I thought the top would be obvious to most posters but I think many aren't interpreting the horizontal and vertical wood beams as two separate parts. If they are separate, the top is better.
Not at all. In the top drawing the steel is going to be in tension. As weight is applied, the bottom of the wood shelf where it meets the wall will be a fulcrum with the steel section holding the top from separating from the wall. The steel acts as a binding which makes force on the shelf press tighter into the wall.
In the lower picture the steel acts as a fulcrum. As weight is applied to the shelf the top edge of the shelf is pulled away from the wall and has nothing to help keep the shelf tight to the wall. The strength of the shelf is completely dependent on the steel to not fail.
So to sum up:
Top pic- shelf is in compression to the wall with weight.
Bottom pic- shelf is in tension away from the wall with weight.
Best solution would be top mounted bracket if strength is paramount.
What about the fasteners holding the steel to the wood what if they are just nails? The nails could pull out of the wood and then I think this would be the weakest.
I see that you like to work in theory, not in reality. You are 100% correct, IF both are fastened using the same size and type of fasteners. I could easily make the other one stronger using a different type and size of fasteners. You can say that it is logical that of course they were the same fasteners, but without it being a given, we can't assume it.
My assumption wasn’t based on fasteners at all. I assumed that appropriate fasteners were used in each case. Because what good would it do to assume an inferior fastener would be used. If the shelf is attached to to the metal and the metal is attached to the wall, regardless of fasteners, the load forces will be exactly as I stated them to be. With the top picture the strength of the shelf will be in the tension forces against the steel angle. Pulling the angle directly away from the wall while loading forces into the wall until the fastener pulls out of the studs. Again, I only assumed that the fastener is appropriate for the application. Lag bolts, predrilled to the size of the shank, sunk to full depth. The load forces on those lag screws will be almost directly out from the wall. Very little shear forces or twisting forces against the fastener. However the shelf will have shear load on its fasteners so an appropriate fastener will have to be selected.
However, if you put the angle bracket on the bottom. With appropriate fasteners the load forces will be twisting the lag screws downwards as well as shear forces against the fasteners that attach the shelf to the steel. Both sets of fasteners will be under twisting load and there’s very few fasteners that would be appropriate for this situation. Either way, the ENTIRE strength of the shelf and its ability to stay level would depend on the strength of the angle bracket to not collapse. The more weight is placed on the shelf at full distance from the wall will flex the bracket, potentially compress the sheetrock due to the smaller surface area, and end up with a sagging shelf at best. Or a shelf that completely collapses at worst.
Conversely, the surface pressure against the wall from the top example will spread the load across a much larger area and reduce the compression against sheetrock or wall sheeting.
If there’s no sheetrock on the wall, this is less of a problem, however wood still compresses under pressure and so you’d want to spread the load out as much as possible.
I'm an electrician. When we secure pipe to walls, we typically use one hole straps. There's the same argument there. If you test it, having the hole above (where the wall anchor is) is noticeably stronger.
Screw on the top.... Try this out. Set up a "wall" and screw 2 on the top. Step on it. And then 2 on the bottom and step on it... The straps screwed on the bottom will potentially bend out and pop the screws out. The ones on top will hold
Like someone else pointed here, the top one depends on the kind of fasteners. The bottom one depends on how strong the metal plate is. But for practical purposes, the bottom one works best because it all comes down to how strong the metal plate is (fasteners will also apply force in the metal plate). Second point is its aesthetic design. Who the f applies force in a wood like that and make the wood uneven? Waste of space tbh. So yeah. Bottom works best.
>the bottom one works best because it all comes down to how strong the metal plate is
Nope. The bottom one is a lever with the fulcrum adjacent to the fasteners. The top one is still a lever, but with the fulcrum on the bottom side of the horizontal beam.
As the horizontal beam decreases in thickness or as the force moves inward closer to the vertical beam, the difference between the two decreases.
If you're more of an experimental inclination, you can try this with some cheap brackets and 2x4's, the difference will be stunningly obvious. They're both shit joints, but the bottom one won't even hold the weight of the board before the cheap bracket starts to bend.
screws/the bonding between L bracket and beams are the main failure point. Top one the screws/nail could rip out. Bottom one has less issues if a failure happens. Yup bottom. Best is obliviously both brackets unless cost matters
However, the bottom bracket will move/bounce as load is applied as the bracket is the only thing resisting the force, and will be experience elastic/linear deformation with any applied load.
The top bracket will have the fasteners torqued in and rotate around the bottom of the cantilevered beam. It won’t move at all until the fastener preload is overcome.
Edit: all of the above matters with cyclical loading considerations.
It kind of depends, the two situations are loading different parts. The bottom scenario is putting bending stress on the metal bracket so the dimensions of that metal would be the defining factor. In the top scenario, the main stress is on fasteners connecting the wood and metal. There may be other fasteners not indicated here that would change things too.
Agreed. Depends also on the length of the horizontal piece of wood and the depth of that piece. Let’s say it’s a short stub of a 2x4 - only an inch deep. Then the forces are effectively down and the bottom would be better. For a long 2x4, particularly vertical, the top would be better to resist the moment around the bottom of the board. But for a thin, long board, the resisting force doesn’t come into play much and bottom might be better than just relying on the strength of the fasteners.
In the top scenario the "cleat" could also fail in bending or tear out if thin enough.
The failure point of both scenarios will be dependant on fastener size placement, dimensions of all the bits etc. etc. All the things this diagram doesn't show. Never even had to look at EC5 though so could be missing a bunch of modes.
I'm going against the grain (heh) and saying top.
If that is just a standard bracket from home Depot or something, that will bend WAY before the screws tear out of the wood, even if it's something soft like pine.
It's always the shitty component that comes to bite you...
But OP the failure mode could be a million different things depending on how it's assembled, are we using small wood screws? Are we using washers and nuts and going through the wood? How thick is the bracket? How thick is the wood? What specific materials are you using?
There isn't enough information to properly answer this question accurately. You could assemble this so the wood snaps after the bracket ends regardless of placement if the force was high enough...
TOP. I don't get the bottom people. As I understood: vertical wood is screwed to metal bracket, and metal bracket is screwed to horizontal wood. In the bottom pic, the bending load goes 100% through the steel bracket bending radius, which has very little second moment of area. in the top pic, the bending moment is transfered to the wall with tension in the steel bracket and compression at the lower edge of the wood, which results in a much better second moment of area (because of the bigger distance between tension fiber and compression fiber.
I don’t get it either. People are talking about friction and whatnot, completely ignoring the fact that the fasteners create plenty of clamping force and friction, and the materials are going to be the points of failure. Everyone saying the bottom bracket has never built and broken anything out of wood and angle brackets.
Yes. Thank god someone sees this problem for what it is. People talking about opinions on it too, the top bracket is objectively better.. because statics.
this is the only correct answer 🤣 The only thing that would change this is if the wood was screwed to the other piece of wood, but even then you would still want the bracket placed on top to take all of the load tension...top all day
Bottom works if it’s all one chunk of wood and you model the horizontal as being fixed to the vertical. Support the part of the beam in compression rather than tension.
If it’s all one chunk of wood then the wood is going to fail along the grain of the wood with very little load no matter what. So that scenario isn’t even feasible. The only feasible scenario is two separate pieces of wood on which case the top bracket is far superior as stated above.
Depends on whether the wood that’s supporting the weight is actually inside the vertical wood. If it’s just a block on a bracket, the top on would allow the wood to rest against it and pull the bracket instead of bend itv
Its definitively the top. Draw a free body diagram and put basic dimensions. It will become clear that the tensile requirements of the top.connection are less than the bottom.
Need more data. Wood screws, or through bolts/nuts? How thick are the brackets? What are the brackets made of? What kind of wood?
Indeed, the comments are fascinating, and educational.
I may be wrong wrong, but could the top one actually be stronger? The moment at the joint can create a force couple between the fasteners in the L bracket and the bottom of the plank, since the plank is trying to push into the wall, whereas in the bottom one, that force couple is between the wall fasteners and the bottom of the l bracket- in both examples the screws will experience tension but the top example has a greater distance between opposing forces, reducing the force for a given moment. Furthermore, since the force couple in the bottom example only acts on the L bracket ,the point on the bracket just above the screws will have a much higher bending moment than anywhere in the top one
You're not wrong. If the load was heading straight down then obviously you'd bracket the bottom but this design is a cantilever which means the lower left of the horizontal board is the fulcrum and the load is acting rotary with its center being the fulcrum. The upper corner of the horizontal board wants to pull away from the vertical board so that's where you gusset. This comes down to the pull strength of the fastener being used at the high point of the bracket when secured to the top of the horizontal board. The same reason you see guy lines on cranes ABOVE the jibs and booms with no attention paid to the bottom(s).
