Andrea Frangi

ELASTO-PLASTIC MODEL FOR TIMBER-CONCRETE COMPOSITE BEAMS WITH DUCTILE CONNECTION

This paper describes an elasto-plastic model for timber-concrete composite beams with ductile connection. The first part looks at the elastic behavior and modeling of timber-concrete composite beams, in the second part an elasto-plastic method for timber-concrete composite beams with ductile connection is presented and compared to test results.

Shear behaviour of bond lines in glued laminated timber beams at high temperatures

A comprehensive research project has been carried out at the Swiss Federal Institute of Technology (ETH) on the fire behaviour of timber-concrete composite slabs (Frangi and Fontana 2000). The glued laminated timber beams used for the fire tests were bonded with a one-component polyurethane (1-K-PUR) adhesive. As one fire test on a slab showed an unexpected shear failure of a glued laminated timber beam, a series of tests was carried out to study the shear behaviour of different types of adhesives at high temperatures. The first part of the paper describes the results of the shear tests at elevated temperatures, in the second part the shear test results are compared to the fire test on a slab.

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).

Fire Performance Of Timber Structures Under Natural Fire Conditions

In recent years the use of wood as a building material has become popular, especially for dwellings. One of the preconditions for its use is adequate fire safety. Technical measures, especially sprinkler and smoke detection systems, well equipped fire brigades and a better knowledge in the area of structural fire design of timber structures allow the use of timber in a wider field of application. Full scale tests on wooden modular hotels were performed under natural fire conditions to look at the efficiency of different fire safety concepts. In a first series the efficiency of technical measures, especially fast response sprinkler systems, was studied. The second series showed the possibility and limits of structural fire safety measures. Special attention was given to the influence of combustible room surfaces on fire growth and fire spread inside and outside the room. The tests enlarged the experimental data for validation of natural fire simulations (temperatures, fire spread etc.) and for verifying the methods for the fire resistance calculation of wood constructions.

Experimental Analysis of the Structural Behavior of Timber-Concrete Composite Slabs made of Beech-Laminated Veneer Lumber

AbstractComposite, timber-concrete slabs as structural floor systems for office and residential buildings, offer several technical advantages over traditional, exclusively timber floors. The connection between timber and concrete in current systems made of spruce relies on mechanical steel fasteners to transfer shear forces between the two materials. The mechanical properties of beech-laminated veneer lumber (LVL), which are higher and more reliable than spruce, allow the development of an innovative timber-concrete composite slab made of a thin beech-laminated veneer lumber plate and a concrete layer. The connection between the two materials is accomplished with notches in the timber plate instead of mechanical steel fasteners. The structural performance of this system was evaluated with a series of bending tests. The results demonstrated that this type of timber-concrete composite system was able to reach high load-carrying capacity and that the structural behavior and failure modes of the composite ele...

Mechanical behaviour of finger joints at elevated temperatures

Finger joints are commonly used to produce engineered wood products like glued laminated timber beams. Although comprehensive research has been conducted on the structural behaviour of finger joints at ambient temperature, there is very little information about the structural behaviour at elevated temperature. A comprehensive research project on the fire resistance of bonded timber elements is currently ongoing at the ETH Zurich. The aim of the research project is the development of simplified design models for the fire resistance of bonded structural timber elements taking into account the behaviour of the adhesive used at elevated temperature. The paper presents the results of a first series of tensile and bending tests on specimens with finger joints pre-heated in an oven. The tests were carried out with different adhesives that fulfil current approval criteria for the use in load-bearing timber components. The results showed substantial differences in temperature dependant strength reduction and failure between the different adhesives tested. Thus, the structural behaviour of finger joints at elevated temperature is strongly influenced by the behaviour of the adhesive used for bonding and may govern the fire design of engineered wood products like glued laminated timber beams.

Overview of Design Issues for Tall Timber Buildings

Timber buildings, like any others, exhibit exemplary performance when materials are used appropriately, when structural forms and construction details address overload and serviceability requirements, and when geometry and interior layouts address fire safety. Many building codes restrict timber buildings to four and six storeys, reflecting societal consciousness of effects of conflagrations like the Great Fire of London in 1666. However, the regulatory landscape is changing to recognize contemporary capabilities to detect, suppress and contain fires within buildings. This is freeing architects and engineers to fully exploit structural capabilities of timber as a construction material. On the basis of the notion that tall modern timber buildings means those of approximately 10 storeys to a maximum of about 20 storeys, this paper is a commentary on the main structural engineering issues and how to address them systemically.

Fire Behaviour Of Timber-concrete Composite Slabs

The experience of fire spread in old timber houses has resulted in a limitation of the use of timber in multi-storey buildings in the fire regulations of many countries. Timber-concrete composite elements show promise to overcome this handicap thus allowing an extended use of the sustainable building material timber. Results of fire tests on the behaviour of timberconcrete composite slabs are described and compared with design methods for timber in fire.

Long-Term Behavior of Posttensioned Timber Connections

AbstractTests regarding the long-term behavior of posttensioned timber connections have been performed at the ETH in Zurich. The aim of these tests is to estimate the loss in tendon force that can be expected during the lifetime of a structure. Several posttensioned beam and beam-column timber specimens exposed to controlled and uncontrolled environmental conditions and loaded only with the axial prestressing force have been monitored for more than one year. The force in the tendon was measured together with the strains in the specimens and temperature and relative humidity in the testing environment. Creep tests performed on small glulam timber blocks loaded in compression have been started as well. The estimated creep coefficients parallel and perpendicular to the grain are used to calculate the losses with an analytical model for the larger posttensioned specimens. A prestressing loss in the range of 5–10%, depending on the geometrical properties and environmental conditions, has been found at the end ...