IBS2 – Wood Trusses – Strength, Economy, Versatility
Wood trusses are engineered frames of lumber joined together in triangular shapes by galvanized steel connector plates, referred to commonly as truss plates. Wood trusses are widely used in single- and multi-family residential, institutional, agricultural and commercial construction. Their high strength-to-weight ratios permit long spans, offering greater flexibility in floor plan layouts. They can be designed in almost any shape or size, restricted only by manufacturing capabilities, shipping limitations and handling considerations. Metal plate connected roof trusses were first introduced into the North American market in the 1950’s. Today, the majority of house roofs in Canada and the United States are framed with wood trusses and increasingly, wood floor trusses are being used in residential and commercial applications. Wood truss use is not limited to North America. They are gaining acceptance around the world and are widely used in Europe and Japan.
The Historical Development of the Building Size Limits in the National Building Code of Canada
The use of wood is limited in larger and taller buildings by the National Building Code of Canada (NBCC) based on concern of increased fire risk. The current requirements were developed long ago, under much different conditions than today. Since then the industry’s knowledge of fire science has evolved considerably, fire service equipment and capabilities have improved, detection and suppression systems have advanced, construction materials and techniques have changed significantly, and public awareness and education regarding fire safety has increased. Having an understanding of the knowledge, capability, materials and methods used to develop the height and area limits and the risks they were intended to mitigate, sets the basis for re-examination of those limits in a current context. This can be achieved through a historical examination of the development of the limits and their bearing on the use of combustible construction in buildings.
Ontario Mid-Rise Reference Guide
On September 23, 2014, after many years of research, development, stakeholder feedback and discussion, the Ontario Ministry of Municipal Affairs and Housing announced amendments to the 2012 Ontario Building Code (OBC) that permit 5- and 6-storey combustible construction for Group C and D occupancies. e amendments to the OBC increase opportunities for designers and builders to create versatile and affordable new buildings. The changes recognize the advancements in wood products and systems as well as in fire detection, suppression, and containment systems. Densification is mandated in almost all municipal growth plans in the province. Mixed-use mid-rise buildings are seen as an important solution that will help create higher density and attract businesses and families to urban centres. Previous code restrictions on combustible construction made non-combustible solutions the only option for mid-rise development and many potential developments were stalled because they were deemed cost-prohibitive. Developers now have a new, cost effective option to provide mid-rise solutions. Decisions about how and where we build our communities have significant impacts on the natural environment and on human health. Wood is a natural, sustainable material and the processing of raw material into building materials has a lower environmental impact when compared to other major building components. e use of sustainable materials and components reduces the negative impact our buildings have on the environment and assists in mitigating climate change. The amendments to the OBC have created exciting new opportunities but there are also new design and construction challenges to consider. Ontario Wood WORKS! developed this guide to explain the new provisions in the OBC and to discuss the opportunities as well as the challenges.
Design Example of Wood Diaphragm on Reinforced CMU Shearwalls
This document is design example of Wood Diaphragm on Reinforced CMU Shearwalls. It uses a school gymnasium located in Surrey, British Columbia as the example. The plan dimensions are 20m x 30m, with a total building height of 7m. The walls are 190 mm reinforced CMU, and the roof diaphragm consists of plywood sheathing and SPF framing members. The roof plan is shown in Figure 1. The site is Seismic Class ‘C’. Wind, snow and seismic data specific to the project location are taken from the latest version of the National Building Code (2010). Roof dead load is assumed to be 0.9 kPa and the wall weight is 2.89 kPa. The weight of non-structural items including mechanical equipment has not been included in this example for simplicity.
Design Example of Wood Diaphragm Using Envelope Method
This document is a design example of Wood Diaphragm Using Envelope Method. it uses a typical one-storey commercial building located in Vancouver, BC as the example. The plan dimensions are 30.5 m x 12.2 m (100’ x 40’), with a building height of 5 m. The walls are woodbased shearwalls, with a wood diaphragm roof and a steel moment frame at the storefront. The roof plan is shown in Figure 1. The site is Seismic Class ‘C’. Wind, snow and seismic figures specific to the project location are taken from the current version of the British Columbia Building Code (2012). Roof dead load is assumed to be 1.0 kPa and the wall weight is 0.5 kPa. The weight of nonstructural items including mechanical equipment and the storefront façade has not been included in this example for simplicity.
