The construction sector is a major contributor to CO2 emissions, responsible for approximately 37% of global and 23% of Switzerland’s total emissions. Addressing this substantial carbon footprint requires innovative and sustainable materials, advanced construction techniques, and comprehensive stakeholder engagement. This paper discusses the key challenges and opportunities in transitioning towards reduced carbon emissions within the construction sector, focusing on the Swiss industry and road bridges as a case study. An extensive dataset of Swiss road bridge infrastructure is assessed herein to understand the current state in Switzerland. An engineering-oriented critical review of high-performance materials such as non-metallic reinforcements, lower impact concrete mixtures and timber products is made in comparison to established construction materials. Circular principles and design for disassembly are explored as strategies for reducing environmental impact. This paper identifies the critical role of availability of early-stage information regarding environmental impact, standardization of emerging materials and techniques, and stakeholder engagement in driving the construction sector towards practices with reduced carbon emissions. Emphasis is put on the requirements and alternatives for achieving reduced carbon emissions in newly constructed bridges, while the potential for extending the service life of existing bridges and its importance for achieving net-zero infrastructure goals is acknowledged but not explored.

The influence of size effects on the shear strength and stiffness of glued-laminated timber (GLT) made from European ash (Fraxinus excelsior L.) was assessed based on a comprehensive experimental campaign. The experiments were performed on full-scale GLT beams with rectangular cross-sections width × height = b × h = 120 × 480-800 mm2, shear lengths Lv = 720-1500 mm, and ratios between the shear length Lv and the beam height h, i.e. α = Lv/h = 1.2-2.5. The influence of the test configuration (3-point bending and asymmetric 4-point bending) was also assessed. The obtained shear strengths of European ash GLT had mean values fv, mean = 10.2 N·mm-2 (coefficient of variation CoVfv = 14

The use of timber in construction has seen a rapid increase in demand in recent years. However, some question the capacity of the industry to supply sufficient amounts of structural grade timber in a sustainable and affordable manner as the demand will increase further. As such, the motivation for using all the available timber and increasing the efficiency of the timber is high. Currently, a large fraction of the available timber is used for non-structural purposes because of their unknown or unfavourable mechanical properties, or because of alternative use. To utilise more of the available timber for structural purposes and to increase the material efficiency, flexurally reinforced timber beams are attractive options. In this study, analytical bending capacity models for reinforced timber beams were derived. The bending capacity models were experimentally validated on full-size reinforced glued laminated timber beams with carbon-fiber reinforced polymer sheets. The experimental results showed an increase in the flexural rigidity of up to 65% and a strength increase of 74% when compared with unreinforced beams under pure bending. Moreover, a 44% reduction in the timber volume and three times higher global warming potential was demonstrated for reinforced timber beams when compared with unreinforced timber beams.

Timber-framed shear walls play a crucial role in providing stiffness and resistance to timber buildings subjected to horizontal forces induced by wind or earthquakes. Enhancing the load-carrying capacity of a timber-framed shear wall subjected to horizontal forces, is achieved most effectively by reinforcing the connection between sheathing and framing members. Since however, the shear resistance of such a wall is determined by the resistance of the individual wall elements, strengthening the sheathing-to-framing connection is possible only to an extent where the shear resistance is not limited by the resistance of the sheathing panel.This study presents experimental investigations of the shear resistance of OSB/3 panels, when used as sheathing material in timber-framed shear walls, which revealed that the shear resistance of the OSB/3 sheathing was reduced in comparison to the shear strength of the OSB/3 panels themselves. The reduction is attributed to additional stresses in the panel, and is accounted for in design rules specified in the German National Annex of Eurocode 5 (DIN EN 1995-1-1/NA:2013-08) and in the CEN Enquiry (ENQ) draft of Eurocode 5 (prEN 1995-1-1:2023-09). The results of the investigations confirm the reduction factor which is proposed in prEN 1995-1-1:2023-09, for wall elements with one-sided sheathings. However, the reduction factor specified for the design of wall elements with two-sided sheathings could not be confirmed. The results of this study performed with comparably massive and rigid timber framing revealed no difference in the reduction factor for timber-framed shear walls with one- or two-sided sheathings.

One of the obstacles to the recent trend toward taller timber buildings is the limited load-carrying capacity of softwood columns. With the aim of promoting the structural use of European beechwood (Fagus sylvatica L.) in high-performance applications, the buckling behavior of beech glued-laminated timber (GLT) columns reinforced with glued-in steel bars was investigated experimentally and numerically. Axial compression experiments were carried out on full-scale stocky and slender columns, and a finite-element model was developed and validated against the experimental data. The influence of geometric and material parameters on the load-carrying capacity of the steel-reinforced beech GLT columns was studied in parametric analyses. The experimental and numerical data demonstrate the high potential of this new structural product for high-strength columns in demanding residential, office, and industrial applications. The load-carrying capacity mainly depends on the cross section size, the column slenderness, the position and diameter of the reinforcement bars, and the initial deformed shape of the column. An eccentric layout with steel bars in the corners of the cross section is very effective in increasing the load-carrying capacity. Four corner steel bars of 20 mm diameter, 50 mm edge distance, and grade ST900/1100 were found to increase the load-carrying capacity of a 200-mm-wide square GL48h column by almost 40% across the slenderness ratios relevant to structural applications. The glued-in steel reinforcement is also expected to be able to provide an alternative load path for structural robustness, by enabling the columns to carry tensile forces. A design method for corner-reinforced beech GLT columns under axial compression was developed based on the empirical and numerical data.