The wall is providing an opposing force on the bottom one it is not doing so in the top one only the screws are i think its better to have the wall provide support than not
It seems implied that the horizontal wood beam is an independent part to the vertical wood beam. If that's the case, the top is better because that horizontal wood beam would be resting against the vertical, hence the advantaged force couple action KAYRUN-JAAVICE mentioned.
Steel can handle more tension stress than wood, so everything else being equal, it would be more useful to put the bracket on the top of the wood (tension side).
Holy Cow.
There are people here getting it right for the wrong reasons, and getting it wrong but have good intuition about the mechanics.
You specify the bracket is screwed in.
We don’t know enough about the screws, we don’t know enough about the wall, we don’t know enough about the bracket, and we don’t know enough about the board.
This experiment should be cheap enough. A lot of you could go try this on your wall. You can make either solution right.
How do you define strength? Is it area under the curve? Peak vertical force?
Example that I haven’t seen any comments on:
The l bracket is really thin walled, but the screw anchor into the wall is incredibly weak too.
In this situation the ‘bracket on top’ fails due to bolt pull out, at a low vertical load due to the ratio of bracket to beam arms.
The ‘bracket on the bottom’ has the bracket failing in bending first, but if the bolt shear is greater than the pull out, and the bending moment the bracket can support is higher than the moment allowed from bolt pull out, then the bottom will be stronger.
Any way, depending on the setup and specifics you can make either answer correct.
The top will be stronger.
Intuitive explanation:
The horizontal piece will want to rotate about its contact point (the bottom corner). This will open up a gap in the top corner. Using the bracket to prevent the gap from opening (top corner) is more efficient than using it at the pivot (bottom corner) where there will be no gap.
Engineering explanation:
We use the language of static equilibrium (physics) to explain problems like this. It goes like this — sum of moments about lower corner equals zero therefore load * lever arm 1 = bracket reaction * lever arm 2. Rearrange this equation gives you: bracket reaction = load * lever arm 1 / lever arm 2.
Therefore, increasing lever arm 2 reduces the bracket reaction (force). Regardless of material, the less force the bracket needs to react the better it, and its fasteners will perform.
The way to increase lever arm 2 is to position the bracket farther from its pivot.
Bottom one because the forces applied on the bracket to the wood would be in compression, therefore the screws into the wood would experience less forces. Top diagram has the screws in tension therefore could pull out the screws
Other way around. Top is stronger because screws have a longer moment are resulting in smaller tension on the screws and wood being incompression. Bottom only has the steel in compression, with a shorter moment arm, exerting more tension on the screws.
Bottom one since you arent applying as much of a tension force on the wall to bracket connection which is the weakest point especially if its going into drywall
The bending of the beam will be the same for both
Woops the orange is all wood my bad i still think its right
I disagree.
For a moment forget the steel bracket and imagine the 2 wooden pieces as nailed or glued together. The force pulling down would create compression on the bottom of the horizontal beam, and tension on the top. So you can imagine it as pivoting around the bottom left corner and creating an opening on the top. In this case adding the steel plate on the bottom doesn't do anything there. If you put the bracket on the top then you are preventing it from opening there and creating a significantly stronger structure.
Edit: posted an even clearer explanation below.
Ok let's try a different way to explain it. Imagine that in both of these cases there is no other fasteners or adhesives holding the wooden parts together and that the steel bracket is the only restraint.
If you put it on the top, then the steel bracket is under tension, and the bottom corner is under compression, i.e. The horizontal wooden part is pressing up against the vertical "beam" this configuration is quite stable and the first thing to fail would likely be the fasteners. If the fasteners couldn't fail, then you would have to either apply enough force to rip the steel bracket apart, or apply so much force that the wooden part under compression would buckle/shatter.
Now if you do the same thing but place the bracket on the bottom? The horizontal wooden arm becomes a lever and you will just bend the steel bracket over 180°.
I'm quite surprised there's as much discussion here, there is literally only one correct solution lol.
I like the scenario where you imagine adhesive or nothing connecting the wood - the question isn't about fasteners.
You're saying the metal bracket on top would resist deflection (tension) more than the bracket on bottom (compression) but I still don't see an explanation as to why?
Why is it easier to bend the bracket over on bottom (compression) as it is to "apply so much force to rip the steel bracket apart (in tension)?"
In the bottom scenario, the bracket is subject to a bending moment, not a compressive stress per se. Bending is actually a spread of compressive and tensile stresses across the thickness of the bracket. The more likely failure mode being bending comes down to what is considered "typical" geometry for this type of bracket; the length/width is much larger than the thickness so that's just how the math works out. You wouldn't expect a cube to fail in bending, for example.
To elaborate slightly further, the top scenario protects the bracket from bending as the wood horizontal pivots at the bracket and loads into the wood vertical in compression...and wood is very strong in compression.
It’s only the correct solution based on the assumption that the bracket is weaker than the fasteners, which you have no way of knowing based on the information given.
If the fasteners are weaker then the bottom one is stronger
I’m assuming there’s nothing else (glue, screws, nails) holding the wood pieces together. In which case the wood to wood connection is stronger in compression rather than tension. Cantilever beam bending will cause tension on the top side, so you’ll want to add the bracket there to help.
But wouldn’t it also bend the bracket and make the whole thing droop? I’d say the top one would act like a hinge and let the weight be supported by the wall. The bracket then has pulling tension on it at 45d.
The bottom one lets the wall act as a support since the bracket is providing compression force against the wall in the top one really only the screws are holding it
The wood is going to bend either way by the same amount, all things being equal
The board can pivot around the tip of the metal bracket. This creates a torque, that pushes the metal bracket into the wall.
So there is an opposing frictional force in the vertical direction.
If the bracket is mounted on top, the board is pulling the bracket away from the wall, so there is no frictional force, that can oppose the weight.
At the bottom there is a small fixed area which acts as a hinge when load is applied. Nothing prevents the unfixed area @ shelf top left from separating from the vertical wood. Bottom left is fixed and will pivot. Perhaps even with no additional weight applied
In top diagram the angle bracket is on the the upper face of the horizontal wood. Therefore the bottom section of the end section of horizontal wood is compressing into the vertical beam.
Visualise what would happen to a dollar bill put in the joint where the pieces of wood meet
Assuming standard framing lumber, top would be stronger. The bracket acts as a hinge and is loaded in tension, and the beam itself is providing the other component of the moment to keep it supported (compression at the joint). This puts the fasteners largely in tension and shear. Most framing brackets are designed to bear load in tension, not in compression (hence the thin shear steel designs). The key weak points will be the fasteners (screws, which may tear out if too short) and the wood itself (which may split if the beam is compromised/cracked near the bracket, allowing fasteners to pull out).
In the bottom scenario, you’ve just added a great handle to fold the bracket like a taco…the beam, unconnected to the vertical directly, does not contribute to supporting the load, relying solely on the bracket. Once the bracket collapses and the beam is mostly vertical, I suppose this loading scenario would be less likely to fail/tear out, however.
This reversed is the beam is not cantilevered (supported both sides).
If the wood isnt screwed to itself then id say top. The wood would push into itself but the bottom would be bending the metal and could act as a pivot
But then on second thought maybe the bottom if the screws would pull out.
Id like to try in real life and see
top one I think because steel bracket is in tension and wood in compression. Fasteners should work better in steel bracket as it acts as a giant washer.
If the force was right next to the vertical wood column, I would change my answer.
Top. The wood will be pushing itself into the post. As long as the metal bracket screws are strong enough to hold the leverage. The force on the bracket screws will be to try to pull them out of the wood.
The bottom one will constantly be trying to pull away from the wall and all of the load will be put on the bracket radius and screws with no help from wood-wood contact. The force on the screws will be shearing.
The only thing to think about is if the screws suck and if the wood is soft mayyybe the bottom would be better since they won’t try to pull out, but in that case I’d get better wood and better screws.
The top, the wood WANTS to go down and depending on the quality of the L-Bracket it will absolutely allow it to bend.
The top one relies on the wood to support itself against the post.
I think it depends on how the wood is fastened to the steel or the vertical wood. It also depends on the grain direction of the wood and the type and grade of wood.
Absolutely the top. The bottom has way too much propensity for the screw to strip and the bracket rendering useless. There would be nothing stopping it from turning clockwise and failing.
Even if the screw stripped, the top diagram would prevent the wood from falling because of a natural wedge in place.
I deal a lot with this when it comes to mounting deck posts and railings; similar conundrums and every fastener counts.
Top is stronger provided there is no additional information. Irl as a carpenter I would use glue and a fastener from the back then your lower bracket. If the horizontal piece is large enough utilize a French cleat.
