Experimental and analytical studies of steel connections and energy dissipators

After a brief overview of the building seismic design, nonlinear structural response spectra for strength, ductility, energy and number of yield reversals as a function of building period and structure strength for several strong motion earthquakes are presented. These results are compared with conventionally evaluated elastic response spectra and code criteria.; The basic reasons for the fractures that occurred in steel moment-resisting connections during the 1994 Northridge earthquake are examined from a fundamental point of view. The possible modes of failure are examined, showing the very limited view in the code design. The unfused material between a column face and a backing bar forms an "artificial" edge crack, the methods of nonlinear finite element analysis combined with fracture mechanics were brought to bear. Three SAC Pre-Northridge specimen tests subjected to cyclic loading are critically examined. Good comparisons are found using the above theory.; Next, the beam strength reduction by drilling holes in flanges is introduced for steel connection protection. Experiments on eight W12x26 beams with different perforation patterns are reported. The results show that a well-designed perforated beam can have its moment capacity reduced and its ductility increased. Two large size connections with beam flange perforated are tested. Test results show that the ductility of both specimens is enhanced without severe strength degradation.; The design methods of braced frames with Slotted Bolted Connections (SBCs) are reported. The advantages of using such frictional connections are demonstrated by comparing seismic structural responses. Finally, the Rotational Slotted Bolted Connection (RSBC), a new variety of SBC, a rotational friction damper in essence, is designed for use in steel moment-resisting connections. Two large size RSBC specimens were designed and tested. A simple analytical model can predict the behavior of RSBC with reasonable accuracy. Test results show that the energy dissipation capacity of RSBC is outstanding. This non-destructive connection shows no degradation in hysteresis loops or damage in material after a severe test, it is durable to withstand several strong earthquake events without retrofit.