Seismic rehabilitation of pre-Northridge steel moment connections: A case study

The effectiveness of using both the welded haunch and rib plates for the seismic rehabilitation of pre-Northridge steel moment connections for a 13-story office building in Los Angeles was studied. Full-scale cyclic testing of two pre-Northridge moment connections with simulated welding defects was conducted and used as a benchmark for the rehabilitation scheme. Four rehabilitated moment connections were then tested to validate the proposed scheme. A correlation study using a nonlinear finite element program (ABAQUS) was also performed. Both the experimental and analytical results showed that the use of welded haunch and rib plates significantly reduced strain demands at the beam flange groove welds. Doubler plates that were offset from the column web were effective in resisting shear in the panel zone region. Test results also showed that the inclination angle of the haunch, which was recommended to be within 30±5 degrees in an AISC Design Guide, can be extended to 50 degrees.