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A 4-foot by 20-foot cross-laminated timber panel in a building under construction at Oregon State University failed earlier this month, prompting the university to hire an outside engineer to investigate but leaving its commitment to the construction technique intact.
剥落的一端后面板下降了3月14日,according to an article在里面Gazette-Timesin Corvallis, Oregon. The 7 1/2-inch thick panel was made from five layers of 2×6 boards glued up at right angles (see image #2 below). No one was hurt in the incident.
当完成时,3 -story, 80,000-square-foot building called Peavy Hall will be the new home of the College of Forestry. The panel was manufactured by D.R. Johnson in Riddle, Oregon, the first fabricator in the country to manufacture跨层压木材（CLT）panels certified for structural applications.
Steve Clark, the university’s vice president for marketing and university relations, said by telephone there have been no other problems with CLT panels on the project, and that the university remained “completely committed” to the construction technique.
“It came completely out of the blue,” he said, adding that unexpected problems can crop up with virtually any building material.
D.R. Johnson referred questions to its outside public relations representative, but the call was not returned.
Clark said that 574 CLT panels had been set at the time of the incident, and that only 60 of them remain to be installed. The inquiry by an outside engineering firm was to extend into next week.
It’s a rare sour note for a building material that is seeing wider use on commercial projects in the U.S. and Canada. Proponents say CLTs have a smaller carbon footprint than more conventional steel-and-concrete structures, and can shorten construction times. Panels have been used successfully on a number of well-publicized projects around the country, including a building at the University of Massachusetts (see the “Related Articles” sidebar above) and anoffice tower in Minneapolis. A number of other buildings made with CLTs are in the works.
Clark says the university intends to complete Peavy Hall with the panels, as soon as engineers have taken a look at the one that failed and certified that others on the project are sound. The building is due to be completed early in 2019.
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Of course, defects can happen at any time but I know the timber industry in Canada is really pushing these CLT beams for high rise projects. They are trying to take a bite out of the steel and concrete high-rise market. They claim a smaller footprint with the CLT's but as pointed out by another GBA article earlier this week, the "sustainable" harvesting of trees from forests has turned out to be mostly bunk. Once you take into consideration the heavy equipment, semi truck hauling, milling, etc., it's a wash in the end.
你有数学吗？@ Peter L
“一旦您考虑了重型设备，半卡车拖拉，铣削等，最终就洗了。”
There's a lot of heavy equipment and materials transport in the manufacture of concrete & steel too, as well as a HUGE amount of materials processing energy & carbon emissions going into baking the limestone, smelting the iron ore, etc. If it's really a wash I'd be curious to see at least the napkin math version of how that all pencils out.
Just because sustainable forestry certification programs aren't really working as-intended doesn't mean that sustainable forestry isn't possible, or at the timber industry average practices the total impact is as heavy as that of steel & concrete construction.
Dancing on the edge of a razor blade just to prove they can
对于非木工来说，这种建筑技术在数千年的木工历史上飞行。艰难的教训是，鉴于几个高湿度和低湿度的循环，跨颗粒胶接头通常会失败。原因是木材吸收空气中的水分并在整个谷物上变大，但沿谷物的大小没有变化。因此，当您将胶水粘合到另一个干燥的12英寸平方板上时，将12板粘合在另一个干燥的12英寸平方板上时，木材试图扩展说7％左右，胶水通常会含有大量的力。木材移动到足以膨胀，但是当它干燥时，胶水固定时，木材会失败，裂缝离开缝隙。其他时候，胶水可以足够弯曲，可以在几个周期中生存，但是随着年龄的增长，它变得脆弱并且失败了。
I am sure the engineers have numbers to show that everything is fine, but from here it looks like they are dancing on the edge of a razor blade just to prove they can.
LCA for Laminated Timber
"The results indicated that the laminated timber building design offered a lower environmental impact in 10 of 11 assessment categories. The cradle-to-gate process energy was found to be nearly identical in both design scenarios (3.5 GJ/m2), whereas the cumulative embodied energy (feedstock plus process) of construction materials was estimated to be 8.2 and 4.6 GJ/m2 for the timber and concrete designs, respectively; which indicated an increased availability of readily accessible potential energy stored within the building materials of the timber alternative."
-Robertson AB，Lam FCF，Cole RJ。中期办公室建筑替代方案的比较摇篮到门环的生命周期评估：层压木材或钢筋混凝土。建筑物，2012年
作者发现，质量木材生产的原料能量较高（主要来自PRF和PU粘合剂），但是尽管如此，同等设计的中层质量钉结构在每个环境度量方面都具有统计学上的显着改善（全球变暖，富营养化，富营养化，除化石燃料耗竭外，臭氧耗竭等）。
CLT is just plywood on a
CLT is just plywood on a large scale. The glues used are stronger than the wood itself. Cross-grain movement is certainly an issue that every woodworker has dealt with, but the plywood industry (and the CLT industry) figured out the answers a long time ago.
Adhesives
I can't think of a building nowadays that doesn't rely on a combination of wood fibre and glues. Plywood, OSB, underlayments, LVLs, Glu-lams, composite siding. Both concrete and drywall are essentially aggregate and binders.
Michael lets think about how
Michael lets think about how they make ply wood. One of the first things they do to the logs when making ply wood is put the log on a lathe and peal the log so thickest bit of cross grain is 1/8 of an inch. When ply wood absorbs water and swells up, the 4 foot and 8 foot dimension change very little what does change is the thickness. Oriented strand board is the same in that they make the strand by breaking the wood along the grain and glue it back together so when it swells it gets thicker but not longer or wider.
沃尔特
我附近的OSB植物从8英寸高的芯片中制成5/8“床单，胶水压向最终宽度。
我不确定这有什么关系。一群坐在棚子里喝啤酒的家伙并没有提出层压木材产品。它们是由与几乎所有其他产品相同的工程过程开发的。我认为他们不会以某种方式忘记材料固有的运动。
And they aren't new. Many of the grocery stores around me in the '70s were supported on huge glu-lam arches. Most are still in use today.
沃尔特，我了解木头
沃尔特，我了解木头technology, and agree that CLT asks more of the wood fibers than veneer-core plywood or parallel-laminated lumber. But CLT has also been in regular use in Europe for a couple of decades, so while it's not as time-tested as plywood, there are enough built projects to know that it's a sound concept. I'm not sure what happened with the Oregon panel failure, but I bet the people responsible will find out and it won't happen again.
Regarding plywood, the expansion coefficient of lumber radially and tangentially is rarely more than a factor of two apart, vs. a factor of ten more than expansion along the length of the fiber, so thin veneers (sliced tangentially) don't affect movement all that significantly compared to CLT, which is a combination of tangentially- and radially-cut lumber. But the number of glue joints do matter, as does the strength of the material itself. My guess on the panel failure is that it wasn't a glue failure, but a shear failure within the lumber. I'm sure the lumber used in CLT is machine-stress-tested, but that won't find every defect.
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