## Welding Capacity Calculation

## Welding Capacity Calculation

(OP)

Hello!

P1 and P2 have exactly the same conditions except top, bottom horizontal welding.

I thought P2 could support greater vertical load.

But...

Which one do you think can support greater load? Why?

Thanks!

JW

R

P1 and P2 have exactly the same conditions except top, bottom horizontal welding.

I thought P2 could support greater vertical load.

But...

Which one do you think can support greater load? Why?

Thanks!

JW

R

## RE: Welding Capacity Calculation

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## RE: Welding Capacity Calculation

If the welds are all the same effective throat and you ignore any bearing compression development with the embedded plate.

The two configurations have equal capacity using an elastic analysis because the elastic section modulus Sx is unchanged.

My Personal Open Source Structural Applications:

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## RE: Welding Capacity Calculation

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

## RE: Welding Capacity Calculation

## RE: Welding Capacity Calculation

_{x(bottom)}of one configuration becomes the S_{xtop}of the other and vice-versa. I believe that is what Celt83 was alluding to in his identification that the Sx would be the same.## RE: Welding Capacity Calculation

The only difference will be which is Sw,top or bottom with the same applied moment = P*e, consistent effective weld throat, and no compression development with the embed.

for Bending stress:

In the P2 orientation the max unit stress on the weld will be a compressive stress at the bottom of the vertical weld lines, P*e/Sw,bottom

In the P1 orientation the max unit stress on the weld will be a tensile stress on the top of the vertical weld lines, P*e/Sw,top

However with the flipped orientation Sw,bottom for P2 is = Sw,top for P1, so the magnitude of the stresses will be equal

For Vertical Shear Stress:

In all cases the contribution to the unit stress from P is just P/A,weld, where A,weld is assumed to equal to total length of weld.

With the magnitude of the weld unit stress being √ σ,shear^2 + σ,bending^2 , resulting in equal design unit stresses for either orientation.

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## RE: Welding Capacity Calculation

## RE: Welding Capacity Calculation

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## RE: Welding Capacity Calculation

_{TOP}= A_{BOT}, then for same bending on the cross section T ≡ C, and lever arm distance remains the same, so the capacity.## RE: Welding Capacity Calculation

I agree with you... P2 can support greater vertical load. If we consider shear , both alternatives have exactly the same shear capacity. However for bending, P1 upper sections of vertical weldments will experience more tension stress and will start yielding before P2 case. This is due to bearing compression development with the embedded plate which the NA will be lower than P2 case.

## RE: Welding Capacity Calculation

BA

## RE: Welding Capacity Calculation

and to reiterate... it's easier to weld... seems like a win win situation.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

## RE: Welding Capacity Calculation

## RE: Welding Capacity Calculation

For P1, the horizontal weld does nothing if the angle is placed firmly against the embedded plate - in this case there is direct bearing between angle and plate. If there is a gap then the weld must transmit the compressive forces, but it is more likely that the angle would be placed tight against the embedded plate.

For P2, I don't think the horizontal weld is fully effective until the vertical welds start to fail. Think about how the angle has to deform to deliver load to the horizontal weld...you would develop separation between the angle and embedded plate, which can't happen because of the vertical weld.

For both cases the horizontal weld is mostly for show. I consider both details to be equal. P2 would be better if you could flip the angle and put the vertical leg down and keep the weld on top.

## RE: Welding Capacity Calculation

While we all appreciate your enthusiasm and contributions to this forum, you do tend to post incorrect or misleading statements with alarming frequency.

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just call me Lo.

## RE: Welding Capacity Calculation

The calculation was to clear up my comment made before - strength-wise, the two cases are identical.

I don't quite understand your bringing "bearing" into traditional weld design calculation. Question for you, don't you count the horizontal weld for shear, though it's not needed for compression?

## RE: Welding Capacity Calculation

I think that even as shown, the P2 horizontal leg will contribute slightly to the weld group capacity because of some weld ductility at the top corners. But depending on the proportions, I would be unlikely to rely on it fully or even partially due to the concerns CANPRO raised.

----

just call me Lo.

## RE: Welding Capacity Calculation

I would count the horizontal weld for direct shear resistance, but in comparing the two details this contribution is identical.

