This paper presents the shear lag phenomenon occurred in steel box moment connections by considering the local effect of column flange flexibility. The stress concentration due to shear lag in steel box member is one of the major concerns for steel box moment connections. When welding is utilized, the connections are susceptible to cracking or failure in the weld parts. Therefore, the maximum stress in the steel box moment connection is always checked during a preliminary design stage. In this study, the stresses due to shear lag were evaluated using least-work solution, considering the flexibility of column flange. The local flexibility of the connection, which caused by the column flange and diaphragms, is represented by an axial spring model, and contributed to stress distribution in the beam flange. Using the presumed longitudinal displacement functions for both the beam flange and web, the stress concentrations were evaluated to increase significantly compared with that obtained from a cantilever beam model. The finite element assessment was also conducted to check the validity of the manual prediction of the stress in various ranges of the beam and column section properties. The results are further summarized, discussed, and showed that more flexible column flange and diaphragm provided higher stress concentrations.
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