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KinAlberta Member	# Posted: 8 Jun 2022 12:42pm - Edited by: KinAlberta Reply The strength of beams is a fascinating topic to me. Thought Iâ€™d start a thread on misc. knowledge. Eg. Came across this website: â€œLab Tested Stronger than Steelâ€ https://singcore.com/news/how-to-build-any-structure-insulated-lightweight-high-stren gth This is also interesting: Beam strength Adding 2â€ more adds near 50%!!! â€œthree 2x12s offer 48% more bending resistance than three 2x10s.â€ http://www.finehomebuilding.com/1995/01/01/using-plywood-in-built-up-beams Floor Truss â€” Component Talk http://www.componenttalk.com/floortruss Beam on top of beam, not connected, and of different length. - Structural engineering general discussion - Eng-Tips https://www.eng-tips.com/viewthread.cfm?qid=379229

KinAlberta Member	# Posted: 24 Nov 2024 02:09pm - Edited by: KinAlberta Reply Question: If someone were to stack two 2xs on edge with some kind of joinery, how much added strength could be obtained? eg. Put 2 2x12s together to make a 2x24” (Actually: creating a 1 1/2” x 22 1/2” board) Maybe using dowels or steel pegs. Or some sort of surface joinery like boards or those prickly galvanized mending/joining plates Note: Someday I’d like to build a narrow footbridge over a creek in a hard to reach location (upwards of 30’+ long). I could build open web wood trusses but they could eventually rot and be unsafe even if made of PT wood due to the cut ends, trapped moisture and fastener corrosion. Simple but long beams might be a lot easier to get on site, build or reassemble on site and easier to protect from the elements.

ICC Member	# Posted: 24 Nov 2024 08:57pm Reply I never saw the OP that references beam strength. Here is a reference tool for calculating beam sizes as well as a few other calculators that can be useful. The webpage is by a carpenter, not an engineer. He is a smart guy though. The calculators on his site use formulas recognized by engineers, but may not take in as many variables as a licensed engineer msy use in some conditions. To use the simple beam calculator some strength figures are required. The calculator refers to the NDS tables, but the link is no longer valid. Use Google or use the table values for fiberstress in bending, modulus of elasticity and Horizontal shear from the Forestry Forum webpage. The Forestry Forum table is by the same guy I referenced. His name is Don. The FF also has his calculator for beams online. Link at the bottom of the table page, and in the text below... Timbertoolbox.com calculators index page Try his Simple Beam Calculator Forestry Forum table of Design Values for Visually Graded Timbers 5" X 5" and Larger (note that the values for large timbers are usually lower than the values for dimensional lumber like 2x materials.) Example: When we laminate three (or more) 2x to make a beam (with supports under any joints in a layer) the fiberstress in bendig and modulus of elasticity are increased. Beam Calculator on The Forestry Forum ~~~~~~~~~~~~~~~~~~~ Another online resource for beam calculations as well as many other design tools is Medeek Design. Medeek design is operated by a WA state licensed architect who is also a WA state licensed Professional Engineer. He has developed all the calculators and tools he has on his site. His Beam Calculator is here. Nathans calculators are not free for unlimited use. The beam calc may be used once a day for free. A user key is required for more than once a day. Monthly or annual plans are available. He also has some terrific plugins available for use with ketchup. Membership subscriptions are needed. The plugins are excellent for designing floors, walls, electrical systems, etc. etc. Superb tools. Use costs as they are great and took time to develop and fine tune. I've used them in the past as a tool in my work. He has a very nice snowload map tool. One free use per day.