Round timber and wood products are measured, sorted, and graded at different stages in the wood-value chain starting already at the stem level in the forest. This chapter gives an overview of grading methodologies and techniques for the measurement and grading of round timber, sawn timber, veneer, and wood-panel products. The section concerning round timber focuses on the grading and sorting of logs for sawmill and veneer production. For sawn timber, visual and strength grading are discussed, for both the European and the North American markets. Techniques for measurement and process control in the wood-panel industry are finally discussed, where the different industrial methods used today are in focus rather than the specific grading rules used in the industry. The technologies presented have a broader application outside the field of the wood-panel industry, and can be of interest for the measurement of wood composites in general.

For lateral force-resisting systems of multi-storey timber-framed buildings, the usual policy of current standards is to only consider timber-framed shear wall segments ranging continuously from the ground floor to the top edge of the building and to neglect wall elements with openings.Developing a design method that allows taking wall elements with openings into account, would make the lateral force-resisting system more efficient and respective buildings more economic.This paper presents investigations of the combination of sheathing thickness and arrangement of the fasteners connecting the sheathing to the framing to maximize the load-carrying capacity of the wall while guaranteeing a ductile failure of the connection.The results of the study provide the basis for further experimental investigations on one-and two-story wall elements with large openings with the final goal of developing a design method for timber-framed shear walls with openings.

The influence of volume effects on the shear strength and stiffness of glued-laminated timber (GLT) made from European ash (Fraxinus excelsior L.) was assessed based on a comprehensive experimental campaign.The experiments were performed on full-scale GLT beams with rectangular cross sections b×h = 120 × 480 -800 mm 2 , shear lengths Lv = 720 -1500 mm, and shear length/height ratios = Lv/h = 1.2 -2.5.The influence of the test configuration (3-point bending and asymmetric 4-point bending) was also assessed.The obtained shear strengths of European ash GLT had mean values fv,mean = 10.2 (CoVfv = 14%) and 12.2 N mm -2 (CoVfv = 15%), for the 3-point and asymmetric 4-point bending test configurations.The shear strength showed some size dependency, with k = 0.2-0.4 for a strength modification factor (h/600) -k as a function of the beam height h.

Image-based local fibre direction data, generated based on the analysis of the medullary spindle pattern, were used to improve the prediction of the tensile strength parallel to the grain of European beech (Fagus sylvatica L.) boards. An approach to characterise the local fibre orientations in a board using a single numerical grading parameter was further developed. This parameter was used, in combination with the dynamic modulus of elasticity, to develop a regression model providing very good predictions of the experimentally determined tensile strength parallel to the grain (R-2 = 0.84). Subsequently, machine-learning techniques were used to improve the strength model. Non-destructive and destructive tests were performed on (N =) 47 boards. A data (sub-) set (n = 36) was used to train different machine-learning techniques (Support-Vector Machines, Decision Tree, Random Forest, and Artificial Neural Network) using a 6-k cross-validation approach. The generalisation ability of the models was then assessed by a hold-out dataset (n = 11). The results showed that all machine-learning models presented good prediction accuracy (R-2 up to 0.88 and MAPE below 8%). The support-vector machine and random forest methods showed the best performance. The combination of experimental methods with machine learning allows for a more precise strength grading of timber and, thus, can contribute to a more resource-efficient use of wood and may open new and more demanding fields for high-level timber applications in structures.

Sheathed timber frame shear walls (STFSW) with strong anchorage have recently been studied to be used as the main lateral force resisting system in timber buildings. The first part of this research project highlighted the enhancement of the shear stiffness and strength of the STFSWs with strong anchorage in comparison with the established configuration of light-frame timber shear walls under monotonic horizontal loading. In this paper, the in-plane seismic behavior of STFSWs with strong anchorage was further investigated by means of quasi-static monotonic and cyclic loading tests on large-scale timber shear walls. The boundary conditions of the specimens were considered more realistically by applying a combination of vertical force and bending moment on top of the walls. In addition to the ISO 21581, the walls were tested under a new horizontal cyclic loading protocol especially developed for the low-to-medium seismicity regions. The STFSWs with strong anchorage showed a marginally higher shear resistance under cyclic loading. Nevertheless, in terms of ultimate displacement, they did not evidently perform as well as under monotonic loading when subjected to cyclic loading. Withdrawing of staples was the main failure of the stapled connections resulting in the out-of-plane displacement of the sheathing panels, which was clearly observed by the 3D digital image correlation measurement system. The low-to- moderate seismicity loading protocol was not highly influential on their shear resistance and displacement capacity.

