SUMMARY
In the study, the performance and structural behaviors of door-type modular steel scaffolds with different degrees of initial geometrical imperfections were evaluated through experimental and analytical investigations. Two one-story and nine two-story modular steel scaffolds were tested to failure. When the number of stories increased from 1 to 2, a 14.8% reduction in load capacity was obtained for the scaffolds with relatively straight columns. The capacity reduction was mainly due to flexibility at column joints and an increase in the deviation from the vertical alignment. The average capacity reductions increased to 18.9% when the out-of-straightness approached the limit provided by the standards. The effective length factors for capacity calculation were determined. In conjunction with the initial imperfections, the results indicated that the flexibility at column joints and the stiffness of beam and sub-frame elements on modular frames significantly affected the failure mode and ultimate load. The beam and sub-frame elements prevented the buckling failure in the modular-frame plane. Hence, the initial imperfections in the plane of cross bracings were more critical than that of the modular-frame plane, and it is necessary to closely inspect the same while using scaffolds in construction.