Using the bridge repair system in Problem P5.15, develop two additional two dimensional configurations that utilize different suspension arrangements. The following design requirements must be met: Two-level access to the bridge must be provided with the top platform at 90 in. below the road and the lower level 185 in. below the road; each level must accommodate no more than two 200-lb workers; standard structural steel cables (S_y = 250 Mpa) of 0.50-in. diameter with varying lengths are to be used. Evaluate the three designs (your two and the one from Problem P5.15) with respect to their factor of safety in worst-case loading conditions and identify which configuration has the highest factor of safety.

Problem P5.15

A two-tier system to repair bridge infrastructures is supported by two steel cables for each platform (Figure P5.15). All the support cables have a diameter of 0.50 in. Assume the applied loads are at the midpoint of each platform. Determine how much each cable stretches at points A–D.

Figure P5.15

140 in. 90 in. 250 lb 185 in. A 190 in. 400 lb D