Steel lintel 2

[mike0123m]

I came across a design problem that I am not sure if I have enough information to solve. I have a 6x6 steel angle supporting 500 plf of brick. Deflection is limited to L/600. What is the minimum thickness of the angle? I am not sure how to go about this when the span of the lintel is unknown.

 

[desertfox]

Hi mike0123m

Yes I agree, I suppose you could select a length like say 10 metres or whatever and workout the thickness then pro-rata it if and when you do now the length.
Why haven't you got the length whats the reason for that?

desertfox

 

[mike0123m]

I saw the question in a textbook and thought it was odd that the length was not given. I thought there might be a way to solve it so I decided to post the question and see if there really is a way to solve it.

 

[desertfox]

hi mike0123m

In that case I wonder whether you solve it for a minimum length of 1ft, then I would check the answer if you have it in the book.

desertfox

 

[JAE]

Well, if the angle is a ledge angle, bolted to the wall, the problem might be aimed at determining the angle thickness necessary to extend out the 6" and support the brick. L/600 on that, thuogh, is questionable whether it applies.

 

[ishvaaag]

Other typical case is when some header brickwork is hanged from a floor. Then typically spacing between hangers (they may or need to be braced) uses to be within 2 and 3 ft; this spacing is common with lesser size angles and so you might start to check on the upper range.

 

[desertfox]

hi mike0123m

Even working a deflection for a beam only a foot long probably won't be very accurate because the length to depth ratio for beam formula is to small.
Anyway mike any chance you can upload the question and/or give the answer in the book?

desertfox

 

[steellion]

You can determine the required thickness based on the localized case of leg local bending and shear, but you need to know the span to fully design the lintel. Even if it is attached to a wall using expansion anchors for instance, the span would be the distance between the anchors.

 

[paddingtongreen]

A lintel usually supports the masonry over an opening such as a door or window. I've never considered them loaded uniformly, I take account of the arching of the brick or block, up from the support points.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[concretemasonry]

It is a little bit of a trick problem and paddingtongreen is on the right track. - The arch action is critical since it changed the dead load distribution and dead load forces. If you have enough height of bonded masonry above the opening, the the vertical load on the lintel is just the triangle of masonry bearing on the lintel, which can be much, much less than the weight if you look at the wall as being composed by vertical columns of dead load. If you have some architectural patterns (stack bond or soldier courses) this can have an effect on the arch stability and lateral thrust.

Since you have a weight of the brick veneer of 500 plf, that indicates a significant height of veneer above the opening, which indicates arch action is very possible. The arch action dramatically reduces and almost eliminates the deflection.

You are right that it all depends on the opening width, which does affect the load in the lintel, but if you have enough height over the lintel, the arch action will reduce the load on the lintel dramatically and the Romans recognized this principal very quickly.

Dick

 

[cntw1953]

So, can we estimate/guess the unit weight of the brick veneer, and assume the 500 plf is the peak load (tip of a 45 degree triangle). From there, h is known, and L = 2h, any comments?

 

[druminman]

Due to the prolific inclusion of control joints in masonry veneers, I don't consider the arching action any longer. I've seen large openings with a control joint at each side of an opening as well as smaller openings near a corner with a control joint on the opposite side. In this case no arch can develop as there is not enough brick to resist the thrust on the corner side.

Patrick

 

[concretemasonry]

The 500 plf is not the "peak" load, since the arch action reduces the maximum load on the lintel. The lintel just carries the weight of the triangular shape of veneer bearing on it and the amount above the peak of the triangle is distributed to the areas between the openings below. This is why the height of the masonry above the lintel must be high enough to create the arching and load distribution effects. The 45 degree assumption is common in masonry, although some engineers will use a slightly different assumption.

Since the compressive strength of the veneer is not a problem, it usually is a mute point.

Pay attention to any shelf angles and soft horizontal joints that will disrupt the arching action and then you have a simple vertical load bearing situation with none of the benefits or arching. Depending on the properties of the veneer (clay brick expands with time) and concrete masonry and concrete have some long term shrinkage/creep. Woof frame has serious shrinkage and stability issues and usually will have a horizontal shelf angle at 16'or so. I have seen 7 story buildings without a shelf angle and the top floor windows suffered because of the 2" different vertical movement between the vertical expansion of the brick and the relative stability of a concrete frame.

Since you have a 6x6 angle, you probably have a true masonry veneer with an air space or insulation between the veneer and the structural back-up. Wall ties provide the horizontal resistance/alighnment to transfer horizontal loads to the structure

Dick

 

[cntw1953]

The above is just trying to figure out the missing info in the "trick" problem. For real world project, do all suggestions by others.

 

[dhengr]

The answer to the OP and the first half of the thread is; you can’t design a beam (lintel) without knowing its span length and bearing conditions. And, otherwise; that you can guess all day at the intent of an incomplete question.

From paddingtongreen’s post of 16DEC, 10:57 and down, there is much good, real world info. on lintel design, once you know the span length. But, read and digest druminman’s post before you apply this real world info.

 

[steellion]

Agreed with druminman. A control joint negates arching action. I assume a rectangular stress distribution acting on the lintel from the weight/load above. If that is too much to get a reasonable-sized lintel to work, I use arching action but ensure that a CJ is not placed on either side of the opening.

 

[concretemasonry]

steellion -

The vertical control joint also destroys the arch effect since the horizontal thrust cannot be recognized.

I agree since I neglected the vertical control joints that negate the advantages of the arch action that the ancient Romans did not have to deal with for permanent construction in total masonry construction with is historically proven for the total structural performance.

Dick

 

[cntw1953]

I think location of the control joint is key to whether arch action is possible or not.

In middle of the opening - possible
On sides beyond bearing areas - possible
On edges of the opening - not possible

The OP question wasn't a trick, it was seriously flawed. Where was that question came from?

 

[hokie66]

Not in the middle either. I agree with druminman. Ignore arching action unless you can't get it to work any other way.

 

[cntw1953]

Yes, I agree the above.
The "possibility" has no practical value.