Inspection and Monitoring
1. General and Specialist Testing and Monitoring Techniques for Bridge Investigation
| General Inspection Techniques | Specialist Inspection Techniques | Testing Techniques | Monitoring Techniques |
|---|---|---|---|
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2. Specialist Inspection Techniques for Bridge Investigation
| Technique | Comments |
|---|---|
Sonics |
This technique is dependent on measuring changes in the velocity of sonic pulses travelling in a solid material, on the basis that velocity is dependent on the density and elastic properties of the material. Internal discontinuities (e.g. cracks, voids, boundaries between material types) can potentially be detected using this technique. |
| Conductivity | Electrodes are inserted into the structure or ground in order to determine its electromagnetic conductivity and hence estimate the moisture content of the masonry or the presence of voids etc |
| Ultrasonics | The velocity of ultrasonic pulses travelling in a solid material depends on the density and elastic properties of the material. Pulses are not transmitted across voids, so by measuring apparent speeds of pulses it is possible to determine the competence of the material and the location of delaminations etc. |
| Infra-red Thermography | Thermography involves the measurement of small variations in surface temperature (0.1 degree Celsius) which are used to predict internal conditions. |
| Impact Echo | This technique can be used to determine the depth of delaminations (e.g. ring separation) and the thickness of structural elements. It is based on the use of impact-generated stress waves that propagate through the structure and are reflected by internal flaws and/or external surfaces. |
| Tomography | Involves the measurement of a net of stress waves (sonic) through the structure. This gives information in 3-dimensions that enables an assessment of the location of possible defects to be made. |
| GPR Techniques | Ground Penetrating Radar (GPR) is an echo sounding technique where electromagnetic impulses are transmitted into the bridge and a receiver detects reflections from material boundaries. It can be used to determine construction details and conditions including delamination and voiding. |
| Photogrammetry | Several digital images are recorded of the structure from different locations. Using the collected information a 3-dimensional image of the structure can be created using specialist computer software and used to study the condition of the masonry and crack patterns. |
| Strain Measurement | Strain measurements may be taken as part of an ongoing monitoring programme or during loading of the bridge to determine the structural response. Two things must be remembered when measuring strain in masonry or brick structures. Firstly, the structure already has a strain history and so any measurement only relate to a change in the strain-state. Secondly, masonry and brickwork are not isotropic, homogeneous materials and so interpreting the strain gauge output is not straightforward. |
| Acoustic Emission | As micro-cracking develops in the structure under increasing load and/or material deterioration, small amounts of strain energy are released in the form of elastic stress waves that travel through the material. These waves can be 'listened' to by a transducer and the level of activity interpreted in terms of structural condition. |
| Electrical Conductivity | This electromagnetic technique is used to map variations in the electrical conductivity of the sub-surface. The technique can be used to locate areas of moisture, voids and variation in fill material. |
| Remote Visual Inspection | Remote visual inspection can take the form of rigid endoscopes or flexible image-scopes, both provide still and video records. Access can be through existing holes/cracks or small holes (typically 10-20mm) drilled into the structure. |
| Scour detection techniques | There are a number of techniques currently available to measure and monitor the effects of scour. CIRIA publication C551 (2002) Manual on Scour at Bridges and Other Hydraulic Structures presents a detailed review of the current techniques. |