Timber Buildings Research Articles

Numerical and experimental investigations of cracked light-frame timber walls

This study investigates the impact of sheathing panel cracks on the structural performance of light-frame, modular-based timber buildings, focusing on the racking stiffness and strength of the individual timber walls in the modules. Previous research has investigated such walls for decades and lead to practical design methods in the harmonized European design code, Eurocode 5. Such hand calculation methods are effective for simple geometries but for walls with openings or complex forms, a correct prediction of stiffness and strength is considerably harder to achieve and load levels where cracks initiate are almost impossible to predict. The paper presents both experimental and numerical studies to investigate how significant cracking in sheathing panels affects the load-carrying capacity of various light-frame timber walls. Finite element simulations using Abaqus are conducted to model the cracking of sheathing panels with the extended finite element method. Moreover, an orthotropic elasto-plastic connector model is introduced for the nail joints. The results indicate that significant cracking of the sheathing panels influences the stiffness and the load-carrying capacity of the wall elements and that the crack initiation and propagation is strongly affected by factors such as the location of openings, the shape of the sheathing panels and the type and position of sheathing-to-framing connections. The numerical results presented align satisfactory with the experimental data particularly regarding load levels at crack initiation and propagation. Furthermore, a parametric study investigates how cracks, orthotropic connector properties and vertical constraint of bottom rails influence the racking strength of different timber walls.

Seismic loss assessment of direct-DBD platform-type cross-laminated timber shear wall systems using FEMA P-58 methodology

An efficient design method should provide practitioners with a means for sizing timber buildings to meet specific performance levels against estimated earthquake intensities. Displacement and energy design considerations in force-based design (FBD) procedures are not as precise as intended in complex systems, such as mid- to high-rise timber buildings. The main aim of this study is to tailor the direct displacement-based design (D-DBD) classical framework to platform-type cross-laminated timber (CLT) shear wall structural systems and validate their performance for low-rise to high-rise timber mixed-use buildings. A comparison with results obtained via the FBD analyses is also provided. To this end, timber buildings with heights of 4, 8 and 12 stories are designed via the D-DBD and FBD methods. The seismic performance of platform-type CLT wall buildings is assessed in terms of the repair cost, repair time and casualty rate using FEMA P-58 methodology. The seismic response of CLT shear walls shows that the FBD method may lead to an expensive overdesign, especially in high-rise platform-type CLT walls. Conversely, the D-DBD method develops structural systems which can sustain a comparable level of damage from low- to high-rise platform-type CLT walls. Although the seismic loss assessment of buildings shows slightly better performance for the FBD method than the D-DBD method, it is worth noting that the D-DBD method does not lead to an unsafe building. Consequently, the D-DBD method sounds like a proper alternative approach for designing the CLT shear walls to achieve target performance levels without requiring a premium upfront cost.

LCA Operational Carbon Reduction Based on Energy Strategies Analysis in a Mass Timber Building

LCA Operational Carbon Reduction Based on Energy Strategies Analysis in a Mass Timber Building

Life Cycle Assessment and Cost Analysis of Mid-Rise Mass Timber vs. Concrete Buildings in Australia

Life Cycle Assessment and Cost Analysis of Mid-Rise Mass Timber vs. Concrete Buildings in Australia

Experimental and parametric study on friction-type high-strength bolted connections between steel frames and cross-laminated timber infill walls

Timber-steel hybrid structural systems provide a prospective solution for utilizing timber in multi-storey and high-rise buildings. The system of steel frame with infilled cross-laminated timber (CLT) shear walls is an effective hybrid timber-steel one. In the design of this kind of hybrid system, the connections between CLT walls and steel frame beams are key issues, because they have great impacts on the distribution of lateral forces in structures. In this paper, a friction-type high-strength bolted connection (FHBC) between CLT walls and steel frame beams is proposed. To investigate the performance of the proposed FHBC, experiments were conducted on the FHBCs fabricated with three- and five-ply CLT. The mechanical behaviors of the connections were evaluated. The pretension loss in the tested FHBCs with three-layer CLT is less than 15 % within a displacement of 10 mm. Besides, enhancement of axial force in the high-strength bolt was observed in the five-layer connections during the loading procedure. Theoretical analysis was performed to provide recommendations on the initial pretension force of FHBCs. Furthermore, a solid element-based numerical model was developed and validated by the experimental results. The parametric analysis was conducted to investigate the effect of friction coefficient and initial pretension force on the mechanical behaviors of FHBC. The numerical simulation results show that the greater the initial pretension force is, the bigger the slip activation force and ultimate load-carrying capacity of the FHBC are. When the friction coefficient between CLT wall and steel beam is greater than 0.4, the ultimate load-carrying capacity does not increase much. The experimental and numerical results demonstrate that such connections can provide sufficient stiffness, strength, and ductility to transfer the shear force between the CLT shear walls and the steel frame beams.

