A “Toolbox” for Forensic Engineers

Establishing the Load Transfer Path 63
Figure 3.1 Stepstool ladder placed in the doorway where an accident occurred.
have been caused by the forces generated if these safety instructions were
being properly observed.
Figure 3.1 shows a stepstool ladder alleged to have failed within an hour
or so of purchase while being used to paint the gutters of a house. The user
was a tall, heavy man but within the weight specified on the labeling of the
steps for “light domestic use.” The foot of the left stile is bent inward and the
steps can no longer be placed on the floor without the front frame tilting so
far that anyone attempting to climb them would topple sideways. The stile
is a rectangular box section aluminum alloy that has buckled inward opposite
the bottom tread, and the rivet holes at that side are torn, as shown in
Figure 3.2. The plaintiff alleges the steps were of defective construction
and/or that the box section was not strong enough or that there was a fault
in the metal.
As in all designs of step stool ladders the front and back legs splay outward
so that, whether viewed from the front, back or the sides, when they are
opened out and placed on a firm, level floor the four feet are farther apart
than any of the steps or side braces. Thus any load acting downward from
someone mounting or standing on the upper treads generates compressive
forces in the stiles that are reacted to by the floor and hence set up force
components acting to spread the feet outward. How then could the bottom