The objective of the project is to develop/improve practical, reliable and internationally recognized methods for assessing/pre-screening the long-term structural performance of engineered wood products used in residential and non-residential applications.
The main sources of lateral loads on buildings are either strong winds or earthquakes. These lateral forces are resisted by the buildings’ Lateral Load Resisting Systems (LLRSs). Adequate design of these systems is of paramount importance for the structural behaviour in general. Basic procedures for design of buildings subjected to lateral loads are provided in national and international model building codes. Additional lateral load design provisions can be found in national and international material design standards. The seismic and wind design provisions for engineered wood structures in Canada need to be enhanced to be compatible with those available for other materials such as steel and concrete. Such design provisions are of vital importance for ensuring a competitive position of timber structures relative to reinforced concrete and steel structures.
In this project a new design Section on Lateral Load Resisting Systems was drafted and prepared for future implementation in CSA O86, the Canadian Standard for Engineering Design in Wood. The new Section was prepared based on gathering existing research information on the behaviour of various structural systems used in engineered wood construction around the world as well as developing in-house research information by conducting experimental tests and analytical studies on structural systems subjected to lateral loads. This section for the first time tried to link the system behaviour to that of the connections in the system. Although the developed Section could not have been implemented in CSA O86 in its entirety during the latest code cycle that ended in 2008, the information it contains will form the foundation for future development of technical polls for implementation in the upcoming editions of CSA O86.
Some parts of the developed Section were implemented in the 2009 edition of CSA O86 as five separate technical polls. The most important technical poll was the one on Special Seismic Design Considerations for Shearwalls and Diaphragms. This technical poll for the first time in North America includes partial capacity design procedures for wood buildings, and represents a significant step forward towards implementing full capacity-based seismic design procedures for wood structures. Implementation of these design procedures also eliminated most of the confusion and hurdles related to the design of wood-based diaphragms according to 2005 National Building Code of Canada. In other polls, the limit for use of unblocked shearwalls in CSA O86 was raised to 4.8 m, and based on the test results conducted during the project, the NLGA SPS3 fingerjoined studs were allowed to be used as substitutes for regular dimension lumber studs in shearwall applications in engineered buildings in Canada.
With the US being the largest export market for the Canadian forest products industry, participation at code development committees in the field of structural and wood engineering in the US is of paramount importance. As a result of extensive activities during this project, for the first time one of the AF&PA Special Design Provisions for Wind and Seismic includes design values for unblocked shearwalls that were implemented based on FPInnovations’ research results. In addition, the project leader was involved in various aspects related to the NEESWood project in the US, in part of which a full scale six-storey wood-frame building will be tested at the E-Defense shake table in Miki, Japan in July 2009. Apart from being built from lumber and glued-laminated timber provided from Canada, the building will also feature the innovative Midply wood wall system that was also invented in Canada. The tests are expected to provide further technical evidence for increasing the height limits for platform frame construction in North America.
The goals of the project are to expand the use of wood and wood products in structural applications by enhancing seismic and wind design provisions for engineered wood-based structural systems. The project will develop new research information, as well as compile the existing research information necessary for development of new Lateral Load Design Provisions for engineered wood-based structural systems in the Canadian Standard for Engineering Design in Wood (CSA O86). When the appropriate code committees and industry associations implement these design provisions into the next edition of CSA O86, they will provide designers and specifiers more structural options for wood-based lateral load resisting systems, similar to those offered in other material codes.
In this research program, studies were carried out to assess the wind and seismic requirements for conventional wood-frame construction. This report contains information on seismic research. Information on wind research is provided in a separate report entitled ‘Wind and Seismic Design Provisions for Small Wood Buildings - Part B: Wind’.
For the seismic research, it consists of four main study areas: shake table tests on small houses, targeted braced wall tests, evaluation of code bracing requirements for conventional wood-frame buildings, and recommendations for improvement.
Results of shake table tests of two two-storey full-size wood frame buildings, funded under the Canada Wood/FII China Codes and Standards project, have been used to study the performance of small wood buildings with different braced wall lengths. The results showed that the two-story building specimen could withstand successive application of three different seismic ground motions in the order of 0.55 g Peak Ground Acceleration (PGA). Test results are in general agreement with the results observed in actual earthquakes in California, New Zealand and Japan, that wood-frame buildings without major structural deficiencies withstood seismic shaking in the order of 0.5 to 0.6 g PGA without collapse (Rainer & Karacabeyli, 2000).
A series of supplementary full-size braced walls were tested to quantify the effect of floor / upper wall and corner wall on the lateral load capacities of braced walls. Test results showed that floor or / and upper wall could greatly increase the lateral load capacities of braced walls. For a 1.22 m braced wall with continuous top plate extended over braced wall panels, test results indicated that the lateral load capacity of the wall was approximately 50% of that of the walls that are fully restrained. Braced walls with 1.22 m corner walls had similar performance as walls that are fully restrained. The results indicate that the mechanics-based method implemented in CSA O86-1 is very conservative for determining the lateral load capacities of braced walls.
