Navaratnam, Satheeskumar, Humphreys, Mitchell, Mendis, Priyan, Nguyen, Kate T.Q., and Zhang, Guomin (2020) Effect of roof to wall connection stiffness variations on the load sharing and hold-down forces of Australian timber-framed houses. Structures, 27. pp. 141-150.

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Abstract

Roof to wall connections (RWCs) play a major role in wind load sharing and load transfer of timber-framed houses. The lack of coherence in the load sharing and load transfer can cause premature failure of timber-framed houses. Thus, it is essential to provide RWCs with adequate strength and stiffness, to ensure the dynamic roof wind loads are adequately shared and transferred through the structural system to the foundations. Typical construction defects in RWCs (i.e. missing nails) reduce the stiffness of the RWCs, introducing discontinuities in load paths, contributing to total roof failure under windstorms. This study combines realistic spatially and temporally varying wind loads, captured from model-scale wind tunnel-studies, with a validated finite element model of the roof structure, that accurately describes the load sharing through the structural system and evaluate the effect of RWC stiffness variations and realistic wind loading variation on the load sharing and hold-down forces of Australian contemporary timber-framed houses. The combined effect of RWC stiffness variations and realistic wind loading variation are compared to the traditional design method approach (i.e. tributary area method and use of simplified design roof pressures from wind loading standard AS/NZS 1170.2 (2011)). Results show that the maximum RWC hold-down force from AS/NZS 1170.2 (2011) is about 10% greater relative than the maximum RWC hold-down force from realistic dynamic wind loads, and overestimates wind loads for most wind angles. The maximum RWC hold-down force derived by the load sharing method with defective connections (i.e. single and double nails missed on the RWCs), induced hold-down forces 10% higher than that of the traditional method at neighbouring RWCs. Further, hold-down force variation between traditional and load sharing methods can increase up to 50% in a real house roof structure, as the stiffness of their RWCs vary throughout the system due to the material non-linearity and construction defects/human errors.

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