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This paper presents large-scale bending test, up to 19 m length, on glued laminated timber (GLT) beams with well-known beam setup and a model to predict the tensile strength of finger joint connections (FJ). Machine graded timber boards, with information about the dynamic stiffness and local knottiness were used to fabricate 12 GLT beams. The position of the timber boards were tracked throughout the GLT fabrication. To quantify the quality of the FJ additional FJ were fabricated and tested in tension. Based on the results, a model to predict their strength properties based on the grading information of the involved timber boards was developed using maximum likelihood estimation for censored data., International Wood Products Journal, 12 (4), ISSN:2042-6445, ISSN:2042-6453

Timber-concrete composite slabs are more and more in use: the combination of timber and concrete combines the advantages of both materials and offer a valid solution for the increasing demand for sustainable construction. The connection between timber and concrete is the crucial element, yet its potential regarding material and time expenses is not exploited. This paper presents the novel connection system micro-notches, an interlocking concept between timber and concrete with indentations in the millimetre range. Micro-notches provide a continuous shear transfer without additional steel fasteners such as screws or dowels. The paper presents the development of the micro-notch concept in an extensive experimental program supplemented with analytical and numerical models, a calculation model, and practice-relevant guidelines. The results of the investigations show that micro-notches feature an approximately rigid composite action between timber and concrete and a sufficient shear strength for the use in office and residential buildings., Engineering Structures, 245, ISSN:0141-0296

Fire Safety Journal, 107, ISSN:0379-7112, ISSN:1873-7226

A framework to model timber connections at normal temperature and in fire, based on combined finite-element (FE) heat-transfer analyses and temperature-dependent Johansen-type load-carrying models, was developed and applied in a parametric study of previously tested beam-to-column steel-to-timber dowelled connections. Comparison with experimental results shows that the FE heat transfer models provide good estimates of measured temperatures and the load-carrying model gives good approximations of the load-carrying capacity at normal temperature (for dowel and embedment failures) and under standard fire exposure. For the degrees of utilisation expected in fire E fi / R 20 ≈ 0.3 , the developed models are able to predict the failure mode of each dowel and the expected load-carrying capacity. Simulation results showed a clear influence of the thickness of the side members on the fire resistance of the analysed connections. The influence of dowel spacing is not so clear, as it also depends on the dowel diameter. A smaller dowel diameter seems to slightly improve the fire resistance, namely for smaller degrees of utilisation or thinner side members, but compromises the load carrying capacity at normal temperature.

The performance of light timber frame wall and floor assemblies in fire depends on their composition. The assemblies' ability to form fire-separations between building compartments (separating function) can be assessed by full-scale fire testing or calculation methods. Calculations are the low cost and more flexible alternative. The component additive method is a commonly used calculation method for fire design of timber structures. The method considers the insulation ability of the material layers present in the assembly. The component additive method described in this article is developed to be flexible to implement different materials and products of different dimensions. However, the amount of different materials currently included in this method is rather limited and there is no generally accepted procedure to implement new materials. This paper presents a common agreement of the procedure to implement new materials which comprises of: (1) the design and execution of model-scale fire tests; (2) determination of the modified thermal properties needed for simulations; (3) thermal simulations of assemblies in fire conditions; (4) development of design equations and; (5) verification by one or more full-scale fire test(s). The abovementioned steps have been clearly presented in this paper and supported by examples.

Knowledge on the short and long term deformation behavior of highly loaded components in tall timber buildings is important in view of improving future design possibilities with respect to serviceability, both in the construction and in the operational state. In this paper, we present the results of a monitoring case-study on a tall timber-hybrid building in Switzerland, a 15 storey and 60 m high office building completed in 2019. A fibre-optic measuring system showed an increase of the deformation with increasing load during the construction phase of highly stressed spruce-GLT and beech-LVL columns. However, the highest strain values were not reported in the columns themselves but at the ceiling transitions and in the area near their supports. The measurements on the columns were compared with model calculations for long-term deformation of timber elements in order to differentiate single components of the total deformation caused by load, time, and changes in climate during the construction. Over a monitoring period of a year, good agreement of the modelled deformations could be confirmed, which indicates that such models could be well suited for future usage in serviceability design of tall timber buildings., Engineering Structures, 234, ISSN:0141-0296

Timber–concrete composites (TCC) are smart solutions for slabs in residential and office buildings regarding the sustainable and performance-optimized use of materials. However, a non-negligible disadvantage is the deflection of the timber elements caused by in-situ concrete casting during construction. This paper presents an approach to camber timber elements without external forces by using the innate swelling capacity of wood. Oven-dried hardwood inlays can be inserted transversally into cuts on the top side of a timber element. After an increase of the moisture content in the inlays, the swelling pressure will result in a self-camber of the timber element. In this study, a procedure for prediction of the self-camber is derived and the model is validated using an experimental test series. The results demonstrate that the self-camber of spruce elements using beech inlays is both feasible and predictable. On this basis, practical application scenarios for TCC elements in timber engineering are shown and discussed., Construction and Building Materials, 308, ISSN:0950-0618

