Bamboo Cob House testing, UTS Shake Testing
Jean-Michel, an Engineering student mixing cob for model house inside UTS Materials Testing Laboratory
Luke Punzet, engineering student and Peter Hickson building the lower floor section of the half scale model house with bamboo reinforced cob
Peter Hickson constructing the attic roof frame for assembly with the bamboo cob base
The model house assembed on the shake table
Peter Hickson proposed, designed and built a low cost housing solution for South East Asia in Gingoog City, Misamis Oriental Province, Minanao, The Philippines in 2006.
He stated that it was affordable, comfortable, durable and safe. He could prove it was affordable by building one. He could prove it comfortable by living in it. It was proving itself durable.
He needed to test the strength of bamboo reinforced cob especially in regards earthquakes that are a real problem throughout Asia. Peter believes if it is able to survive the racking forces of an earthquake it will also likely survive other hazards such as strong wind and perform better in storm surge and landslide.
Fortunately Peter was able to conduct shake table testing in the materials testing laboratory at the University of Technology, Sydney in 2008. Peter worked as an industry supervisor with Professor Bijan Samali and Domonic Dowling supervising two final year engineering students as their Capstone research project. The students Jean Michel Albert Thernet and Luke Punzet and Peter constructed and tested "U" shaped panels. The testing was a to determine the relative strength of cob and bamboo reinforced cob. A direct comparison with Dominic Dowling's PhD research project into improving earthquake resistance of existing mudbrick walls. The "U" shaped test panels were subjected to a standard list of simulated earthquakes from around the world and proved very difficult to break even when repeated simulations of up to 200% intensity were used. The testing was written into a thesis by the two engineering students.
Peter and the students then constructed a 0.5 scale model of half of the building he built in the Philippines. This was outside the scope of the Capstone project however the testing was vital in determining the safety of the whole system rather than the wall panels themselves. The model included three windows with bamboo ladder lintels, a first floor and attic roof frame.
So testing was able to establish the strength of the whole structure as it was intended to be constructed with minimum length returns at corners and between openings, the slenderness ratio of walls, the connection of the walls to the base and to the floor diaphragm, the impact of the additional weight in the upper floor floor wall and roof assembly on the lower cob walls and of course the effectiveness of the vertical and horizontal bamboo reinforced cob walling system in resisting collapse or structural failure.
The building was subjected to a total of four simulations of the 2001 El Salvador Earthquake measuring 7.8 on the Richter Scale. This earthquake was devastating to mudbrick buildings with significant loss of life and injury and was the inspiration for Dom Dowling's Quakesafe Adobe work.
The shake table was initially set for two simulations. The first was 100% intensity and the next 125% intensity equating to around 8.4. A this point the building was examined. Small hairline cracking was visible on one side only around an opening top and bottom and along the top of the wall where a floor bearer was set into the cob wall. These were marked with chalk. The cracking was in an inplane wall on the side where a hold down assembly had loosened with the testing. The cracking though superficial was unexpected and Peter believes it was a torsional loading in what was a perfectly symetrical building. This unintended torsion was perhaps a useful additional test to the back and forth movement of the shake table.
At this stage the testing was a huge success as the testing hadn't resulted in collapse or significant structural damage that would render the building unsafe for further occupation. In order to establish whether the building would be safe to reoccupy further simulations were required. Two further simulations both at 100% intensity resulted in no further damage. Please follow the links to media releases from UTS.
The real building is now proving itself durable over time being nine years old and enduring the worst flooding in Gingoog's history, a small earthquake and several monsoons. Unfortunately as a desplay house it is often unoccupied and not maintained.