Timber Structures Research Articles

Quantitative assessment of the extent of damage to timber structures during the full course of a real fire using the energy equivalence method

In this study, an innovative method, the Energy Equivalence Method (EEM), is proposed in the context of the Performance-Based Fire Engineering (PBFE) framework for quantitatively assessing the degree of damage of timber structures during the full process of a real fire. To verify the validity of the method, glued laminated timber (GLT) specimens and GLT columns were selected as the subjects of fire action, and a series of equivalent fire experiments were conducted by using a parametric fire model (referred to as the DNI fire model), which is currently used in Germany, to simulate real fire scenarios. By comparing the equivalence of charring depth (CD), pyrolysis zone temperature, and residual load-carrying capacity of the test specimens after the action of the DNI fire and its equivalent standard fire, the validity of the EEM in quantifying the degree of damage to timber members after the DNI fire was fully verified. Subsequently, based on the fire experimental data, accurate thermal and structural models were developed, and these models were utilized to further validate the effectiveness of the EEM in quantifying the extent of damage to timber members under the action of a DNI fire over an arbitrary time period. The results of the study show that the proposed EEM not only can be used to assess the extent of structural damage during fire action and the residual load carrying capacity of the structure after fire action, but also promotes the transition from standard fire safety design to the PBFE design.

The effect of temperature and moisture content on drilling resistance measurements in wood (Pinus sylvestris L.)

ABSTRACT Drilling resistance (DR) measurements is widely used for nondestructive testing and evaluation of wood in growing trees and timber structures. A DR method can be applied in the regions with a cold climate and in wood with temperatures below zero degrees Celsius and varied moisture content (MC), which raises a question of correct interpretation of DR profiles and prediction of wood properties. Laboratory tests were conducted on Scots pine specimens with four levels of MC (7.4%, 11.0%, 23.5%, 147.9%) and temperature (+20°С, +2°С, −2°С, −10°С) variations. In-field tests were made on 33 growing trees at +18°С and −15°С. An IML-RESI PD 400 tool with a fixed rotational frequency of 2500 rpm and a feed rate of 1.5 m·min−1 was used. In most cases, wood temperature and MC had a significant influence on DR, but differences in an absolute value could be slight. A drastic increase in DR and feeding resistance was observed for water-saturated specimens tested at −10°C. For structural health assessment of timber structures at temperatures below 0°C, it is recommended to control wood MС. The effect of MC on DR was pronounced for groups of specimens with temperatures below and above the fibre saturation point. The in-field tests confirmed an increase in DR for frozen wood that can be used for studying water-conducting layers in growing trees.

Applications of Spatial Timber Structures in China and Research on the Performance of Their Typical Connections

Timber, being a versatile and sustainable material, has been used for residential and public buildings throughout history. In recent years, advancements in engineering and construction technology have resulted in the development of innovative timber spatial structures that push the boundaries of traditional timber construction. Especially, numerous spatial timber structures have been constructed in China in recent years. This study aims to provide an overview of notable examples of spatial timber structures in China, including their architectural features, structure arrangement and construction method. Additionally, the configuration of some timber connections utilized in the Taiyuan Botanical Garden project are analyzed and the mechanical behavior of connections are investigated by a brief introduction of experimental tests. The research will provide a reference for engineering design of spatial timber structures in the future.

Introduction to special issue—advances in mass timber structures

Introduction to special issue—advances in mass timber structures

Bonding strength between spruce glulam and birch plywood at different load-to-plywood face grain angles

