Projects and Solutions

Reliability of wood houses under extreme wind loading

Codified design is aimed at ensuring life safety and reducing economic losses. This could be achieved if structural collapse or failure during rare events such are strong wind caused by hurricane is minimized or eliminated. However, damage to low-rise wood frame structures subjected to hurricane winds is often observed and the reliability and risk of this type of structure are poorly understood. This is partly due to the difficult in assessing the responses of low-rise wood frame structures under extreme wind loads considering the nonlinear material behaviour, the complex interaction between many fasteners and wood frames, and temporal- and spatially varying wind pressures.

Previous studies focused on the responses of wood houses under extreme wind loads often assume that nonlinear material effects can be ignored, use of code specified static wind pressures is adequate, and/or dynamic effect can be ignored. These assumptions can be adequate for some applications or objectives but do not reflect the actual structural responses. The discrepancies of load (actual wind load effect and assumed static uniform load) and structural behavior (linear and nonlinear) for design purposes contributes to the varying level of reliability for wood roof panels, especially if a quantitative structural reliability analysis is of concern. To overcome this problem, a detailed nonlinear finite element model of the wood house, especially focused on the roofing systems, is to be developed, and numerical analyses considering temporal and spatial varying wind pressure and dynamic load effects are to be carried out. The obtained results are to be used for reliability assessment of roof systems, by considering and ignoring human errors.

At present and as first step, nonlinear and linear elastic responses of plates, mimicking the sheathing panels, has been completed. Draft articles describing our findings are to be submitted for possible publications. Furthermore, a three-dimensional (3D) finite element model representing the actual dimension of the house test specimen at “3LP” site has been developed. The model is shown in the following figure.

three-dimensional (3D) finite element model

The model includes detailed modeling of nonlinear connections between sheathing panels and roof trusses. The developed model serves as the basis for a series of numerical experiments to be conducted. Considerable preliminary numerical tests using the developed finite element model have been carried out. For example, response analysis using the developed finite element model under static wind pressure, time varying pressure has been conducted. Currently, probabilistic assessment of nonlinear dynamic responses using the developed finite element model is under consideration. The obtained results are to be employed for the development of the fragility curves (i.e., curve representing the probability of failure for given mean wind speed), and reliability evaluation of wood houses. Furthermore, assessment of human error on the responses and reliability of the wood house is being conducted at present. It is expected that the results will provide guidance on the adequate of current design practice and lead to possible necessary changes to further improve the performance and resilience of wood houses.

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Updated June 22, 2010 by contactWE
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