Markus Knobloch

Fire Design of Timber-Concrete Composite Slabs with Screwed Connections

The structural behavior of timber-concrete composite slabs is mainly governed by the shear connection between timber and concrete. When a timber-concrete composite structure is exposed to fire, it is of particular importance to know the changes in stiffness and strength that the shear connection is subjected to. For the calculation of the fire resistance of timber-concrete composite slabs a simplified design method was developed on the basis of the calculation model for mechanically jointed beams with flexible elastic connection given in EN 1995-1-1 and the reduced cross section method given in EN 1995-1-2. The effects of temperature on the mechanical properties of timber, concrete, and connection are taken into account by modification factors kmod,fi . For the strength and stiffness properties of the screwed connections simplified formulae for the calculation of the modification factors kmod,fi were developed, based on the results of an extensive experimental study on the fire behavior of the screwed con...

Fire behaviour of cross-laminated solid timber panels

Cross-laminated solid timber panels represent an interesting technical and economical product for modern timber structures. The use of large prefabricated cross-laminated solid timber panels for load-bearing wall and floor assemblies has become increasingly popular in particular for residential timber buildings. The fire behaviour of cross-laminated solid timber panels has been experimentally and numerically studied during two different ongoing research projects carried out at the Institute of Structural Engineering of ETH Zurich, Switzerland and the Trees and Timber Institute CNR-IVALSA in Trento, Italy. The paper presents the main results of the experimental and numerical analyses. Particular attention is given to the comparison of the fire behaviour of cross-laminated solid timber panels with homogeneous timber panels. The results of the analysis have shown that the fire behaviour of cross-laminated solid timber panels depends on the behaviour of the single layers. If the charred layers fall off, an increased charring rate needs to be taken into account. The same effect is observed for initially protected timber members after the fire protection has fallen off. Thus the fire behaviour of cross-laminated solid timber panels can be strongly influenced by the thickness and the number of layers. Further vertical structural members (walls) may show a better fire behaviour in comparison to horizontal members (slabs).

Numerical Analysis and Comparative Study of the Cross-Sectional Capacity of Structural Steel Members in Fire

The cross-sectional capacity of steel sections subjected to fire is strongly affected by the decreasing stiffness during heating and the nonlinear stress-strain relationship of steel at elevated temperatures. This paper analyses the cross-sectional capacity of common steel sections subjected to combined axial compression and biaxial bending moments at both ambient and elevated temperatures considering section yielding and local buckling effects. The results of a parametric study using the finite element approach are presented as temperature-dependent normalized N-M interaction curves and are compared to results using elastic and plastic interaction formulae. A comparative study shows that European fire design models may lead to conservative results for semi-compact and slender cross sections (class 3 and 4 sections) due to the partial plastic capacity of these sections. However, for steel members predominately subjected to axial compression the design models may lead to unconservative results due to local buckling deflections that occur even for plastic and compact sections (class 1 and 2).

ISO Standard Fire Tests of Concrete-Filled Steel Tube Columns with Solid Steel Core

AbstractConcrete-filled steel tube columns with solid steel core are prefabricated innovative composite columns that are especially designed to achieve high fire resistance, even with high slendern...

Fire Design Concepts for Tall Timber Buildings

Based on the current knowledge in the area of fire design of timber structures this paper presents a generic fire safety concept for tall timber buildings. The first part of the paper gives an overview of fire action and fire safety concepts and presents the main differences between medium-rise and tall buildings with regard to fire safety. The analysis enables the formulation of a generic fire safety concept for tall timber buildings. In the second part of the paper some experimental results on the fire performance of timber structures under natural fire conditions relevant for tall timber buildings are presented.

Local buckling behavior of steel sections subjected to fire

The local buckling behavior of steel sections subjected to fire is strongly affected by the nonlinear stressstrain relationship of steel at elevated temperatures, non-uniform temperature distributions as well as thermal strains and stresses. This paper proposes a strain-based calculation model found to be particularly suitable for analyzing the load-carrying behavior of steel members subjected to local buckling and fire. This model uses strain-based capacity curves – based on a plastic mechanism and results of a comprehensive numerical parametric study – for calculating the load-shortening behavior of stiffened and unstiffened elements (internal compression parts and outstand flanges) under fire conditions. Additionally, the model takes into account thermal strains and stresses during heating in fire as well as uniform and nonuniform temperature distributions. Strain-based models avoid classification of cross-sections and consider local buckling even for compact cross-sections. The strain-based calculation model accords well with results obtained from a parametric study using the finite element approach.

Load-carrying Behavior Of Unstiffened Elements At Elevated Temperatures In Fire

Unstiffened elements affect markedly the resistance of commonly used open steel sections under fire conditions. The distinct non-linear material behavior of steel at elevated temperatures requires large strains to activate the increase of cross-sectional capacity due to plastification. The yield line theory in conjunction with temperaturedependent second order elastic theory including equivalent geometric imperfections has been used to describe the load-carrying behavior of unstiffened elements in compression and bending at elevated temperatures in fire. Using both theories, the complete loadcarrying behavior in the pre- and post-buckling range can be analyzed. In addition, the results obtained from these analytical solutions were compared to numerical results using a geometrical and physical non-linear finite element approach.

