Numerical and experimental studies of self-centering post-tensioned steel frames
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In this research, numerical and experimental studies were conducted to evaluate the seismic performance of Self-Centering Post-Tensioned (SCPT) steel frames and Steel Moment Resisting Frames (SMRF). Numerical analyses of Single-Degree-of-Freedom (SDOF) and Multiple-Degree-of-Freedom (MDOF) Self-Centering Systems (SCS) and Elasto-Plastic Systems (EPS) were conducted under simulated strong ground motions. A Relative Performance Index (RPI) was developed as an evaluation criterion of the seismic performance of both systems. A design procedure for SCPT frames was also developed. These results obtained from the numerical analyses indicated better seismic performances of the SCS/SCPT systems compared to the EPS/SMRF systems. The MCEER Demonstration Hospital building was used as a prototype of a SMRF building in the numerical studies. An experimental study was carried out on the five degrees-of-freedom shake table at the University at Buffalo. Two 3-story, 2-bay, steel plane frame models incorporating SCPT connections and conventional fully welded moment-resisting connections were used in this test. The SCPT frame, unlike traditional welded steel frames, incorporates high strength post-tensioned strands along with sacrificial yielding elements in each beam-to-column connection and is particularly appealing for hospital buildings from an initial investment stand point. These two test models were subjected to various ground motions of increasing intensities. The results of the tests indicated that the displacement response of the SCPT frame was very similar as that of the fully-welded SMRF and the acceleration response was reduced. While the beams of the SMRF yielded under the largest seismic excitations, the energy dissipation mechanism of the SCPT frame was limited to the Energy Dissipating (ED) bars without inelastic deformations of the beams and columns. The experimental results suggested that only the ED bars would need to be replaced in the SCPT frame compared to the costly replacement of the damaged beams or columns sections in the SMRF building after a significant earthquake.