This Interim Report of the research project "Improved prediction of seismic resistance of Part 9 Houses" under the CMHC External Research Program presents a detailed literature review of research relevant to lateral resistance of conventional wood-frame construction and an assessment of three mechanics-based methods for calculating lateral capacity.
The relative performance of the three mechanics-based methods is ascertained by comparing the test data of lateral capacities of partially restrained wall specimens having window openings with the predicted results from the calculation methods. Method 1 by Ni and Karacabeyli (2000, 2002) is the simplest to use and gave the most conservative results; Method 2 by Källsner et al., (2001, 2002) is less conservative but more complicated, and Method 3 by Källsner and Gurhammar (2005, 2006) gives non-conservative results.
In the next phase of the project, these mechanics-based methods will be further calibrated against pertinent shake table results from the recent UBC "Earthquake 99" project and from the Forintek – Tongji University tests of conventional wood-frame construction. They will then be employed in the determination of the seismic response of houses as prescribed by the seismic part of the Engineering Guide for Wood Frame Construction published by the Canadian Wood Council.
Support industry to expand its markets for wood and wood products by providing designers and specifiers with design provisions and practical design solutions for wood-based lateral load resisting systems in engineered wood construction. This four-year project will address two main issues:
Develop and compile the fundamental information needed to establish a Lateral Load Resisting Systems Design Section in CSA O86, which will be consistent with the 2005 edition of the National Building Code of Canada (NBCC 2005).
Develop and compile the information needed to link the new Lateral Load Resisting Systems Design Section in CSA O86 with the Fastenings Section in terms of connection behaviour required to satisfy the specified system response to lateral loading.
This project aims to capitalize on seismic and wind performance of wood frame construction under extreme wind and earthquake loads and make incremental improvements in wind and seismic design procedures. This year seismic work focused on laboratory testing to evaluate the corner wall and upper storeys on the lateral load capacities of braced walls, and the development of a mechanics-based model to accurately predict the lateral load capacities of braced walls with openings. Wind research work focused on the test house in Fredericton, NB and related activities on modelling.
Earthquakes - Effect on building construction
Building construction - Design
Wood - Construction Materials - Environmental Aspects
Wood design standards in Canada and the United States provide design values for floor and roof diaphragms with sheathing thickness ranging from 9.5 mm (3/8 in) up to 18.5 mm (3/4 in), that are supported by joists spaced less than 610 mm (24 in) on centre. This range of sheathing thicknesses is adequate for housing and small buildings, but for large non-residential structures, diaphragms with thicker sheathing and wider joist spacing may be more appropriate.
This paper includes the findings of a study aimed at providing research information suitable for implementing design values for diaphragms with thick sheathing in the North American wood design standards. Results from quasi-static monotonic tests on fifteen full-scale 7.3 m (24 ft) long by 2.4 m (8 ft) wide diaphragms framed with 38x191 mm or 38x235 mm (nominal 2x8 and 2x10, respectively) solid sawn lumber or laminated strand lumber and sheathed with plywood or oriented strand board are discussed.
A numerical model was developed using the finite element method. The basic properties of the sheathing, framing members and nailed connections were implemented in the model to replicate the structural behaviour of the diaphragms with thick panels. The numerical model was successfully validated against the experimental data. The shear resistance values for the diaphragms with thick panels tested in this study were calculated. The model may be used to interpolate between various diaphragm configurations and calculate shear resistance values for other configurations of diaphragms with thick sheathing.
In the long run, it is hoped that the use of thicker sheathing will enable the use of structural systems that are cost effective for wider joist or beam spacing than systems made with dimension lumber and traditional sheathing thickness. The experimental data and the model developed in this project will be used to develop proposals for implementation of wood floor and roof diaphragms with thick panels in the Canadian and United States wood design standards.
Transformative Technologies - Federal Initiative Final Report 2007/08
Vancouver, British Columbia
"Creating value via innovation". That principle is at the core of FPInnovations' value proposition. This report acknowledges that and takes a multi tier approach to better understand the innovation process and it is divided into three levels: manufacturer, R&D, and user. A careful reading of FPInnovations' vision and mission reveals that the consolidation has brought change and challenge, taking the organization beyond research and assuming a protagonist role as an integrator of the innovation efforts carried out by its members, the R&D community and its own staff (Research Program 2008/2009). Accomplishing such demanding goals will demand acquiring and mastering a number of tools, management practices and knowledge base that this report has tried to examine. It also recognizes the role that the external environment plays and therefore it includes sections looking at industry structure considerations, cooperation networks and such. From an internal point of view, the report outlines some guidelines meant to serve as an aide in the operationalization of the mission and vision set for FPInnovations by our board.
The merger and new guidelines have added a new innovation component to the Divisions' successful record of value creation for their members. This new component is a much needed response to the challenging times the industry is going through. FPInnovations recognizes the value proposition of innovation while also acknowledging the merits of best practices for those companies favouring a more traditional approach to doing business.
The objectives of the site visit were to document the damage to wood-frame and other wood buildings from the May 12, 2008 Wenchuan (Sichuan) earthquake and to compare the performance of wood-frame buildings with non-wood buildings of similar size.
Because of the limited number of wood-frame buildings in the affected region, all the available wood construction close to the seismically affected area was investigated as follows:
2 wood-frame houses in Dujiangyan
3 solid timber cabins in Dujiangyan
2 houses of wood-frame construction in Chengdu
6 houses of post-and-beam construction with wood-panel infill in Songpan.
