Data processing: measuring – calibrating – or testing – Testing system – Of mechanical system
Reexamination Certificate
1998-06-24
2001-07-17
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Of mechanical system
C702S033000, C073S662000
Reexamination Certificate
active
06263293
ABSTRACT:
BACKGROUND OF THE INVENTION
The study of damage to buildings during earthquakes has resulted in buildings which can better withstand damage from an earthquake. Each time an earthquake occurs, such a Loma Prieta in 1989, Northridge in 1994, Koba in 1995 and others, the damage is assessed. The cause of that damage is postulated, and ways to avoid that damage in the future may be also determined. Building codes can be modified to reflect new understandings of the mechanisms of failure.
For example, the recent earthquakes have caused concrete highway overpasses to fail. The Northridge earthquake caused cracking of steel columns in high rise buildings. Loma Prieta and Koba caused liquefaction of soil which itself caused damage. All of these damage mechanisms can be reflected in new building designs and can be used to try to mitigate the damage.
It is simply not acceptable to wait until the next earthquake to get more conceivably life saving information. Hence, the science of earthquake simulation has evolved. This includes the use of computer code to model structures and simulate the response to certain input motions. The large number of different possibilities, however, has made it difficult to model this satisfactorily.
A more real-time system forms a physical model of a structure or a portion of a structure. That structure is built on a shaking table. The shaking table is moved to simulate the earthquake ground motion. The system described in the preferred embodiment defines a new kind of structure shaking system which addresses certain drawbacks and limitations in the current system.
Current shaking tables range in size, with a large table being fifty feet or more. A large machine can be used for testing a small full size building, or a full scale component such as joint. All of the machines have in common a rigid table supported by a very large electro-hydraulic cylinder. The hydraulic cylinder is driven by a computer system to form the motion simulating an earthquake. The dynamic forces move the table as a whole, using thousands of tons of force as necessary to simulate the earthquake.
The nature of the ground motion in an earthquake can complicate this system. The ground moves more or less randomly in the horizontal plane, the x and y directions, as well as in the plane orthogonal to the horizontal plane, the z direction. Rotational movements are also developed in each of the x, y and z directions. This results in a total of six degrees of freedom.
Different simulating systems allow different numbers of degrees of freedom. Each additional degree of freedom greatly increases the complexity of construction and hence the cost. Moreover, each actuator system must inevitably react against the stationary object. This often provides forming large and heavy reaction masses in the nearby ground to prevent the vibration from being transmitted to nearby buildings.
SUMMARY
The system described in the preferred embodiment teaches a new design for a shaking system. This shaking system uses a number of separated shaking units are used to form a single large apparatus. Each shaking unit preferably includes three degrees of freedom. Each shaking unit is placed under a place of support of a structure to be tested. For a building structure, for example, the base of each column of the building is supported on a shaking unit. That shaking unit then moves the column base dynamically and laterally in multiple component directions.
The system as disclosed includes a number of advantages that are not taught or suggested by the prior art. Specifically, a prior art shake table uses a rigid system which vibrates all of the footings using the same amount of input motion. In contrast, the system of the preferred embodiment allows separately changing the components of motion on each column base. This allows each unit to have only three degrees of freedom. However, since all the units can be moved separately, more complicated motions, each of which could be considered as a separate degree of freedom, are possible.
For example, the vertical component of motion on each column base could be applied slightly out of phase in order to impart rocking motion about different axes. This provides more ability to simulate complicated motions, such as would occur during an earthquake. The inventor believes this to represent a better and more accurate response of the earth, since the earth's crust will not, in general, move like a flat rocking table.
REFERENCES:
patent: 4181029 (1980-01-01), Talbott, Jr.
patent: 4602555 (1986-07-01), Bushey
patent: 5009412 (1991-04-01), Roodenburg et al.
patent: 5737239 (1998-04-01), Horiuchi et al.
patent: 5969256 (1999-10-01), Hobbs
Barbee Manuel L.
California Institute of Technology
Fish & Richardson PC
Shah Kamini
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