There is growing interest recently in reducing the usage of metals in timber structures. Birch plywood possesses satisfactory mechanical properties compared to other wood-based panels and is promising to be utilized in timber connections as a substitute for the more conventional slotted-in metal plate. There are essentially two possibilities to connect plywood plates and other timber elements by means of either mechanical connections or adhesively bonded connections. Despite the more commonly adopted mechanical connections in current timber structures, the adhesively bonded connections hold the distinct advantages of being more cost-effective, stiffer, and with a lower risk of moisture penetration in the timber elements. When employing birch plywood in timber structure applications such as trusses and frame corners, stresses from different directions need to be transmitted by the plywood gusset plate. However, it is still uncertain how the bonding strength is affected by different loading angles to the face grain. This research question, specifically concerning the bonding strength between birch plywood and spruce glulam, has been addressed in this paper. It was found that the bonding strength varies within a relatively small range when the load-to-plywood face grain angle varies from 0° to 90°, which is promising for the development of adhesively bonded joints. Failure mainly occurred in glulam at 0° and 15°; while at other angles, a mixture of cohesive failure in glulam and plywood face veneer was dominant. The weak angle-dependence of the bonding strength can be explained by further checking the shear strength of the weaker wood adherends between glulam and plywood. A strong positive correlation was observed between bonding strength and the wood shear strength.

Photovoltaic Manufacturing Factories and Industrial Site Environmental Impact Assessment

Life cycle inventories (LCIs) and life cycle assessments (LCAs) of photovoltaic (PV) modules and their components focus on the operations of PV factories, but the factories and industrial site product and construction stages are either not or only partially tackled. This work contributes through the bottom-up, model-based generation of LCIs and LCAs for setting up a vertically integrated 5 GWp/a PV industrial site, including the manufacturing of silicon ingots, wafers, solar cells, and PV modules, on a 50 ha greenfield location. Two comparative LCAs are performed. The first compares the annualized environmental impacts of the developed LCI sets with four existing inventories in the Ecoinvent v3.8 database. The second comparative LCA explores the environmental impact differences concerning the industrial site when using different building systems for the factories. Here, the reference system with a steel structure is compared with two alternative building systems: precast concrete and structural timber. The results show that the wafer, cell, and module factories’ annualized environmental impacts with the Ecoinvent LCIs are strongly overestimated. For the ingot factory, the opposite result is identified. The impacts of all four factories show reductions of between 11.7% and 94.3% for 14 of the 15 impact categories. High mean environmental impact shares of 79.0%, 78.2% and 79.2% for the steel, precast concrete and timber structural building systems, respectively, are generated at the product stage. The process and facilities equipment generates 54.2%, 54.4% and 58.2% of the total product and construction stages’ mean environmental impact shares. The proposed alternative timber building system reduces the environmental impacts in 14 of the 15 evaluated categories, with reductions ranging from 1.1% to 12.4%.

Mechanical properties of multi-bolted Glulam connection with slotted-in steel plates

The Bolted Glulam Connection with Slotted-in Steel Plates (BGCSSP) is widely employed in modern timber structures due to its advantages of convenient installation and reliable force transmission. However, the current design methods lack rigorous mechanical derivation and fail to consider various influencing factors comprehensively. Furthermore, designing multiple dowel connections based on the behavior of individual dowels impedes optimization and limits the applicability of design rules. To systematically investigate the failure modes and mechanical characteristics of Multi-bolted Glulam Connection with Slotted-in Steel Plates (MGCSSP), specimens from 12 groups (6 specimens per group) were subjected to parallel grain tensile tests, considering four key influencing factors: bolt quantity, bolt arrangement, bolt diameter, and base material thickness. The experimental results indicate that as the number of bolts increases, the failure transitions from double-hinge failure to single-hinge failure. Additionally, there is an observable upward trend in both initial stiffness and peak load for the same type of specimen as the quantity of bolts increases, accompanied by a decreasing trend in the ductility coefficient. The analysis of experimental results reveals that both the quantity and diameter of bolts impact the initial stiffness and peak load of MGCSSP specimens. Based on experimental observations, dual-parameter calculation models for the initial stiffness and peak load of MGCSSP are proposed. The calculated results of the models align well with experimental data, providing references and convenience for the design of MGCSSP.

