Innovative Engineered Timber Building Systems for Non-Residential Applications, Utilising Timber Concrete Composite Flooring Capable of Spanning Up to 8 to 10m
This project has developed technologies for prefabricated structural systems constructed from engineered wood products for floors and building frames, suitable for buildings up to eight stories in height. The project included the design of a virtual multi-storey timber building, a review of commercial flooring systems, and the development of interim design procedures for timber concrete composite (TCC) floors. Compared with either solid concrete or timber floors, TCC floors provide an excellent balance between increased stiffness, reduced weight, better acoustic separation and good thermal mass.
Outcomes from the project have confirmed TCC floors as a viable alternative to conventional flooring systems. The life cycle analysis of the virtual timber building has highlighted the potential advantages of timber-based building systems for commercial applications. The project also resulted in the formation of the Structural Timber Innovation Company, a research company that will continue to develop timber building systems in non-residential buildings in Australia and New Zealand.
Bridges built in timber are enjoying a significant revival, both for pedestrian and light traffic and increasingly for heavier loadings and longer spans. Timber's high strength-to-weight ratio, combined with the ease and speed of construction inherent in the off-site prefabrication methods used, make a timber bridge a suitable option in many different scenarios.
This handbook gives technical guidance on forms, materials, structural design and construction techniques suitable for both small and large timber bridges. Eurocode 5 Part Two (BS EN 1995-2) for the first time provides an international standard for the construction of timber bridges, removing a potential obstacle for engineers where timber construction for bridges has not – in recent centuries at least – been usual.
Clearly illustrated throughout, this guide explains how to make use of this oldest construction material in a modern context to create sustainable, aesthetically pleasing, practical and durable bridges. Worldwide examples include Tourand Creek Bridge, Canada; Toijala, Finland; Punt la Resgia, Switzerland; Pont de Crest, France; Almorere Pylon Bridge, the Netherlands.
Transition Strategies: Accelerating Social Acceptance and Removing the Barriers to Prefabricated Multi-Storey Timber Urban Infill Developments in Australia Using CLT Construction Systems
This report was commissioned to review and formulate strategies for the accelerated uptake and social acceptance of living in multi-storey cross-laminated timber (CLT)-constructed buildings in infill developments to: remove cultural barriers, meet the sustainability expectations of potential buyers and obtain a better understanding of how we can facilitate the rapid introduction of this innovative construction technology in Australia.
An extensive review of literature within the field was conducted to gather an overview of the barriers that inhibit consumers, governments and industry in the uptake and acceptance of CLT constructed buildings for infill development. Data was collected on CLT buildings worldwide, to build a comprehensive picture of multi-storey timber buildings using CLT-construction systems.
This paper describes the design of a novel semi-prefabricated LVL-concrete composite floor that has been developed in New Zealand. In this solution, the floor units made from LVL joists and plywood are prefabricated in the factory and transported to the building site. The units are then lifted onto the supports and connected to the main frames of the building and to the adjacent units. Finally, a concrete topping is poured on top of the units in order to form a continuous slab connecting all the units. Rectangular notches cut from the LVL joists and reinforced with coach screws provide the composite action between the concrete slab and the LVL joists. This system proved to be an effective modular solution that ensures rapid construction. A design procedure based on the use of the effective flexural stiffness method, also known as the “gamma method” is proposed for the design of the composite floor at ultimate and serviceability limit states, in the short and long term. By comparison with the experimental results, it is shown that the proposed method leads to conservative design. A step-by-step design worked example of this novel semi-prefabricated composite floor concludes the paper.
Ninth European Conference on Noise Control (Euronoise)
Research Status
Complete
Notes
June 10-13, 2012, Prague, Czech Republic
Summary
In residential multi-storey buildings of timber it is of great importance to reduce the flanking transmission of noise. Some building systems do this by installing a vibration-damping elastic interlayer, Sylomer or Sylodyn , in the junction between the support and the floor structure. This interlayer also improves the floor vibration performance by adding damping to the structure. In the present work the vibration performance of a floor with such interlayers has been investigated both in laboratory and field tests. A prefabricated timber floor element was tested in laboratory on rigid supports and on supports with four different types of interlayers. The results are compared with in situ tests on a copy of the same floor element. The effect on vibration performance i.e. frequencies, damping ratio and mode shapes is studied. A comparison of the in situ test and the test with elastic interlayer in laboratory shows that the damping in situ is approximately three times higher than on a single floor element in the lab. This indicates that the damping in situ is affected be the surrounding building structure. The achieved damping ratio is highly dependent on the mode shapes. Mode shapes that have high mode shape coefficients along the edges where the interlayer material is located, result in higher modal damping ratios. The impulse velocity response, that is used to evaluate the vibration performance and rate experienced annoyance in the design of wooden joist floors, seems to be reduced when adding elastic layers at the supports.
