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The RED Letter
RED Engineering & Design
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| Check out the new installment of Engineering in a Box |
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Engineering in a Box Video Series
Check out our
Engineering in a Box series on
www.brianmoskow.com. Or, click on the YouTube button at the bottom of this newsletter and go directly to the videos.
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There's a new class of timber that's getting a lot of attention!
More architects are using this material
CLT, known as cross-laminated timber, is gaining interest among architects and engineers these days. A member of a new class of lumber materials called massive (or "mass") timber products, CLT is a large, flat panel of solid wood manufactured from dimension lumber or structural composite lumber. So large, in fact, it is available in 8 feet by 40 feet panels, and it is not a "stock" product. It is project specific.
Similar to glue-laminated timber (GLT), CLT is manufactured from dried dimension lumber where adhesives are applied between laminations. CLT uses include floor, roof, and wall framing. There are buildings where CLT has been used for all structural framing above the foundations. In other buildings, CLT has been used as floor decking.
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It was January 24, 2009, when Cyclone Klaus made landfall in Bordeaux, France, and traveled across Western Europe into Germany, Italy, Spain and Switzerland. Leaving thousands without power, the wind damage was significant, especially in forests. Meteorologists reported that sustained winds averaged 110 mph.
In the aftermath, damage assessments indicated more than 60% of trees were knocked down in areas where wind speeds topped 90 mph. For trees that had been broken in half by the storm, it didn't matter the height of the tree, the circumference of the trunk, or the species.
In the U.S. there are currently three manufacturers of CLT: DR Johnson Wood Innovations, Nordic Structures, and Structurlam Products.
The take away: Because of the size and strength of CLT panels, they provide alternative building materials to concrete, steel, and masonry.
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A big welcome to Trace Allard, EIT! Trace joined us as an EIT from North Carolina State University where he is also continuing his education to include a master's degree in business administration.
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Congratulations to our intern, Chris Pinkus! Chris was awarded the first-annual Structural Engineers Association of North Carolina scholarship. Chris comes to us from North Carolina State University where he is pursuing his degree in structural engineering.
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Concrete Creep
Mystery solved!
Maybe we're not thinking about Halloween, quite yet, but there is a lot of "creepy" concrete out there. And it's everywhere!
Concrete-for all that it does in the built environment-has an inevitable tendency to "creep." In other words, it progressively deforms under mechanical stress. This is a known fact to engineers and scientists and the rest of us see evidence of concrete deterioration everyday on bridges and roadways. Creeping concrete is a given, but why it crumbles and cracks has never been fully investigated-until now.
According to Gaurav Sant, associate professor in the Department of Civil and Environmental Engineering at UCLA, engineers' current standard practice is to use empirical data to model concrete creep. This technique is a poor predictor of creep rate which leads to eventual deterioration. Sant has devised a better model.
"By careful unification of experimental and computational data, we clarified that creep originates from a dissolution-precipitation process that acts at nanoscale contact regions of C-S-H [calcium-silicate-hydrate] grains," he explained. To better understand the dissolution-precipitation process, think about what we sometimes see in caves. This is how stalactites and stalagmites are formed. A chemical reaction takes place where minerals dissolve and reform into these geologic formations. Concrete does the same thing, but on a microscopic and atomic scale that is called "creep."
About the image above:
This is a visualization of the dissolution of a C-S-H grain following its repetitive contact with an aqueous solvent. These visualizations which were enabled using vertical scanning interferometry (VSI) provide access to the surface topography at nanoscale resolution.
Credit: G. Sant and M. Bauchy/UCLA
By using the dissolution-precipitation process and being able to analyze the mineral content of concrete on a nanoscale through the method of vertical scanning interferometry, Sant and his associates have been able to establish a predictive rate associated with concrete creep. They are using this rate methodology to put together a comprehensive description of concrete creep from a macro scale to an atomic scale.
The take away: Engineers will have a much better idea of how and when concrete will deteriorate and can factor this into the lifecycle costs of daily infrastructure on which we depend.
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