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Calculation of test load and load utilization of steel reinforced concrete columns in fire tests
(2026)
Calculating the test load is a key aspect of conducting column fire tests. The level of applied load affects the load-bearing and deformation behavior as well as the failure time of the structural element in a fire test. Therefore, the test load also influences the fire resistance classification of steel reinforced concrete columns. A literature review shows that there are significant differences in the methods used to calculate the test load. Furthermore, documentation of the methods used is often incomplete. This makes it difficult to trace and compare test results. This contribution analyzes and compares the various approaches to calculate the test load for fire tests of steel reinforced concrete columns, based on normative standards. It is focusing on evaluating the effects of different stress-strain models for concrete (parabola-rectangle diagram and parabolic approach) and the material strengths used (tabulated values according to Eurocode and experimentally determined values) on the load-bearing capacity at ambient temperatures and the derived test load. Recommendations are formulated based on comparative calculations, for a standard-compliant, transparent and practical determination of the test load that considers both safety-relevant and economic aspects.
In real fire scenarios, the mechanical and thermal boundary conditions typically differ significantly from those in prescriptive, single member fire tests. For example, interactions between a fire exposed steel reinforced concrete column and the entire building structure, as well as the resulting restraint effects, are not considered in standard fire tests. Using the substructure method, the behavior of a steel reinforced concrete column under fire exposure can be investigated while considering its interaction with the entire building structure. First, the stiffness of the surrounding structure must be identified, e.g., analytically or by numerically based approaches. The result is then used as input for the substructure method. In the presented study, a linear elastic spring is used to model the stiffness of the building. The interaction between the fire exposed column and the surrounding structure may have both positive and negative effects on the fire resistance of the tested structural element.
The use of carbon‑fibre‑reinforced polymer (CFRP) grids with high tensile strength and inherent corrosion resistance provides an alternative to conventional prestressing steel strands and allows for minimal concrete cover, enabling slender prestressed components. The research project CaPreFloor builds on this potential to develop a thin‑walled concrete floor system. However, such elements pose challenges regarding their structural behaviour at elevated temperatures. This contribution presents and discusses two relevant experimental investigations. First, flexural tests at elevated temperatures were performed on slender concrete beams reinforced with CFRP grids with different prestress levels to evaluate their load‑bearing capacity under thermal exposure. Two failure modes were identified, i.e., tensile rupture of the CFRP reinforcement occurred at high prestress levels, whereas bond failure between the concrete and CFRP reinforcement dominated at low prestress levels. Second, fire tests were conducted to assess the susceptibility to spalling and the effectiveness of mitigation strategies. The presence of the CFRP grid resulted in earlier spalling relative to the unreinforced specimen. To avoid spalling, two fire protection measures were examined: the application of an intumescent coating and the addition of PP fibres to the concrete mixture. While PP fibres successfully prevented spalling for both investigated CFRP grid types, the intumescent coating proved effective only for specimens reinforced with one of the grids used.
Poly(limonene carbonate) (PLimC) is a green polymer produced from renewable limonene oxide and CO₂ as a green carbon feedstock. Previous fire-behavior results showed that PLimC responds best to flame retardants (FRs) typically used in polyolefin systems. To develop a sustainable formulation, we evaluated melem phytate, biochar, phosphorylated lignin, and aluminum hydroxide (ATH) individually, and subsequently combined melem phytate with each of the three environmentally friendly adjuvants.
Techniques including cone calorimetry were used to understand the thermal stability and fire behavior of all formulations. Figure 1, using the biochar system as an example, demonstrates a stepwise reduction in pHRR for melem phytate and biochar alone, with their combination yielding the greatest shift toward the origin in the Petrella diagram. This result highlights a sustainable FR strategy, as combining melem phytate and biochar, as well as with ATH and phosphorylated lignin, improves fire performance using renewable, low-hazard compounds.