Influence of friction between wood and support elements in the design of timber structures for roofing

Throughout history, wood has played a crucial role in all phases of building construction. Despite existing prejudices in Brazil regarding its use in structural systems, primarily due to the lack of dissemination of technical information, wood is gradually gaining more space in the market as a viable and environmentally sustainable alternative. With exceptional mechanical properties, wood is compatible with other widely used construction materials in the Brazilian structural market, such as concrete and steel. In this context, this research aims to analyze the influence of considering the friction coefficient caused by the sliding of the support with free horizontal displacements in isostatic trusses, investigating its impact on the design of the components that make up the truss. Such sliding generates a lateral friction force that promotes a restraining effect on the structure, potentially relieving stresses on the lower chord members. For this purpose, the Finite Element Method (FEM) is used as an analytical tool, supported by the iTruss verification software to validate the obtained results. By considering the frictional force generated on the support links of the analyzed trusses, the numerical results revealed changes in the design of structural profiles for all existing wood strength classes (D20, D30, D40, D50, and D60) in situations of friction between wood and wood, and between wood and concrete. A reduction in the volume of wooden pieces was observed, ranging from 5.88% to 8.54%, suggesting that the inclusion of the friction coefficient during structural calculations can result in savings, not only from a financial standpoint but also promoting environmental benefits by encouraging a more responsible use of wood in civil construction.

Research on Lateral Resistance Performance of Prestressed Cross-Laminated Timber-Concrete Composite Structures under Reciprocating Loads.

Cross-Laminated Timber (CLT) and concrete composite structures represent an architectural system that integrates the strengths of both materials. In this innovative configuration, the CLT and concrete collaborate synergistically, harnessing their individual merits to achieve enhanced structural performance and functionality. Specifically, the CLT offers a lightweight design, superior bending resistance, and immense engineering plasticity, while concrete boasts exceptional compressive strength and durability. This study investigates the mechanical performance of CLT-concrete composite structures through quasi-static reciprocating loading tests in three full-scale CLT shear wall samples. Designed with varying initial prestressing forces and dimensions of the CLT panel, the prestressed CLT-concrete structures demonstrated a reduced dependence on the steel nodes, resulting in an increase in yield load, yield displacement, and maximum load-carrying capacity. Maximum capacity increased by 39.8% and 33.7% under initial prestressing forces of 23 kN and 46 kN on steel strands. Failure occurred due to localized compressive failure on prestressed steel strands and anchor plates. ABAQUS finite element analysis established three refined models, revealing that the increased initial prestressing force moderately enhanced stiffness but reduced ductility under similar cross-sectional dimensions. Furthermore, under consistent CLT material, dimensions, prestressing force, and loading conditions, prestressed CLT-concrete structures exhibited a higher maximum load-bearing capacity than prestressed CLT-steel composite structures. This study proposes structural design recommendations based on experimental and simulation results, incorporating specific assumptions.

Prediction Distribution Model of Moisture Content in Laminated Wood Components.

Shrinkage cracks are some of the most common defects in timber structures obtained from woods with an uneven distribution of moisture content and are subject to external dynamic environmental changes. To accurately predict the changes in the moisture content of wood components at any time and position, this study first applied the principles of food drying and established a moisture field model for laminated wood based on the analogy between heat and humidity transfer. A model for predicting the moisture content of wood that considers time and spatial distribution was then proposed. Second, by collecting relevant experimental data and establishing a finite element analysis model, three moisture absorption conditions (0-9.95%, 0-13.65%, and 0-17.91%) and four desorption conditions (34-5.5%, 28-8.3%, 31-11.8%, and 25.5-15.9%) were analyzed. In the moisture absorption comparison, the time needed to reach 95% equilibrium moisture content was 2.43 days, 4.07 days, and 6.32 days. The rate at which the internal components reached equilibrium moisture content exceeded 10 days. The temporal and spatial distribution of wood moisture content revealed the correctness of the proposed wood moisture field model. Finally, the moisture content prediction model was applied in the order of characteristic equation solutions, moisture content gradient difference, and laminated wood size. The results revealed that the established humidity field model can predict the wood moisture content and how it changes over time and in space. Notably, 1-2 orders for the solution of the characteristic equation are recommended when applying the prediction model. The greater the difference in moisture content, the faster the equilibrium moisture content is reached. The moisture content varies greatly based on the component size and position. Notably, the influence of moisture gradient and wood size on the average wood moisture content cannot be ignored.

