This issue contains a number of state of the art contributions on Timber Structures and Engineering. They are written by scientists, architects and engineers interested in promoting the use of timber as a construction material.

In fact, when trying to find a reliable timber engineering solution, the designers of structural elements are facing a major challenge, i.e. although timber is one of the most widely used materials in the world, it lacks the reliability of stone, concrete and other materials. Indeed, it is easy to understand why the Eurocodes only accept its use under simple uni-axial load conditions, in view of its anisotropy, heterogeneity and many other imperfections.

Timber has been regarded in the past as an unreliable material. Its main advantage was its local availability, which made its use easy and economical.

However, a major structural engineering revolution took place in the XXth Century. It was the emergence of composites, for which synergy between different materials offers a reliable and strong structural solution. One thus discovers the advantages of “composite materials solutions” in combination with more mechanically reliable materials, plus others that offer thermal, acoustic, insulation, fire resistance, anti seismic behaviour, and other properties.

Timber has gained credibility in structural applications despite its incertitudes in mechanical properties and its limited possibilities in the case of traction structural joints or multi-axial states of stress. It is also a beautiful material, which can be used for a multitude of complex structural forms which has led to its ever-increasing use in the modern built environment.

Panels protect timber elements in timber frame assemblies during fire. The influence of the panels can be incorporated into calculations according to EN 1995-1-2, Annex C [1]. The number of panels incorporated in this standard is limited. Moreover, the calculations performed according to this standard result in overestimation of the charred area. In this work, experimental analysis of the protective behaviour was performed. Small-scale fire tests were used to monitor the temperature inside the timber element and the timber frame assembly. The measured results are compared with calculations according to the standard.

Timber–concrete composite structures are often used as floor solutions in new and existing buildings to combine better acoustic separation and improved thermal insulation with increased stiffness and greater load-carrying capacity. The choice of a structurally effective yet cheap shear connection between the concrete topping and the timber joist is crucial to make the composite floor a viable solution that can compete with reinforced concrete and steel structures. The use of inclined screws is a possible option to maximize the slip modulus of the connection and, at the same time, keep the construction cost within acceptable values. In this paper, the results from an experimental and numerical investigation carried out on such a type of shear connection are reported. Push-out tests were carried out at the Laboratory of the Department of Civil, Building and Environmental Engineering of the University of L’Aquila. Each specimen consisted of a timber block connected to two concrete slabs by means of two 8 mm diameter screws per side produced by Rotho Blaas. A layer of OSB was interposed to reproduce the timber flooring often used as permanent formwork for the placement of the concrete slab in new floors or the existing timber flooring when strengthening existing timber structures. Two different screw lengths and interlayer thicknesses were investigated. For each configuration, 10 push-out specimens were tested. The results were statistically assessed by computing the mean slip moduli and the characteristic values of the shear strength. Numerical simulations were also carried out to investigate the dependency of the slip modulus upon the screw inclination and the interlayer flooring thickness.

A 3D Finite Element (FE) model has been developed, which accounted the geometric nonlinearity of flange and web portions of I-beams. The nonlinear FE model was reviewed against tests on castellated timber beams having a web with hexagonal holes. Load carrying capacity, load-deflection responses and failure modes for castellated beams in flexure were predicted and compared to the experimental results. An additional parametric study involving two different web opening shapes (circular and rectangular) was performed using the presented FE model to study the effects of the change of shapes of holes in web portions on the strength and buckling behaviour of castellated beams in bending. The parametric study has shown that castellated timber beams failing due to web-post buckling modes exhibited a strong decrease in the initial load capacity.

Over the last few years, Cross-Laminated Timber (CLT) panels have become increasingly popular in many structural applications. The growth in CLT uptake by the construction sector is likely to continue in line with the pressing need for sustainable construction. Although current design methods exist for CLT, often these have limits of applicability. In order to gain upmost efficiency, there is a need for improved analytical methods to fully determine the structural behaviour of CLT. In this article, CLT panels will be investigated as a novel application of the State Space Approach (SSA). As CLT is a laminated composite panel, the 3D analytical approach provided by the SSA is highly applicable. Comparison with existing experimental results for different CLT panels are explored for simply supported orthotropic CLT panels under different types of loading. The effect of the plate thickness on displacements and stresses is described quantitatively. The results demonstrate the capability of the SSA method to capture the nonlinear distribution of the stresses through the depth of the plates over a range of thicknesses, thus offering an improved understanding of CLT structural behaviour.

