Bond stress distribution and suggestions for anchoring length of deformed steel bars in different types of cementitious grout

Eight sets of pull-out specimens were tested by considering four types of cementitious grout (CGM-380, CGM-340, CGM-300, and CGM-270) and two anchoring lengths (3d and 10d) in this study. Discussions were had on the failure modes, bond load-slip curves, stress distribution of steel bars, and bond stress distribution. Results indicated that the relationship between the magnitude of peak bond load of 3d-group specimens composed of different types of cementitious grout was shown as CGM-270>CGM-300>CGM-340>CGM-380. Simultaneously, the stress of the steel bars in specimens gradually increased with the increase in external load, and the steel bars were in the elastic stage. For the 10-group specimens, the peak bond load of each specimen was basically the same, and the steel bars had yielded when the specimen was damaged. In addition, the stress distribution of the steel bars was similar to that of 3d-group specimens before the steel bars yielding. After the load reached the yield load, however, the yield position gradually shifted toward the free end with the load further increased, and the yield section length of the steel bars gradually increased. Besides, in contrast to the unimodal bond stress distribution curves of the 3d-group specimens, the bond stress distribution curves of the 10d-group specimens were all in the shape of a multimodal distribution. The peak bond stress of 10d-group specimens were located near the loading end before the steel bars yielding. However, as the load was raised continuously after the steel bars yielded, the bond stress in the yield section dramatically dropped, the yield penetration depth progressively grew, and the peak bond stress gradually shifted towards the free end. Additionally, design suggestions for the critical anchoring length of steel bars in cementitious grout and the anchoring length of steel bars after yielding were provided.