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At present, the popularity of timber as a structural material is booming. However, the current knowledge on disproportionate collapse prevention and extreme loading of timber buildings is scarce. To prevent disproportionate and progressive collapse, catenary action is an important mechanism, where the axial capacity of bending members is activated. Because of the brittle behavior of timber in the relevant failure modes, it can only achieve catenary action via strengthening. In this paper, analytical expressions are derived for the elastic, plastic, and catenary capacity of laterally loaded wood and timber beams with a tension-side strip reinforcement. A load-path dependent M-N interaction diagram with damage accumulation explains the ultimate catenary capacity and the transition between the bending- and catenary-dominated load-carrying mode. The analytical expressions are validated and discussed based on tests on beech clearwood specimens reinforced with carbon fibers in a polyurethane matrix. Furthermore, a case study on glued laminated timber beams is presented to demonstrate the potential of reinforcing timber beams subjected to extreme loading., Construction and Building Materials, 385, ISSN:0950-0618

The finite element method is the most widely used numerical method for progressive collapse analysis and analysis of structures subjected to extreme loading. However, it is computationally expensive for problems where discontinuities occur. In progressive collapse analysis, an example of a discontinuity is when two or more elements separate because of failure. Variations of the finite element method, such as the extended finite element method and other numerical methods, can model such discontinuities but become computationally expensive. For large-scale analyses of progressive collapse, the method must be computationally efficient and be able to model relevant discontinuities. In this paper, a discrete method called the mixed element method is presented and compared with the finite element method in a case study. Results from the case study demonstrate small deviations between the two methods in modal analyses and different static and transient loading situations. The mixed element method uses elements that are available in common finite element software and can therefore be implemented in any finite element software., Lecture Notes in Civil Engineering, 326, ISSN:2366-2557, ISSN:2366-2565, Proceedings of the 2022 Eurasian OpenSees Days, ISBN:978-3-031-30125-4, ISBN:978-3-031-30124-7

Timber-concrete composite (TCC) slabs play an essential role in modern timber construction. Consisting of a timber member in the tension zone, a concrete layer in the compression zone and a shear connection between the two parts, TCC slabs feature a number of advantages that make them ideally suitable for use in both office and residential buildings. However, currently used TCC slab systems carry loads only in one direction. In the frame of a large research project in cooperation with the industry, an innovative, light-weight, two-way spanning timber-concrete composite slab using beech laminated veneer lumber with steel tubes as connectors was developed. This paper presents the main results of the research project. First, the structural behaviour of the connection is characterised and discussed based on extensive experimental and analytical analysis. Second, the load-bearing behaviour of the TCC slab investigated in uniaxial bending tests is presented. The uniaxial bending tests showed a remarkably ductile global load-bearing behaviour due to the ductile failure mode in the connectors. A developed analytical model can describe the observed load-bearing behaviour of the tested TCC members accurately. Finally, the biaxial load-bearing behaviour of the TCC slab is characterised and discussed based on a large-scale experiment that allowed to perform static and dynamic tests on the same specimen in different support conditions. A substantial increase in stiffness and fundamental frequency in biaxial versus uniaxial support conditions was observed and accurately modelled, showing the great potential of the novel TCC slab., Engineering Structures, 286, ISSN:0141-0296

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

This paper presents the results of extensive investigations on the lamination strength grading, the production and the mechanical properties of European beech (Fagus sylvatica L.) glued laminated timber (GLT). Based on the analysis of potential influencing parameters on strength and stiffness as well as subsequent tension tests parallel to the grain on single boards, a combined visual/machine approach for grading the raw material into tensile strength classes T50, T42, T33 and T22 was developed. Boards strength graded with the developed procedure were then finger-jointed by a Swiss GLT producer and the strength of the finger joints was investigated by means of tension and bending tests. The strength and durability of the bonding was investigated and verified by means of tensile-shear and delamination tests. It could be shown that the required finger-joint and bondline strengths for GLT of strength classes GL40 and GL48 can be achieved, but that the process parameters for finger jointing (in particular the geometrical properties of the finger joint profile) have to be optimized in order to be able to produce GLT of strength class GL55. Finally, an extensive experimental testing campaign was performed to investigate the mechanical properties of European beech GLT produced based on the strength grading rules and production techniques developed before. Bending, tensile and compressive parallel to the grain, as well as shear tests were carried out on GLT specimens of strength classes GL40, GL48 and GL55 in different sizes in terms of cross-section and length. Based on these investigations and complementing numerical simulations, characteristic strength and stiffness values and formulae for consideration of size effects in bending, tension and shear were determined.

