Failure Analysis of Stepladders Manufactured From Extruded Aluminum

Abstract

Despite advances in materials and manufacturing techniques for extruded aluminum and fiberglass reinforced composite structures, accidents involving ladders cause an estimated 300 deaths and 130,000 injuries annually. Although the origins of accidents are rarely known, the causes are usually attributed to the actions of the user and not the failure of the structure. To better understand the material and structural characteristics of common, commercially available aluminum stepladders, and the potential role they play in accidents, a structural analysis was performed on several typical designs. Stress analysis of common structural geometries revealed that the potential modes of failure are complex, and might often be the result of a combination of compression, bending, and torsion in the front side rails. In addition, some loading scenarios suggest failure can result from elastic buckling in either the front or rear side rails. Measurements to quantify variations in the material and geometric properties of the ladder components revealed that significant variations can exist and are attributable to several different aspects of the manufacturing process. In some instances, actual rail strength and section properties did not meet the specifications of the ladder manufacturer. Overall, the susceptibility of these structures to failure under certain loading scenarios, coupled with the inherent variations associated with extrusion manufacturing, indicate that aluminum stepladders, especially Type II and Type III, are not adequately designed for strength, and that current designs do not demonstrate a factor of safety sufficient to meet the standards required by the ladder industry.

Failure Analysis of an Aluminum Extension Portable Ladder

“…Based on a study conducted on the 24,882 ladder falls of 1987, OSHA estimates that 53% of the ladders are involved in the accidents broke during use. The main cause of ladder failure is the sliding of the bottom and the top ladder ends [1]- [3] and the buckling of the beam side rails [4]. While the former cause is rather simple to verify the second cause is often stated in the incident reports without giving the origin and intensity of the loads developed to cause such a buckling failure.…”