ZHU C X, LIU X,et al.Study on the bearing characteristics of variable-section anchor bolts under pullout loads[J].Journal of Henan Polytechnic University(Natural Science) ,2026,45(1):95-102.

doi:10.16186/j.cnki.1673-9787.2023100051

Received:2023/10/23

Revised:2023/12/25

Published:2025-12-03

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

Zhu Changxing, Liu Xu

School of Civil Engineering， Henan Polytechnic University， Jiaozuo 454000， Henan， China

Abstract: Objectives To address the problem that the pullout resistance of the steel at the tail of resin anchor 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 capacity of the anchorage segment of the variable-section anchor bolt under pullout loads. This revealed the influence 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 nonlinear 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 fracture at the variable-section. Based on their occurrence conditions， formulas for calculating the elastic bearing 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 established 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 theoretical guidance for improving the economic efficiency of coal roadway support systems and addressing the low steel utilization problem in conventional anchor bolts.

Key words:variable-section anchor bolts;bearing characteristics;failure mode;elastic bearing capacity