Answering your questions about the remote monitoring of bridges

Many of the bridges that make up Europe’s critical infrastructure were built in the 1950s and are now reaching the end of their design lives. As a result, the monitoring of their integrity and structural safety is a matter of ever-increasing importance. Making that process as accurate and cost-effective as possible is a priority. In a recent webinar on IoT Remote Monitoring of Bridges, we took a deep dive into how the Internet of Things (IoT) is meeting the challenges of this critical task.

Chaired by Worldsensing Area Sales Manager Arnau Carbonell, the session featured expert speakers Antonis Chrysovergis, Structural Health Monitoring Project Manager at mageba, and Victor Salinas Naval, a Geophysicist and Project Manager at Worldsensing. Unsurprisingly, this highly informative webinar resulted in a wide range of questions from online attendees. Here are the top queries and their answers—and for more information on monitoring bridges don’t miss out on the full webinar.

Questions

What developments are there in measuring the geotechnical and foundation elements of bridges?

What do you mean by IoT?

Do you need license for LoRa?

Could structural health monitoring replace some visual inspections on bridges and, if so, how?

What is your preferred technology for monitoring bridges: LoRa WAN, Sigfox 0G or aerospace IoT?

How do you deal with LoRa payload limitations? Is there a maximum number of loggers that can be on the network?

How powerful and what sizes are the solar panel and batteries used in Switzerland? Which installation do you use for supplying the gateway with power?

Can we replace the wire sensors with IoT-based sensors? And what is the price comparison between the two?

Are you able to determine the 3D stress sensor at a particular point in the structure?

What about the future for monitoring breaches? Will it be satellite, 5G or some other technology?

Regarding the cost and efficiency of satellite being connected with the technology, do you think it can become viable or it will be a matter of price?

What can you tell us about dynamic monitoring?

What developments are there in measuring the geotechnical and foundation elements of bridges?

Victor Salinas: Understanding the foundations and the geotechnical environment is very important, and we can provide a lot of devices that outperform typical geotechnical sensors.

What do you mean by IoT?

Victor Salinas: In general terms, IoT stands for Internet of Things. It refers to the interconnection between elements, creating a group containing sensors and software. IoT consists of a pool of interrelated, mutually communicating technologies. They can communicate with other systems and provide relevant information for the owner. Essentially, it’s a network that receives information from sensors, automatically and remotely, and ensures the data follows the correct channels through processing software.

Do you need a license for LoRa?

Victor Salinas: No. What we provide is perfect for operating in this bandwidth. So if you are buying from us you have devices ready to go in the field, and they are prepared to comply with all the regulations in different countries, for emission and transmission.

Could structural health monitoring replace some visual inspections on bridges and, if so, how?

Antonis Chrysovergis: We’ve seen that using crack meters can replace some visits to bridges. We also have the example of anchor monitoring, where engineers had to go on-site and take measurements until we installed the wireless system. Finally, there’s the case of displacement monitoring of bearings. You can use the system to see the movement of the bearings without having to go on-site to physically check what’s going on.

Victor Salinas: You can automatize the visits or collect data without going into the field. But you can also use the data to study how to evolve from periodic maintenance to predictive maintenance. You can spread your visits out into longer periods, not be required to make visits if the situation is not critical—and prioritize other structures.

What is your preferred technology for monitoring bridges: LoRa WAN, Sigfox 0G or aerospace IoT?

Victor Salinas: Different protocols and different kinds of technology all have pros and cons for monitoring bridges. LoRaWAN, which we are using, and Sigfox are pretty similar because they are both low-power wide-area networks. We prefer to use LoRaWAN. Maybe for other applications, Sigfox makes sense, but for geotechnical or structural applications we use LoRaWAN because when you purchase a gateway you become the owner of the infrastructure in the coverage area.

For Sigfox, you are dependent on third-party technology from the service provider. I’m not sure if I understand the idea of aerospace IoT: maybe it’s referring to the satellite IoT, which is pretty new. For now, it doesn’t have much coverage, but this is a technology to pay attention to in the future because it has a lot of possibilities.

