Previous tests in the medium-sized MiniFUR furnace could only be performed on unloaded samples. These tests were primarily used for indicative verification of integrity (limit state E) and insulation properties of structures (limit state I), but not their load-bearing capacity and stability in fire (limit state R). "Mechanical loading is crucial for the resulting fire resistance, as it can significantly affect it negatively – for example, by accelerating the loss of load-bearing capacity, promoting excessive deformation and cracking, or leading to premature failure of connections. Our goal was to bring indicative fire tests closer to real-life conditions, where structures are simultaneously exposed to high temperatures and mechanical stress during a fire," says Martin Hataj from the Structural Engineering team at UCEEB CTU.
The newly developed device consists of a modular loading frame that can be adapted to different types of tests. It allows wall panels and columns to be loaded with pressures of up to approximately 200 kN, as well as testing of bar elements (such as beams, tie rods, or joints) with tensile forces of up to 100 kN. This allows the MiniFUR furnace to be used to test both wall components and structural elements, as well as their details, such as structural joints.
Teams from Structural Engineering, Electronic Systems and Diagnostics, and Fire Safety collaborated on the development of the device. The steel frame design was created at UCEEB, as was the hydraulic system, which calculates the load and enables continuous monitoring and recording of pressure in the hydraulic system.
For industrial customers and research partners, the new device offers the opportunity to verify the load-bearing capacity of structures in the event of a fire, optimize their design prior to certification testing in accredited laboratories, and test critical structural details. The device has been successfully adjusted using calibration force gauges and verified by validation tests in compression and tension, and has already found commercial application.
One of the first applications, for example, was the verification of various types of protection for steel fasteners in wooden beam joints in cooperation with Michna&Perháč s.r.o. "Fire tensile tests were performed on wooden joints, during which we observed how structural details affect the behavior of joints when combined with high temperatures and mechanical loads. We tested various designs of pins and grooves and their effect on the rate of load-bearing capacity loss and joint failure in a fire. The ability to verify the behavior of joints in such detail and realistically is key to the design of safe and durable wooden structures," said Ondřej Perháč from the management of Michna&Perháč s.r.o.