Seismic Isolation to Protect Buildings

Abstract

If a concrete slab is poured with a very smooth upper surface and coated with a grease of low viscosity, it can serve as the base of a thick reinforced concrete slab, which if made an integral part of a building built above it, will protect that building against sideways forces that are the main source of destruction during an earthquake.

Description

TECHNICAL FIELD

The present application relates generally to construction practice for buildings located in seismically active areas.

BACKGROUND AND SUMMARY

Seismic construction is an important design consideration for the construction of buildings in areas of the world that have a medium to high risk of earthquakes. Most of the damage that results during the brief earthquake happens from the side-to-side motion or the motion in the plane perpendicular to the gravity field lines. This motion or sway is especially detrimental if a resonance occurs with the building structure and if the building in constructed of ceramic materials, as opposed to metal.

Prior art design rely on either: attachment to the bottom slab or foundation, so sideways sway can only be partially prevented; those that are completely isolated, which are generally complicated and expensive; and those that are partially isolated.

Examples of anchoring the bottom slab or foundation, so that sideways sway can only be partially prevented, are: a ball and socket design of WO2001038646 A1; a ball in cone of WO1995022012 A1; a rubber bearing of WO1995014830 A1; a series of plates such as US20040200156 A1, U.S. Pat. No. 5,904,010 A, U.S. Pat. No. 5,797,228 A, U.S. Pat. No. 5,682,712 A, U.S. Pat. No. 5,490,356 A, U.S. Pat. No. 4,933,238 A, JP9302983 A and U.S. Pat. No. 6,180,711 B1; a series of rollers such as US20050150179 A1; complicated devices like devices of U.S. Pat. No. 7,090,207 B2, U.S. Pat. No. 5,215,382 A, and U.S. Pat. No. 5,386,671 A; and pendulum devices like U.S. Pat. No. 6,966,154 B1. Some devices have inherent faults: like JP2000080731 A which permits very little lateral motion and the pin release feature in JP1062310 A, which is not fail safe Examples of completely isolated designs are: WO2008126120 A2, which requires hundreds of steel balls at each station; WO2008098982 A2, which requires many expensive steel and rubber plates at each station; designs which are expensive to construct such as US20070044395 A1 and US20060174555 A1; US20030099413 A1, which is expensive and complicated.

Examples of limited or partially isolated designs are: U.S. Pat. No. 5,862,638 A, which is limited in isolation in lateral direction; JP2001182366 A, which requires very thick, heavy steel members for all but light buildings. The support footings themselves would be vulnerable to earthquake damage in EP698156 B1 and the upper support beam would require a very expensive steel structure.

US20070261323 A1 is only useful for protecting an individual apparatus.

Some only work in one direction, so would only be useful for a structure like a bridge, such as WO2005031088 A2; US20040131287 A1; US20030099413 A1; U.S. Pat. No. 6,971,795 B2; U.S. Pat. No. 4,517,778 A. Unless you were certain which direction the earthquake motion was coming, these designs have limited usefulness for buildings.

Those that depend on rubber such as US20040123530 A1, EP1590579 B1, and U.S. Pat. No. 4,910,930 A are in danger of future deterioration.

JP2003301625 A is only for small light buildings.

U.S. Pat. No. 6,289,640 B1 and U.S. Pat. No. 4,599,834 A work on the principle of sliding surfaces and so have the advantage that they can handle earthquake sway from any direction. Unfortunately, these two designs are elaborate and expensive to construct.

In summary, all previous designs have disadvantages of either high cost, low reliability, or they don't protect the building. The designs with the principle of sliding surfaces have the best merit, but but they are too expensive and the elaborate construction can potentially lead to reliability issues. This invention will avoid these issues.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side section view of the first claim of the invention, for a flat surface interface design.

FIG. 2. is a side section view of the second claim of the invention, for a spherical surface interface design. The section of the spherical surface shows as a circular arc.

DETAILED DESCRIPTION

Refer to FIG. 1 for this description. If a concrete slab 1 is poured, into an excavated foundation hole in the earth 5 (or on the surface if a small building in frost free areas),

