Investigation of Retrofit Techniques for Seismic Resistant Steel Moment Connections

Typical steel moment resisting frame (SMRF) connections were shown to be vulnerable to brittle failures in the Northridge Earthquake. A study was undertaken to determine the effectiveness of two possible retrofit methods for typical pre-Northridge SMRF connections. The retrofit methods involved moving inelastic deformations away from the column face and consisted of either haunch or dogbone (reduced beam section) designs. Both methods were restricted to the bottom flange only. An experimental study was conducted in which six full scale interior beam-column subassemblages were tested. Alternating specimens included a composite concrete slab in order to study the effects of a composite slab on retrofit behavior. Specimen behavior was reported both in general terms as well as through a detailed series of analyses. The results were used to develop a methodology for the design of both haunch and dogbone retrofits. A complete design method was presented based on the findings of this study and previous research. Design was based on limiting the applied stresses at the column face to critical weld stress values which vary depending on the degree of weld modifications. These methods could be applied towards new construction as well.