How do you deal with LoRa payload limitations when monitoring bridges? Is there a maximum number of loggers that can be on the network?

Antonis Chrysovergis: The system depends on the number of nodes and the data acquisition rate that you want. We have systems with 25 nodes and data acquisition as part of an experimental program. That provides one measurement every minute and it worked okay. It depends on the protocol.

Victor Salinas: We have to focus on two dimensions when discussing network limitations. The first is the number of LoRas and the second is how often you receive data. You can have a small network that provides new information every 30 seconds, for example. In that case, the limitation on the number of nodes you can have is greater. But if you are collecting measurements with our system, the parameters of your network can be increased a lot.

With our multi-gateway architecture, you can support more sensors because you have more gateways. Of course, you have to design the network properly, but you can have up 500 sensors for monitoring bridges, which is not a bad number.

How powerful and what sizes are the solar panel and batteries used in Switzerland? Which installation do you use for supplying the gateway with power?

Victor Salinas: It was maybe a half-square-meter solar panel, and a battery that can remain idle or uncharged for an extended period of time. The battery was 12 Volts, smaller than a car battery. We didn’t have any problems with that combination. Of course, sometimes there was snow and for some weeks the system was offline until the snow had gone. Then the gateway started up by itself, and we started receiving measurements again.

Can we replace the wire sensors with IoT-based sensors? And what is the price comparison between the two?

Victor Salinas: We have many protocols, so I’ll address the LoRa protocol here. The LoRa protocol will not allow you to take fast measurements, let’s say at 100 hertz, so there are some limitations. I can’t say much about the price comparison. When you exceed the number of sensors, the wireless system becomes cheaper, but I cannot give an exact answer. It would depend on the scope and on what kind of enterprise it was applied to. And you would have to factor in if measurements needed to be taken very regularly.

Are you able to determine the 3D stress sensor at a particular point in the structure?

Victor Salinas: Worldsensing supplies technology for a connectivity provider. So we focus our efforts on providing the best connectivity for the geotechnical and technical sensors. Our aim is to provide pure data to third-party software, which can process that data.

Antonis Chrysovergis: We prepare the data to deliver to the third party for processing, so the answer must be no, we are not providing that for the stress tensor. But we will be launching some interesting solutions in the future, which will put intelligence inside the edge device to capture, process and send the data via LoRa.

What about the future for monitoring breaches? Will it be satellite, 5G or some other technology?

Victor Salinas: No one knows for sure, but we can see the LoRa technology is in very good shape. So in the future, it seems it’s going to increase in popularity. And in terms of maintenance of the structure, if you have to rely on something in space, it’s certain you have to rely on your service provider. Maybe the service is good and it’s working well but with LoRa you are the owner.

This will be important in the future when considering 5G and satellite communication.

Antonis Chrysovergis: I think people are looking for a stable system that can deliver data over a time horizon of years. Usually, when you install too many computers, one computer will fail or will disconnect, or something will happen to the hard drive. And when that happens you have to drive 500 kilometers just to change one cable, for example. I think the future trend is towards stable measurements and static measurements, where you can see the evolution of stress and cracks over the years.

This is what is important for you at the end of the day, this is the information that you want.

Regarding the cost and efficiency of satellite being connected with the technology, do you think it can become viable or it will be a matter of price?

Victor Salinas: Right now the coverage and prices are not the best, but the trend is toward cheaper prices and better coverage. So, I guess in the future it’s going to be possible to make an efficient migration. But I’d say the cost of the maintenance or the property of the infrastructure is going to be different depending on the solutions.

What can you tell us about dynamic monitoring?

Victor Salinas: Right now, LoRa is not able to transmit the amount of data you’d need for dynamic, vibrational or strain gages, for example. But if we can establish some key parameters, we can process this data in the node, and this is coming in the future. Now we are launching a system based on what we call data by exception.

This is event detection, which means you are monitoring dynamically and when something happens we send the information and a nearly real-time alert to warn the user that something has happened with the structure. This is more focused on an embankment or slope stability, but these kinds of things could affect structures such as bridges, too.