Was kennzeichnet einen Holzbau?

The new online encyclopaedia www.holzbaukultur.ch from the Bern University of Applied Sciences presents Swiss timber buildings across six centuries and shows lineages of development. The wide range of examples initiates a debate about the characteristics of timber buildings. Switzerland is generally associated with craftsmanship and traditional timber buildings in the Alpine region. The attempt to develop timber architecture in the spirit of modernism in the 20th century was not very successful. The proportion of timber in total building volume decreased significantly. In recent decades, Swiss timber construction, which is now highly technologised, has repositioned itself, and architecture and structural planning have come closer together and realised remarkable, pioneering projects. Timber construction is now the subject of urban spaces and must find new forms accordingly. The approaches to these new forms have so far been very different. Answering the question “What characterises timber construction?” therefore appears to be a key to the visibility and success of a forward-looking Swiss timber construction culture.

Innovation ecosystems beyond construction projects – a case study of Swedish cross laminated timber building networks

ABSTRACT While innovation ecosystems have been proven effective for driving innovation in high-tech industries, their application in construction with cross laminated timber (CLT) products have received limited attention, with most studies adopting a broad perspective on ecosystems, encompassing the entire supply network around individual building projects. This study explores niche innovation ecosystems within the context of construction with CLT products. Data from 15 CLT-based building projects in mid Sweden were collected through observations and interviews and analysed using a method combining existing theory on innovation ecosystem structure with social network analysis. Innovation ecosystem structure was identified within five of the projects, encompassing two unique ecosystems. These ecosystems feature interorganisational links and actor-level expected value capture in two dimensions: value creation within the standard contractual framework of the projects and the innovation ecosystem superimposed on these projects. The novel method bridges the gap between innovation ecosystem research and CLT practices. The findings reveal that niche innovation ecosystems interact with CLT-based building projects through collaborative efforts across multiple projects and partners. These ecosystems feature alignment links that indicate both intra – and inter-project interdependencies, potentially driving innovation in construction. Role extensions within these ecosystems highlight the complexity and adaptability required in the construction industry.

Measurement and documentation recommendations for reporting footfall floor vibration performance in mass timber buildings

Construction methods utilizing mass timber are increasingly offering more sustainable and eco-friendly solutions for vibration sensitive buildings that have traditionally used only concrete or concrete and steel materials. Regardless of the building material, it is important to consider vibration serviceability with respect to occupants or sensitive equipment as part of the design process. Several references are now available to help with the footfall vibration design of mass timber floors. These references borrow heavily from established methods outlined in American and European design guides for steel and concrete construction. What cannot be borrowed from these guides is the wealth of empirical validation data that has been obtained from measurements in steel buildings. As more mass timber buildings are built, it will benefit the community to have floor vibration performance measurements to further inform and validate prediction and design methods. This paper discusses measurement methods and documentation items to report floor vibration performance in existing mass timber buildings. The consistent reporting of the collected empirical data will help standardize future design prediction methods and validations with these structures.

Method for Predicting Internal Defect Areas of Timber Components Based on an Adaptive Neuro-Fuzzy Inference System

ABSTRACT Internal defects in the timber components of ancient architecture can reduce their effective cross-sectional areas, deteriorate their mechanical performance, and increase the risk of structural failure. To accurately and rapidly determine the extent of internal damage in components of ancient architecture, this study performed damage detection tests on Larix gmelinii (Larch) column specimens using stress wave nondestructive testing technology. An adaptive neuro-fuzzy inference system (ANFIS) model was developed using the cross-sectional wave velocity ratio after investigating the laws of defect identification through stress-wave testing. Stress-wave detection could identify the relative positional correlation of defect areas. However, the accuracy of the defect area detection was inconsistent (8%–98%). The accuracy of the ANFIS model exhibits a diminishing trend as both parameters rejection rate and influence range increase. However, the ANFIS outperformed the stress-wave detection technique and linear regression model with correlation coefficient and prediction accuracy of 0.99 and 88%, respectively. The root mean square error for the ANFIS was reduced by 79% and 70% compared to the stress wave detection method and linear regression model, respectively. Thus, the ANFIS model can precisely forecast areas of internal damage in timber components of historical edifices and can be used to evaluate the safety of ancient timber buildings.

