Cross-laminated Timber Structures Research Articles

Seismic control of cross laminated timber (CLT) structure with shape memory alloy-based semi-active tuned mass damper (SMA-STMD)

Cross laminated timber (CLT) is becoming increasingly popular for constructing multiple-story buildings due to its alignment with Sustainable Development Goals of United Nations. However, such structures can be susceptible to excessive vibrations during earthquakes. While tuned mass dampers (TMDs) can be used to control these vibrations in CLT structures, their effectiveness can be reduced due to the lightweight nature of CLT and changes in its structural mass or deterioration of the wood. To address this issue, this paper proposes the use of shape memory alloy-based semi-active tuned mass dampers (SMA-STMDs) for controlling vibrations in CLT structures. This study includes the design and experimental testing of a full-scale, novel spring-pendulum combined SMA-STMD system, which utilises the mechanical properties of SMAs that change with temperature to achieve semi-active control. Finite element method simulations demonstrate that the proposed SMA-STMD system can effectively reduce structural seismic vibrations in CLT structure. By adjusting the SMA temperature, the SMA-STMD system can effectively address the issue of TMD system off-tuning caused by changes in the CLT structural properties. Overall, the proposed SMA-STMD system offers a promising solution for seismic control in CLT structures and has the potential to promote the development of CLT structures.

System identification using Bayesian model updating with cross-signature correlations

In this paper, a novel likelihood function for Bayesian model updating algorithms is proposed, in particular for the transitional Markov chain Monte Carlo algorithm. The likelihood function is based on a measure of fit in which the prediction errors between the measured and simulated frequency response functions are evaluated using the cross-signature correlation. This formulation avoids the problem that for the commonly used modal measure of fit, the obtained results are ambiguous (i.e., correlated) when both the mass and stiffness properties are uncertain. Validation is first performed on simulated test data of cross-laminated timber structures and, in a second application, on real experimental data of a cross-laminated timber panel by performing Bayesian model updating on a finite element model of the specimen under consideration.

Fire spread in a large compartment with exposed cross-laminated timber and open ventilation conditions: #FRIC-01 – Exposed ceiling

Exposing cross-laminated timber (CLT) structures in buildings is increasingly popular in modern buildings. However, large timber surfaces, window facades, and different geometries can change the fire dynamics in a compartment. The effect of those parameters, therefore, needs to be studied. Two large-scale CLT compartment fire experiments (95 m2) have consequently been performed. The experiments were designed to represent a modern office building with an open-plan space and large window openings. In this experiment, #FRIC-01, the ceiling was exposed. The wood crib fire developed slowly and travelled approximately 1.5 m before the ceiling ignited at 32.5 min. Thereafter the fire spread rapidly across the ceiling and wood crib before it shortly after retracted. Three such cycles of rapid spread followed by a retraction occurred within 13 min, whereby the wood crib fire grew larger for each cycle. After the flames extended through the compartment for the fourth time, the fire remained fully developed. After a short period of intense burning, the CLT self-extinguished while the wood crib fire was still burning. The compartment withstood full burnout, and no reignition occurred despite some delamination and using an adhesive that lacks a demonstrated resistance against glue-line integrity failure.

Investigating the effect of the structural interactions due to floors and lintels on the lateral response of multi-storey Cross-Laminated Timber shear walls

The lateral behaviour of multi-storey Cross-Laminated Timber (CLT) structures is significantly influenced by the effects of the structural interactions between primary and secondary structural elements and their connections. In case of platform-type structures, in addition to the connections placed at the base of the walls, other structural components including the floor diaphragms and the lintels above the openings influence the lateral performances of the CLT shear walls. However, it is common practice in structural design to model multi-storey CLT shear walls by considering the wall base connections, while neglecting the effects of these structural interactions. This study investigates in detail the lateral behaviour of multi-storey CLT shear walls, comparing the results of simplified modelling strategy, typically adopted in practical design, and more advanced modelling strategies that take into account the effects of these structural interactions. Different shear wall configurations, including different geometries, number of storeys, and connection properties were analysed by means of linear elastic and nonlinear static analyses. The results of the numerical analyses highlighted significant differences between the lateral behaviour of multi-storey CLT shear walls modelled with these different modelling strategies and suggest that simplified modelling strategies may not always be reliable to describe the behaviour of multi-storey CLT shear walls.

