The need to lower the embodied carbon impact of the built environment and sequester carbon over the life of buildings has spurred the growth of mass timber building construction, leading to the introduction of new building types (Types IV-A, B, and C) in the 2021 International Building Code (IBC). The achievement of sustainability goals has been hindered by the perceived first cost assessment of mass timber systems. Optimizing cost is an urgent prerequisite to embodied carbon reduction. Due to a high level of prefabrication and reduction in field labor, the mass timber material volume constitutes a larger portion of total project cost when compared to buildings with traditional materials. In this study, the dollar cost, carbon emitted, and carbon sequestered of mass timber beam–column gravity system solutions with different design configurations was studied. Design parameters studied in this sensitivity analysis included viable building types, column grid dimension, and building height. A scenario study was conducted to estimate the economic viability of tall wood buildings with respect to land costs. It is concluded that, while Type III building designations are the most economical for lower building heights, the newly introduced Type IV subcategories remain competitive for taller structures while providing a potentially significant embodied carbon benefit.
This InfoNote briefly introduces the promising mass timber seismic force resisting systems, and the corresponding analytical and finite element models to support their adoptions in structural design offices.
Mass timber (MT) products, such as Glued Laminated Timber (GLT), Cross Laminated Timber (CLT), Laminated Veneer Lumber (LVL), Nail Laminated Timber (NLT), Dowel Laminated Timber (DLT), Laminated Strand Lumber (LSL), Parallel Strand Lumber (PSL), Mass Plywood Panels (MPP) and others, provide options for developing efficient structural systems to resist gravity and lateral loads. Such systems can be competitive alternatives to their steel and concrete counterparts. This InfoNote briefly introduces the MT Seismic Force Resisting Systems (SFRSs) that will be implemented in the 2020 National Building Code (NBC) of Canada, their height limits, and the main design requirements according to Canadian Standard for Engineering Design in Wood CSA O86-19. Differences among height limits for MT gravity and lateral load resisting systems are also discussed.
Advanced sustainable lateral load resisting systems that combine ductile and recyclable materials offer a viable solution to resist seismic load effects in environmentally responsible ways. This paper presents the seismic response of a post-tensioned timber-steel hybrid braced frame. This hybrid system combines glulam frame with steel braces to improve lateral stiffness while providing self-centreing capability under seismic loads. The proposed system is first presented. A detailed numerical model of the proposed system is then developed with emphasis on the connections and inelastic response of bracing members. Various types of braced frames including diagonal, cross and chevron configurations are numerically examined to assess the viability of the proposed concept and to confirm the efficiency of the system. A summary of initial findings is presented to demonstrate usefulness of the hybrid system. The results demonstrate that the proposed system increases overall lateral stiffness and ductility while still being able to achieve self-centring. Some additional information on connection details are provided for implementation in practical structures. The braced-frame solution is expected to widen options for lateral load resisting systems for mid-to-high-rise buildings.
This study aimed to present a solution in glued laminated timber to replace frame structures built in reinforced concrete and metallic structure, which are common in agricultural buildings in western Paraná such as those destined to laying poultry house building by agricultural cooperatives. Structural behavior of frames build from Araucaria angustifolia glued boards and vegetable oil-based polyurethane adhesive was evaluated. Tests were carried out to characterize wood and adhesive to obtain verification/sizing parameters. Initially, a full-scale structural project was conducted to meet standard laying poultry house specifications. Afterwards, five units of straight three-articulated frames on a 1:2.5 reduced scale were designed, built, and subjected to strength tests until breaking. They were built with a 2-meter free span and a 15° slope, suitable for using metal roof tiles. The average for structure ultimate strength was 4.14 times the design load. Structures had satisfactory mechanical performance and displacements lower than those recommended by NBR 7190 (1997) standard (ABNT). Therefore, building glued frames with Parana pine boards and vegetable oil-based glue is technically feasible.
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.
