Wang and Filiatrault 2008
The authors discuss seismic shake table tests on a 3-story, 2-bay steel frame with a SCPT. In this system, high strength post tensioned strands were implemented in each beam to column connection with sacrificial yielding elements. Two test models, a SCPT and a SMRF, were formed and subjected to various ground motions of increasing intensities. The displacement response, acceleration response and the ED of the two frames were compared. Finally, improved detailing of the SCPT connections was suggested.
System Concept
In the SCPT steel frame, there is no welding in the connections between the beams and the columns. PT strands are installed along the beam to provide a clamping force at the beam-column connections. These PT strands provided a re-centering capability to the structural system under lateral earthquake loading. The energy-dissipating mechanism comes from four ED bars welded to each beam-column connection. When gap openings between the beam-column interfaces occur under large lateral deformations the ED bars yield in tension and compression and absorb energy.
Experimental Study, Results and Discussion
Two series of shake table tests were performed on both the SMRF and SCPT frame models. In the first series, a selected ground motion was used, while in the second series, the direction of the ground motion was reversed. Different amplitudes of selected ground motions were used during tests.
It was concluded that the acceleration response was reduced in the SCPT model when compared to SMRF model. It was important to reduce the acceleration response in order to decrease the damage of the acceleration-sensitive nonstructural components and the corresponding economic loss after seismic hazards. After severe earthquakes, only ED bars were yielded in the SMRF structures; while beams were damaged in the SMRF structures. Therefore, the repair cost of SCPT steel frame was less than SMRF. However, an unexpected vertical movement of the beam ends in the SCPT model was observed under severe seismic excitations. In order to avoid this, installation of additional shear tabs in the beam-column joints are suggested.
Reference
Wang, D. and Filiatrault, A. (2008). “Shake Table Testing of a Self-Centering Post-Tensioned Steel Frame,” Proceedings of the 14th World Conference on Earthquake Engineering 2008, Beijing, China, October 12-17.