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Seismic Performance of Link-to-Column Connections in Steel Eccentrically Braced Frames

Okazaki, Taichiro

2004

This dissertation describes a research program on the seismic performance of link-to-column connections in steel eccentrically braced frames (EBFs). Since the 1970’s, EBFs have been accepted as a high performing steel building system for seismic regions. Many of the same design, detailing, and construction features that contributed to the widespread damage in welded moment connections in the 1994 Northridge Earthquake are present in link-to-column connections in EBFs. However, little research has previously been conducted on link-to-column connections. The research program combined an experimental investigation involving large-scale cyclic loading tests, and an analytical study including detailed finite element simulations to study link-to-column connections. A total of sixteen large-scale link-column specimens were tested in the experimental study. Four different connection types with varying configuration and welding details were tested. Each of the four connection types was tested with a variety of link lengths to consider a wide range of force and deformation environment at the link-to-column connection. The specimens representing the pre-orthridge practice failed after developing only half of the inelastic link rotation required in the building code provisions. Implementing improvements in welding was beneficial, but this alone was not nearly sufficient to improve the connection performance to the required level. Improved connection details developed for moment connections did not necessarily provide good performance for link-to-column connections. The force and deformation demand at EBF link-to-column connections were found to be significantly more severe than at moment connections. The local stress and strain environment predicted by finite element simulations correlated well with the fracture behavior observed in the test specimens. The finite element simulations also agreed with the experimental observations in that fracture of the link flange near the groove weld connecting to the column flange is a major concern for links of all practical lengths. The findings from this research suggest that until further research is available, EBF arrangements with links attached to columns should be avoided.

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