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The Influence of the Physical and Chemical Properties of Hardened Cement Paste on the Fire‐induced Spalling of Concrete A number of major fire incidents in recent decades, particularly in tunnels and indoor car parks, have increased the awareness among construction designers towards the potential susceptibility of concrete to fire‐induced explosive spalling. In some fields of application, this violent breaking‐off of concrete layers may reduce the fire resistance time of fire‐exposed construction elements. The mechanisms causing explosive spalling are not yet fully understood and discussed controversially among scientists.Fire tests of concrete specimens have shown that the type of cement may have a marked influence on the susceptibility of concrete to explosive spalling. Three common characteristics of those concretes that were found to have an increasedsusceptibility of spalling were identified. For each of the three common characteristics, acorresponding hypothesis describing its possible contribution to the fire‐induced concretespalling was proposed. This second part of the article describes the experiments to verify the hypotheses using a dedicated test programme. The evaluation of the tests identified the main mechanisms by which spalling is caused. [ABSTRACT FROM AUTHOR]

The Influence of the Physical and Chemical Properties of Hardened Cement Paste on the Fire‐Induced Spalling of Concrete A number of major fire incidents in recent decades, particularly in tunnels and indoor car parks, have increased the awareness among construction designers towards the potential susceptibility of concrete to fire‐induced explosive spalling. In some fields of application, this violent breaking‐off of concrete layers may reduce the fire resistance time of fire‐exposed construction elements. The mechanisms causing explosive spalling are not yet fully understood and discussed controversially among scientists. Fire tests of concrete specimens have shown that the type of cement may have a marked influence on the susceptibility of concrete to explosive spalling. The main objectives of the experimental programme described in this article were therefore to – determine the way in which the physical and chemical properties of the hardened cement paste influence the spalling propensity of heated concrete; and in this manner – contribute to a better understanding of the mechanisms causing explosive spalling. Three common characteristics of those concretes that were found to have an increased susceptibility of spalling were identified. For each of the three common characteristics, a corresponding hypothesis describing its possible contribution to the fire‐induced concrete spalling was proposed. The first part of this article describes the tests in which the influence of the type of cement on the susceptibility of concrete to explosive spalling was investigated, as well as thethree hypotheses. Each of the three hypotheses in turn was verified through a dedicated experimental programme. The experiments to verify the hypotheses are described in the second part of this article. The evaluation of the experiments identified the main mechanisms by which spalling is caused. [ABSTRACT FROM AUTHOR]

Fire risk of electric vehicles and fuel‐driven vehicles in open car parks Due to the policy discourse of climate changes, the number of modern vehicles and drive technologies in open car parks is increasing. This arises the question whether modern vehicles such as electric vehicles leads to an increased fire risk as well as an increased release of heat. In this paper, an approach to evaluate the fire risk of electric vehicles compared to vehicles with combustion engine with respect to the fire resistance of the structural elements in open car parks is presented. For this purpose, modeling approaches of the vehicle dimensions are presented, which based on a statistical data of the Federal Motor Transport Authority. The vehicle dimensions are used to determine the fire spread between vehicles. Furthermore, heat release rates of different vehicle are analyzed and an approximated approach for modern vehicles is derived. Furthermore, possible fire scenarios in open car parks and the probabilities of vehicle combinations are presented to calculate temperatures and evaluate the failure probability of structural elements in open car parks under electric vehicles fires. [ABSTRACT FROM AUTHOR]

Concretisation of evaluation criteria for the calculation of the combustion efficiency The combustion efficiency χ is an essential factor in determining the heat release rate and the fire load density when applying the Eurocode fire protection verifications. However, a calculation method for determining χ has not yet been standardised. In this paper, recommendations are given regarding the choice of evaluation criteria for the calculation of combustion efficiency. For this purpose, laboratory‐scale and real‐scale fire tests were carried out at the Institute for Building Materials, Solid Construction and Fire Protection (iBMB) at the Technische Universität Braunschweig. The objects tested were everyday objects and commercially available floor coverings. The eight criteria most frequently used in practice were used for the evaluation of the experimental investigations. The differences between the evaluation criteria lie in the temporal relationships of their input parameters. In addition, the combustion efficiency was formed from the mean values of several criteria. It was shown that possible outlier values can be captured by averaging. The criterion fuel load also proved to be very robust. The results were compiled in a table with recommendations regarding the selection of evaluation criteria and methods. [ABSTRACT FROM AUTHOR]

An alternative method of fire design of reinforced concrete columns with tabulated data – Explanations of new Annex C in DIN EN 1992‐1‐2/A1 In November 2019, an A1‐amendment to Eurocode 2 – DIN EN 1992‐1‐2: Structural design for fire exposure has been published. This A1‐amendment contains seven design tables in the new Annex C: „Buckling of columns under fire conditions" for fire resistance classes R30 to R240. With these design tables an alternative method is available for the fire design of reinforced concrete columns with a rectangular cross section in braced and non‐braced structures. The introduction by the building authorities in the administrative regulations of the federal states is probably expected in 2021/2022. The scientific background and the validation of the new Annex C and the associated restrictions are explained in this paper. On this basis, the tables of Annex C can now also be used in Germany (A2 amendment to the National Annex). The paper demonstrates the practical application of the new tables in two design examples and concludes with a brief outlook on the planned extension of the scope of these tables in the next Eurocode generation. [ABSTRACT FROM AUTHOR]

