Based on the former experimental and theoretical researches on the reinforcement mechanisms of anchor bolt in jointed rock mass at home and abroad

and comprehensive considering of the tangential and axial deformability of anchor bolt

a deformation model of joint bolts under shear load is proposed. The deformation of joint bolts is divided into two parts: elastic deformation zone and crushing failure zone. A variable is introduced to express the length of crushing failure zone. Mechanism of interaction between bolts and rock mass is analyzed. Relationships between tangential load and tangential displacement

and axial load and axial displacement are deduced respectively. Through the analysis of yield failure model of bolt

a method to calculate the length of the crushing failure zone is proposed. Finally

a calculation example is presented to study the relationship between the length of crushing failure zone and the parameters

such as the bolt diameter

the rock mass strength

anchorage angle and so on. It is concluded that: (1) The shear resisting function of joint bolts is actually that the bolts arouse the compressive strength of rock mass to resist the shear load of the joint plane. In the hard rock with higher compressive strength

the crushing failure zone is limited near the joint plane and the influence area of bolt is small; while in soft rock with lower compressive strength

the length of crushing failure zone and shear deformation and the influence area of bolt is larger. (2) The yield failure mode of anchor bolt is related to rock properties and diameter of the bolt. Shear yield occurs in hard rock and bending yield occurs in soft rock. Bolt with little diameter usually go through shear yield and bolt with large diameter may go through bending yield. After yield failure

the plastic hinge appears. The length of the crushing failure zone on one side of the joint is 1-2 times of the bolt diameter

however

it no longer increases with the increasing of shear load. (3) The optimal anchor supporting angle of joint anchor bolt varies with rock properties. Hard rock has a smaller anchor supporting angle and the soft rock has a larger one.