Cross-laminated timber, typical abbreviations CLT or XLAM, is currently one of the most innovative product in building with wood. This solid engineered timber product provides advantages compared to other solid timber slabs as the dimension stability, i.e. swelling and shrinkage, is controlled by the crosswise laminations. As for other components, the fire resistance has to be verified for this type of product. While fire testing is time consuming and costly, simulations provide flexibility to optimize the product or to develop simplified design models for structural engineers. In this paper, a simulation technique is presented which can be used to determine the fire resistance of CLT. The technique was then used to develop simplified design equations to be used by engineers to predict the behavior of CLT in fire resistance tests and verify its fire resistance. Following existing models, the simplified design model aims for a two-step process whereby in a (i) first step the residual cross section and in (ii) a second step the load bearing capacity of the partly heated residual cross section is determined. The presented simulations consider the effective thermal–mechanical characteristics of wood exposed to standard fire and perform an advanced section analysis using a temperature profile corresponding to the actual protection and the location of the centroid together with the possibility of plasticity on the side of compression. It was shown that simulation results agree well with test results and that they can be used to determine layup specific modification factors used by the reduced properties method or zero-strength layers used by the effective cross section method. It was shown that the use of the zero-strength layers is favorable compared to the modification factors to calculate the resistance of the residual cross section. This is due to the large range of modification factors answering the typical layup of CLT comprising layers with their fiber direction cross the span direction. Subsequently, the methodology was used to determine design equations for initially unprotected and protected three-, five- and seven-layer CLT in bending and buckling. While the zero-strength layer for glulam beams in bending is assumed to be 7 mm (0.3 in), for CLT the corresponding value is in most of the cases between 5 mm and 12 mm but is different for other loading modes such as buckling (wall elements) and depending on the applied protection.

The results of an experimental programme on the structural behaviour, fire behaviour, and fire resistance of CLT rib panels are presented. The floor system consists of cross-laminated timber (CLT) plates rigidly bonded to glued-laminated timber ribs by means of screw-press gluing. The experimental programme comprised ultimate-load tests at normal temperature as reference tests and full-scale fire resistance tests on four cross-sections. In addition to the reference tests, shear tests of the glue line between CLT plate and glued-laminated timber rib were performed for analysis of the cross-sections’ composite action. The results of the reference tests show good agreement with results based on the simplified method according to EN 1995-1-1 [1] and its final draft of CLT design [2]. The importance of the glue line’s quality was confirmed. The fire resistance tests show results on the safe side compared to predictions of the fire behaviour according to EN 1995-1-2 [3] and its actual draft [4]. However, the fire resistance was underestimated due to conservative assumptions about the composite cross-section’s structural behaviour. The experimental programme addressed the fire behaviour and fire resistance of CLT rib panels currently not covered in standards. The project’s overall aim is the development of design rules in fire for EN 1995-1-2., Engineering Structures, 246, ISSN:0141-0296

This paper presents an analytical model of timber-concrete composite slabs made of laminated veneer lumber (LVL) with notched connection. Timber-concrete composite slabs could be used as alternative to timber slabs or conventional reinforced concrete slabs and represent an interesting solution due to ecologic, economic and structural advantages. The use of LVL products guarantees for controllable and homogeneous properties of the timber part of the composite member and allows taking advantage of the high mechanical properties of hardwood (e.g. beech). The advantages of the notch as timber-concrete connection system are its high stiffness and the possibility to achieve a ductile compressive failure of timber. The presented analytical model is based on simple equilibrium formulations and allows the development of a ductile and reliable design procedure based on notch yielding. Because of the difference between the material properties of LVL and concrete, local LVL deformations within the notches may compromise the shear-carrying mechanism in concrete, leading to premature failure of the composite member. This problem can be solved by installing vertical reinforcement. The model has been validated by means of full scale bending tests on timber-concrete composite members made of beech LVL plates.

The advances of timber engineering in the field of tall buildings raised a need for high performance connections that can accommodate increased demands due to higher loads and longer spans. A semi-rigid connection with glued-in rods was designed to fulfill these requirements. Moment-rotation behavior of this connection was investigated in a series of quasi-static cyclic tests. A moment-resisting connection was established between timber columns and steel base plates. Three different timber products, including hardwood and softwood species, and two different rod diameters were used. The columns were subjected to shear force and bending, to simulate the loading conditions of a column in a frame under lateral loads. The tests were performed with increasing rotation demand on the column until the failure. The connections provided high moment capacity and rotational stiffness. All of the tested specimens demonstrated ductile response, while the connections with hardwood performed especially well. No strength degradation was observed in multiple cycles, therefore the hysteretic energy dissipation was significant in cycles with high target displacement. The nature of the connection response was studied in detail and an analytical model was developed to describe the relationship between the moment and the rotation at the column base. The model is capable to predict the envelope of the cyclic response and corresponds well to the experimental results.

