Piotr Turkowski

The FRP reinforcement gained importance due to high tensile strength, high durability and ecological friendliness [1–7]. Its usefulness as the internal or Near Surface Mounted reinforcement in bent concrete elements has already been proven. Though, in terms of the compressive behaviour of the bars and concrete elements incorporating them, there are still few experimental and numerical considerations, especially when high temperatures are considered. This article contains further considerations on the performance of concrete columns with BFRP main reinforcement in fire resistance tests on the basis of previously presented authors’ numerical analyses. Comparative analysis in terms of temperatures, deformations and stresses of concrete columns with BFRP and steel main reinforcement in fire resistance tests is presented by the example of two columns, for which also experimental investigations were performed. Also, a comparative analysis of stress-strain relations for BFRP, steel and concrete at temperatures up to 600°C is presented. It can be concluded that BFRP bars’ properties are strongly different when compressive and tensile performance is considered, especially at elevated temperatures. Tensile strength was higher for BFRP than steel at room temperature, but along with temperature growth, it came the other way (at around 600°C). The compressive strength of the BFRP bars was higher than the value for concrete, but only for temperatures lower than 200°C.

The fire resistance of reinforced concrete (RC) beams strengthened with externally bonded reinforcement carbon fibre-reinforced polymers (EBR CFRP) depends on the load level and degree of strengthening. Design guides for this type of structure recommend strengthening limits to prevent collapse of the structure due to vandalism, damage or fire. In practice, however, it is not uncommon to exceed the proposed limits. This necessitates protection of the CFRP adhesive against high temperatures, namely glass transition temperature levels. This paper presents the results of 10 full-scale experimental fire resistance tests of reinforced concrete beams with EBR CFRP strengthening, with and without fire protection and under various load levels including full utilisation. It was demonstrated that in cases where CFRP strengthening was not needed to carry load in an accidental fire scenario, test specimens with and without it achieved the same fire resistance. It was also proven that in cases where CFRP failure influenced the failure of the entire beam, fire protection was crucial for maintaining the beam’s load-bearing capacity and its thickness had to be substantial. A fire resistance rating of over 4 h was achieved, nevertheless.

Fibre-Reinforced Polymer (FRP) reinforcement bars are gaining interest in terms of using them as an internal reinforcement in concrete construction parts due to their high tensile strength, corrosion resistance, low weight, and electrical indifference. Nevertheless, low elasticity and difficulties related to a high reduction in mechanical properties at even slightly elevated temperatures seem to limit this potential, due to existing fire safety requirements for buildings. Basalt FRP, which is the subject of this experimental study, is a relatively new type of non-metallic bars, and their environmental friendliness has been underlined in previous studies. The aim of this study is to determine the mechanical properties of BFRP bars, such as tensile and compressive strength and elasticity modulus, at normal and elevated temperatures up to 200 °C. The medium values of compressive strength at room temperature were in the range of 441.2–466.8 MPa, and it was significantly lower than the tensile strength (930.5–1121.3 MPa). Additionally, low values of elasticity modulus, especially when comparing to steel bars (typically about 210 GPa), were found in both compression (mean values: 31.0–38.4 GPa) and tension (mean values: 43.3–44.6 GPa). Low elasticity modulus may lead to difficulties with excessive deflections and crack widths, when designing bent elements with such reinforcement. Moreover, reduced mechanical properties at compression should not be neglected when designing compressed parts. Additionally, the phase change parameters, e.g., glass transition temperature, have been determined by means of DMA method, and the glass transition temperature was found to be equal to 107.5 °C.

W artykule przedstawiono nową metodę badania odporności ogniowej kanałów kablowych wg normy PN-EN 1366-11. Podano wymagania wynikające z polskich przepisów techniczno-budowlanych, zakres zastosowania metody badawczej oraz przebieg badania wraz z kryteriami oceny jego wyników i rzeczywistym zachowaniem w czasie badania odporności ogniowej.

W artykule zaprezentowano wyniki badania odporności ogniowej obciążonego słupa żeliwnego o przekroju okrągłym zamkniętym (CHS), zabezpieczonego zaprawą ogniochonną. Ponadto badaniu poddano słupy nieobciążone zabezpieczone tą samą zaprawą w celu określenia wpływu obciążenia na skuteczność ogniochronną materiału oraz dwa kolejne słupy nieobciążone, zabezpieczone inną zaprawą ogniochronną. Uzyskane wyniki pokazują, że słupy żeliwne mogą być zabezpieczane ogniochronnie nie tylko reaktywnymi, ale także biernymi materiałami ogniochronnymi. Wymagana grubość izolacji może być ustalana na podstawie tablic uzyskanych w badaniach elementów stalowych, zgodnie z EN 13381. Metody określania temperatury krytycznej stali, podane m.in. w normie EN 1993-1-2, mogą być z powodzeniem stosowane także w odniesieniu do konstrukcji żeliwnych.

The origins of standardised fire testing can be traced back to 1870’s, and the origin of the standard temperature-time curve to 1917. This approach, based on a 19th-century intuition is still in use up to this day, to design the 21st-century structures. Standardized fire-testing ultimately disregards the conservation of energy in the fire, as in every test the resulting temperature of the test must be the same (precisely as the temp.-time curve). To maintain this, different amount of heat is required in every test, which means that every time a different fire is modelled within the furnace. The differences between furnace fire sizes are ignored in the certification process, but can be interesting for fire researchers to understand how different materials behave in fire conditions. In this paper, Authors explore this topic by investigating the energy balance within the furnace, and comparing different fire tests together.