Papers by Author: B. Culshaw

Abstract: The concept that the civil engineering infrastructure may be streamlined through the use of Smart technology has been mooted for well over a decade. The thought is particularly appealing for large artifacts such as major buildings and bridges. The infrequent but extremely dramatic catastrophic failures particularly of major bridge structures inevitably reignite the debate. This paper endeavours to present a critique of the Smart Bridge both from a technical and socioeconomic perspective. Whilst the basic sensing technology is undoubtedly available there do remain significant areas for necessary improvement, notably in sensor location and damage identification. Additionally the link between the socioeconomic and political domains and the technologists has only recently attracted serious attention. The conclusion is that the tantalising prospect of the Smart Bridge whilst attractive, continues to need substantial technical development and a more effective interface into the economic and planning communities.

Abstract: The measurement of changes in the properties of ultrasonic Lamb waves propagating through structural material has frequently been proposed as a method for the detection of damage. In this paper we describe work that uses optical fibre sensors to detect the Lamb waves and show that the directional properties of these sensors allow us to not only detect damage, but also to locate it. We look at two types of optical fibre sensor, a polarimetric sensor and the fibre Bragg grating. The polarimetric sensor measures the change in birefringence of a fibre caused by the pressure wave of the ultrasound acting upon it. This is an integrated sensor since the fibre length bonded to the sample needs to be greater than the ultrasonic wavelength in order to obtain the required sensitivity. The maximum sensitivity of this sensor is when the fibre is positioned normal to the direction of wave propagation. Fibre Bragg gratings are essentially point sensors since the grating length needs to be a fraction of the ultrasound wavelength to obtain maximum sensitivity. Ultrasound is detected mainly through the in-plane strain it produces and maximum sensitivity is therefore produced when the grating is aligned parallel to the direction of wave propagation. Holes drilled into sample plates can be detected using both type of sensor by examining the changes in either the transmitted Lamb wave or through detection of the reflections produced by the hole. The sensitivity of the technique is shown to be determined by the relative positions of the acoustic source, the hole and the sensor. If we use fibre Bragg gratings in a rosette configuration (i.e. 3 gratings forming an equilateral triangle) then the direction of the Lamb wave can be determined using the directional sensitivities of the gratings. Using two such rosettes allows us to calculate the source of the wave from the intersection of two of these directions. If the source of the wave is the hole (which acts as a passive source), then the location of that hole can be determined.