Abstract
This paper presents an experimental study on the seismic performance of a bidirectional self-centering reinforced concrete (RC) frame structure. In the structure, the column-base joints, which were installed with external mild steel (MS) dampers, could uplift freely and the beam-column joints could open effectively under earthquake excitations. Angle steels and MS dampers were installed at the beam-column joints in the structural X and Y directions, respectively. During the gap opening of the joints, unbonded posttensioned (PT) steel wires, which passed through the plastic ducts inserted in the RC beams and columns, provided the structure with the ability to return to pre-earthquake positions, and the yielding MS dampers and angle steels dissipated the seismic energy. A 1/2-scale two-story model structure was designed and constructed. Shaking table tests were performed on the structure under four different types of earthquake excitations with increasing seismic hazard levels. The test results indicated that the self-centering RC frames installed in both the directions showed satisfactory seismic performance, with only slight damage to the main structure after extreme earthquakes. The natural frequencies of the self-centering frames installed in both the directions degraded progressively, mainly because of the prestress loss of the PT steel wires and the yielding of the MS dampers. The structure showed desirable self-centering ability with very small residual deformation under ground motions of all hazard levels. The structural deformation was mainly concentrated at the column-base and beam-column joints, and hence, damage to the concrete beams and columns was considerably alleviated. In addition, the residual gap opening of the joints was minimal.
Highlights
Recent earthquake events have caused severe damage to conventional concrete structures and induced massive economic losses, and people are finding it increasingly difficult to cope with such losses
Based on shaking table tests performed on a 1/2-scale twostory bidirectional self-centering reinforced concrete (RC) frame structure, the following conclusions could be drawn: (1) e self-centering RC frames installed in both the X and Y directions showed satisfactory seismic performance and could return to their preearthquake positions with minimal residual deformation even under extreme earthquakes with a PGA of 1.56 g
(2) e initial natural frequencies were 3.66 Hz (Y direction) and 3.82 Hz (X direction) and decreased by 27.5% and 17.1% under extreme earthquakes with a PGA of 1.56 g. e lateral stiffness of the selfcentering frame installed in the Y direction was smaller than that of the frame installed in the X direction. e lateral stiffness of the self-centering frames installed in both the directions degraded progressively, mainly because of the prestress loss of the PT steel wires and the yielding of the mild steel (MS) dampers
Summary
Recent earthquake events have caused severe damage to conventional concrete structures and induced massive economic losses, and people are finding it increasingly difficult to cope with such losses. Under such circumstances, self-centering structural systems are expected to mitigate structural damage and reduce economic losses resulting from earthquakes. E concept of self-centering reinforced concrete (RC) frames was developed as part of the Precast Seismic Structural Systems research program [1, 2]. E structural deformation is mainly concentrated at the beam-column and column-base joints, which exhibit an open-close behavior of the gap under earthquake excitation. Many ED devices have been developed, ranging from internal mild steel (MS) rebars [3,4,5, 8] to external dampers mounted at joints, which are easy to replace after failure, such as MS dampers [7, 9, 12, 13], friction dampers [6, 10], and angle steels [15, 16]
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