Pushed to pieces

A full-scale model of a brick house was pushed to pieces in the Stevin laboratory last month. It was the interim climax of a research program into the vulnerability of brick houses to earthquakes.

“We’ve worked up from small tests on the strength of mortar and bricks, via the testing of complete walls to the ultimate test of a full-scale house”, said Dr. Roel Schipper, lecturer and researcher at the department of structural engineering of the Faculty Civil Engineering and Geosciences. Professor Jan Rots heads the research program, which is financed by the Dutch gas company NAM.

The Stevin lab houses half a dozen brick walls, framed by steel beams. The large cracks traversing the walls are the result of various stress and load tests that they were subjected to. The crack patterns vary, but a large X-shaped pattern forms a recurring feature.

Recent earthquakes in the Groningen area due to gas extraction and increasing damages to houses have motivated the research program. Schipper said the research aims to establish the strength of mortared brick walls and houses to validate simulation programs. Ultimately, if a computer model adequately describes the stress and damage that occur to houses, it may also be used to evaluate various forms of reinforcing measures.

A full-size 2-floor house was built in the Stevin laboratory. Then, before the test, it was fully wired up with over 200 mechanical sensors that measured deformations, 20 vibration sensors and seven cameras. During the test that took four days, the foundation of the building was fixed to the floor while the top was pushed and pulled horizontally with a maximum amplitude of 8.5 centimetres in both directions.

After the test, some walls bulged outwards dangerously far. Large cracks, wide enough to look through, had formed, and only steel frames kept the crumbled layers of bricks together. The slow motion test seems to have been as devastating as a fast earthquake. A similar house has been subjected to a shaking table in a laboratory in Italy. The results of the real-time and slow-motion earthquake test will be compared once the data have been analysed.

The advantage of slow testing, said Schipper, is the gradual build-up of damages. “You see a crack occurring in a wall, and you know that crack will influence the structural behaviour. By going step by step, we can better match the lab test with computer models”, said Schipper.

Wilco van der Mersch MSc simulated the push-over test of a similar structure. His graduation research (June 2015) focused on a computer model that calculates stresses in masonry structures under a horizontal load.

The test team will shortly start analysing the data of the full-scale laboratory test. In about a month time, Schipper expects to be able to compare the test results with the numeric predictions that were made by various teams before the test.

Editor Redactie

Do you have a question or comment about this article?

Comments are closed.