负载下环口板焊接加固T形钢管相贯节点试验研究

Experimental study on compressive behavior of reinforcing CHS T-joints with welding collar plates when in service

负载下焊接加固将对大跨度建筑和钢桥的安全产生影响。为研究负载及焊接高温在加固过程及加固后对钢管节点的影响,完成4个焊接环口板加固T形圆钢管节点的轴压试验,实测了节点在负载焊接加固全过程的温度、位移及应变演化规律,分析焊接高温和负载对节点破坏模式、荷载-变形曲线、受压承载力等的影响。试验结果表明:主管负载受压会降低节点承载力,0.37的主管初始应力比可使节点受压承载力下降16%;焊接温度场具有局部高温和快速衰减的特征,其局部瞬时升温最高可达1808℃,并在约3.1 cm×1.7 cm的椭圆形范围内衰减至600℃,钢材的局部软化效应不明显;负载不影响焊接温度场,焊接及冷却过程中的热胀冷缩则会影响节点的应变分布和残余变形;负载及焊接高温均未改变节点的破坏模式。基于试验结果,考察了现有规范负载折减系数对于负载下焊接加固钢管节点的适用性,结果表明,GB 51367—2014《钢结构加固设计标准》中规定的负载承载力折减系数偏于安全。

Welding reinforcement under load will affect the safety of large-span buildings and steel bridges.In order to study the effect of preload and welding temperature on circular hollow section(CHS)joints during and after reinforcement,four collar plate reinforced CHS T-joints were experimentally tested under axial compressive load.The evolution law of temperature,displacement and strain of the joints in service during the whole welding process under load were measured,and the effects of chord pre-load and high-temperature welding on the behaviors,such as failure modes,load-deformation curves and compressive strength,of specimens were analyzed.The results demonstrate that the compressive load on chord will decrease the ultimate capacity of the joint,and an initial stress ratio of 0.37 on applied to the chord leads to 16%reduction on in the compressive strength of the joint.The temperature field of welding demonstrates the characteristics of localized high temperature with fast attenuation,where the instantaneous peak temperature increases rapidly 1808℃in local area and decays to 600℃in the elliptic range of about 3.1 cm×1.7 cm.Therefore,the local softening effect of the steel under high temperature is not obvious.The preload on chord has little influence on the welding temperature field,while the thermal expansion and contraction during the process of welding and cooling affects the strain distribution and residual deformation of joints.Besides,the preload on chord and the welding thermo do not change the failure mode of the joints.Finally,based on the experimental results,the applicability of the reduction coefficient prediction by existing specification on the compressive strength of welding platereinforced CHS joint in service was compared and discussed.And the results also show that the reduction factor of load capacity stipulated in GB 51367—2014“Standard for design of strengthening steel structure”is safe and can be applied to the design of welding reinforcement joint under laodin service in this paper.