考虑混凝土粘结效应的盲眼螺栓抗拉性能研究

Tensile Behaviour of Hollo-bolts Embedded in Concrete

为了研究混凝土的粘结效应对盲眼螺栓抗拉性能的影响,采用抗拉装置,对预埋于钢管混凝土的盲眼螺栓进行了抗拉试验.首先得到各种工况下试件的破坏模式和荷载-位移关系曲线;其次对各种工况下试件的破坏模式和荷载-位移关系曲线进行比较分析,得到有无混凝土以及不同混凝土强度等级对盲眼螺栓初始刚度、强度和延性的影响;最后分析考虑混凝土粘结效应后盲眼螺栓的抗拉受力机理,并提出了改良盲眼螺栓的合理措施.研究结果表明:混凝土的粘结效应改变了盲眼螺栓的抗拉传力机理,使其整体受力从套管转移到中心螺杆,从而使其破坏模式由套管提前破坏失效转化成中心螺杆强度破坏;混凝土强度等级对盲眼螺栓刚度有显著影响,混凝土强度从C30提高至C50时,其初始刚度由15.1%提高至35.7%,其屈服后刚度也分别提高了1.27和1.64倍;盲眼螺栓的抗拉屈服强度和延性主要由套管的性质决定,抗拉极限强度则取决于中心螺杆的承载力,混凝土的强度等级对其无影响.

To examine the tensile response of Hollo-bolts considering the bonding effect of concrete, a new device to perform pullout tests was used to investigate the tensile behaviour of Hollo-bolts embedded in concrete. First, the tensile force-displacement relationships for all specimens under different experimental conditions were obtained. Then, the failure modes and the tensile force- displacement relationship curves were compared and analysed to examine the influence of the tested experimental variables, which include the concrete strength grade and tubular sections with or without concrete filling, on the initial stiffness, strength, and ductility of the structure. Finally, the tension loading-bearing mechanism of Hollo-bolts was analysed considering the bonding effect of concrete. In addition, reasonable measures to improve the tensile-behaviour of Hollo-bolts were subsequently suggested. The test results revealed that the bonding effect of concrete changes the tension loading-bearing mechanism of Hollo-bolts, as the load on the Hollo-bolt eventually shifts from the bolt sleeve to focus on the centre screw. Accordingly, the failure model of the Hollo-bolt changes from sleeve failure to centre screw failure. Furthermore, it was determined that the concrete strength grade significantly influences the stiffness of Hollo- bolts. When the concrete strength grade increased from C30 to C50, the initial stiffness increased from 15. 1 % to 35. 7 % and the post-yield stiffness improved 1.27 and 1.64 times compared to the specimens for which the bonding effect of concrete was not considered. However, the findings indicate that the yield tensile strength and ductility of Hollo-bolts are primarily determined by the capacity of the sleeve, while the ultimate tensile strength of Hollo-bolts is influenced by the capacity of the centre screw, as the concrete grade shows no significant effect on the tensile strength of Hollo-bolts.