Seismic Testing of A Self-Centering Post-Tensioned Steel Frame
A three-story steel frame incorporating innovative Post-Tensioned Energy Dissipating (PTED) connections will be seismically tested on a shake table for the first time in the Structural Engineering and Earthquake Simulation Laboratory (SEESL) at UB from March 19-23.
The PTED steel system, unlike traditional welded steel frames, incorporates high strength post-tensioned bars along with sacrificial yielding elements in each beam-to-column connection and is particularly appealing for hospital buildings from an initial investment stand point. The tests, being part of MCEER’s Hospital Project (Thrust Area 2), are being conducted by UB Ph.D. student Dong Wang under the supervision of MCEER and SEESL Deputy Director Andre Filiatrault.
Concept of post-tensioned energy dissipating (PTED) connections for steel framed structures
The figure shows the Post-Tensioned Energy Dissipating (PTED) steel frame concept proposed by Christopoulos et al.1 , in which beams are post-tensioned to the columns instead of having the beams and columns welded together. PTED connections are designed to undergo large inelastic deformations without any damage in the beam or column and with minimal residual drift. The post-tensioning (PT) force is provided at each floor by high strength bars or tendons located at mid-depth of the beam. Four symmetrically placed energy-dissipating (ED) bars are also included at each connection to provide energy dissipation under cyclic loading. These ED bars are threaded into couplers which are welded to the inside face of the beam flanges and of the continuity plates in the column for exterior connections, and to the inside face of adjacent beam flanges for interior connections. Holes are introduced in the column flanges to accommodate the PT and ED bars. To prevent the ED bars from buckling in compression under cyclic inelastic loading, they are inserted into confining steel sleeves that are welded to the beam flanges for exterior connections, and to the column continuity plates for interior connections. The ED bars are initially stress-free since they are introduced into the connection after the application of the PT force. The PTED connection relies on the PT force to maintain contact between the beams and columns. Horizontally slotted shear tabs may be welded to the column flanges and bolted to the beam web to provide stability during construction and to ensure an alternative vertical shear transfer mechanism from the beam to the column. The slots in the tabs need to allow the free opening and closing of the gap at the beam-to-column interface. Nonlinear elastic action is introduced by gap openings at each beam-to-column interface. Inelastic action takes place through yielding of the ED bars once the gap is opened.
1Christopoulos, C., Filiatrault, A., Folz, B. and Uang, C-M., 2002. "Post-Tensioned Energy Dissipating Connections for Moment-Resisting Steel Frames", ASCE Journal of Structural Engineering, 128 (9), 1111-1120.