Mechanical Response of Unbraced Wood Composite I-Joist to Walking Loads

Abstract

Lateral buckling of unbraced wood composite I-joists is a form of instability that causes the joist to deflect laterally and rotate. This instability may be a cause of worker falls and should be explored to understand the range of loading and out-of-plane motion required to cause lateral buckling. While walking on unbraced joists is uncommon on construction sites, understanding the movement of unbraced joists is needed to model more commonly observed partially braced joists. This paper investigated the load and out-of-plane movement of several unbraced wood composite I-joists subjected to human walking loads. Vertical load at the ends of the joist, top and bottom horizontal loads at one end of the joist, as well as lateral deflection and rotation at the midspan and quarter-span were measured while participants traversed the joist. Lateral buckling of joists was observed due to walking loads. Total vertical load measured was similar to participant weight, while horizontal loads ranged from 9.6 to 13.7% of participant weight. Differences were observed in I-joist behavior between different lengths and manufacturers studied. Load, lateral deflection, and rotation of the joist increased as participant weight increased. Vertical load at each end, lateral deflection, and rotation were positively correlated with participant weight. A set of curves demonstrating the lateral deflection and rotation for different joists as a function of participant weight was developed.