Structural Health Monitoring

Our research

What do we really know about the properties of our buildings? Will a pillar or a wall work as planned in a few years or decades? Will connections still hold when eight people load the balcony, or has it rotted away? Does the roof meet the sealing requirements so that water stays out? Does the insulation work as it should to keep heat in during the winter and out during the summer?

These and many other questions are asked about our buildings to ensure performance. Over many years, buildings are subjected to wear and tear. Within this research area, we aim to provide answers to these questions, with a focus on wooden structures. The purpose is to increase lifespan and improve safety so that we can safely use these buildings.

The six general steps for projects in monitoring systems.

Generally, projects within structural health monitoring consist of six steps:

• Step 1: Define the objectives of the monitoring system.
• Step 2: Select appropriate sensors and locations of measurement points.
• Step 3: Develop and install the hardware and software components.
• Step 4: Manage data collection and storage operations.
• Step 5: Develop and apply algorithms for data analysis and visualization.
• Step 6: Data interpretation and eventual decision-making.

Methods

Data collection is the basis of structural health monitoring, typically conducted continuously over long periods. In our research, measuring moisture properties is a central aspect, as the moisture content in wooden structures is crucial for performance, and many damages come from excessive moisture.

Moisture is measured using various types of sensors, most often indirectly through parameters like temperature and relative humidity in the surrounding air or through electrical resistance. Settlements are measured using, e.g., potentiometers, but strains or forces can also be measured.

In recent years, we have developed a system in collaboration with our partner Saab. This system has been installed in several fixed installations and is also used for shorter measurements, e.g. in laboratory environments.

The dynamic properties of buildings allow for an overall assessment of the entire structure. For this purpose, individual accelerometers or geophones can be used to measure natural frequencies and possible deviations from expected values. When multiple sensors are employed, modal analysis can also be performed.

Here, too, a system has been developed with Saab that allows measurement with multiple devices without the need for them to be connected during measurements. This is a quite unique solution that significantly reduces disturbances for residents or at a building site due to cables.

Evaluation and visualisation

In structural health monitoring, one quickly reaches a point where handling and evaluation can no longer be done using traditional methods. The amount of data becomes too large and complex, making it necessary to use automated systems.

Several systems are therefore employed, ranging from simple and predetermined visualization to advanced exploration with interactive evaluation. These tools are primarily used for research purposes. However, parts of them will be available to our partners, such as the owner of the buildings, property developers, or manufacturers. Within the national initiative InfraVis, the tool TimberVIS was developed.

Detection of damage cases

Structural health monitoring leads to increased knowledge about a building's performance and its conditions. Through evaluation, we can determine if there has been any unwanted water leakage or if settlements are too large. It is also possible to link measurement data with the evaluation, for example, by assessing the risk of mold.

Comparison with computational models

Computer models are created during the design phase of a building, where its static and dynamic performance is evaluated. Additionally, corresponding calculations are made for aspects such as heat consumption.

By using data collection, these design models can be compared to the actual behavior of the building. This allows for verification of the calculations and their underlying models, such as the impact of moisture variation on dynamic behavior. The goal is to assist designers and the industry in ensuring correct assumptions.