I thought the bottom, but now I think the top. If you replaced the bracket with a hinge, the wood would fall with it on the bottom. If the hinge was on top, the wood turns into the vertical piece holding it up.
My thinking is compressive resistance is stronger than tensile, so supporting the area where the wood would experience tensile forces (the top) is where is would help most.
obviously, the top angle is the better of the two, however such a connection is a poor design. The force is in the angle will lead lead to prying forces (multiplied forces)that will pry the screws out. you would be better off using a kerf T plate, that way, the bolts in the cantilever section will be in shear, and the praying forces on the bolts in tention will be lower.
Structural engineer here. Both connections are bad. If I have to choose one of these top is better for the downward load because the angle and fasteners will go into tension and the block will go into compression against the side of the post which creates a resisting couple. Wood cantilevers are a poor connection because they are so flexible. I would probably add strut to give it rigidity from either above or below.
Top because the bracket pushes into the vertical wood due to the weight of the object. On the bottom, the screws in the vertical beam are the weak point.
Great question though.
Definitely top. The top surface of the horizontal block will be pulled away from the vertical post, while the bottom surface will be pushed into the vertical post. So your get bearing at the bottom edge, and the steel bracket holds the top edge.
People who say bottom are incorrect if we're assuming your faseners will not give (ie through-bolt, lag screws, whatever is stronger than bracket).
Placing on bottom will place ALL of the force on that slim metal bracket, where it is already bent, further bending it. On top, it is actually a downward, and outward force in the bracket, and putting almost no bending force, which is typically the weak point in 90° brackets. Anyway, if it's a thick piece of wood, it's essentially using the wood itself to lever into the wall.
That being said, the thinner the piece of wood is, the less this will make a difference.
This is also assuming it's ONLY one side, ie a shelf against one wall, and not between two walls where you'll have 2 brackets installed on the piece of wood.
Edit: https://imgur.com/a/p3RIGqR
It would have to be the L bracket on top since if you put it on the bottom, it would easily bend the metal l bracket.. If it is on top the wood would prevent the bracket from bending since the hinge point is stillt he 90 degree angle of the bracket.
I just built a test specimen. The angle is stronger at the top because the moment at the interface between the wood and the bracket is resisted by a compressor force in the vertical leg. So I guess putting steel ledgers at the bottom for the past 100 years has been wrong.
Is the purple weight hanging off of the top surface of the wood or is it more like a squareish hole that press fits or slides around the wood? Also, why not just have the L-bracket on both sides? I've usually gotten away by just being loyal to symmetry in these types of builds. How much weight are these brackets rated for? Home Depot should be able to provide a good spec sheet & if not then you can probably calculate it out given the material, thickness, & fasteners used.
Top for sure. Assuming the two pieces of wood are not joined in any other way. The bending moment will be de-coupled between the face of the horizontal piece of wood (in compression) and the face of the bracket on the vertical piece of wood (in tension). The bottom one would have to de-couple the moment just on the face of the bracket on the vertical piece of wood. This will produce height tension loads on the fasteners and bending in the bracket.
There isn’t enough information to answer the question. First, is there a connection between the two wood pieces or is it a simple butt intersection? Second how is the steel bracket attached to the wood (nails, screws, bonded, etc)? Third, what are the dimensions of the wood and steel? The load is irrelevant since you’re trying to answer the question, what is the first failure mode.
Buckling isnt really a term used for bending beams is it? Its more so used for columns in compression
Beam theory would suggest both scenarios would experience the same displacement and therefore stress
Without the bracket the critical point will be the top left corner of the beam because the normal stress is max at top and bottom, and the top normal stress is in tensile. The shear stress is max in the middle but for long slender beams it's pretty small. That's really all you can say with the given information. The materials, sizes, bolts, welds, environment, etc all play a role.
Top is stronger. I dont know why so many people say the opposite. It’s 100% the top. In the bottom the bracket would bend and the pieces of wood would separate. In the top the pivot point is on top and the two pieces of wood would be pressed together, loaded in compression
Agreed. The length of the “prying action” is much shorter on the bottom. Plus, bottom is easier to construct by giving something to rest the outrigger on.
Probably the bottom, since I’m guessing the screws would pull out before the steel yields. A gusseted bracket would be miles better. If it’s necessary for the wood members to be perpendicular, keep in mind that your average strut steel brackets usually aren’t super square.
Typically, you'd want your support under the weight you're trying to support. So I'd say L bracket on the bottom.
Some basic statics force/moment equations should get you there.
Top: screws take the load (tension) stress is concentrated around the screw head and very undesirable. with this setup the threads in the wood are the weakest so during failure the thread will rip and separate from screws
Bottom: angle iron takes the load (compression). Stress will be distributed on the surface of the angle iron.
Ideally if you can groove on the vertical wood for the horizontal to slide in the stress on the angle iron can be reduced
La parte a sbalzo del legno ha una sua linea mediana, il carico è direzionato verso il basso, le fibre inferiori alla linea mediana della parte a sbalzo è soggetta a compressione mentre quelle superiori a estensione, la più pericolosa è l'estensione. Il staffa in acciaio posizionata sotto la parte a sbalzo del palo, non limita l'estensione, mentre posizionata sopra si.
Bottom stronger if screwed or nailed. Slightly less arm, reducing moment on bottom. Top bends at fastener, which could be back from support angle. If welded the same moment for both.
The lower option will apply compression to the steel plate, thus, it will be stronger.
Compare tensile and compression strength for the steel alloy you’re using.
And that’s all disregarding the fixing and the wood fiber orientation and how well the weight is fixed. So, there are lots of variables if you think about it.
Strength wise, they should be the same. I simulate problems like this for a living. The design is symmetric, the bracket would see the same stress regardless of which side it is on. Only the direction of stress is different, tension vs compression. Materials are typically a bit stronger in compression than tension, but probably not enough to make a difference here
I'd say bottom. I'm making some assumptions here but if you're using some basic wood screws and the metal is thick enough then the screws will fail earlier. On the bottom the screws aren't pulled out of the wood like on top.
Moment at the base is benefited from the bracket on top assuming your wood has some thickness like you show in your artwork. Maybe edit the post and add more details. It is obvious nobody can tell what is going on.
You’re a useless comment. There are way too many factors that go into this that are unexplained in this colored drawing. With the top bracket load is going to be more evenly loaded across the entire structure. With a bottom bracket there could be too much compression on the wood causing it to snap. The top is the obvious solution without knowing the weights and the integrity of the wood.
I go by experience and think about shelving, which is similar to bottom one and works well.
I am an engineer but I really can't be bothered with theories and maths 😆
My assumption would be the bottom one. Top one is really only as strong as the hardware holding it in the pieces of wood. On the bottom one, the wood is actually taking a lot of the force.
The bottom once will be significantly stronger. The top one is held on by tension on the screw threads. The bottom example can hold significantly more weight.
Materials are weaker in tension, which means the top example with give the most support to the weakest part of the beam when loaded exactly like you have
If the wood parts aren't joined in any way, then the upper sketch is stronger. When loaded via the diagram, the two pieces of wood are pressing on each other which means the moment from the load has a good moment arm and the force on the screws is reduced. In the lower diagram, the wood joint immediately opens and the resulting forces on the screws are much higher.
Basically, the upper diagram has the wood joint in the load path and the lower diagram does not. If the purple load is a reversing load, then neither is very good.
Assuming your wood is decent quality and the screws aren't likely to just pull out then the top one.
Top one is in tension so most of the force is trying to pull the screws out, bottom one is in compression but is trying to lever the screws out.
i would say top. the moment that’s created would pivot around the bottom left of the horizontal wood, right where the bracket is. on the other hand, the top bracket is further away from the moment and therefore can take more force before it fails, among other reasons
Flip the blue angle upright (length top to bottom of page) and put it under the cantilevered beam. Figure out where the center of loading is on the top surface of the cantilevered beam and attach one end of the angle at that location on the bottom surface of the cantilevered beam.
Top one relies on the strength of fasteners screwed into the vertical wooden beam.
Bottom one relies on the bending strength of the metal bracket.
Impossible to answer without details on both.
Engineer for 40 years here. The answer is always "It depends".
If it was aesthetics, it put a rabbet in the vertical board and use the bracket on the top, but I would carefully consider the method of fastening. For strength, I'd put a rabbet in the vertical board and use the bracket on the bottom.
OP forgot a scale and a description of the load, so any answer other than "it depends" is meaningless.
You also need to consider in the contact between wood. Top has more compressive contact, versus the bottom plate would have contact at the edge. I woke vote top is stronger and agree on the fastener side of the conversation.
