Bamboo back in the frame

Wood Focus magazine
30 Dec 2011
bamboo roof

Marginally-engineered building techniques used in rural residential shelters are being investigated to initiate a mainstream engineering code for bamboo.

Bamboo has a centuries-old place as a construction material across the developing world, but most of the knowledge about its application is based on cultural tradition. In rural areas, where specialist knowledge and engineering may not be available, they also defer to traditional practices.

A collaborative group at the University of Pittsburgh in Pennsylvania, USA, and the Pontifical Catholic University of Rio de Janeiro, Brazil, (PUC-Rio) has centred on establishing the two-dimensional pushover behaviour of a prototype water- treated Phyllostachys aurea bamboo portal frame structure.

The structure is based on one observed at a school in Darjeeling, India, but was built at half-scale and tested at PUCRio. Testing consisted of applying an incremental lateral load to the frame and collecting displacement data at each step. The frame was loaded and unloaded to capture the hysteretic behaviour of the frame and connections.

Researchers expected the frame to remain relatively rigid, but the tests revealed larger displacements than anticipated. The behaviour of the column bases was examined, by by testing additional column base specimens in measured load increments. This caused them to rotate at the base – so much so that the apparent lateral stiffness of the column was only about 20% of what was expected. The team then built a finite element model of the frame’s behaviour, which was validated using the experimental results.

Professor Kent Harries of the University of Pittsburgh explains the initial results, ‘The portal frame is just one component of a larger structure system, so we need to understand its behaviour in order to better understand the overall system behaviour’.

If bamboo construction can be better codified, Harries says, its stigma as a ‘poor man’s material’ will be dispelled and its use in, for example, earthquake or monsoon regions would become more viable. It could also be used for rapidly deployable post-disaster temporary shelters in regions where it is indigenous.

He continued,‘We believe that bamboo culms have a place in the construction industry in regions where appropriate species are found. Bamboo offers a viable alternative to the most widely used timber species given the issue of deforestation in some parts of the world.’

Wood consultant Gervais Sawyer comments, ‘Standardising designs will make structures easier to assemble and enable people to add value to their local raw material. I am impressed with the researchers’ achievements, which must have been under difficult conditions away from familiar supplies and equipment. Bamboo is a truly remarkable building material. Unlike wood, however, it presents problems in making fixings, as you can’t use nails. Although construction with bamboo follows traditional methods, new designs can simplify construction while achieving greater durability.’