The demolition sector generates a large amount of timber waste that could be directly reused or recycled in other products for structural purposes. Timber should be graded before it is used for structural purposes, and visual strength grading standards designed for new timber do not properly grade recovered timber. Cross Laminated Timber (CLT) is now one of the most common wood products used in construction. CLT would therefore be a good option for recycling timber due to the high quantity of material used in CLT manufacturing. This paper investigates the possibilities of using recovered timber from demolition to manufacture CLT. Twelve CLT panels from recovered and new timber were manufactured and tested. The static modulus of elasticity was found to be the same between recovered and new timber, while the bending strength of CLT from recovered timber was lower than it was for CLT from new timber. Non-destructive testing for the estimation of mechanical properties of boards and CLT panels was successfully developed.
Project contact is Cristiano Loss at the University of British Columbia
This research aims at developing novel multi-material deconstructable hybrid connections for mass timber prefabricated buildings. Connections will be conceived in order to (i) meet multi-objective structural performance, (ii) favour modular construction, (iii) favour quick erection of buildings, (iv) quick disassemble and possible reuse of the timber members, and (v) provide seismic-resistant structural assemblies.
Timber has been used for building construction for centuries, until the industrial revolution, when it was often replaced by steel and concrete or confined to low-rise housings. In the last thirty years however, thanks to the development of mass timber products and new global interest in sustainability, timber has begun to make a resurgence in the building industry. As building codes and public perception continues to change, the demand for taller and higher-performance timber buildings will only grow. Thus, a need exists for new construction technology appropriate for taller mass timber construction, as well as for fabrication and deconstruction practices that respect wood’s inherent sustainable nature. With this in mind, this research program aims to develop a new hybrid shear connection for mass timber buildings that allows for easy construction, deconstruction, and reuse of the structural elements.
This report includes results of Phase 1, which focused on connections consisting of partially threaded 20M and 24M steel rods bonded into pockets formed in CLT and surrounded by thick crowns of high-strength three-component epoxy-based grout. A total of 168 specimens were designed and fabricated, and push-out shear tests carried out with a displacement-controlled monotonic loading protocol. Strength and stiffness values were assessed and effective failure modes in specimens identified. These latter, along with the recorded load-deformation curves, indicate that it is possible to develop mechanics-based design models and design formulas akin to those already used for typical dowel-type fastener timber connections. Additionally, the specimens were easily fabricated in the lab and quickly fastened to the test jig by means of nuts and washers, suggested such connections have a strong potential for prefabrication, disassembly, and reuse.
This paper highlights research results from a joint effort between the Forest Products Laboratory (FPL) in the United States of America (USA) and the University of Coimbra (UC) in Portugal (PT). The main objective is the development of a Timber-Concrete Composite system (TCC) that utilizes precast concrete deck panels that accelerate construction times and can easily be removed to facilitate bridge repair/rehabilitation efforts and reuse options. The research is focused on various critical aspects such as the type of interconnection between the concrete deck and the glued laminated timber beams or the interconnection between the precast concrete deck panels. Several practical requirements were addressed that are important to the bridge industry in Portugal and in the USA, such as: accelerated bridge construction time, cost-competitiveness with existing bridge solutions, and eliminating the need for specialized labour skills.
The study investigates the environmental benefits of reusing Cross Laminated Timber (CLT) panels. The Global Warming Potential (GWP) of a single-stored Coffee shop built in 2016 in Kobe city was calculated, considering different CLT reuse ratios, forest land-use and material substitution possibilities. The results showed that as the rate of reused CLT panel increases the total GWP decreases. Moreover, in all cases, the option with smallest GWP is when the surplus wood is used for carbon storage in the forest, revealing the importance of a growing forest for increasing the environmental benefits of timber utilisation. The results suggest the systematic reuse of CLT panels offers a possibility to increase the carbon stock of Japanese Cedar plantation forests and further mitigate the environmental impact of construction.
Mass timber products such as cross-laminated timber have increased in popularity in the past decades. Their relative novelty, however, means that there is little actual experience of what happens to the products at end of life. Despite promoting the use of natural capital, biotic materials are not often covered in discussions on construction in the circular economy. Equally, it is unclear what model is most appropriate for construction to incorporate circular thinking. Different actions for circularity are reviewed against sustainable construction ambitions, and a simple model with basic circular actions is proposed as a means to review mass timber construction. Suggestions for how to adapt mass timber systems to include circular methods are presented, including design for combined manufacture and assembly and disassembly, the identification of future markets, improving the durability of timber buildings and acknowledging the wider system value of forestry.
The aim of this study is to investigate the economic, environmental and technological challenges, as well as the environmental potential, of prolonging the life cycle of construction materials with focus on structural timber in Finland. To achieve this, a literature review was conducted along with interviews with actors pertinent to timber construction. Moreover, a case study of life cycle environmental impact assessment was conducted to quantify the potential of reusing timber to abate global warming and other environmental burden. The literature review highlighted the possibility of reusing structural timber, but pointed to the need for efficient and standardized assessment criteria. The interviews indicated interest towards the concept of circular economy applied to construction and demolition wood material, although this appears to be driven more by policy and regulation rather than for business reasons. Therefore, a reconfigured conceptual framework to achieve circularity for wood is proposed, where material brokers would be used to connect different actors along the value chain. The paper concludes with a case study showing that reusing structural timber components can result in a significant reduction of the environmental burden.