An innovative steel-timber hybrid floor diaphragm with modular prefabricated composite elements is presented. Building elements have been designed to be quickly joined on site using only bolts and screws. The paper mainly deals with an experimental study on the response of the hybrid floor under horizontal loads. Monotonic and cyclic shear tests of a full-scale floor were executed in order to investigate the in-plane stiffness, bearing capacity, effective stress state and strain state, as well as damage to floor components. The forces transmitted through the timber and steel components were also assessed. The test results showed that the main deformations of the floor were localised at the beam-to-beam steel joints while the steel-timber hybrid elements behaved elastically without breakages. The use of CLT panel-to-panel connections was very effective in increasing the stiffness and the ability to recover the initial non-deformed shape after the removal of the acting loads. The findings revealed how the diaphragm behaviour of the floor was influenced by the mutual interaction between the modular staggered composite elements and in particular by the response of the connections. Several design recommendations for steel and timber connections are therefore provided here.

The concept of post-tensioned timber structures has been developed and implemented since 2005. The technology relies on unbonded post-tensioned timber elements to create a moment-resisting ...

Recently, some comments about Cross-Laminated Timber (CLT) appeared in journals, online press and lobby documents that highlighted “inconsistencies” of the product when it comes to its fire safe use. The actual document summarizes relevant fire characteristics of CLT, which were brought up, and addresses them accordingly with respect to common understanding, established experience, European standardization and available design guidance. This document shows that currently fire design is not fully covered by codes, but safe design is possible using additional sources as guideline and state of the art documents. The authors of this document share the opinion with CEN/TC 250/SC5/WG4 that fire safe design of CLT is achieved when actual state of the art guidance is followed., Civil Engineering Research Journal, 7 (5)

The load bearing capacity of glued laminated timber beams is size dependent. A material based size effect occurs due to the natural variability of the timber properties and can be explained with the Weibull weakest link theory. The Weibull type size effect has received much attention in the timber research community in the past as it is the dominating size effect regarding the load bearing capacity of timber beams. In this paper, it is shown that a further deterministic size effect, which originates from the timber fracture behavior, influences the load bearing capacity of glued laminated timber beams. It is the size effect associated with quasi-brittle behavior. The paper covers a short theoretical review on fracture related size effects and a study comparing experimentally tested beams of several sizes with detailed numerical simulations considering the natural growth characteristics of timber. Further, an analytical model illustrating the features of the fracture related size effect on the load bearing capacity of glued laminated timber beams is presented. It is demonstrated that the simulated load bearing capacity of the tested glued laminated timber beams distinctively improves if the quasi-brittleness is taken into account by using a softening constitutive law.

This paper describes experimental investigations on timber-concrete composite members made of beech laminated veneer lumber (LVL) with notched connection. Timber-concrete composite slabs represent interesting building solutions, and can substitute conventional reinforced concrete slabs and timber slabs. LVL based materials have controllable and homogeneous properties, and allow to exploit the potential of some hardwood species (e.g. beech). The purpose of this experimental work was to validate an analytical model for ductile design of the composite member based on the fact that a plastic compressive failure of LVL within the notches shall be the governing failure mode. The test setup simulated a uniformly distributed vertical load, the specimens were made of beech LVL panels, and the most significant parameters varied in the experiments were the presence and the amount of vertical reinforcement. The test results allowed to validate the design model and showed that the structural behavior of the composite member can be governed by a plastic compressive failure of LVL, and that vertical reinforcement is indispensable to allow development of plasticity. Thanks to the elevated mechanical properties of beech wood, the specimens tested exhibited high strength and stiffness.

This research paper presents the implementation of Bayesian updating to an innovative post-tensioned timber frame structure, which has recently been erected at ETH Zürich as the main lateral load carrying system of the ETH House of Natural Resources (HoNR). In this innovative timber frame, the columns and beams are solely connected via a straight tendon running through the beams at mid-height, in this way creating a moment-resisting frame structure. A numerical model of the post-tensioned frame structure is set up and updated on the basis of modal vibration data offering a deeper insight into the system’s behavior and corresponding parameters. The modal testing data is derived from laboratory testing of a 2D-frame set-up, investigated under different support conditions. The dynamic acceleration response of the structure was processed by means of subspace identification methods for inferring the modal characteristics of the structure (frequencies, mode shapes, and damping ratios). Parallel to the modal vibration tests, an a priori numerical model of the structure has been established, which nonetheless relies on a number of assumptions on defining structural properties, including material, support, and rigidity parameters. Bayesian model updating is adopted for the updating of these parameters by exploiting the value of information contained in the testing data. The finally rendered updated model features parameters of reduced uncertainty, which is attested by the superior fit to the experimental data. The updated model may now be employed for investigating further the dynamic behaviour of the existing frame system as implemented in the HoNR., Procedia Engineering, 199, X International Conference on Structural Dynamics, EURODYN 2017

Post-tensioned timber frames are investigated at ETH Zurich in the context of the development and promotion of efficient hybrid timber structures made of hardwood. These structures can be prefabricated and are quickly assembled on site, making them suitable for multi-storey buildings. A post-tensioned timber frame with hardwood reinforcement was analysed with a series of static pushover-tests. The frame was loaded with a horizontal force while the displacement was recorded. The results of these pushover-tests are presented herein and will be compared with pushover-curves obtained from an analytical spring model. Attention will be given to the behaviour of the beam–column connections, where several LEDs were attached to analyse the connection behaviour and the influence of the tendon force on the lateral stiffness of the frame. All tests were performed with a controlled load level, which was estimated using a simple analytical spring model. The test verified the analytical spring model and showed the self-centring behaviour of such structures.