During the last few years, the merging of timber building tradition with the application of new technologies has produced new prefabricated building systems in Europe and North America. Mid-rise buildings present a unique opportunity to apply new timber technologies. Chile has shown sustained growth of buildings construction during the past decades but little further development in the use of wood. To establish the feasibility of timber systems applied to the Chilean context this research considered social aspects, technical aspects and local standards related to the manufacture and construction using timber components. A project proposal is used to analyze the architectural applications of timber systems according to the Chilean context. The design considers the case of densification in the city of Santiago and investigates the possibility of developing mid-rise structures using the structural properties and features of timber systems. So far only two systems applied to mid-rise structures have been tested for seismic resistance on full scale prototypes: Midply and Cross Laminated Timber. Both systems are suitable for the Chilean context despite their different features. However, it is essential to modify the Chilean Structural Code in order to properly incorporate the seismic performance of timber structures. Also, further research is needed on the application of softwoods and local construction techniques are required for timber panel systems in order to change the negative perception of users about timber housing. The Chilean context has interesting design opportunities to develop buildings that use prefabricated timber panel systems. These structures are flexible, light and have shear high-resistance. However, it is necessary further exploration on architectural possibilities that could expand the use of these alternatives.
Prefabricated engineered solid wood panel construction systems can sequester and store CO2. Modular cross-laminated timber (CLT, also called cross-lam) panels form the basis of low-carbon, engineered construction systems using solid wood panels that can be used to build residential infill developments of 10 storeys or higher. Multi-apartment buildings of 4 to 10 storeys constructed entirely in timber, such as recently in Europe, are innovative, but their social and cultural acceptance in Australia and North America is at this stage still uncertain. Future commercial utilisation is only possible if there is a user acceptance. The author is part of a research team that aims to study two problems: first models of urban infill; then focus on how the use of the CLT systems can play an important role in facilitating a more livable city with better models of infill housing. Wood is an important contemporary building resource due to its low embodied energy and unique attributes. The potential of prefabricated engineered solid wood panel systems, such as CLT, as a sustainable building material and system is only just being realised around the globe. Since timber is one of the few materials that has the capacity to store carbon in large quantities over a long period of time, solid wood panel construction offers the opportunity of carbon engineering, to turn buildings into ‘carbon sinks’. Thus some of the historically negative environmental impact of urban development and construction can be turned around with CLT construction on brownfield sites.
Developing a Prefabricated Low-Carbon Construction System Using Cross-Laminated Timber (CLT) Panels for Multistorey Inner-City Infill Housing in Australia
In this chapter I describe a multidisciplinary research project into cross-laminated timber (CLT) panels which aims to transform the Australian construction and development industry and involves a range of key partners. This project will introduce CLT panels as a way to build with a lightweight prefabricated low-carbon construction system that is advantageous for urban infill and residential buildings. The challenge, research questions, and the advantages of this system are explained herein.
Cross-laminated timber (CLT) is a prefabricated solid engineered wood product made of at least three orthogonally bonded layers of solid-sawn lumber or structural composite lumber that are laminated by gluing of longitudinal and transverse layers with structural adhesives to form a solid rectangular-shaped, straight, and plane timber intended for roof, floor, or wall applications. While this engineered wood product has been used in Europe for over 15 years, the production of CLT and design of CLT structural systems have just begun in North America. For the acceptance of new construction materials or systems in North America, such as CLT, a consensus-based product standard is essential to the designers and regulatory bodies. This paper describes and documents the background information and some key issues that were considered during the development of the ANSI/APA PRG 320 Standard for Performance-Rated Cross Laminated Timber. This standard was developed based on the consensus standard development process of APA-The Engineered Wood Association as a standards developer accredited by the American National Standards lnstitute (ANSI). The CLT stress classes incorporated in this product standard are also discussed. The ANSI/APA PRG 320 standard has been approved by the Structural Committee of the lnternational Code Council (lCC) for the 20'15 lnternational Building Code (lBC).