The houses in Chengdu and in Dujiangyan are located, respectively, in low intensity and moderate-to-high intensity regions of shaking during that earthquake. From the inspection of the four houses and other concrete buildings nearby, it can be stated that even under light and moderate-to-high levels of seismic shaking the wood-frame houses examined suffered significantly less damage than nearby reinforced concrete houses of comparable size.
Based on a design-oriented analysis of seismic capacity it is shown that the wood-frame Houses A and B can withstand a pseudo-spectral acceleration of at least 0.89 and 1.01 g, respectively. This is judged to be a conservative estimate since the positive contribution of the exterior stucco and the second interior gypsum wall board (GWB) has not been included in the analysis.
The three timber cabins examined in Dujiangyan also performed very well, showing no signs of seismic-induced distress. The six post-and-beam wood buildings with wood-frame infill in Songpan also showed no signs of seismic damage, although for the latter the intensity of shaking was quite low.
From some examples of damaged concrete buildings, it was observed that numerous infill walls were damaged or had collapsed and thus subjected the inhabitants to mortal danger. Lightweight wood-frame infill walls for concrete frames could provide a safer alternative to the heavy and relatively brittle brick infill walls. Furthermore, the resulting reduction in building weight would further enhance seismic safety of the entire building.
It is recommended that for the Chinese code the GWB contribution be considered for normal seismic loading. However, the GWB should not be included in the design check for rare earthquakes because of the limited ductility of shear walls sheathed with GWB at the high levels of shaking associated with the rare seismic events.
Non-residential building construction in North America is a vast market for wood-based products in structural and non-structural applications. For a variety of reasons, this market is currently dominated by steel, concrete and masonry structures. Promotional efforts by the forest products industry are making positive effects in convincing specifiers to use wood-based systems in some non-residential applications. Platform-frame wood construction is the most common wood-based structural system that is currently dominating the low-rise residential market in North America. With slight modifications, this system is also well suited for use in single-storey box-type non-residential buildings with heights up to 10.7 meters (35 feet). Incremental research contributions are needed if such tall wood-frame walls are to make serious inroads into the non-residential construction market.
This project provides a literature survey on the topic of tall wood-frame walls. It identifies the important issues related to the design and performance of tall walls used in construction of single-storey non-residential box-type buildings. In addition, it gives an overview on the marketing aspects of use of tall walls in non-residential applications, as well as information on the concrete tilt-up, masonry and steel structural systems as main competitors for the market share. The results of this project will be used as a basis for planning of the future research activities in the field of tall wood-frame walls.
In order to maintain the competitive advantage in existing and new markets situated in seismic and high wind zones such as the Pacific Rim and the southeastern U.S., it is proposed to study deflections in walls, floor and roof assemblies. The proposed project will also be very useful in: a) setting deflection criteria as will be demanded by performance-based codes, and b) responding to the inevitable transition to displacement-based seismic design.
This report summarises the findings in a project directed at determining what is known about the fire performance of connections between heavy timber members.
In Canada, where a 45 minute fire-resistance rating is required, the NBCC lists minimum dimensions of solid sawn or glulam columns (loaded in compression), beams (loaded in bending) and trusses (bottom chord loaded in tension) which achieve the rating. Methods for designing connections between solid sawn or glulam members that preserve the 45-minute rating are also provided. Where a one-hour fire resistance rating is required, the NBCC provides equations to calculate the dimensions of glulam columns (loaded in compression) and beams (loaded in bending) which achieve the rating. However, no guidance is given for designing glulam members loaded in tension and no guidance is given on connections between glulam members that preserve the one-hour rating. Furthermore, no guidance is provided for designing solid sawn members (or their connections) when loaded in compression, bending or tension.
In the U.S.A., the minimum cross-sectional dimensions of glulam and solid-sawn timber beams and columns that achieve a 1-hour rating can be calculated from the same simple formulae provided in NBCC. As an alternative, a more advanced mechanics-based method can be used to calculate minimum cross-sectional dimensions of glulam and solid-sawn timber loaded in bending, compression and tension. Where a 1-hour fire-resistance rating is required, connectors and fasteners must be protected from fire exposure by wood, fire-rated gypsum board, or any coating approved for the required fire-resistance time. This approach does not account for any inherent fire resistance of the connection but rather requires it be protected by wood, fire-rated gypsum board or a coating that can provide the entire 1-hour rating.
In Europe, guidance is provided on how to design wooden structures and their connections to achieve fire resistance ratings up to one hour. Extensive guidance is given for connections consisting of two structural members spliced together with side plates of wood or steel and held together with dowel-type fasteners (nails, bolts, dowels and screws). Unprotected wood-to-wood connections of this sort, designed in compliance with ambient (non-fire) design standards, have an inherent fire resistance rating of at least 15 minutes. The fire-resistance rating can be increased to 30 minutes or even 60 minutes by the application of wood, wood-based or gypsum board panels with thickness calculated using simple formulas. As an alternative, a fire-resistance rating up to 60 minutes can be achieved using connections with internal steel plates.
There is currently no guidance provided to designers in Canada on how to design a connection between heavy timber members that can ensure a 1-hour rating. As this seems inappropriate, it is strongly recommended that Canadian building code committees be approached and requested to adopt either the approach taken in the USA or the one in Europe.