This paper presents the results of long-term experiments performed on three timber-concrete composite (TCC) beams. An innovative fabricated steel plate connection system, which consists of screws and steel plates embedded in concrete slabs, was adopted in the TCC beam specimens. The adopted shear connection can provide dry-type connection for TCC beams. Steel plates were embedded in concrete slabs while the concrete slab was constructed in factories. The timber beam and concrete slab can be assembled together using screws at the construction site. In this experimental programme, the beam specimens were subjected to constant loading for 613 days in indoor uncontrolled environments. The influence of long-term loading levels and the number of shear connections on the long-term performance of TCC beams was investigated and discussed. The mid-span deflection, timber strain, and interface relative slip at the positions of both connections and beam-ends were recorded throughout the long-term tests. It was found the long-term deflection of the TCC beam increased by approximately 60% while the long-term loads were doubled. Under the influence of the variable temperature and humidity, the TCC specimens with 8 shear connections showed slighter fluctuations compared with the TCC beam with 6 shear connections. In the 613-day observation period, the maximum deflection increment recorded was 6.56 mm for the specimen with eight shear connections and 20% loading level. A rheological model consisting of two Kelvin bodies was employed to fit the curves of creep coefficients. The final deflections predicted of all specimens at the end of 50-year service life were 2.1~2.7 times the initial deflections caused by the applied loads. All beam specimens showed relative small increments in mid-span deflection, strain and relative slip over time without any degradations, demonstrating the excellent long-term performance of TCC beams using the innovative steel plate connection system, which is also easily fabricated.
A balanced combination of heat flows creates suitable conditions for thermal comfort—a factor contributing to the quality of the internal environment of buildings. The presented analysis of selected thermal-technical parameters is up-to-date and suitable for verifying the parameters of building constructions. The research also applied a methodology for examining the acoustic parameters of structural parts of buildings in laboratory conditions. In this research, selected variant solutions of perimeter walls based on prefab cross laminated timber were investigated in terms of acoustic and thermal-technical properties. The variants structures were investigated in laboratory but also in model conditions. The results of the analyses show significant differences between the theoretical or declared parameters and the values measured in laboratory conditions. The deviations of experimental measurements from the calculated or declared parameters were not as significant for variant B as they were for variant A. These findings show that for these analyzed sandwich structures based on wood, it is not always possible to reliably declare calculated values of thermal-technical and acoustic parameters. It is necessary to thoroughly examine such design variants, which would contribute to the knowledge in this field of research of construction systems based on wood.
Properly designed wooden truss bridges are environmentally compatible construction systems. The sharp decline in the erection of such structures in the past decades can be led back to the great effort needed for design and production. Digital parametric design and automated prefabrication approaches allow for a substantial improvement of the efficiency of design and manufacturing processes. Thus, if combined with a constructive wood protection following traditional building techniques, highly efficient sustainable structures are the result. The present paper describes the conceptual design for a wooden truss bridge drawn up for the overpass of a two-lane street crossing the university campus of one of Vienna’s main universities. The concept includes the greening of the structure as a shading design element. After an introduction, two Austrian traditional wooden bridges representing a good and a bad example for constructive wood protection are presented, and a state of the art of the production of timber trusses and greening building structures is given as well. The third part consists of the explanation of the boundary conditions for the project. Subsequently, in the fourth part, the conceptual design, including the design concept, the digital parametric design, the optimization, and the automated prefabrication concept, as well as the potential greening concept are discussed, followed by a summary and outlook on future research.
Tall wood buildings have been at the foreground of innovative building practice in urban contexts for a number of years. From London to Stockholm, from Vancouver to Melbourne timber buildings of up to 20 storeys have been built, are under construction or being considered. This dynamic trend was enabled by developments in the material itself, prefabrication and more flexibility in fire regulations. The low CO2 footprint of wood - often regionally sourced - is another strong argument in its favour. This publication explains the typical construction types such as panel systems, frame and hybrid systems. An international selection of 13 case studies is documented in detail with many specially prepared construction drawings, demonstrating the range of the technology.
