Study on the bearing characteristics of variable-section anchor bolts under pullout loads

Zhu Changxing; Liu Xu

doi:10.16186/j.cnki.1673-9787.2023100051

Abstract：Objectives To address the problem that the pullout resistance of the steel at the tail of resin an-chor bolts in coal mine roadways cannot be fully utilized,a variable-section anchor bolt with a hollow tail is proposed,and its load-bearing characteristics under pullout loads are investigated.Methods Theoretical analysis was employed to examine the internal force distribution,failure modes,and elastic bearing capac-ity of the anchorage segment of the variable-section anchor bolt under pullout loads.This revealed the influ-ence of the hollow section on the bolt's bearing performance.The theoretical findings were validated through laboratory pullout tests.Results Compared to conventional bolts,the hollow section causes a nonlin-ear increase in the axial force distribution of the bolt and an increase in the maximum shear stress at the resin-rock interface.The magnitude of these changes grows with the size of the hollow section.Two failure modes are identified for the variable-section anchor bolt:debonding at the resin-rock interface and bolt frac-ture at the variable-section.Based on their occurrence conditions,formulas for calculating the elastic bear-ing capacity and the critical state equation for each failure mode were derived.By comparing the elastic bearing capacity and safety under the two failure modes,debonding at the resin-rock interface is estab-lished as the primary failure mode.When this debonding occurs,the elastic bearing capacity of the variable-section anchor bolt decreases with increasing hollow section size:initially it declines gradually,then accelerates,showing a negative exponential decay pattern.Conclusions These findings provide theo-retical guidance for improving the economic efficiency of coal roadway support systems and addressing the low steel utilization problem in conventional anchor bolts.