Study on the Mechanical Properties of Primary-Secondary-Beam Joints of U-Shaped Steel-Encased Concrete
研究表明:节点核心区截面抗弯刚度明显低于其他位置,核心区混凝土首先发生压碎;受到次梁方向传递较大侧向力作用,主梁钢腹板发生横向变形,在节点连接处增设加劲肋后,变形明显减小,且节点的承载力提升了 7%,转动能力控制在较低水平,延性也有一定提升;为增强节点上侧受拉能力所设置的盖板对受拉区产生的效果低于配置钢筋所带来的作用;次梁采用工字钢形式时,节点的承载力相对较低,施工操作简单,当次梁跨度较小时可采用此类形式设计,减少材料使用。通过对节点的参数化分析,得知节点受负弯矩作用影响较大,上侧钢筋配置对节点的承载力、转动能力以及变形能力影响显著,截面转角过大容易导致翼缘板开裂,故需要控制节点转动能力。此外,混凝土翼缘板内钢筋对节点受力性能也发挥了重要作用,2 m范围内的板内钢筋应力水平较高,节点极限承载力计算时建议考虑有效翼缘宽度范围内的钢筋在内。混凝土强度等级与加劲肋板厚对节点力学性能也有着一定影响。主次梁节点按照刚性连接设计时,宜采用设置有加劲肋的短梁或端板连接形式。Abstract: 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.
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