Tall Timber Buildings Research Articles

Risk assessment of CLT-RC hybrid building: Consideration of earthquake types and aftershocks for Vancouver, British Columbia

Tall-timber buildings using cross-laminated timber (CLT) have become a viable sustainable system. This paper presents seismic vulnerability and risk assessment of a 10-story CLT-reinforced concrete hybrid building. The building is designed for the seismicity of Vancouver, and detailed 3D finite element model is developed in OpenSees. The evaluation is undertaken within a performance-based earthquake engineering framework in which seismic demand limits are defined with respect to the earthquake return periods. Two engineering demand parameters, i.e. maximum inter-story drift ratio in both X and Z directions, as well as their combination are considered. Using 30 mainshock and mainshock-aftershock earthquake records (two horizontal components per record), multiple stripe analysis and cloud analysis are performed, and the corresponding fragility and risk are quantified. In addition efficiency of different intensity measures are considered. The vulnerability and risk assessment results show viability of the hybrid building in high seismic zones.

Perforated steel structural fuses in mass timber lateral load resisting systems

Attention towards high-rise timber buildings has been increasing in recent years as part of the global trend of designing sustainable structural systems. Cross-laminated timber (CLT) shear walls and mass timber braced frames (TBF) are two feasible and sustainable options that can be employed as lateral load resisting systems (LLRS) to stabilise buildings against wind and earthquake loads while reducing the environmental footprints of conventional structures. Tall timber buildings using such systems have been built around the world, mainly in non-seismic or low-seismic locations and locations with regular wind loading. Their application in high seismic or wind regions requires more research on the behaviour of the systems and their components with respect to the corresponding loading, particularly in the connections. This paper presents an experimental study on the use of perforated steel plates as a dissipating energy device, also called structural fuse, to enhance structural performance during extreme loading events. Panel-to-panel connections and hold-downs within CLT shear walls and end brace connections within TBF were selected as potential locations for structural fuses. The strength, stiffness, ductility, over-strength, and failure mechanism of the perforated plate systems were determined to investigate the use of the system as a reliable energy dissipating mechanism. It was found that perforated steel plates provide a reliable yield mechanism with predictable yield and ultimate strength, and that damage in timber elements can be avoided when the fuses are combined with capacity-protected dowel-type fasteners. While the results of monotonic tests demonstrate considerable ductility for the various connections, a significant reduction in post yield dissipation is observed under cyclic loading, despite large non-pinching hysteretic curves.

Smoke Hazards of Tall Timber Buildings with New Products

Timber buildings can now stand very tall using new products. As timber materials are expected to be easily ignitable, the fire hazard of timber is a concern. Charring of the timber surface would maintain structural stability, but would also be accompanied by smoke. Although treating timber products with fire retardants would delay the ignition time under low radiative heat flux, toxic combustion products and unburnt fuel would be emitted immediately upon burning. More smoke and higher toxic gas concentrations such as carbon monoxide would be given off upon burning some fire retardants under high flashover heat fluxes. Due to the fast upward movement of smoke under stack effect, spreading of toxic smoke in tall timber buildings would lead to a hazardous environment. Engineered timber consists of derivative timber products. New engineered timber products are manufactured with advanced technology and design, including cross-laminated-timber (CLT), laminated veneer lumber (LVL) and glue-laminated timber (Glulam). The fire behaviour of timber products has been studied for several decades. However, the smoke hazards of using new timber products in building construction should be monitored. The objective of this study is to inspire stakeholders in fire safety of timber buildings, inter alia smoke hazards, to use new timber products to build tall buildings.