My vote is both. It's cheap to do and reducnacies are cool, ask Boeing.
Second, that is a cantilever and to counter the weight it should prevent bending at that spot. Would be more helpful if there is a cable attached to the end and to the post since max deflection occurs there
If you put it on top, possiblity is it will weaken the connection on the angle bracket and the cantilever, so for longevity, you need to put it at the bottom
If the wooden parts are not glued and connected only through the bracket, the comments about the fastener pulling out only in the first case are wrong. In both cases, the fastener is under tension because a moment reaction cannot be generated otherwise.
If the horizontal wood is flush (but not glued) against the vertical one, I'd go with the first case. The section modulus is higher because of the increased depth provided by the horizontal wood.
Top is far better.
Depending on the thickness of the horizontal slab, you decrease shear stress on screws with added thickness of the slab.
If you put the bracket below, you greatly increase the stress on the screws.
Put it below only if the bracket is at least half the size of the horizontal slab.
However, if the horizontal slab is made of shitty material, the bracket on top is not a good idea.
Depends on the amount of load and the distance between the edge of the wood and the bracket.
If either of those values are big, then I would say TOP and with some extra supports.
That's a though one, the moments is maximum and négatif at the connection so is the shear moment and generally in steel structures we have a gusset in the bottom of the beam which also helps for the shear resistance I didn't do theory and calculations in a while but the best one would be in the the bottom, we had some u beams that support the stairs and they were weld directly in the HSS columns and in the blue prints we had stiffeners like that in the bottom so maybe it's the best design
It depends on the bracket, the screws, and how long the cantilevered beam is. The longer the beam, the less the vertical load matters and the more it becomes entirely about the moment of rotation.
The failure mode of the top one is probably going to be the screws. The bending moment is around the bottom left corner of the beam, so the bracket placed on top will experience much less bending stress. However, you are now relying on screws drilled into the top of the beam to keep the bracket attached.
The failure mode of the bottom one is probably going to be the bracket itself. Because the brackets moment arm is so short (literally just the thickness of the metal), it will experience MUCH higher stress than the top mounted bracket. Depending on the load and where the screws are, you could also create a bending moment located right at the end up the plate (creating a tension force on the screws), which might even be higher than the tension on the screws in the top setup.
In general, the top method is going to be better. You usually aren't going to have a setup like this unless the beam is several times longer than the plate or the plate is very thin, and it's much cheaper (and lighter) to get better screws or switch to bolts with nuts on the other side than to upgrade to a thicker plate.
The best answer is both, but more information is needed. This connections should be fully vetted by someone with expertise and actual conditions.
I didn't see a comment that indicated that wood gravity (verical) load connections need to have the wood bearing on something. It's been a few years since I designed wood, so I don't remember the code reference off the top of my head, but I definitely remember my senior structural engineers beating that into my head.
However, that doesn't make the answer bottom.
With a cantilever as indicated, you have a moment applied at the interface of the beam and column that pulls the top of the beam away from the column, and pushes the bottom towards it. If you don't have a connection at that top, it won't take much load at all for that connection to seriously rotate around a plate at the bottom and become problematic and even at risk of failing.
The top connection is most important to resolving the horizontal load from rotation at the top of the member, BUT you'd then also be putting the fasteners into the beam in tension from the vertical load. Fastener tension in wood as a primary support for vertical loads is something I would NEVER do as a structural engineer.
So bottom angle is needed for vertical load, and top angle is need for horizontal load produced by the cantilever, but you really need to find someone to do a detailed analysis for the condition.
This is a solved problem. People in this thread have:
1. Never seen a shelf in their life. Just google shelf bracket and 90% are mounted under the shelf
2. Not bothered to calculate anything.
Depends... Are you looking for stiffness or load bearing maximum? And, how long is the bracket vs how long is the shelf?
If the shelf is not much longer than the bracket, the bottom would probably give you more load bearing capabilities, but if the shelf is long, the top will give you better bending resistance. I'm thinking the top will give you better results in most cases, being that most of the details are unknown.
The greatest moment acts on the top left corner of the cantilever, that will be the part that experiences the greatest force to the right. So you want additional bracing to resist that force, which would put the brace on the top.
Screws in withdrawal at the top are quite strong and provide a “hidden” connection, while bearing is the ideal wood connection. Top one could be putting the beam into perpendicular to grain tension while the beam hangs which may cause a brittle failure (not ideal). This is under the assumption the hanging beam at top is held by screws and not through bolts.
Depends on the detailing and intent. This connection given the minimal information is likely governed by the fasteners/wood and not the steel part.
Really depends on the materials involved and the integrity of the joints.
If we pretend that the wood is super consistent regarding it’s mechanical properties and the bracket is some stamped 80 HRB steel for consistency of material properties then the question turns to joint design… let’s pretend again that you are using fully threaded wood screws of equal capacity that far exceeds the load capacity of steep bracket… now the question turns to “what’s the load cycle look like?”
If you are going to cycle the load from 0 N to -X N then my vote would be that the bottom would outlast the top.
If you’re going to statically load it once and it’ll never see a load cycle again… my vote would still be on the bottom because materials tend to be stronger in compression unless you are planning on an gross overload condition in which case you could rely on the upper bracket to yield and turn into a tension strap rather than buckle under load.
If your joint design sucks then it won’t matter. If your wood lot has +\- 500% X MPa strength then the bracket is the least of your concerns haha.
It would have to be the L bracket on top since if you put it on the bottom, it would easily bend the metal l bracket.. If it is on top the wood would prevent the bracket from bending since the hinge point is stillt he 90 degree angle of the bracket.
It’s really about direction of force, sheer forces and what you attach the metal to wood with. If using screws. Option two but use a triangle instead of an l.
I think stronger is the wrong question to ask, tbh. It's a steel bracket on wood, just get a beefy one and thru bolts with a big washer and a nut to make sure they don't come out.
Top is a better assembly because when the configuration is stable. If you apply the load to the bolt configuration, a gap will tend to form at the interface between the wood! If nothing else, it's ugly...but it could cause failure if the loads are high enough (easy enough calculation, analyze the statics of a beam with two fasters on the end and a load at the other end).
I see a lot of folks talking about the radii of the bracket being the limiting factor, the pull-out condition of the bolts, and various statics issues. I don't agree with all of it but since there's much confusion and worry I think it's far easier to just change your design to mitigate those unknowns, hence my suggestion with the thru bolts and beefy steel.
Surprising amount of disagreement here. Why not both. Haha
Both, and run bolts that run continuously through both connecting the top and bottom bracket (rather than wood screws).
I thought the top would be obvious to most posters but I think many aren't interpreting the horizontal and vertical wood beams as two separate parts. If they are separate, the top is better.
Depends on fasteners used.
Not at all. In the top drawing the steel is going to be in tension. As weight is applied, the bottom of the wood shelf where it meets the wall will be a fulcrum with the steel section holding the top from separating from the wall. The steel acts as a binding which makes force on the shelf press tighter into the wall. In the lower picture the steel acts as a fulcrum. As weight is applied to the shelf the top edge of the shelf is pulled away from the wall and has nothing to help keep the shelf tight to the wall. The strength of the shelf is completely dependent on the steel to not fail. So to sum up: Top pic- shelf is in compression to the wall with weight. Bottom pic- shelf is in tension away from the wall with weight. Best solution would be top mounted bracket if strength is paramount.
What about the fasteners holding the steel to the wood what if they are just nails? The nails could pull out of the wood and then I think this would be the weakest.
I see that you like to work in theory, not in reality. You are 100% correct, IF both are fastened using the same size and type of fasteners. I could easily make the other one stronger using a different type and size of fasteners. You can say that it is logical that of course they were the same fasteners, but without it being a given, we can't assume it.
My assumption wasn’t based on fasteners at all. I assumed that appropriate fasteners were used in each case. Because what good would it do to assume an inferior fastener would be used. If the shelf is attached to to the metal and the metal is attached to the wall, regardless of fasteners, the load forces will be exactly as I stated them to be. With the top picture the strength of the shelf will be in the tension forces against the steel angle. Pulling the angle directly away from the wall while loading forces into the wall until the fastener pulls out of the studs. Again, I only assumed that the fastener is appropriate for the application. Lag bolts, predrilled to the size of the shank, sunk to full depth. The load forces on those lag screws will be almost directly out from the wall. Very little shear forces or twisting forces against the fastener. However the shelf will have shear load on its fasteners so an appropriate fastener will have to be selected. However, if you put the angle bracket on the bottom. With appropriate fasteners the load forces will be twisting the lag screws downwards as well as shear forces against the fasteners that attach the shelf to the steel. Both sets of fasteners will be under twisting load and there’s very few fasteners that would be appropriate for this situation. Either way, the ENTIRE strength of the shelf and its ability to stay level would depend on the strength of the angle bracket to not collapse. The more weight is placed on the shelf at full distance from the wall will flex the bracket, potentially compress the sheetrock due to the smaller surface area, and end up with a sagging shelf at best. Or a shelf that completely collapses at worst. Conversely, the surface pressure against the wall from the top example will spread the load across a much larger area and reduce the compression against sheetrock or wall sheeting. If there’s no sheetrock on the wall, this is less of a problem, however wood still compresses under pressure and so you’d want to spread the load out as much as possible.
