Abstract:Up to now,the analytical estimation of critical anchorage length,which is a very important parameter in bolts design,is not available. A perfectl elasto-plastic load-transfer model is used to derive an analytical solution for this problem. Based on the developed analytical solution,an analytical critical anchorage length (ACAL) formulation,which relates the anchorage diameter,anchorage deformation modulus,and anchorage layer characteristic coefficient with the critical anchorage length,is obtained. The analytical solution also shows a trend of more uniform distribution of the frictional resistance when the anchorage length is less than ACAL. The frictional resistance distribution becomes very uneven when the anchorage length is larger than half of the ACAL. Further study shows that the ultimate bearing capacity of the bolt increases significantly as the anchorage length increases within half of the ACAL,while the anchorage length is larger than half ACAL the effect of anchorage length on bearing capacity is limited. Based on the above findings,it can be seen that half ACAL is a very important parameter indicating the efficiency of the bolts. Thus,it is defined as“engineering critical anchorage length”and it is suggested that the designed anchorage lengths of bolts should be below their engineering critical anchorage lengths. Two convenient methods for practical use of estimation of the engineering anchorage length are presented with examples.