8.8级国产单向螺栓连接轴向拉伸刚度试验研究

Experimental Study on the Axial Tensile Stiffness of 8.8 Grade Domestic Blind Bolt Connections

单向螺栓是一种用于钢结构节点连接的新型螺栓。针对某国产单向螺栓连接轴向拉伸刚度较小的问题,分析了其轴向拉伸刚度不足的原因是:安装扭矩过小导致预拉力不足、单向螺栓锥头与套筒之间相对滑移过大等,并提出了对应的改进措施:增加单向螺栓的安装扭矩、通过改进锥头材料和表面氮化处理增加锥头的硬度、将单向螺栓钢垫圈和套筒一体化处理。对3种改进后的8.8级单向螺栓分别进行了试验,得出各组试验的轴向拉伸荷载-位移曲线。依据试验结果,得出单向螺栓轴向拉伸过程可以分为3个阶段:有预拉力阶段、无预拉力阶段、螺杆屈服后阶段。结合实际工程需要,将荷载-位移曲线拟合为双折线模型,并给出不同方案和安装扭矩对应的第1阶段刚度、第2阶段刚度及转折荷载等参数。将改进后的单向螺栓和国产单向螺栓试验结果进行比较,发现改进后的单向螺栓的轴向拉伸刚度有明显提高。

Blind bolt is a new type of bolt used for the connection of steel structure joints.One type of domestic blind bolt is short in the axial tensile stiffness and the reasons of these shortcomings are analyzed in this paper.The major reasons are the mounting torque is too small which causes insufficient pre-tension,and the relative slip between the cone head and the sleeve is too large.Therefore,the corresponding improvement measures are proposed,including increasing the mounting torque of blind bolt,increasing the hardness of cone head through improving cone material and the surface nitrogen treatment,fixing the steel washer and the sleeve of blind bolt into a whole.The experiments of three types of 8.8 grade improved blind bolts are carried out,and then the axial tensile load-displacement curves are obtained.According to the experiment results,it is concluded that the axial tension process of blind bolt can be divided into three stages;pre-tension stage,non-pre-tension stage,screw yielding stage.In order to meet practical engineering needs,the load-displacement curve is fitted to the bilinear model and the first stage stiffness,the second stage stiffness and the turning load of different schemes and mounting torques are given in this paper.By comparing the axial tensile stiffness of improved blind bolts with the experiment results of the domestic blind bolts,it is found that the axial tensile stiffness of the improved blind bolts is better than that of the domestic blind bolts.