FPInnovations carried out a survey with consultants and researchers on the use of analytical models and software packages related to the analysis and design of mass timber buildings. The responses confirmed that a lack of suitable models and related information for material properties of timber connections, in particular under combination of various types of loads and fire, was creating an impediment to the design and construction of this type of buildings. Furthermore, there is currently a lack of computer models for use in performance-based design for wood buildings, in particular, seismic and fire performance-based design.
In this study, a sophisticated constitutive model for wood-based composite material under stress and temperature was developed. This constitutive model was programmed into a user-subroutine and can be added to most general-purpose finite element software. The developed model was used to model the structural performance of a laminated veneer lumber (LVL) beam and a glulam bolted connection under force and/or fire. Compared with the test results, it shows that the developed model was capable of simulating the mechanical behaviour of LVL beam and glulam connection under load and/or fire with fairly good correlation.
With this model, it will allow structural designers to obtain the load-displacement curve of timber connections under force, fire or combination of the two. With this, key design parameters such as capacity, stiffness, displacement and ductility, which are required for seismic or fire design, can be obtained.
It is recommended that further verification and calibration of the model be conducted on various types of wood products, such as CLT, glulam, SCL and NLT, and fasteners, e.g. screw and rivet. Moreover, a database of the thermal and structural properties of the wood members and fasteners that are commonly used in timber constructions need to be developed to support and facilitate the application of the model.
Through the coordinated initiatives of industry and the Provincial and Federal governments, Canada has made significant progress in the acceptance of Canadian wood products and wood-frame construction in the codes and standards of China, Taiwan and South Korea. Technical input to support favourable revisions to the codes and standards in these countries has been spearheaded by Forintek staff, with support from representatives from various national organizations in Canada and the US. In this process, Forintek also has established a network of experts in these countries, which Canada can use in addressing potential future technical barriers.
The effort has resulted in changes to the Chinese quality inspection code (GB 50206) and the timber design code (GB 50005). The GB 50206 was released in July 2002. The inclusion of North American wood frame construction and products has helped speed up inspection for wood frame construction in China.
The GB 50005 was released in January 2004. The newly enacted code allows local engineers to design North American platform frame construction and specify North American species groups of structural lumber that are graded to rules that are compatible with those in Canada. Fire protection regulations have also been revised to position wood frame construction on the same playing field as buildings made of concrete and steel: for example, wood frame construction can now be built up to three storeys, and spatial separations can be as close as 4 m.
Progress has also been made in Taiwan. The revised Taiwanese timber design code approved in 2003 contains engineering and pre-engineered designs adopted from North America standards. The submission of technical comparisons of the Canadian and Taiwanese standards to the Taiwanese government will help the Canadian forest industries to obtain Taiwanese regulatory recognition that Canadian wood products in compliance with Canadian standards will meet the pertinent Taiwanese standards. This recognition will give Canadian suppliers a head start in establishing a share of the Taiwanese market.
The effort in 2003-04 builds on the successful working relationship established with the various codes and standards committees in China and Taiwan to assist them in introducing the North American wood frame construction system. Although it is understood that there are still a number of technical and market support items to address, this program ensures that a coherent infrastructure is developed to support the use of Canadian wood products in the Far East markets.
Building construction - Specifications - China
Building construction - Specifications - Taiwan
Building construction - Specifications - South Korea
Structural engineering - Specifications - China
Structural engineering - Specifications - Taiwan
Structural engineering - Specifications - South Korea
Diaphragms are essential to transfer lateral forces in the plane of the diaphragms to supporting shear walls underneath. As the distribution of lateral force to shear walls is dependent on the relative stiffness/flexibility of diaphragm to the shear walls, it is critical to know the stiffness of both diaphragm and shear walls, so that appropriate lateral force applied on shear walls can be assigned.
