SHM of Bridges and other structures
Bridges and tunnels are critical infrastructures which require continuous and safe usage. Periodic inspection to guarantee their reliability is mandatory in most countries. In some cases, when the structure is somewhat deficient a timely assessment of the structure could avoid catastrophic failures and therefore a Structural Health monitoring approach is more suitable.
Structural Health Monitoring (SHM) of bridges and buildings can be carried out by means of Acoustic Emission.
Acoustic Emission testing is a non-destructive testing that allows the continuous monitoring of structures such as bridges, dams, buildings, etc. for long periods of time. The main advantages of the use of acoustic emission for this purpose are the following:
- Unlike other non-destructive testing methods, acoustic emission can detect active cracks, i.e., cracks which are growing.
- Acoustic emission helps to detect hidden cracks or cracks in places which are not easy to access.
- Acoustic emission is one of the few non-destructive testing methods appropriate for the continuous monitoring of structures, for long periods of time.
Following a study from RAC thousands of UK bridges are at risk of collapse (see reference here Substandard Road Bridges). To be precise, the RAC study study reports that 3203 of the roughly 72000 thousand bridges on the local road network are somewhat deficient, representing 4.4% of the existing network.
The structural deficiencies in the bridges that have exceeded their useful life span are mainly the appearance of cracks in the concrete and corrosion in the metallic elements, mainly the suspension cables. The 100% comprehensive Inspection of these huge structures is an engineering challenge, the best possible solution is the application of Structural Health Monitoring or SHM, which is the process of implementing systems to detect damage to structures through continuous monitoring using sensors and applying statistical analysis to assess the condition of a structure.
Monitoring systems can offer operational optimization and possible lifetime extension of assets. This valuable tool for operators helps to manage financial, environmental and human risks.
Critical “hot spots” are equipped with appropriate sensors for monitoring and analysing activities inside.
Using Vallen Systeme’s Acoustic Emission solution, you´ll get your monitoring challenge under control using only one measurement system. The Vallen Systeme’s Acoustic Emission monitoring system can use a variety of sensors to record different parameters (acoustic emission, strain gauges, wind speed, temperature) 24 hours a day, 7 days a week, allowing defects to be detected during the operation of the structure without interrupting its operations.
The system is customizable and can be adapted to the different needs of your projects, integrating all the information obtained by the different sensors through the Vallen Monitoring Software.
The data can be uploaded to the cloud to carry out remote monitoring, integrate all the information obtained to carry out its analysis, and generate both a report on the current structural state of the structure and trigger alarms:
Case study – Full scale AE testing of wire breakage
This case study describes the results obtained on bridge using the AMSY6 Acoustic Emission monitoring system. The scope of this monitoring campaign is to detect wire breaks that could lead the bridge to collapse in the future.
The system installed was an AMSY6 MB 19, 8 ASIP-2 / S measurement cards, each with transient recorder modules fitted. For the measurement of the noise level, the system was operated in “continuous mode” and the recording of transients was disabled. We are using VS30-SIC with 0 dB preamplifier coupled to the structure with MAG4SI magnetic holders and hot glue.
The tension wire breaks are recorded and clearly identified. As shown in the image below (Figure 1), several wire breaks have been detected. The red marks indicate the wires affected by breakages.
Figure 1. General schematic of the bridge
Waveform of a wire break
When a wire break is detected by the acoustic emission system it creates a waveform.
The transients for tension wire breaks are known as burst signals – they have a clear beginning and end. The rapid rise to their maximum amplitude fades away with time. An example of a transient for a wire break is shown in Figure 2.
Figure 2. Example of wire break waveform.
Confirmation of wire breakage
After the examination of the bridge in the location indicated by the acoustic emission system (with a precision of 20 to 50cm), it was visually verified that the wire was actually broken. Figure 3 shows the exposed broken wire.
Figure 3. Exposed wires after Acoustic Emission wire break detection.