitable for analyzing the bending bearing capacity and stiffness of the strengthened steel beams with precast concrete slabs.