The resistance to horizontal loads provided by timber constructions is determined by the racking resistance of the timber frame walls within the structure. In Eurocode 5 (EN 1995-1-1), two methods are described to assess the racking resistance of these structural elements. Method A refers to a mechanical model while method B is empirically based and therefore less attractive. When using method A, full anchorage of the leading stud is needed. Moreover, contributions of wall panels with openings are neglected in the assessment of the racking resistance. In this paper, an experimental campaign studying the racking resistance of partially anchored walls with different wall and loading configurations is presented. The study shows that window and door openings lead to a reduction of the racking resistance of the wall depending on the size of the opening. Additionally, a comparison between the experimental data and several design methods for the assessment of the racking resistance of the wall panels is made.

Infrared is a part of electromagnetic spectrum not visible for the human eye, but contain important information regarding material status. Several scientific methods have been developed during years to acquire, analyse and interpret the infrared radiation in active and passive way. The technology become especially interesting nowadays when infrared measuring instruments become portable and affordable, being reasonably accurate at the same time. This research summarizes some possibilities of implementing modern instruments available on the market but also presents prototype solutions developed for the research needs in the laboratory. Near- and mid-infrared spectroscopies as well as hyperspectral and thermal imaging in different configurations are briefly described with a special focus on the specific application in assessment of timber structures. Advantages for implementation but also limiting factors for each technology are listed and discussed.

This paper presents an innovative lateral load-resisting wall system, which is an evolution of the light-timber frame (LTF) shear walls currently available on the market. In comparison to traditional LTF walls, the novelty aspect is the use of cross-laminated timber (CLT) beams and studs instead of solid timber elements. Thanks to this ‘hybrid’ approach, this new system combines some peculiar aspects of LTF structures (such as the limited weight and the high dissipative behaviour) with the potentials of CLT. Moreover, the use of CLT elements limits the issues due to the compressive deformations on bottom beams and permits to employ some innovative connections with high mechanical properties. Cyclic shear tests are carried out on two configurations of interest, assembled by considering different layouts of the load-bearing elements. Test results are compared to the experimental data obtained on similar LTF systems and differences are critically discussed.

Laminated timber-concrete (LTC) and steel-timber-concrete composite beam (S-LTC) members with adhesive interlayer connections were experimentally investigated. This paper presents the results of the acoustic emission (AE) investigation performed during short-term static ramp-loading to failure tests. The beam specimens were continuously monitored using accelerometers connected to a four channel dynamic signal analyzer. For LTC beams, the failure of the timber in tension was typically observed; therefore, a steel layer was added to the tension side of the timber layer to increase the strength and to induce a ductile behaviour. The results of the AE investigations on two LTC and two S-LTC specimens reveal the progression of the failure as it initiates and gradually develops within the beams, leading to the tension failure and shear failure modes for the LTC and S-LTC specimens, respectively. The results confirm that the fast Fourier transformation (FFT) and waterfall type of spectral analysis have an important role in supplying substantial and reliable amounts of information for the identification of different phenomena in connection with the failure process of the investigated structural members.

Wood is referred to as a material but in the true material sciences definition, a material is uniform, predictable, continuous, and reproducible. No two pieces of wood are the same even if they came from the same tree and the same board. Wood is better described as a composite and, more accurately, as a porous three-dimensional, hydroscopic, viscoelastic, anisotropic bio-polymer composite composed of an interconnecting matrix of cellulose, hemicelluloses, and lignin with minor amounts of inorganic elements and organic extractives. So, even solid wood is a composite. The characteristics we deal with at the solid wood level (swelling/shrinking, biological attack, and strength) are derived from the properties at the cell wall matrix and polymer level. Moisture sorption and desorption in the cell wall polymers results in dimensional instability and changing mechanical properties. Many different types of microorganisms recognize wood as a food source and are able to break it down resulting in both weight and strength losses. One technology that has now been commercialized to achieve high levels of stability, durability, and improved wet mechanical properties is acetylation: a reaction between the hydroxyl groups in the wood cell wall polymers and acetic anhydride. While all woods contain a low level of acetyl groups, increasing this acetyl content changes the properties and, thereby, the performance of the reacted wood. When a substantial number of the accessible hydroxyl groups are acetylated consistently across the entire cell wall, the wood reaches its highest level of stability and durability.

