Mezzanine/Support Design

[Keigi]

Hello,

I just started my career as a mechanical research engineer, for a about a month now, and I am required to design a support system for a furnace; people will also walk on the support system so I call it a Mezzanine/Support furnace.

Note: I reviewed the OSHA safety codes for safety on high surfaces 1926.502.

Onto my question, attached is a image of the support system I am creating. The black view is a top view down onto the support system; The blue is a front view; and the red is a side view.

The Beams 2 and 3 are spaced like that to support a 5000 lbf load. I am also assuming a 100lbf/ft^2 load across the entire mezzanine.

I have done deflection calculations, and the max total deflection is around 1/8 of an inch using:

W 12 x 22 (For Beams A and B)
C 10 x 15.2 (For Beams 1, 2, 3, and 4)
Structural Tubing 4 x 4 For the Columns

My question is, how do I determine the angle bracing of the beams; the "angle iron" from the column to the beam?

For the red view, not knowing how to calculate this I just looked at another mezzanine and noticed the support started 1/3 from the top of the column and went the same distance out to the beam. I just followed that same rule with my design, not knowing why!

For the blue view, the plan was to keep things clear under beams 1, 2, 3, and 4, So I didn't want to have the "orange" angle iron braces. Nothing if the "orange" braces were required, but not knowing this I just designed one big one across the back, under beam 1, and re positioned things to work with that...

To restate my question(s):

1. Do I even need angle iron bracing on beams 1, 2, 3, and 4, or even on beams A and B, to the columns? I guess I do not have a good understanding for what the bracing does.

2. How would I calculate the need for such bracing?

***The two reasons why I see the need for the angle bracing are:

1. Another way to transfer the load from the beam to the column(decrease deflection).

2. A way to make the platform more rigid? I do not understand this one, outside of my experience making wooden platforms.

I searched through these forums, the internet, and my engineering text books, but was unable to find an answer to my question. Any help would be welcomed!

Thank you,

-Keigi

 

[JAE]

I would guess that this is an industrial company you work for and if so then technically you wouldn't need a licensed structural engineer to design, seal and sign the design.

However, I'm not sure, if I was you, I'd try designing something like this without some mentoring help from someone who knows how to do structural designs.

The mezzanine must support the required dead loads as well as some appropriate live loads...your 100 psf would probably be OK but I'd want to know clearly that storage usage would not be permitted up there.

The diagonal "knee" braces you are questioning are for lateral stability of the mezzanine. These would be based on lateral seismic forces in all directions and would be based upon your actual local building codes.

The problem you are facing is that you've been tasked with designing a mezzanine without knowing how to do it - this means you might personnally be exposing yourself to a high degree of risk or liability should something go wrong.

Your lack of knowledge [blue]"I just started my career, how do I determine the angle bracing, not knowing how to calculate this I just looked at another mezzanine, I just followed that same rule with my design, not knowing why!, I do not understand this one, outside of my experience"[/blue] tells me you should seek help from someone who can:

1. Review all the project conditions with you.
2. Understand the strength and serviceability requirements
3. Show you how to design the beams, columns, braces - how to determine appropriate lateral loads on the mezzanine, and
4. Show you how to properly draw and detail the design to communitcate it to steel fabricators and contractors to build.

 

[JedClampett]

These forums get a lot of questions like this. Regular participants almost always give the same initial advice. You need to engage the services of a structural engineer.
But to your mezzanine design. I can't make a lot of comments or give you answers since you gave no dimensions. C10's are fine sections in some situations, but I like to use them at edges only to give a flat surface to mount handrail. For your interior sections, "W" sections are more efficient (more bang for your pound of steel) and have other properties that are advantageous with regards to deflection.
You can make your mezzanine more rigid by using bracing from column base to the joints. There's straight bracing, wind bracing (that's what you show), K bracing and chevron bracing. But that makes more interferences for access. I'm confused by your question about bracing the interior members (2 & 3).
You could design this as a rigid frame and eliminate all bracing. But that would require much more knowledge than I'm afraid you possess.
100 psf live loads and 5000 lb point loads are not to be taken casually. You need a structural engineer to design this or assist you.

 

[TXStructural]

You will get the standard (correct) answer of "hire a structural engineer". This is important because you cannot represent yourself as qualified to the state (or a court) if something goes wrong, and none of us want anyone hurt or worse. You should hire someone for this design, then work with him/her on the design so you understand the requirements.

You don't indicate any dimensions, or where it is located, so I can't be much help. I will try to answer your questions:

>1. Do I even need angle iron bracing on beams 1, 2, 3, and 4, or >even on beams A and B, to the columns? I guess I do not have a >good understanding for what the bracing does.

The bracing you show is to keep the platform from falling over as the connections between beams and columns would have to be rigidly connected without them (not the standard type of connection)

>2. How would I calculate the need for such bracing?

There are requirements for how much bracing is required.

>***The two reasons why I see the need for the angle bracing are:

>1. Another way to transfer the load from the beam to the >column(decrease deflection).

