Patent Grant
7640817
This application is a Section 371 filing of International Application No. PCT/FR2005/050859 filed on Oct. 17, 2005 and published, in French, as International Publication No. WO2006/042996 on Apr. 27, 2006, which claims priority of French Application No. 0452375 filed on Oct. 20, 2004, which applications are hereby incorporated by reference herein, in their entirety.
The present invention relates to a method for determining the physical and sanitary state and establishing a diagnosis of a wooden support such as a wooden telephone pole or electricity pole or any other wood-based structure with a round or other cross-section.
Millions of wooden utility poles are in use and are periodically inspected in order to ensure maintenance of such lines. Despite chemical pre-treatment, these wooden poles gradually deteriorate due to atmospheric action and fungal attack. One of the main problems encountered with such wooden supports is inspecting them periodically in order to check their condition in order to decide whether they are suitable for use, require maintenance or need replacing.
Document EP-634.655 discloses a device making it possible to inspect the physical state of a wooden support simply, effectively and quickly. This device makes it possible to measure hardness and hygrometricity simultaneously.
However, this device does not take into account other important parameters such as the type of timber or its treatment which may cause changes and variations in the measured hardness and hygrometricity. In addition, using the two measured variables, the interpretation of values is complex and can even result in erroneous results.
The main problem which the invention aims to solve is to develop a simple, fast method for determining the state of a wooden support. The second problem is to devise a method that makes it possible to include new parameters specific to the support in order to improve the reliability of the diagnostic results obtained. The third problem is to implement a method for diagnosing the state of a wooden support on the basis of two measurable parameters—the hardness and the hygrometricity of the wooden support.
As is known, a method for determining the state of preservation of a wooden support and establishing a diagnosis in order to find out whether the wooden support is in a state which is suitable for use, in a state requiring a maintenance operation or in a state requiring its elimination, consisting of measuring:
According to a first aspect of the invention, the method is characterised in that it also comprises the following steps:
where α, β, and ε are calibration coefficients that depend on the timber species and the treatment previously applied to the wooden support; and
In other words, by including new parameters (timber type and the treatment applied to the timber), the calculation performed by determining the residual stress will improve the diagnoses for inspected timbers. Moreover, correlating the strength of the timber with the moisture content of the timber in order to calculate the residual stress will facilitate and speed up determination of the state of the timber and produce an accurate diagnostic result.
A diagnosis of this type therefore ensures the reliability of the wooden supports as well as improved maintenance management. All the actual data is measured and stored. Comparison is performed by a programmable machine which converts the signals into displays for the user by using LEDs to indicate various states, for instance “very good condition”, “good condition”, “weakening or weakened” and “severely weakened and hazardous”.
In a first embodiment, if the treatment previously applied to the wooden support is based on metallic salts, α>0, β≧0 and ε<0 can be used as calibration coefficients. In a second embodiment, if the treatment previously applied to the wooden support is based on phenolic compounds, α>0, β>0 and ε>0 can be used as calibration coefficients.
In an especially advantageous manner, the method may also comprise the following steps:
where ƒ is a function that associates the stress of the pole to its natural frequency.
The method may preferably also comprise the following steps:
where σs is the calculated safety residual stress, σz is the stress associated with the pole's natural frequency and ζ is a calibration coefficient that depends on the species of the timber and the treatment previously applied to the wooden support;
The invention and its various advantages and different characteristics will be more readily understandable from the following description given merely by way of example.
The species used for wooden supports are as follows: pine, fir, larch, spruce, cedar, chestnut and eucalyptus in southern hemisphere regions.
The most widely used treatments for wooden supports are:
The device described in Document EP-634.655 measures the force (F) expressed in daN, the humidity (H) expressed in % after the spikes of the device have penetrated into the timber by 40 mm for poles having a diameter of 10 cm to 35 cm or more.
The safety residual stress resulting from F and H, expressed in N/mm2, is calculated using the formula: σ=α.F−β.H+ε
In the following Tables, in terms of safety, “Good σ” is equivalent to a “Very good condition” diagnosis, “Average σ” is equivalent to a “Good condition” diagnosis, “Mediocre σ” is equivalent to a “Weakening and weakened” diagnosis and “Poor σ” is equivalent to a “Severely weakened and hazardous” diagnosis.
In the following Tables, in terms of maintenance operations, “Good σ” is equivalent to a “Very good condition” diagnosis, “Average σ” is equivalent to a “Needs monitoring” diagnosis, “Mediocre σ” is equivalent to a “Needs replacing” diagnosis and “Poor σ” is equivalent to a “Severely weakened and hazardous” diagnosis.
In order to supplement these measurements, a third physical parameter may be included in order to take into account damage below ground level—natural frequency. This frequency is a function of the ratio: σz=ƒ(D3/L3), where D is the diameter of the pole at ground level and L is its length.
The natural frequency falls very quickly if the buried length has deteriorated.
In fact, a utility pole that has deteriorated significantly 20 cm or 30 cm below ground level cannot be detected by the test nor by any other non-destructive test method. By exciting the pole manually, for instance by banging it with the hand or by striking it with a hammer, one can cause it to resonate and one can use a chronometer or even an accelerometer or equivalent system to measure its natural frequency.
A natural-frequency test is therefore added to the basic model if damage to the foundation is suspected.
Results
For France, the calibration coefficient values α, β, and ε are as follows:
As far as safety is concerned, calculating the resulting safety residual stress values (σ) gives the following results:
As far as maintenance operations are concerned, calculating the average maintenance safety residual stress values (σ) gives the following results:
For Germany, the calibration coefficient values α, β, and ε are as follows:
For the United Kingdom, the calibration coefficient values α, β, and ε are as follows:
For Switzerland, the calibration coefficient values α, β, and ε are as follows:
For Canada, the calibration coefficient values α, β, and ε are as follows:
For Austria, using Austrian Standard ÖNORM E4200 (Overhead Power Lines; Wooden Poles), the values of calibration coefficients α, β, and ε are as follows for larch:
As far as safety is concerned, calculating the resulting safety residual stress values (σ) gives the following results:
As far as maintenance operations are concerned, calculating the average maintenance safety residual stress values (σ) gives the following results:
The present invention is not confined to the embodiments described and illustrated. Numerous modifications can be made to this method after recalibration for new timber species and new timber treatments without thereby extending beyond the defined framework and scope of the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 04 52375 | Oct 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2005/050859 | 10/17/2005 | WO | 00 | 4/17/2007 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2006/042996 | 4/27/2006 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4926691 | Franklin | May 1990 | A |
| 5094890 | Smith et al. | Mar 1992 | A |
| 5731096 | Besner et al. | Mar 1998 | A |
| 6753016 | Ghosh | Jun 2004 | B2 |
| 7008997 | Kovacs | Mar 2006 | B2 |
| Number | Date | Country |
|---|---|---|
| 0 634 655 | Jan 1995 | EP |
| 2 758 883 | Jul 1998 | FR |
| 2 816 710 | May 2002 | FR |
| Number | Date | Country | |
|---|---|---|---|
| 20080028836 A1 | Feb 2008 | US |