Purpose This paper aims to present the results of an extensive experimental programme on the fire behaviour of timber beam-to-column shear connections, loaded perpendicularly to the grain. Design/methodology/approach The experimental programme comprised tests at normal temperature and loaded fire resistance tests on beam-to-column connections in shear. Twenty-four full-scale tests at normal temperature were performed covering nine different connection typologies, and 19 loaded fire resistance tests were conducted including 11 connections typologies. Findings The results of the fire resistance tests show that the tested typologies of steel-to-timber dowelled connections reached more than 30 and even 60 minutes of fire resistance. However, aspects such as a wider gap between the beam and the column, reduced dowel spacing, and the presence of reinforcement with self-drilling screws all have a negative influence on the fire resistance. Originality/value The experimental programme addressed the fire behaviour of timber beam-to-column shear connections loaded perpendicularly to the grain in a systematic way testing a wide range of common connection typologies significantly enlarging their experimental background.

A new model to determine the bending resistance of fibre reinforced glulam beams is presented. The model grounds on basic mechanical relations. New approaches are introduced to model the softening behaviour of the timber in the compression zone and the mechanical interaction of the reinforcement with the timber in the tension zone. This interaction considers the crack-bridging effect of the reinforcement. Localised phenomena such as the initiation of cracks in the tension zone or the formation of compression folds are modelled in a mechanical coherent way. In comparison with small-scale and full-scale experiments, the new model provides good results on both the characteristic as well as the mean level of the bending resistance. The new model is formulated in such a way that it can be implemented in a spreadsheet.

This paper presents a summary of experimental results from various studies conducted these twenty last years on the behaviour of steel-to-timber or timber-to-timber connections with dowel-type fasteners exposed to fire. The majority of the tested connections are loaded in tension parallel-to-grain and some of them loaded in tension at 45°, 90° and bending. The geometrical configurations of the tested connections are detailed and commented to facilitate further use. The tests in normal conditions are realized in order to obtain the real ultimate loads of the tested connections used as a basis to define the mechanical load in fire tests. Based on the fire resistance times of the tested connections, the experimental results are compared with those given by the design rules of EN 1995-1-2. The experimental results are presented in such a way that they can be used to validate numerical investigations that can be developed in order to understand the complex thermo-mechanical behaviour of timber connections. Thus, the paper provides to the researchers a database, of the main experimental results available in the world, related to the fire resistance of dowelled and bolted timber connection exposed to ISO fire.

Fire Technology, 46 (1), ISSN:0015-2684, ISSN:1572-8099

This paper addresses rebirth of timber as a material suitable for urban construction. It lost currency during the late nineteenth and throughout the twentieth century, with the main reasons being concern about fire safety and the emergence of structural steel as a material well suited to expression of architectural modernism. Now the wheel of fortune is turning again, but in timber’s favour, with driving forces being continued population growth and urbanisation, and the need to create sustainable liveable cities. Also, technical knowhow now exists to address fire performance of timber buildings and timber materials have evolved to a level where some claim they are ‘better than steel’, or reinforced concrete. Research and development of fire engineering as a rigorous science are enabling implementation of performance-based design methods that literally revolutionise the design space for timber buildings. Tall timber buildings dot many recent city landscapes, but even so the possibilities largely await exploitation.

In this paper, a probabilistic approach for modelling the load-bearing capacity of glued laminated timber is presented. The specific characteristic of this approach is that, at first, timber boards are simulated according the natural growth characteristic of timber. Subsequent, glued laminated timber beams are virtually composed out of the simulated timber boards. Thereby, every kind of fabrication procedure, such as the length of the timber boards or the beam dimensions, can be recreated. Afterwards, a numerical model is used to estimate the load-bearing capacity, the bending stiffness and the type of failure of the simulated GLT beams. To ensure the quality of the numerical model it is validated with 24 GLT beams with a precisely-known beam setup; a wide agreement between the measured and the estimated material properties is identified. For a probabilistic investigation of different input parameters a Monte Carlo simulation is performed. The application of the presented approach is illustrated on selected examples (size effect, the quality of finger joint connections and grading criteria).