Numerical Analysis on Global Serviceability Behaviours of Tall Glulam Frame Buildings to the Eurocodes and UK National Annexes

Glued-laminated timber (Glulam) is an innovative engineered timber product and has been widely used for constructing spatial grand timber structures and tall timber buildings due to its exceptional natural attraction, easy processing, decent fire resistance and outstanding structural performance. However, global serviceability performances of tall timber buildings constructed from Glulam products for beams, columns and bracings and CLT products for lift core and floors under wind load are not well known yet though they are crucial in structural design and global analysis. In this study, finite element software SAP2000 is used to numerically simulate the global static and dynamic serviceability behaviours of a 105 m high 30-storey tall Glulam building with CLT lift core and floors assumed in Glasgow, Scotland, UK. The maximum horizontal storey displacement due to wind is 58.5% of the design limit and the maximum global horizontal displacement is 49.7% of the limit set to the Eurocodes. The first three lowest vibrational frequencies, modes and shapes of the building are obtained, with the fundamental frequency being 33.3% smaller than the code recommended value due to its low mass and stiffness. The peak acceleration of the building due to wind is determined to the Eurocodes and ISO 10137. The results show that the global serviceability behaviours of the building satisfy the requirements of the Eurocodes and other design standards. Parametric studies on the peak accelerations of the tall Glulam building are also conducted by varying timber material properties and building masses. Increasing the timber grade for CLT members, the generalised building mass and the generalised building stiffness can all be adopted to lower the peak accelerations at the top level of the building so as to reduce the human perceptions to the wind induced vibrations with respect to the peak acceleration.

Comfort assessment of high‐rise timber buildings exposed to wind‐induced vibrations

SummaryThe current trend of increasing the height limits of timber buildings makes wind‐induced vibrations a non‐negligible issue. The dynamics of high‐rise timber structures are discussed, focusing on accelerations and comfort assessment of the currently tallest timber building in the world, namely, the 18‐storey timber building in Norway. Verifications according to available standards were firstly carried out. Then, computational fluid dynamic analyses with Kratos Multiphysics were performed to simulate the wind flow around a rigid body. Afterward, the wind loads were applied to a single‐degree of freedom model and to a reduced finite element model, performing a one‐way coupling between the wind flow and the structure. Wind‐induced vibrations resulted particularly strong in the across‐wind direction, which is the most sensitive to the wind flow and the shape of the building. Provisions in international standards resulted to be not always enough to avoid discomfort in the occupants. Therefore, fluid dynamic analyses are suggested to simulate the actual response and verify the comfort criteria of tall timber buildings susceptible to wind‐induced vibrations.

A Review of Architectural and Structural Design Typologies of Multi-Storey Timber Buildings in Europe

Numerous countries across the globe have witnessed the recent decades’ trend of multi-storey timber buildings on the rise, owing to advances in engineering sciences and timber construction technologies. Despite the growth and numerous advantages of timber construction, the global scale of multi-storey timber construction is still relatively low compared to reinforced concrete and steel construction. One of the reasons for a lower share of high-rise timber buildings lies in the complexity of their design, where the architectural design, the selection of a suitable structural system, and the energy efficiency concept strongly depend on the specific features of the location, particularly climate conditions, wind exposure, and seismic hazard. The aforementioned shows the need for a comprehensive study on existing multi-storey timber buildings, which correspond to the boundary conditions in a certain environment, to determine the suitability of such a construction in view of its adjustment to local contexts. Apart from exposing the problems and advantages of such construction, the current paper provides a brief overview of high-rise timber buildings in Europe. Moreover, it addresses the complexity of the design approach to multi-storey timber buildings in general. The second part of the paper highlights the importance of synthesising the architectural, energy, and structural solutions through a detailed analysis of three selected case studies. The findings of the paper provide an expanded view of knowledge of the design of tall timber buildings, which can significantly contribute to a greater and better exploitation of the potential of timber construction in Europe and elsewhere.

