Hybrid Masonry Wall Offset

[Pixy]

Topic is independent and thread must stand alone.

Has anyone built anything like this?

The masonry wall and I-beam are offset by 2" distance. How do you detail it if there is such offset? Or imagine the masonry wall going above it and you are bracing it at the side.

The original unedited illustration came from aligned wall and I-beam below. Is anyone here member of the National Masonry Concrete Association. Or know a member or just aware of their documents or just know? Can you ask them illustration or details for offset masonry wall and I-beam?

Or is it a rule that I-beam and masonry wall below must always be aligned at all times? (so misaligned wall must be demolished and raise anew in right position)?

Codes ultimately followed: ACI

 

[Pixy]

This is the w8x21 specs:

The 6 meter (19.68") w8x21 ibeam is not connected to anything except the columns supporting it. Not to any diaphragm or steel deck or concrete slab. The rafters supporting light metal sheet roof is connected to the column top baseplate. And the beam is also welded at the baseplate top. And 4 more baseplates would be added around it create almost unmovable concrete top baseplate cap. The entire column top has to suffer similar to base shear for the baseplate to become detached. So shear capacity is 400 kips or more. This is to ensure the wall has lateral strength competent support.

Abut the weak axis strength to support the wall. What do you think will happen? Will the ibeam bend or be so flexible that it cant be made to work to brace the wall which is very stiff? like the wall can suffer cracks because the ibeam is so soft?? pls. see ibeam specs above.

 

[jayrod12]

Yes my opinion, without running a number, is that beam may not be stiff enough to support the wall and meet typical deflection requirements. It's a pretty slender beam. But you're the designer, design it.

 

[Pixy]

The building was designed by a company who built 50 storey buildings all over the country:

https://rbsanchez.com/

You have a point about weak axis bending they might not have checked as they only use Etabs in designs of hundreds of 50 storey buildings and most of their operators can't do manual computations.

My job is manually verifying each details especially something that may not get inputted in their Etabs.

https://www.aisc.org/globalassets/c...proceedings/2019/bhowmick_et_al_ssrc_2019.pdf

If the wall deflects so much. Can the wall crack, and in your experience, can it also fall down??

 

[jayrod12]

Crack yes. Fall down, maybe but unlikely.

 

[Pixy]

jayrod12 and those who encountered this scenario before,

In the design files. There were two kinds of beams designed for the roof, reinforced concrete beam and I-beam. The I-beam was chosen because it was easier to construct.

But with the I-beam weak axis and possible deflections in the soon to rise wall causing cracks, and the worries it can bring. It is being discussed whether to remove the existing I-beam and replace with reinforcement concrete beam.

This was file photo before the top portion of column was filled with 4000 psi concrete.

This was after it was filled with 4000 psi concrete.

We will remove the present I-beam, baseplates, even rafters, and chip the top to make the bars appear like in previous. This was in the alternative concrete beam plan.

In the above. 20mm rebar is 25/32". Size of 6 meter (19.6 feet) concrete beam span (with no diaphragm ) is 15.75" depth and 7.87" width.

I just want to know in your experience whether for roof perimeter beam, you can develop the beam rebars to make it an integral beam-column joint in the above case? I know roof perimater beam are weaker owing to lack of top column above the joint for restrain.

 

[jayrod12]

I'm not definitively saying it will crack. It is your job, from what I understand, to check the design and if it's good, great, if not change it. You seem to be taking the opinions of strangers on the internet as gospel instead of running the numbers yourself.

Are you sure you should be performing this job if you can't make those decisions on your own? Is there not a senior designer at you office who can help?

 

[Pixy]

The textbook I followed mostly is Arthur Nilson "Design of Concrete Structures". And I'm only familiar with reinforced concrete.

Here most use reinforced concrete. Wide flanges have so many disadvantages.

