Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Reexamination Certificate
1999-09-09
2001-12-25
Noori, Max (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
C073S849000
Reexamination Certificate
active
06332365
ABSTRACT:
DESCRIPTION
The present invention relates to a method of detecting flexion in a structure.
The present invention also relates to flexion detection devices.
The present invention furthermore relates to a structure equipped with such a device, for example a geotechnical, mechanical, building or civil engineering structure etc.
From EP-A-0 264 622 it is known to measure a variation in length along a measuring line able to have a length of several meters, decameters or hectometers by means of an optical wave guide which is associated with the structure all along the measuring line. As is well-known, the tensile forces applied on the optical wave guide have the effect of dampening the light pulses sent through the guide in a manner which varies according to the intensity of these forces. By measuring the attenuation of the light pulses, a measurement of the elongation of the wave guide with respect to its nominal length is obtained indirectly from a characteristic curve. EP-A-0 264 622 also reveals the pre-stressing the wave guide in tension in order to be able to also detect a compression of the structure along the line of detection, because of the reduction in the elongation of the guide with respect to its pre-elongated state when the structure is in the rest state. It is also known from EP-A-0 264 622 how to arrange the measuring line along a path which is particularly likely to exhibit a significant variation in length in a predetermined direction under the effect of the load applied to the structure. The variations in length of the measuring line will be interpreted in terms of flexion of the structure or of the part of the structure in question.
This known method does however have various limitations.
Firstly, errors are possible in certain cases, in particular when the structure does not deform in the predicted manner. In such a case the interpretation of the measured elongation will be inexact. Secondly, it is not always possible to place the measuring line in the position which would be the most favourable for the application of the known detection method.
The purpose of the present invention is to overcome these disadvantages by proposing a detection method and devices which make it possible to determine the orientation and amplitude of flexion with remarkable reliability even on structures of which certain parts at least are very difficultly accessible, like structures that are partially or totally buried in the ground, and/or exposed to road or rail traffic etc.
An idea which is at the basis of the invention consists in associating with the structure a model for which it is easy to predict the deformation modes and the effects of these deformations on a measurement line. The deformation of the model is evaluated and conclusions are drawn therefrom regarding the deformation of the structure or the part of the structure in question.
Thus, according to a first aspect of the invention, the method for detecting flexion in a structure is characterised in that there is coupled in flexion with the structure a long-shaped model having in cross-section at least one dimension which is sufficiently large that under the effect of flexion, the elongations are sufficiently different at the two ends of this dimension, at least one detection line having a length at least equal to about two meters being suitably positioned with respect to the cross-section of the model and/or with respect to the positioning of the model in the structure so that the variations in length detected by means of the measuring line can be interpreted in terms of direction and amplitude of the flexion of the model.
The measuring line gives results which can be interpreted for the deformation of the model and these results can, in their turn, be interpreted in order to know the deformation of the structure itself, or for the section of structure concerned itself.
Two main lines of development of the idea which is at the basis of the invention and more particularly of the above method are envisaged.
According to a first line, the model comprises a matrix which is heterogeneous with respect to the structure and it is stressed in flexion with the structure, and the detection line, judiciously placed in the matrix, undergoes variations of length which reveal the deformation in flexion of the matrix.
For implementing this first line of development, it is possible to place the matrix in a groove in material bound to the structure, for example a groove formed in a face of the structure or a grove produced by means of a gutter or casing fixed to the structure. The matrix becomes deformed in flexion with the structure, and there is at least one detection line which is associated with the matrix and makes it possible to measure its deformation in flexion, and consequently that of the structure.
According to another line of development of the idea which is at the basis of the invention, the model essentially comprises two detection lines which are associated with the deformation in flexion of the structure and which are sufficiently separated from one another for this flexion to cause them to undergo different variations in elongation. By comparatively analysing the variations in length undergone by the two detection lines, indications of the flexion of the structure can be derived therefrom.
It is even possible to provide at least a third detection line spaced from the other two and not coplanar with them in order to obtain indications of the flexion in two planes forming an angle between them, in particular two perpendicular planes.
The two lines of development are compatible: it is possible to provide two lines of detection separated from one another or even three line of detection which are not coplanar in the matrix according to the first line of development.
Furthermore, the number of detection lines is not limited to three, at least one fourth line can be provided, for example for corroboration purposes.
The detection lines can in practice be materialised by pre-elongated optical wave guides cords. This technology is preferred because it provides very accurate measurements of the integral of the local deformations, without drift. But many other technologies could be envisaged (measurement of mechanical tension or of electrical resistivity of a wire, etc.) provided that they allow “long-based” detection.
The invention relates in fact to the field of measurement known as “long-based”. This expression indicates that the deformation of a structure or of a part of structure is perceived on a macroscopic scale over a distance which is of the order of one meter, one decameter or one hectometer, that is to say not locally or at a particular place such as can be achieved by strain gauges or inclinometers, nor simply between two separated points, but by the cumulative picking up of local phenomena over a section considered to be critical. In this way there is obtained an average of the deformations which is representative of the overall deformation at the place considered to be critical.
According to a second aspect of the invention, the flexion detector device is characterised in that it comprises at least one line for detecting length variations, having a length of at least about two meters, closely bonded with a matrix intended to be coupled in flexion with the structure whose flexion is to be determined, the detection line being off-centred with respect to the cross-section of the matrix.
According to a third aspect of the invention, the flexion detector device is characterised in that it comprises at least two length variation detection lines, having a length of at least about two meters, and disposed parallel with and closely bonded to a structure whose flexion is to be detected, and means of comparatively analysing the length variations undergone by the two detection lines.
According to a fourth aspect of the invention, the latter also relates to a structure such as a geotechnical, civil engineering, building, mechanical and similar structure equipped with a device according to the second or third aspect.
Other featur
Noori Max
Young & Thompson
LandOfFree
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