Experimental study on the effect of pre-tensioning torque on tensile performance of rockbolts
The pre-tightening state of rockbolt has a significant effect on its subsequent performance.Using a self-developed comprehensive experimental platform to assess the mechanical performance of rockbolts,taking the installation of the tray perpendicular to the bolt as an example,varying pre-tighte-ning torques are applied to the rockbolt system to compare the mechanical response during stages of pre-tightening installation and axial tension.The transformation mechanism of axial force on the bolt is re-vealed,and the influence of initial installation on the subsequent performance is explained as well.The experimental results show that there is a linear relationship between the pre-tightening force of bolt and pre-tightening torque,and a nonlinear relationship between the residual torque and pre-tightening torque.During axial tension stage,the residual torque of rockbolts continuously decreases,especially in the elas-tic and yield stages,where the reduction is most significant;while in the strengthening stage,the torque remains roughly constant.The ultimate bearing capacity of bolts decreases in the combined tension-torsion state,equivalent to 89.65％-93％of rockbolts material strength.Although the pre-tightening torque has almost no effect on the ultimate bearing capacity of rockbolts,its increase leads to a conti-nuous decrease in the elongation of the rockbotls at the ultimate bearing point.Notably,at a pre-tighte-ning torque of 450 N·m,the elongation rate of rockbolts decreases by 2.2 percentage points compared to the base material.Compared the results of different testing schemes,a reasonable value for pre-tightening torque is determined to be 350 N·m.Mechanical analysis shows that the shear stress generated by the re-sidual torque is the main reason for the reduction in its bearing capacity and elongation.It is recommen-ded to pre tighten rockbolts to eliminate the adverse effects caused by pre-tightening friction at rockbolts tail threads.
万方数据
维普