Effect of Alternate Drying Techniques on Cross-Laminated Timber after Exposure to Free-Water Wetting

Cross-laminated timber (CLT) panels are commonly used in mass-timber multistorey constructions due to their prefabrication, construction flexibility, environmental credentials and weight-to-strength ratio advantages compared to competing building materials. However, the long-term durability and service life of these mass timber panels require further understanding of their performance when exposed to free water. Wetting and drying trials were conducted by exposing Radiata pine (Pinus radiata) CLT sections to either free water (pooling on a single surface) or submerged water (all directions exposed) saturation, followed by either ambient or fan drying. The panels exposed to water pooling only reached MC above the FSP up to 40 mm of the panel depth. For submerged panels, the MC reached values above the fibre saturation point (FSP) at depths of 30 to 40 mm penetration on both panel faces. When comparing the ambient and fan-drying panel sections over the same time period, a less uniform MC profile was observed for the ambient drying, whereas the fan-dried panels fell below the FSP faster and with a more consistent MC profile. A complementary study was conducted on a standalone 3.0 × 3.0 m CLT room, where the room was wetted during a simulated pipe burst event. The moisture monitoring of wall and floor panels during fan drying of the room showed that an MC reduction from an excess of 40% to below 20% could be reached in less than 96 h for the panels’ surface; however, the middle sections of the panels dried slower than the surface sections. The CLT structure fan drying required a longer drying time than the CLT sections tested due to the closed sections (overlaps and connected faces) and a lower rate of airflow. The study of drying CLT sections highlighted the product reaching and maintaining MC higher than FSP points and the need for further drying applied to minimise long-term decay development. Further study is recommended to investigate the effects of closed sections (connected faces) and the duration of drying needed for semi-finished and finished buildings.

Fire Spread in Multi-Storey Timber Building, a CFD Study

The purpose of this paper is to investigate the fire performance in a multi-storey cross-laminated timber (CLT) structure by the computational fluid dynamics (CFD) technique using the Fire Dynamics Simulator (FDS v.6.7). The study investigates fire temperature, heat release rate (HRR), and gas concentration (O2, CO2). The importance of this research is to ensure that the fire performance of timber buildings is adequate for occupant safety and property protection. Moreover, the proposed technique provides safety measures in advance for engineers when designing buildings with sufficient fire protection by predicting the fire temperature, time to flashover and fire behaviour. The present numerical modelling is designed to represent a 10-storey CLT residential building where each floor has an apartment with 9.14 m length by 9.14 width dimensions. The pyrolysis model was performed with thermal and kinetic parameters where the furniture, wood cribs and CLT were allowed to burn by themselves in simulation. This research is based on a full-scale experiment of a two-storey CLT building. The present results were validated by comparing them with the experimental data. Numerical simulation of CLT building models show a very close accuracy to the experiment performed in the benchmark paper. The results show that the CFD tools such as FDS can be used for predicting fire scenarios in multi-storey CLT buildings.

Interpretable machine learning models for the estimation of seismic drifts in CLT buildings

An accurate estimation of drift demands is crucial for designing and assessing structures under seismic loads. Given the novelty of massive timber buildings, predictive models for the estimation of drifts in mid-to high-rise CLT structures are lacking, particularly in the form of simple models suitable for preliminary design evaluations or regional seismic assessments. In this paper, we present and compare several Machine Learning (ML) models for the estimation of peak inter-storey and roof drifts in multi-storey Cross-Laminated Timber (CLT) walled structures. The ML techniques used include: Multiple Linear Regression, Regression Trees, Random Forest, K-nearest Neighbor, and Support Vector Regression. To this end, 69 structures spanning mid-rise to tall timber buildings are subjected to a large collection of acceleration records and used to create the training and testing datasets. Different structural configurations and behaviour factors, related to the assumed energy dissipation capacity of the buildings, are considered. A diversity of feature selection techniques informs our choice of parameters to the reduced input space leading to a set of six most efficient features: the spectral acceleration at the building's fundamental period (Sa(T1)), the Peak Ground Velocity (PGV), tuning ratio (T1/Tm), behaviour factor (q), wall height (Hw), and the wall subdivision ratio (Wr). After verifying the high accuracy of our model predictions, the SHapley Additive exPlanation method (SHAP) is used to gain insight into the influence of key input features on the ML model outputs. Finally, our ML drift estimations are compared against previous proposals and design code assumptions, and the potential causes of disagreement are discussed.