Massive timber plate elements, specifically cross laminated timber (CLT), has gained popularity recently in North America as major alternative construction material for building components offering competitive advantages relative to traditional reinforced concrete slab for medium rise applications. There are two major structural applications for this kind of timber plate, as floor slab or shear wall components of multi-storey buildings. The following study will be focused on the structural performance of hybrid multi-storey buildings constructed using CLT plate as the floor slab elements. The specific objective of this paper is to investigate lateral deformability of floor diaphragm that is composed of CLT slab in combination with reinforced concrete and steel floor framing loaded under seismic excitation. Critical irregular floor layouts of medium rise buildings are selected and modeled using computer structural and building analysis software ETABS. Major outputs including lateral floor deformation (drift), storey shear and dynamic characteristic analyses are analyzed and contrasted with the current design practices, i.e. building code application with respect to diaphragm assumption for seismic design. As in the reinforced concrete-based floor diaphragm, expected general outcome from this study is to provide input for design code provision regarding whether rigid, flexible, or in-between (semi-rigid) assumption of CLT-based diaphragm is adequate for performing design standard procedure for seismic design of hybrid multi-storey buildings. Structural analysis and modeling challenges for CLT-based diaphragm used in hybrid multi-storey buildings are presented and design recommendations will be given.

In the field of timber engineering, adhesive bonding remains a promising, though poorly developed, joining technique that may increase the structural stiffness and capacity of timber joints and structures. Selecting ductile adhesives may further allow to conceive ductile joints, which can compensate for the missing material ductility of timber. To demonstrate the potential of this approach, adhesively bonded double-lap timber joints were manufactured using a ductile acrylic adhesive and then subjected to axial tension and compression. The load–displacement responses were captured and compared to those of the same joints composed of a brittle epoxy adhesive. The effect of the different adhesives on the joint ductility has been studied and quantified.

As a natural raw material timber shows indisputable environmental excellence and certainly represents one of the best choices for sustainable construction. The use of glazing in buildings has always contributed to openness, visual comfort and better daylight situation. The features of the both building materials lead to the development of a new type of highly attractive structures, the so-called timber–glass buildings. However, in a view to maximising the use of natural solar radiation gains, the most of the glazing is usually placed in the south facade of such buildings, which can lead to many structural problems, especially when the building is exposed to heavy horizontal loads. In such cases it is usu- ally to assure a horizontal stability by using additional visible diagonal elements or by internal wall elements. In this study we are presenting another solution by using timber-frame wall elements with fixed insulating glazing placed on the external side of the timber frame where the glass pane is consid- ered as a load-bearing element. It is presented that such timber–glass load-bearing wall element can significantly contribute to the overall horizontal resistance of the whole building. The behaviour of load-bearing timber–glass wall elements is additionally modelled with FE model where the bonding line is modelled with spring elements. With such developed mathematical model it is possible further parametrically to analyse many various parameters which significantly influence on the capacity, stiff- ness and failure mechanism of such composite elements.

This work investigates the exploitation of a historical timber device used as masonry reinforcement in seismic prevention in the Mediterranean area. Such a technology is realized by means of a three-dimensional timber frame embedded in stone masonry in order to bind together the various structural parts, and contribute to the overall seismic resistance. Very often, such a constructive principle was extended not only to the weakest parts but to the whole building, creating new structural configurations that were able to absorb the effects of seismic ground motions. From Roman times (opus craticium), this system spread all across the Mediterranean area becoming common during the eighteenth century in Italy (Bourbon casa baraccata), in Portugal (Pombaline gaiola), in Turkey (hımış), etc. However, examples of timber devices and frameworks may be found almost worldwide: in the continental northern Europe, including those countries that are usually not subjected to earthquakes, as well as in Central Asia or in Japan, to America and North Africa. A large number of examples are reported to show how some traditional technologies, along with the suboptimal rules of the art, made a robust construction possible. Furthermore, by means of philological criterion and detailed analysis of seismic vulnerability improvement, the knowledge of such a system may allow developing novel designs and specific preservation works that could ensure the structural safety of historical constructions without modifying their main structural configuration. From such a perspective, this study examines the aspects of using diffused timber frameworks with masonry infill that go beyond anti-seismic technology, describes the common constructive features and helps develop guidelines for preservation of such systems.

