Reinforced concrete and steel are the most commonly used materials in bridge applications in Quebec (Canada). The production of these materials has a significant environmental impact and contributes to the scarcity of non-renewable resources due to the numerous maintenance requirements during the life of the structure. Consequently, there are governmental initiatives and efforts in the province of Quebec to promote the use of aluminum and engineered wood in the construction and rehabilitation of roadway bridges. Those two materials are not widely used due to the short-term vision of decision makers and the lack of technical knowledge for structural uses in highway bridge structures. However, they can be competitive materials due to their local production, durability and recyclability. The life cycle assessment method allows for an analysis of the use of complementary materials, considering all the stages of the life cycle of a structure. The comparison of a roadway bridge made of an aluminum deck on glulam timber beams against a bridge made of an aluminum deck on steel girders shows that, due to the local production and low environmental impact of glulam timber, the aluminum-to-timber bridge is economically and environmentally more advantageous than the aluminum-to-steel bridge. Similarly, a comparison of this alternative aluminum/wood solution to the conventional concrete slab-on-steel girder bridge solution shows a decrease in overall cost by 86% and a decrease in environmental impacts by 88% due to the ease of prefabrication and the relatively low number of interventions over its lifetime.
There is widespread enthusiasm toward utilizing mass timber panels (MTP), mainly cross-laminated timber (CLT), in construction, including for the basements of low-rise buildings. CLT is deemed a sustainable alternative to the widely used concrete foundation walls due to significant advantages such as less vulnerability to cracking due to uneven load distribution and presence of concentrated loads, higher thermal resistance, less construction time due to whole-wall prefabrication and installation, and less detrimental environmental effects. This study is part of an extensive research program aimed at developing the structural analysis and design concepts and methodology for constructing house foundation walls using MTPs, focusing on the usage of CLT. After comparison of CLT basements with their equivalent concrete ones from the sustainability point of view, and a brief discussion on geotechnical and hygrothermal considerations, the main theme of the article includes the structural analysis and design methodology, requirements, and the procedure to achieve a reliable and efficient design of a CLT basement. A simplified analysis procedure to design the laminate thicknesses and the number of layers in CLT foundation walls for different scenarios considering various variables such as soil type and backfill height is discussed, and results in the form of pre-engineered design tables are provided. The findings of this study demonstrate that, depending on the soil type and backfill height, 3–7-ply CLT panels would be needed for net wall heights of up to 3 m. Additionally, advanced finite element analyses are performed on sample architypes to validate the simplified analysis procedure used for design. It is shown that the proposed analysis procedure and the pre-engineered tables produce conservative and efficient results.
Environmental and urbanization challenges during the last few decades encouraged steady growth of mass timber construction where attention is drawn to cross laminated timber (CLT) as one of the most interesting products in terms of mechanical properties, versatility, efficient prefabrication and sustainability. Standardisation and codification regarding testing and design of CLT elements are hence pointed out as one of the main issues within the ongoing revision procedure of Eurocode 5. A consistent and unified design approach for CLT at pure in-plane shear loading conditions (shear walls) and at in-plane beam loading conditions is however still missing. This paper deals with analytical models for the determination of stress components related to predictions of load bearing capacity of CLT with respect to shear failure mode III – shear failure in the crossing areas constituted by the flatwise bonded areas between laminations of adjacent layers. This failure mode is relevant for both pure in-plane shear loading and in-plane beam loading conditions. The paper presents a review of previously proposed models for the prediction of shear stresses in crossing areas of CLT, for both loading conditions. Comparisons between FE-results and model predictions are reviewed indicating significant differences between them concerning the predicted influence of the CLT element lay-up and values of maximum shear stresses. Based on simplifications of models previously presented, a unified design proposal that is based on a rational and consistent mechanical background for both loading situations and that shows overall good agreement with FE-results is presented.