Carbon fiber reinforcements are applied in timber engineering thanks to their high strength, but their fossil origin compromises sustainability. Furthermore, applications for which an increase of stiffness is beneficial, such as in slab-type elements, still remain unexploited. Here, we reinforced beech wood with an emerging bio-based fiber type, densified delignified wood (DDW). We comparatively adhered DDW, flax, and carbon fibers to wood using a polyurethane adhesive. The specimens’ stiffness was tested before and after reinforcement using bending tests, and tensile tests of the isolated fiber composites were performed for modeling purposes. Whereas no beneficial effect was reported for flax fibers, DDW and carbon fibers were able to provide a stiffness increase of up to 10.5% and 16.7%, respectively, demonstrating the potential of DDW. On this basis, a design case study conducted for a timber–concrete composite slab showed that a DDW stiffness reinforcement can be a material saving alternative., Composites Part A: Applied Science and Manufacturing, 163, ISSN:1359-835X, ISSN:1878-5840

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

With the ever-increasing popularity of engineered wood products, larger and more complex structures made of timber have been built, such as new tall timber buildings of unprecedented height. Designing for structural robustness in tall timber buildings is still not well understood due the complex properties of timber and the difficulty in testing large assemblies, making the prediction of tall timber building behaviour under damage very difficult. This paper discusses briefly the existing state-of-the-art and suggests the next step in considering robustness holistically. Qualitatively, this is done by introducing the concept of scale, that is to consider robustness at multiple levels within a structure: in the whole structure, compartments, components, connections, connectors, and material. Additionally, considering both local and global exposures is key in coming up with a sound conceptual design. Quantitatively, the method to calculate the robustness index in a building is presented. A novel framework to quantify robustness and find the optimal structural solution is presented, based on the calculation of the scenario probability-weighted average robustness indices of various design options of a building. A case study example is also presented in the end. © 2020 The Authors, Engineering Structures, 227, ISSN:0141-0296

In the frame of an ongoing research project, the fire behaviour and fire resistance of CLT rib panels are studied. The floor system consists of cross-laminated timber (CLT) plates rigidly bonded to glued-laminated timber ribs by means of screw-press gluing using a one-component polyurethane adhesive. The experimental programme comprised reference tests and fire tests for fire resistances up to 120 min. In addition to the reference tests, shear tests of the bondline between CLT plate and glulam rib were performed at normal temperature. Further knowledge of the bondline’s behaviour was required for a wider range of temperatures. Therefore, shear tests of the bondline were performed at elevated temperatures. This paper focuses on the analysis of the cross-sections’ composite action in fire and under elevated temperatures. The fire resistance tests confirmed the assumption that the effect of the composite action was maintained in fire. The shear tests at normal temperature emphasized the required quality control as basic requirement for the composite action. The shear tests at elevated temperatures confirmed the bondline’s thermal stability up to 220°C. The residual shear strength at elevated temperatures were used to draw conclusions for the bondline’s performance under ISO-standard fire exposure. The bondline was determined to be intact in fire.

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

The aim of this paper is to investigate the methods available for encouraging the spread of timber constructions in small, peripheral regions such as southern Switzerland. Since 2005, Switzerland has witnessed a major increase in the number of timber constructions, mainly due to the new fire prevention regulations and to the climate and energy goals that the country wants to meet in the near future. This growth has been less significant in southern Switzerland. Data given by the Federal Office for the Environment (FOEN) shows the climatic advantages of the spread of timber constructions. Therefore, the opportunities for increasing the growth of such constructions in southern Switzerland have been researched. In order to identify and take advantage of the unique features of the use of wood in this region, two recent timber buildings, the Nordic Ski Centre by Durisch & Nolli, and the House in Ludiano by Tocchetti & Pessina, are analyzed and presented in this paper. The case of southern Switzerland can be a model for the spread of timber constructions in other similar regions.