Space Efficiency in European High-Rise Timber Buildings

Space Efficiency in European High-Rise Timber Buildings

Assessing carbon in timber buildings: how to factor in connections, fire protection and soundproofing

The embodied carbon of timber buildings is often miscalculated at early design stages. Primary materials in mass timber developments typically include glulam and cross-laminated timber, the volume of which is estimated and used to quantify upfront carbon emissions. However, to ensure like-for-like comparisons, the impact of metallic connections and, where needed, fire protection (boarding or treatment) and acoustic insulation should also be considered, even at early stages. This is particularly relevant when comparing timber against concrete schemes, which normally do not require additional allowances for connections, fire protection and soundproofing. This study suggests the upfront embodied carbon of a timber superstructure may increase by up to 60% in residential developments and 30% in commercial buildings when considering secondary components critical to the structure. Note that this is an initial study and that more real-world data should be collated to improve the accuracy of these findings, especially for residential buildings.

Confrontation and cooperation between timber-imitating appearance and brick masonry in the Wuliang Hall: a case study of Manjusri Hall and Samantabhadra Hall of Longchang Temple

ABSTRACT The Manjusri Hall and Samantabhadra Hall of Longchang Temple in Baohua Mountain are representative of a series of Wuliang Halls, a distinctive architectural heritage type in China. To better understand the technical and artistic characteristics of the timber imitation by bricks of the Wuliang Hall, the spatial, formal, and structural features of the two halls are analyzed. Firstly, an accurate survey of the architectural heritage is conducted to obtain precise geometric dimensions, enabling analyses of spatial and formal aspects of the hall. Subsequently, the structural performance of the hall under static load is analyzed by finite element method. The results indicate that barrel vaults and arches of different sizes serve distinct spatial functions. The appearance form of the Wuliang Hall generally aligns with the style of the Ming and Qing official timber buildings, while the detailed construction methods may be adjusted due to material or structural considerations. Vault and arch structures are employed to adapt to brick masonry, but the sill walls, tops and imposts of arches and vaults are prone to tensile damage under vertical loads or seismic actions. These results could contribute to the interpretation of the technical motivations and human ideologies for Chinese masonry timber-imitating structures, and making conservation strategies for buildings of this type.

Tool Development for Life Cycle Cost (LCC) of Wooden Building Envelope

The main goal of this study is to provide a platform for LCC calculation rules for timber buildings that comply with the Standards EN 16627:2015 and EN 15643-4, by employing a refined technical service life estimation. The database includes economic data for the building envelope and structural elements at the product level. In addition, the use phase of the building is included as maintenance, and the relevant economic data related to design failure, user preferences, and technical defects due to moisture. This model is under development as part of the WoodLCC project, with partners from Germany, Sweden, Norway, Estonia, Slovenia, and Austria, aiming to implement advanced methods to calculate accurate technical service life estimations and give the users the opportunity to evaluate the differences in building and maintenance costs based on different parameters. In this study, a data structure is created based on the necessary indicators and parameters for LCC calculation. An Excel model is developed, which will be used as a base for a software development in the WoodLCC project. Only wooden material is being considered for building envelope and bearing system. All material price data and installation times for each element is taken from a Norwegian dataset. This data is then modified for the selected European country using country specific labour cost- and material cost-indexes, convertible to the inquired currency. Inflation and escalation rates are considered for calculating the maintenance or repair that will occur in future. Material prices for different species and modification are included. Improved service life input data will enable more precise LCC for wood-based products, resulting in improved economic impact. LCC finds common acceptance only if reliable input data are available and complemented with knowledge about user expectations. We will evaluate the possibility of future improvements of such models.

