“Connections between structural elements are essential parts of the frame, as the failure of a single joint could lead to the collapse of the whole structure. Steel is sensitive to high temperatures, and the deterioration of steel’s mechanical properties at elevated temperatures can lead to joint failure. To ensure satisfactory structural design, the joint performance and resistance must be reliably determined under normal and fire conditions. However, considerably less research is available on the failure modes and mechanical behaviour of joints at elevated temperatures.”, says Jolanta Bączkiewicz.
Developing analytical methods to determine temperature and fire resistance of tubular joints is essential to efficient design.
In her thesis, Jolanta Bączkiewicz focused on square hollow section (SHS) joints. A set of full-scale experimental tests with unloaded various joint types and loaded T-joints, as well as numerical simulations and parametric studies were conducted to define the performance of SHS joints at elevated temperatures.
Based on the research, the exact temperature development pattern of SHS joints was identified. The thesis proposed also better estimation of the joint design temperature as the mean value of the brace and chord temperatures, determined in accordance with EN 1993-1-2.
The analysis of the T-joints under axial compression showed that the failure modes of the tested joints at elevated temperatures are the same as the failure modes for the respective joints at ambient conditions calculated according to EN 1993-1-8 and that the reduction factor of the elastic modulus due to high temperature represents accurately the degradation of the steel strength.
Finally, taking into account all obtained results, the thesis proposed a design method to calculate the resistance of SHS T-joints at elevated temperatures. The method is based on the design equations of EN 1993-1-8 for ambient conditions, modified by the reduction factor of the elastic modulus at a given design temperature defined in the thesis.
The doctoral dissertation of MSc (Tech) Jolanta Bączkiewicz in the field of civil engineering titled Resistance of Axially Loaded Square Hollow Section T-Joints at Elevated Temperatures will be publicly examined in the Faculty of Built Environment at Tampere University at 14 o’clock on Friday 1 October 2021. The venue is Rakennustalo building auditorium RG202 (Korkeakoulunkatu 5, Tampere). Professor Milan Veljkovic from Delft University of Technology, Netherlands, will be the opponent while Professor Mikko Malaska from the Faculty of Built Environment will act as the custos.
The event can be followed via remote connection.
The dissertation is available online at the: http://urn.fi/URN:ISBN:978-952-03-2081-2.
Photo: Olavi Penttilä