Rigid Foundations

Modern houses in Christchurch are built on concrete slab called a “floating foundation”. This slab acts a floor and supports the walls and roof. The timber framing on most houses has coped with the earthquake well. The big problem is that the concrete slabs of many larger houses have broken in two and drifted apart, sometimes leaving two or three inch gap. This is almost impossible to repair.

Most of the experts are saying that the problem is with the land on which the houses are built. I am wondering if there is a problem is the basic design.

The design of high-rise building has changed significantly in recent years. Older buildings with rigid structures do not cope well with earthquakes. The new approach is building structures that are flexible. A building that can move and flex when an earthquake hits does not collapse. This approach has worked really well with high-rise buildings.

Despite this knowledge, we are persisting in building our houses on rigid foundations. The timber framing flexes when an earthquake hits and does not fall. Even brick walls seem to flex a bit. Unfortunately, the rigid foundation does not flex, so it breaks in half under the stress of an earthquake. The larger the house, the greater problem seems to be.

The best solution may be to design concrete foundations that are less rigid. Maybe the concrete foundation for our houses should be built in smaller sections, with flexible joints between the sections that would not break under the stress of the earthquake.

I wonder if any of the experts are thinking about this solution.