New tables for fire design of reinforced concrete walls for EN 1992‐1‐2 The fire protection design of load‐bearing reinforced concrete walls can be carried out according to DIN EN 1992‐1‐2 [1] using design tables, simplified or general calculation methods. The design table for load‐bearing walls in the current version of Eurocode 2 Part 1‐2 (DIN EN 1992‐1‐2) [1] was taken over in simplified form from DIN 4102‐4 of 1994 [2]. However, the design table contains some restrictions. Only two load utilizations are tabulated. Furthermore, when transferring the design table from DIN 4102‐4, a possible increase in load utilization due to the semi‐probabilistic safety concept compared to the values of DIN 4102‐4 based on the global safety concept was not taken into account. As a result, the scope of the design table for concrete walls in DIN EN 1992‐1‐2 is currently limited. In a research project sponsored by the Initiative Praxisgerechte Regelwerk im Bauwesen (PRB) [3], new design tables for the fire design of load‐bearing concrete walls exposed to fire from one side and two sides have been developed for practical application. Greater variety with regard to the load utilization and the support conditions was taken into consideration. The aim is to provide the design engineer with an easy‐to‐use design method that allows for the fire design of concrete walls to be economically optimized and safely carried out. Parts of the newly developed design tables are directly incorporated into the amended version of prEN 1992‐1‐2 [4] [5]. This article describes the basics and the procedure for the development as well as the proposal of the new design tables. [ABSTRACT FROM AUTHOR]

Derivation of thermal material values for concrete under natural fire exposure on the basis of experimental investigations The fire safety design of concrete and reinforced concrete components is standardized in Eurocode 2‐1‐2. The contained design specifications and material properties are based on the thermal exposure to the ISO 834 standard fire. As an alternative to this exposure the current Eurocodes provide the application of natural fire models. The fundamental difference between the temperature‐time curves is that the ISO 834 is characterized by a continuously increasing logarithmic function, while natural fire models consist of a heating and a cooling phase. This article describes the experimental determination of the thermal material properties of normal, high and ultra‐high strength concrete in the cooling phase. Exemplary, based on the test results, material values for concrete in the cooling phase of a fire are derived. These in turn serve as input parameters for numerical simulations. [ABSTRACT FROM AUTHOR]

Simplified design methods for steel columns under localised fire DIN EN 1991‐1‐2:2010 [1] currently contains a simplified design method that allows the calculation of thermal effects under localised fires. Based on the work of Heskestad and Hasemi, the temperatures in the fire plume and the net heat flux in the ceiling area (Ceiling Jet) of structural elements under localised fires can be calculated. The design method have been validated by experimental investigations and have proven themselves in application. In the Draft of EN 1991‐1‐2 Annex C, the mentioned design method are to be extended by new analytical design approach. The new design approach calculates the net heat flux of structural elements (vertical) which are offset to the flame axis of the localised fire. Within the scope of a DIBt research project [2] the plausibility and applicability of the new design approach was tested. In this article the simplifications and the application of the new design approach for steel columns under localised fire are shown. Furthermore, a validation is carried out on the basis of comparative calculations between the results of the new design approach, simulation results with the Fire Dynamics Simulator as well as measurement data of real pool and wood crib fires. [ABSTRACT FROM AUTHOR]

Do imperfections have to be taken into account when designing reinforced concrete columns exposed to fire? This paper examines the influence of imperfections on the reliability of fire‐exposed reinforced concrete cantilever columns – with focus on fire resistance class R 90. "Reliability" in sense of DIN EN 1990 is understood as the ability of a structural component to fulfil the specified requirements within the planned lifecycle. Reliability is usually expressed by probabilistic values. The investigations were triggered by a contribution by Pauli in [1] in which it was pointed out that the verification with the general calculation method according to DIN EN 1992‐1‐2 often results in a lower fire resistance duration than the verification with tabulated values or with the simplified calculation method. The missing rule control of imperfections in connection with a structural fire design was named as the cause of the discrepancies. [ABSTRACT FROM AUTHOR]

New approach on thermal conductivity of concrete in case of fire The design of concrete elements in case of fire by using fire safety engineering methods as described in Eurocode 2 is getting more and more common practice. An essential step within this calculation is to determine the cross‐sectional temperature under transient thermal stress. DIN EN 1992‐1‐2 provides temperature‐dependent curves for the thermal conductivity of concrete. As regulated by the national annex of DIN EN 1992‐1‐2 the so‐called upper limit function of thermal conductivity has to be used in Germany. Thermal calculations using this limit function lead to results, for which the insulation criterion in case of fire is not complied with the tabulated minimum thicknesses of section 5 in DIN EN 1992‐1‐2. This paper presents a new approach on thermal conductivity of concrete, which was verified by comparison of numerical calculations to experimental determined temperature‐time curves. Experimental data of 15 different tests on wall, ceiling and column specimens, carried out at Institute of Building Materials, Concrete Construction and Fire Safety (iBMB) of TU Braunschweig and furthermore European Institutes, was used. [ABSTRACT FROM AUTHOR]

