FLEXIBILITY ASSESSMENT

Abstract

A method to assess the integrity of a structure is provided and comprises the steps of: i) applying a sinusoidally varying force to the structure at a frequency or frequencies below the lowest frequency that could cause resonance in the structure whereby to set up a dynamic response dominated by the stiffness of the structure; and ii) monitoring the dynamic response of the structure. A device to assess the integrity of a structure is also provided.

Claims

1. An integrity assessment method for a surface or structure, comprising the steps of: i) forcing an inertial mass to oscillate thus generating reaction loads to excite a surface or structure under test and so as to apply a sinusoidally varying force to the surface or structure at a fixed frequency that is pre-set to be below an anticipated lowest frequency that could cause resonance in the surface or structure, whereby to set up a dynamic response dominated by the static stiffness of the surface or structure; ii) providing a sensor to measure the excitation force being applied to the surface or structure; iii) providing a separate sensor to measure the response motion of the surface or structure; and iv) determining the ratio of response motion to excitation force at the excitation frequency.

2. A device to assess the static stiffness of a surface or structure, comprising: i) means for applying a sinusoidally varying force to the surface or structure at a fixed frequency that is below the lowest frequency that could cause resonance in the surface or structure whereby to set up a dynamic response dominated by the static stiffness of the surface or structure; and ii) means for monitoring the dynamic response of the surface or structure.

3. A method as claimed in claim 1, comprising a step of determining or estimating the first natural frequency of the floor whereby to determine or estimate the lowest frequency that could cause resonance in the floor.

4. (canceled)

5. (canceled)

6. A method as claimed in claim 1, where the relative contribution from the stiffness of the structure to the response is at least 90%.

7. A method as claimed in claim 1, comprising measuring dynamic force applied to a structure.

8. A method as claimed in claim 1, in which one or more force sensors are provided at an interface with the structure for measuring the force being applied to the structure.

9. A method as claimed in claim 1, in which the acceleration of an inertial mass is measured to allow the force being applied to the surface or structure to be calculated.

10. (canceled)

11. A method as claimed in claim 1, comprising measuring a response sensor to measure the motion of the surface or structure being loaded.

12-17. (canceled)

18. A method as claimed in claim 1, in which the frequency is less than 10 Hz.

19. A method as claimed in claim 1, in which the frequency is approximately 2 Hz.

20. A device as claimed in claim 2 and configured as a building floor integrity assessment device.

21. A method as claimed in claim 1 and configured as a building floor integrity assessment method.

22. Equipment that performs a stiffness assessment on a surface or structure, the equipment comprises a linear motor supported in a support frame, a rigid mass is attached to a carriage of the motor so that any acceleration of the mass will result in reaction loads being applied to the support frame.

23. Equipment as claimed in claim 22, in which a motor controller can accept drive signals that enable specific waveforms of force to be generated.

24. Equipment as claimed in claim 23, in which the motor controller sets the acceleration of the carried mass, and this is directly proportional to the excitation force.

25. Equipment as claimed in claim 22, in which the support frame has three feet.

26. Equipment as claimed in claim 22, in which an accelerometer is fitted to the inertial rigid mass and outputs the acceleration signal from which the force can be calculated.

27. Equipment as claimed in claim 22, comprising a separate accelerometer which is fitted to the surface or structure being tested and gives a response signal.

28. Equipment as claimed in claim 22, in which the FRF, H(ω), is calculated at the excitation frequency by a separate software application and converted to the flexibility value Φ.

29. Equipment as claimed in claim 22 and configured to assess a surface or structure selected from the group: floors of buildings; balustrades; handrails; steps; stairways; bridges; walls; balconies; roofs; towers; monuments; stadiums.

Description

[0116] Embodiments of the present invention are shown, by way of example, with reference to the accompanying drawings, in which:

[0117] FIG. 1 shows a chart of an exemplary dampening factor;

[0118] FIG. 2 shows an exemplary embodiment of the invention;

[0119] FIG. 3 illustrates an exemplary testing structure; and

[0120] FIG. 4 show a chart of an exemplary relationship between load and deflection.

[0121] The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternative forms and should not be construed as limited to the examples set forth herein.

[0122] Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

[0123] Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealised or overly formal sense unless expressly so defined herein.

[0124] In the following description, all orientational terms, such as upper, lower, radially and axially, are used in relation to the drawings and should not be interpreted as limiting on the invention.

[0125] Referring now to FIG. 2 an embodiment of the invention comprises a linear motor (1) supported in a stiff framework (2). A rigid mass (3) is attached to the carriage of the motor (4) so that any acceleration of that mass will result in reaction loads being applied to the support for the frame at the three feet (5). A motor controller (6) can accept drive signals that enable specific waveforms of force to be generated. In this embodiment, sinusoidal forces can be used for the flexibility measurement and typically random forces for determining the natural frequencies. The motor controller sets the acceleration of the carried mass, and this is directly proportional to the excitation force. An accelerometer (7) that is fitted to the inertial rigid mass outputs the acceleration signal from which the force can be calculated. A separate accelerometer (8) is fitted to the structure being tested and gives the response signal. The FRF, H(ω), is calculated at the excitation frequency by a separate software application and converted to the flexibility value Φ.

[0126] By the method outlined above, the deflection at location A from an excitation at location A can be measured. This gives the point flexibility value for A denoted by Φ.sub.AA. In a similar way, the deflection at location B from excitation at location A can also be measured. This gives the cross flexibility between A and B denoted by Φ.sub.BA. If the test includes n locations there are n.sup.2 measurements of cross and point flexibility that can be measured. The assembly into matrix form is known as the flexibility matrix, [Φ].

[0127] If there is a proposed pattern of loads to be applied at the n locations, described by the force vector {F}, then the deformation at the n locations, described by the displacement vector {x}, will be given by:

{x}=[Φ]{F}

[0128] From the calculated displacements, other important structural integrity values such as stress and strain can be calculated.

[0129] Referring to FIG. 3, a wooden test floor was constructed that consisted of a pair of primary beams (110), a set of joists (112) and a covering of floorboards (113). The ends of the primary beams were simply supported and the joists were pinned to the primaries and simply supported at their free ends. A loading point was identified on the floor (114) with a measurement point (115) about 200 mm away.

[0130] A static load was applied to (114) using increments of mass of 1 kg up to 10 kg. The deflection of the floor was measured at (115) using a dial gauge. The relationship between load and deflection is shown in the chart of FIG. 4.

[0131] The gradient of the line in the chart is the flexibility between the load and measurement point and the value for the test was 2.84 mm/kN.

[0132] An embodiment of the invention (for example the embodiment of FIG. 2) was used to measure the flexibility between positions (114) and (115) using an excitation frequency of 2 Hz, and the value of 2.90 mm/kN was obtained. Further measurements showed that the first natural frequency of the floor was 18.85 Hz and the damping factor was 0.0112. The correction factor for these parameters is 0.989 giving the corrected flexibility value of 2.87 mm/kN which is less than 1% different from the value derived from the static test.

[0133] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiments shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.