Seismic analysis of steel moment frames with column-tree connections

Column-tree connections are commonly used for steel moment frame buildings in East Asian countries because they can reduce labor and construction time. However, a column-tree connection has an inherent issue of splice slip between the stub beams and the mid-portion of the beam. In this study, analytical modeling to account for slip behavior of the column-tree connection is proposed and examined by comparing sub-assemblage test results and then applied to a nonlinear dynamic analysis of steel intermediate moment frame (SIMF) buildings. In the nonlinear dynamic analyses, two example buildings that use welded unreinforced flange-welded web connections and column-tree type connections, respectively, were designed, and their responses were compared. Comparison of the analysis results to sub-assemblage test results indicate that a macro model based on the lumped plasticity assumption can adequately simulate the behavior observed in test results. The distribution of plastic deformations among the beam, column, and beam-to-column joint was similar to those of the test results. The nonlinear dynamic analyses indicated that column-tree connections with a splice slip have positive effects on frames with a weak panel zone. The splice slip increased the rotational capacity of the assembly and reduced the inelastic demand of the panel zone because early slips occur at the beam splice before the weak panel zone yields. Column-tree construction is therefore a viable method for constructing SIMF buildings in areas of low-to-medium seismicity.