European beech wood (Fagus sylvatica L.) is currently used only to a very limited extent for the production of glued laminated timber (glulam). Although this most widespread hardwood species in Central Europe has a very high potential in terms of strength and stiffness, besides its application to railway construction (as sleepers), it has so far been mainly used by the furniture industry and for heating purposes. One main reason for this is the lack of standards and guidelines regulating the production, quality control and specifying the mechanical properties of beech glulam. In this paper, an extensive research project aiming at determining the mechanical properties of beech glulam is presented. Based on bending, tension, compression, buckling and shear tests on beech glulam specimens of different cross sections and strength classes and taking into account previous investigations as well as the results of numerical simulations, the mechanical properties of beech glulam are determined. Furthermore, formulas to account for the effect of the member size on the bending and shear strength as well as buckling curves for the design of columns made of beech glulam are presented.

Das Holz der Rotbuche (Fagus sylvatica L.) wird gegenwärtig nur in sehr geringem Maße für die Produktion von Brettschichtholz (BSH) verwendet. Obwohl diese in Mitteleuropa am weitesten verbreitete Laubholzart ein sehr hohes Potenzial hinsichtlich Festigkeit und Steifigkeit besitzt, wurde sie, neben dem Einsatz im Bahnbau (Schwellen), bisher überwiegend in der Möbelindustrie eingesetzt oder wird – mit geringer Wertschöpfung verbunden – häufig thermisch verwertet. Ein Hauptgrund dafür sind fehlende Normen und Richtlinien, welche die Herstellung und die mechanischen Eigenschaften von BSH aus Buche regulieren würden. In diesem Beitrag wird eine umfangreiche Forschungsarbeit zur Bestimmung der mechanischen Eigenschaften von BSH aus Buche vorgestellt. Es wurden Biege‐, Zug‐, Druck‐, Knick‐ und Schubversuche an Buchen‐BSH‐Bauteilen unterschiedlicher Querschnitte und Festigkeitsklassen durchgeführt, welche durch numerische Modellierungen ergänzt wurden. Die daraus abgeleiteten mechanischen Eigenschaften von Buchen‐BSH, Formeln zur Berücksichtigung von Größeneffekten bei Biege‐ und Schubbeanspruchung sowie Knickkurven für die Berechnung stabilitätsgefährdeter Stützen aus Buchen‐BSH werden in diesem Bericht präsentiert.

In this work, the relationship for a socket-type connection in wooden foundation piles is investigated, and a trilinear moment-rotation diagram was determined by means of experiment. Numerical and analytical models confirmed that the material properties for compression perpendicular to the grain are governing for the connections’ strength and stiffness properties. This was similar to the response found in the experiment, where ductile behaviour was observed, which can be explained from the plasticization after the compression strength perpendicular was reached. Although because of the specific configuration (confined in a circular tube) the found strength perpendicular to the grain cannot be assigned to other configurations, a good estimation of the stiffness of the connection can be made with FEM models, assuming an MOE90 of 70 N/mm2 for a fully saturated pile. With a conservative assumption for the strength perpendicular to the grain the influence of the connection in a pile-soil model can be investigated also for other configurations than the tested one. A procedure to study the influence of tangential (usually horizontal) soil displacements on timber piles with concrete extensions piles on top is proposed. The outcome of a specific situation from practice with high horizontal loads showed that the bending capacity of the timber pile will in most cases be governing and not the investigated socket connection.

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 ($$\textit{f}_{\mathrm{c,0}}$$) and the modulus of elasticity parallel to the grain ($$\textit{E}_{\mathrm{c,0}}$$) were experimentally determined in tests on stocky columns (slenderness ratio $$\lambda = 12.5$$) of strength classes GL 40h, GL 48h, and GL 55h. Subsequent experimental buckling tests on slender columns with buckling lengths of 2.40 m ($$\lambda = 41.5$$) and 3.60 m ($$\lambda = 62.3$$) 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 $$\lambda _{\mathrm{rel,0}} = 0.25$$ and the fitted straightness factor $$\beta _{\mathrm{c}} = 0.25$$. In addition, the numerical simulations allowed for an extension of the scope of the investigations.

•Increasing interest in the application of structural health monitoring.•Structural health monitoring and non-destructive testing for timber structures.•Case studies of monitoring of timber structures.•Survey about monitoring of timber structures.

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.

The paper presents experimental investigations of friction properties (a) between adjacent sheathing panels made of Oriented Strand Board (OSB) and (b) between OSB panels and glued laminated timber (GLT) frame members as they occur, for example, between parts of light-frame timber shear walls. The friction stresses are evaluated for different levels of compressive stress and different loading rates in monotonic and cyclic tests. The test results confirm that the static friction coefficients are larger and have a larger variability than the kinetic friction coefficients. The friction coefficients between the GLT frame members and the OSB panels are in general smaller than the friction coefficients between the sheathing panels themselves. The tests show that the friction coefficients decrease with increasing cumulative sliding displacement. Analysis of the contact surface before and after the shear test indicates that the sliding reduces the height of the asperities of the contact surfaces. However, after a cumulative displacement of about 100 mm the friction coefficients remain approximately constant.