Cовременные требования по противопожарной защите многоквартирных жилых зданий с применением конструкций из перекрестноклееной древесины

Introduction. Widespread and effective introduction of cross-laminated timber structures into construction of residential buildings substantiates the need to develop modern requirements for the design of fire protection systems for these buildings to limit the spread of fire, ensure safe evacuation and rescue of people from these buildings, increase the effectiveness of firefighters performing rescue operations and fire suppression, and optimize the cost of space-planning and design solutions. Goals and objectives. The purpose of the article is to substantiate modern requirements for the design of fire protection systems of residential buildings having not more than four storeys, if their structures are made of cross-laminated timber, and to develop engineering solutions to implement these requirements in compliance with provisions of the Federal Law of the Russian Federation dated July 22, 2008 No. 123-FZ “Technical regulations on fire safety requirements” (hereinafter — No. 123-FZ). Methods. An analytical method is used to substantiate and formulate requirements for the design of fire protection systems for residential buildings whose structures are made of cross-laminated timber, as well as the engineering solutions needed to implement these requirements for buildings having up to 4 floors in compliance with provisions of No. 123-FZ, the design experience, results of ire resistance and fire hazard testing of building structures and analysis of the influence of the fire resistance factor of building structures on human safety in case of fire. Results. The results of the work, if integrated into standards of corporate entities and codes of practice, allow for the mass construction of residential buildings having structures made of cross-laminated timber. Conclusions. This research project substantiated modern fire safety requirements for space-planning and design solutions, fire resistance limits and fire hazard classes of cross-laminated timber structures of residential buildings, as well as requirements for emergency exits and evacuation routes, composition of active fire protection systems and the functional efficiency of these systems. The results of the work allow for the mass construction of 4-storey residential buildings whose structures are made of cross-laminated timber.

Design for Seismic Resilient Cross Laminated Timber (CLT) Structures: A Review of Research, Novel Connections, Challenges and Opportunities

As a sustainable alternative to steel and concrete, cross laminated timber (CLT) shear wall systems are getting increasingly popular in mid-rise and high-rise construction, and that imposes new challenges on their seismic performance. The conventional connections used in this system, such as steel hold-downs and angle brackets, are, however, susceptible to brittle failures, thus being inappropriate for use in structures in seismic regions. A series of innovative connections have therefore been proposed in recent years for achieving better seismic behaviours in CLT structures, characterised by an adequate capacity, significantly improved ductility and dissipative capacity, as well as more controllable ductile failure modes. This paper first reviews the recent studies of CLT shear wall systems and conventional connections. Connection systems and shear wall reinforcement methods that have been recently proposed for seismic resilient CLT structures are then introduced, with their design strategies being summarised accordingly. The connections are then discussed comprehensively in terms of structural performance, manufacturability and constructability, employing similar criteria that have previously been proposed for steel modular connections. It is found that much improved ductility along with more predictable, ductile, timber damage-free deformation modes are achieved in most of the new connections. Some new connectors are designed with additional functionalities for optimised seismic performance or for easing the construction process, which, however, lead to complex designs that may add difficulties to the mass production. Therefore, comprehensive considerations are needed in connection design, and the discussion of this paper aims to assist in the future development of connection systems for seismic resilient multi-storey CLT buildings.

