Earthquake construction

Earthquake construction is a branch of architectural engineering concerned with making sure structures withstand as severe an earthquake shock as possible given the materials available.

When the structure in question is a human habitation, the questions of surviving earthquake damage become much more serious. Examples of inhabited structures collapsing during earthquakes abound and are sadly all too frequent. Areas of the world frequently hit by fatal earthquake damage include Japan, Turkey, Algeria, and countless other regions on or near tectonic plate boundaries.

Earlier in mankind's history (during the Neolithic, for instance), mankind lived in tents, which can withstand earthquakes quite well. We moved on to more comfortable structures of timber, mud brick, limestone, wattle and daub, and even just stacked rubble.

Some of these materials can be used form solid, earthquake resistant structures. The important part is to use them wisely and with an understanding of how earthquakes really apply stresses to structures in practice. A structure might have all the appearances of stability, yet offer nothing but danger when an earthquake strikes. The crucial fact is that for safety, earthquake resistant construction techniques are as important as using the correct materials.

The specific mode of failure in an earthquake for most structures is the lateral (sideways) shaking. It frequently collapses walls, or moves them enough that the roof displaces and falls in. Both of these effects, obviously, can be deadly to any occupants.

Development of Earthquake Construction Techniques

People living in frequently shaken areas like Japan started early in developing earthquake resistant buildings based scientific study. Other countries likewise have and continue to study intensely how to make their citizens safer by understanding the problems posed by earthquakes more accurately.

Until the last 75 years or so, the only way to run "frequent tests" was to build on a fault and hope. Even then, earthquakes may only happen at any given spot every couple of hundred years, and construction techniques may not therefore take account of earthquake concerns. Modern shake tables have helped this; large motors and computer control systems try to precisely simulate earthquake movements.

Modern materials like concrete and reinforced concrete can help, but they also must withstand the same lateral (sideways) forces.

Good earthquake construction pays careful heed to lateral forces. Proper concrete construction involves significant use steel reinforcing bar (rebar). All the joints (where beams meet the columns), are carefully tied in with rebar. The concrete is of very high quality, and high strength. Brick infill is avoided for the walls.

Most countries have a building code that specifies lateral strength. These codes are reliant on strict enforcement however.

Modern Techniques

Modern construction techniques for earthquake zones involved designing structures that fail in predictable ways at predictable energy levels based on quantified earthquake severerities. Many historic buildings have been subjected to a seismic retrofit.

In the Los Angeles, California area, it is legal to build an apartment building near the San Andreas Fault with a setback limit of 50 feet. The apartments are typically designed to withstand an earthquake of 7.8 on the Richter Scale and fail in predictable ways at that level. The reasoning is that an earthquake above 7.8 will bring down almost any structure and it is very difficult to design a reasonably priced structure that will withstand anything above 7.8 quakes.

In residential structures, buildings are designed to have the roof fall in right in the middle of a room, but staying up near the walls. People are always urged to take refuge in doorways and away from the middle of the room, and are therefore safe in these buildings.