Load and Capacity Considerations for Stringers in Shoring Towers

Shoring, formwork, and falsework systems for the support of overhead construction often utilize proprietary, modular truss towers consisting of vertical tubular metal posts interconnected with diagonal cross bracing. These towers are typically offered and specified via a maximum shoring height and a “per-leg/post” vertical load capacity. The tops of the posts are often fitted with adjustable leg extensions or screw jacks that can support timber or aluminum beams for the support of the soffit formwork panels. These aluminum beams, typically with I-shaped cross section with relatively thin webs and flanges, carry the distributed soffit and wet concrete weight to the post shores. In practice, these beams are sometimes designed and installed in a manner that unintentionally reduces the stiffness and vertical load capacity of the shoring system. Specific applications may cause loading conditions or local section failures that were unaccounted for in the shoring design and construction. Case studies of collapses of such formwork are presented along with finite-element analyses of the failures to highlight the importance of considering the presence and detailing for these beams in the overall shoring system design and construction.