Experimental assessment of modal properties of hybrid CFRP-timber panels

Hybrid timber composites are becoming increasingly widespread to efficiently enhance timber performance. While carbon fibre reinforcement has been explored for strength in timber structures, its impact on vibration performance remains understudied and is crucial as mass timber buildings extend their spans and heights. This work explores the effect of carbon fibre reinforcement on the vibration performance parameters of CLT floor systems. Natural frequency, mode shape, damping and stiffness parameters are evaluated from experimental testing using the Natural Excitation Technique (NExT) combined with the Eigensystem Realization Algorithm (ERA) and robust techniques for selection of physical dynamic properties, verified against numerical finite element models. The findings reveal that, in the case of three-ply Cross-laminated Timber (CLT) panels with depths ranging from 115 mm to 135 mm, introducing reinforcement at ratios below 0.67% led to an enhancement in frequencies, registering an increase of 6% to 11%, although not explicitly accounting for changes in environmental conditions. Moreover, these reinforced panels showed a relevant increase in effective flexural stiffness, ranging from 15% to 22%, when compared to their unreinforced counterparts. This means an improved maximum span of around 4%–6% within current design limits for timber floors influenced by vibration performance. These findings enhance the understanding and design of high-performance composite timber floors, promoting the use of renewable building materials in construction.

Out-of-plane bending properties of cross laminated timber (CLT)

In Europe the structural timber building product cross laminated timber (CLT) is regulated via European Technical Assessments (ETAs), which require large and voluminous test campaigns to obtain. So far, there is no standardised CLT strength class system nor a set of harmonised properties. Such a strength class system and tabulated values could be accompanied by a set of so-called load-bearing models, analogous to the current regulations for glued laminated timber (GLT). The aims of this contribution are to comprehensively analyse the first known load-bearing model for out-of-plane bending of CLT from 2006 and to validate and benchmark this approach with possible further candidates. The aim is to initiate the establishment of a European strength class system for CLT based on its out-of-plane bending properties, for a more reliable, regulatory compliant structural building product and for enhancing its market acceptance. Therefore, a comprehensive analysis of various potential influencing parameters on out-of-plane CLT bending properties is effected by means of stochastic-numerical investigations as well as a large amount of test campaigns, the latter in the form of a retrospective study. The first approach from 2006, in particular in its adapted version, is successfully validated and confirmed as a valuable candidate for the future regulation of CLT due to its overall more accurate and more reliable strength predictions compared with the other candidates. In addition, models for the density and the modulus of elasticity parallel to the grain, as currently defined for glulam, are confirmed to be applicable also for CLT. An analysis of the variation in the properties of the base material and CLT motivates additional efforts towards grading and quality assurance in order to meet the expectations of the nominal strength class of boards and to fulfil minimum requirements for finger joint quality to better utilise the high performance of CLT and to increase its reliability.

Experimental and analytical evaluation of semi-rigid timber connection with screwed-in threaded rods and steel coupling part

A major challenge for mid and high-rise timber buildings is fulfilling serviceability requirements. Moment-resisting timber frames with semi-rigid moment-resisting connections as the primary lateral load-resisting system can be an alternative to buildings with wind bracing or shear walls, allowing for more free space, enhanced building performance, and architectural flexibility. Moreover, introducing semi-rigid timber connections can improve the performance of floors against human-induced vibrations and potentially decrease the material used. The performance of moment-resisting frames depends mainly on the properties of their beam-to-column connections. The paper presents an experimental investigation of semi-rigid moment-resisting connections with long screwed-in threaded rods and a steel coupling part. Long threaded rods (i.e., screwed-in threaded rods with wood screw threads) feature high axial stiffness and resistance and allow for immediate load transfer without initial slip. Due to these properties, threaded rods are preferred over conventional dowel-type fasteners such as bolts and dowels. Five full-scale moment-resisting timber connections were tested under cyclic and monotonic loading to investigate moment resistance, rotational stiffness, and energy dissipation. The stiffness obtained by cyclic and monotonic tests was compared with numerical and analytical methods. The beam-to-column moment-resisting connections demonstrated a high moment resistance of 92.2 kNm and rotational stiffness of 8049 kNm/rad without initial slip. The experimental results and analytical calculations of rotational stiffness differed only by 5 %, whereas the finite element model exhibited a discrepancy of approximately 35 %. The equivalent viscous damping was determined based on cyclic load tests at service load levels and was found to be in the range of 5.5 %–10.0 %. Finally, a parametric study is presented to discuss the effect of semi-rigid connections on the performance of the timber floors and material savings. The increase in rotational stiffness of the beam-to-column connections could lead to up to 13 % material savings.