Abstract: Conceptual optimisation of smoke extraction in atria Due to their special geometric conditions, requirements for flexible and broadly based user‐concepts, as well as often limited possibilities for sprinkler protection, atria create special challenges for performance‐based conception of smoke extraction. Especially in buildings with evacuation concepts using such atriazones, where deviations from building regulations already exist, or where the use of atria as functional or common areas is planned, special concepts will be required to ensure that all given target criteria can be fulfilled. This can be achieved by using methods and tools of fire protection engineering, and furthermore allows for a technically optimised smoke extraction concept. The following article describes challenges of smoke extraction of atria, identifies the main influencing parameters and shows possible solutions to reach the set target criteria. The solutions consider a project structure divided into several phases and an associated iterative conception. Starting with the clarification and definition of conceptual principles, on to simple plume‐calculations and finally using smoke extraction concepts for complex geometries using CFD calculations, the appropriate process is outlined. [ABSTRACT FROM AUTHOR]

Abstract: Thermal material properties of fire protection materials for natural fire scenarios In this paper experimental investigations regarding the thermal behaviour of selected fire protection materials (FPM) for steel elements exposed to natural fires are presented. Material properties, such as specific heat, thermal conductivity and density of FPM, have not been investigated in detail yet, especially for natural fire scenarios with different heating and cooling rates. For this purpose, experimental investigations of material properties of perlite plaster, gypsum fire protection boards and intumescent coatings will be presented. Currently, the determination of the thermal behaviour is based on investigations under the standard fire curve (ISO 834). For this approach, the thermal material properties of the FPM are not required. In addition to the standard fire design, the Eurocodes also enable a performance‐based design for a natural fire scenario. In contrast to the standard fire, which assumes a rapid and continuous rise in temperature, a realistic model of a fire (development phase, fully developed fire, cooling phase) is presented. The natural fire curve depends on fire loads, ventilation conditions and room configuration. Therefore, the properties of FPM for natural fires cannot be obtained from the standard fire tests. For the performance‐based design of protected steel components under natural fire the temperature‐dependent thermal material properties are therefore indispensable. [ABSTRACT FROM AUTHOR]

Abstract: Fire design of reinforced and prestressed concrete columns – To practical use of Method A in DIN EN 1992‐1‐2 This paper provides practical guidance on the fire design of reinforced concrete columns using Eurocode 2 (DIN EN 1992‐1‐2) Method A by giving explanations, diagrams and extended tables for columns with fire exposure on more than one side and on only one side. For columns fire exposed on one side extended tabulated data are given, which were calculated with the Advanced calculation method. [ABSTRACT FROM AUTHOR]

Application of performance-based fire safety design - natural fires and their calculation The present article describes the conditions under which an application of natural fire models is useful for the fire protection assessment. An overview of the various verification methods of the Eurocode fire safety design parts is given and their formal adoption into the various Building Codes is introduced. In addition to the dimensioning tables known from DIN 4102-4, the Eurocodes also provide simplified and general calculation methods. With the latter, the load-bearing and deformation behavior of components in case of a fire can be calculated taking account of temperature-dependent material properties and thermal expansion. However, due to the complexity and the comparatively high outlay of these design methods, they are particularly suitable for natural fires. Such design, however, requires an official application process for deviation from the affected part of the Building Code and is only applicable in consultation with the approval authorities. The application of a natural fire model for the fire safety design is shown using an example. It is a former submarine hall, which is converted into a sales center and in which the fire protection requirements change as a result. Due to the historical steel construction, the visibility of the load-bearing structure should be maintained so that the proof was carried out with the help of the natural fire models. This contribution presents the boundary conditions, the application limits and the corresponding methods. [ABSTRACT FROM AUTHOR]

Experimental study regarding the load and displacement behavior of fire exposed tunnel elements Incidents like the fire in the Channel Tunnel, where concrete spalling with a depth of 30 cm over a length of 500 m was determined, have led to requirements in limiting the spalling depth and involved zone to local and compatible magnitudes. To account for the high heating rate of tunnel fires, the fire resistance of railway tunnel structures was investigated using the German EBA tunnel fire curve, which was derived from large scale fire tests on railway cars. The behavior of structural tunnel elements exposed to fire and mechanical loads have been investigated in several research programs during the last years. In this paper, the results of an extensive research program investigating the fire behavior of two concrete mixtures four small- and two large-scale tests are presented. The small-scale tests prior to the main tests were conducted to determine an appropriate concrete mixture for the large-scale tests. For those tests, real-scale tunnel segments representing a design-relevant sector of an existing railway tunnel were used. During the large-scale tests, the tunnel segment is loaded with horizontal and vertical loads derived from a calculation taking into account the ground pressure, water pressure and dead loads corresponding to the situation of the existing railway tunnel. Additionally, the resulting restraint forces were calculated using the soil stiffness and the EBA tunnel fire curve as fire scenario and induced via hydraulic jacks (force controlled). In order to avoid additional restraint forces during the experiment, thermal strains due to fire exposure were allowed by the statically determined boundary conditions. [ABSTRACT FROM AUTHOR]

