Theoretical and experimental basis of the analysis of the effectiveness of composite reinforcements of thin-walled steel structures, taking into account the influence of spatial work

MINIATURA 6

Funding Organization: National Science Centre

Project title: Theoretical and experimental basis of the analysis of the effectiveness of composite reinforcements of thin-walled steel structures, taking into account the influence of spatial work

Agreement number: DEC-2022/06/X/ST8/00489

Project implementation period: 03.09.2022 - 02.09.2023

Principal Investigator: dr inż. Ilona Szewczak

Project value: 32 427,00 PLN

Funds granted for Lublin University of Technology: 32 427,00 PLN

Abstract: The development of thin-walled steel structures is related, first of all, to the technical progress in manufacturing and assembly, as well as the desire to minimize material consumption. In the work (by Bródek, Łubiński) it was noted that the development of thin-walled structures contributed to the reduction of steel consumption by up to 50% compared to traditional structures made of hot-rolled sections, reduced assembly time to 60% and construction costs to 25%. Due to these advantages, in recent years thin-walled elements have found more and more use not only as building envelope elements, but also as the main elements of the load-bearing structure. However, it should be remembered that such a wide application is also associated with the possible need for reinforcement in the event of e.g. design errors or an increase in external loads. Unfortunately, structures made of steel cold-formed elements are characterized by a limited possibility of their strengthening. Due to the very thin walls of the cross-section (from 1 mm to 3 mm), it is practically impossible to make welded joints, and the implementation of joints with the use of mechanical connectors is significantly limited. Therefore, it becomes necessary to search for an effective and easy method of strengthening this type of structure. One of them may be the use of carbon fiber tapes embedded in an epoxy matrix (CFRP - Carbon Fiber Reinforcement Polymers) joined with the beam through an adhesive.
Based on the available scientific publications, it can be concluded that the use of composite materials to strengthen hot-rolled steel structures is quite well recognized. Unfortunately, it is a bit different in the case of cold-formed steel elements. The high efficiency of strengthening hot-rolled steel structures with the use of CFRP strips makes one optimistic that this material can also be widely used for reinforcing thin-walled steel structures. For this purpose, detailed analyzes should be carried out to answer the question of how the connection of two low-stiffness elements (thin-walled elements and CFRP strips) will affect the load-bearing capacity of the reinforced element. Positive results of laboratory and numerical tests will allow to create new space for composite materials.
While conducting literature studies, a limited number of publications were found on the reinforcement of thin-walled steel structures with the use of composite materials, the vast majority of which concern the research of compression elements. In the available literature, there is a shortage of works devoted to the reinforcement of bending thin-walled cold-formed beams. There were also no works in which the spatial work of a reinforced thin-walled element connected with other structural elements was taken into account. This is an important issue because these elements are used as roof purlins, and in a two-branch system as frame transoms in steel halls. The preliminary research carried out by the author of the application on the reinforcement of thin-walled sigma beams subjected to a uniformly distributed load and tested in the four-point bending scheme showed a beneficial effect of the use of CFRP tapes on the reduction of displacement and deformation of the tested beams. Due to the need to develop a method of strengthening thin-walled steel elements, for example used as purlins, the author of the application decided to recognize the effectiveness of strengthening bending thin-walled sigma beams connected to a sandwich panel using glued CFRP tapes. For this purpose, it is planned to conduct a pilot laboratory test in which 9 cold-formed steel beams with a sigma cross-section and a span of 3 m, connected to a sandwich panel, will be tested in the four-point bending scheme. During the test, strain gauges will be used to measure deformations, and Aramis and Tritop systems will be used to measure displacements. The three beam-to-slab samples will be tested without reinforcement and will be used as reference samples. The remaining samples will be reinforced with CFRP strips in two different arrangements in order to find the most advantageous location of the CFRP strips when reinforcing cold bending sigma section steel beams cooperating with a sandwich panel. The entire project is carried out in the field of Civil Engineering and Transport.