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.
The Equivalent Viscous Damping (EVD) parameter is used to simplify the dynamic problem, passing from a non-linear solution of the system to a simple linear-elastic one. In the case of Direct Displacement-Based seismic Design (DDBD) methods, the EVD value allows direct design of structures, without an iterative computational process. This paper proposes a rational analytical formula to evaluate the EVD value of timber structures with dowel-type metal fastener connections. The EVD model is developed at the ultimate limit state, as a solution of the equilibrium problem related to an inelastic configuration. For a specific joint configuration, the EVD predicted via an analytical model was compared to experimental results. The proposed EVD model was validated using non-linear dynamic analysis on a portal frame, built with dowel-type fasteners arranged in two concentric crowns.
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.
Project contact is Chris Pantelides at the University of Utah
Summary
A mass timber buckling-restrained braced frame is proposed to enhance the seismic resilience of mass timber buildings. Constructed using wood generated from the national forest system, the mass timber buckling-restrained brace will be integrated with a mass timber frame for structural energy dissipation under seismic or wind loads. The team will improve and optimize the design of structural components based on feedback from a real-time health monitoring system. Outcomes include guidelines for a lateral force resisting system of mass timber buildings in high seismic or wind regions.
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.
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.
Building owners often state requirements that new buildings shall have open and flexible architecture in order to allow flexible use and future changes. A way to improve timber buildings in that direction is to increase the stiffness of the connections between horizontal and vertical members of the structural systems. This paper presents some numerical and analytical considerations with respect to the stiffness requirements for moment resisting timber connections. It also presents experimental tests and results for a moment resisting connection with inclined threaded rods installed in predrilled holes.
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.
The construction of mid- and high-rise wooden buildings has attracted more attention in the last decade, particularly due to the utilization of engineered materials and related construction methods. The wood industry offers a wide range of engineered wood products, such as glue-laminated timber (GLT), cross-laminated timber (CLT) or timber concrete composites (TCC), which have improved mechanical qualities and the freedom to select shapes and sizes. As a consequence, attention has shifted to solve structural design issues to meet specific building requirements, such as their seismic, fire and serviceability performance. The objective of this work is to explore some of the technologies currently available for wooden mid-rise buildings using a 5-storeys case study building under gravity and earthquake loads. An innovative construction method, obtained by combining TCC floors, CLT shear-walls and GLT columns to ensure a fast erection on site is presented and the building response analyzed by means of static and dynamic seismic analyses. Specifically, the gravity load resisting system was designed to meet ultimate and serviceability limit state requirements according to Eurocode. Different seismic bracing technologies are compared: CLT cores (i) and hybridized cores with (ii) post-tensioned tendons and (iii) steel link-beams.
The unbonded post-tensioned rocking and dissipative technology was first developed as the main outcome of the PRESSS (PREcast Seismic Structural Systems) Program in US. After the first developments and significant refinement, the technology was extended to steel and, more recently, timber structures. The timber version, referred to as Pres-Lam (Prestressed laminated) system can be either implemented for timber walls (single or coupled) or frames or combination of the above, with unbonded post-tensioning and supplemental dissipation devices.
In unbonded post-tensioned dissipative wall systems a combination of re-centering capacity and energy dissipation leads to a “controlled rocking” mechanism which develops a gap opening at the wall base. This generates an uplift displacement which is transferred to the floor diaphragm. This vertical displacement incompatibility can represent a potential issue if the connection detailing between floor and lateral resisting system is not designed properly. The same issue can be mitigated by adopting an alternative configuration of the rocking/dissipative wall system, based on the use of a column-wall-column post-tensioned connection. This concept, originally proposed for precast concrete walls and referred to as PreWEC (Prestressed Wall with End Column), has been extended and adapted to posttensioned timber structures and validated through experimental testing.
The paper presents the design, detailing and experimental testing of a two-thirds scale wall specimen of this alternative configuration. Different wall configurations are considered in terms of post-tensioning initial force as well as dissipation devices layout. The experimental results confirm the excellent seismic performance of the system with the possibility to adopt multiple alternative configurations.
