4 differences between anchorage force and pullout resistance

by Anna S. Optimization Specialist

Anchorage force is the binding force of anchor bolt on surrounding rock, which can be subdivided into working anchorage force and design anchorage force. The anchoring force usually refers to the working anchoring force. Pullout resistance is the force that prevents the anchor bolt from pulling out of the rock.

These are 4 differences between anchorage force and pullout resistance:

1）Anchorage force restricts the deformation of surrounding rock and plays an initiative support role. The pullout resistance is the ultimate load that the anchorage part or hollow bar can bear during the pull-out test. It reflects the force that prevents the bolt from pulling out of the rock after the hollow bar, anchoring agent, and rock bond together.

2）The anchorage force increases with the deformation and expansion of the supported surrounding rock, which is a dynamic and changing force. The pullout force is a fixed value, which does not change with the surrounding rock deformation and the force of the anchor bolt.

3）Rock-bolt dynamometer is used to measure the anchorage force, usually simultaneous installation with an anchor bolt. The purpose of anchoring force monitoring is to monitor the force condition of the anchor bolt, which requires long-term observation. The bolt tension meter can be used at any time to detect the pullout resistance after installing the anchor bolt. The purpose of testing the pullout resistance is to check the hollow bar, anchoring agent, and rock bonding effect. When doing anchor pull-out tests during construction, generally reach the designed pullout resistance. During the destructive test, stop until the anchor bolt is broken or pulled out.

4）Check the pull-out resistance when checking the construction quality of the anchor bolts. Analyzing the working condition of the anchor bolt should measure the anchoring force. Its purpose is to verify the support reliability and provide evidence for modifying the support design in the future. In the design and construction, it is necessary to ensure that the bolt's pull-out capacity is greater than the bolt's broken force. That is, the anchor bolt will be broken when the bolt's stress exceeds its breaking strength, but it cannot be pulled out. A common mistake design is that the bolt's pull-out capacity is less than the bolt's breaking force.