Barry Sunderland

A step, forming part of an outdoor stairway on the University of Limerick campus, was modeled and analyzed in ABAQUS/CAE. The maximum Von Mises stresses and maximum deflection predicted by the software were compared to hand calculations and the factor of safety for the step was also calculated. The step's design was altered to reduce weight without reducing the factor of safety.

Figure 1: Half the step was modeled to reduce computational time. The boundary conditions at the center of the step prevented movement in the z - direction which replicates the behavior of the full step. A load was applied over the approximate area of half a foot print.

Figure 2: This image shows the maximum Von Mises stresses at the centre of the step. As expected, stress concentrations are observed at the surfaces of the holes. These were found to be 24 N/mm2. ABAQUS/Explicit was used to examine the dynamic response of the step when it is loaded. A steadily increasing load equivalent to the force of a footstep was applied over 0.5 s and immediately removed over 0.5 s. The following two graphs show the displacement and stress response caused by this loading.

The step was then redesigned to reduce weight. The height of the riser at the front of the step was reduced by 40 mm and a web was added to the back of the step. This reduced the weight by nearly 7 % and also halved the maximum deflection experienced by the step.

Displacement contours (left) and Von Mises stress (right) on the redesigned step.