Edinburgh Napier University

  Platform timber frame construction is considered an efficient building method for multistorey dwellings where timber walls and diaphragms provide the overall stability for the structure to resist lateral forces such as those generated by wind action. Although, so far, many research studies have been conducted on the racking performance of platform timber frame walls, there remain some gaps in knowledge in a number of key areas which this research has aimed to address.

A quantitative assessment of the racking performance of partially anchored timber framed walls has been carried out via experimental test campaign. Timber framed walls, sheathed with oriented strand board (OSB) panels and/or British gypsum plasterboards (PB) were constructed from a combination of material types under different loading configurations and tested according to standardized procedure. The experimental study was designed to examine the influence of a range of geometrical parameters, such as (panel-to-frame) fastener size and spacing, wall length, arrangement of studs and horizontal members, and the effect of vertical loading on the racking strength and stiffness of the walls.

When subjected to a vertical load, the wall’s racking strength has been found to be more sensitive to variations in the fastener spacings, compared to the racking strength of similar walls without applied vertical loads. Conversely, it is racking stiffness to be more sensitive to variations in fastener spacings when no vertical load is applied to the wall. In such a case, the stiffness increase was up to three folds when the fastener spacing was reduced from 150 to 50 mm. However, such gain in stiffness did not occur in similar walls when they were subjected to a vertical loading of 25 kN, with stiffness increasing by only 24%.

The comparison of experimental results, with the results from the UK design code formulae, showed that, on average, the design code underestimated the racking strength by 25% for walls under vertical loading of 25 kN and by 54% for walls without any vertical loading.

The influence of test procedure on the racking performance of timber framed walls was also examined in an extensive experimental and analytical programme which investigated the compatibility and suitability of the test method in BS EN 594:2011 with the racking design method of BS 5268-6.1:1996. The research findings led to appropriate recommendations for determination of the design racking values from the test results.

The effects of openings/discontinuities caused by windows and doors on racking performance of OSB walls with and without the use of trimmers, as well as spreaders were also examined. The results led to determination of a relationship between the size of the opening for a window or a door and the percentage reduction in the racking performance of the wall.

Finally, this research examined the racking strength and stiffness of a recently developed shear wall referred to as “Mid-ply wall”. Comparing the performance characteristics of the Mid-ply walls with the “standard walls”, the Mid-ply walls performed significant ly better in both strength and stiffness terms, therefore providing a considerable potential for use in the UK and European timber frame construction.