Effect of Primer and Fibre Orientation on Softwood–Hardwood Bonding

Softwood is widely employed in construction and faces high demand. Australia is grappling with substantial timber scarcity, specifically related to radiata pine, which is the dominant structural timber in the construction sector. However, Australia has a significant hardwood population, which can be utilized to reduce the high demand for radiata pine. This paper aims to investigate the bond properties of both Australian softwood (radiata pine) and hardwood (shining gum). It also discusses the potential to combine softwood and hardwood in glue or cross-laminated timber by evaluating the bond properties of the radiata pine–shining gum interface. For hardwood, the effect of primer is also investigated to determine its efficacy in improving failure mode, bond strength, and stiffness. Lastly, both glulam and cross-laminated timber bonding scenarios are simulated for bond testing by examining the effect of relative fibre orientation on the bond properties of the aforementioned species individually and in combination. Instead of conventional block shear testing, which is predominantly used for same-species bond testing, push-out testing is adopted in this study. However, a comparison with block shear testing is also made in this article. The results indicated that the use of primer on hardwood reduced the inconsistencies in the bond properties and improved wood-side failure rates. It was also concluded that the effect of fibre orientation in a CLT scenario with combined hardwood and softwood failure modes can vary significantly, which leads to a higher standard deviation in the results. Nevertheless, this study outlines the challenges and opportunities for producing hardwood–softwood hybrid glue or cross-laminated timber.

Effects of environmental humidity on the gap of mortise-tenon joints: Experimental and numerical investigations

Mortise-tenon (MT) joints play a vital role in the lateral deformability and seismic performance of traditional timber structures. However, moisture exposure can cause shrinkage-induced gaps and then affect the durability of MT joints. Limited knowledge exists on the humidity response of MT joints. To investigate the effect of environmental humidity on the gaps between mortise and tenon, multiple measurements of moisture content (MC) and shrinkage deformation were conducted on straight MT joints that were subjected to humidity variations. Different ambient conditions and exposure levels were taken into account. Three-dimensional numerical models were established to simulate the humidity response of MT joints. Model validation was then performed by comparing the simulation and experimental results in terms of moisture distribution and gaps. On this basis, quantitative analysis was made to reveal the development mechanism and main influence factors of moisture-induced gaps. Results show that straight MT joints are vulnerable to environmental humidity changes. The observed gap is estimated to cause a decrease of up to 23.1% in the initial elastic stiffness. Although only contributed by the shrinkage deformation of tenons, the vertical gap is theoretically larger than the horizontal one which is attributed to a combination of both mortise and tenon. A clear linear relationship is found between the vertical gaps and the MC decrease, with the product of the radial shrinkage coefficient and tenon height as the theoretical ratio. Controlling the moisture exposure is considered the most effective way to reduce moisture-induced gaps in MT joints.

Survey as method: field trips of the Society for Research in Chinese Architecture, 1930–1937

In 1932, the Society for the Research in Chinese Architecture (SRCA) undertook a field trip to the Dule Temple, a Buddhist temple complex located 100 km from Beijing. Led by the Ivy-League trained Liang Sicheng, this survey opened up a new chapter for research into historic architecture in China. Supplemented by a series of other field trips, the Society sought to understand the constructional logic of ancient Chinese timber structures, and to communicate their findings in texts and drawings to architects, scholars, and the wider public, both in China and internationally. In order to explore these field trips, their methods and techniques, findings and dissemination, this article uses various outputs produced by the Society alongside photographs, drawings, and descriptions of the work undertaken on site. Set within the context of a nascent national identity that was in flux during the Republican period in China (1928–1937), this article considers surveying as a fundamental research method to record historic buildings, enable cross-examination with literature sources, and synthesise evidence for a new generation of Chinese scholars and architects.

