48 research outputs found

    EXPERIMENTAL AND NUMERICAL ANALYSIS OF ULTRA HIGH PERFORMANCE CONCRETE (UHPC) MEMBERS IN CASE OF FIRE

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    The research activity in progress and the advancements in concrete technology are leading to an increased use of high performance and ultra high performance concrete in structural engineering. Due to its high compressive strength and ductile behavior in combination with steel fibres, UHPC structural members can be designed as slender and light structures compared to standard concrete design. This increasingly leads to the option in architectural design to highlight the bearing capacity of the building without hiding the structural components.In case of fire safety design a disadvantageous behavior of UHPC compared to normal strength concrete is well known and documented. The high packing density of the cement matrix is the main reason for explosive spalling behavior when exposed to fire. To avoid spalling, an appropriate amount of polypropylene fibres has to be introduced in the concrete mix design. In addition, slender and light structures are in general more sensitive to fire exposure due to the higher surface to volume ratio.In this paper, the analysis of the thermal and mechanical material properties using experimental and numerical methods is presented. The investigations were carried out during the priority program 1182 in the research project “Theoretical and experimental determination of the high temperature behavior of ultra high performance concrete (UHPC)”, funded by the German Research Foundation (DFG), see (Schmidt 2014) and (Hosser et al. 2014).In the project the thermal properties heat conductivity, specific heat capacity and the temperature dependent density as well as the mechanical properties like the temperature dependent stress-strain-relation and thermal expansion were experimentally determined. In addition, the optimum fibre content was determined. The findings of the project were used to develop a material model and checked against experimental results on fire exposed UHPC columns using a FE model

    Der TRPA1 Kanal als Zielstruktur bei der Zinkchlorid-Exposition in vitro

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    Design of multi-storey steel structures for realistic fire-exposure

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    Die Brandschutzanforderungen an Bauteile beziehen sich auf die Einheitstemperaturzeitkurve (ETK), die alle den Brand beeinflussenden Randbedingungen auf der sicheren Seite liegend abdecken soll. Durch diese pauschalisierende Bemessungsgrundlage sowie der Bemessung von aus dem Gesamttragwerk herausgelösten Einzelbauteilen resultieren teilweise überhöhte und undifferenzierte Anforderungen, die die Stahlbauweise im Vergleich zu massiven Bauweisen benachteiligen. Die Konsequenz daraus führt i. d. R. dazu, dass Stahlbauteile bekleidet werden müssen. In dieser Arbeit werden Verfahren vorgestellt, mit denen einerseits die thermische Einwirkungen realer Brände in mehrgeschossigen Gebäuden bei einer realistischen Brandentwicklung und andererseits die Tragreserven in Bauwerksystemen mehrgeschossigen Stahl-Verbundkonstruktionen unter Berücksichtigung von Lastumlagerungen von brandbeanspruchten zu nicht-brandbeanspruchten Tragwerksteilen in Ansatz gebracht werden können. Durch diese risikogerechte brandschutztechnische Beurteilung und Bemessung können übermäßige Anforderungen gesenkt und Kosten bei Brandschutzmaterialien wie z. B. Bekleidungen und dämmschichtbildenden Anstrichen eingespart werden. Auf der Grundlage eines definierten Bemessungsfeuers werden Temperaturzeitverläufe natürlicher Brände in Abhängigkeit der tatsächlich vorhandenen Randbedingungen ermittelt, mit vereinfachten Gleichungen in Form von sogenannten Realbrandkurven formuliert und nach verschiedenen Methoden validiert. Mit den Realbrandkurven lassen sich die thermischen Einwirkungen eines natürlichen Brandes in mehrgeschossigen Wohn- und Bürogebäuden für die Bauteilauslegung realistischer als mit der ETK erfassen, ohne auf die Anwendung relativ komplizierter Wärmebilanzmodelle angewiesen zu sein. Im Vergleich zu anderen vereinfachten Verfahren zur Bestimmung von Temperaturzeitverläufen in Wohn- und Bürogebäuden zeichnet die Realbrandkurven aus, dass sie auf einem international anerkannten Ansatz für die Energiefreisetzungsrate basieren und die vorhandenen Ventilationsverhältnisse sowie ggf. auch Änderungen der Randbedingungen (Glasbruch, Wanddurchbruch, Zellenbauweise, Eingriff der Feuerwehr) berücksichtigen können. Für die Durchführung von Tragwerksanalysen im Brandfall wird ein Rechenmodell beschrieben, mit dem das Trag- und Verformungsverhalten von Gesamttragwerken mit Bauteilen aus Stahl und Beton mittels FE-Analyse simuliert werden kann. Das Rechenmodell wird durch Nachrechnung von Brandversuchen an Bauteilen und Teiltragwerken validiert. Auf der Basis der numerischen Berechnungen wird aufgezeigt, wie Bauwerksysteme in Stahl-Verbundbauweise aus der Sicht des Brandschutzes optimiert werden können. Durch Optimierung der Träger/Stützenverbindungen können die im Brandfall auftretenden Zwangkräfte in den Stahlträgern und Anschlüssen reduziert werden. Aufgrund von Parameterstudien für verschiedene Brandszenarien werden Randbedingungen formuliert, unter denen die Ausführung ungeschützter Stahlbauteile in einem Gesamttragwerk möglich ist. Bei der Brandschadensanierung bieten Bauwerksysteme mit momentfreien Stahlbauanschlüssen sowie aufliegenden Beton-Fertigteilelementen große Vorteile. Aufgrund des modulartigem Aufbau des Tragwerks können Stahlträger und Deckenplatten im geschädigten Bereich entfernt werden, ohne dass das Resttragwerk in seiner Standsicherheit gefährdet wird.The current basis of requirements regarding fire-protection in building codes in Germany and most other countries of the world is the ISO 834 temperature-time curve. It is supposed to cover all boundary conditions concerning fire load, ventilation and construction on the safe side. Because of this simplified design basis and the design of single components isolated of the overall structure, excessive requirements may partially result. These requirements can lead to a disadvantage of the steel construction compared to solid constructions. Consequently, steel structures usually have to be protected. A fire safety design that considers the actual boundary conditions has to take into account the load-bearing and deformation behaviour of structural elements embedded in the entire structure. In this dissertation a method is presented that can be used to describe the thermal action of natural fires in multi-storey buildings considering a realistic fire spread. It is shown how the load carrying capacity of multi-storey steel-composite structures can be utilised considering the load redistribution of fire-exposed parts of the structure to non fire-exposed parts. As a result of a so-called risk-oriented fire safety design method, excessive requirements and costs of fire protection materials can be reduced. On the basis of a defined design fire temperature-time curves of natural fires are determined by heat balance simulations and formulated in simplified equations as so-called real fire curves. The real fire curves are validated by comparison calculations as well as experimental data. In contrast to the ISO 834 temperature-time curve the thermal action of a fire in multi- storey residential and office buildings can be grasped realistically by the real fire curves. The real fire curves enable a simplified method to ascertain the thermal exposures of a natural fire to the structure without applying sophisticated heat balance models. In comparison to existing simplified methods for calculating the temperature-time-curve of a natural fire, the real fire curves offer a lot of advantages: They are based on an internationally accepted approach of the rate of heat release, they consider the actual ventilation conditions and the modification of the boundary conditions (breakage of glass, compartmentation failure, cell construction, fire fighting) as well. By numeric simulations on the basis of a validated computer model it is shown, how steel and composite structural systems can be optimised to reduce the forces caused by the axial and flexural restraint in case of a fire. For different fire scenarios the load and deformation behaviour of a module-like building system is investigated. It is shown that unprotected steel members can be used if they are embedded in an overall structure and some rules of structural detailing are observed. Therefor a realistic development of the fire considering a successive fire spread has to be taken into account. For structural restoration and repair after a fire building systems with pinned steel connections and prefabricated floor slabs offer advantages. Due to the module-like assembly of the structure steel girders and floor slabs in the affected area can be removed without endangering the stability of the rest of the structure