Experimental and numerical investigations of fire scenarios in front of façades considering various distances Constructional boundary conditions, e. g. walls or façades, close to ignition sources affect the fire formation and the plume. It is already known, that boundaries (e. g. walls) constrain the entrainment of air and oxygen into the plume and the combustion of gas or flammable products is completed at larger heights. How far the location of the fire sources, the building geometry and the heat release rate affect the characteristics of a flame is investigated at the Institut für Baustoffe, Massivbau und Brandschutz (iBMB) of TU Braunschweig in line with a series of experiments with a square gas burner. For the implementation of the fire tests the test rig in Braunschweig is provided with extensive measurement techniques to determine heat flux, wall-bounded temperatures, temperatures for plume measurements and upward velocity. In this paper the data of the fire tests are discussed and compared with the results of a CFD-Model and selected empirical calculation approaches. [ABSTRACT FROM AUTHOR]

The European requirements for fire safety design and testing of structural masonry members are already the governing requirements in many cases. In principle, both the European and the German classification may be used according to the Bauregelliste. However, the latter may only be used when European classification of a member or construction material is not possible because the appropriate European standards do not exist. The European standards do not differ fundamentally from the German standard DIN 4102-2. One significant difference is that according to the DIN 4102-2, it was required to carry out two tests with the most unfavourable result governing, while according to the European standard, only one test is required. According to the EN Standard, the tests for fire resistance and the reaction to fire are carried out separately. There are other differences related to the pressure in the furnace as well as the use of plate thermocouples instead of jacketed thermocouples. Fire safety design of masonry is carried out in accordance with EC 6-1-2 and the National Annex. Only the members not regulated in the EC 6-1-2, e.g. pre-cast masonry members, non-load-bearing walls, lintels, connections and joints, should be designed and checked according to the revised DIN 4102-4. [ABSTRACT FROM AUTHOR]

Im Hinblick auf die Brandsicherheit zukünftiger Gebäude stehen neue Bauweisen aus digital gefertigten Bauteilen und aus nachwachsenden Rohstoffen, aber auch neue Produkte, die in die Gebäude eingebracht werden, wie Energiespeicher und Elektrofahrzeuge, im Fokus. Digitalisierung, Klimawandel, Ressourceneffizienz im Bauwesen - wie kann die Stadt der Zukunft brandsicher gebaut werden? Im vorliegenden Heft wird eine Vielzahl von Themen, die für die Brandsicherheit der Stadt der Zukunft von Bedeutung sind, präsentiert. [Extracted from the article]

Die außergewöhnliche Bemessungssituation Brand als Lasteinwirkung auf Bauteile und Tragwerke ist in DIN EN 1991‐1‐2:2010‐12, Eurocode 1: Einwirkungen auf Tragwerke – Teil 1‐2: Allgemeine Einwirkungen – Brandeinwirkungen auf Tragwerke geregelt. Im zugehörigen Nationalen Anhang DIN EN 1991‐1‐2/NA werden die national festzulegenden Parameter bzw. nationale Festlegungen sowie die Anwendung informativer Anhänge für Deutschland definiert. Neben der Einheits‐Temperaturzeitkurve (ETK) als standardisierte thermische Einwirkung werden in DIN EN 1991‐1‐2 und zugehörigem Nationalen Anhang auch Naturbrandmodelle geregelt, mit denen die thermischen Einwirkungen leistungsorientiert in Abhängigkeit der vorhandenen Brandlasten, Ventilationsverhältnisse, Brandraumgeometrie und thermischen Eigenschaften der Umfassungsbauteile berechnet werden können. In der Musterliste der Technischen Baubestimmungen von März 2014 werden Randbedingungen für die Anwendung der Naturbrandverfahren beschrieben. Im Rahmen dieses Aufsatzes werden die zur Ermittlung der thermischen Einwirkung mit Naturbrandmodellen zugrunde zu legenden Brandszenarien und Bemessungsbrände dargestellt und auf deren Eignung und sinnvollen Anwendungsbereich eingegangen. Thermal actions of components and structures exposed to natural fires The exceptional case of fire load on construction parts and structures as action for building components is regulated by DIN EN 1991‐1‐2: 2010‐12, Eurocode 1: Actions on structures – Part 1‐2: General actions – fire actions on structures. In the National Annex DIN EN 1991‐1‐2/NA the national determined parameters and national requirements as well as the application of informative annex for Germany are defined. The DIN EN 1991‐1‐2 and the associated National Annex regulate the standard temperature‐time curve (ETK) as standardized thermal load and furthermore natural fire models which can be used for performance based fires safety design considering the actual fire loads, ventilation conditions, geometry of fire room and thermal properties of the structural components. In the Musterliste der Technischen Baubestimmungen of March 2014 boundary conditions are described for the application of natural fire method. This paper shows fire scenarios and design fires for determination of the thermal load with natural fire models and their suitability and practicable application. [ABSTRACT FROM AUTHOR]