In recent decades, there is a trend in Scandinavian countries to build multi-storey residential houses using prefabricated timber modules. It is a highly efficient construction process with less environmental impact and less material waste. A significant building element in the timber modules is the light-frame timber wall, which has to be carefully analysed and optimized in this process. This paper presents a new parametric Finite Element (FE) model that can simulate both in-plane and out-of-plane deformations in the light-frame walls. A new and flexible (Eurocode based) approach to define the properties of the mechanical connections is introduced. A numerical model is presented through simulations of several walls that were verified with full-scale experiments. The results indicate that the numerical model could achieve fairly reasonable accuracy with the new approach. Furthermore, several parametric studies are presented and discussed from global and local points of view, to investigate the effects of certain parameters that are not considered in the design method according to Eurocode 5.
Densely populated cities characterize urbanized territories, and most public buildings fail to meet many of the new demands imposed by the pandemic and the modern lifestyle. The need to expand spaces has become imperative, although, at the same time, it is necessary to reduce land consumption and preserve green spaces. If we consider the existing heritage a resource, these problems could represent an opportunity to improve existing structures both from a technological and structural point of view. It is possible to effort a holistic approach by improving the energy impact of new buildings and the heritage seismic behaviour facing the problem in a multidisciplinary way. Starting from the “building on the built” philosophy, this paper presents a possible use of engineered wood, such as cross-laminated timber (CLT), to pursue this strategy. The proposal is the realization of volumetric additions to existing buildings without further land consumption. This type of intervention, mentioned as “parasitic architecture”, positively impacts urban regeneration strategies. The use of prefabricated timber components (CLT) endorses the speed of realization, reducing the interferences with the surroundings and improving the healthiness and safety of the environment.
This thesis focuses on the structural performance of mass timber panel-concrete composite floors with notches. Mass timber panels (MTPs) such as cross-laminated timber, glue-laminated timber, and nail-laminated timber, are emerging construction materials in the building industry due to their high strength, great dimensional stability, and prefabrication. The combination of MTPs and concrete in the floor system offers many structural, economic, and ecological benefits. The structural performance of MTP-concrete composite floors is governed by the shear connection system between timber and concrete. The notched connections made by cutting grooves on timber and filling them with concrete are considered as a structurally efficient and cost-saving connecting solution for resisting shear forces and restricting relative slips between timber and concrete. However, the notched connection design in the composite floors is not standardized and the existing design guidelines are inadequate for MTP-concrete composite floors.
To study the structural performance of notched connections and notch-connected composite floors, this thesis presented experimental, numerical, and analytical investigations. Push-out tests were conducted on the notched connections first, and then bending tests and vibration tests were conducted on full-scale composite floors. Finite element models were built for the notched connections to derive the connection shear stiffness. Finally, analytical solutions were developed to predict the internal actions of the composite floors under external loads.
This study shows that the structural performance of notched connections is affected by the geometry of the connections and material properties of timber and concrete. The notch-connected MTP-concrete composite floors showed high bending stiffness but were not fully composite. The floors with shallow notches tended to fail in a ductile manner but had lower bending stiffness than floors with deep notches. The composite floors with deep notches, however, often fail abruptly in the concrete notches. By reinforcing the notched connections with steel fasteners, the composite floor can achieve high bending stiffness, high load-carrying capacity, and controlled failure pattern. The proper number and locations of notched connections in the composite floors can be determined from the proposed composite beam model.
This thesis presented promising results in terms of the static and dynamic structural performance of notch-connected MTP-concrete composite floors. The test investigations added additional data to the current research body and prompted further evolvement of timber-concrete composite floors. The proposed empirical equations for estimating the connection stiffness and strength and composite beam model for predicting the serviceability and ultimate structural performance of composite floors provide useful tools to analyze the notch-connected MTP-concrete composite floors. The design recommendations for MTP-concrete composite floors with notches are provided in the thesis.