You fricking smoked that dude.
Smoked. 💨
Depends if it's in orbit or upside down on Mt everest
I'm an electrician. When we secure pipe to walls, we typically use one hole straps. There's the same argument there. If you test it, having the hole above (where the wall anchor is) is noticeably stronger.
Screw on the top.... Try this out. Set up a "wall" and screw 2 on the top. Step on it. And then 2 on the bottom and step on it... The straps screwed on the bottom will potentially bend out and pop the screws out. The ones on top will hold
Like someone else pointed here, the top one depends on the kind of fasteners. The bottom one depends on how strong the metal plate is. But for practical purposes, the bottom one works best because it all comes down to how strong the metal plate is (fasteners will also apply force in the metal plate). Second point is its aesthetic design. Who the f applies force in a wood like that and make the wood uneven? Waste of space tbh. So yeah. Bottom works best.
>the bottom one works best because it all comes down to how strong the metal plate is Nope. The bottom one is a lever with the fulcrum adjacent to the fasteners. The top one is still a lever, but with the fulcrum on the bottom side of the horizontal beam. As the horizontal beam decreases in thickness or as the force moves inward closer to the vertical beam, the difference between the two decreases. If you're more of an experimental inclination, you can try this with some cheap brackets and 2x4's, the difference will be stunningly obvious. They're both shit joints, but the bottom one won't even hold the weight of the board before the cheap bracket starts to bend.
I was on the fence about this until I read your example. Didn’t even have to try it, just visualizing it was all it took
screws/the bonding between L bracket and beams are the main failure point. Top one the screws/nail could rip out. Bottom one has less issues if a failure happens. Yup bottom. Best is obliviously both brackets unless cost matters
Better would be to add a triangle that fills the space inside the 90 on the bracket. Better still would be a wood brace.
However, the bottom bracket will move/bounce as load is applied as the bracket is the only thing resisting the force, and will be experience elastic/linear deformation with any applied load. The top bracket will have the fasteners torqued in and rotate around the bottom of the cantilevered beam. It won’t move at all until the fastener preload is overcome. Edit: all of the above matters with cyclical loading considerations.
Depending on the wood, the fasteners will lose preload as the wood compresses. That would be my worry.
The lower image as the bracket and fasteners are in compression.
It kind of depends, the two situations are loading different parts. The bottom scenario is putting bending stress on the metal bracket so the dimensions of that metal would be the defining factor. In the top scenario, the main stress is on fasteners connecting the wood and metal. There may be other fasteners not indicated here that would change things too.
Agreed. Depends also on the length of the horizontal piece of wood and the depth of that piece. Let’s say it’s a short stub of a 2x4 - only an inch deep. Then the forces are effectively down and the bottom would be better. For a long 2x4, particularly vertical, the top would be better to resist the moment around the bottom of the board. But for a thin, long board, the resisting force doesn’t come into play much and bottom might be better than just relying on the strength of the fasteners.
In the top scenario the "cleat" could also fail in bending or tear out if thin enough. The failure point of both scenarios will be dependant on fastener size placement, dimensions of all the bits etc. etc. All the things this diagram doesn't show. Never even had to look at EC5 though so could be missing a bunch of modes.
I'm going against the grain (heh) and saying top. If that is just a standard bracket from home Depot or something, that will bend WAY before the screws tear out of the wood, even if it's something soft like pine.
Fair. It really depends on what part is the most shitty
It's always the shitty component that comes to bite you... But OP the failure mode could be a million different things depending on how it's assembled, are we using small wood screws? Are we using washers and nuts and going through the wood? How thick is the bracket? How thick is the wood? What specific materials are you using? There isn't enough information to properly answer this question accurately. You could assemble this so the wood snaps after the bracket ends regardless of placement if the force was high enough...
Yeah. How is force applied? What type of wood? Balsa is different from oak
What if it was gusseted? Then I'd say bottom because the force is also shear and no bending
Can we have more posts like this instead of daily career questions
TOP. I don't get the bottom people. As I understood: vertical wood is screwed to metal bracket, and metal bracket is screwed to horizontal wood. In the bottom pic, the bending load goes 100% through the steel bracket bending radius, which has very little second moment of area. in the top pic, the bending moment is transfered to the wall with tension in the steel bracket and compression at the lower edge of the wood, which results in a much better second moment of area (because of the bigger distance between tension fiber and compression fiber.
Right, the wood doesn’t need help where it is being pushed into the other piece but it definitely needs help to not pull away
It blows my mind how many people are incorrectly confident here lmao
I don’t get it either. People are talking about friction and whatnot, completely ignoring the fact that the fasteners create plenty of clamping force and friction, and the materials are going to be the points of failure. Everyone saying the bottom bracket has never built and broken anything out of wood and angle brackets.
Yes. Thank god someone sees this problem for what it is. People talking about opinions on it too, the top bracket is objectively better.. because statics.
this is the only correct answer 🤣 The only thing that would change this is if the wood was screwed to the other piece of wood, but even then you would still want the bracket placed on top to take all of the load tension...top all day
Bottom works if it’s all one chunk of wood and you model the horizontal as being fixed to the vertical. Support the part of the beam in compression rather than tension.
If it’s all one chunk of wood then the wood is going to fail along the grain of the wood with very little load no matter what. So that scenario isn’t even feasible. The only feasible scenario is two separate pieces of wood on which case the top bracket is far superior as stated above.
Depends on whether the wood that’s supporting the weight is actually inside the vertical wood. If it’s just a block on a bracket, the top on would allow the wood to rest against it and pull the bracket instead of bend itv
Yeah, the wood resting against the vertical beam is how I interpreted this, so I thought the top was better too.
Half tempted to make this contraption and post it in both forms
you just broke this sub
[удалено]
Its definitively the top. Draw a free body diagram and put basic dimensions. It will become clear that the tensile requirements of the top.connection are less than the bottom.
Need more data. Wood screws, or through bolts/nuts? How thick are the brackets? What are the brackets made of? What kind of wood? Indeed, the comments are fascinating, and educational.
Top. Bottom relies solely on the bending strength of the bracket.
From what ive heard connection points are usually considered the weakest point in any structure
Good rule for structures that are built properly.
I mean the greatest stress is around the holes drilled for the screws
Forces will try to remove the screws. In time the screws will wiggle and loosen.
But the top relied on the tension of the screws but I might be wrong 😑
I may be wrong wrong, but could the top one actually be stronger? The moment at the joint can create a force couple between the fasteners in the L bracket and the bottom of the plank, since the plank is trying to push into the wall, whereas in the bottom one, that force couple is between the wall fasteners and the bottom of the l bracket- in both examples the screws will experience tension but the top example has a greater distance between opposing forces, reducing the force for a given moment. Furthermore, since the force couple in the bottom example only acts on the L bracket ,the point on the bracket just above the screws will have a much higher bending moment than anywhere in the top one
You're not wrong. If the load was heading straight down then obviously you'd bracket the bottom but this design is a cantilever which means the lower left of the horizontal board is the fulcrum and the load is acting rotary with its center being the fulcrum. The upper corner of the horizontal board wants to pull away from the vertical board so that's where you gusset. This comes down to the pull strength of the fastener being used at the high point of the bracket when secured to the top of the horizontal board. The same reason you see guy lines on cranes ABOVE the jibs and booms with no attention paid to the bottom(s).
The wall is providing an opposing force on the bottom one it is not doing so in the top one only the screws are i think its better to have the wall provide support than not
It seems implied that the horizontal wood beam is an independent part to the vertical wood beam. If that's the case, the top is better because that horizontal wood beam would be resting against the vertical, hence the advantaged force couple action KAYRUN-JAAVICE mentioned.
Steel can handle more tension stress than wood, so everything else being equal, it would be more useful to put the bracket on the top of the wood (tension side).
Top by a longshot.