Aufgrund gestiegener ästhetischer Anforderungen an Gebäudetragwerke werden vermehrt sehr schlanke Bauteile eingesetzt, wobei die fortschreitende Forschung und Entwicklung in der Betontechnologie es ermöglicht, diese Bauteile auch aus ultrahochfestem Beton (UHPC) auszuführen. Verglichen mit Normalbeton führen die hohen Packungsdichten von UHPC sowie die Zugabe von Stahlfasern zu einer sehr hohen Druckfestigkeit bei gleichzeitig duktilem Verhalten. Aus brandschutztechnischer Sicht ergeben sich aus den Materialeigenschaften und den schlanken Bauteilen allerdings grundsätzliche Nachteile. Eine hohe Packungsdichte führt bei der Verdampfung des physikalisch gebundenen Wassers zu hohen Dampfdrücken und Betonabplatzungen, welche entweder die Bewehrung freilegen oder auch das komplette Bauteil zerstören können. Das für den Brandfall ungünstige Verhältnis von Oberflächen‐ zu Volumen schlanker Bauteile führt außerdem zu einem schnelleren Durchwärmen und somit zu schnellerem Verlust der Tragfähigkeit. Im Rahmen des Forschungsprojekts “Theoretische und experimentelle Untersuchungen zur Ermittlung und Optimierung des Brandverhaltens von ultrahochfestem Beton” des Schwerpunktprogramms 1182 der Deutschen Forschungsgemeinschaft wurden zwei repräsentative UHPC‐Rezepturen entwickelt, welche durch betontechnologische Maßnahmen und die Beigabe von Polypropylenfasern hinsichtlich des Abplatzens ertüchtigt wurden. Außerdem wurden Untersuchungen zur Bestimmung der thermischen und mechanischen Materialeigenschaften durchgeführt. Als Validierungsgrundlage wurden abschließend vier Stützenversuche durchgeführt. In diesem Beitrag wird die numerische Modellierung des Tragverhaltens von brandbeanspruchten UHPC‐Stützen mithilfe eines Finite‐Elemente‐Modells gezeigt und anhand der Versuchsergebnisse validiert. Numerical analysis of fire exposed ultra‐high performance concrete (UHPC) columns Due to higher aesthetical requirements for the load bearing structure, an increasing amount of slender components is used. The ongoing research and development in concrete technology yields to the possibility to process this slender components out of ultra‐high performance concrete (UHPC). Compared to normal strength concrete, the high packing density and the addition of steel fibres leads to a high compressive strength and ductile behavior. In case of fire protection, these material properties and slender dimensions are disadvantageous, because the high packing density leads to high pore pressure and concrete spalling when the remaining water content is evaporating. The higher surface to volume ratio of slender components additionally leads to higher temperatures and reduced load bearing capacity in case of fire. During the research project “Theoretical and experimental determination of the high temperature behavior of ultra high performance concrete (UHPC)” of the priority program 1182, funded by the Deutsche Forschungsgemeinschaft, two general UHPC mixtures were developed. The prevention of explosive spalling was achived by adding polypropylen fibres. Furthermore, the thermal and mechanical material propertiers were assessed in small‐scale experiments. To validate the material properties and check the model capabilities, four large‐scale experiments were conducted assessing the load bearing capacity of UHPC columns exposed to fire. In this paper, the numerical modelling of the structural behavior of fire‐exposed UHPC‐columns with finite element method is depicted. The model is compared with the experimental results. [ABSTRACT FROM AUTHOR]

Das Baustoffverhalten von Beton im Hochtemperaturbereich q ≤ 1200 °C wird i. A. mit Hilfe stationärer Druck- und instationärer Kriechversuche untersucht. Die unterschiedliche Versuchsdurchführung wird detailliert in den RILEM-Empfehlungen beschrieben. Die experimentellen Ergebnisse werden anschließend in Form von temperaturabhängigen Spannungs-Dehnungslinien aufbereitet, die die Grundlage für die numerische Berechnung des Trag- und Verformungsverhaltens von brandbeanspruchten Bauteilen darstellen. Bei deren Anwendung müssen die Randbedingungen beachtet werden, wie z. B. die Aufheizgeschwindigkeit. Bereits früher wurde am Beispiel von Normalbeton gezeigt, wie aus den experimentellen Ergebnissen vereinfachte temperaturabhängige Spannungs-Dehnungslinien ermittelt werden. In diesem Beitrag wird das Vorgehen auf ultrahochfesten Beton angewendet. Die theoretischen Überlegungen und die Ableitung baustoffspezifischer Materialkennwerte werden beispielhaft an der Betonrezeptur B5Q durchgeführt. Developing simplified materials laws in the form of temperature-dependent stress-strain relations for ultra high performance concrete. The behaviour of concrete as a building material at temperatures in the region of q ≤ 1200 °C is normally investigated using steady state and transient creep tests. The various experimental methods are described in detail in the RILEM recommendations. The results of the experiments are then displayed in the form of temperature-dependent stress-strain diagrams. These diagrams represent the basis for the numerical calculation of the load-bearing and deformation behaviour of components exposed to fire. When such diagrams are used, the boundary conditions must also be considered, such as the heating rate. The example of normal concrete has already been used to show how simplified temperature-dependent stress-strain diagrams may be derived from experimental findings. The present paper applies the same procedure to ultra high performance concrete. As an example, the theoretical considerations and the derivation of building material-specific parameters are applied to one concrete mix composition. [ABSTRACT FROM AUTHOR]

