Progressive Failure Process and Influencing Factors of Bolts Under the Loading of Pullout

To study the progressive failure mechanism and the stress distribution law of anchorage interface of bolts under the loading of pullout, based on the four-linear bond-slip model, the influence of residual strength on the length of dilatancy and softening stress regions was considered. The previous load-displacement analytical equations of dilatancy-softening-debonding stage, softening-debonding stage and complete debonding stage proposed were corrected by the equilibrium condition of force through anchorage unit. The analytical model was calibrated and validated against two pull-out experimental studies. The sensitivity of Young's modulus, the bolt radius and anchorage length to load-displacement and stress distribution curves were discussed. Results show that the increase of the bolt radius and Young's modulus can improve the ultimate load and greatly limit the ductility of bolts. The load-displacement curve before the loading end entering the debonding stress state is independent of the anchorage length. The Young's modulus is positively correlated with the peak value of axial stress; however, the bolt radius is negatively correlated with the peak value of axial stress.