Timber slabs design is currently limited to grid layouts derived from prefabricated rectangular panels. The lack of adaptability of timber slabs to accommodate multiple span directions makes it difficult to compete with reinforced concrete slabs constructed on site. This paper describes an adaptive slab system composed of thin Cross-Laminated Timber (CLT) panels and robot-fabricated beam networks for reinforcement. The beam network was developed through intricate negotiation of structural optimization and fabrication constraints, which can adapt to changes in slab span and directions. A mobile robot platform that allows for on-site assembly of timber sticks into continuous beam networks was developed. The robot platform and slab system were tested with a case study pavilion. The co-design of the robot platform and the slab system fills the gap in on-site robotic timber construction and expands the design freedom of timber buildings.
In this paper, the bending properties of a 3-ply cross-laminated bamboo and timber (CLBT), prefabricated with the bamboo mat-curtain panel and hem-fir lumber, were examined in the major and minor strength directions, and a 3-ply hem-fir cross-laminated timber (CLT) was taken as a control group. The analytical model for the sum of the orthogonal apparent bending moduli with the two types of layer classifications were proposed, and the two kinds of contribution models were developed to analyze the apparent bending modulus variation behavior of the CLBT and CLT panels in the major and minor strength directions. The experimental results showed that since the CLBT group had more internal orthogonal structures, its difference in the bending properties between the major and minor strength directions was lower than that of the CLT group. Furthermore, the proposed contribution models quantitatively analyzed the relationship between the apparent bending moduli of the CLBT and CLT panels and the corresponding composition layer characteristics. The contribution model to characterize the apparent bending modulus in major and minor strength directions demonstrated good agreement with the test results. Based on this model interpreted by three-dimensional figures, the contribution variation characteristics in the major and minor strength directions were revealed.
Wooden construction constitutes a specific branch of the building industry that focuses on high-quality materials, a developed sense of aesthetics connected with comfort and functionality, and concern for ecology and durability. This type of construction has a positive effect on human quality of life. This article focuses on modular frame construction and technological aspects of wooden houses built according to Canadian or Scandinavian technologies. Taking weather conditions of Scandinavian countries into consideration, timber is a popular building material, which, when preserving certain parameters such as density of rings, may provide durability of a modular wooden building even up to 200–300 years. This article is a review and presents the possibility of producing frame buildings in Europe (Poland) in accordance with the applicable standards, including a heat transfer coefficient U = 2 [W/(m²·K]. In Poland, wooden frame buildings can be traced back to the 14th century. Wooden frame buildings and modular wooden frame buildings were produced even earlier in Norway. Wooden construction continued in the mid-1800s in various forms (with wooden filling and/or panels). In the mid-1900s (1941), certain dimensioning became regulated by law, which then applied to different types of insulation fillings. Prefabricated modular wood frame houses were common in the 1960s.
As mass timber becomes increasingly popular in the United States and around the world, there comes more demand for mass timber in larger buildings. With this demand comes a necessity for these buildings to be able to withstand seismic forces; and in some locations, these forces can get quite high. Typical mass timber lateral systems (such as CLT shear walls) have worked fine for lower seismic forces and shorter buildings, but with this new demand comes a need for newer systems. Rocking timber walls is one of these systems. The goal of a rocking timber wall is to allow the lateral wall system to move in the case of high seismic force, thus reducing the loading the wall experiences. This is done with vertical post tensioning (PT) within cross-laminated timber panels (CLT). In addition, easily replaceable energy dissipation devices, such as U-shaped flexural plates (UFPs), allow for concentration of inelastic deformation during rocking of the walls, which keeps the CLT and PT components free from harm. Another system used to handle seismic load in tall mass timber structures are inter-story isolation systems. These systems can isolate the force at separate levels, effectively decreasing the load the foundation takes from the building's movement. Even newer than these systems is the Floor Isolated Re-centering Modular Construction System (FIRMOC), which utilizes rocking timber walls, inter-story isolation, and the addition of prefabricated modular mass timber to create a system capable of effectively and efficiently dealing with large seismic forces. This report seeks to present these innovative, capable, and effective lateral systems for seismic forces in large scale mass timber structures in a manner that provides understanding of how they work and what makes them effective.