In the fire safety part of Eurocode 2, material properties for conventional concrete (CC) up to a strength class of C 50/60 and high performance concrete (HPC) of strength classes C 55/67 to C 90/105 are provided. These given values were derived from experimental investigations of heated components based on the thermal exposure of the ISO 834 standard fire. Ultra-high performance concrete (UHPC) has not been standardized yet. While the ISO 834 standard fire is only characterized by a heating phase, a natural fire consists of a heating and a cooling phase. In this paper, the investigation of the thermal and thermo-mechanical material properties of UHPC, considering natural fires, is presented. The thermal properties, including the heat conductivity, the specific heat capacity and the temperature-dependent density as well as the mechanical properties like the temperature dependent stress-strain-relation were experimentally determined. In addition for validation purpose, real-scale experiments on columns were carried out. [ABSTRACT FROM AUTHOR]

Fire risk analysis of electric vehicles and internal combustion vehicles in open car parks: part 2: fire safety and reliability analysis In order to counteract climate change, it is necessary to switch from vehicles with combustion engines to electric vehicles. Consequently, an increasing number of electric vehicles can be observed in Germany. In this context, the question arises whether and if how this development influences the fire risks in open car parks. Answers to this question are the subject of a research project under the leadership of the Institute of Steel Construction of Leibniz University Hannover in cooperation with the iBMB, Division of Fire Safety, of TU Braunschweig. In particular, the project is investigating the influence of a fire scenarios with electric vehicles compared to vehicles with combustion engines on the load‐bearing behaviour structure of an open car park. In this paper, the methodological approach to evaluate the fire risk based on a reliability analysis for the load‐bearing structure of these car parks is explained. By means of the reliability analysis, the fire risk assessment procedure is illustrated for the composite beam using exemplary fire scenarios. As a result, it can be concluded from the fire risk analysis that fire scenarios with electric vehicles do not have a higher fire risk than conventional vehicles with combustion engines and fulfil the required safety level. [ABSTRACT FROM AUTHOR]

Concrete-filled hollow section (CFHS) columns with a solid steel core have gained popularity in the construction of tall buildings due to their robust load-bearing capacity, slender design, ease of prefabrication, and exceptional structural fire resistance. In this research paper, we introduce an innovative approach aimed at enhancing the structural performance of these columns. Our method involves replacing the solid steel core with high-strength bar bundles and substituting concrete with grout to achieve superior fire resistance. These modified columns are referred to as “bar-bundle columns.” The paper presents the results of extensive fire tests conducted on three bar-bundle columns, each with different bar-bundle sizes, quantities, and configurations. Additionally, we determine the temperature-dependent material properties of the high-strength steel used for reinforcing bars and the thermal properties of the grout used as a filler through standard experimental tests, which are crucial for numerical simulations. An advanced nonlinear finite element model is describe which is capable of predicting the fire behavior of bar-bundle columns. Finally, this numerical model is employed to conduct parametric analyses and propose a simplified design model for bar-bundle columns under fire conditions.Our findings indicate that the bar-bundle configuration and using grout as a filler significantly delays the heating of the steel core, resulting in enhanced fire resistance when compared to CFHS columns with a solid steel core. The simplified method proposed in this study can be used to estimate the fire resistance of slender bar bundles, but further experimental testing could further refine and improve its accuracy. [ABSTRACT FROM AUTHOR]

Fire performance of insulating materials made from renewable resources – Part 2: Investigations on the use as compartment filling in timber panel constructions In the previous article on the research project "more than just insulation – additional benefits of insulating materials made from renewable resources", the experimental investigations on the initiation, process and extinguishing behavior of smoldering processes, the effect of flame retardants and the emissions released in the combustion process were presented. In this paper, the investigations on the structural use of renewable insulation materials, instead of the previously required non‐combustible insulation, is presented in the context of wood panel construction. First, the final large‐scale fire test on the natural fire behavior of wood panel building components with renewable insulation materials is presented. Then, the development of analytical and numerical models for the separating function is illustrated. The paper concludes with an outlook on the research project "PyroProBiD", in which advanced transport and reaction models are being developed. [ABSTRACT FROM AUTHOR]

Background and basics for the application of fire protective coverings in timber construction This article summarises the current knowledge in the application of fire protective coverings for timber constructions. The different types of fire protective coverings, their definitions in standards and building codes and their performance requirements are discussed and the associated differences are compared. From the discussion of the backgrounds, an expanded view of the criteria to be verified for fire protective coverings for timber members is developed, which enables an optimised and resource‐saving application while maintaining the requested safety level in fire protection. [ABSTRACT FROM AUTHOR]