Model updating of seven-storey cross-laminated timber building designed on frequency-response-functions-based modal testing

Based on the experimental estimation of the key dynamic properties of a seven-storey building made entirely of cross-laminated timber (CLT) panels, the finite element (FE) model updating was performed. The dynamic properties were obtained from an input-output full-scale modal testing of the building in operation. The chosen parameters for the FE model updating allowed the consideration of the timber connections in a smeared sense. This approach led to an excellent match between the first six experimental and numerical modes of vibrations, despite spatial aliasing. Moreover, it allowed, together with the sensitivity analysis, to estimate the stiffness (affected by the connections) of the building structural elements. Thus, the study provides an insight into the as-built stiffness and modal properties of tall CLT building. This is valuable because of the currently limited knowledge about the dynamics of tall timber buildings under service loadings, especially because their design is predominantly governed by the wind-generated vibrations.

Numerical Analysis on Global Serviceability Behaviours of Tall CLT Buildings to the Eurocodes and UK National Annexes

Cross-laminated timber (CLT) is an innovative engineered timber product and has been widely used for constructing tall timber buildings due to its excellent structural performance and good strength with its multi-layers of boards in both perpendicular directions. However, the global serviceability performance of tall timber buildings constructed from CLT products for the lift core, walls, and floors under wind load is not well known yet, even though it is crucial in a design. In this study, the finite element software SAP2000 is used to numerically simulate the global static and dynamic serviceability behaviours of a 30-storey tall CLT building assumed in Glasgow, Scotland, UK. The maximum horizontal storey displacement due to wind is only 16.6% of the design limit and the maximum global horizontal displacement is only 13.8% of the limit set to the Eurocodes. The first three lowest vibrational frequencies, modes and shapes were obtained, with the fundamental frequency being 19.9% larger than the code-recommended value. Accordingly, the peak acceleration of the building due to wind was determined as per the Eurocodes and ISO standard. The results show that the global serviceability behaviours of the building satisfy the requirements of the Eurocodes and other design standards. Parametric studies on the peak accelerations of the tall CLT building were also conducted by varying the timber material properties and building masses. By increasing the timber grade for CLT members, the generalised building mass and the generalised building stiffness can all be adopted to lower the peak accelerations at the top level of the building, so as to reduce human perceptions of the wind-induced vibrations with respect to the peak acceleration.

Long-term deformation behaviour of timber columns: Monitoring of a tall timber building in Switzerland

Knowledge on the short and long term deformation behavior of highly loaded components in tall timber buildings is important in view of improving future design possibilities with respect to serviceability, both in the construction and in the operational state. In this paper, we present the results of a monitoring case-study on a tall timber-hybrid building in Switzerland, a 15 storey and 60 m high office building completed in 2019. A fibre-optic measuring system showed an increase of the deformation with increasing load during the construction phase of highly stressed spruce-GLT and beech-LVL columns. However, the highest strain values were not reported in the columns themselves but at the ceiling transitions and in the area near their supports. The measurements on the columns were compared with model calculations for long-term deformation of timber elements in order to differentiate single components of the total deformation caused by load, time, and changes in climate during the construction. Over a monitoring period of a year, good agreement of the modelled deformations could be confirmed, which indicates that such models could be well suited for future usage in serviceability design of tall timber buildings.

Influence of core stiffness on the behavior of tall timber buildings subjected to wind loads

This study analyzes the feasibility of the use of cross-laminated timber (CLT) as a load-bearing structural element in a 40-story building based on Chinese design requirements. The proposed design of the high-rise concrete—CLT building utilizes the core—outrigger system. Concrete is used for the central core and outriggers, and CLT is used for the rest of the structure of the building. Finite element models with different types of connections were developed using SAP2000 to analyze the lateral behavior of the building under wind action. The finite element models with rigid connections deduce the wind load distributions on individual structural elements, which determine the total number and the stiffness of fasteners of the CLT panels. Accordingly, spring links with equivalent stiffness that simulate the mechanical fasteners were employed in SAP2000. The results indicate that CLT increases the lateral flexibility of the building. A closed concrete core was substituted by two half cores to measure the requirement of the maximum lateral deflection. However, the acceleration at the building top still exceeded the limitation prescribed in Chinese Code JGJ 3–2010 owing to the lightweight of CLT and decreased stiffness of the hybrid building. To restrict this top acceleration within the limit, further approaches to increase the stiffness in the weak direction of the building are required. Methods such as the modification of the floor layout, increase in the thickness of walls, and addition of extra damping capacity should be considered and verified in the future.