International Conference on New Advances in Civil Engineering
IOP Conference Series: Materials Science and Engineering
Related to sustainability movement and minimizing the carbon footprint, timber structures are becoming more attractive. Wood, as main structural material, offers many benefits relate mostly to economic and ecological aspects, compared to other materials as steel or concrete. On the other hand, physical characteristics of wood complicate the usage of a timber for high-rise or large-span structures. It brings a new challenge for architects and engineers to deliver feasible solution for usability of timber, despite its features. One of the possible solutions could be implementation of CLT (Cross-Laminate Timber) panels in structural systems developed earlier for buildings made of prefabricated concrete slabs. SOM in cooperation with Oregon State University are currently testing composite slabs made of CLT and thin concrete layer reinforcing the wood and protecting it from fire. Although the system solution looks promising, and could bring the result, slabs limit using of the space in layout. On the other hand, frame structures would be much more efficient. This article comes up with an idea of modular frame structure, which could help to solve the problem. The scheme is based on "gridshell" type systems, where rods form a more efficient shell for dealing with stress forces.
Initially, timber was considered only as an easily accessible and processable material in nature; however, its excellent properties have since become better understood. During the discovery of new building materials and thanks to new technological development processes, industrial processing technologies and gradually drastically decreasing forest areas, wood has become an increasingly neglected material. Load-bearing structures are made mostly of reinforced concrete or steel elements. However, ecological changes, the obvious problems associated with environmental pollution and climate change, are drawing increasing attention to the importance of environmental awareness. These factors are attracting increased attention to wood as a building material. The increased demand for timber as a building material offers the possibility of improving its mechanical and physical properties, and so new wood-based composite materials or new joints of timber structures are being developed to ensure a better load capacity and stiffness of the structure. Therefore, this article deals with the improvement of the frame connection of the timber frame column and a diaphragm beam using mechanical fasteners. In common practice, bolts or a combination of bolts and pins are used for this type of connection. The subject of the research and its motivation was to replace these commonly used fasteners with more modern ones to shorten and simplify the assembly time and to improve the load capacity and rigidity of this type of frame connection.
With the increased number of multi-storey buildings in seismic areas, research efforts have been focused on developing earthquake resilient systems, such as low-damage techniques based on the combination of post-tensioning and dissipating devices. This paper describes the experimental study performed on a 3-storey post-tensioned timber framed (Pres-Lam) building equipped with energy dissipating systems. The testing project consisted of three phases adopting different configurations of the experimental model: (1) post-tensioning to beam-column joints only, (2) post-tensioning and dissipative rocking mechanisms and (3) post-tensioning and dissipative braces. The main objective of this paper is to experimentally investigate on the seismic response of a large-scale specimen with dissipative braces located in high seismic area, considering construction details similar to those adopted in practical applications. During the experimental campaign, the test frame was subjected to more than one hundred ground motions considering a set of seven spectra-compatible earthquakes at increasing intensity levels. The dissipating bracing system with external replaceable hysteretic dampers improves the seismic resilience of multi-storey Pres-Lam buildings, showing inter-storey drift comparable to those with rocking walls, with full recentring capability and without structural damages or post-tensioning losses through seismic tests.
Since 2010, the construction of post-tensioned wooden buildings (Pres-Lam) has been growing rapidly worldwide. Pres-Lam technology combines unbonded post-tensioning tendons and supplemental damping devices to provide moment capacity to beam–column, wall–foundation, or column–foundation connections. In low seismic areas, designers may choose not to provide additional damping, relying only on the post-tensioning contribution. However, post-tensioning decreases over time due to creep phenomena arising in compressed timber members. As a consequence, there is a reduction of the clamping forces between the elements. This reduction affects the seismic response of Pres-Lam buildings in the case of low- and high-intensity earthquakes. Therefore, understanding and accounting for the post-tensioning losses and their uncertainty are paramount for a robust assessment of the safety of Pres-Lam constructions. So far, however, there have been no comprehensive studies which tackle the overall seismic performance of such systems in the presence of time-varying post-tension losses and the associated uncertainty. This study tackles this research gap by introducing a comprehensive seismic evaluation of Pres-Lam systems based on time-dependent fragility curves. The proposed fragility analysis is specifically designed to account systematically for time-varying post-tension losses and the related uncertainty. The method is applied to two case studies, designed, respectively, with and without supplemental damping devices. In terms of structural performance, results show that the use of additional dissipaters mitigates the effect of post-tensioning loss for earthquakes of high intensity. Conversely, performance under low-intensity earthquakes is strongly dependent on the post-tensioning value, as the reduction of stiffness due to the anticipated rocking motion activation would lead to damage to non-structural elements.