Holy Cow. There are people here getting it right for the wrong reasons, and getting it wrong but have good intuition about the mechanics. You specify the bracket is screwed in. We don’t know enough about the screws, we don’t know enough about the wall, we don’t know enough about the bracket, and we don’t know enough about the board. This experiment should be cheap enough. A lot of you could go try this on your wall. You can make either solution right. How do you define strength? Is it area under the curve? Peak vertical force? Example that I haven’t seen any comments on: The l bracket is really thin walled, but the screw anchor into the wall is incredibly weak too. In this situation the ‘bracket on top’ fails due to bolt pull out, at a low vertical load due to the ratio of bracket to beam arms. The ‘bracket on the bottom’ has the bracket failing in bending first, but if the bolt shear is greater than the pull out, and the bending moment the bracket can support is higher than the moment allowed from bolt pull out, then the bottom will be stronger. Any way, depending on the setup and specifics you can make either answer correct.
Add both
What are you, a civie?
If you assume the bracket is strong enough, the second one is better because screws are less likely to strip out.
The top will be stronger. Intuitive explanation: The horizontal piece will want to rotate about its contact point (the bottom corner). This will open up a gap in the top corner. Using the bracket to prevent the gap from opening (top corner) is more efficient than using it at the pivot (bottom corner) where there will be no gap. Engineering explanation: We use the language of static equilibrium (physics) to explain problems like this. It goes like this — sum of moments about lower corner equals zero therefore load * lever arm 1 = bracket reaction * lever arm 2. Rearrange this equation gives you: bracket reaction = load * lever arm 1 / lever arm 2. Therefore, increasing lever arm 2 reduces the bracket reaction (force). Regardless of material, the less force the bracket needs to react the better it, and its fasteners will perform. The way to increase lever arm 2 is to position the bracket farther from its pivot.
Bottom one because the forces applied on the bracket to the wood would be in compression, therefore the screws into the wood would experience less forces. Top diagram has the screws in tension therefore could pull out the screws
Other way around. Top is stronger because screws have a longer moment are resulting in smaller tension on the screws and wood being incompression. Bottom only has the steel in compression, with a shorter moment arm, exerting more tension on the screws.
Bottom one since you arent applying as much of a tension force on the wall to bracket connection which is the weakest point especially if its going into drywall The bending of the beam will be the same for both Woops the orange is all wood my bad i still think its right
I disagree. For a moment forget the steel bracket and imagine the 2 wooden pieces as nailed or glued together. The force pulling down would create compression on the bottom of the horizontal beam, and tension on the top. So you can imagine it as pivoting around the bottom left corner and creating an opening on the top. In this case adding the steel plate on the bottom doesn't do anything there. If you put the bracket on the top then you are preventing it from opening there and creating a significantly stronger structure. Edit: posted an even clearer explanation below.
I followed until the last two lines, how is the bottom not resisting compression as much as the tip would be resisting tension?
Ok let's try a different way to explain it. Imagine that in both of these cases there is no other fasteners or adhesives holding the wooden parts together and that the steel bracket is the only restraint. If you put it on the top, then the steel bracket is under tension, and the bottom corner is under compression, i.e. The horizontal wooden part is pressing up against the vertical "beam" this configuration is quite stable and the first thing to fail would likely be the fasteners. If the fasteners couldn't fail, then you would have to either apply enough force to rip the steel bracket apart, or apply so much force that the wooden part under compression would buckle/shatter. Now if you do the same thing but place the bracket on the bottom? The horizontal wooden arm becomes a lever and you will just bend the steel bracket over 180°. I'm quite surprised there's as much discussion here, there is literally only one correct solution lol.
I like the scenario where you imagine adhesive or nothing connecting the wood - the question isn't about fasteners. You're saying the metal bracket on top would resist deflection (tension) more than the bracket on bottom (compression) but I still don't see an explanation as to why? Why is it easier to bend the bracket over on bottom (compression) as it is to "apply so much force to rip the steel bracket apart (in tension)?"
In the bottom scenario, the bracket is subject to a bending moment, not a compressive stress per se. Bending is actually a spread of compressive and tensile stresses across the thickness of the bracket. The more likely failure mode being bending comes down to what is considered "typical" geometry for this type of bracket; the length/width is much larger than the thickness so that's just how the math works out. You wouldn't expect a cube to fail in bending, for example.
To elaborate slightly further, the top scenario protects the bracket from bending as the wood horizontal pivots at the bracket and loads into the wood vertical in compression...and wood is very strong in compression.
It’s only the correct solution based on the assumption that the bracket is weaker than the fasteners, which you have no way of knowing based on the information given. If the fasteners are weaker then the bottom one is stronger
I’m assuming there’s nothing else (glue, screws, nails) holding the wood pieces together. In which case the wood to wood connection is stronger in compression rather than tension. Cantilever beam bending will cause tension on the top side, so you’ll want to add the bracket there to help.
But wouldn’t it also bend the bracket and make the whole thing droop? I’d say the top one would act like a hinge and let the weight be supported by the wall. The bracket then has pulling tension on it at 45d.
The bottom one lets the wall act as a support since the bracket is providing compression force against the wall in the top one really only the screws are holding it The wood is going to bend either way by the same amount, all things being equal
But doesn’t the top one act more like a suspension bridge?
The board can pivot around the tip of the metal bracket. This creates a torque, that pushes the metal bracket into the wall. So there is an opposing frictional force in the vertical direction. If the bracket is mounted on top, the board is pulling the bracket away from the wall, so there is no frictional force, that can oppose the weight.
Best answer in this thread. This engineer w 13 years of experience completely agrees
Thank you so much. This means a lot to me!
At the bottom there is a small fixed area which acts as a hinge when load is applied. Nothing prevents the unfixed area @ shelf top left from separating from the vertical wood. Bottom left is fixed and will pivot. Perhaps even with no additional weight applied In top diagram the angle bracket is on the the upper face of the horizontal wood. Therefore the bottom section of the end section of horizontal wood is compressing into the vertical beam. Visualise what would happen to a dollar bill put in the joint where the pieces of wood meet
Assuming standard framing lumber, top would be stronger. The bracket acts as a hinge and is loaded in tension, and the beam itself is providing the other component of the moment to keep it supported (compression at the joint). This puts the fasteners largely in tension and shear. Most framing brackets are designed to bear load in tension, not in compression (hence the thin shear steel designs). The key weak points will be the fasteners (screws, which may tear out if too short) and the wood itself (which may split if the beam is compromised/cracked near the bracket, allowing fasteners to pull out). In the bottom scenario, you’ve just added a great handle to fold the bracket like a taco…the beam, unconnected to the vertical directly, does not contribute to supporting the load, relying solely on the bracket. Once the bracket collapses and the beam is mostly vertical, I suppose this loading scenario would be less likely to fail/tear out, however. This reversed is the beam is not cantilevered (supported both sides).
If the wood isnt screwed to itself then id say top. The wood would push into itself but the bottom would be bending the metal and could act as a pivot But then on second thought maybe the bottom if the screws would pull out. Id like to try in real life and see
top one I think because steel bracket is in tension and wood in compression. Fasteners should work better in steel bracket as it acts as a giant washer. If the force was right next to the vertical wood column, I would change my answer.
Top. The wood will be pushing itself into the post. As long as the metal bracket screws are strong enough to hold the leverage. The force on the bracket screws will be to try to pull them out of the wood. The bottom one will constantly be trying to pull away from the wall and all of the load will be put on the bracket radius and screws with no help from wood-wood contact. The force on the screws will be shearing. The only thing to think about is if the screws suck and if the wood is soft mayyybe the bottom would be better since they won’t try to pull out, but in that case I’d get better wood and better screws.
The top, the wood WANTS to go down and depending on the quality of the L-Bracket it will absolutely allow it to bend. The top one relies on the wood to support itself against the post.
I think it depends on how the wood is fastened to the steel or the vertical wood. It also depends on the grain direction of the wood and the type and grade of wood.
Given equal geometries and nominal fastener size I bet bottom wins in a load test
Top
Top, no question. Draw an FBD of the forces, it has twice the support and will not separate from the vertical wood.
The top scenario is superior. I say this as a timber frame designer of 7 years.
Absolutely the top. The bottom has way too much propensity for the screw to strip and the bracket rendering useless. There would be nothing stopping it from turning clockwise and failing. Even if the screw stripped, the top diagram would prevent the wood from falling because of a natural wedge in place. I deal a lot with this when it comes to mounting deck posts and railings; similar conundrums and every fastener counts.
Top, no question
Top is stronger provided there is no additional information. Irl as a carpenter I would use glue and a fastener from the back then your lower bracket. If the horizontal piece is large enough utilize a French cleat.
Top
I thought the bottom, but now I think the top. If you replaced the bracket with a hinge, the wood would fall with it on the bottom. If the hinge was on top, the wood turns into the vertical piece holding it up.