## RE: Welding Capacity Calculation

Do not agree with these statements if your going to rely on the compression development between the angle and the embed then flipping the angle so the flexible leg vs the rigid heel works to develop the compression block is an inherently worse condition.

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## RE: Welding Capacity Calculation

I guess I understand the stress concentration/raiser problem at the weld corner. My mistake to use such example. But even with breaking up the weld lines, will both case stay the same? Please show me the "correct" method, thanks.

## RE: Welding Capacity Calculation

(For clarity, my comment is dealing entirely with the moment eccentric to the embed face. I'm not concerned here with the shear parallel to the face.)

----

just call me Lo.

## RE: Welding Capacity Calculation

agree, however in my experience more often than not the embed plate is askew and the angle seat is constructed with some small gaps filled with weld material. So so you'd need to work thru the weld deformation prior to engaging the plate in bearing, so the conservative design capacity would only consider the welds effective, then I have the bearing compression block as back pocket help if needed.

If we are talking about field welds absolutely agree, if were talking about a shop weld the weld to the angle toe probably requires more material as its flare bevel weld because the toe fillet vs standard fillet at the right angle heel. If this is Bent plate and not an angle then I am in full agreement with your statement.

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## RE: Welding Capacity Calculation

For load in the downward direction, parts in initial contact, and a sufficiently stiff angle (which may or may not be present), the peak tensile stress is at the top of the weld group.

As you illustrate, because of the neutral axis location, the tensile stress (stress=M/S) at the top is lower for the "P2" configuration (your 0.023 when using a unit moment) than P1 (0.035)

As a general rule, I'm rarely concerned with the compressive stress in cases like this because of the possibility of bearing between the angle and embed plate (e.g. the weld isn't loaded). So I would check the combined tensile and shear stress at the top of the group and call it a day.

(Of course, some rare geometries and/or applications will change the validity of that last statement.)

----

just call me Lo.

## RE: Welding Capacity Calculation

If you go with this analogy a smaller moment arm begets larger tension/compression couple forces required for equilibrium which results in higher tensile stresses in the weld.

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## RE: Welding Capacity Calculation

The method used was the classic elastic method for stress analysis, with the weld treated as a line. I don't know another method/approach, and would like to learn. Can you share, please.

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You are entitled to your approach, but it's something I wouldn't do - weld the tension side only. Is this statement sounds "incorrect" or "misleading", please advise.

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BA

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P2 would carry more load because P1 would probably be on the floor!

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P2 carries more because P1 will carry zero. P1 would pivot on the horizontal weld.

Celt83, I saw your reply to my comment...pretty busy so I didn't read over that closely, but I hope to later.

## RE: Welding Capacity Calculation

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Okay, so the horizontal weld in P2 is better placed than the one in P1; so why is this not still true when vertical welds are added?

BA

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They would be identical, r13, so the failure loads would be the same.

BA

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BA

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I don't get that. The geometry center of the angle does not align with weld center then. Can you elaborate your view?

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BA

## RE: Welding Capacity Calculation

If you allow compression bearing development:P2 will always result in the higher capacity

If you do not rely on compression development between the beam and embed and define failure as weld rupture:P2 and P1 have equal design capacity

P2 is ultimately a safer condition because after you reach the failure criteria of the vertical weld lines in compression you then have the additional redundancy of the compression bearing development creating an additional load equilibrium condition.

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

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## RE: Welding Capacity Calculation

BA

## RE: Welding Capacity Calculation

So back tracking a bit the better connection detail would be to match the AISC recomendations.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

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## RE: Welding Capacity Calculation

BA

## RE: Welding Capacity Calculation

So provided the shear stress is kept within allowable limits for the external load applied to the angle it doesn’t matter which way round the angles welded.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

## RE: Welding Capacity Calculation

Whatever AISC, Celt83 or desertfox says, I think the answer is P2.

EDIT: In fact if they were both built properly , P2 would be a great deal more than P1.

BA

## RE: Welding Capacity Calculation

From analytical point of view, all mentioned parties are correct. You are correct on your conviction, from material strength point of view, as there are literatures indicating that the transverse weld has higher strength than the vertical weld. Correct me, if I am wrong.

