Ewan's final output was a simple to use spreadsheet tool which gave almost immediate answers to questions regarding the suitability of fixings for CLT, removing the need to undertake much more complex finite element analysis.

Competition judges

Smith and Wallwork, a Cambridge based structural engineering firm who specialise in cross laminated timber (CLT), approached the Department of Engineering with a research proposal inspired by their design of a school building in Bishops Stortford. The company had been building a finite element model for the folded plate roof and it was difficult to model the connections between CLT panels. They wanted to understand the rotational behaviour of half lap joints between CLT panels better as it would affect the deflections within the roof. The rotational stiffness is also important when assessing the vibration compliance of floor slabs, a key concern within the CLT industry.

Ewan worked on this research proposal as his 4th year student project and one of his results was a brand new calculation method that enables the rotational stiffness of half lap joints to be predicted quickly and easily with a spreadsheet. “This avoids the need for a complicated finite element model and can be used by industry professionals who previously lacked a method for predicting the parameter,” explained Ewan.

His project aimed to understand the rotational stiffness through a combination of  finite element modelling, theory and experiments. Detailed 3D finite element models were created using Abaqus to model the interaction between the screws and the timber and the results were compared to physical tests carried out in the structures lab. 

Throughout the experiments the joint behaviour was visualised using Particle Image Velocimetry (PIV). This technique is relatively new in the field of structural testing and a piece of software written by Allan McRobie was developed to enhance its capabilities. The PIV results displayed movements that were imperceptible to the naked eye and provided useful insights throughout the testing.

Ewan's simplified calculation method was developed to estimate half lap joint rotational stiffness through a spreadsheet that features a variety of design parameters and manufacturers. The findings of Ewan's research have already been incorporated into a design tool that Smith and Wallwork can use in many future projects.

The Timber Trade Journal awarded Ewan a prize for his research, he won the Innovative University Timber Research category a new prize category that acknowledges the work that university students carry out, at both undergraduate and postgraduate level, pushing forward our understanding of ever-expanding applications for timber.

Ewan graduated in 2016 and is now working as a structural engineer with Arup in Bristol.