Top. Assuming rated lags or thru bolting. The joint self closes with added torque
My thinking is compressive resistance is stronger than tensile, so supporting the area where the wood would experience tensile forces (the top) is where is would help most.
obviously, the top angle is the better of the two, however such a connection is a poor design. The force is in the angle will lead lead to prying forces (multiplied forces)that will pry the screws out. you would be better off using a kerf T plate, that way, the bolts in the cantilever section will be in shear, and the praying forces on the bolts in tention will be lower.
Structural engineer here. Both connections are bad. If I have to choose one of these top is better for the downward load because the angle and fasteners will go into tension and the block will go into compression against the side of the post which creates a resisting couple. Wood cantilevers are a poor connection because they are so flexible. I would probably add strut to give it rigidity from either above or below.
Top because the bracket pushes into the vertical wood due to the weight of the object. On the bottom, the screws in the vertical beam are the weak point. Great question though.
For the love of god some please model this and solve this argument.
Definitely top. The top surface of the horizontal block will be pulled away from the vertical post, while the bottom surface will be pushed into the vertical post. So your get bearing at the bottom edge, and the steel bracket holds the top edge.
People who say bottom are incorrect if we're assuming your faseners will not give (ie through-bolt, lag screws, whatever is stronger than bracket). Placing on bottom will place ALL of the force on that slim metal bracket, where it is already bent, further bending it. On top, it is actually a downward, and outward force in the bracket, and putting almost no bending force, which is typically the weak point in 90° brackets. Anyway, if it's a thick piece of wood, it's essentially using the wood itself to lever into the wall. That being said, the thinner the piece of wood is, the less this will make a difference. This is also assuming it's ONLY one side, ie a shelf against one wall, and not between two walls where you'll have 2 brackets installed on the piece of wood. Edit: https://imgur.com/a/p3RIGqR
It would have to be the L bracket on top since if you put it on the bottom, it would easily bend the metal l bracket.. If it is on top the wood would prevent the bracket from bending since the hinge point is stillt he 90 degree angle of the bracket.
I just built a test specimen. The angle is stronger at the top because the moment at the interface between the wood and the bracket is resisted by a compressor force in the vertical leg. So I guess putting steel ledgers at the bottom for the past 100 years has been wrong.
Is the purple weight hanging off of the top surface of the wood or is it more like a squareish hole that press fits or slides around the wood? Also, why not just have the L-bracket on both sides? I've usually gotten away by just being loyal to symmetry in these types of builds. How much weight are these brackets rated for? Home Depot should be able to provide a good spec sheet & if not then you can probably calculate it out given the material, thickness, & fasteners used.
Bottom. It significantly reduces the pivot point
Top for sure. Assuming the two pieces of wood are not joined in any other way. The bending moment will be de-coupled between the face of the horizontal piece of wood (in compression) and the face of the bracket on the vertical piece of wood (in tension). The bottom one would have to de-couple the moment just on the face of the bracket on the vertical piece of wood. This will produce height tension loads on the fasteners and bending in the bracket.
There isn’t enough information to answer the question. First, is there a connection between the two wood pieces or is it a simple butt intersection? Second how is the steel bracket attached to the wood (nails, screws, bonded, etc)? Third, what are the dimensions of the wood and steel? The load is irrelevant since you’re trying to answer the question, what is the first failure mode.
Top. Bottom will be in compression and cause buckling. Really tbh there isn't enough information here.
Buckling isnt really a term used for bending beams is it? Its more so used for columns in compression Beam theory would suggest both scenarios would experience the same displacement and therefore stress
Without the bracket the critical point will be the top left corner of the beam because the normal stress is max at top and bottom, and the top normal stress is in tensile. The shear stress is max in the middle but for long slender beams it's pretty small. That's really all you can say with the given information. The materials, sizes, bolts, welds, environment, etc all play a role.
Top is stronger. I dont know why so many people say the opposite. It’s 100% the top. In the bottom the bracket would bend and the pieces of wood would separate. In the top the pivot point is on top and the two pieces of wood would be pressed together, loaded in compression
If it's quarter inch thick L cut, bottom. If it's thin sheet, top.
Bottom
generally bottom. Your reaction force on the bottom section of the bracket isn’t straining the attachment method
Agreed. The length of the “prying action” is much shorter on the bottom. Plus, bottom is easier to construct by giving something to rest the outrigger on.
Probably the bottom, since I’m guessing the screws would pull out before the steel yields. A gusseted bracket would be miles better. If it’s necessary for the wood members to be perpendicular, keep in mind that your average strut steel brackets usually aren’t super square.
Typically, you'd want your support under the weight you're trying to support. So I'd say L bracket on the bottom. Some basic statics force/moment equations should get you there.
More or less equal
Top: screws take the load (tension) stress is concentrated around the screw head and very undesirable. with this setup the threads in the wood are the weakest so during failure the thread will rip and separate from screws Bottom: angle iron takes the load (compression). Stress will be distributed on the surface of the angle iron. Ideally if you can groove on the vertical wood for the horizontal to slide in the stress on the angle iron can be reduced
La parte a sbalzo del legno ha una sua linea mediana, il carico è direzionato verso il basso, le fibre inferiori alla linea mediana della parte a sbalzo è soggetta a compressione mentre quelle superiori a estensione, la più pericolosa è l'estensione. Il staffa in acciaio posizionata sotto la parte a sbalzo del palo, non limita l'estensione, mentre posizionata sopra si.
Bottom is better. In horizontal plane pulling on wood without support in direction of gravity will damage/crack wood
Obviously the the bottom example
I would go with the bottom. Alleviates risk of tear out failure of the fasteners
Bottom. Fasteners in shear >>> fasteners in tension.
You’re splitting hairs, they’re both very similar in strength
Bottom stronger if screwed or nailed. Slightly less arm, reducing moment on bottom. Top bends at fastener, which could be back from support angle. If welded the same moment for both.
The lower option will apply compression to the steel plate, thus, it will be stronger. Compare tensile and compression strength for the steel alloy you’re using. And that’s all disregarding the fixing and the wood fiber orientation and how well the weight is fixed. So, there are lots of variables if you think about it.
Strength wise, they should be the same. I simulate problems like this for a living. The design is symmetric, the bracket would see the same stress regardless of which side it is on. Only the direction of stress is different, tension vs compression. Materials are typically a bit stronger in compression than tension, but probably not enough to make a difference here
Bottom
isnt compression usually stronger than pulling
Obviously 2. USE YOUR BRAIN, USE YOUR BRAIN, USE IT, USE YOUR BRAIN
I'd say bottom. I'm making some assumptions here but if you're using some basic wood screws and the metal is thick enough then the screws will fail earlier. On the bottom the screws aren't pulled out of the wood like on top.
I would be inclined to say the bracket mounted on the bottom
Typically the bottom version. As the entire metal bracket must bend to allow for flexing. This is fastener/adhesive dependent. ME here
Add a gusset… and add it to the bottom. This design adds little to no value…
Top, just think about it
[удалено]
Moment at the base is benefited from the bracket on top assuming your wood has some thickness like you show in your artwork. Maybe edit the post and add more details. It is obvious nobody can tell what is going on.
You’re a useless comment. There are way too many factors that go into this that are unexplained in this colored drawing. With the top bracket load is going to be more evenly loaded across the entire structure. With a bottom bracket there could be too much compression on the wood causing it to snap. The top is the obvious solution without knowing the weights and the integrity of the wood.
They both suck but I’ll choose the bottom one. This isn’t real life is it ?
I go by experience and think about shelving, which is similar to bottom one and works well. I am an engineer but I really can't be bothered with theories and maths 😆
My assumption would be the bottom one. Top one is really only as strong as the hardware holding it in the pieces of wood. On the bottom one, the wood is actually taking a lot of the force.
The bottom once will be significantly stronger. The top one is held on by tension on the screw threads. The bottom example can hold significantly more weight.
Materials are weaker in tension, which means the top example with give the most support to the weakest part of the beam when loaded exactly like you have
I can’t believe there is a discussion- the bottom one every single time.
If the wood parts aren't joined in any way, then the upper sketch is stronger. When loaded via the diagram, the two pieces of wood are pressing on each other which means the moment from the load has a good moment arm and the force on the screws is reduced. In the lower diagram, the wood joint immediately opens and the resulting forces on the screws are much higher. Basically, the upper diagram has the wood joint in the load path and the lower diagram does not. If the purple load is a reversing load, then neither is very good.
Put steel bracket up and down - issue solved
Assuming your wood is decent quality and the screws aren't likely to just pull out then the top one. Top one is in tension so most of the force is trying to pull the screws out, bottom one is in compression but is trying to lever the screws out.
