Study on the Mechanical Properties of Primary-Secondary-Beam Joints of U-Shaped Steel-Encased Concrete

U-shaped steel-encased concrete composite beam is developed on the basis of traditional composite beam,which has the characteristics of high bearing capacity,large stiffness and good stability.This kind of composite structure is relatively complicated in the joint position of primary beam and secondary beam,so it is of great significance to study the reasonable joint structure form and give full play to the mechanical properties of steel and concrete.Reference to steel structure connection mode,and it gave out the primary and secondary beam joint with the short end plate was connection beam connection signal hint:steel-encased secondary beam through the end plate was connected to the primary beam,or short beam was welded in advance on the web of primary beam,the secondary beam overlapped on the short beam was connected to the primary beam by bolts to reduce the field welding,facilitate construction hoisting,simplify the construction process.The finite element model of the primary and secondary beam joints was established by using ANSYS finite element software,and the stress mechanism and failure mode of the joints were analyzed.The influence of different structural measures such as stiffening rib,connecting cover plate and I-steel secondary beam on bearing capacity,connection stiffness,stability and deformation capacity of the joint was studied.The influence of structural parameters such as reinforcement ratio,concrete strength grade and stiffener thickness on the mechanical properties of the primary and secondary beam joints was studied by parametric analysis.
The results show that the bending stiffness of the section in the core area of joints is obviously lower than that in other areas,and the concrete in the core area is crushed first.The steel web of the primary beam is subjected to transverse deformation due to the large lateral force transferred from the direction of the secondary beam.After adding stiffeners at the joints,the deformation is significantly reduced,and the bearing capacity of the joints is increased by 7%,the rotational capacity is controlled at a lower level,and the ductility is also improved to a certain extent.The cover plate is set to enhance the tension capacity of the upper side of the joint.After analysis,the effect of the cover plate on the tension area is lower than that of the reinforcement.When the secondary beam adopts I-steel form,the bearing capacity of the joint is relatively low,and the construction operation is simple.When the span of the secondary beam is small,this form can be used to design and reduce the use of materials.Through the parametric analysis of the joint,it is found that the joint is greatly affected by the negative bending moment,and the upper reinforcement configuration has a significant impact on the bearing capacity,rotation capacity and deformation capacity of the joints.Excessive cross section angle is easy to cause the flange cracking,so it is necessary to control the rotation capacity of the joints.In addition,the reinforcement in the concrete flange plate also plays an important role in the mechanical properties of the joint.The reinforcement in the 2 metres range is relatively high,so it is recommended to consider the reinforcement in the effective flange width when calculating the ultimate bearing capacity of the joint.The strength grade of concrete and the thickness of stiffened ribs also have a certain influence on the mechanical properties of the joint.When the primary and secondary beam joints are designed as rigid connections,short beams or end plates with stiffening ribs should be used.