A holistic framework for designing for structural robustness in tall timber buildings

With the ever-increasing popularity of engineered wood products, larger and more complex structures made of timber have been built, such as new tall timber buildings of unprecedented height. Designing for structural robustness in tall timber buildings is still not well understood due the complex properties of timber and the difficulty in testing large assemblies, making the prediction of tall timber building behaviour under damage very difficult. This paper discusses briefly the existing state-of-the-art and suggests the next step in considering robustness holistically. Qualitatively, this is done by introducing the concept of scale, that is to consider robustness at multiple levels within a structure: in the whole structure, compartments, components, connections, connectors, and material. Additionally, considering both local and global exposures is key in coming up with a sound conceptual design. Quantitatively, the method to calculate the robustness index in a building is presented. A novel framework to quantify robustness and find the optimal structural solution is presented, based on the calculation of the scenario probability-weighted average robustness indices of various design options of a building. A case study example is also presented in the end.

Fire Safety in Tall Timber Building: A BIM-Based Automated Code-Checking Approach

Fire safety regulations impose very strict requirements on building design, especially for buildings built with combustible materials. It is believed that it is possible to improve the management of these regulations with a better integration of fire protection aspects in the building information modeling (BIM) approach. A new BIM-based domain is emerging, the automated code checking, with its growing number of dedicated approaches. However, only very few of these works have been dedicated to managing the compliance to fire safety regulations in timber buildings. In this paper, the applicability to fire safety in the Canadian context is studied by constituting and executing a complete method from the regulations text through code-checking construction to result analysis. A design science approach is used to propose a code-checking method with a detailed analysis of the National Building Code of Canada (NBCC) in order to obtain the required information. The method starts by retrieving information from the regulation text, leading to a compliance check of an architectural building model. Then, the method is tested on a set of fire safety regulations and validated on a building model from a real project. The selected fire safety rules set a solid basis for further development of checking rules for the field of fire safety. This study shows that the main challenges for rule checking are the modeling standards and the elements’ required levels of detail. The implementation of the method was successful for geometrical as well as non-geometrical requirements, although further work is needed for more advanced geometrical studies, such as sprinkler or fire dampers positioning.

Shape optimization of braced frames for tall timber buildings: Influence of semi-rigid connections on design and optimization process

With the recent development of timber as a viable structural material for high-rise structures, glulam braced frames have been recently introduced in lateral load-resisting systems of timber buildings. Based on a simple shape optimization problem of a braced frame, this paper explores one of the specificities of timber structures: the influence of semi-rigid connections on their overall structural behavior and design. Dowel-type connections are first studied to obtain a simplified relation between joint stiffness and axial load-carrying capacity. Then, the established local behavior law is introduced in the shape optimization process and design of a discrete braced frame subject to lateral drift constraint under wind load. The problem is solved by a COBYLA optimization method, combined with Optimality Criteria (OC) member sizing techniques. Solutions are then evaluated and compared with classical steel/concrete design. The semi-rigid behavior of connections finally leads to a significant increase in the volume of timber but also affects the optimal shape and topology of the X-braced frame compared with classical results.

Seismic Design of Timber Buildings: Highlighted Challenges and Future Trends

Use of timber as a construction material has entered a period of renaissance since the development of high-performance engineered wood products, enabling larger and taller buildings to be built. In addition, due to substantial contribution of the building sector to global energy use, greenhouse gas emissions and waste production, sustainable solutions are needed, for which timber has shown a great potential as a sustainable, resilient and renewable building alternative, not only for single family homes but also for mid-rise and high-rise buildings. Both recent technological developments in timber engineering and exponentially increased use of engineered wood products and wood composites reflect in deficiency of current timber codes and standards. This paper presents an overview of some of the current challenges and emerging trends in the field of seismic design of timber buildings. Currently existing building codes and the development of new generation of European building codes are presented. Ongoing studies on a variety topics within seismic timber engineering are presented, including tall timber and hybrid buildings, composites with timber and seismic retrofitting with timber. Crucial challenges, key research needs and opportunities are addressed and critically discussed.