Structural Fire Engineering: Introduction

Connections are critical structural elements of building frames, and in a fire are subject to forces very different from those at the ambient temperature for which they are designed. The fracture of a connection can cause the collapse of the connected beam, which may lead to a progressive collapse sequence affecting the entire building. This paper overviews the sequence of research on connection behaviour in a fire at the University of Sheffield. Early work focused on studying connections in terms of their moment–rotation behaviour alone. Concurrent full-scale building fire tests led to the realization that the tying capacity of connections is of prime importance for maintaining the structural stability in a fire. For wholestructure numerical modelling in performance-based fire engineering design, the development of the component-based approach, which was initially introduced for ambient temperature connection design, is an appropriate way to rationalize and model connection behaviour under these complex loadings. The effect of high co-existent rotation on the tying capacity of connections has been studied in furnace tests at various temperatures, which have provided data to assist in the characterization of the component-based model. A general component-based connection element, into which appropriate component models can be inserted, has been developed so that full connection performance, including fracture of components, can be integrated into global non-linear structural fire analysis. This will allow buildings to be modelled for a range of fire scenarios so that they can be designed to avoid progressive collapse in a fire.

Composite Slab with Integrated Installation Floor Using Cellular Beams

The paper presents a new composite floor system using cellular beams. A major benefit of the novel system is the integrated installation floor, adding additional value to the floor without extra costs. The system is based on half cellular beams made of existing hot-rolled sections. The openings in the cellular beams allow placing all kind of installations in all directions, thus providing excellent flexibility to the user when changing installations. First the paper presents the general design and details of the construction of the novel floor system. Then the paper experimentally analyses the load-carrying and dynamic behaviour of two floor elements with a span of 7.2 m. The results are compared to common calculation models for composite slabs.

Umbau Dock B am Flughafen Zürich

Grossmassstabliche Versuche an Blechverbunddecken (Holorib 51) wurden vom Institut fur Baustatik und Konstruktion (IBK) der ETH Zurich im Zuge der Umbaumassnahmen am Dock B am Flughafen Zurich durchgefuhrt. Das Flughafendock B wurde 1974 mit einem Tragwerk aus Stahlrahmen und Blechverbunddecken erstellt. Nach 35 Jahren Nutzung wurde es im Sommer 2009 im Zuge des Beitritts der Schweiz zum Schengen Raum um- und teilweise ruckgebaut. Das Tragwerk besteht aus einer Stahlrahmenkonstruktion, das uber Sekundartrager in Querrichtung das Auflager fur eine Blechverbunddecke bildet. Die experimentellen Untersuchungen sollten insbesondere das Verbundverhalten der Verbunddecke zwischen Profilblech und Beton uberprufen. Es wurden insgesamt zehn grossmassstabliche Biegeversuche an Einfeldtragern mit unterschiedlichem Abstand der Belastung vom Auflager durchgefuhrt. Hierdurch konnte die Langsschubtragfahigkeit sowie der Einfluss der 35 Jahre Nutzung untersucht werden. Zudem wurden Versuche an Durchlauftragern, an Kragarmen sowie an Offnungen durchgefuhrt. Weitere Versuche zur Untersuchung des Durchstanzverhaltens erganzten das umfangreiche Versuchsprogramm. Zur Durchfuhrung der Versuche wurden die Versuchskorper mit einer Diamantsage aus der Verbunddecke freigeschnitten. Anschliessend wurden mit einer speziell entwickelten Versuchseinrichtung die Versuche auf der Baustelle durchgefuhrt. Um den Ruckbauprozess nicht zu behindern, mussten die Versuche innerhalb der zwei Wochen Bauferien durchgefuhrt werden. Die generierten Versuchsdaten ermoglichten es eine Entscheidung hinsichtlich Ruckbau oder Umnutzung des Flughafendocks mit wirtschaftlichen und okologischen Folgen zu treffen. Die Versuche wurden mit den gangigen Bemessungsansatzen m-k-Methode und Teilverbundverfahren ausgewertet und die Tragfahigkeit der Verbunddecke ermittelt. Die Versuche zeigen, dass noch ein ausreichender Verbund zwischen Profilblech und Beton vorhanden ist und die Bemessungsmodelle den Tragwiderstand auch nach langerer Nutzung noch gut vorhersagen. Im ersten Abschnitt dieses Versuchsberichts werden die Versuche detailiert beschrieben. Im darauffolgenden Abschnitt werden die Versuchsergebnisse dargestellt und ausgewertet. In conjunction with the conversion of Dock B at Zurich Airport an experimental study on composite slabs with profiled steel sheeting (Holorib 51) was performed by the Institute of structural Engineering (IBK) of ETH Zurich. The examined structure was built in 1974. After 35 years in service it will be converted to implement the Schengen agreement with the European Union. The structure consists of composite floor slabs, a steel frame with stub-girder beams and hot rolled steel columns as supporting structure. The experimental investigation focused on the bond behavior of the composite slabs and the influence of the 35 years service life. In total ten large-scale tests were carried out on simple beams with different shear span length to evaluate the shear capacity between the steel sheeting and the concrete. In addition, tests on continues beams, on cantilever beams as well as tests on openings and punching tests completed the extensive test program. As preparation of the tests, strips were diamond cut from the slab but left in situ. Further, a special testing device was developed that’s frame had to be light but stiff and easy to adapt to perform the different type of tests on site in a very short time. The entire testing program had to be carried out within two weeks to avoid any interference with the ongoing reconstruction process. The data generated by these tests enabled the assessment of the composite slabs regarding demolition or adaption of the structure with the associated economic and ecologic effects. The evaluation of the results was done with common design methods, such as the m-k-method and the partial shear connection theory. The tests showed that a sufficient bond still exists between the steel sheets and the concrete and that current design rules properly assess the loadbearing capacity of structures after long-term use. In the first part of this report the performed tests are described in detail. In the following section, the results of the tests are presented and evaluated.