A new timber frame structural system consisting of continuous columns, prefabricated hollow box timber decks and beam-to-column moment-resisting connections is investigated. The hollow box timber decks allow long spans with competitive floor height and efficient material consumption. To achieve long spans, semi-rigid connections at the corners of deck elements are used to join the columns to the deck elements. In the present paper, experimental investigations of a semi-rigid moment-resisting connection and a mock-up frame assembly are presented. The semi-rigid connection consists of inclined screwed-in threaded rods and steel coupling parts, connected with friction bolts. Full-scale moment-resisting timber connections were tested under monotonic and cyclic loading to quantify rotational stiffness, energy dissipation and moment resistance. The mock-up frame assembly was tested under cyclic lateral loading and with experimental modal analysis. The lateral stiffness, energy dissipation, rotational stiffness of the connections and the eigen frequencies of the mock-up frame assembly were quantified based on the experimental tests in combination with a Finite Element model, i.e., the model was validated with experimental results from the rotational stiffness tests of the beam-to-column connections. Finally, the structural damping measured with experimental modal analysis was evaluated and compared with FE model using the material damping of timber parts and equivalent viscous damping of the moment-resisting connections.
Friction-based dampers are a valid solution for non-invasive seismic retrofitting interventions of existing structures, particularly reinforced-concrete (RC) structures. The design of friction-based dampers is challenging: underestimating the slip force prevents the full use of the potential of the device, which attains the maximum admissible displacement earlier than expected. By contrast, overestimating the slip force may cause delayed triggering of the device when the structure has suffered extensive damage. Therefore, designing the appropriate slip force is an optimization problem. The optimal slip force guarantees the highest inter-story drift reduction. The authors formulated the optimization problem for designing a specific class of friction-based dampers, the asymmetric friction connection (AFC), devised as part of the ongoing multidisciplinary Horizon 2020 research project e-SAFE (Energy and Seismic AFfordable rEnovation solutions). The seismic retrofitting technology involves the external application of modular prefabricated cross-laminated timber (CLT) panels on existing external walls. Friction dampers connect the CLT panels to the beams of two consecutive floors. The friction depends on the mutual sliding of two metal plates, pressed against each other by preloaded bolts. This study determines the optimal slip force, which guarantees the best seismic performance of an RC structural archetype. The authors investigate the nonlinear dynamic response of a coupled mechanical system (RC frame-friction damper) under a set of strong-motion earthquakes, using non-differential hysteresis models calibrated on the experimental cyclic responses. The solution of the optimization leads to the proposal of a preliminary simplified design procedure, useful for practitioners.
ICSI 2021 The 4th International Conference on Structural Integrity
Research Status
Complete
Series
Procedia Structural Integrity
Summary
Rigid timber to concrete connection is the most effective solution for timber-concrete composite members subjected to the flexure which provides full composite action and better structural behaviour. One of the most used technologies to produce glued connection of the timber-concrete composite is “dry” method, which includes gluing together of timber and precast concrete slab. This technique has high risk of forming a poor-quality rigid connection in timber-concrete composite, and there are difficulties in controlling the quality of the glued connection. The effect of the non-glued areas in connection between composite layers on the shear stresses and energy absorption were investigated by finite element method and laboratorian experiment. Three timber-concrete composite panels in combination with carbon fibre reinforced plastic composite tapes in the tension zone with the span 1.8 m were statically loaded till the failure by the scheme of three-point bending. Mid-span displacements were measured in the bending test. One specimen was produced by dry method, by gluing together cross-laminated timber panel and prefabricated concrete panel. Timber-concrete qualitative connection of the other two specimens was provided by the granite chips, which were glued on the surface of the cross-laminated timber by epoxy, and then wet concrete was placed. Dimensions of the crushed granite pieces changes within the limits from 16 to 25 mm. The investigated panel with different amount and sizes of non-glued areas in the timber to concrete connection was numerically modelled. Obtained results shown, that the increase of shear stresses is influenced not so much by a total amount of non-glued areas, but by the size of the individual defective areas. Moreover, large non-glued areas significantly reduce the energy absorption of elements subjected to the flexure, which was observed experimentally for defective panel produced by the classical dry method with almost 4 times larger mid-span displacements than for panel with full composite action provided by the proposed production technology of the timber to concrete rigid connection. So, the proposed technology based on the use of granite chips, provides a high-quality connection between timber and concrete layers, with insignificant ration between possible defect and total connection surface area, which is equal to the area of one granite chips edge.