The big shake: designing tall timber buildings that are resilient to earthquakes

The big shake: designing tall timber buildings that are resilient to earthquakes

INCORPORATING TIMBER EDUCATION INTO EXISTING ACCREDITED ENGINEERING PROGRAMS

The demand for large and tall timber buildings is increasing across Canada. The recently constructed Brock Commons building in Vancouver and the upcoming Arbour building in Toronto are two such examples. These buildings are challenging for practitioners to design, and presently only a limited number of engineering institutions across Canada offer a course in timber design. There is a growing demand for engineering graduates who can contribute to the creation of these structures; however, the number of graduates who meet this criterion is lagging. Separate courses in timber could be introduced to more universities, however the addition of a new course may overload students, whose course schedules are already tightly regulated by the Canadian Engineering Accreditation Board. Moreover, the creation of a new course can take several years and will therefore not meet the current industry demand quick enough. The research herein presents a method of incorporating timber education within the existing civil engineering curriculum in Canada, without the introduction of an additional course. The purpose of the proposed method is to offer an efficient solution that will provide engineering students with knowledge of the timber industry quickly to meet industry demand. Two timber learning modules were integrated within the existing Structural Steel Design course at an accredited university. The timber learning modules paralleled the topics covered within an undergraduate timber design course. Students were surveyed before and after the learning modules were presented to assess level of interest and motivations, knowledge of the industry, and level of understanding. After the learning modules were presented, 76% of students indicated they had some level of confidence in contributing to the design of a timber building. These results show that the timber learning modules were successful at introducing and generating an interest in timber design, and that students gained basic knowledge they could apply in practice.

INCORPORATING TIMBER EDUCATION INTO EXISTING ACCREDITED ENGINEERING PROGRAMS

The demand for large and tall timber buildings is increasing across Canada. The recently constructed Brock Commons building in Vancouver and the upcoming Arbour building in Toronto are two such examples. These buildings are challenging for practitioners to design, and presently only a limited number of engineering institutions across Canada offer a course in timber design. There is a growing demand for engineering graduates who can contribute to the creation of these structures; however, the number of graduates who meet this criterion is lagging. Separate courses in timber could be introduced to more universities, however the addition of a new course may overload students, whose course schedules are already tightly regulated by the Canadian Engineering Accreditation Board. Moreover, the creation of a new course can take several years and will therefore not meet the current industry demand quick enough.
 The research herein presents a method of incorporating timber education within the existing civil engineering curriculum in Canada, without the introduction of an additional course. The purpose of the proposed method is to offer an efficient solution that will provide engineering students with knowledge of the timber industry quickly to meet industry demand. Two timber learning modules were integrated within the existing Structural Steel Design course at an accredited university. The timber learning modules paralleled the topics covered within an undergraduate timber design course. Students were surveyed before and after the learning modules were presented to assess level of interest and motivations, knowledge of the industry, and level of understanding. After the learning modules were presented, 76% of students indicated they had some level of confidence in contributing to the design of a timber building. These results show that the timber learning modules were successful at introducing and generating an interest in timber design, and that students gained basic knowledge they could apply in practice.