The use of partial connection theory for composite beams at ambient temperatures is state of the art according to Eurocode 4 (EN 1994-1-1 2009), hereby the number of shear connectors can be reduced up to a minimum degree of shear connection. When designing for fire resistance, the partial shear connection theory is, however, not directly applicable in accordance to Eurocode 4—Part 1-2 (EN 1994-1-2 2008). Due to the different behaviour of steel and concrete components at elevated temperatures, high residual stresses are to be expected in the composite beam. In certain situations, the effect of these stresses on the composite joint may lead to a slip of the composite joint higher than the minimum ductility of the headed stud shear connectors given in the Eurocode 4 (EN 1994-1-1 2009). This paper shows how the usage of partial connection theory affects the load carrying capacity of a composite beam in the event of fire. A series of four large-scale fire tests was conducted to investigate various effects of a reduced degree of shear connection on the deflection behaviour and the composite joint. The experimental setup will be described, as well as the 9.0 m composite beams and test sequence. Furthermore, the deflection and temperature measurements as well as the given boundary conditions will be explained. The presented results of one fire test provide an initial conclusion about the deflection behaviour of the composite girder with a reduced degree of shear connectors as well as the behaviour of the composite joint at elevated temperatures. Due to the transient thermal conditions in the composite section and the following variation of the reduction of the yield stresses in the components of a composite section, a rising degree of shear connection has to be expected with rising temperature. Furthermore, three major effects on the slip caused by rising temperature on the composite joint will be presented. [ABSTRACT FROM AUTHOR]

Structural behaviour of high‐strength composite columns and material behaviour in case of fire Concrete‐filled steel tubular composite columns are increasingly used in enineering practice, as they provide competitive solutions, for buildings with high demands on the load‐bearing capacity and cross‐sectional dimensions. Additionally, composite columns are characterised by high fire resistances. The use of high‐strength materials for composite columns also facilitates the realisation of more sustainable, efficient and economical steel‐concrete composite structures and thus to maintain the long term competitiveness of steel and composite structures. The use of high‐ and ultra‐high‐strength materials for composite columns is currently still limited by the application range of Eurocode 4. The research projects of the HOCHFEST, which are strongly supported by the research association FOSTA, address exactly this limitation and are presented in this issue of Stahlbau. The HOCHFEST research network comprises a total of 15 research projects, which investigate the multiple application potential of high‐strength steels. The research projects P 1287, P 1349, P 1500, P 1501 and P 1502 address the load‐bearing behaviour of high‐performance composite columns and the material behavior of high‐strength steel at ambient temperature as well as in case of fire and under earthquake conditions. The findings of the research projects therefore are essential for the future development of design methods for high‐performance composite columns. [ABSTRACT FROM AUTHOR]

Bar bundle columns with high‐strength reinforcing steel As part of the AiF project "Bar bundle columns with high‐strength reinforcement steel" the load‐bearing behavior of bar bundle columns in cold and fire conditions was investigated. Bar bundle columns are a new type of composite columns. To this purpose, a bundle of high‐strength reinforcing bars with a yield strength of 670 MPa is placed in a steel tube and then grouted with mortar. The bundle can consist of 1, 3, 7 or 19 bars. To analyze the load‐bearing behavior, relevant material parameters were determined in cold and in fire conditions. Subsequently, large‐scale buckling tests were carried out under room temperature and in fire case. Considering the obtained results, an FE model was created and calibrated. On this basis, a design concept was developed. [ABSTRACT FROM AUTHOR]

Experimental investigations on novel composite columns with a concrete filled hollow section and high‐strength steel plates as core in ambient and fire conditions High‐performance composite columns are commonly carried out with solid steel sections as core profiles. These profiles imply limitations due to reductions of the yield strength depending on the thickness and high residual stresses. In this publication, the authors present a novel section consisting of a concrete filled circular hollow section with locally connected steel plates as core. To increase the load bearing capacity, steels with yields strengths up to 960 N/mm2 are used. Experimental investigations for ambient conditions and in case of fire are presented. The columns showed a promising load bearing behaviour. These investigations will serve as basis for a systematic development of this innovative, high‐performance composite column with a corresponding design concept. [ABSTRACT FROM AUTHOR]

Universal high‐performance columns made of high‐strength steels without welding In recent years, steel‐concrete composite columns made of normal‐strength steels are seldom used owing to the economic and technological advantages of precast reinforced concrete columns. Though, the use of high‐strength structural steels bears high potential for the efficient production of composite columns with excellent structural performance that are economically competitive to precast concrete columns, there are currently major obstacles to use of the ultra‐high‐strength steels (UHSS) in Germany. Hollow section composite columns with embedded high strength steel core without welded connections provide an opportunity to regain lost market share. A research project, funded by the AiF (Arbeitsgemeinschaft industrieller Forschungsvereinigungen), is intended to explore the potential of UHSS composite columns by experimental and theoretical investigations. The present paper demonstrates the concept of such composite columns with UHSS and gives first exciting insights into the research results. In addition to column tests under ambient and fire conditions, small scale tests are necessary to investigate various influencing factors and to create the basis for new and easy to use design and construction principles that allow efficient application. [ABSTRACT FROM AUTHOR]