with a very smooth upper surface and coated with a grease 3 of low viscosity, it can serve as the base of a thick reinforced concrete slab 2, which if made an integral part of a building 4 built above it, will protect that building 4 against sideways forces that are the main source of destruction during an earthquake. The building 4 is attached at the interface line 6 between the upper slab 2 and the building 4 in FIG. 1, using conventional techniques (e.g. bolts protruding from the upper slab 2 surface (not shown) and then later attached to the lower sill of the walls of the building 4 using nuts, welded reinforcing rods if a concrete building, etc). In this way, the building will ride with the upper slab's 2 motion, without any relative side motion at the interface 6. This will be especially effective, if the upper slab 2 is a large fraction of the total weight of the building 4, especially if the building 4 is tall or high (shown as line breaks in FIG. 1). This should-be less expensive than current isolation methods. Even with the cost of excavating a somewhat deeper and wider foundation and adding the extra base slab 1 and retaining wall 8, this should allow for less reinforcement of the supported building 4 and also allow for taller buildings 4. This is especially so since the upper slab 2 does not have to be smooth on top and can have its weight increased by incorporating boulders, for instance. Furthermore, its efficacy can be further enhanced by sandwiching more than one slab (i.e. multiple layers of slab 1) on top of each other before the final slab 2 that is integral with the building 4 is reached. The most efficacious grease 3 would be silicone grease, because of its inherent slipperiness and its resistance to temperature change. But, almost any lubricant can be used, even layers of slippery plastic sheet. Any material that behaves as a lubricant under the side to side motion of the earthquake.

This method is also practical for retrofitting an existing building built over a basement, since it could be installed a hundred square feet at a time by leaving the reinforcing rods protruded in order to later weld on to the next section. Once the bulk of the building is supported by vertical risers, the basement walls can safely be removed and a trench dug to complete the pour of slab 1 and installation of the retainers 7,8 that extends beyond the basement.

An additional advantage of this method is that inertia can be greatly increased low down in the building 4 at a low cost. Thus sidewise inertial forces would be low down where they would not contribute to toppling tall buildings.

The top slab 2 should have restraint 7 from the sides, such as air filled pneumatic pistons, springs, large rubber bumpers, foam fill, etc. These restraints 7 may be spaced away from the slab 2 as is shown in FIG. 1 with a gap, or they may have a pre-load on them to attempt to keep a centering force on the slab 2 at all times (not shown). The restraints 7 will be either attached at the outside end to slab 1 (e.g. bolted to slab 1—not shown), or a retaining wall portion 8 of slab 1 may be molded in place with forms to restrain the outside end of the restraint parts 7. The retaining wall 8 must extend to the full perimeter of the slab 2 and the restraints 7 should be also arrayed around the full perimeter between the wall 8 and the slab 2.

FIG. 2 shows a modification of the shape of the surfaces of slab 1, grease 3 and slab 2 of FIG. 1. For this variant, the slab 1 concrete is poured and the top surface is smoothed into the shape ODF a shallow spherical surface of concave upwards. This is shown as a shallow curve, but the curve represents a three dimensional spherical smooth surface. This surface can be made in a variety of ways. One way is to position a long center metal bolt in the center of slab 1 and fixture the bolt to a wooden screed shaped or bent into an arc. Then, the surface can be screed into the poured concrete by rotating the screed 360 degrees about the center bolt. When partially set, the screed and bolt would be removed and the spherical surface smoothed.

The rest of the FIG. 2 construction would be the same as shown in FIG. 1, except that the grease 3 and the lower surface of slab 2 will conform to the spherical shape of slab 1.

The net effect of having a spherical shape to the grease 3, is that the side to side forces of an earthquake will cause the building to rise slightly without imparting significant side ways motion. Because of the high moment of inertia of the slab 2 and the building 4, the motion of the building 4 will tend to be a rocking and up & down motion, instead of a side-to-side motion of slab 1 and the earth 5. The springs 7 will tend to keep the rocking about the center of the spherical cavity to a minimum. The height of the center of the spherical cavity would be much higher than the center of inertia of the building 4 and slab 2, so the net effect will be minimal side forces on the walls of the building during an earthquake. As the building 4 moves sidewise it would require energy to move it slightly upward and less energy for the restraints 7 to move it back down slope.

Claims

1. A method of constructing a building having at least two flat masses for the base structure separated by smooth surface(s).

2. The method of claim 1, where the smooth surface, or surfaces, is flat.

3. The method of claim 1, where the smooth surface is slightly concave upward.

4. The method of claim 1, where one or both of the masses are composed of concrete (i.e. cement and aggregate rock of various sizes)

5. The method of claims 1, where a low friction material, is used to separate the masses and reduce friction. Some typical liquids being grease, oil, silicone liquids, fine sand, clay powder coated with silicone, etc.

6. The method of claim 1, where mild restraint from lateral motion is added.

7. The method of claim 6, where the restraint is a perimeter bank of springs (e.g. air springs, coil compression type metal springs, leaf metal springs).

8. The method of claim 7, where the restraints are attached to the lower flat mass at the end of the restraint away from the upper mass.

9. The method of claim 8, where the restraints are attached to the lower mass at a wall.