In the context of the development and promotion of innovative and efficient hybrid timber structures, a pilot building, the ETH House of Natural Resources, has been designed. The building comprises three innovative structural systems, a post-tensioned timber frame, a composite beech laminated veneer lumber–concrete floor and a biaxial timber slab made of cross-laminated timber and beech laminated veneer lumber. The building will serve as an office building for the laboratory of hydraulics, hydrology and glaciology of ETH Zurich; as a ‘living lab’ for the implementation of a permanent sensor network for long-term monitoring purposes; and as a setup for a field testing campaign of in situ tests at different construction stages. Results of the first two series of this testing campaign and the derived modal characteristics of the structure are presented in this paper. The obtained modal data will extend the knowledge base on innovative hybrid timber structures and help to predict structural response for the case of significant loads such as high wind loads or earthquakes, through an extended model element updating procedure.

Since 2010, twelve post-tensioned timber (Pres-Lam) buildings have been constructed throughout the world. The technology relies on unbonded post-tensioning tendons to provide moment capacit...

Am Institut fur Baustatik und Konstruktion IBK der ETH Zurich wurde der Prototyp einer neuartigen Holz-Beton-Verbunddecke aus Laubholz entwickelt. Die Verbunddecke besteht aus dunnen (40 mm dicken) Furnierschichtholzplatten aus Buche (BauBuche) und einer 120 bis 160 mm dicken Betonschicht. Die Buchenplatten ubernehmen sowohl die Funktion der Schalung als auch der Zugbewehrung. Als Verbund zwischen Beton und Holz werden 15 mm tiefe Kerben ins Holz gefrast, die zu einer steifen mechanischen Verzahnung zwischen Beton und Holz fuhren. Der Artikel stellt die Leitidee der Verbunddecke sowie die umfassenden durchgefuhrten experimentellen Untersuchungen vor. Dieses neuartige Deckensystem wurde im ETH House of Natural Resources (www.honr.ethz.ch) erstmals weltweit umgesetzt. At the Institute of Structural Engineering of the ETH Zurich, an innovative timber-concrete composite slab made of hardwood has been developed. This composite slab is made of a 40 mm thick beech laminated veneer lumber plate (BauBuche) and a 120-160 mm thick concrete layer. The beech plates act as formwork and tensile reinforcement. The connection between the two materials is accomplished with 15 mm deep notches in the timber plate, which ensure a stiff composite action. This paper presents the basic concept of the composite slab as well as the extensive performed experimental investigations. This innovative slab system was implemented for the first time in the ETH House of Natural Resources (www.honr.ethz.ch). © 2015 Ernst & Sohn Verlag fur Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

Design models for timber structures with fire-resistance requirements usually take into account the loss in cross section due to charring and the temperature-dependent reduction in strength...

A newly developed bonding technology makes it possible to rigidly connect timber elements parallel to the grain. This technology allows to build two-way and point-supported flat slabs in cross-laminated timber (CLT). In such a structure high loads have to be transferred from the slab into the columns. This paper presents punching tests on different CLT plates. The results of these tests allow for a better understanding of the important parameters of a point-supported CLT slab and should help create the basic design criteria for these connections. To transfer vertical forces from higher storeys through the CLT slab without subjecting it to stresses perpendicular to the grain, the columns are directly connected to each other through an opening in the slab. Even though the opening leads to a stress concentration in the CLT plate, the rolling shear failure was the governing failure mode during the tests. With numerical models the behaviour of the tested plates was simulated and the strains around the opening were calculated. The results show good correlation with the measured strains. After the punching tests, every plate was cut in cubes and the visible failures were recorded. In addition, material samples were cut out of the plates and tested to determine the rolling shear strength of single boards. The achieved shear resistance in the punching tests was 1.4 times higher, than the rolling shear strength determined in shear tests on single boards would allow. An additional rolling shear test series showed that an anchoring effect contributes to the increased rolling shear resistance in punching tests. The results of the punching tests confirm the potential of CLT slabs to be used as biaxial, continuous, point-supported floor slabs.

This paper presents an experimental study on the cross-sectional capacity and flexural buckling resistance under fire conditions. Steady state stub and slender column tests were carried out at ambient and elevated temperatures on square and rectangular hollow sections as well as H-sections. In addition, transient state slender column tests were performed on H-section test specimens. The compressive load was applied centrically or eccentrically to the test specimens. The paper presents the testing programme, the geometry of the test specimens including initial geometrical imperfection measurements, elevated temperature material properties, test setup, the execution and the results of the stub and slender column tests.

The moment-rotation-behaviour of a post-tensioned beam–column timber joint has been analysed extensively with a series of static bending tests. The timber joint was loaded at the end of the beams in order to apply a moment to the connection. The tests were conducted with various forces in the tendon, from 300 kN up to 700 kN. The bending tests were performed with a controlled load level, so that no failure perpendicular to the grain in the column occurred. The maximal allowable vertical load to be applied was estimated using a simple spring model. A final bending test was conducted in order to study the failure mode of the post-tensioned timber joint. The vertical load on the beams was increased until the tendon elongation got so high that the test had to be aborted. The results of bending tests of the post-tensioned timber joint are presented herein. Attention will be given to the structural behaviour and to the influence of the applied post-tensioning force on the connection stiffness. The experimental results will be compared to the results obtained using a simplified analytical calculation model.

