Low-rise buildings constructed using wood are vulnerable to extreme wind storms and earthquakes. While several experimental measurements of the environmental loads (mostly wind) on the building envelope have been made at full scale, none of these studies directly linked these external loads with the internal forces and displacements of the structure.
This report presents the experimental and analytical work on two light-frame wooden structures, with one that already existed (Forintek shed in Québec City) and the other (UNB house) that was built specifically for the research project on the University of New Brunswick campus in Fredericton. The research goal was to devise and demonstrate methods of identifying load paths in light-frame wood buildings subject to environmental loads. This goal was achieved by carrying out experiments at the element level (studs, sheathings), subsystem level (shear walls) and on the whole-building level (finished and “realistic” light-frame timber buildings). The responses of these buildings to controlled static tests as well as natural environmental loads were observed and compared with a wind tunnel study and with detailed finite element models with good agreement.
Shear walls were tested in isolation and as a part of the whole structure. The tests indicated that neither the strength nor the stiffness decreased by the same magnitude as the wall effective length is reduced. For the Forintek shed, the structural monitoring was based on measurements of deformations within a representative segment of the wall and roof surfaces and a matching grid of wall and roof wind pressure taps supplemented with a wind tunnel study at Concordia University. In general, it was shown that the building surroundings had a great effect on the pressure distribution of the surface on the structure and that these effects cannot always be determined intuitively. Both mean and peak pressure coefficient were measured and they compared well with corresponding values obtained in the wind tunnel tests.
Results from controlled static loads on the UNB house indicated that the load was distributed to all walls, and significant load sharing was observed. The stiffness of the roof was sufficient to distribute load to walls farthest away from the load application point. It was also found that the internal forces are concentrated near the corners of the building. Under vertical loading on the roof, the load at the roof-to-wall interface was concentrated in a small region of the building plan around the application point. The test results also showed that the load was transferred to the transverse walls, even though there were only nominal connection between the wall and the roof trusses.
Analytical modeling results showed good agreement with the full-scale test results for shear walls as well as for the whole building. The 3-D model was able to simulate the sharing of racking forces between shear walls, based on experiments reported in the literature. In general, the errors in the numerical prediction were small. The model was able to predict the interaction between the roof system and the walls and the interactions amongst walls.