Measuring and testing – Testing by impact or shock
Patent
1991-11-04
1993-09-28
Razavi, Michael T.
Measuring and testing
Testing by impact or shock
173112, 173202, G01N 334
Patent
active
052478351
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to apparatus and methods for the evaluation of the integrity of building structures and the like, particularly foundation piles for buildings and structures.
BACKGROUND ART
It is known to apply a mechanical shock to a pile, detect the resulting vibrations of the pile, and analyse them to provide data about the pile. Such methods are known variously as `acoustic`, `sonic`, or `transient dynamic` pile survey. Essentially, the method measures the pile-head's vertical motions in response to a mechanical shock. The shock may be generated by a manually-delivered blow downwards on the pile-head, sometimes via a `load cell` which measures the force of the initial shock, and the subsequent vertical motions of the pile-head, or it may be that the concrete is struck directly and the resulting motions are registered by a velocity or acceleration transducer firmly attached to the concrete nearby the shock position.
The shock causes the concrete to be momentarily compressed, and vertical motions of waveform approximating a decaying sinusoid follow the blow, as measured at the pile-head. In descending the column of the pile, reflection of proportions of the shock wave occur wherever the column varies in cross-sectional area, or in density. On returning to the pile-head such reflections `interfere` with the decaying sinusoid motions there, and interpretation of this resultant complex waveform enables predictions as to the existence of defects in the pile column, and confirmation or otherwise that it is of the correct length. The technique is now well-established in the Construction Industry.
There are three essential conditions for the acquisition of the pile shock vibration data:
1. the vibration transducer must be held in firm contact with the concrete of the pile-head
2. a shock (or `impulse`) must occur
3. a record of the vertical vibration motions of the transducer (and thus the pile-head) must be made
In addition, a means should exist for recording the identity (its site number) of the pile under test.
In many site circumstances, access to the piles may not be straightforward. They may be relatively distant from a position to which a vehicle can be conveniently brought, or the pile-heads may be covered in mud, water or other site debris, and site plant and other obstacles may be inimical to the presence of the recording apparatus and the normal preparations necessary for the tests to proceed.
Existing methods are slow in execution, and may be difficult or impossible to carry out in the face of such usual construction site obstacles as mud, flooding, deep trenching, shuttering, site traffic and so on.
DISCLOSURE OF THE INVENTION
It is an objection of this invention to provide an apparatus that can acquire the necessary information to enable an evaluation of piles' soundness and fitness for their purpose in as short a time as possible and with the minimum possible disruption of the normal site activities, and with minimum hazard to the pile surveyor and other site personnel.
According to the present invention there is provided apparatus for use in testing structures, comprising a self-contained unit comprising shock means for delivering a mechanical shock of predetermined magnitude to a structure; transducer means for sensing vibrations of a structure caused by said shock and producing a corresponding electrical signal; and memory means coupled to said transducer means for storing electrical signals from it;
said shock means comprising potential energy storage means adapted to be gradually charged and suddenly discharged to deliver said mechanical shock; wherein the apparatus includes a probe arranged to transmit said shock from said shock means to a structure, and to transmit said vibrations to said transducer means; and the probe is arranged to effect said gradual charging by a force acting on the probe when the probe is urged against the structure to be tested.
Suitably the shock means includes a mass and means whereby it is guided to strike, with constant force, a rigi
REFERENCES:
patent: 1572046 (1926-02-01), Seiler
patent: 2455270 (1948-11-01), Ravella
patent: 3268013 (1966-08-01), Sussman
patent: 3888108 (1975-06-01), Brands
patent: 4359890 (1982-11-01), Coelus
patent: 4682490 (1987-07-01), Adelman et al.
patent: 4967587 (1990-11-01), Sirica
Soviet Journal of Nondestructive Testing, vol. 23, No. 2, Feb. 1987, Plenum Publishing Corp., New York, US.
Patent Abstracts of Japan, vol. 13, No. 104.
Journal of Physics E: Scientific Instruments, vol. 17, 1984.
May Timothy J.
Razavi Michael T.
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