1. Wide flanges are not fireproof
2. Wide flange weak axis is poor
3. Wide flange is poor in torsion.
4. Wide flange can conduct electricity and get one electrocuted.
5. Wide flange needs expert welders, here our welders earn $15 a day and mostly poor people weld

So wide flange are seldom used. So I don't get why most of you love wide flanges.

I'll compute for the weak axis deflection from the I-beam given moment of inertia, and sectional properties and forces.
Most doesn't know how to compute for wide flange properties because we only mostly handle reinforced concrete.

Anyway. I'm looking for references or strengthening the wide flange or I-beam weak axis by putting plates on the top and bottom flanges at side (imagine making one side square). Do you have references of such wide flange or I-beam weak axis strengthening?

 

[Pixy]

By the way, jayrod12, here is a very important question that can't be modeled by ordinary equations. In fact this can be used as human test in website anti robot spam authentication.

If the masonry wall top are right below the I-beam and the rebars are welded to the bottom at the middle of the I-beam or aligned with the web.

Contrast this with the case where the masonry wall is at the side of the I-beam.

Can the former have more resistance to weak axis bending of the I-beam? My reasoning is that since the rebars in the former case are welded right below the I-beam, it is more straight. See the following illustration:

For the straight vertical rebars to sway to left, it has to lengthen to say 13 inches from 12 inches which is not possible. So it can stay more vertical and the I-beam won't deflect much compare to the 2nd case where the wall is at side of I-beam. What do you think? Again computation can't simulate this because in beam deflection computations, you don't tell which part of a portion in 3D at same distant is being engaged.

 

[jayrod12]

I agree that the results would be different from the wall running past the beam and loading it perfectly horizontal from the wall underneath and fastened to the bottom of the beam. But I disagree with you assessment that the deflection would be less.

In my opinion if the wall is connected at the bottom of the beam only, you're going to get the full amount of weak axis deflection of the w-beam, PLUS the deflection from torsional warping of the wide flange beam. Maybe the actual value of torsional deflection is relatively minor, but it exists nonetheless. I haven't put a single calculation towards your problem, I'm just trying to point out potential issues that you as the designer should be checking and either addressing if an issue or dismissing if not an issue.

 

[Pixy]

I can't find the formula for beam with fixed end (instead of simply supported at ends).

What is the formula for fixed ends?

And given there is fixed end formula, can you apply it sideways to the weak axis of a wide flange? Or do you somehow use some kinds of components (since it's sideways and there is also gravity load)? Or does the formula for deflection only depend on the load, Young's modulus and moment of inertia and you can apply this at any angle of the beam??

Let's compute.

Let's use the formula for simply supported with uniform load.

Deflection = 5/384 (w L^4 / EI)

given: a 6" CHB wall has 2.73 kN/m2 x 1.5 meter = 4kN/m (half wall contribution to the top I-beam support of 3 meter high wall).
(In lateral movement computations, half of wall goes to top support and bottom support (or floor/diaphragm)).

Let's take lateral acceleration to be 0.25 g or about 1 kN/m. This is used as load for the weak axis of the I-beam, right?
Length of I-beam between column supports = 6 meters
Young's modulus = 200 GPa (for A36 steel wide flange).
Moment of Inertia = 0.0000040666 m^4

Or let's convert all of them from metric to imperial units so the numbers can be more familiar to you.

uniform load = 1 kN/m = 0.0057 Kips/Inch
l = 6 meters = 236.22 inches
Young's modulus = 200GPa = 29000 ksi
Moment of Inertia for W8x21 wide flange weak axis = 0.0000040666 m^4 = 9.77 in^2

Deflection = 5/384 * (w L^4 / EI) = 0.817 inch.

When designing masonry buildings ACI 530 states an out of plane deflection limit of 0.007*h.

Since wall height is 3 meters or 118 inches. And 0.007 x 118 " = 0.826 inch.

So the 6 meter length I-beam weak axis deflection is within the wall deflection limit. But then, what is the formula for fixed ends with uniform load and can you apply this sideways to the I-beam weak axis?

Many thanks!