Construction details affecting flanking transmission in cross laminated timber structures for multi-story housing

The desire of the building developers to leave the surfaces of cross laminated timber constructions in multi-story housings visible for the building user, leads to acoustic problems with the flanking sound transmission that cannot be controlled by means of wall linings. As a result, controlling flanking sound transmission by measures directly in the joint is getting increasingly important. The main parameter for describing the vibrational power transmission over a junction between structural elements is the vibration reduction index Kij. For this quantity, some planning values are spread over numerous publications. None of the currently available data sources represents a holistic view on the building acoustic performance of the on the market available products for elastic interlayers and fasteners which are used in a wall-ceiling junction. The following paper shows results of measurements of vibration reduction indexes of different configurations of a wall-ceiling joint in a test facility. Different elastic interlayers and fasteners were investigated. The vibration reduction indexes spread from 16db to 26dB as a function of the joint configuration and the load applied on the joint. The measurement results obtained are discussed and the essential parameters for influencing the flanking sound transmission are worked out and quantified.

RESISTANCE OF CROSS-LAMINATED TIMBER TO ATMOSPHERIC ACTIONS

Introduction. Cross-laminated timber (CLT) has started to win a market in Russia. Humidity plays an important role in ensuring the operational reliability of buildings based on timber structures. The lack of comprehensive studies on the influence of varying temperature and humidity actions, including atmospheric ones, hinders the development of CLT.Aim. In this work, the influence of atmospheric actions on various types of CLT building structures was determined in order to amend the requirements in SP 64.13330.2017 for the design and protection of CLT structures.Materials and methods. Samples of CLT wall panels and floor slabs manufactured as per the current regulatory documents were used as an object of research. Field tests were developed in order to determine the influence of atmospheric actions on the strength and elastic characteristics of CLT panels.Results. Atmospheric actions have an adverse effect on the strength and elastic characteristics of CLT panels. The decrease in the strength and elastic characteristics varies for the samples of floor slabs and wall panels.Conclusion. It is proposed that several recommendations given based on the experimental results on the resistance CLT to atmospheric actions are to be included in SP 64.13330.2017 for the design, manufacture, and construction of buildings using CLT structures.

Experimental testing of platform-type and balloon-type cross-laminated timber (CLT) shear walls with supplemental energy dissipators

CLT technology is gaining notable popularity in both residential and non-residential applications throughout the world, providing a prospective solution to the height limitation of timber buildings. Recently, a growing number of studies have been focusing on energy dissipation strategies for CLT structures since the energy dissipation capacity of CLT structures might sometimes be challenged in seismic design. This paper presents an experimental investigation into the lateral performance of platform-type and balloon-type CLT shear walls with supplemental energy dissipators. Such supplemental energy dissipators are located between coupled CLT wall panels, intending to deform and dissipate energy through the rocking mechanism of CLT shear walls. Two kinds of energy dissipators were adopted, respectively, called O-shaped Flexural Plate (OFP) dissipator and Plate with Openings (PO) dissipator. Quasi-static tests were conducted on four one-third-scale two-story CLT shear wall specimens considering platform and balloon construction methods and these two types of supplemental energy dissipators. The experimental observations, load-displacement responses, energy dissipation capacities, stiffness degradation, and combined single-coupled wall behaviors of the specimens were obtained and compared. The test results showed that the OFP dissipator was quite efficient in dissipating energy, while the PO dissipator exhibited limited energy dissipation capability because it was prone to low cycle fatigue fracture. The supplemental energy dissipators dissipated more energy in balloon-type CLT shear walls compared to those in platform-type CLT shear walls due to the influence of construction methods on the demand of supplemental energy dissipators. In platform-type CLT shear walls, the coupled wall behavior of the walls in the second story was more evident than that of the walls in the first story.

