Strength variability of conventional slab formwork systems

Wooden formwork design is currently based on the criteria developed for the design of wood in new condition. To develop formwork design criteria that include the effect of material reuse and formwork installation workmanship, data on actual formwork member resistances and installation inaccuracies are required. In this paper, wooden slab formwork installation inaccuracies and strength variabilities are investigated. The formwork structural properties presented are based on laboratory experiments on formwork members collected from eight construction sites located in Chicago, Illinois, Milwaukee, Wisconsin, and Minneapolis-St. Paul, Minnesota. From each construction site, samples of shores, stringers, and joists were collected. In addition to formwork member sample collection, during site visits, installed shore out-of-plumb angles and stringer, joist, and sheathing spans were also measured. In this paper the observed formwork member physical conditions, installation inaccuracies, shore compressive strengths, and bending and shear strengths of the stringers and joists are presented. The observed structural properties are summarized with appropriate probability distributions.