sbe22 Berlin D-A-CH conference: Built Environment within Planetary Boundaries (SBE Berlin)
Research Status
Complete
Series
IOP Conference Series: Earth and Environmental Science
Summary
Reducing the embodied emissions of materials for new construction and renovation of buildings is a key challenge for climate change mitigation around the world. However, as simply reducing emissions is not sufficient to meet the climate targets, using bio-based materials seems the only feasible choice as it permits carbon storage in buildings. Various studies have shown that bio-based materials allow turning overall life cycle impacts negative, therefore, having a cooling effect on the climate. In recent years, scholars and policy makers have focused almost exclusively on the advancement of wooden buildings. Timber structures stand out as they can be prefabricated and used for high-rise buildings. Yet, one important aspect seems to be overlooked: the consideration of supply and demand. Large forest areas that allow sustainable sourcing of woody biomass only exist in the Northern hemisphere, notably in North America and Europe. In these regions, though, urbanization rates are mostly stagnating, meaning new construction rates are low. The largest amount of material requirements in these regions are derived from the refurbishment of the existing stock. Moreover, in areas where structural material is needed for new construction, in Asia, Africa and South America, rain forests need to be protected. Therefore, we need to rethink the desire to find one solution and carelessly implement it everywhere. Instead, we need to consider locally available material and know-how for grounded material choices. This paper explores the supply of a range of bio-based materials and matches it against the material demand of global building stocks. It is based on various previous studies by the authors, of South Africa, China, Portugal, and more. The analysis divides between structural materials for new construction, such as wood and bamboo, and thermal insulation materials for the refurbishment of existing buildings, such as straw and hemp. The results emphasize the need for diversifying bio-based material solutions.
The building sector has revealed a need for process optimization, mirrored by the ongoing discussion around industry 4.0 and increasing automation in building design and construction. Within this context, the prefabrication and standardization of building elements provide interesting opportunities for optimizing the construction process. Off-site fabrication of building envelope and systems can provide significant advantages in terms of process, quality and safety management. This paper presents an outline of state-of-the-art building opaque envelope prefabrication, with particular focus on timber building skins, through a collection of best practices both in the field of building retrofit and new construction. This research is the result of shared research interests and synergies among the Institute for Renewable Energy at Eurac Research and the Innovation in Applied Design (IAD) Lab at the University of Sydney. Results highlight current limitations of envelope prefabrication and outline development opportunities both at technical and production process level. These findings and the conclusions we draw from them will set the foundations for expanding the adoption of an industrialized fabrication approach in the construction environment.
This paper presents an innovative and sustainable timber constructive system that could be used as an alternative to traditional emergency housing facilities. The system proposed in this study is composed of prefabricated modular elements that are characterized by limited weight and simple assembly procedures, which represent strategic advantages when it comes facing a strong environmental disaster (e.g. an earthquake). The complete dismantling of structural elements and foundations is granted thanks to specific details and an innovative connection system called X-Mini, capable of replacing traditional anchoring devices (i.e. hold downs and angle brackets) by resisting both shear and tension loads. This constructive system, denoted as Hybrid Timber Frame (HTF), takes advantage of the strong prefabrication, reduced weight of light-frame timber systems, and of the excellent strength properties of the Cross Laminated Timber (CLT) panels. Specifically, the solid-timber members typically used in the structural elements of light-frame systems are replaced by CLT linear elements. The results of experimental tests and numerical simulations are critically presented and discussed, giving a detailed insight into the performance of the HTF under seismic conditions.
