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Summary The purpose of this study is to evaluate the structural behavior of concrete‐filled steel tube (CFT) column to H‐beam connections with vertical through‐plate through full‐scale experiments and examine retrofit methods using the finite element method to improve the connection performance. For this purpose, monotonic loading tests were performed on three full‐scale specimens with varying thickness of vertical through‐plate. The experiments showed that the specimens suffer from a brittle failure due to the stress concentrations and residual stresses at the welds before the beams reach their plastic moment capacity. A series of sectional analyses were conducted to evaluate the effects of the thermally induced residual stresses due to welding and then the strain concentrations in the welded connection were estimated by comparing the experimental maximum strain and the analytical mean strain values. Based on these results, a retrofit model for reinforcing a stiff plate on the upper flange of the beam was proposed and analyzed to reduce the stress concentrations in the welded connection. The results showed that using the proposed retrofit approach, the stress concentration at the connection between the vertical through‐plate and the top flange is reduced by 72%, and the strength of the connection is increased by 70%, which is 10% higher than the analytical plastic moment capacity of the beam.

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