This study examines two comprehensive approaches to reducing the amount of antimony trioxide (ATO) in brominated flame retardant (tris(2,4,6‐tribromophenoxy)‐s‐triazine bromine) (Br) in acrylonitrile–butadiene–styrene (ABS). One approach systematically substitutes Br/ATO with magnesium hydroxide (MH), while the other substitutes ATO with calcium borate, zinc borate, zinc oxide, zinc sulfide, and zinc stannate. We investigated the pyrolysis (thermogravimetry), flammability (limiting oxygen index and UL 94 tests), smoldering (smoke density chamber), and fire behavior (cone calorimeter). The study reveals that the synergism between Br and ATO is essential and sensitive to any changes. None of the additives fully replaced the Br/ATO mixture or ATO alone while maintaining the same level of flame retardancy. Replacing the Br/ATO mixture with MH reduces smoke emission during burning but increases flammability in the ignition scenario. Zinc and calcium salts considerably lower the peak of heat release rate due to the enhanced formation of a protective char layer. The residual protective layer hinders mass and heat transfer, and prolonged residence time of the decomposition products in the pyrolytic zone results in smoke reduction. This systematic investigation illustrates the challenges of replacing Br/ATO or ATO in ABS, but it also emphasizes the relevant benefits and remarkable potential of partial replacement.
ISO/TS 19021 specifies a method for time-resolved quantification of selected fire effluent gases generated in the ISO 5659 single-chamber smoke test using Fourier Transform Infrared (FTIR) spectroscopy. To support the revision of ISO/TS 19021 and establish updated precision statements, an interlaboratory trial (round-robin) was organised with 16 laboratories and designed in three steps: (1) assessment of equipment and set-up conformity to ISO/TS 19021 requirements, (2) qualitative and semi-quantitative processing of five shared reference spectra, and (3) replicated testing of four common materials under prescribed irradiance and flaming conditions. Step 1 highlighted deviations that can materially influence performance, including insufficient minimum detection limits for some target gases and heterogeneous calibration descriptions. Step 2 demonstrated strong agreement on major species in spectra dominated by target gases (e.g., CO, CO2, HCl), but also revealed practical limitations: only five laboratories could fully reprocess externally supplied spectra due to software import constraints, and reported numerical values below the ISO/TS 19021 quantification capability (≤ 15 μL/L for most gases; ≤ 300 μL/L for CO2) were not robust for quantitative comparison. Step 3 data were analysed in accordance with the ISO 5725 series to estimate repeatability and reproducibility for smoke metrics and gas concentrations at defined times and maxima. Comparison with historical datasets indicates consistency for several measurands while confirming that interlaboratory variability increases markedly at low concentrations and for species detected by a limited subset of laboratories. These findings support targeted clarifications in ISO/TS 19021 regarding quantification limits, spectral interpretation, and harmonised reporting.
Poly(lactic acid) (PLA) is the most important player in the biopolymer market. So far competing with commodity plastics for packaging dominates PLA consumption. Developing flame retardant PLA composites enables the replacement of higher-priced technical polymers in electrical engineering. Sustainable, bio-based, and compostable PLA composites are the ultimate goal, thus using natural fibres and eco-friendly/bio-based flame retardants are on the short list of the current and urgent research tasks. Some opportunities and tasks, milestones and innovations are adumbrated using different examples taken from our recent research projects [1-6]. The challenge to maintain the molecular weight during processing is underlined as well as the impact of viscosity on the flammability. Natural fibres are discussed with respect to their impact on the mechanical performance and fire behaviour of PLA composites. Innovative bio-derived adjuvants and flame retardants such as biochar, cork, in wastewater P-enriched microalgae, phosphorylated lignin, and different phytates are proposed.
Der Forschungsbericht beschreibt die Entwicklung einer minimal-invasiven in situ Prüfmethode zur Bewertung der Wirksamkeit von reaktiven Brandschutzsystemen (RBS). Mit dieser Methode lässt sich die tatsächliche thermische Schutzwirkung von RBS an bestehenden Stahlkonstruktionen, die eine reale Bewitterung und Alterung durchlaufen haben, beurteilen. Diese Information kann für den Nachweis der Feuerwiderstandsdauer der Bestandkonstruktion verwendet werden.