ICC Member	# Posted: 24 Nov 2024 09:14pm - Edited by: ICC Reply Quoting: KinAlberta If someone were to stack two 2xs on edge with some kind of joinery, how much added strength could be obtained? Strength will be dependant on the strength of the joint between the two members. That has many variables so I doubt we will find any real useful info available in simple form. If such a 2x24 beam was used there would be quite a challenge in preventing beam/joist roll-over. Very good blocking would be required to hold the 2x24 in a vertical position. The "prickly galvanized mending/joining plates" that you mentioned would be basically unusable for a DIY. Those are designed to be pressed into the wood by a hydraulic press capable of 20 to 50 tons of pressure. Trying to hammer them in does not work. Each different size plate has a design strength. IIRC a 3x6 truss plate can resist a lateral pull of over 4000 lbs. The engineer uses software than does all the plate and timber sizing for the loads and data that is input. Theroreticall two 2x12 could be stacked to make a 2x24 beam. However, the cost of those materials would be too high to make that commercially viable. A built up truss would be better, but not for a DIY'er. ~~~~~~~~~~~~~~~~~ RE the 30 foot footbridge..... For a DIY project I think a suspension bridge would be more practical and still a challenge. The NF has built several footbridges over creeks here in NM using glulam builtup beams. They are weatherproof beams and were not cheap. Very heavy too and none were 30 feet long. A suspension bridge would need to be anchored to solid rock of a good poured concrete anchor. A timber framed truss bridge could be built as in the old trestle bridges of old railroads. Or a welded or bolted steel truss bridge like the highway bridges of yesteryear.

ICC Member	# Posted: 24 Nov 2024 09:28pm Reply FWIW, engineers designing structural elements such as wood beams that will be laminated and built up on site do not like to use adhesives. For example, the plywood that man people laminate between layers of 2x material when building a beam. THeir reason is that the application of the adhesive is beyond their control. Many variables enter into the equation. Most adhesives have an allowable "open time". That's the time the adhesive can be left open to the atmosphere. If open to the air too long the adhesive can skin over and will not stick properly to the other layer face. Recently there was a topic here regarding problems with spray on foam insulation. One of the articles referenced there noted that one of the big sources of problems with that foam comes from the improper use of the foam. Specifically the improper proportions of the two chemicals used for the foam. THis is similar to the issues that can arise when glue laminating wood to make a beam. In a factory sheets of foam can be made with great precision of chemical mix, temperature and humidity. In the field those are hard to impose le to control with precision. Same thing for the application of adhesive to hold beams together. So, for the most part we do not see engineered field assembled beams, unless they are simply nailed ad properly supported at joints.

KinAlberta Member	# Posted: 28 Nov 2024 06:07pm - Edited by: KinAlberta Reply Yeah my issue is building while standing in water or in the uneven, steeply sloped and mucky ground thick with trees and crappy prickly bushes beside the creek. Any glue would likely be dry before I managed to manhandle the boards into place. Interestingly the beavers keep trying to build under our galvanized metal bridge. So another permanent bridge might create another make-work project. (A few years ago we had 8 dams along our portion of the creek.) Temped to just put in dock stands and long pier/dock sections with a draw-bridge style cable and winch system to raise them up before freezeup or the spring runoff which would take out any midpoint supports.

ICC Member	# Posted: 9 Dec 2024 08:52pm Reply Quoting: KinAlberta Someday I’d like to build a narrow footbridge over a creek in a hard to reach location (upwards of 30’+ long). Something happened that made me remember Leonardo DaVinci's bridge. Maybe you can use this idea? Google finds many pages.... https://leonardodavincisinventions.com/civil-engineering-inventions/da-vinci-bridge/ https://news.mit.edu/2019/leonardo-da-vinci-bridge-test-1010

socceronly Member	# Posted: 10 Dec 2024 09:52am Reply I think there was something about this some time ago on this forum. Called Keyed beam. If you stack the two and do not key them you don't get any benefit. You can get 30ft LVL/Glulam beams. I think there are ground contact PSL ones as well. But I doubt they are cheap.

gcrank1 Member	# Posted: 10 Dec 2024 11:17am Reply Neighbor here used old telephone poles.

montecristo Member	# Posted: 14 Dec 2024 01:36pm Reply Quoting: gcrank1 Neighbor here used old telephone poles. That's what I used for a temporary bridge. Was strong enough to drive a full size pick-up over.