Repair of cracks in chimney

Problem statement

The problem statement for the project at the YARA plant in Köping was to investigate and analyze the cause of two existing vertical cracks that run from the top of the chimney down to about 30-35 meters above ground level. These cracks raised concerns about the structural integrity and load-bearing capacity of the chimney, which required a comprehensive inspection and analysis to assess the severity of the cracks, identify the causes behind them, and propose the necessary measures to ensure the safety and long-term durability of the structure.

Outcome

The results of our investigation provided a detailed understanding of the cause of the vertical cracks in the chimney. We identified that the cracks were mainly caused by a combination of uneven wind pressure distribution (ovalization) and thermal effects, together with insufficient horizontal reinforcement. Our solution led to recommendations for the installation of a monitoring system to track crack development and temperature changes, as well as suggestions for local repair measures and reinforcement with carbon fiber fabric. This helped to increase safety, prevent future damage and increase the rigidity of the chimney.

Solution

We took a thorough and multi-pronged approach to address the problems with the 100 meter high concrete chimney. Our solution included:

1. Used drones and mobile crane for visual inspection and collected concrete samples for laboratory analysis. Non-destructive testing methods such as strain gauges, ground penetrating radar (GPR) and ultrasound (tomography) were used.
2. Installation of measurement equipment: We installed advanced measurement systems to continuously monitor various parameters for about a year, including wind speed and direction, temperature variations, crack movements, accelerations and inclination of the chimney. This ongoing monitoring is crucial to capture real-time data.
3. Integration of measurement data: The collected measurement data was integrated into a comprehensive calculation model. This model helped us to confirm that the chimney was indeed undersized.
4. Carbon fiber fabric: To increase the load-bearing capacity and stiffness of the chimney, carbon fiber fabric was applied both vertically and horizontally.

Planned Reinforcement work: Based on the analysis and identified risks, a reinforcement plan has been developed and is scheduled for implementation in summer/autumn 2024.

Standards

ISO 16311-2:2024 – Maintenance and repair of concrete structures – Part 2: Assessment of existing concrete structures. ISO 13822:2010 – Bases for design of structures – Assessment of existing structures.