Step Ladder Failure Analysis: A Comparison of Analytical Methods

Abstract

When a user falls from a step ladder, the accident can be accompanied by damage to the ladder. A common area of damage is in the vicinity of the connections between the front side rails and the lowermost step. When determining the cause of a fall, it is important to understand how this damage occurs and whether it may be causal to the accident or a result of the accident. Commonly, engineers investigating such accidents have relied on three methods of structural analysis: classic analytical methods (so-called “hand calculations”), computational methods (finite element analysis) and laboratory testing. These three methods each have strengths and weaknesses that affect how the results should be used and interpreted by the investigating engineer. Factors such as the assumptions and simplifications used as input to an analysis, the type and amount of results available as output and cost are examined. These issues are discussed in the frame work of a case study wherein all three methods are applied to the analysis of a step ladder damaged in the field. The results show that, while step ladders may, at first, appear to be relatively simple structures they are, in fact, quite complex. As a consequence, it becomes very important to understand the analysis technique being used and its inherent limitations. Without consideration of these factors, the investigating engineer can be drawn to an incorrect understanding of the damage and its cause. This, in turn, may lead to an erroneous determination of the cause of the accident.

Failure Analysis of an Aluminum Extension Portable Ladder

“…This is because the assumptions, simplification and conditions for the simulations to reproduce the incident are difficult to make. Kenner et al [5] examined such factors in the analysis of step ladder damaged in the field and concluded that these structures were more complex than they might appear. In fact, in an investigation on the root cause analysis [6] they showed that the ladder was damaged as the result of the user impact of the ladder after substantially tipping over.…”