Research Team: Professor Ahmed Elghazouli (Imperial College London, UK), Dr. Christian Málaga-Chuquitaype (Imperial College London, UK), Sebastian Kaminski (Arup, UK), Andrew Lawrence (Arup, UK)

Background

Wattle-and-daub was a popular traditional housing style in many countries around the world, and continues to be used in some developing areas. These buildings use local materials such as timber, cane and bamboo to form a composite wall matrix, which is then plastered in mud to form shear walls. Such houses are inexpensive, sustainable and relatively seismically resistant when well-constructed and free from damage such as decay and insect attack.

However, these constructions require a significant amount of maintenance. Also, wattle-and daub is not a popular housing choice for poor communities striving to achieve a better standard of living, due to their association with low-income groups.

An engineered wattle-and-daub type technology has been developed in collaboration with Arup and the NGO REDES. This construction type builds upon the traditional design but ensures the frame and wall matrix are properly treated against insect attack. The new design incorporates adequate details for the frame and base connections and replaces the mud render with a cement mortar. This technology uses a timber frame clad with local cane.

In order to characterise their seismic response, an experimental investigation has been carried out at Imperial College London into the behaviour of various full-scale wall specimens subjected to cyclic loading.

Fig 1: Testing of a Sustainable Composite Cane and Mortar Panel. Test set-up (left) and damage state of the interior face after testing (right)
Fig 1: Testing of a Sustainable Composite Cane and Mortar Panel. Test set-up (left) and damage state of the interior face after testing (right)

Outcomes

The results of the full-scale testing suggest that wall panels of small diameter cane/bamboo and cement render work compositely to resist in-plane forces. However, the bond between cane and the cement mortar is considerably worse than between reinforcement and mortar. In addition, the cold joint created by rendering from either side separately contributes to create a weak point from which delamination starts. The indicated that the capacity and ductility of the simple low-cost panel developed will be adequate for typical design scenarios.

The tests indicate a range of ultimate strengths that are greater than the design load considered (equivalent to a design earthquake of 0.4g, conservatively assuming no reduction for ductility). At ultimate loads, following failure of the window lintel (acting as coupling beam), the final failure mechanism of the wall was found to involve cracking and delamination of the mortar, starting from the base of the wall where the loads and deformations are greatest, and then propagating upwards with increasing levels of deformation. The amount of spalling can be controlled by the incorporation of a galvanized wire (chicken) mesh.

References

  • Elghazouli AY, Malaga-Chuquitaype C, Lawrence A, Kaminski S 2013, Seismic testing of sustainable composite cane and mortar walls for low-cost housing in developing countries, Institution of Civil Engineers Research & Development Enabling Fund, Project Report, London, UK
  • Malaga-Chuquitaype C, Elghazouli AY 2014, Structural response of low-cots timber frames with caña brava and mortar to earthquake loading, World Conference on Timber Engineering, Quebec, Canada