Timber is amongst the oldest building materials used by humankind. We have been building with timber for millennia, and in its various forms timber has consistently remained a key structural and building material in most cultures (along with masonry and, more recently, concrete and steel). However, various conflagrations in largely timber-built towns and cities around the world throughout the history of civilization—typically called the ‘‘Great Fires’’ (e.g. of Rome, Constantinople, Hangzhou, Utrecht, Amsterdam, London, Baltimore, Tokyo, etc.)—led to the use of timber structural and cladding materials being reduced or explicitly restricted within dense conurbations, with a preference for non-combustible structural framing, cladding, and roofing materials—particularly for multistory and high-rise construction. In most places, timber has remained a critically important and widely used building material in a range of applications, however during recent centuries the structural use of timber (either as heavy timber elements or light timber framing) has typically been limited to low-rise construction of smaller volume buildings with fewer than four-to-five storeys; the use of timber cladding has also been widely restricted or avoided. However, spurred on by the sustainability and constructability credentials of timber as compared with concrete, masonry, or steel—and by the development of novel engineered timber materials and prefabricated systems incorporating engineered timber joists and trusses, glued-laminated timber (glulam) and cross-laminated timber (CLT)—timber has experienced an accelerating resurgence/emergence as a primary material in multi-storey buildings [1]. A range of publications during the past 5 years has highlighted the opportunities to build large, multi-storey buildings in engineered timber [2–4]. Timber buildings of up to nine or ten storeys are increasingly being proposed internationally, and numerous proposals have been made for predominantly timber—or hybrid timber-steel or timber-concrete—buildings of 30 storeys or more [2]. Timber is also increasingly being proposed by architects and engineers for innovative, sustainable, and attractive building facades and cladding systems.

Cross-laminated timber (CLT) panels are relatively new engineered wood products that can be used as load bearing walls, floors and roof elements in innovative and high quality modern timber structures. The fire behavior of cross-laminated timber panels requires careful evaluation to allow the expansion of CLT elements usage in buildings. A University of British Columbia study has been conducted at the Trees and Timber Institute CNR-IVALSA in San Michele all’Adige, Italy to experimentally evaluate the fire performance of Canadian CLT panels. In total, ten loaded fire tests were performed using standard fire curves (ULC/ASTM and ISO) to study the influence of different cross-section layups on the fire resistance of floor and wall elements and to investigate the influence of different anchors on the fire behavior of wall elements. This paper presents the main results of the experimental analyses and discusses in particular the charring rate, one of the main parameters in fire design.

In timber–concrete composite members with notched connections, the notches act as the shear connections between the timber and the concrete part, and have to carry the shear flow necessary for composite action. The shear transfer through the notches generates shear and tensile stresses in both parts of the composite member, which may lead to brittle failure and to an abrupt collapse of the structure. Although simplified design formulas already exist, some structural aspects are still not clear, and a reliable design model is missing. This paper summarizes current design approaches and presents analytical models to understand the shear-carrying mechanism, to estimate the shear stresses acting in the timber and concrete, and to predict failure. The analysis concentrates on three problems: the shearing-off failure of the timber close to the notch, the shear failure of the concrete, and the influence of the shear flow on the gap opening between the timber and concrete. Parts of the model calculations could be compared to experimental observations. The conclusions of this paper contribute to improving current design approaches., Materials and Structures, 50, ISSN:1359-5997, ISSN:1871-6873

The behaviour of timber members subjected to axial compression or combined axial compression and bending is characterised by the non-linear increase of the deformation due to the increasing eccentricity of the axial load and due to the non-linear material behaviour. The paper presents a strain-based model taking into account these effects. Design approaches given in timber structures design codes are compared and differences in the results obtained with the different approaches are identified. Furthermore, a strain-based model to analyse the load-bearing capacity of centrically and eccentrically loaded timber columns is described and its power is assessed. It is shown that in particular the non-linear behaviour of timber when subjected to compression parallel to the grain considerably influences the load-bearing capacity. The model is validated on the basis of experimental investigations on solid Norway spruce beams loaded in combined axial compression and bending. A good agreement was found between the estimated values using the strain-based model and the experimentally derived values. A comparison of the model with the design approaches given in the codes shows that the load-bearing capacity can be overestimated under certain conditions. Finally, it is illustrated how the design approaches can be modified in order to reach a more consistent design.

This research work aims at deriving an optimal sensor configuration for the modal identification of an innovative timber structure. The goal is to extract the maximum possible information from the structure, while minimizing the amount of deployed sensors. Several different optimal placement methods are implemented, including the effective independence method (EFI), the modal kinetic energy method (MKE) and the information entropy method (IEI). Additionally, a modified version of the IEI method, incorporating a prediction error correlation term is introduced. This addition alleviates sensor clustering around a single location, which often occurs if the modal input data is generated from a finite element model of a dense mesh of possible sensor positions. The study shows, that to obtain an optimal sensor setup, prediction error correlation effects should be considered in order to avoid sensor clustering, and the multiaxiality of sensors should be taken into account during the optimization process.

