Wikipedia:Reference desk/Archives/Science/2017 January 1

= January 1 =

Cross laminated timber versus Plywood
How is Cross laminated timber different from Plywood? I read "It is similar to plywood but with distinctively thicker laminations." What are the differences and advantages/disadvantages of these two types of Engineered wood products? Bus stop (talk) 16:43, 1 January 2017 (UTC)
 * The advantages of CLT are discussed here. I think it mainly comes down to the finished product being much thicker than plywood and so offering greater structural stability and better thermal properties. Richerman    (talk) 17:36, 1 January 2017 (UTC)
 * CLT is somewhere between plywood, glulam and blockboard. It's a form of plywood, but it's made from much thicker veneers.
 * Advantages are primarily its price. A thick board can be produced with much less splitting and gluing of plies. It's also (like blockboard) strong and quite a bit lighter. Wood is nature's own composite: it's quite strong and light on its own, although it doesn't have cross-plies and so doesn't have the omnidirectional strength that plywood does. Plywood strength depends a lot upon the timber species, but other things (and overall thickness) being equal, an equal thickness of three plies of CLT is stronger than 9 plies of plywood.
 * Its disadvantage is the need to make it from thick plies. These are sawn from logs, unlike plywood which is unrolled like a giant pencil sharpener shaving. So CLT also needs to be joined from multiple narrower slabs, rather than single sheets. Andy Dingley (talk) 21:16, 1 January 2017 (UTC)
 * Why is "an equal thickness of three plies of CLT ... stronger than 9 plies of plywood"? Bus stop (talk) 23:50, 1 January 2017 (UTC)
 * I see here that it is quite different than plywood. Bus stop (talk) 00:13, 2 January 2017 (UTC)
 * A thick veneer of grown timber is stronger than the same thickness made from glued-up veneers. This is the purpose of blockboard, which is one thick veneer with two decorative face veneers on it. It's used for tasks like bookshelves which need to be stiff.
 * "Stronger" (when comparing a thick veneer to plywood) is a matter of average strength. For a natural material like timber, strength (and especially stiffness) depends a lot on direction. It might be "strong", yet be considerably weaker in the "wrong" way. Another virtue of laminating is that these weak aspects can be minimised, as separate plies don't have to place them in the same place or direction. Andy Dingley (talk) 00:24, 2 January 2017 (UTC)
 * Perhaps in a sense some of the intrinsic strength in wood as it naturally grows is taken away from the wood when it is shaved off of the log in the process of making plywood. The shaved off wood used in making plywood is also forced to lie in a flat plane whereby when it was part of a tree it was an arc of a circle. But cross laminated timber is allowed to retain much of the same structural integrity that it had when it was part of a tree. Bus stop (talk) 03:26, 2 January 2017 (UTC)

PID bacteria
What are the bacteria (sexually transmissible only) that can cause pelvic inflammatory disease other than chlamydia and gonorrhoea? 2A02:C7D:B964:4400:CC02:3209:AB66:CBA9 (talk) 23:39, 1 January 2017 (UTC)


 * Pelvic inflammatory disease? μηδείς (talk) 00:59, 2 January 2017 (UTC)