Stability study on scaffolds with inclined surfaces and extended jack bases in construction

A scaffolding system is a temporary structure that is commonly adopted on construction sites. As steel scaffolds are modular members manufactured with fixed dimensions, the total height of a scaffolding system seldom fits the headroom of a building when scaffolds are set up in multiple stories. This results in a difference in elevation, i.e. gap, between the top of the scaffolding system and the ceiling slab. In addition, scaffold configurations may need to be adjusted if the interior of a building has inclined planes on the ceiling slab or stairs on the ground. This study shows that the gap between the scaffold and the ceiling slab can be eliminated by altering the lengths of adjustable base jacks or adjustable U-head jacks. When the ceiling slab is inclined, it is suggested that a combined system of scaffolds with wooden shores of different lengths should be installed in the out-of-plane direction of the scaffold unit. This system can also be used when the ceiling slab is inclined and the ground has a difference in elevation (e.g., stairs) in a building. By using the second-order elastic analysis with semi-rigid joints, the load-bearing capacity and failure model are found to be very close to those obtained in the loading tests using various scaffold configurations. In the loading tests for reused scaffolds, the lower bound of the load-bearing capacity of the scaffolding systems can be obtained by applying a subsequent load on the scaffolding systems, which are commonly adopted on the construction sites. The strength reduction factor (ϕ) of these scaffolding systems installed by reused scaffolds can be obtained by calculating the mean value and standard deviation, which can serve as a reference for the strength design of scaffolding systems with different safety requirements.