Robustness of Large Timber Buildings - investigating the capacity of timber connections to accommodate large deflections and rotations

Over the past decade, timber has been used in the construction of larger and taller buildings than ever before. A major reason for this is the development of engineered wood products, which use strips of wood cut and glued together to make large, reliable structural elements. Engineered wood products are currently being used to build the 18-storey Mjostarnet, and have been used in 100m-span roofs, major road bridges and several buildings of 8 storeys and more in the UK.

These large structures bring with them new challenges, and an important one is design against disproportionate collapse. A building cannot be designed to resist every load it could possibly be subjected to. Some loads, such as explosions, intense fire or vehicle collision will inevitably cause damage to the structure. The UK building regulations 2010 require that “The building shall be constructed so that in the event of an accident the building will not suffer collapse to an extent disproportionate to the cause”. For example, if an accidental load destroys a beam, it may be unavoidable that the area of floor supported by that beam collapses. A disproportionate level of collapse would be if the collapse of that floor area brought down the columns either side of it, and went through the floor below it.

Engineers design against disproportionate collapse by providing redundancy, and alternative load paths through the structure, and occasionally by designing certain key elements to resist very high accidental loads. The provision of alternative load paths can be a particularly efficient approach, but it requires connections that can cope with the large deformations and rotations that result from accidental loads.

This PhD will investigate the capacity of timber connections to accommodate these large deflections and rotations, while still providing sufficient load resistance to support the structure. This will require extensive laboratory work, using novel test setups and measurement techniques to ensure large inelastic deformations are properly measured and recorded. You will investigate the properties of the timber and connectors which lead to resilient, ductile connections, and devise design and reinforcement strategies which ensure the necessary behaviour.