Seismic performance evaluation of weak axis column-tree moment connections with reduced beam section

• Common weak axis column-tree connection details experienced the brittle failures.
• Weak axis column-tree connection with tapered beam showed ductile behavior.
• Weak axis column-tree connection with RBS confirmed to be the proper solution

The purpose of this study was to evaluate the seismic behavior of weak axis column-tree connections used in steel moment resisting frames. Column-tree connections are composed of a shop-welded and field-bolted steel structure. Column-tree connections are well known to provide high quality and economy with shop-welding and field-bolting. In addition, column-tree connections are easier to assemble than field-welded connections. For these reason, column-tree connections are frequently used in steel moment resisting frames in Korea and Japan. Unlike the US and Europe, where strong axis connections are used, weak axis column-tree connections with a beam connection to the column web are often used for convenience in Korea. In this study, a basic weak axis column-tree connection that has been used in Korea was tested to evaluate its seismic performance. Also, two weak axis column-tree connections with a reduced beam section and a tapered beam section at the stub beam were fabricated and tested. The two specimens with the reduced beam section and tapered beam section successfully developed ductile behavior without brittle fracture until 5% story drift ratio. Therefore, the two specimens met the qualification criteria demanded by the AISC Seismic Provisions for use in SMFs. Although a basic weak axis column-tree connection specimen successfully reached 5% story drift ratio, brittle fracturing was detected at the backing bars near the beam-to-column connection. When compared with the energy dissipation capacity at the stub beam for each specimen, the specimen with the reduced beam section showed stable and ductile behavior.