In design, diaphragms can be treated as flexible, rigid or semi-rigid. For a diaphragm that is designated as flexible, the in-plane forces can be assumed to be distributed to the shear walls according to the tributary areas associated with each shear wall. For a diaphragm that is designated as rigid, the loads are assumed to be distributed according to the relative stiffness of the shear walls, with consideration of additional shear force due to torsion for seismic design. In reality, diaphragm is neither purely flexible nor completely rigid, and is more realistically to be treated as semi-rigid. In this case, computer analysis using either plate or diagonal strut elements can be used and the load-deflection properties of the diaphragm will result in force distribution somewhere between the flexible and rigid models. However, alternatively envelope approach which takes the highest forces from rigid and flexible assumptions can be used as a conservative estimation in lieu of computer analysis.
n collaboration avec l’Université de Victoria, on a mis au point un mur de cisaillement à haute capacité comportant deux rangées de clous au périmètre du revêtement. On a mené un programme d’essais pour évaluer la performance du mur de cisaillement proposé, ce qui comprend la résistance aux charges latérales et aux déplacements, le comportement hystérétique, la rigidité et la ductilité.
This study was designed to evaluate the performance of a new wood-based portal frame system developed originally by APA with the purpose of providing alternative bracing systems to conventional prescribed details of small wood buildings. To achieve this objective, the study was divided into three components:
Study the performance of full-size portal frames with different configurations;
Evaluation of portal frame corners to optimize corner details and finally,
Develop a numerical model for portal frames to evaluate effect of the various parameters on performance and predict portal frame performance. Supplementary connections and material tests were conducted to generate input data for the finite element modelling of the portal frame.
Results from this preliminary test indicate that the lateral load carrying capacity of portal frames is approximately 75% the capacities of identical frames with hold-down. Those assemblies also had greater ultimate displacements than assemblies without hold-downs. Compared to portal frames without metal straps, the lateral load carrying capacity is slightly increased for with metal straps installed over sheathing. Same finding was observed in portal frame corner assembly tests. Full size portal frame and corner assemblies sheathed on one side without hold down had the lowest capacity among all assemblies tested. The addition of OSB sheathing to both sides of the portal frame corner has increased the moment resistance and rotational stiffness of the corner frame assembly.
Key findings from the FE modelling of portal frames with different types and locations of metal straps showed that the tensile strength of metal straps has the highest impact on the lateral load capacities and stiffness of portal frames assemblies. Portal frames assemblies with sheathings attached on both sides of the framing have approximately 30% higher lateral load capacities and stiffness than the walls with sheathings attached on one side of the framing. Moreover, it was found that it is more efficient to place metal straps directly on framing members. The efficiency is reduced if the metal straps are placed over the sheathing. The contribution of double bottom plates is insignificant. For portal frame assemblies with double bottom plates and two rows of nails fastened to the bottom plate, the stiffness and lateral load capacities are slightly increased compared to the walls with single bottom plate.
Originally developed in Europe, self-tapping screws (STS) have become the proprietary fastener of choice in recently built mass timber buildings in North America. STS offers some advantages over other types of fasteners, such as (a) installation of STS inside wood members is easier as it does not require pre-drilling of holes inside members, (b) the yield moment, torsional strength and tensile strength of STS is comparatively high as the material forming the screw is usually hardened after rolling the thread, (c) the stiffness of the resulting connection is higher and the chances of slipping are less (Frese and Blass, 2009), and (d) STS with long threaded lengths makes it feasible for use in large structural members, e.g., mass timber products.
Recently, issues have been raised on failures of STS due to shrinkage and swelling of wood products resulting from moisture content changes, particularly during construction in the coastal climates. Failures of STS have been reported by structural engineers and contractors of several mass timber projects in NA. This has greatly increased the liability of practitioners involved in mass timber construction.
This project will investigate the material properties of several types of mass timber products and self-tapping screws. These material properties will be used in an analytical and numerical prediction model to describe the behaviour of self-tapping screws in mass timber products under moisture content variation.
