Experimentally Determined Structural Load Paths in a 1/3-Scale Model of Light-Framed Wood, Rectangular Building

Abstract

It has been speculated that much of the losses from hurricane damage to single-family wood-framed residential structures is due to design based on faulty understanding of the structural load paths in these buildings. This NSF-supported research presents a new approach to understanding load paths in wood-frame residential structures and establishes a relationship between spatially varying wind loads and structural load paths. A 1/3-scale wood frame gable roof building was constructed with geometrically scaled wood members, sheathing, and nails. The model scaled the flexural stiffness ( EI ) of the roof sheathing for wind loads applied normal to the surface. A dense grid of point loads were used to develop the influence coefficients (and surfaces) for 20 vertical reactions located at roof-to-wall and wall-to-foundation connections. The linear elastic structural response for roof-to-wall connections was limited on the roof surface to within two trusses of the applied load location. As expected there was a greater spread of load effect at the foundation level (6–8 trusses) because the exterior wood stud walls acted as stiff, vertical diaphragms. The influence functions were combined with wind tunnel pressure data for a similar shaped model from which the dynamic wind loads were estimated using a database-assisted design methodology. There was reasonable agreement between the dynamic reaction load traces with design loads obtained by components and cladding (C&C) design approach of ASCE7. Results also suggest the main wind force resisting system (MWFRS) method underestimates the design wind loads at roof-to-wall connections.