Diaphragm Flexibility
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
A Mechanics-Based Approach for Determining Deflections of Stacked Multi-Storey Wood-Based Shearwalls
The 2009 edition of CSA Standard O86, Engineering Design in Wood (CSA 2009), provides an equation for determining the deflection of shear walls. It is important to note that this equation only works for a single-storey shear wall with load applied at the top of the wall. While the equation captures the shear and flexural deformations of the shear wall, it does not account for moment at the top of the wall and the cumulative effect due to rotation at the bottom of the wall, which would be expected in a multi-storey structure. In this fact sheet, a mechanics-based method for calculating deflection of a multi-storey wood-based shear wall is presented.
Design of Stacked Multi-Storey Wood Shearwalls Using A Mechanics Based Approach
This document is a Design example of Stacked Multi-Storey Wood Shearwalls Using A Mechanics Based Approach. It shows a floor plan and elevation along with the preliminary shear wall locations for a six=storey wood-frame building. It is assumed some preliminary calculations have been provided to determine the approximate length of wall required to resist the lateral seismic loads.
Linear Dynamic Analysis for Wood Based Shear Walls and Podium Structures
With the height limit for combustible construction limited to four stories under the National Building Code of Canada, it was uncommon for designers to perform detailed analysis to determine the stiffness of shear walls, distribution of forces, deflections, and inter-storey drifts. It was only in rare situations where one may have opted to check building deflections. With the recent change in allowable building heights for combustible buildings from four to six storeys under an amendment to the 2006 BC Building Code, it has become even more important that designers consider more sophisticated methods for the analysis and design of wood-based shear walls. As height limits increase, engineers should also be more concerned with the assumptions made in determining the relative stiffness of walls, distribution of forces, deflections, and inter-storey drifts to ensure that a building is properly detailed to meet the minimum Code objectives. Although the use of LDA has not been common practice, the more rigorous analysis, as demonstrated in the APEGBC bulletin on 5- and 6-storey wood-frame residential building projects (APEGBC 2011), could be considered the next step which allows one to perform an LDA. This fact sheet provides a method to assist designers who may want to consider an LDA for analyzing wood-frame structures. It is important to note that while LDA may provide useful information as well as streamline the design of wood-frame structures, it most often will not be necessary. However, designers may consider using LDA for the following reasons: Consider the effect of higher mode participation on force distributions and deflections. Better determine building deflections and floor drifts. Allow for three-dimensional modelling. Reduce the minimum Code torsional effect required under the equivalent static design. Better consider the effect of podium structures (vertical changes in RdRo). Compare the stiffness of various shear wall systems where mixed systems are used.
Administration and Training Facility (Alberta Boilers Safety Association)
The new ABSA facility is located in Edmonton’s Research Park (Figure 1), joining 35 other technology companies and agencies. To accommodate staff and increased visitor traffic, the new ABSA facility has 51 parking spaces on the site and another 49 in the parkade below the building. Completed in May 2006, the ABSA facility utilizes glulam beams and columns to achieve the Building Committee’s design objectives for aesthetics, lighting, energy and environment.
Algonquin College Perth Campus
Algonquin College is a major provider of post-secondary education in Eastern Ontario, with campuses in Ottawa, Perth and Pembroke. The Perth Campus is located in the Town of Perth, approximately 65 km west of Ottawa. In keeping with Perth’s historic involvement with the Rideau Canal World Heritage Site, the Perth Campus’ area of excellence is heritage preservation training, which draws students from the local community and from around the world. In 2009, planning began for a new building capable of accommodating more students. During construction of the new building, comprised of the Academic Hall and the Construction Wing (Figure 1), classes continued in an old building that was subsequently demolished. A new outdoor construction pad is located over the footprint of the old building. The new building was ready for classes in September 2011, one year after the start of construction. The town of Perth has a rich history, reflected in the nineteenth-century mills and factory buildings along the Tay River, Victorian storefronts and grand, century-old, timber-frame buildings. The Algonquin College Perth Campus building sought to blend with this fabric through the use of traditional forms, locally sourced materials, and woodframe construction.
B.C. Schools (Crawford Bay Elementary-Secondary & Richmond Christian)
Crawford Bay is a small and remote community on the east shore of Kootenay Lake in the southern interior of British Columbia. A community of about 500 people, it is one of several such communities collectively known as the East Shore communities. Historically, the area has relied heavily on logging for employment but, since the 1960s at least, has also been home to grassroots environmentalists and, more recently, to highly educated exurbanites who form part of a ‘back to the land’ movement. There is also a strong artisan community with a broad range of skills in carving, weaving, ironwork and other arts. The village of Crawford Bay has been home to a one-room school house since 1946, and the need to replace this aging facility provided the impetus for this project. A feasibility study quickly determined that rehabilitation and expansion of the existing building was not cost effective, nor could the existing site readily accommodate a new structure and the required ancillary facilities such as playing fields and parking lots. Accordingly, a new site was selected and design of the new school commenced in 2004.