Advanced industrialized construction methods enable complex building components and systems to be built with high precision and quality. This manufacturing technique has an advantage to provide cost-competitive and high energy efficient building components and systems for both retrofits and new construction. This document gives an overview of the use of prefabricated panels in building Net Zero Energy Ready wood-frame multi-unit residential buildings (MURBs) in Edmonton.
Proceedings of the Canadian Society of Civil Engineering Annual Conference 2021
Research Status
Complete
Notes
Page 53
Summary
Mass timber has quickly risen in global popularity as a sustainable building material that shortens building processes, provides a high level of prefabrication and modularity, enhances aesthetic quality, and lessens environmental impact. Most notably, cross-laminated timber’s structure of orthogonal layers of laminate allows panels to span great distances and provide significant structure, allowing much taller wood buildings than traditional wood structures. Furthermore, the high level of prefabrication allows a deeply integrated design process, resulting in less waste and a streamlined assembly process. This paper describes the variety of mass timber products and examines their use in mass timber structures, highlighting connections and building practices. It also outlines the benefits of mass timber, with an emphasis on the positive environmental impact in comparison with concrete and steel, including factors such as its low embodied carbon, reusability, and waste reduction. Advice for maximizing positive environmental impact is given and justification is provided for a shift towards mass timber as a primary building material for tall structures, especially in regions where timber is plentiful.
Timber usage in the Australian construction industry has significantly increased due to its strength, aesthetic properties and extended allowances recently introduced in building codes. However, issues with acoustic performance of lightweight timber buildings were reported due to their inherit product variability and varying construction methods. This article reviews the recent literature on the transmissions of impact and airborne sounds, flanking transmission of timber buildings, and the state of computer prediction tools with reference to the Australian practice. An in-depth analysis of issues and an objective discussion related to acoustic performance of timber buildings are presented. Timber is a lightweight material and shows low airborne sound resistance in low frequency range. Attenuation of sound transmission with addition of mass, layer isolation, different products like cross-laminated timber and prefabrication are discussed. Challenges in measuring sound transmissions and reproducibility of results in low frequency ranges are discussed. Well-defined measurement protocols and refined computer simulation methods are required. The serviceability design criteria for modern lightweight timber applications in Australia need to be re-evaluated in the area of impact generated sound. Developing computer tools to predict airborne and impact sound transmission in lightweight timber buildings is quite challenging as several components such as timber members and complex connections with varying stiffnesses are non-homogeneous by nature. Further, there is a lack of experimentally validated and computationally efficient tools to predict the sound transmission in timber buildings. Computer prediction tools need to be developed with a focus on mid-frequency transmission over flanks and low-frequency transmission of timber and prefabricated buildings.
The present article gathers examples of modular dwelling concepts, where Cross Laminated Timber (CLT) and other timber-based products are the primary elected material, and makes comparisons between the ‘prefabrication construction process and marketing strategies’ for modular dwellings with the ‘automotive industry’. The article is divided in three parts. First section of the article provides an analysis of the environmental impacts of transportation and building sector, then identifies reaction trends between electric vehicles and prefab modular homes. The second section deals with work flow, emphasizing the prefabrication process of house modules, the constraints given by transportation and storage, and arguing for the personalization of a mass production product demonstrated through six case studies. The third section debates possible marketing strategies, evoking business models based on collectible concepts, cataloging, mass customisation principles and image/brand for tourist/urbanistic developments.
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