Timber-concrete composite structures were originally developed for upgrading existing timber oors, but during last decades, they have new applications in multistorey buildings. Most of the research performed on these structures has focused on systems in which wet concrete is cast on top of timber beams with mounted connectors. Recently investigations on composite systems were performed at Luleå University of Technology in Sweden, in which the concrete slab is prefabricated off-site with the connectors already embedded and then connected on-site to the timber joists. Similar studies have been carried out also on timber-concrete composite structures with prefabricated FRC slabs at Lund University in Sweden. Two kinds of shear connectors were incorporated in the prefabricated FRC concrete slabs. These last systems can be considered globally as partially prefabricated structures because only the slabs were cast off-site with already inserted shear connectors and then the connection with the timber beams is done on the building site. An innovative composite system for floor applications is presented in this thesis. The entire structure is prefabricated off-side, transported and direct mounted to the building on site, that can be seen as full prefabricated structures. Noticeable benefits of a full prefabricated structure are that the moving work from the building site to the workshop reduces construction costs, is more simple and fast of manufacture and erect, and of sure, has better quality, that means more durability. Self-tapping full-threaded screws to connect concrete slabs to timber beam were used. Dimensions of the composite beams and the spacing between the screws has been chosen by discussing different FE model in order to reach the optimal solution. The experimental campaign included:
(i) two short-time bending tests carried out on two dierent full-scale specimens,
(ii) dynamic tests conducted on one full-scale specimen,
(iii) long-time bending test carried out on one full-scale specimen,
(iv) compression tests on three cubes of concrete,
(v) nine withdrawal tests of the screws with different depth in the concrete.
The results of the experimental tests show that the composite beams have a very high level of resistance and stiffness and also allow to reach a high degree of efficiency. Last, comparisons between FE results, analytical calculations and experimental values have been performed and from them it can be concluded that FE model and theoretical calculations well interpret the behavior of the composite structure and provide reliable results.
This thesis examines the development of a superstructure for a slab-on-girder wood-concrete composite highway bridge. Wood-concrete composite bridges have existed since the 1930's. Historically, they have been limited to spans of less than 10 m. Renewed research interest over the past two decades has shown great potential for longer span capabilities. Through composite action and suitable detailing, improvements in strength, stiffness, and durability can be achieved versus conventional wood bridges. The bridge makes use of a slender ultra-high performance fibre-reinforced concrete (UHPFRC) deck made partially-composite in longitudinal bending with glued-laminated wood girders. Longitudinal external unbonded post-tensioning is utilized to increase span capabilities. Prefabrication using double-T modules minimizes the need for cast-in-place concrete on-site. Durability is realized through the highly impermeable deck slab that protects the girders from moisture. Results show that the system can span up to 30 m while achieving span-to-depth ratios equivalent or better than competing slab-on-girder bridges.
New Zealand Society for Earthquake Engineering Conference
Research Status
Complete
Notes
April 26-28, 2013, Wellington, New Zealand
Summary
This paper describes options for seismic design of pre-fabricated timber core-wall systems, used as stairwells and lift shafts for lateral load resistance in multi-storey timber buildings. The use of Cross-Laminated Timber (CLT) panels for multi-storey timber buildings is gaining popularity throughout the world, especially for residential construction. This paper describes the possible use of CLT core-walls for seismic resistance in open-plan commercial office buildings in New Zealand. Previous experimental testing at the University of Canterbury has been done on the in-plane behaviour of single and coupled Pres-Lam post-tensioned timber walls. However there has been very little research done on the behaviour of timber walls that are orthogonal to each other and no research into CLT walls in the post-tensioned Pres-Lam system. This paper describes the proposed test regime and design detailing of two half-scale two-storey CLT stairwells to be tested under a bi-directional quasi-static loading. The test specimens will include a half-flight stair case with landings within the stairwell. The “High seismic option” consists of post-tensioned CLT walls coupled with energy dissipating U-shaped Flexural Plates (UFP) attached between wall panels and square hollow section steel columns at the corner junctions. An alternative “Low seismic option” uses the same post-tensioned CLT panels, with no corner columns or UFPs. The panels will be connected by screws to provide a semi-rigid connection, allowing relative movement between the panels producing some level of energy dissipation.