Fire performance of insulating materials made from renewable resources – Part 1: Experimental investigations of smouldering processes and emissions In the research project "more than just insulation – additional benefits of insulating materials made from renewable resources", several sub‐projects investigated the moisture protection, thermal protection, noise insulation and fire protection as well as the sustainability and emission effect of insulating materials made from renewable resources. The primary goal of the research network was to significantly increase the applicability of renewable insulating materials and to eliminate obstacles to their use. In the field of fire protection behavior, the smoldering and burning of renewable insulation materials was analyzed and application limits defined in the context of multi‐storey buildings. The presented article deals with the experimental investigations on initiation, process and extinguishing behavior of smoldering, the effect of flame retardants and the emissions released in the combustion process. In the following article, the structural use of renewable insulation materials, instead of the previously required non‐combustible insulation, is presented in the context of wood panel construction. [ABSTRACT FROM AUTHOR]

TIMpuls basic research on fire protection in timber construction: charring rate, protection times of claddings and post‐burning behaviour of timberThis paper presents excerpts from first results and experiments within the TIMpuls research project on charring rate of timber, the performance of fire protection claddings and the post‐burning and extinguishing behaviour of timber components. By means of small‐scale tests, charring rates for various types of timber under standard fire exposure were determined. The investigations of the performance of fire protection systems comprise the state of the art in application and the classification criteria. Based on this, an explanation of the small‐scale test setup and the experimental test results is given. Based on the test results an evaluation of the performance of the fire protection claddings is presented. Furthermore the behavior of timber structures in the decay phase of a fire is investigated. Here, boundary conditions for achieving self‐extinguishing in a fire compartment, experiences with the extinguishing process and constructive measures to avoid cavity fires are discussed. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a probabilistic methodology based on the thermo-mechanical finite elements analysis to investigate the impact of the variability of the thermal properties of the concrete in the fire safety of structures. This is meant to evaluate if characteristic values or safety factors for the conductivity and specific heat are required during the semi-probabilistic structural fire safety assessment. To illustrate the use of the proposed methodology, this work includes a case-study with a tunnel lining which considers the uncertainties related to the thermal and mechanical properties of the concrete, the soil load, and the temperatures described by the standard temperature-time curve. Two failure criteria are considered: one was the maximum temperature of 300 °C at the reinforcement and the other based on the temperature-dependent strength as provided in the Eurocode EN 1992-1-2. Several finite element analyses are performed. The design of experiments is executed by a Correlation Latin Hypercube Sampling. The calculated probability of failure has different values depending on the adopted failure criteria. A sensitivity analysis using the Spearman's rank correlation coefficient was carried out and demonstrates that the uncertainty related to the specific heat has the greatest impact on the results. [ABSTRACT FROM AUTHOR]

Minimum degree of shear connection of composite beams in fire In the scope of the research project „Mindestverdübelung von Verbundträgern bei Brand" (Minimum degree of shear connection of composite beams in fire) numerical and experimental investigations were conducted to derive design rules and limitations for the use for the partial connection theory in fire. In this paper, the conducted investigations as well as the most important influences of the elevated temperatures on the composite beam and especially on the composite joint are presented. The slip in the composite joint and its reasons are discussed for a single span beam in a fire situation. It is shown that with the use of a minimum degree of shear connection for the limitation of the maximum slip of the composite joint, there is no influence of the degree of shear connection on the load carrying capacity of a composite beam in case of fire. Due to the quickly rising temperatures of a composite beam in fire, the resistance of the composite joint quickly exceeds the tensile resistance of the steel section. The derived design rules for a safe use of the partial connection theory in fire situations based on the degree of shear connection as well as on the relation between the concrete tensile capacity and the shear capacity of the composite joint are presented. [ABSTRACT FROM AUTHOR]

Structures may collapse during the cooling phase of a fire, yet standard furnace tests only measure the response under heating. There lacks experimental test protocols and design methods to assess resistance until burnout. This paper describes a new experimental approach for burnout resistance evaluation, reports experimental data on loaded reinforced concrete columns in furnace tests with cooling down phases, and presents numerical models of the tests. The test results show that columns designed for a standard fire resistance of 60 min exhibited a fire resistance of 83 min in the furnace but failed during the cooling phase when the burners were shut off after 72 min while the load was maintained. Two other specimens survived exposure to heating of 45 and 55 min, respectively, and their residual capacity was measured. Finite element analyses show agreement with the tests, showing applicability of numerical methods for evaluating burnout resistance of concrete columns. These findings demonstrate experimentally that delayed thermal-mechanical effects can jeopardize structural stability in real fires, and provide a framework to measure these effects. Moving beyond fire resistance to quantify the response until burnout will support designs for safety of occupants and firefighters throughout the fire and promote repairability and resilience. [ABSTRACT FROM AUTHOR]