Experimental and numerical studies on influences of wedge reinforcement on seismic performance of loose penetrated mortise-tenon joints

Wooden wedges significantly affect the rotational stiffness and load-bearing capacity of penetrated mortise-tenon joints (PMTJ). To clarify the role of wedges on the seismic performance of loose penetrated mortise-tenon joints, three types of full-scale PMTJs, including reference, loose, and wedge-reinforced joints, were tested under quasi-static loading. The deformation characteristics, hysteresis curves, rotational stiffness degradation behavior, and energy dissipation of PMTJs with wedge were analyzed. Three-dimensional nonlinear finite element models were established to simulate the wedge effects, and the stress states of joint were analyzed. The results indicated that the ultimate bending moment capacity of reference and loose joints was reached when the splitting failure of tenon occurred, while the wedge-reinforced joint reached such capacity when the transverse compression failure occurred at the wedges. The maximum bending moment of PMTJ with a 10 mm gap and a 25 mm gap were 18.3 % and 55.3 % lower than that of reference joint, while maximum bending moments of wedge-reinforced joint with a 10 mm gap and a 25 mm gap were 12.6 % and 17.03 % larger than that of reference joint, respectively. Numerical simulation showed that wooden wedge reduced stress concentration in the tenon and alleviated compression damage of the tenon. Higher load-bearing capacity and rotational stiffness were observed in joints when hardwood wedges were used, compared with that of soft wood. Wedge reinforcement could effectively improve the load-bearing capacity of loose PMTJ. These results yielded valuable data for the performance evaluation and retrofitting of penetrated mortise-tenon joints with wedges in traditional timber structures.

Typology, current state and non-destructive testing of timber roof trusses of historic churches in the West Vistula Delta, Poland

This paper presents the current state of conservation of historic roof churches located in the Żuławy of Gdańsk (Poland). It also describes the architecture of these temples, the region itself and old carpentry techniques for constructing roof trusses. Interdisciplinary tests were carried out in six churches. The geometry of the load bearing structures, the moisture content and the carpentry technique were specified. The field survey also included visual inspections and non-destructive testing of timber structural elements of the roof constructions. The ground penetrating radar and ultrasonic testing methods were used to assess the structure and extent of the damage to the timber elements. The interdisciplinary research presented in this article is important in the planning of historic buildings conservation works and it might be applied to other timber structures.

RuiXue Multi-Hall-Human machine collaboration in reciprocal structures

This article centers on the RuiXue Multi-Hall architectural design project in Chengdu, China, with a specific focus on a comprehensive workflow framework that integrates reciprocal geometric design and digital construction methods, primarily within the context of shell structures. The research expands on the concepts of structural design, adjustments of performance parameters, and the optimization of free-form shells. In addition, it outlines the spatial design approach for the shell structure. The study delves into reciprocal geometric design for the existing shell structure, establishing a library of reciprocal geometric shapes suitable for architectural design. The primary focus is on the application of these shapes to the shell structure, optimizing parameters for several grids within the library, and comparing various design schemes. Furthermore, the article discusses digital construction methods for the existing shell space and reciprocal structure, with a specific emphasis on the material performance of timber components. This discussion includes reciprocal timber structures and 3D-printed roofs for shell surfaces, all guided by a geometric control system to facilitate an interactive design and construction process. This research on reciprocal geometric design and digital construction methods for shell structures holds dual significance. It not only traces the historical development of reciprocal structures but also explores innovative construction methods using digital technology. The establishment of a comprehensive framework for reciprocal geometric design-construction is expected to catalyze innovative breakthroughs in future architectural design, spanning aspects such as space, form, materials, and structure.

Space efficiency in timber office buildings

Timber offices indicate a growing field, principally thanks to their potential to offer noteworthy ecological and financial gains over their entire life. Like many other building types, space efficiency is a crucial design parameter in timber structures to ensure a project's feasibility. This factor is especially significant in office buildings, where maximizing rental income reflects effective planning. Currently, there is a lack of exhaustive inquiry providing a thorough insight of space efficiency in modern timber office buildings. This study fills this gap in the literature by collecting data from 33 buildings through literature reviews and case study method to investigate space efficiency with the key architectural and structural factors that influence it. The results showed that: (i) central cores stood out as the prevailing core layouts, while peripheral arrangements were noted as alternative preferences. Prismatic shapes emerged as the most favored options; (ii) timber was extensively used as a primary building material, closely followed by combinations of timber and concrete. Load-bearing systems mainly relied on shear walled frames and configurations; (iii) average space utilization across examined cases was 88 %, with variances ranging from 75 % to 95 % among different instances; (iv) average ratio of core area to GFA was 10 %, showing variations between 4 % and 19 % across various scenarios; and (v) there were no substantial variances noted in the effect of different core planning strategies on spatial efficiency. Similar conclusions were drawn regarding building forms and structural materials. Our paper will assist in crafting design principles customized for diverse stakeholders, including architectural designers of timber offices.