There is a strong trend to industrially produce multi-storey light weight timber based houses. This concept allows the buildings to be manufactured to a more or less prefabricated extent. Most common types are volume/room modules or flat wall and floor modules. When assembling the modules at the building site, elastomer isolators are used in several constructions to reduce flanking transmission. The sound insulation demands in the Nordic countries are relatively high and therefore the flanking transmission must be well controlled, where elastomer isolators are an alternative. Decoupled radiation isolated walls is another. There are though no working studies or mathematical models of the performance of these isolators. They are only treated as simple mass-springs systems that operate vertically, i.e. one degree of freedom. In this paper there is an analysis of experimentally data of the structure borne sound isolating performance of elastomer isolators that are separating an excited floor from receiving walls. The performance dependence of structure type is also presented. An empirically based regression model of the vibration level difference is derived. The model is based on measurements of six elastomer field installations, which are compared to five comparable installations without elastomers. A goal is that the model can be used for input in future SEN prediction models for modeling of sound insulation.
European Conference on Cross Laminated Timber (CLT)
Research Status
Complete
Notes
May 21-22, 2013, Graz, Austria
Summary
Cross laminated timber (CLT) has been developed to a worldwide well-known and versatile useable building material. Currently increasing rates in production volume and distribution can be observed. In fact CLT, thanks to its laminar structure making it well suited for use in construction, provides new horizons in timber engineering, in areas which had until now been the realm of mineral building materials like concrete and masonry.
After a short introduction, this paper aims to demonstrate current production processes used for rigid CLT. In section 2 the process steps are described and essential requirements, as well as pros and cons of various production techniques, are discussed. Latest results of R & D and of development and innovation in production technology are presented. In section 3 test and monitoring procedures in the area of the internal quality assurance, known as factory production control (FPC), are presented. Diverse regulations, in the form of technical approvals for CLT as well as in the CLT product standard prEN 16351 [1], are discussed. Additionally, some technological aspects of the product, CLT, together with a comparison of geometrical and production relevant parameters of current technical approvals in Europe are provided in section 4.
In the final and main part of the paper, production and technology is presented in a condensed way. The outlook for current and future developments, as well as the ongoing establishment of the solid construction technique with CLT, is given. The product, CLT, comprises an enormous potential for timber engineering as well as for society as a whole. Standardisation and further innovation in production, prefabrication, joining technique, building physics and building construction make it possible for timber engineering to achieve worldwide success.
This paper presents energy and environmental performance analyses, a study of summer indoor temperatures and occupant behavior for an eight story apartment building, with the goal to combine high energy efficiency with low environmental impact, at a reasonable cost. Southern Portvakten building is built with prefabricated timber elements using passive house principles in the North European climate. Energy performance was analyzed through parametric studies, as well as monitored energy data, and complemented with analysis of occupant behavior during one year. Results show that airtight, low-energy apartment buildings can be successfully built with prefabricated timber elements in a cold climate. The monitored total energy use was 47.6 kWh/m2, excluding household electricity (revised to a normal year), which is considerably lower than of a standard building built today in Sweden—90 kWh/m2. However, the occupancy level was low during the analyzed year, which affects the energy use compared to if the building had been fully occupied. Environmental analysis shows that the future challenges lie in lowering the household and common electricity use, as well as in improving the choices of materials. More focus should also lie on improving occupant behavior and finding smart solar shading solutions for apartment buildings.
This study explores the use of Cross Laminated Timber (CLT) in a 10-story residential building as an alternative building method to concrete and steel construction. The study is not meant to be exhaustive, rather a preliminary investigation to test the economic viability of utilizing this new material to increase density, walkability and sustainable responsiveness in our built environment.
Based on international precedent, CLT is an applicable material for low-rise, as well as mid-rise to high-rise construction and has a lighter environmental footprint than traditional concrete and steel construction systems. Cross-laminated timber is a large format solid wood panel building system originating from central Europe. As a construction system it is similar to precast concrete in which large prefabricated panels are lifted by crane and installed using either a balloon frame or platform frame system. The advantages to using CLT are many, but the main benefits include: shorter construction times, fewer skilled laborers, better tolerances and quality, safer work environment, utilization of regional, sustainable materials, and reduction of carbon footprint of buildings. As a new, unproven material in the Pacific Northwest, this study investigates the cost competitiveness of CLT versus traditional materials for “low high-rise” buildings.
