Experimental evaluation of earthquake resistant posttensioned steel connections

Nine large-scale subassembly tests were conducted to investigate the behavior of an innovative posttensioned wide flange beam-to-column connection for steel moment resisting frames subjected to seismic loading conditions. The connection includes top and seat angles bolted to the beam and column. Strands are placed along the length of the beam, passing through the column and posttensioned to provide a precompression of the beam against the column. The parameters investigated in the study include the angle thickness, angle gage length, beam flange reinforcing plates, connection shim plates, and posttensioning force. The test results demonstrate that posttensioned connections provide excellent elastic stiffness, strength, and ductility under cyclic loading, with energy dissipation occurring primarily in the angles. The connection initial elastic stiffness is comparable to that of a fully restrained welded connection. In addition, the connection has essentially no residual deformation following several cycles of inelastic story drift. Simple design models are developed and verified by the test results for estimating the connection decompression moment and moment capacity, as well as the increase in posttensioning strand force due to connection deformation.