冷弯薄壁型钢螺钉连接抗拔性能试验研究

为了研究钢板的材料强度、厚度以及螺钉外直径、内直径、螺纹间距、钻头处直径对冷弯薄壁型钢螺钉连接的拔出破坏模式和抗拔承载力的影响，选取板厚为0.8、1.0、1.2mm的LQ550及板厚为0.8、1.5、2.0mm的S350冷弯型钢，采用不同螺钉参数，进行了287个试件的拔出试验。结果表明：1.0mm及以上厚度板件主要发生螺纹剪切破坏，随着板厚增加，螺纹剪切破坏越明显；0.8mm厚超薄板件主要发生钉孔挤压破坏，且螺钉直径越大、板材强度越低，钉孔挤压变形越显著。螺纹间距对抗拔承载力影响较小，抗拔承载力随着螺钉外直径增加而增大，内直径增大而减小，且二者对超薄板件的影响更大。对于自钻自攻螺钉应采用内直径与钻头处直径的较大值计算抗拔承载力，螺钉钻头处直径越小承载力越大。我国GB 50018—2002《冷弯薄壁型钢结构技术规范》中抗拔承载力计算公式对于螺钉连接LQ550高强钢板偏于不安全，尤其对于0.8mm厚的超薄板件。最后，提出考虑钢板材料强度、厚度以及螺钉外直径、内直径、螺纹间距、钻头处直径的设计承载力计算式，其具有较好的适用性和可靠性。

Experimental study on pull-out capacity of screw connections for cold-formed thin-walled steel structures

In order to investigate the effects of the steel strength, the sheet thickness, the outer diameter and inner diameter of screws, the thread pitch and the diameter of drill points on the failure mode and pull-out capacity of screw connections for cold-formed thin-walled steels, the pull-out tests were carried out on 287 specimens using LQ550 steel with the thicknesses of 0.8mm, 1.0mm and 1.2mm, and S350 cold-formed steels with the thicknesses of 0.8mm, 1.5mm and 2.0mm in combination with various screw combinations. The experimental results show that the major failure mode of sheets with a thickness larger than 1.0mm is thread shear failure, and the thread shear failure mode is more pronounced when the thickness is higher. For ultra-thin sheets with a thickness of 0.8mm, the screw hole extrusion is the major failure mode, which becomes more significant when the outer diameter of screws is large and the steel strength is low. The influence of thread pitch on the pull-out capacity is small. The pull-out capacity increases with the increase of the outer diameter of screws and decreases with the increase of the inner diameter of screws, and this trend is more notable for ultra-thin sheets. For self-drilling screws, the pull-out capacity should be calculated with the larger value between the inner diameter and the diameter of the drill point,and the pull-out capacity increases with the decrease of the diameter of the drill point. It is indicated that the formula for the pull-out capacity of LQ550 high-strength steel sheets in the Chinese code gives unsafe results, especially for ultra-thin sheets with the thickness of 0.8 mm. Finally, a new formula for the pull-out capacity considering the steel strength, the sheet thickness, the outer diameter and inner diameter of screws, the thread pitch and the diameter of drill points was proposed with higher applicability and reliability.