Seismic shear and acceleration demands in multi-storey cross-laminated timber buildings

A realistic estimation of seismic shear demands is essential for the design and assessment of multi-storey buildings and for ensuring the activation of ductile failure modes during strong ground-motion. Likewise, the evaluation of seismic floor accelerations is fundamental to the appraisal of damage to non-structural elements and building contents. Given the relative novelty of tall timber buildings and their increasing popularity, a rigorous evaluation of their shear and acceleration demands is all the more critical and timely. For this purpose, this paper investigates the scaling of seismic shear and acceleration demands in multi-storey cross-laminated timber (CLT) buildings and its dependency on various structural properties. Special attention is given to the influence of the frequency content of the ground-motion. A set of 60 CLT buildings of varying heights representative of a wide range of structural configurations is subjected to a large dataset of 1656 real earthquake records. It is demonstrated that the mean period (Tm) of the ground-motion together with salient structural parameters such as building aspect ratio (λ), design force reduction factor (q) and panel subdivision (β) influence strongly the variation of base shear, storey shears and acceleration demands. Besides, robust regression models are used to assess and quantify the distribution of force and acceleration demands on CLT buildings. Finally, practical expressions for the estimation of base shears, inter-storey shears and peak floor accelerations are offered.

Unitised timber envelopes. A novel approach to the design of prefabricated mass timber envelopes for multi-storey buildings

Tall timber building is today both possible and desirable due to the advantages that timber construction offers the industry in terms of productivity gains and sustainable development. Prefabrication certainly represents a unique opportunity for timber technologies to lead the construction sector's shift towards a more industrialised approach, and new solutions need to be put in place for future generations of tall timber buildings. This paper examines the design of newly-conceived timber-based envelope systems for multi-storey buildings, which are fully preassembled off-site to maximise construction efficiency and safety. The prefabricated external wall assemblies are provided with all functional layers (including windows and cladding) to enable site installation from the constructed floor without scaffolds or any action from the outside of the building. An aluminium/gasket frame system is integrated within the external walls to guarantee air and water tightness at panel interfaces and guide the installation of the “mega-panels” on-site. The technical solution is presented in the form of 2D technical drawings and a three-dimensional model, developed for the application in a load bearing CLT-based envelope configuration. A full-scale (though small-size) mock-up was assembled to account for fabrication and installation issues, as well as to demonstrate the versatility of the solution for the use-case of a non-load bearing curtain wall configuration. The research innovation is found in the systematic and novel design approach to the development of industrialised timber-base envelopes, rather that in the specific instance of the design outcome presented and analysed here. This is a particularly important innovation because, as the key mitigating barrier for buildings, envelope design is context-related and has to be conducted on a case by case basis. This article presents the most substantial design outcome of the first author's doctoral research and is now being further developed as part of an industry embedded research project investigating industrialised construction and tall timber buildings.

Cross-Laminated Timber Shear Walls in Balloon Construction: Seismic Performance of Steel Connections

In the context of the global trend of designing sustainable structures, the attention towards high-rise timber buildings of 8 to 25 storeys has been increasing in recent years. Balloon construction technique using a relatively new heavy timber material, cross-laminated timber (CLT), has been shown to be promising for high-rise building applications, given its compatibility with off-site construction techniques and its desirable mechanical characteristics. To date, tall timber buildings using CLT have been built mainly in non-seismic or low-seismic locations around the world, whereas their application in high seismic regions has been limited to platform construction. More research on the behaviour of CLT structures during seismic events in terms of system behaviour as well as the behaviour of components, particularly connections, is required. The research presented in this paper seeks to initiate the process of seismic design of tall wood buildings using a balloon construction technique. Two buildings, one three-storey fictitious building and one to-be-constructed ten-storey building, both located on the west coast of Canada, were considered and designed based on the NBCC 2015 seismic provisions. The loads on the shear walls, which span over three storeys, were extracted in order to estimate realistic demands on lateral load resisting systems (LLRS) in the balloon construction. Different connections, including base shear connections, panel-to-panel shear connections, as well as high-capacity hold-downs, were designed accordingly. An experimental program was developed to investigate the behaviour of these connections, focusing on yielding and failure mechanisms in each connection category. This paper explains different phases of the experimental program and introduces connection details designed to achieve the research goals. The results of this study will contribute to the body of knowledge on seismic behaviour of prefabricated mass timber buildings, and will benefit engineers and practitioners using timber to design high-rise structures.