Modelling the Response of Timber Beams Under Fire

A fundamental requirement for analysing timber structures under fire is to consider the degradation of material properties with temperature. Therefore, the objective of this study is to propose a model that accounts for the variation of the thermo-physical properties, the development of char, and its evolution with temperature. This model integrates a sequential coupling of heat transfer analysis with structural response. The degradation of the material properties is accounted for through the regulatory approach recommended in Eurocode 5. The stress analysis employs an elasto-plastic model with nonlinear isotropic hardening. Implementation of the model is achieved within the Abaqus suite of finite element software using external subroutines. The model's predictions align well with experimental data, accurately reproducing both thermal and structural responses. Specifically, the model accurately predicts temperature profiles, displacements, and the depth of the charred layer, which initiates above 300 °C. Additionally, for rectangular sections, it was observed that exposure of all faces to fire results in a non-rectangular residual section. Furthermore, employing the temperature-dependent thermal property curves suggested by EC5 yields satisfactory results when predicting the fire resistance of softwood timber structures.

Strength classes of brazilian hardwoods for structural design

For the elaboration of projects on timber structures, the Brazilian standard (ABNT, in Portuguese Associação Brasileira de Normas Técnicas) 7190 (ABNT 1997) ensures the correct application of physical-mechanical properties according to strength classes of lignocellulosic materials. This procedure eliminates the need for botanical identification of woods, since these strength classes support the efficient utilization of a wide range of woody varieties available in Brazil. Due to high mechanical resistances, the hardwoods are usually applied for structural projects of timber construction. This Brazilian standard document prescribes four strength classes (C20, C30, C40 and C60) for these woods, which are determined by characteristic value from the compressive strength parallel to the grain (fc0,k). But, these classes were obtained from experimental outcomes using a few wood varieties. The reorganization of strength classes should result in the best use of mechanical potentials of woods since the updating of these categories leads to the optimization of structural projects for timber construction in order to reposition this biomaterial at even more competitive levels. In this context, the present study aims to verify the current strength classes of hardwoods and if they lead to a good allocation of the fc0,k characteristic values. Otherwise, new strength classes can be determined for better allocations for efficient structural uses. As a result, 56 hardwoods were considered using 672 experimental determinations. Statistically, the current categories can lead to 12,5 % of incorrectly allocated values. The inclusion of C50 and C70 classes allow greater representation for these categories, in order to optimize the use of the hardwoods given the new strength classes. These findings ought to support future revisions of this Brazilian standard document.

Comparison of mass timber structure and RC structure with regard to sustainability by life cycle assessment

Since the 18th-century Industrial Revolution, high-rise have played a crucial role in addressing urbanization challenges, remaining a primary solution for urban living. However, this architectural advancement has also contributed to environmental decline. Presently, steel and concrete stand out as the predominant materials for high-rise construction, with well-documented significant carbon emissions. This paper delves into the potential of timber as an environmentally friendly alternative in high-rise construction to address such environmental concerns. Furthermore, it examines the impact of these structures on land load. The paper conducts a comprehensive review of life cycle assessment (LCA) studies and offers a comparative analysis of the climate change impacts associated with timber versus conventional materials like reinforced concrete (RC), underscoring the urgent need for sustainable development in the vertical expansion of our cities. The findings demonstrate that both the mass and carbon emissions of high-rise timber structures, in comparison to RC structures, can be reduced by approximately half. The paper aims to underscore the benefits of timber in comparison to conventional reinforced concrete methods, thereby informing material selection in favor of sustainable urban development.