Experimental and Analytical Studies of Door-Type Modular Scaffolds with Initial Geometrical Imperfections

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

Monitoring Damage in PC Slabs by Modal and Ultrasonic Tests

The effectiveness of modal and ultrasonic tests for monitoring the damage in precast prestressed concrete slabs was experimentally investigated. Four slabs with two different span lengths and corresponding modes of failure (interfacial shear and flexural failures) were subjected to loading steps until failure. The variations in fundamental natural frequency, damping ratio, ultrasonic pulse velocity (UPV), and ultrasonic wave attenuation in relation to the damage severity and failure mode were investigated and compared. It was observed that the natural frequency was sensitive to flexural crack development. A significant change in the damping ratio was obtained in the slabs with moderate damage. The UPV was not affected by a moderate degree of interfacial shear damage and a low degree of flexural damage; however, it was strongly related to the progression of flexural damage at the severe stage. Among the various indexes, ultrasonic wave attenuation was most sensitive to the development of damage. The method could detect interfacial-shear and flexural cracks at an early stage