Topology optimization applied to the core of structural engineered wood product

Structural-engineered wood products are used in construction as a sustainable alternative to concrete and steel. The most commonly used engineered wood products are Glued-Laminated Timber (GLULAM) and Cross-Laminated Timber (CLT), which in most productions are made of layers of wood glued under pressure. In the GLULAM, the wood fiber directions are parallel stacked in layers, while in CLT, the layers have a typical rotation of 90°. This work develops a topology optimization method with an objective function in displacement and volume constraint applied to the core of engineered wood products such as GLULAM and CLT structures, seeking new product designs with reduced material consumption. The optimization considers the wood’s orthotropic nature and the layers’ stacking. Two numerical examples are performed, the first evaluating the core of a GLULAM structure with and without periodicity constraints and the second on the core of a CLT structure with periodicity constraints. The results show that the proposed procedure can be effectively applied to the core of the engineered wood products. In addition, applying periodic constraint result in optimized topologies that help the manufacturability of the new designs. Furthermore, the proposed procedure highlights the structural differences in layer importance.

ロッキング機構を付与したCLT制振架構の開発研究

To effectively use the large supplies of wood material obtained from forest thinning, research focused on developing cross-laminated timber (CLT) structures is increasing globally. However, the earthquake resistance of CLT structures is considered insufficient owing to the relationships between the force and deformation of CLT structures exhibiting pinched hysteresis behavior with slippage.

Ultimate failure load analysis of cross-laminated timber panels subjected to in-plane compression

Cross-laminated timber (CLT) panels have proved their efficiency as vertical and horizontal load-carrying structures, and their design methods for serviceability and ultimate limit states are well defined. However, there is a lack of more general and versatile analytical methods for the ultimate load carrying capacity determination of CLT structures. In this paper, the classical layered beam theory is adopted for the ultimate failure load estimation of axially compressed CLT panels. The proposed method retains its accuracy both with an asymmetric layer setup and when the number of CLT layers exceeds five. The presented method is validated by adopting experimental test data from two test series produced by other researchers.

Investigating the effect of perpendicular walls on the lateral behaviour of Cross-Laminated Timber shear walls

Cross-Laminated Timber (CLT) structures are realized by joining CLT panels using metal connections, which represent the main source of deformability for lateral loads and energy dissipation in case of seismic events. CLT building construction types can be distinguished in “box type”, in which the perpendicular walls in the corner of the building are joined along the wall vertical edges, and “shear wall type”, in which the perpendicular walls in the corner of the building are not mutually connected. Regardless of the construction type considered, the calculation models used to design the shear walls of CLT buildings take into account the connections at the base of the shear walls, while neglecting the presence of connections between perpendicular walls. This paper presents a study on the effects of the perpendicular walls on the lateral response of CLT shear walls. Two analytical models of laterally loaded CLT shear wall that consider the wall base connections, hold-downs and angle brackets, and the contribution of the connections between the shear wall and the perpendicular wall are presented. These analytical models were validated against two- and three-dimensional numerical models developed in SAP2000. Both analytical and numerical models are used to perform a parametric analysis in which different geometrical and mechanical properties of CLT shear walls are considered. The aim of the parametric analysis is to validate the correctness of the analytical models and to quantify the increase of lateral stiffness and lateral capacity of the shear wall due to the interaction with the perpendicular wall. Results showed that the interaction between shear wall and perpendicular wall increases the rocking stiffness, the lateral capacity, and modifies the rocking behaviour of the shear wall.

An ensemble learning approach to condition assessment of dissipative CLT connections based on piezoceramic sensor data