Society of Wood Science and Technology International Convention
The application of deconstructable connectors in timber-concrete composite (TCC) floors enables the possibility of disassembly and reuse of timber materials at the end of building’s life. This paper introduces the initial concept of a deconstructable TCC connector comprised of a self-tapping screw embedded in a plug made of rigid polyvinyl chloride and a level adjuster made of silicone rubber. This connection system is versatile and can be applied for prefabrication and in-situ concrete casting of TCC floors in both wet-dry and dry-dry systems. The paper presents the results of preliminary tests on the shear performance of four different configurations of the connector system in T-section glulam-concrete composites. The shear performance is compared to that of a permanent connector made with the same type of self-tapping screw. The failure modes observed are also analyzed to provide technical information for further optimization of the connector in the future.
Recent interests in adopting sustainable materials and developments in construction technology have created a trend of aiming for greater heights with timber buildings. With the increased height these buildings are subjected to higher level of lateral load demand. A common and efficient way to increase capacity is to use shearwalls, which can resist significant part of the load on the structures. Prefabricated mass timber panels such as those made of Cross-Laminated Timber (CLT) can be used to form the shearwalls. But due to relatively low stiffness value of timber it is often difficult to keep the maximum drifts within acceptable limit prescribed by building codes. It becomes necessary to either increase wall sizes to beyond available panel dimensions or use multiple or groups of walls spread over different locations over the floor plan. Both of the options are problematic from the economic and functional point of view. One possible alternative is to adopt a Hybrid system, using Steel Plate Shear Walls (SPSW) with timber moment frames. The SPSW has much higher stiffness and combined with timber frames it can reduce overall building drifts significantly. Frames with prefabricated timber members have considerable lateral load capacity. For structures located in seismic regions the system possesses excellent energy dissipation ability with combination of ductile SPSW and yielding elements within the frames. This paper investigates combination of SPSW with timber frames for seismic applications. Numerical model of the system has been developed to examine the interaction between the frames and shear walls under extreme lateral load conditions. Arrangements of different geometries of frames and shear walls are evaluated to determine their compatibility and efficiency in sharing lateral loads. Recommendations are presented for optimum solutions as well as practical limits of applications.
The Tallwood House project was intended to advance the design and
manufacture of mass timber products in Canada and demonstrate
that mass timber is a viable structural option for mid-rise and
high-rise buildings. The use of mass timber and engineered wood
products in high-rise construction is becoming more common
around the world leading to a growing interest in the performance of
mass timber over time.
This report describes the performance of the mass timber structure
in Tallwood House, between September 2017 and August 2019,
based on measurements of the moisture content in the prefabricated
CLT floor panels and the displacement of the vertical structural
system. It is intended to initiate discussions on the performance of
mass timber structure elements during building occupancy and lead
to further research that can explore the influential factors.
Cross-laminated timber (CLT) is revolutionizing the use of wood in the construction sector of North America as a solution for walls and diaphragms in mid-rise or even high-rise timber structures on account of its environmental advantages, high strength-to- weight ratio, fire-safety performance, and propensity for prefabrication. However, considering the hygroscopic nature of wood, moisture intrusion can affect material properties and, moreover, moisture increases the possibility of biological degradation, which can directly affect the durability of CLT structural members and their connections. The favorable seismic performance of connections in the CLT structural systems has been well researched in numerous studies. In addition, even though several research efforts have been conducted to understand the hygrothermal performance of CLT panels, knowledge of the CLT connections when subjected to moisture cycling is minimal. In this study, a CLT shear wall-to-diaphragm L-bracket connection is exposed to two high moisture exposure conditions - flood and simulated rain with increased humidity as well as different exposure durations to investigate the connection performance under the effects of moisture intrusion. Currently, there are four major species that are used for CLT, namely, Douglas-fir, Southern yellow pine, Norway spruce, and Spruce Pine Fir. All four species were incorporated into the study. A total of 264 cyclic tests were performed on wall-to-diaphragm L-bracket connection specimens to evaluate the connection performance in terms of strength, stiffness, and energy dissipation along with the development of two force-displacement engineering models. Results from both exposure studies suggest no significant degradation in connection performance after a moisture cycle of wetting and drying apart from a significant decrease in energy dissipation in flood exposure. However, the effects of multiple moisture cycling merit further study.
