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. The method is very sensitive and helps detect even emerging cracks.

Following a study from RAC thousands of UK bridges are at risk of collapse (see reference here https://www.racfoundation.org/research/economy/substandard-road-bridges-foi-2017) . 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 analyzing 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.

Case Study: Full scale AE testing of wire breakage

This case study describes the results obtained on a bridge using the AMSY6 Acoustic Emission (AE) monitoring system. The scope of this testing campaign was to demonstrate wire breaks detection and precision using Acoustic Emission on a real bridge.
The system installed was an AMSY6 with ASIP-2/S electronic boards, each with transient recorder modules fitted. Some VS30-SIC sensors with 0 dB preamplifier were coupled to the structure with MAG4SI magnetic holders and hot glue.
The bridge owner allowed to break some wires on this bridge that is no longer used for vehicle transit to confirm the precision of the AE system when detecting wire breaks. The image below (Figure 1) shows a wire breakage induced at the location identified with a green X.

Figure 1. General schematic of the bridge

Waveform of a wire break

When a wire break is detected by the acoustic emission system, we can record a wave travelling within the structure.
The waveform for tension wire breaks is a burst signal with clear beginning and end. The rapid rise to the maximum amplitude fades away with time. The transient wave for the wire break in Figure 1 is shown in Figure 2.

Figure 2. Wire break waveform.

Visual confirmation of wire breakage and AE precision

The client visually verified the wire breakage location and the location of the breakage identified using the AE system. As a result, the AMSY6 system precision in locating the wire break was between 20cm and 50cm in all cases (more than one breakage was simulated in this study). Figure 3 shows the exposed broken wire.