Long-Term Behavior of Timber–Concrete Composite Structures: A Literature Review on Experimental and Numerical Investigations

Timber–concrete composite structure is a type of efficient combination form composed of concrete floors and timber beams or floors through shear connectors, and shows good application potential in the floor system of timber buildings. The long-term performance of the timber–concrete composite structures is complex and is affected by the creep of timber and concrete, as well as the long-term slip of the shear connectors. This article presents a comprehensive overview of the research status on the long-term behavior of timber–concrete composite members and different shear connectors. For the shear connectors, the effects of loading levels, environments, and component materials on their creep coefficients are summarized. As to the timber–concrete composite members, both the experimental and numerical investigations are gathered into discussions: the connection types, component materials, loading conditions, and durations in the long-term tests are also discussed; various models for describing long-term behavior of timber, concrete, and connection systems are provided, and then a comprehensive description of the progress of numerical investigations over the last decades is made. In addition, the suggestions for future research are proposed to reach a clearer understanding of the bending mechanisms and mechanical characteristics of timber–concrete composite structures.

Hygrothermal performance of timber-framed walls in Turkey – Long-term monitoring

The increasing energy consumption emphasizes the urgency of sustainable building practices. Worldwide, there is a tendency towards local, natural, durable, and recyclable materials like timber. Furthermore, timber's excellent thermal insulation and natural hygroscopic properties enable it to efficiently regulate indoor humidity levels, ensuring stability and comfort. In Turkey, timber construction declined significantly in the 20th century due to the shift towards vertical reinforced concrete, however, recent years have witnessed a renewed interest driven by earthquake concerns and global inclination. Despite this resurgence, timber construction practices are still limited, and the hygrothermal performance of exterior walls in both restoring traditional timber buildings and constructing new ones is often disregarded. Furthermore, there is a lack of scientific research in this area. Understanding the hygrothermal behaviour of these structures is essential for meeting modern energy efficiency standards. This study evaluates the hygrothermal performance of prevalent practices in timber-framed constructions in Turkey. Long-term monitoring in a full-scale test cabin exposed to real climatic effects provides insights. Findings indicate the exterior plywood sheathing on the North-west facing walls being more susceptible to moisture, particularly when the indoor relative humidity is elevated. South-east facing walls are better at drying, but air barrier membrane slows down drying. Timber cladding with ventilated cavity offers improved protection but its high exposure to rainfall in North-west, and solar radiation in South-east, implies potential performance degradation over time. Installing suitable vapour retarders and additional exterior thermal insulation particularly to the North-west facing walls could possibly reduce risks associated with moisture, as well as preventing thermal bridges.

Bayesian model updating of eight-storey CLT building using modal data

The serviceability of tall timber buildings due to wind-induced vibrations is often a governing design criterion. However, accurate modelling of such buildings for their serviceability is a challenge, partly because certain non-structural building elements (e.g. plasterboards, façade, screed) act structurally, and no guidelines exist on how to effectively include them in the model. Model updating may be helpful in revealing their as-built characteristics. This paper presents findings of a surrogate-based Bayesian model updating of a lightweight eight-storey cross-laminated-timber building. In particular, the focus was on patterns and correlations between mass distribution and modal characteristics, as well as the effects of joints, non-structural building elements, and the foundation. Model updating utilised the results of ambient vibration testing, which is commonly used in civil engineering for structural identification or health monitoring, however, it generally offers a relatively low number of identified modes. To this end, the study investigates the sensitivity of the updating process to the number of modes involved in the analysis.

Understanding Compartmentation Failure for High-Rise Timber Buildings

The traditional concept of compartmentation guaranteed by fire resistance is mainly concerned with the problem of destructive internal spread potential. External convective spread potential pertains to the loss of compartmentation associated with windows and facade systems. As such, it is assumed that internal fire spread occurs following mechanisms of excessive heat conduction and/or successive failure of the compartment boundaries, which can be, in most cases, conservatively characterised using traditional methods of performance assessment such as fire resistance. Nevertheless, external fire spread represents a potentially more effective route by which fire can spread through the convective advancement of flames and hot gases. This is particularly important in cases such as timber construction, where the presence of exposed timber can result in increased convective spread potential and where loss of compartmentation can result in disproportionate consequences. A simplified compartment fire model is proposed with the objective of quantifying the fuel contribution of exposed timber elements to the compartment fire and determining the impact of variable percentages of exposed timber on the convective spread potential. The overall results show that the convective fire spread potential increases with the increasing percentage of available timber.