The two primary considerations for construction project management are budget and time management. Modular construction has the potential to improve construction productivity by minimizing time and costs while improving safety and quality. Cross-Laminated Timber (CLT) panels are beneficial for modular construction due to the high level of prefabrication, adequate dimensional stability, and good mechanical performance that they provide. Accordingly, CLT modular construction can be a feasible way to speed up the construction and provide affordable housing. However, an in-depth study is needed to streamline the logistics of CLT modular construction supply chain management. CLT modular construction can be performed by two primary means based on type of modules produced: panelized (2D) and volumetric (3D). This research aims to help the Architecture, Engineering, and Construction (AEC) industry by developing a tool to assess the impact of various logistical factors on both panelized and volumetric modular construction productivity. Discrete-Event Simulation (DES) models were developed for panelized and volumetric CLT modular construction based on a hypothetical case study and using data collected from superintendents and project managers. Sensitivity analysis is conducted using the developed models to explore the impact of selected manufacturing and logistical parameters on overall construction efficiency. Comparing volumetric and panelized simulations with the same number of off-site crews revealed that the volumetric model has lower on-site process duration while the off-site process is significantly longer. Accordingly, from manufacturing to the final module assembly, the total time for the volumetric model is longer than panelized model. Moreover, the simulations showed that volumetric modular construction is associated with less personnel cost since the main process is performed off-site, which has lower labor costs and a smaller number of crews required on-site. This framework could be used to identify the optimum construction process for reducing the time and cost of the project and aid in decision-making regarding the scale of modularity to be employed for project.
This project identifies drivers for, and barriers to, the increased use of prefabricated timber building (PTB) systems in Class 2 to 9 commercial buildings, such as apartments, hotels, office buildings and schools.
PTB systems in Australia are in a formative stage and yet to achieve broad acceptance in the marketplace as a conventional method of building.
Opportunities for PTB systems can use timber’s well-established benefits such as high strength-to-weight ratio; design and construction flexibility; general environmental credentials including carbon sequestration; and prefabrication’s suitability for use on brown-field, restricted access and difficult sites and developments. In addition legislative constraints have now been largely removed (e.g. through changes to the 2016 National Construction Code).
An increase in large scale mid-rise prefabricated buildings, and with the increasing nationalisation and internationalisation of the top tier building companies, suggests market acceptance will grow as PTB buildings are seen as ‘normal’.
Many strategies have been investigated seeking for efficiency in construction sector, since it has been pointed out as the largest consumer of raw materials worldwide and responsible of about 1/3 of the global CO2 emissions. While operational carbon has been strongly reduced due to building regulations, embodied carbon is becoming dominating. Resources and processes involved from material extraction to building erection should be carefully optimized aiming to reduce the emissions from the cradle to service. New advancements in timber engineering have shown the capabilities of this renewable and CO2 neutral material in multi-storey buildings. Since their erection is based on prefabrication, an accurate construction management is eased where variations and waste are sensible to be minimized. Through this paper, the factors constraining the use of wood as main material for multi-storey buildings will be explored and the potential benefits of using Lean Construction principles in the timber industry are highlighted aiming to achieve a standardized workflow from design to execution. Hence, a holistic approach towards industrialization is proposed from an integrated BIM model, through an optimized supply chain of off-site production, and to a precise aligned scheduled on-site assembly.