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I would like to figure out how to estimate the impact on load bearing of different solid structure wood (german Konstruktionsvollholz/KVH norm) beam connections. Assume I have a connection like this with 100mm x 100mm posts and main beam (pink) and 50mm x 50 mm side post and connected beam (green) and want to put unrealistic heavy plants on the beams: How would the connection of the green beam influence the load bearing of the pink beam? How can this be applied to a series of connections (up to 8 green beams connected to the pink one)?

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I found

  • an expert book (François Colling, Holzbau Grundlagen, Bemessungshilfen, 2., überarbeitete Auflage, Vieweg +Teubner | GWV Fachverlage GmbH, Wiesbaden 2008) stating that removing parts of a beam does't influence it's load bearing capacities as long as the removed part is filled with and equally strong or stronger material, but I'm not sure if that accounts for more than some mm screw holes
  • Is it safe to drill small holes in load-bearing concrete beams for expansion bolts? stating that you can drill "surprising large holes" in beams which isn't overly precise and doesn't account for the fact that I want to fill the cut out space with another beams end and
  • What is the maximum number of load bearing studs in a row that can be notched? gives reference to useful recommendation about notching and drilling parts of beams, but judging from the other references it matters whether the whole is filled with material or not.

Can the two diy.SE questions be applied to wood beams? Can someone clarify, please?! I'm building everything from scratch, so there's nothing previously calculated where I could rely.

  • I think you'd make a good structural engineer...you ask all the right questions. By the way, after you figure the beams out, you can start worrying about the columns. – Lee Sam May 1 '17 at 2:40
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All loads on beams / columns matter. So, if you are adding beams (loads) to existing beams, you are right to worry about its affect. However, there are three things in your favor: 1) everything is designed with a "safety factor", 2) residential design is way-over designed, and 3) beams are designed to fail in tension.

1) Structural design has "Working Stress" and "Ultimate Stress". Ultimate stress (failure) is about 150-180% more than working stress (what we design beams, columns, etc. to).

2) Residential design is largely done by non-professionals (architects and structural engineers). So, "what is commonly used" in residential construction is grossly over sized.

3) Beams are designed (design formulas used) to fail in tension. That way, we'll see cracks and presumably investigate, rather than fail by compression, which will fail with a bang...and have a disaster.

So, back to your question, yes, there is a way to determine how much weight can be added to a beam, how big holes (and how many holes) can safely be drilled into a beam, etc. However, unless you're "doubling the load" or excessively drilling an existing beam (1 connector is not excessive), then I think your safe.

You can destroy a concrete beam quicker than steel or wood beams. When drilling the concrete beam, you'll know quickly if it's a poured-in-place beam or a steel beam encased in concrete. In fact, you may not be able to drill through the steel/concrete beam. So, rather than "mess with the concrete beam", why not design a "saddle" to fit over the beam and support your new added beam and lights.

If you decide to proceed with drilling the concrete beam, I'd recommend you contact an architect or structural engineer (not a CIVIL engineer.)

  • Thanks for your input. I realized that the references to the two diy.SE questions are misleading, that I didn't translate the title of the book and that I didn't mention that I want to build with wood from scratch, I'm really sorry. I have to get used to this SE site, because I feel that I'm asking to abstract questions - I want to connect multiple small beams (up to 8) to the large one and am looking for an estimation formular for the impact. – Karl Richter May 1 '17 at 2:57
  • No problem.... us Americans are lazy and never learn a second language. Connecting beams together is considered "point loads" as compared to "uniform loads". The principle of design is the same, but you'd probably need different calculation tables. Unless there are unusually large loads or extra long spans, it could be simple. You draw better drawings than I do. Can you draw a sketch and give an estimate of loads on each beam? – Lee Sam May 1 '17 at 3:30
  • I decided to go with beam shoes from wood which should do the job of a steel shoe. Despite that, you extended my starter knowledge dramatically, thank you. I am finalizing the planning for the project with diy.stackexchange.com/questions/113922/… where you find a load definition and then the question how many joists to choose economically. Please don't hesitate to provide more of your helpful comments and answer there. – Karl Richter May 1 '17 at 15:39
  • Thank you, I prefer to programm the sketches in OpenSCAD because you have no GUI stuff like snapping rasters you have to hit with the mouse and everything can be a variable, so you can change everything in one or two key strokes. – Karl Richter May 1 '17 at 15:41

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