Hybrid construction systems proved to be valid structural solutions for the implementation of multi-storey buildings, especially if they require only the assembly of prefabricated and modular building elements. The structures here considered are designed to make different materials - firstly steel and timber - structurally collaborate, in order to develop a construction system with marked performance and architectonic flexibility features. Such systems can make the most of the heavily industrialized construction technology typical of steel systems, as well as of the advantages offered by CLT panels -lightness and structural stability- in which the timber element is recognized as an eco-friendly and eco-compatible material. Furthermore, in a sustainable urban development prospective, the use of cross-laminated timber panels, in short CLT, is recommended because wood is one of the fewest materials which has the capacity to isolate and store CO2 for a long period of time.
Hybrid structural systems assembled connecting steel elements and cross-laminated timber panels (CLT) can be a valid alternative to traditional systems in the construction of residential buildings. Such systems can combine the industrialized construction technology typical of steel systems with the advantages offered by CLT panels, namely lightness and geometric stability. Moreover, CLT panels are timber-based products, and wood is recognized as an eco-friendly and eco-compatible material. In hybrid structural systems, the seismic-resistant capacity of the structure can be achieved by ensuring an adequate transmission of actions among the resistant elements, namely plain timber panels (floor and wall) and steel frame elements (beams and columns). Specifically, the interaction between the steel frame and the wood panels shall ensure both horizontal and vertical bracing to floors and walls, respectively. The work presented hereafter concerns the study of the connections to be used among the individual building components of the horizontal elements, with the aim of developing an effective collaboration among the materials, maximizing the level of prefabrication and industrialization of the final components. In particular, the preliminary results of the experimental tests carried out on full-scale steel-to-timber floor specimens, loaded by in-plane actions, will be presented.
Compared to light-frame wood shear walls, it is relatively difficult for panelized CLT shear walls to achieve similar levels of lateral deflection without paying special attention to design details, i.e., connections. A design lacking ductility or energy dissipating mechanism will result in high acceleration amplifications and excessive global overturning demands for multistory buildings, and even more so for tall wood buildings. Although a number of studies have been conducted on CLT shear walls and building assemblies since the 1990s, the wood design community’s understanding of the seismic behavior of panelized CLT systems is still in the learning phase, hence the impetus for this article and the tall CLT building workshop, which will be introduced herein. For example, there has been a recent trend in engineering to improve resiliency, which seeks to design a building system such that it can be restored to normal functionality sooner after an earthquake than previously possible, i.e., it is a resilient system. While various resilient lateral system concepts have been explored for concrete and steel construction, this concept has not yet been realized for multistory CLT systems. This forum article presents a review of past research developments on CLT as a lateral force-resisting system, the current trend toward design and construction of tall buildings with CLT worldwide, and attempts to summarize the societal needs and challenges in developing resilient CLT construction in regions of high seismicity in the United States.
Cross-laminated timber (CLT) panels have potential market in North America for building mid-rise or even taller structures due to their good structural and fire safety performance, light weight, and prefabricated nature. However, to ensure long-term durability when used in building enclosures, the hygrothermal performance of CLT wall assemblies needs to be evaluated in terms of wetting and drying potential. A test wall consisting of sixteen 0.6 m by 0.6 m CLT panels made of five different wood species (or species groups) and four different wall assemblies was constructed. The CLT panels were initially wetted with the moisture content (MC) in the surface layers approaching or exceeding 30%, and monitored for MCs and temperatures at different depths over one year in a building envelope test facility located in Waterloo, Ontario. The drying behaviour of these panels was analysed and the measured MCs over time were compared to simulation results using a commercial hygrothermal program. This field study showed that most of the CLT panels dried to below 26% within one month except for CLT walls with a low-permeance interior membrane, which indicated that none of the CLT walls would likely remain at a high MC level long enough to initiate decay under the conditions tested. The simulation results generally agree well with the field data at MCs below 26%. However, it was found that the hygrothermal simulation program tended to overestimate the MC in the centre of the panels by up to 5e10%, and simulated MCs at locations deep into the CLT panels were not as responsive to changes in ambient conditions, as the measurements indicated for assemblies with high exterior permeance.
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