Development of a Frame for Wide Openings in Residential Construction

An increasing demand for wider and taller openings within the confines of a limited wall area in modern housing in New Zealand means that steel frames are often chosen to replace what has traditionally been timber framing. To provide a wood based solution for wide openings, high strength laminated veneer lumber (LVL) and plywood solutions have been developed to provide both lateral bracing for seismic and wind resistance, as well as to support vertical loads.This paper describes static and dynamic testing on timber framed box columns supporting a beam over the opening, with a range of material combinations used to clad the columns. Creep tests on completed frames identified problems with long-term creep deformations that were solved by modifying connection details. The results from two and a half years of creep test show the improved performance of the system. The project has resulted in a set of published span tables that allow the use of LVL by utilising the portal action to reduce deflections and compete with steel.