Behavior of a 1/6th Scale, Two-Story, Wood Framed Residential Structure Under Surge Wave Loading
The goal of this study was to develop an understanding of the nature of surge wave loading on wood framed residential structures for a variety of building configurations and test conditions. The objectives of the study were: (1) to measure forces on a 1/6th scale wood framed residential structure, (2) to evaluate qualitatively the structural response to different loading conditions, (3) to compare the effects of different structural configurations on the structural response, (4) to develop an equation to predict wave forces, and (5) to compare predicted/measured forces with existing building code.
Testing was performed on a 1/6th scale 2-story wood-framed residential structure. The design of the structural model was performed by a Colorado State University research team under the supervision of Dr. John van de Lindt, the details of which can be found in Garcia (2008). The structure was prefabricated at Colorado State University and shipped to Oregon State University's Wood Science and Engineering (WSE) Structures Laboratory for final assembly. The 1/6th scale model was tested in the Tsunami Wave Basin at the O.H. Hinsdale Wave Research Laboratory. The structure was tested in both a flooded and non-flooded condition with the following solitary wave heights: 10 cm, 20 cm, 30 cm, 40 cm, 50 cm, and 60 cm. Additional push over testing was conducted in the WSE Structures Laboratory on a nominally identical model to quantify the stiffness of the structure.
This research was successful at developing an experimental setup to capture surge wave forces on the model structure. The measured forces were mainly overturning moments and uplift forces due to wave loading. The qualitative analysis of the data showed that differences in structural stiffness throughout the structure will cause a different load distribution in the structure, e.g. overhanging eaves above the garage can provide unanticipated loading conditions, water traveling beneath the structure generates predominantly uplift forces, and the effect of waves breaking on or near the structure greatly increases the loading. The average difference in total load from the 0 degree to 90 degree orientation (approximately 2:1 aspect ratio) had a ratio of approximately 4:1. However, the building code equations to predict surge loading does not take this into account. The ratio of force from the windows closed condition to the windows open condition is approximately 2.5:1, a reduction of 40%.
The relationships in equations (1) and (2), developed from analysis of push over testing, were used to determine the lateral wave loading. Calculation of the wave force (PW) on the structure was then accomplished using deflection due to wave loading ( Δ W) and bore height (h) as inputs into (1) and (2).
PW = Δ W·746·exp -0.03648·h (1)
PW = Δ W·4036·exp -0.04677·h (2)
This wave force was then compared to theoretical force calculations in (3) from the City and County of Honolulu Building Code.
FS = 4.5· ρ ·g·h2 (3)
Comparing predicted/measured force data with the theoretical values from (3) shows that there are large differences with changes in structural configuration. As this is the only wave loading guideline accepted for use with building codes, there is clearly a need for additional research in this area.
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