The adequacy of the bracing requirements for conventional wood-frame construction in the 2004 CWC Guide and the proposed Part 9 of 2010 NBCC were assessed. Two buildings, 15 m × 15 m and 4.8 m × 15 m in floor dimension, were studied. The lengths and locations of the braced wall panels in the buildings were chosen to represent as much as possible the most unfavourable case for lateral load resistance. The results showed the imbalance between the required lengths of braced walls in short and long directions of the rectangular building. While the lateral load capacity in the long direction of the building is adequate for the two- and three-storey building and is in fact overly conservative for the one-storey buildings, the lateral load capacity in the short direction of the building is not sufficient to resist the base shear forces. In most of the studied cases, neither the 2004 CWC Guide nor the proposals for the Part 9 of 2010 NBCC meets the seismic requirements of the Part 4 of NBCC 2005 for the high seismic zones.
A new method was proposed to address deficiencies of bracing requirements for conventional wood-frame construction in 2004 CWC Guide and Part 9 of 2010 NBCC proposals. Instead of specifying the minimum length of braced wall panels as a constant percentage of the length of a building parallel to the direction of loading considered, the new method specifies the minimum length of braced wall panels as a function of floor area of the building. Using the new method, it was concluded that the required length of braced wall panels should be a percentage of the building length perpendicular to the direction of loading considered. This will address the imbalance between the required lengths of braced walls in short and long directions of a rectangular building.
With the growing use of wood density as a design property, there is a need for a simple and rapid, but accurate, method of measuring wood density outside of a laboratory environment. In this report, a test apparatus developed at Forintek to accurately measure the relative density of small wood samples is presented. The apparatus was previously developed to measure the relative density of a large number of wood samples from an in-grade lumber testing program. Forintek's test set-up is an adaptation of the ASTM D2395 water immersion method. It consists of a micro-computer software and an electronic balance with a cage for submerging the test specimen. This apparatus may be used with waxed or unwaxed blocks. With this apparatus, test results from unwaxed (Forintek method) specimens may be calibrated to waxed (ASTM water immersion method)specimens provided the specimen size is maintained. In addition to the relative density, the oven-dry moisture content of the test specimen may also be determined using this apparatus. In this report, a comparison of the results from the Forintek method to the ASTM D2395 methods is presented. While not as accurate as the ASTM methods, ease of use, robustness, and level of accuracy make the Forintek method ideal for use in a mill environment, especially for ongoing quality control testing involving a small number of samples.
The bearing strength of Hem-Fir MSR lumber has increased from 11 to 38% over the previous bearing strength values. The upgraded design values will be published in the upcoming supplement to the Canadian Engineered Wood Design code, CSA-O96.1-M94. This code change was assisted in part by data developed in this project on the bearing strength of Hem-Fir. This code change, although it did not affect the bearing strength of visually grade Hem-Fir lumber, is significant to the utilisation of Hem-Fir MSR lumber in the Canadian market. Grades of MSR Hem-Fir lumber 1650f-1.5E or higher now have the same bearing strength values as S-P-F MSR lumber. This simplifies the design code when MSR lumber is specified and allows the full potential of MSR Hem-Fir lumber to be used in engineered wood applications such as trusses. Additional data are being collected on the performance of Hem-Fir lumber under constant loads. This data will create a data base on Hem-Fir lumber similar to that developed for S-P-F and D.Fir-L in 1993-1994.
The complexity of the current timber connection design process is one of the major reasons preventing the wider use of wood products in low-rise non-residential and innovative residential construction. Connections of members in structures, particularly in timber buildings, require the combination of both quantitative and qualitative aspects of design to produce a safe and aesthetically pleasing structure. Knowledge-based expert systems offer designers access to the full range of design methods, allowing the connection design task to be completed with ease and confidence. This study investigates the expert system approach by constructing a framework for such a design aid - a framework that incorporates techniques from artificial intelligence, architecture, and engineering. The design aid has potential for industrial application, and could be developed into an educational tool for timber and wood product design courses at the university level.
In response to a need for technical information to support the design of wood trusses in Canada, the Truss Research Program was established. Forintek's role in the Truss Research Program consisted of two projects: Truss Testing and Analysis, and Strength Variations in Trusses. The first project funded by the wood truss industry, focussed on establishing the structural reliability of residential pitched chord trusses and developing experimental data to verify truss analysis tools used by the truss industry. The second project, funded by the CFS, which is the topic of this report, provided the lumber properties information for the program. The combined loading equipment developed under this project has been used to test 2x4 S-P-F 1650f-1.5E MSR lumber under axial compression and bending loads. This data will now be used to verify a comprehensive stochastic finite element model that is currently under development at the University of British Columbia. A lumber design procedure comprised of a new interaction equation and factors to quantify load configuration effects for truss applications was developed under this project and at U.B.C. The design procedure was accepted in principle by the Technical committee on CSA-O86.