Problem
The approximately 36 meter high masonry chimney in Norrköping, built around 1900 as part of the Norrköping cotton mill, showed extensive damage. Among the problems noted were cracks in the concrete slab at the base, horizontal and diagonal cracks in the mortar joints near the top, brick spalling, discoloration, and missing steel ring joints. The damage was also exacerbated by vegetation and moisture. There was a risk of falling bricks and thus a danger to the surroundings. The aim of the project was to assess the structural status of the chimney, identify the causes of the damage and propose measures to ensure long-term stability and safety.
Results
The investigation showed that the upper seven meters of the chimney were the most damaged, with large horizontal cracks caused by sulphate attack on the mortar. This led to volume increase, uplift and rotation of the chimney head. The concrete slab at the base had severe cracks due to lack of reinforcement, allowing water ingress. Vegetation around the structure contributed to further deterioration of the mortar. Two of the eleven steel rings were missing, while the others showed superficial corrosion. Calculations and FE modeling showed that the structure is partially at the ultimate limit state but not at immediate risk of collapse. Recommended actions were the removal of the concrete slab at the base, reconstruction of the upper part of the chimney, removal of vegetation and cleaning, protection and completion of steel ring joints. In addition, the importance of using compatible sealants for repairs was emphasized.
Solution
The condition assessment was carried out with the following steps:
Visual inspection from ground level and with boom lift to document cracks and surface damage.
Drone survey to create a 3D model and analyze slope and damage along the height.
Non-destructive testing with GPR (wall thickness and reinforcement), Ultrasonic Pulse Echo (MIRA) for voids, videoscope for internal inspection and boom knocking to detect delamination
Destructive testing via foundation excavation and core drilling to analyze concrete and masonry.
Analytical calculations and FEM modelling to assess load bearing capacity, stability and natural frequencies.
The method provided an overall picture of the condition of the chimney and allowed an informed analysis of both material and structural aspects.
Equipment
- Drone (DJI Mavic Pro 2) with photogrammetry
- Georadar (Proceq GPR)
- Ultrasonic Pulse Echo (MIRA)
- Videoscope
- Hammer for boom tapping
- Mini excavator for excavation
- Core drilling equipment
- Visual inspection and documentation equipment
Standards
- EN 1990: Eurocode – Basic design rules
- EN 1991-1-1: Eurocode 1 – General loads
- EN 1991-1-4: Eurocode 1 – Wind load
- EN 1992-1-1: Eurocode 2 – Concrete structures
- EN 1996-1-1: Eurocode 6 – Masonry structures
- BFS 2019:1 EKS 11 – National Board of Housing, Building and Planning regulations
- ISO 16311-1/2 – Condition assessment of concrete structures
