Earthquake testing of earth buildings

I have been involved in undergraduate projects at Bristol University, using the shaking table at the BLADE facility. Many thanks to Joe Harwick and Jon Little for carrying out the work, and to Dr Adam Crewe and Dr James Norman for helping to supervise their work.

Many thanks to Ibstock for providing the bricks for this work, and to the Institution of Structural Engineers for providing a research grant to allow this work to take place.

This page is provided to allow an appreciation of the work carried out, if you would like any futher information, please contact me.

The principle objective of this project is to determine whether there are any similarities or differences between the way in which mud bricks and traditional masonry behave under seismic loading.

Current guidelines for the seismic design of unreinforced earth buildings are based on very simple rules and a small amount of dubious testing. Nevertheless, such guidelines are routinely used by many international NGOs. There is weath of work carried out in the Spanish speaking world on the aseismic reinforcement of earth buildings, but to date there appears to be little work carried out into the behaviour of unprotected earth buildings. This work aimed to review the behaviour of fired and unfired clay bricks to compare their behaviour.

Unfired extruded brick

One quarter scale unfired were supplied by Ibstock. Clay bricks are extruded, and usually fired. However Ibstock were able to divert the bricks before the kiln and provided us with unfired bricks. These bricks were built into walls using a mortar made from the same material as the bricks. Four walls were constructed, and tested in 30 second shakes of increasing magnitude to failure.

Unfired extruded clay brick wall. 30 second shake, lowest magnitude

Unfired clay brick wall, 30 second shake, highest magnitude

Fired extruded brick

Ibstock supplied us with fired versions of the extruded unfired clay bricks used in the tests described above. These bricks were built into identical walls using a similar mortar to that was used in the unfired clay brick wall.

Fired clay brick wall, 10 second shake, lowest magnitude

Fired clay brick wall, 10 second shake, highest magnitude

Handmade

In addition to the extruded bricks, one wall was constructed using handmade bricks. These bricks were formed in timber moulds then left to dry prior to construction.

Handmade adobe bricks – 30 second shake

Conclusions

The testing allowed comparison of the natural frequency, force-displacement behaviour and crack propogation arching action of fired and unfired clay brick walls.

There were few similarities observed between the mud brick and fired masonry walls. The most notable similarity was the initial trend in natural frequency observed in all of the specimens – each experienced a significant decrease in natural frequency during the initial shakes. Following this unfired and fired walls natural frequencies decreased with different until a final value was reached

The yield mechanism and final collapse of the fired and unfired walls differed significantly The fired masonry walls were seen to behave in a more brittle manner than unfired walls in all the experiments. This is likley to have been caused by the weak fired brick-mortar bond, meaning the unfired brick walls behaved in a more homogenous manner, resulting in different collapse mechanisms.

It is hoped that this work will lead to further investigation in this area of research, if you are interested in any of this work please contact me.

Other seismic testing of earth buildings

QuakeSafe Adobe

Dominic Dowling of Sydney University of Technology conducted some tests of QuakeSafe Adobe. Dom has finished his PhD work now, and has set up the Quakesafe Adobe website

Getty Seismic Adobe Project

Leroy Tolles conducted work at Stanford University, resulting in the reports published by the Getty on the Getty Sesimic Adobe Project