The Earthquake Engineering Online Archive

Local bond stress-slip relationships of deformed bars under generalized excitations

Eligehausen, Rolf; Popov, Egor P.; Bertero, Vitelmo V.

UCB/EERC-83/23, Earthquake Engineering Research Center, University of California, Berkeley, 1983-10, 169 pages (515/E45/1983)

This report covers integrated experimental and analytical investigations that permit predicting analytically the local bond stress-slip relationship of deformed reinforcing bars subjected to generalized excitations, such as may occur during the response of reinforced concrete (R/C) structures to severe earthquake ground motions. Some 125 pull-out specimens were tested. Each of these specimens simulated the confined region of a beam-column joint. Only a short length (five times the bar diameter) of a Grade 60 deformed reinforcing bar was embedded in confined concrete. The tests were run under displacement control by subjecting one bar end to the required force needed to induce the desired slip which was measured at the unloaded bar end. The influence of the following parameters on the bond stress-slip relationship was studied: (1) loading history, (2) confining reinforcement, (3) bar diameter and deformation pattern, (4) concrete compressive strength, (5) clear bar spacing, (6) transverse pressure, and (7) loading rate. The detailed experimental results are presented and compared with results given in the literature. Based on the experimental results obtained, a relatively simple analytical model for the local bond stress-slip relationship of deformed bars embedded in confined concrete is developed. The model takes into account the significant parameters that appear to control the behavior observed in the experiments. The main assumption is that bond deterioration during generalized excitations depends on the damage experienced by the concrete which, in turn, is a function of the total dissipated energy. This assumption appears to apply only in the range of low-cycle fatigue; that is, when a small number of cycles at relatively large slip values is applied. The concrete in R/C joints of ductile moment resisting frames outside of stirrup-ties is unconfined. Therefore, based on the evaluation of test data given in literature, the analytical model is modified to include such regions. Furthermore, rules are formulated to extend the validity of the model to conditions different from those present in the tests. The results of the investigation reported are used to offer conclusions regarding the behavior of bond of deformed bars under monotonic and cyclic loading, and recommendations for further work are indicated.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-83-23.pdf (6 MB)