Novel dissipative connections of cross-laminated timber (CLT) structures, showing great ductility and energy dissipation capability in addition to meeting the requirement of strength and stiffness, have gained increasing attraction in CLT shear walls. As important elements of CLT structures, dissipative connections function as the main part to resist seismic loading. It often displays different mechanical behaviors and suffers stiffness degradation when subjected to external loads. Variations of mechanical behaviors would further affect structural performance during service. The traditional method of analyzing mechanical behaviors of CLT connections relies on destructive tests, which are time-consuming and irreversible. Thus, using the non-destructive method to identify the mechanical behavior of dissipative CLT connections is of great significance. An ensemble learning-aided prediction algorithm combined with piezoceramic-enabled sensing technology is proposed in this study to identify mechanical behaviors of dissipative CLT connections under external loading. The main contribution of this study is to build a bridge between the damage-sensitive feature extracted from non-destructive sensing signals and mechanical behaviors obtained by the destructive loading test through the proposed method, which can avoid the requirement of time-consuming destructive tests and the baseline signal in traditional piezoceramic-enabled sensing method. An energy dissipative hold-down connection model is established in numerical simulations to investigate stress wave propagation mechanisms via different loading conditions. In experimental studies, a reusable piezoceramic-based sensor is firstly designed, and its performance is validated through a preliminary test. Then, a loading test was conducted on a CLT joint with a dissipative hold-down connector to further verify the numerical findings and generate an intact-to-failure piezoceramic-based sensing signal dataset through all loading cases. Consequently, fuzzy entropy is extracted from the signal dataset and fed to an ensemble learning classifier to predict loading behaviors. Prediction results imply the great potential of the proposed method for predicting dissipative CLT joint life-cycle performance in field applications.

Seismic Performance and Collapse Fragility of Balloon-Framed CLT School Building

ABSTRACT Most previous research on seismic performance of cross-laminated timber (CLT) structures focused on platform-type construction. This paper investigates the seismic performance and collapse risk of a balloon-framed CLT school building, designed for Vancouver, Canada. Incremental dynamic analysis was performed using a three-dimensional numerical model. Experimental data from connection- and wall-level tests were used to calibrate and validate the model. Twenty-one ground motions (crustal, subduction inslab, and interface) were selected. The results showed the building well met the 2% design drift limit. It had 4.2% probability of collapse at design level by considering uncertainties with a collapse margin ratio of 3.18.

An experimental study of the stiffness and strength of cross-laminated timber wall-to-floor connections under compression perpendicular to the grain

In platform-type multi-story cross-laminated timber (CLT) buildings, gravity loads from upper floors, and vertical reaction forces from horizontal actions, like wind loads, cause substantial compressive forces in the CLT-floor elements. The combination of these high forces with a comparable low compression stiffness and strength perpendicular to the grain of timber, makes the compression perpendicular to the grain (CPG) verification of CLT an important design criterion. In this experimental study, CPG of CLT was investigated by means of typical wall-to-floor connections in CLT platform-type structures. CLT-wall elements were used for load application to transmit forces through the CLT-floor element by CPG. Compared to load application by steel elements, as it commonly is done in experiments, lower stiffness but similar strength were found for CLT walls. The study of different connection types showed the highest stiffness and strength for connections assembled with screws, followed by pure wood-to-wood contact, while connections with acoustic layers between the floor and wall elements showed the lowest stiffness and strength. In addition, these connections were tested for center and edge load position on the CLT-floor element. The strength for center and edge position compared to full surface loaded specimens increased linearly with the activated material volume, as determined by earlier proposed stress dispersion models. The stress dispersion effect was visualized by surface strain measurements using digital image correlation technique. Also, the stiffness increased with the activated material volume. Stress dispersion in the CLT-floor allowed to explain the increase in stiffness and strength with decreasing CLT-wall thickness. Strength values at different strain levels, and stiffness and strength increase factors suitable for the engineering design of CLT structures are provided.

Experimental investigation into lateral performance of cross-laminated timber shear walls made from fast-growing poplar wood

ABSTRACT Structural tests for seven full-scale cross-laminated timber (CLT) shear walls were conducted under cyclic lateral loading to investigate the feasibility of using fast-growing poplar in CLT structures. Connection tests with monotonic loads were performed to calculate the later bearing capacity of CLT shear walls. The effects of wood species, artificial accelerated aging, vertical step joint, and laminate strength class on the later performance of CLT were determined. Test results show that poplar CLT panels had potential application in CLT structures, with only an 8% difference in structural properties compared to spruce CLT. Accelerated aging reduced the mechanical properties of poplar CLT and converted its failure mode from plasticity to brittleness. The elastic stiffness of a poplar CLT shear wall with a vertical step joint decreased, but the energy dissipation capacity increased 3.3-fold. The lamina strength class was not positively related with the lateral bearing capacity of these walls.