This work reports a summary of different type of analyses and modelling approaches, typically adopted by practitioners and researchers for the prediction of the seismic response of multi-storey CLT buildings. Specifically, two different modelling approaches are deeply investigated and compared; the first one is a component approach, which adopts springs (linear or non-linear) for connections, while the second one is based on a simplified phenomenological model where the behaviour of the system is reproduced by means of diagonal springs (linear or non-linear). The advantages and disadvantages of the two approaches are presented and critically discussed with reference to the types of the performed analysis (linear or non-linear).

In order to verify the capability of the two modelling approaches to predict the seismic response of CLT structures performing linear analyses, a series of multi-storey buildings with increasing number of storeys and increasing values of design PGA are investigated. Obtained results are compared in terms of principal elastic periods, internal forces in the connection elements and drifts. Moreover, some correlations between results from the component and the phenomenological approach are given. Then, a first attempt of defining a numerical model suitable for non-linear analyses of a single CLT shear-wall, according to both the component and the phenomenological approaches is presented. Finally, the obtained results are discussed, highlighting the key issues in non-linear modelling of CLT structures.

The need to mitigate damage of buildings even after strong earthquakes has led to the development of high-performance seismic resisting systems. Extensive studies have been made in the last decade on the development and use of jointed ductile connections and on the effects of rocking vibration systems in reducing seismic damage of buildings. A recently developed technology for construction of multi-storey timber buildings called Pres-Lam system uses long lengths of prefabricated laminated timber and binds them together using pre-stressing steel tendons. When appropriately combining unbounded post-tensioned tendons, or rocking columns with additional sources of energy dissipation devices, a hybrid system is obtained, with self-centering and dissipative properties, leading to a characteristic flag-shape hysteresis behaviour.

A three-dimensional, three-storey, two-third scaled, post-tensioned timber frame model was tested at the structural laboratory of the University of Basilicata. During shaking table tests, two different configurations of the test model have been studied considering column-table connections with and without the activation of dissipative steel angles. This paper focuses on different numerical modelling of the rocking mechanisms at the column-foundation connections. Two different modelling have been considered for two different test configurations by means of a pinned base or an appropriate combination of nonlinear rotational springs, for free rocking and a suitable combination of gap elements and linear springs or rotational springs, for dissipative rocking. The numerical outcomes of nonlinear dynamic analysis are compared with experimental test results providing an adequate representation of the seismic response.

The Douglas is one of the most used species in France, especially in the Auvergne-Rhone Alpes Regions. This species found in unprotected outdoor environment is a major resource for the wood industry. However, variations in moisture content (MC), relative humidity (HR) and temperature (T) coupled with creep, can weaken its mechanical resistance. The main objective of this work is to study the mechanical behaviour of cracked wood beams under climate changes (T, HR and MC), the long-term loadings and the defects of wood (cracks, knots, orientation of annual rings etc). In this study, the evolutions of the crack length and the crack opening are presented. The results show the influence of climatic changes on the sustainability of timber structures of Douglas beams.

Throughout the centuries, nearly all signal buildings on the European continent have been built in masonry or concrete – in harsh, ‘stone-like’ materials. Norway differs remarkably from this main trend. We see that the European examples of stone architecture are largely reinterpreted in Norway as architecture in wood. The keywords are climate, economy, knowledge and tradition. Climate: Wood provides significantly better thermal insulation than brick, stone and concrete. Economy: With the exception of the last 50 years, Norway has been a poor country on the edge of Europe; therefore, there were rarely sufficient finances to build resource-intensive, magnificent buildings in stone or masonry. Knowledge and tradition: These factors are interrelated; tradition leads to knowledge and knowledge creates tradition. Norway has always had skilled carpenters, joiners and wood carvers from the Viking era until the present day. Despite poverty and distance, Norway was not an isolated and uninformed country; Norwegians have always been a seafaring people who grasped European impulses and style trends and brought them home.