This article presents experimental and numerical investigations on the buckling behaviour of glulam columns made of European beech (Fagus sylvatica L.) timber and a design proposal. First, the compressive strength parallel to the grain (fc,0) and the modulus of elasticity parallel to the grain (Ec,0) were experimentally determined in tests on stocky columns (slenderness ratio λ=12.5) of strength classes GL 40h, GL 48h, and GL 55h. Subsequent experimental buckling tests on slender columns with buckling lengths of 2.40 m (λ=41.5) and 3.60 m (λ=62.3) allowed investigating the buckling behaviour and quantifying the influence of the buckling length on the buckling resistance. Applicability of the effective-length method, which is the design method for columns in Eurocode 5 (EN 1995-1-1: Design of timber structures - Part 1-1: General - Common rules and rules for buildings. European Committee for Standardization, Brussels, 2010), was evaluated and a proposal for input parameters valid for columns made of European beech glulam is made. Numerical simulations revealed buckling resistances very close to the experimental results, confirming the proposed critical relative slenderness ratio λrel,0=0.25 and the fitted straightness factor βc=0.25. In addition, the numerical simulations allowed for an extension of the scope of the investigations., Materials and Structures, 53, ISSN:1359-5997, ISSN:0025-5432, ISSN:1871-6873

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 current work aims at determining optimal sensor configurations for the modal identification of a post-tensioned timber frame structure. The objective is to maximise the information gained from ...

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 introduces a non-contact method for the identification, quantification, and documentation of fibre direction of European beech wood (Fagus sylvatica L.). The developed approach is based on an automated visual analysis of the spindle pattern formed by the medullary rays, also termed wood rays. Each spindle is identified by means of image analysis technique, its position and orientation is determined, and the fibre direction of discretised elements is calculated. The individual process steps necessary to obtain an estimate of the fibre direction of a board are explained using the examples of five different failure types. In all examples, the estimated fields of fibre direction are congruent with the actual fibre direction determined by means of (1) the orientation of all present shrinkage cracks, which are established indicators for the fibre direction in wood, and (2) the fracture pattern after tensile testing. Employing the presented approach could open up new possibilities for the characterisation of European beech and other hardwood species with multi-row medullary rays in several fields of application, in particular regarding stress grading.

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.

While Timber–Concrete Composite (TCC) construction has been intensively studied in terms of structural behaviour, there is little research on the risk of corrosion of the used metallic shear fasteners in different exposure environments. Due to the marked differences in chemical environments of wood and concrete, however, it can be expected that the fasteners are subject to galvanic corrosion. This was experimentally studied in the present work. TCC specimens were fabricated for electrochemical testing and exposed to two different exposure environments, that is, 95% relative humidity and immersion in water. The moisture content in the wood, the difference in electrochemical potentials and the galvanic current were monitored over 2 months. Two types of fasteners were tested, namely zinc galvanized steel fasteners as well as browned fasteners that have been widely used in the TCC construction industry since 2013. It was found that the fastener parts in the wood generally act as an anode, while the remaining parts in the concrete act as a cathode. However, significant galvanic currents were only observed upon immersion in water. For practical applications in structural engineering, it is concluded that the mass loss of metal of the studied fasteners cannot present a severe risk for structures, especially not at the service classes 1 and 2 according to EN 1995-1-1.

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 post-tensioned timber frames beams and columns are connected by means of a tendon. The tendon presses the beams against the columns which leads to a stress situation where beams are loaded parallel to the grain and columns are loaded perpendicular to the grain. These kind of wood to wood connections are semi-rigid and can therefore resist bending moments. An important factor influencing the behaviour of post-tensioned timber frames is the connection stiffness. Compression tests perpendicular to the grain have been performed in order to estimate the perpendicular to the grain stiffness of a post-tensioned timber connection. The stiffness is represented by the modulus of subgrade reaction, which is the equivalent of a spring constant distributed over an area and which is a parameter frequently used in soil mechanics to calculate deformations and stresses under a foundation. The modulus of subgrade reaction is also needed to calculate the moment-rotation behaviour of post-tensioned timber connections. The compression tests were evaluated using different analytical models based on spring models and the Boussinesq solution in order to estimate the perpendicular to the grain stiffness, i.e. the modulus of subgrade reaction. The test evaluation showed that the modulus of subgrade reaction can be estimated based on the geometrical and mechanical properties of the column solely as suggested by the authors earlier if the Young’s modulus is estimated according to EN 338. However, if the calculation is based on higher values from literature or tests, the stress distribution in the column has to be accounted for in order to get accurate results for the modulus of subgrade reaction. The tests also showed that a reinforcement of the column is necessary in order to obtain a satisfactory stiffness in the post-tensioned timber connection. Reinforcing the Norway spruce (picea abies) column with European ash (fraxinus excelsior) increases the modulus of subgrade reaction significantly compared to a column made of spruce entirely.

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...