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 whole-structure 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.

Die Verwendung von Klebstoffen fur die Herstellung von Holzprodukten ist im konstruktiven Holzbau unerlasslich. Die Tragsicherheit von verklebten tragenden Holzbauteilen wie Brettschichtholz wird durch das Verhalten der eingesetzten Klebstoffe masgeblich beeinflusst. Klebstoffe mussen eine zuverlassige Festigkeit und Dauerhaftigkeit aufweisen, so dass sie unter der vorgesehenen Nutzung ihre Funktionsfahigkeit vollstandig behalten. Diese Leistungsanforderung muss auch im Brandfall sichergestellt sein. Zur Untersuchung des Einflusses des Klebstoffes auf das Tragverhalten von Brettschichtholz im Brandfall wurden umfangreiche Untersuchungen durchgefuhrt. Der vorliegende Artikel fasst die wesentlichen Resultate und Erkenntnisse dieser Untersuchungen zusammen. Die Untersuchungen zeigten den Einfluss des Klebstoffes auf das Tragverhalten bei Brettschichtholz im Brandfall. Bei der flachigen Verklebung (zwischen den Brettlamellen) zeigte sich anhand numerischer Untersuchungen, dass ein Versagen in der Klebstofffuge auch mit Klebstoffen mit geringer thermischer Stabilitat kaum masgebend wird. Die Brandversuche an keilgezinkten Brettschichtholzlamellen zeigten, dass der Feuerwiderstand von der Versagensart dominiert wird. Unter Berucksichtigung der beobachteten Bruchbilder liesen sich keine signifikanten Unterschiede zwischen den gepruften Klebstoffen feststellen. Influence of the adhesive on the fire behaviour of glued laminated timber. Adhesives are commonly used to produce engineered wood products such as glued laminated timber beams. The load-bearing capacity of these structural timber elements is strongly influenced by the adhesive used. As a consequence, adhesives have to meet requirements regarding strength and durability to ensure the functionality of structural timber elements during the whole lifetime. Also during fire, the performance requirements have to be fulfilled for a certain time period. To investigate the influence of the adhesive on the load-carrying capacity of glued laminated timber in fire, comprehensive analysis has been performed. This article summarises the most important results and findings. Based on the numerical analysis performed to investigate the influence of adhesive in the bondline between two lamellas, it can be concluded that also if the adhesive strength in the bondline is strongly influenced by the temperature, in most common design applications failure will occur because the bending resistance of the beam is exceeded. Failure in the bondline is hardly to be expected. The fire tests on finger-jointed timber boards showed that the fire resistance is dominated by the type of failure. Taking into account the different failure modes, no significant difference was observed between the adhesives studied.

Wood Science and Technology, 46 (5), ISSN:0043-7719, ISSN:1432-5225

The paper presents results of experimental and numerical analyses on the fire behavior of concrete elements protected by sprayed protective linings. Particular attention is given to high- (HPC) and ultrahigh performance concrete (UHPC), as HPC and UHPC tend to exhibit explosive spalling in fire due to low porosity. The results provide basic input data for the development of simplified rules for the fire design of concrete structures protected by sprayed protective linings.

Owing to the influence of two-dimensional heat transfer, fire tests and heat transfer calculations show that charring on the narrow side of rectangular timber cross-sections may be considerably greater than charring on the wide side. For timber members unprotected throughout the time of fire exposure as well as members initially protected from fire exposure, it is shown by calculation, that the relationship between charring on the narrow side and time is nonlinear. In order to take into account increased charring on the narrow side of timber members a section factor ks was determined. By calculation it is shown that bending moment resistance is only insignificantly influenced by the effect of two-dimensional heat transfer and the factor ks can therefore be neglected, making the fire design of timber members easier. Copyright © 2011 John Wiley & Sons, Ltd.

Fire Technology, 48 (3), ISSN:0015-2684, ISSN:1572-8099

Fire safety is the main precondition for the use of wood for multistorey timber buildings and is therefore an important criterion for the choice of material for buildings. The Institute of Structural Engineering at ETH Zurich has accomplished several research projects on the fire behaviour of timber structures over the past 15 years. The research projects aimed at supplying basic data and information on the safe use of timber, in particular for multistorey buildings. Further novel fire design concepts and models have been developed based on extensive theoretical studies, element and full-scale testing as well as a large statistical database on fires in timber. The better knowledge in the area of fire design of timber structures from the research projects, combined with technical measures, especially sprinkler and smoke detection systems, as well as well-trained and equipped fire brigades allow the safe use of timber and a wider field of application of timber for buildings. As a result the Swiss fire regulations of 2005 allow the use of timber structures in multistorey medium-rise residential buildings with up to six storeys. Many other countries have also liberalised the use of timber for buildings or introduced fire regulations that allow for the use of timber on the basis of performance. This paper describes the background of the design concept assumed for multistorey medium-rise buildings. It further presents an overview of two novel calculation models for the verification of the separating function of wall-and-floor timber assemblies as well as for the fire resistance of timber connections.

