Projects and Solutions

Full-scale tests of roof-to-wall connections under hurricane wind loads

The goal of the current experiments is to examine the response and failure of toe-nailed roof-to-wall connections under wind uplift. Air boxes were installed on the roof of the test house (4:12 gable roof) and data from a wind tunnel study was obtained for a nearly quartering wind direction of 40o.
Wind tunnel pressure time histories and a sketch of the layout of air boxes on the roof of the full-scale test house This wind direction was chosen because of the presence of the so-called delta wing vortices which produce significant temporal and spatial pressure gradients. Moreover, at this wind angle the highest pressures occurred on the leeward side of the ridge which could produce an interesting response from the structural roof to wall connections. Since we were unsure how failure would occur it was decided that rather than pass a design hurricane over the house, where the wind speed and direction would change over the duration of the test, the same segment of pressures time histories would be re-run several times, but at increasing wind speeds with the wind direction held constant.

Photograph of several PLAs and airboxes as mounted on the roof of the two storey test house

The house was instrumented with 37 displacement transducers, 6 accelerometers, 45 3-component load cells at the foundation of the house, 16 security-type video cameras, 2 HD video cameras and a high-speed camera. Fifty eight PLA’s were mounted on the roof in the layout indicted in the figure below, while a photograph shows some of the PLAs above the roof.

The first experiment was a 15 minutes long run with an equivalent mean roof height 10 min mean wind speed of 20 m/s. Six tests were run in all, with 5 m/s increments in speed; however, by the last test, the duration of the segment was under 7 minutes. The first failures were observed at 25 m/s with slight permanent deflections of the nails. As wind speeds increased these offsets would grow, as can be inferred from the preliminary data shown below.
Vertical displacements of the truss near the most highly loaded leeward edge Photographs of the toe nails before and after the tests indicated that they had moved substantially and that airgaps existed between the bottom chord of the truss and the top plate of the wall at some connections. At 45 m/s, the toe nails had not completely cleared the top plate during the peaks, but they had little capacity left. However, no failure of the gable ends was noted. It should be emphasized that all of this assumes that the house was nominally sealed. Analysis will be used to determine the effects of a major opening on the results. Significant analysis remains to be done on the rich data set provided by these experiments. Future tests will involve replacing the toe-nail connections with load cells and then replaying the experiments to determine the loads passing through each of these connections (utilizing the very high repeatability of the PLAs).

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The University of Western Ontario
London, Ontario, Canada, N6A 5B9 • Tel: 519-661-2128

Updated June 22, 2010 by contactWE
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