Better, more economical wood I-joists

Better, more economical wood I-joists
Value to Wood funded research to improve the engineering properties and economy of wood Ijoists, an important value-added product. The research investment of $326,000 is expected to
generate production cost savings in the millions of dollars.
Background
Wood I-joists are engineered wood products that have obtained a significant
share of the residential and commercial floor framing market. The wood I-joist
industry in North America produces just over 1 billion linear feet of product per
year - a ten-fold increase compared to 10 years ago. There are six wood I-joist
manufacturers in Canada with an annual production of about 300 million linear
feet. About 60% of the joists manufactured in Canada are sold in the US.
Research
Value to Wood funded three projects aimed at improving the performance and economy of
wood I-joists as follows:
1. Enhancing Shear and Bearing Strength of Wood I-Joists: (UNB 3, $130,000, completed
March 2005): The objectives of this project were to: understand the influence of web-flange
joint profile on bearing strength of I-joist, leading to optimum profile and material
selection; evaluate the influence of web hole shape and size, and component properties on
strengths of I-joist with a web hole; and develop a model for predicting the strength of Ijoist with web holes.
2. Optimized Design of Wood I-Joists: (UNB 61, $136,000, completed
March 2007): The objective of this research was to: Evaluate the
component (flange and web) material specifications currently used and
recommend changes leading to material cost saving without negative
impacts on common design floor spans; develop an optimized flangeweb joint profile less prone to producing manufacturing defects and is
able to maintain bearing strength design capacity; and evaluate the
feasibility of improving I-joist design properties by reinforcing flanges with selected
reinforcement material.
3. Influence of OSB Properties on the Performance of Wood I-Joists (UNB 76, $60,000,
completed March 2007): This project sought to establish a relationship between OSB web
properties and the engineering properties of wood I-joists. A database of properties of web
stock quality panels was established and analysed to identify any possible correlation
among the various material properties, and between the OSB properties and I-joist
structural performance.
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Outcomes
1. Enhancing Shear and Bearing Strength of Wood I-Joists: This project developed an
optimum flange-web joint profile that maximizes the resistance against knife-through
failure. It also developed models to predict the strengths of wood I-joists containing square
or round web holes. The research findings can be used to reduce the testing requirements for
new product qualification.
2. Optimized Design of Wood I-Joists: This project increased
knowledge of factors that affect wood I-joist strength. It provided
a cost/benefit analysis for selecting lumber or LVL for flange
stock and established the different performance criteria for
residential and commercial applications. This allows
manufacturers to select cost-effective components to produce
products best suited for both markets.
3. Influence of OSB Properties on the Performance of Wood I-Joists: This project provided
information that a) helps OSB web stock manufacturers optimize their products and b) helps
I-joist manufacturer source web stock that will provide the best performance economically.
This project concluded that the shear strength of wood I-joists can be predicted using a
simple mechanics model based on the shear strength of the web material and the geometry
of the I-joist. This research finding can be used to reduce the testing requirements during
product certification or re-evaluation.
What it Means to Canadian Industry
UNB 3 Enhancing Shear and Bearing Strength of Wood I-Joists
New product qualification of wood I-joists used to require an extensive test program to evaluate
the strengths of wood I-joists with various sizes and shapes of web openings. The cost to an Ijoist manufacturer for contracting such a test program at an accredited laboratory was between
$10,000 and $20,000, depending on the range of joist size and grade marketed by the
manufacturer. The prediction models developed in this project allow manufacturers to reduce
the amount of testing required, potentially saving hundreds of thousands of dollars.
Pedro DaSilva, Boise Cascade Alljoist Ltd.: “The research results are particularly
useful for new I-joists plants that can take advantage of the innovations without
retooling or recertifying. In the case of Alljoist, the work on web openings was used
to maximize performance and flexibility for customers.”
UNB 61 Optimized Design of Wood I-Joists
The current rout depth (the penetration of web into flange in the flange-web joint) used by most
I-joist manufacturers in Canada is about 12 mm. It was found in this study that a shorter rout
depth of 9 mm can be used with adversely affecting overall performance. If the reduced rout
depth is adopted by the industry, for the most common joist depths of 9-1/2” and 11-7/8” this
means a reduction of 3.2% and 2.4% respectively in the quantity of OSB used. Assuming an
annual production of 300 million linear feet of wood I-joists, the estimated annual saving in
OSB cost could potentially be about $4 million.
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Pierre Audet, Toiture Mauricienne: “We used the UNB work to develop the web
profile for a new series of I-joists.”
UNB 76 Influence of OSB Properties on the Performance of Wood I-Joists:
At an annual I-joist production of 300 million linear feet, the Canadian wood I-joist industry
pays an estimated $250 million for OSB panels annually. This project generated knowledge
about how web properties influence I-joist properties. In the long term, the findings will
eliminate over-specifications of OSB properties that are insignificant in terms of their influence
on the quality of I-joists, thereby leading to reduced OSB material costs. A 2% savings in the
cost of OSB webstock would save wood I-joist producers %5 million per year.
Ken Lau, Ainsworth Lumber: “The UNB report has been circulated to the
Ainsworth technical managers who will use it to tailor web stock properties to
wood I-joist manufacturers’ needs.”
Pierre Audet, Toiture Mauricienne: “We will be using the UNB I-joists research
reports to optimize our OSB webs.”
Pedro DaSilva, Boise Cascade Alljoist Ltd.: “The research results are particularly
useful for new I-joists plants that can take advantage of the innovations without
retooling or recertifying. In the case of Alljoist, the information on openings has
been used to optimize performance and flexibility for customers.”
Further Information
1. UNB 3 Enhancing Shear and Bearing Strength of Wood I-Joists:
http://www.valuetowood.ca/html/english/research_development/search_projects_details.php?
prj_id=22
2. UNB 61 Optimized Design of Wood I-Joists:
http://www.valuetowood.ca/html/english/research_development/area_projects_details.php?prj
_id=70
3. UNB 76 Influence of OSB Properties on the Performance of Wood I-Joists:
http://www.valuetowood.ca/html/english/research_development/area_projects_details.php?prj
_id=88
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