Das im Projekt entwickelte Prüfgerät (Prototyp) ermöglicht es, vor Ort am Bauwerk eine lokal begrenzte Bauteilfläche einer definierten Temperatureinwirkung auszusetzen. Grundlage des Prüfszenarios ist die einseitige Erwärmung eines Teilbereiches von etwa 100 x 100 mm² am Steg eines I- oder H-Profils. Eine im Prototyp integrierte elektrische Aufheizvorrichtung liefert einen homogenen und reproduzierbaren Energieeintrag. Das gewählte Heizregime entspricht einer 30-minütigen Temperaturbeanspruchung analog der Einheits-Temperaturzeitkurve (ETK). Als Referenz dienten Ergebnisse aus Brandversuchen am Kleinprüfstand nach DIN 4102-8 an Stahlplatten ohne und mit RBS. Darüber hinaus erfasst ein Laser-Distanzsensor am Prototyp die Aufschäumhöhe des RBS während des Versuchs. Zur Bewertung der brandschutztechnischen Wirksamkeit des RBS werden die Temperatur der Heizelemente, die Stahltemperatur im Zentrum der Prüffläche sowie die Schaumhöhe des RBS kontinuierlich gemessen und aufgezeichnet. Die entsprechenden Thermoelemente werden vorab am zu prüfenden Bauteil angebracht. Durch den kompakten Aufbau sowie die Versorgung des Prototyps mit Standardmedien (16A Starkstrom, Druckluft) lässt sich die in situ Prüfmethode flexibel anwenden. Nach Abschluss des Versuchs muss das RBS lediglich im unmittelbar geprüften Bereich und ggf. lokal angrenzend erneuert werden. Um eine Schädigung und den Festigkeitsminderung der Stahlkonstruktion auszuschließen, wird die Prüfung bei Erreichen einen Stahltemperatur von 400 °C beendet. Dieser Temperaturbereich genügt jedoch, um die Reaktion des RBS auszulösen und seine Wirksamkeit zu beurteilen.
Die entwickelte in situ Prüfung wurde im Brandlabor der BAM an verschiedenen Probekörpergeometrien erprobt. Dazu gehörten Stahlplatten mit einer Dicke von 5, 6 und 10 mm als auch Walzprofile mit offenem Querschnitt (IPE 220 und HEB 260). Die Probekörper wurden sowohl unbeschichtet als auch mit einem wasserbasierten RBS in Trockenschichtdicken von 0,25 und 0,50 mm untersucht. In diesem Zusammenhang wurde auch der Einfluss der Wärmeleitung innerhalb der Prüfkörper untersucht. In allen Versuchen konnte die für RBS typische Reaktion und Aufschäumung erzielt werden. Die Wirksamkeit des RBS zeigte sich zudem anhand der reduzierten Erwärmungs-geschwindigkeit der Stahlbauteile.
Auf Grundlage der Laborerfahrungen konnte die in situ Prüfung auch an einer real gealterten Bestandskonstruktion in einer Logistikhalle erfolgreich angewendet werden. Das Beispiel hat gezeigt, dass die an der BAM entwickelte Methode eine zuverlässige Bewertung der Wirksamkeit von RBS direkt am Bauwerk ermöglicht. Die denkbaren Anwendungs-szenarien der in situ Methode sind im Forschungsbericht beschrieben. Die Nachweis-möglichkeiten ergeben sich in Abhängigkeit der vorliegenden Informationen über das im Bestand applizierte RBS.
Major fire disasters continue to cause substantial loss of life, economic damage, and social disruption worldwide. Although investigations occur in most countries, lessons learned are often fragmented, published in incompatible formats, or not published at all. Therefore, it is recommended that a group be set up of experts to investigate national and international fire incidents in a structured manner and to determine specifically what lessons can be learned for the future.
In real fire scenarios, the mechanical and thermal boundary conditions typically differ significantly from those in prescriptive, single member fire tests. For example, interactions between a fire exposed steel reinforced concrete column and the entire building structure, as well as the resulting restraint effects, are not considered in standard fire tests. Using the substructure method, the behavior of a steel reinforced concrete column under fire exposure can be investigated while considering its interaction with the entire building structure. First, the stiffness of the surrounding structure must be identified, e.g., analytically or by numerically based approaches. The result is then used as input for the substructure method. In the presented study, a linear elastic spring is used to model the stiffness of the building. The interaction between the fire exposed column and the surrounding structure may have both positive and negative effects on the fire resistance of the tested structural element.
