Seismic performance enhancement of steel bolted moment connections.

Abstract

The damage of steel structures caused by recent earthquakes motivated the structural engineering profession to change the prescriptive design guidelines to accommodate for the performance-based seismic design approach. One of its characteristics is that steel structures are expected to go from the linear response to the non-linear response before failure. Thus, the pre-yielding as well as the post-yielding behavior of steel connections is of interest to the structural engineering community. The goal of this research is to investigate innovative techniques to enhance the seismic performance and to lower the fabrication cost of eight-bolt double Tee and extended endplate connections through experimental work and analytical modeling. Despite all the experimental tests and the analytical models conducted on double Tees and extended endplates, very few investigated the influence of the column flange size (thin, medium, and thick), bolt arrangement (circular and rectangular), and omission of continuity plates and stiffeners on the seismic performance. Most importantly, the prying phenomenon caused by the significant bending of the connection (primary prying for the circular bolt configuration) and the column flange (secondary prying) in bolted connections was not experimentally investigated in the literature and not yet included in the current prequalified connections for steel moment frames for seismic applications - ANSI-AISC 358-16. Those prying induced forces in the tension bolts might cause unexpected failure of the connection leading to collapse of moment resisting frames and thus need to be accounted for in the design process. To address the abovementioned shortcomings, first, seven specimens are conducted on double Tee connections subjected to monotonic and cyclic loading. The results of these tests are used to develop stiffness and strength models that predict the behavioral characteristics of the column flange-connection system. This aims at including the secondary prying strength check and associated colu