超500MPa级高强钢承压型螺栓连接承载力试验研究

EXPERIMENTAL RESEARCH ON THE STRENGTH OF BOLTED CONNECTIONS OF HIGH STRENGTH STEEL WITH GRADE OVER 500MPa

高强度螺栓承压型连接的承载力来源于钢板与螺栓的接触行为,承载力的发展伴随着螺栓孔周围材料的应力集中和塑性变形。普通钢延性好,可以克服螺栓孔周围应力集中的不利影响,充分发展承压承载力。随着强度增高,钢材的延性降低、变形能力下降,应力集中的不利影响将更突出。因此,需对高强钢构件的承压型连接进行研究。该文以Q550D、Q690D和Q890D三种国产高强钢共制作50组单螺栓试件,其中24组双剪切面试件、16组单剪切面试件,6组孔径变化试件,并与4组Q345B单螺栓试件进行了对比。研究表明:高强钢仍具备足够的延性,能克服应力集中的不利影响,连接破坏模式与普通钢无明显差异;剪切面数和螺栓孔径对不同高强钢承压强度影响较小,但单剪切面的试件更容易出现螺栓剪断,降低连接的延性,限制承压承载力的利用。基于已有试验的结果与中国现行标准《钢结构设计规范》比较,发现螺栓连接的钢板承压强度设计取值偏保守,对于超500 MPa高强钢可适当提高其设计值,以充分利用高强度钢材的材料强度,合理减少螺栓数量。

In bearing-type bolted connections, the load-bearing capacity is established by the contact between the plate and the bolts. The load-bearing capacity develops with growing bolt hole elongation. Due to the existence of bolt holes, stress concentration exists near the bolt holes. For normal-strength steel, the large ductility can ease the adverse effect of such stress concentration, which ensures the full development of strength. High-strength steel has reduced ductility with lower elongation at bolt holes. The effect of stress concentration may be conspicuous. Therefore, the strength of bolted connections made of high-strength steel should be studied. This paper uses three types of high-strength steel, Q550D, Q690D and Q890D, to produce 24 groups of single-bolt double-shear connections, 16 groups of single-shear connections, 6 groups of connections with changing bolt holes and another 4 groups of connections made of normal-strength steel. The results show that the ductility of high strength steel can also ease the effect of stress concentration. No significant difference is found compared with normal-strength steel. It is also found that bolt shear failure occurs more easily in single-shear connections with increasing steel grade, which reduces the ductility of the whole connection. Based on the existing experimental results, increased design strength in the current Chinese Code for the Design of Steel Structures is suggested, which will make better use of the material strength of high-strength steel and reduce the number of bolts.