Timber buildings have well established economic, social and environmental advantages over other structural options. In particular, their low carbon footprint and high strength to weight ratio makes tall timber construction an attractive solution for satisfying the pressing housing demands in densely populated areas at minimum environmental costs. However, due to the low mass and flexibility typical of tall timber construction, concerns regarding their dynamic behaviour have been raised.
An MSc research project conducted at Imperial College London by Ishan Abeysekera, funded by the Institution of Structural Engineers, has examined the dynamic response of tall timber buildings of different configurations subjected to Tornado and Downburst wind loading. Four buildings incorporating: i) solid cross-laminated-timber (CLT) shear-wall systems, ii) glued-laminated (Glulam) frames, and iii) hybrid systems, were studied.
Buildings of 7, 11, 20 and 30 storeys were modelled and analysed in the Finite Element software SeismoStruct. Particular attention was given to the accurate representation of the connection behaviour as well as material and structural damping. Wind velocity series were generated following typical Tornado and Downburst distributions and extensive response history analyses were performed. The results were discussed in terms of peak acceleration levels attained at selected locations throughout the height of the building considering varying frequency ranges. The software SeismoSignal was employed for post-processing.
A comparison against international performance criteria for user comfort as set out in ISO10137 revealed the inability of the buildings studied here to satisfy the codified acceleration limits. Therefore, additional analyses employing tuned-mass-dampers (TMD) tailored to the most demanding frequency response in each case were carried out. It was found that TMDs with an active mass of 5% of the total building mass are able to produce up to a 50% reduction in peak acceleration levels. The models proposed as part of the present study constitute a fundamental step towards the assessment of alternative response modification strategies as well as the development of numerical tools for the future optimisation of TMD designs.
A poster giving further details of this project and details of the Institution of Structural Engineers Grant Scheme are available at: http://www.istructe.org/education/scholarships-grants-and-bursaries/msc-research-grants. Diagrams and their explanations featured below have been taken from the poster.