    Thermal Behavior of Adhesively Bonded Timber-Concrete Composite Slabs Subjected to Standard Fire Exposure

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    peer reviewedFire tests were performed for the first time on adhesively bonded timber-concrete composite slabs. The two medium-scale (1.8 x 1.25 m) slabs were produced by gluing an 80-mm thick three-layer cross-laminated timber (CLT) board to a 50 mm thick prefabricated reinforced concrete (RC) slab with epoxy and polyurethane (PUR) adhesives, respectively. The behavior of the composite slabs under elevated temperature was monitored by (1) observing the burning behavior of the used CLT, for example, charring and delamination and (2) measuring the temperature development at different locations of the CLT slabs, in the adhesive bond between concrete and timber boards, and in RC slabs. It was found that employing a one-dimensional charring model for pure softwood, as prescribed by Eurocode 5-1-2, underestimated the charring depth of CLT due to the delamination effects. Measurements revealed that the average charring rates in the middle layer of CLT panels were approximately 0.65 mm/min, suggesting that the presence of concrete does not significantly affect the thermal behavior of the CLT panel. Delamination within the CLT was observed when its adhesive temperature was around 230°C. It was followed by the free-fall of delaminated wood plies, which progressed slowly and lasted until the end of the test. At 90 min into the test, the temperatures of epoxy at the nine locations ranged between 55°C and 130°C, while that of PUR between 60°C and 100°C. The adhesive between concrete and CLT could lose stiffness significantly along the rising of temperature after surpassing of glass transition temperature (58°C for epoxy and 23°C for PUR in this study). The results indicated a high risk of weakening the composite action between the concrete slab and timber board. The measured temperatures of steel rebar were lower than 50°C. However, the concrete temperature reached about 120°C and the concrete cracked due to the distinct thermal expansions between concrete and timber and the rigid constraint of adhesive bond.11. Sustainable cities and communitie

    Essais de colonnes en BLC sous feux naturels incluant la phase de refroidissement

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    peer reviewedThis paper presents the data and the results of seven fire tests performed on glue laminated timber columns in a compartment built especially for the tests and in which timber wood cribs created a so-called natural fire. These tests are part of a research programme titled “burnout resistance” to establish a new methodology to better describe performance of structural elements during the whole duration of a fire. Comparisons with similar tests made in a fire resistance furnace allow comparing charring rates observed in standard conditions and in natural fires

    Naturkunde

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    Naturkunde

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