Im Zuge des nachhaltigen Bauens tritt die Multifunktionalitat von Decken immer mehr in den Vordergrund und verdrangt rein statische Uberlegungen beim Entwurf von Decken. Bereits vorhandene individuelle Losungen und multifunktionale Deckensysteme werden vorgestellt. Ein Vorteil dieser Systeme stellt die Integration der Installationsebene in die Konstruktionshohe dar. Eine Weiterentwicklung dieser Ansatze stellt das Deckensystem Topfloor integral dar, welches aus einem halben Wabentrager und einer Betonplatte besteht. Die Offnungen in den Waben ermoglichen eine flexible Installationsfuhrung und fuhren zu einer hohen Materialeffizienz. Versuchsergebnisse von statischen Tragerversuchen werden vorgestellt und mit ublichen Berechnungsmodellen des Verbundbaus verglichen. Anhand der Versuchsergebnisse werden die Schububertragung und die aus ihr resultierenden lokalen Beanspruchungen im Bereich der Waben detailliert diskutiert. Ingenieurmasige Nachweise zum Biegedrillknicken und zur Schubeinleitung in den Beton durch Bewehrungsstabe werden ebenso vorgestellt wie Uberlegungen zum Feuerwiderstand und zum dynamischen Verhalten der Decke. Am Ende des Beitrages werden erste Beispiele von mit dem neuen Deckensystem ausgefuhrten Bauten vorgestellt. Development of a composite slab system with integrated installation floor and increased material-efficiency. The need of sustainable buildings demands the design of multifunctional slabs considering more than only structural aspects. The paper presents state-of-the-art solutions for multifunctional slabs and a novel type of composite floor system using cellular beams. A major benefit of the multifunctional slabs is the integration of an installation floor. The new developed system “Topfloor integral” uses half cellular beams made of existing hot-rolled sections with welded reinforcing bars. The openings in the cellular beams allow the placing of installations in all directions, thus providing excellent flexibility to the user when maintaining or changing installations. The results of tests on the structural behavior and the load-carrying capacity are presented and compared to proposed design models for the “Topfloor integral” slabs. Local stresses caused by shear forces at the web openings are discussed. Additional information about lateral-torsional-buckling, the design of the shear connection using common reinforcing bars, the fire resistance and the dynamic behavior are given. Finally, the paper presents some examples of first buildings where the novel type of floor system is used.

In order to limit fire spread by providing adequate fire compartmentation, elements forming the boundaries of fire compartments are designed and constructed in such a way that they maintain their separating function during the required fire exposure (insulation and integrity criteria). While fire tests are still widely used for the verification of the separating function of light timber frame assemblies, design models are becoming increasingly common. A comprehensive research project on the separating function of light timber frame wall and floor assemblies with cladding made of gypsum plasterboards and wood-based panels was carried out at ETH Zurich in collaboration with the Swiss Laboratories for Materials Testing and Research (Empa). The objective of the research project was the development of an improved design model for the verification of the separating function of light timber frame wall and floor assemblies. A large number of small-scale fire tests permitted the analysis of different parameters on the thermal behaviour of protective cladding made of gypsum plasterboards and wood-based panels. The results of the fire tests allowed the verification and calibration of thermal properties used for thermal finite element (FE) analysis. Based on an extensive FE parametric study, the coefficients of the design model for the verification of the separating function of light timber frame wall and floor assemblies were calculated. The design model was verified by means of full-scale fire tests. The paper first describes the basic structure of the design model for the verification of the separating function of light timber frame wall and floor assemblies. Then, the main results of experimental and numerical analyses are presented. The results permitted the calculation of the coefficients of the design model for the verification of the separating function of light timber frame wall and floor assemblies.

The load-carrying capacity of timber structures is often limited by the resistance of the connections. Thus, highly efficient connections such as multiple shear steel-to-timber connections with slotted-in steel plates and steel dowels are needed for an efficient design. The load-carrying capacity of multiple shear steel-to-timber dowelled connections with slotted-in steel plates in fire primarily depends on the temperature-dependent reduction of embedment strength of the timber members. In order to accurately predict the fire resistance of the connection, knowledge of the temperature distribution in the cross-section as well as the influence of steel elements (slotted-in steel plates and steel dowels) on the charring of the timber members is essential. Based on an extensive experimental and numerical analysis, a design model for the calculation of the load-carrying capacity in fire of multiple shear steel-to-timber dowelled connections with slotted-in steel plates subjected to tension was developed and is presented. The design model is in analogy with the reduced cross-section method according to EN 1995-1-2 commonly used for the fire design of timber members. The proposed design model takes into account different geometries of the connection and the influence of the steel elements on the temperature distribution in the cross-section.

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...

The paper presents a novel type of composite floor system using cellular beams. A major benefit of the system is the integrated installation floor, providing additional value to the floor. The syst...