Huckelbridge and Clough 1977
In this report, the authors explained the effects of allowing column uplift in steel building frames responding to severe seismic loading. In this study, the column uplift effect was observed experimentally and analytically by using 3-story steel frame; and according to the results column uplift reduced seismic loading and ductility demand in the structure when compared with fixed base response. The report was started with an explanation of overturning effect in seismic response, after that the experimental program was explained in terms of test model, instrumentation and results. Then analytical correlation of test data was observed and the report was concluded with summary and results.
System Concept
A major earthquake caused lateral inertial forces and resulted in overturning moment at the base of the structure. This overturning moment could easily exceed the overturning resistance provided by the dead weight. Allowing column uplift to the frame created a fuse effect and limited the applied overturning forces on the structure. So, internal forces and the ductility demand on the system were reduced. Moreover, allowing rocking to the system was an economic way to create fuse effect on the system.
Analytical and Experimental Study, Results, and Discussion
Experimental verifications and analytical studies were performed for more effective design application. In addition, experimental data were used in nonlinear analytical techniques in order to show seismically induced overturning effect in a simple structural system.
Three-story, single bay steel moment frame was used for the initial investigation of the uplift phenomenon by performing shake table tests. Uplift response of this system was investigated and compared with the response to similar excitations during which the column bases were securely anchored to the foundation to prevent uplift.
From analytical and experimental studies, it was concluded that the uplift phenomena resulted in a definite reduction in the structural force response quantities. Internal forces were reduced by about one-third through allowing uplift. Moreover, it was realized that, rigid body motions for the single bay frame with pinned column bases led to larger relative story displacements when uplift was allowed.
Reference
Huckelbridge, A. A. and Clough, R. W. (1977). “Preliminary Experimental Study of Seismic Uplift of a Steel Frame,” Earthquake Engineering Research Center (EERC), Report No. UCB/EERC-77/22.