## RE: Welding Capacity Calculation

You are not wrong about the strength of a weld at 0 or 90 degrees to the line of the weld, but there is the same amount of transverse weld in both schemes, so that does not account for my statement above.

The reason is simply that the top transverse weld has a moment arm equal to the height of the angle. The bottom weld does not. In both cases, failure will be by the angle rotating about the bottom. Scheme P1 will fail by tearing of the vertical weld at the top. Scheme P2 will fail when the top transverse weld pulls away from the embed plate while the bottom of the angle bears directly against the embed plate without the need of a weld. The difference between load P1 and P2 will be substantial.

BA

## RE: Welding Capacity Calculation

Wow! This is not a simple problem.

Thank you very much for diverse opinions!

I would like to use r13's elastic analysis approach which referred to the specific condition of M=P*e=1.

According to r13's analysis, as P (M) increases, failure will start where stress 0.035 is with M=1.

These failures happen at the end tips of vertical welding portion (farthest from horizontal welding);

P2 at the compression (bottom) area, and P1 at the tension (top) area.

In the case of P2, the bottom edge of angle can take compression after welding is crushed

if contact/bearing between angle and embed plate is possible as some engineers mentioned.

But, in the case of P1, as soon as failure starts at the end tip of welding, it will proceed like brittle failure.

Therefore, P1 and P2 have the same capacity as long as they are within the elastic limit.

But, beyond the elastic limit, P1 will cause brittle failure

while P2 can resist additional load as long as it can take advantage of bearing strength from embed plate.

So, P2 is better as some engineers' intuition pointed to...

Questions/Lessons:

Do you check the compression stress, compression failure of welding?

Many engineers used elastic analysis. What about inelastic/plastic method?

Don't they provide another insight?

Thanks!

JRW

## RE: Welding Capacity Calculation

Even if that were true, that is not the capacity by definition. The capacity is the failure load and that does not occur while everything is elastic.

But beyond that, even within the elastic limit, the two schemes are not equivalent because in scheme P2, the bottom of the angle bears directly against the embed plate. That is equivalent to a full transverse weld in compression which cannot resist applied shear.

BA

## RE: Welding Capacity Calculation

We have to set the two conditions on a equal base. In general, we won't adopt P1 for many practical reasons, but if necessary (for no choice), would configuration of P1 support a lesser load than P2, assuming all other materials are adequately sized for the load. The failure mode addressed by you is one of the practical reason that we shy away from P1, but it does not affect the designed strength, if designed/calculated correctly. I think we are recognizing/responding the OP's question from different angles, though the conclusion is the same - The weld configuration of P1 and P2 will yield same computational strength, but P2 is preferred for practicalities.

## RE: Welding Capacity Calculation

That seems to be what you are saying. It is not what I am saying. If properly constructed, P1 and P2 do not yield the same strength, computational or otherwise. Scheme P2 is preferred because it is stronger.

BA

## RE: Welding Capacity Calculation

Now if you use this analysis it would show that the weld shearing stresses for the two configurations would be the same in magnitude and as previously stated if within the elastic limit of the materials involved, the use of either would suffice, why would one want to start analyzing what happens after yield, at that point the joints already failed at the design stage.

How then do we calculate the additional force or the additional strength that P2 will give us over P1?

Or put another way lets see the calculation that shows the magnitude of P2 and compare it with that of P1 bearing in mind we can calculate P1 from weld stress analysis of treating welds as lines.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

## RE: Welding Capacity Calculation

I believe that the P2 configuration would carry about 11/7 or 1.57 times as much as the P1 configuration assuming a square arrangement of welds and e of 3/4 times angle leg length. Please see below.

BA

## RE: Welding Capacity Calculation

I guess you assume the entire section has reached yield as shown. But the neutral axis does not seem right.

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Cant see how you get Mmax for P2?

Looking in Mechanical engineers data by james Carvill the Z value for the weld treated as a line at position P2 is given by

Z= (2bd+d^2)t/3 at the top

Z= d^2(2b+d)t/(3(b+d)) at the bottom

Z = bending modulus, d = depth , b= width

So the bending modulus Z at the top and bottom are different as stated by others in previous posts, however it doesn't matter which way up you weld the the angle all that happens is the Z values top to bottom switch over but the overall capacity of the weld to take bending remains the same, which is exactly what Celt83 stated on the 12th October, or at least thats how I read it.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

## RE: Welding Capacity Calculation

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http://web.aeromech.usyd.edu.au/MECH4460/Course_Do...