No. This induces additional bending into the column, which is not usually desirable.

>2. A way to make the platform more rigid? I do not understand >this one, outside of my experience making wooden platforms.

Rigidity, yes, but the way structural steel is designed, you try to confine forces to certain patterns using standard, bolted connections. The usual method is to reduce field connection complexity to reduce cost

Some of the things considered in a design:

-dimensions required
-loading (which is increased by a set of factors)
-how it will be built
-types of structural connections; standard or moment-resisting; bolted or welded
-allowable drift, deflection, or other serviceability
-availability of steel shapes and suitability for use
-buckling (a few types)
-anchorage and support, bolts, leveling, grout
-baseplate thickness, bolt pattern
-forces from accessories and connections (handrails, furnace support connection) which can induce failure before reaching strength.

And the list goes on.

That's why you won't get advice here on a question like this.

 

[csd72]

Ditto.

Keigi,

We are trying to protect you from yourself here.

If something goes wrong, your bosses that have tasked you with this are probably less qualified (Engineering wise)than you are and therefore the lions share of the blame would land at your feet.

If someone were to die from this collapsing then....

 

[hokie66]

Keigi,

The advice from the four experienced structural engineers above is all good.

You have identified yourself as a mechanical engineer, and it is unusual for mechanical engineers to perform this type of structural design. This is not your fault, but your mentor should know better. If you don't have a mentor, then you are doomed unless you can get help elsewhere.

 

[Keigi]

Thanks for all your advice,

I work in a research lab, so we mainly just run test equpiment. I do have a mechanical PE as a mentor. The first thing he told me was always design for safety first.

He has been checking my work, and I usually show him a design of something and he guides me through changes that will make it safe, or better.

He has designed, and built, platforms and his own house, so he is knowledgable in this subject; most of my design has been based on reverse engineering the mezzazine system he created.

Since he is out of town right now, and along with the reienforcement from your posts, I will make sure that he gets to review the designs next week when he gets back; before anyone starts to bulid anything.

I now have a better idea of what the knee bracing is for, and have some idea that I need to look in codes to determine it's deminsions.

Thank you,

-K

 

[TXStructural]

Steel costs about $2-5/lb for miscellaneous construction (sometimes more) including labor.

Another reason to hire a structural engineer:

If we assume that the platform is 11 feet wide and 11 feet long (the maximum unbraced length for the beam size you suggest, W12x22), and assume that the equipment is a single 5 kip point load applied midspan of a single beam, and the floor load of 100 psf is applied at 3 places (100 psf x 11'/4 trib width x 11' span = 1.5 kips each at quarter points) on the beam:

Wu=30.5 k-ft using 1.2 D + 1.6 L load factors (Which is unreasonably conservative, since you do not propose putting all of the 5 k load on a single point at midspan, but for my purposes it is illustrative; I assumed a self-weight that was double the beam weight as a simplification.)

The beam you suggest is 20-40% heavier than required. If, as I suspect, the platform is not quite so large, and/or we can assume that the intermediate C10x15.3s provide bracing against LTB, the weight difference is more like 12 plf v 22 plf. Just for the 4 perimeter beams, you will spend $2000-4000 instead of $1000-2000. Deflections due to the 5k furnace as a point load at midspan would be on the order of 1/6 inch with W10x12 beams (illustrating that static, gravity performance is no better.)

Similarly, the channels you suggest are probably just as excessive (note the W10x12 above, which is structurally better than the 15.3 plf channel for most cases, is still excessive.)

I suspect your design scheme is probably twice as heavy as needed, and possibly significantly heavier than that.

Now, what kind of connections are you proposing? How many bolts, or how many inches of what kind of weld? (Can you weld it in place safely, and what about removal later requiring a cutting torch?)
What wall thickness for the "4x4 structural tubing", and how does that work with the bolts or welds you want? Are you aware that rigidly welding a frame together makes it behave differently than the design tables expect. Did you decide how much lateral resistance is required, and how much bending the knee braces will put into the tube columns?

I'm only pointing these things out so you will understand that there is value to be obtained by getting help from a structural engineer hired for the purpose. It is truly dangerous to go into such a design cold, without a qualified mentor.

 

[JAE]

and have some idea that I need to look in codes to determine it's deminsions

That isn't true either.

I hope your mentor PE mechanical guy is good.

 

[csd72]

Keigi,

The codes will not tell you how to analyse and design a structure they will only state the minimum standards. There are many things that need to be considered that are not specifically addressed in codes.

 

[paddingtongreen]

Adding to JAE and csd72, the AISC Specification for Structural Steel Buildings says that it is not to be relied on for any specific application without competent examination and verification of it's accuracy, suitability and applicability, by a licensed professional engineer, designer or architect.

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

 

[Keigi]

Update:

I was able to get a structural engineer from my company to help me with the design of the platform. He also showed me a way of bracing for lateral loads sans angle bracing.

Just wanted to thank you all again for your help!