DAMAGE EVALUATION OF PRESTRESSED CONCRETE BEAMS POST-TENSIONED WITH UNBONDED TENDONS

In major earthquake, many reinforced concrete buildings were damaged. Some of the buildings had severe economical losses due to structual or nonstructual damage until after the rehabilitation has been completed, even though the buildings did not collapse. For this reason, demand level for structual design shifted to be higher in japanese society. In order to develop such high perfomance buildings, this study focuses on the unbonded prestressing structures as self-centering system. The structures are able to sustain seismic force with small residual deformation. In PRESSS research program, a hybrid system with self-centering system and energy dissipation devices was developed. The small residual deformation and structural performance of the hybrid system were confirmed by structural tests. However, few studies have been reported on evaluating damage after earthquake for the unbonded prestressing structures. In order to fully take advantage of low damage characteristics of the self-centering system, it is important to investigate structural performance and damage after the earthquakes. Thus, this study report on evaluating damage of post-tensioned precast concrete members. In order to investigate effect of effective prestressing force ratio and shear span ratio on damage or hysteresis characteristics, four specimens were made. A specimen was designed to investigate structural performance of a repaired beam after an earthquake. The structural experiment was conducted using the specimens under cyclic static loading. As an experimental result, small residual drift angle is observed of all specimens. The Shear force versus drift angle responses had S-shape hysteresis behavior which has small amount of energy dissipation The 2015 AIJ prestressed concrete guidelines define four limit states (Serviceability limit state, Reparability limit state I, Reparability limit state II and Safety limit state) and damage evaluation criteria for the limit states. Damage evaluation was conducted using the experimental results and these criteria. As an evaluation result, effective prestressing force ratio is one of important factors in order to control damage in design for unbonded prestressed concrete beams. Furthermore, except for one specimen, the drift angle at serviceability limit state ranged from R=0.5% to R=1.0%. All specimens did not reach safety limit state until R=4%. Thus, excellent low damage performances of unbonded prestressed concrete beams were confirmed.