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## RE: Welding Capacity Calculation

I have included a snippet from your reference below. Please note that in North America, the symbol Z represents plastic modulus and the symbol S represents section modulus. I was (or thought I was) using plastic properties for my calculations. I'm not sure why that is wrong, but in any event, that is not the main source of our difference. In fact, using your formulas, the discrepancy is even larger.

Using your formulas and recognizing bearing at the bottom of the angle, the failure load of P2 in bending is 2.67 that of P1.

P1 = 8w/3 = 2.67w whereas P2 = 21.3w/3 = 7.11w.

It boils down to the question of whether or not you recognize direct bearing of the angle against the embed plate. If you do (and I do) then the P2 connection is much superior to P1.

Even if you don't recognize direct bearing, P1 is liable to unzip at the top of the vertical welds whereas P2, at worst will crush a bit of side weld, causing it to come into direct bearing with the embed plate.

BA

## RE: Welding Capacity Calculation

The treatment of welds as lines doesn’t recognise direct bearing if you look at the last link I gave on the first page it clearly states that the weld only is analysed it also makes reference to Blodget and various other references including Shigley.

So by assuming that the weld only carries the load for either configuration is a more conservative calculation, further if there is no direct bearing as the last poster steveh49 alludes to then you could end up with at joint that fails.

## RE: Welding Capacity Calculation

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I think I have answered that question, notwithstanding opinions to the contrary.

BA

## RE: Welding Capacity Calculation

In a way, it is not more conservative because it puts an extremely poor detail, P1, on a par with an extremely good detail, P2. Failure is far more likely to occur with the former than the latter.

BA

## RE: Welding Capacity Calculation

I disagree totally with you there, if you calculate the Z values on either side of the neutral axis for configuration P1 or P2 the overall Z is the same however the lower value of Z is the one above or below the neutral axis without the horizontal weld, so you would size the weld on the lower value of Z, that in turn ensures that the weld is adequate on the weaker side of the joint and keeps the stresses well within the allowable. I would rather design on that basis than assume something you can’t guarantee (bearing compression)and run the risk of over loading a joint.

Doing it using the elastic method ensures that the joint is safe and if there was any bearing compression to be had, then that would be a bonus. It’s worth noting I have never seen any codes or specifications that take into account bearing compression in welded joints.

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BA

## RE: Welding Capacity Calculation

At the case for P1, wasn't there a force of C1 = 4fy (see sketch). With or without weld, the compression was counted. I am confused on your used of full member depth as the lever arm.

## RE: Welding Capacity Calculation

That is really what the disagreement has been about. It is not a theoretical disagreement as we all agree (I think) about the capacity of the weld when direct bearing is not considered. When direct bearing is considered, reactions T1 and C1 are separated by 4 units.

If the back surface of the angle or the exposed surface of the embed plate is not planar, the argument is that there could be bearing somewhere between b and c (see below). If that were the case, however, inspection should reveal a gap at point b, in which case steel packing could be added between the two surfaces. It is also true that, as P2 is increased, any gap at point b will tend to close.

BA

## RE: Welding Capacity Calculation

## RE: Welding Capacity Calculation

I have copied an extract from the Steel Construction Manual see attachment it clearly states the calculation doesn't take account of any compression connection between mating parts, which as BAretired said is were we differ.

Also I have pasted the link to the site for reference.

https://www.bgstructuralengineering.com/BGSCM14/BG...

## RE: Welding Capacity Calculation

We are in line with each other. The compression BA mentioned is something else, that is usually not considered in the weld design. Thanks for the reference, which is quite illuminating.

## RE: Welding Capacity Calculation

I might do the same, especially now after all this discussion, but if you were to ask me which would carry more load, the weld as shown on your sketch or a weld placed on the bottom, I think you know what my response would be.

BA

## RE: Welding Capacity Calculation

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BA

## RE: Welding Capacity Calculation