Earthquake Resistant Buildings

Earthquake-resistant structures are structures designed to withstand earthquakes. While no structure can be entirely immune to damage from earthquakes, the goal of earthquake-resistant construction is to erect structures that fare better during seismic activity than their conventional counterparts.

Currently, there are several design philosophies in earthquake engineering, making use of experimental results, computer simulations and observations from past earthquakes to offer the required performance for the seismic threat at the site of interest. These range from appropriately sizing the structure to be strong and ductile enough to survive the shaking with an acceptable damage, to equipping it with base isolation or using structural vibration control technologies to minimize any forces and deformations. While the former is the method typically applied in most earthquake-resistant structures, important facilities, landmarks and cultural heritage buildings use the more advanced (and expensive) techniques of isolation or control to survive strong shaking with minimal damage. Examples of such applications are the Cathedral of Our Lady of the Angels and the Acropolis Museum.

Although earthquakes can produce more than one kind of shock wave (some travel vertically, some horizontally, and others in circular patterns), it is horizontal acceleration (the side-to-side movement of the earth) that causes the greatest amount of severe damage. The concrete foundation of a building tends to move with these vibrations during a tremor, and if the above-ground portion of the structure is not firmly secured to the base, the framework can break away . . . resulting, of course, in partial — or total — collapse.

According to the Uniform Building Code (UBC), which has been adopted widely by inspection authorities throughout the world as a standard for all new construction, wood-frame structures with concrete or reinforced masonry foundations must be affixed to their bases by a specific method:

 First, anchor bolts of at least 1/2" in diameter (most builders use hardware that's 5/8" in diameter by 10" long) are embedded vertically 7" or more into the foundation — all along the perimeter, at intervals of no more than 6' — with a portion of each bolt projecting above the mortar or concrete. Then the building's sill plates (the bottom most, horizontal wooden members of a frame structure) are drilled so they'll slip down over the protruding anchor bolts, and once the plates are set in place — flush against the foundation — nuts are tightened down onto the wood.

This method of anchoring sill plates does keep the boards attached to the foundation during an earthquake, but it fails to help the structure as a whole absorb and withstand the forces of seismic shock. However, this technique — a simple variation of the standard procedure — allows a building to move with its foundation during the course of a quake, and also provides a bit of flexibility and cushioning between the base and the sill . . . thus offsetting at least some of an upheaval's shearing effect.

Low-Cost, Low-Tech, earthquake resistant Building Technique

The only additional building materials required for this anti-quake construction technique are
[1] Oversize washers (in other words, washers with center holes matching the diameter of your anchor bolts and relatively large outside diameters such as 1 1/4" or 1 1/2") and
[2] Self-sealing weather stripping at least 1 1/2" wide. You'll need as many washers as there are anchor bolts in the foundation, and an amount of weather stripping equal to the total length of the building's sill plates.
Now, when drilling holes in your sill plates to enable you to slip the boards down onto the anchor bolts, bore the cavities 1/8" larger in diameter than the bolts themselves. (Thus, if you're using 5/8" anchors, you'll drill 3/4" holes.) But before actually installing the sills, place the weather stripping directly on top of the foundation, between the anchor bolts, where the boards will lie. Then carefully position the pre drilled sills over the anchor bolts and press the plates down firmly onto the cushioning material.

Finally, drop an oversize washer over each anchor bolt and tighten a nut firmly down onto the disk. The washer should actually bite into — in other words, make a depression in — the wooden sill. In some regions, the local building codes may require placement of a termite barrier — a strip of aluminium or galvanized steel — between the foundation and sill. If that's the case in your locality and you're following my technique, simply install the barrier first, place the weather stripping on top of the metal, and then fasten down the plates.
Drilling the sill-plate hole 1/8" larger than the anchor bolt's diameter provides a minute amount of side-to-side "give" that reduces the brittleness of the conventional sill-to-foundation attachment and thus helps to prevent shearing. In addition, the weather stripping acts as a cushion between the base and framework, making the whole assembly somewhat more flexible and able to absorb ground shocks (by the way, the self-sealing material also provides a watertight seat between the foundation and the sill).

Of course, much of the beauty of this method is its extraordinarily low cost. When quake-proofing a typical 24' X 40' building, for example, you might use as many as 40 anchor bolts, and the total length of the sill plates would be 128'. In my part of the country, 5/8" X 1 1/2" washers cost 30 cents apiece, and 1 1/2" weather-stripping runs 20 cents a foot. You'd pay $12.00 for the 40 washers, therefore, and $25.60 for the cushioning . . . for a total cost of $37.60. That's a mighty small investment compared with the repair (or rebuilding) expenses that it could help you avoid!
Building inspectors have approved this technique as an effective way to minimize the potentially destructive forces of seismic shock (be sure to get a similar OK from your local officials, though, before you incorporate my method into your own construction). I certainly don't claim, however, that it's a guarantee against damage from an earthquake. In fact, there's probably no real protection from the forces of a truly substantial quake (the energy released by the 1964 Alaska earthquake, for instance, was estimated to equal the power of 12,000 Hiroshima-type nuclear bombs!). But at least there's something you can do — for relatively little money — to give your home and outbuildings a better chance of surviving tremors or a quake of minor, or perhaps even moderate, magnitude. And that extra measure of protection, I think, is well worth the little additional expense and effort!

no matter how hard it may be but we shall rise again.