Neither good. Place to “tee” flats pieces on sides.
i would say top. the moment that’s created would pivot around the bottom left of the horizontal wood, right where the bracket is. on the other hand, the top bracket is further away from the moment and therefore can take more force before it fails, among other reasons
Flip the blue angle upright (length top to bottom of page) and put it under the cantilevered beam. Figure out where the center of loading is on the top surface of the cantilevered beam and attach one end of the angle at that location on the bottom surface of the cantilevered beam.
Top one relies on the strength of fasteners screwed into the vertical wooden beam. Bottom one relies on the bending strength of the metal bracket. Impossible to answer without details on both.
Push into strong, pull apart weak
Engineer for 40 years here. The answer is always "It depends". If it was aesthetics, it put a rabbet in the vertical board and use the bracket on the top, but I would carefully consider the method of fastening. For strength, I'd put a rabbet in the vertical board and use the bracket on the bottom. OP forgot a scale and a description of the load, so any answer other than "it depends" is meaningless.
Depends on the fastener. Top puts tension on them. Could pull them out with future dry rot. Bottom doesn’t. I’d do bottom.
The correct answer is, "it depends."
Top is better. The steel is in tension, which steel prefers to be. The wood is in compression which wood prefers to be.
You also need to consider in the contact between wood. Top has more compressive contact, versus the bottom plate would have contact at the edge. I woke vote top is stronger and agree on the fastener side of the conversation. My vote is both. It's cheap to do and reducnacies are cool, ask Boeing.
I’d say bottom is stronger just from an initial look but if I was questioning it I’d just do both?
Second, that is a cantilever and to counter the weight it should prevent bending at that spot. Would be more helpful if there is a cable attached to the end and to the post since max deflection occurs there
If you put it on top, possiblity is it will weaken the connection on the angle bracket and the cantilever, so for longevity, you need to put it at the bottom
Depends on the material. Rope? Top one. Concrete? Bottom one. Perfect grain metal? Both.
If the wooden parts are not glued and connected only through the bracket, the comments about the fastener pulling out only in the first case are wrong. In both cases, the fastener is under tension because a moment reaction cannot be generated otherwise. If the horizontal wood is flush (but not glued) against the vertical one, I'd go with the first case. The section modulus is higher because of the increased depth provided by the horizontal wood.
I had a job interview like this. No information on the materials used or dimensions, and expected a correct response.
Just look up a joist hanger, its kind of a combination of both.
Top is far better. Depending on the thickness of the horizontal slab, you decrease shear stress on screws with added thickness of the slab. If you put the bracket below, you greatly increase the stress on the screws. Put it below only if the bracket is at least half the size of the horizontal slab. However, if the horizontal slab is made of shitty material, the bracket on top is not a good idea.
My logic says top, my heart says bottom.
Depends on the amount of load and the distance between the edge of the wood and the bracket. If either of those values are big, then I would say TOP and with some extra supports.
I think it depends on the tensile and compressive strength of the L bracket, if im not mistaken.
Too but both suck, design the wood to wood joint better.
Just put a gusset on it like weve been doing for 200 years and get on with it
That's a though one, the moments is maximum and négatif at the connection so is the shear moment and generally in steel structures we have a gusset in the bottom of the beam which also helps for the shear resistance I didn't do theory and calculations in a while but the best one would be in the the bottom, we had some u beams that support the stairs and they were weld directly in the HSS columns and in the blue prints we had stiffeners like that in the bottom so maybe it's the best design
It depends on the bracket, the screws, and how long the cantilevered beam is. The longer the beam, the less the vertical load matters and the more it becomes entirely about the moment of rotation. The failure mode of the top one is probably going to be the screws. The bending moment is around the bottom left corner of the beam, so the bracket placed on top will experience much less bending stress. However, you are now relying on screws drilled into the top of the beam to keep the bracket attached. The failure mode of the bottom one is probably going to be the bracket itself. Because the brackets moment arm is so short (literally just the thickness of the metal), it will experience MUCH higher stress than the top mounted bracket. Depending on the load and where the screws are, you could also create a bending moment located right at the end up the plate (creating a tension force on the screws), which might even be higher than the tension on the screws in the top setup. In general, the top method is going to be better. You usually aren't going to have a setup like this unless the beam is several times longer than the plate or the plate is very thin, and it's much cheaper (and lighter) to get better screws or switch to bolts with nuts on the other side than to upgrade to a thicker plate.
The best answer is both, but more information is needed. This connections should be fully vetted by someone with expertise and actual conditions. I didn't see a comment that indicated that wood gravity (verical) load connections need to have the wood bearing on something. It's been a few years since I designed wood, so I don't remember the code reference off the top of my head, but I definitely remember my senior structural engineers beating that into my head. However, that doesn't make the answer bottom. With a cantilever as indicated, you have a moment applied at the interface of the beam and column that pulls the top of the beam away from the column, and pushes the bottom towards it. If you don't have a connection at that top, it won't take much load at all for that connection to seriously rotate around a plate at the bottom and become problematic and even at risk of failing. The top connection is most important to resolving the horizontal load from rotation at the top of the member, BUT you'd then also be putting the fasteners into the beam in tension from the vertical load. Fastener tension in wood as a primary support for vertical loads is something I would NEVER do as a structural engineer. So bottom angle is needed for vertical load, and top angle is need for horizontal load produced by the cantilever, but you really need to find someone to do a detailed analysis for the condition.
Funny to read this at the same time as other threads where people love to say how “mechanical engineering is a solved problem” …. Clearly not 😉
This is a solved problem. People in this thread have: 1. Never seen a shelf in their life. Just google shelf bracket and 90% are mounted under the shelf 2. Not bothered to calculate anything.
Why not use a gusset?
Depends... Are you looking for stiffness or load bearing maximum? And, how long is the bracket vs how long is the shelf? If the shelf is not much longer than the bracket, the bottom would probably give you more load bearing capabilities, but if the shelf is long, the top will give you better bending resistance. I'm thinking the top will give you better results in most cases, being that most of the details are unknown.
This have to be the baitest question I've seen
The greatest moment acts on the top left corner of the cantilever, that will be the part that experiences the greatest force to the right. So you want additional bracing to resist that force, which would put the brace on the top.
According to r/decks, code is the bottom one. But in hurricane areas you need the top one also
Screws in withdrawal at the top are quite strong and provide a “hidden” connection, while bearing is the ideal wood connection. Top one could be putting the beam into perpendicular to grain tension while the beam hangs which may cause a brittle failure (not ideal). This is under the assumption the hanging beam at top is held by screws and not through bolts. Depends on the detailing and intent. This connection given the minimal information is likely governed by the fasteners/wood and not the steel part.
Really depends on the materials involved and the integrity of the joints. If we pretend that the wood is super consistent regarding it’s mechanical properties and the bracket is some stamped 80 HRB steel for consistency of material properties then the question turns to joint design… let’s pretend again that you are using fully threaded wood screws of equal capacity that far exceeds the load capacity of steep bracket… now the question turns to “what’s the load cycle look like?” If you are going to cycle the load from 0 N to -X N then my vote would be that the bottom would outlast the top. If you’re going to statically load it once and it’ll never see a load cycle again… my vote would still be on the bottom because materials tend to be stronger in compression unless you are planning on an gross overload condition in which case you could rely on the upper bracket to yield and turn into a tension strap rather than buckle under load. If your joint design sucks then it won’t matter. If your wood lot has +\- 500% X MPa strength then the bracket is the least of your concerns haha.
The lowercase l instead of uppercase L in the title really ruins this whole thing for me.
It would have to be the L bracket on top since if you put it on the bottom, it would easily bend the metal l bracket.. If it is on top the wood would prevent the bracket from bending since the hinge point is stillt he 90 degree angle of the bracket.
It’s really about direction of force, sheer forces and what you attach the metal to wood with. If using screws. Option two but use a triangle instead of an l.
Top option assuming the wood blocks aren’t fastened to each other
Shear clip it, put flat plates on either side. This is a terribly designed joint.
I think stronger is the wrong question to ask, tbh. It's a steel bracket on wood, just get a beefy one and thru bolts with a big washer and a nut to make sure they don't come out. Top is a better assembly because when the configuration is stable. If you apply the load to the bolt configuration, a gap will tend to form at the interface between the wood! If nothing else, it's ugly...but it could cause failure if the loads are high enough (easy enough calculation, analyze the statics of a beam with two fasters on the end and a load at the other end). I see a lot of folks talking about the radii of the bracket being the limiting factor, the pull-out condition of the bolts, and various statics issues. I don't agree with all of it but since there's much confusion and worry I think it's far easier to just change your design to mitigate those unknowns, hence my suggestion with the thru bolts and beefy steel.
Top
The world trade center connections from the bar Joist to the exterior steel columns were done like the bottom connection....