PEMB Guide to getting preliminary designs 1

[diegotorres1]

Hello colleagues, I am a EIT and i have been put to a task on getting some preliminary design for a project. i was wondering if anyone has had to select a company to design a PEMB before. From my experience, it has been the architect's job to do so. The purpose of the building is a storage unit that is 110'x55' and 25' tall. Is it possible to get a preliminary design from them to pass down to the client and make sure this is something he agrees on? we have a very quick time frame for this.

 

[StrucPEng]

Not sure I understand the question entirely. Are you asking for specific companies that do PEMB or do you want to know the questions to ask them?

If its the former, a google search in your area should bring up multiple suppliers with contact information. Send your specs to a few of them asking for pricing and preliminary layout and see what you get back. I imagine you wont get very detailed drawings until you agree to purchase anything but you can probably get some general layouts.

I also assume you're company is not looking to design any of the building yourself?

 

[diegotorres1]

Sorry for the confused question. I would like to know the best way to approach a company, we are not considering doing any of the design except for the foundation. We are trying to get some preliminary sizes on the members as we have a very quick deadline to present preliminary designs and sizes, which is very important for the architects as they want to be able to see the roof beam depths. I was thinking i can do a quick design on my own to size some members as i'm sure no manufacturer will be able to get a preliminary design in a week or so. The building is very simple, but still not sure if this would be easy on their side.

 

[StrucPEng]

I understand now. Yea I would just get a list of 2-3 suppliers in the area of your project and contact them (most have forms you can fill out online with the building size) ideally by phone given your deadline. If you give them the building information you are looking for and let them know your timeline along with your critical information that you need (i.e. roof beam depth) I don't see why they cant get you that information in a week. With that said, I have never dealt with PEMB specifically but the many suppliers i have dealt with are usually receptive and understand deadlines. Seeing as how these are supposed to be pre-engineered, beam sizing should be something fairly typical that they could provide.

I would avoid designing something yourself and submitting that for a multitude of reasons. One, its work that is outside your scope that it doesn't seem like you have the timeline to do. Two, it sounds like that is driving the architects decisions so if you give sizing that is not right and have to come back later with a deeper beam, you will be on the hook for the architects time to redesign, so ultimately more liability for you and your company. I would leave that to the PEMB company to take that risk.

 

[diegotorres1]

Awesome! thank you so much for the guidance on this. I would really want to avoid any possible design especially with the deadline. I'll be contacting some companies in the area. Thanks a lot!

 

[structSU10]

Any PEMB building I have dealt with the architect/owner engaged a PEMB company, and gave me their load info to work from. Mainly because column spacing / frame arrangement is set to meet architectural requirements. If your architect has some bay spacing in mind that will work, get that from them to present to a PEMB company if you must do the leg work. Generally your biggest issue to deal with are thrust and uplift loads from the frames/bracing.

What type of storage is this - is it storage units or just a big warehouse? I know there are some specialty modular PEMBs made by storage unit companies that are quite economical, but they are popular and have long lead times last I knew.

 

[bhiggins]

Are you the engineer of record for the project? If so then it is your job to coordinate with the architect to define project requirements such as load requirements and deflection requirements which you will communicate to the PEMB supplier. You can also coordinate with the architect to produce a layout for frame grids and spacing and provide that to the PEMB supplier. I would definitely not do any preliminary frame designs because that would be a waste of time and is not your responsibility. It sounds like the architect is in a rush and trying to push your company to do unnecessary things.

 

[southard2]

Since you are an EIT I highly recommend these two books or manuals by Alexander Newman. There is a lot more to the foundation design than you might think. Specifying the drift is also very important these days now that architects want to use these for office buildings as well. Save yourself a lot of time and pick up these books and read through them. I wish I had. It is a real eye opener as I think most engineers make some pretty non conservative assumptions when designing the foundations for these types of buildings.

"Metal Building Systems: Design and Specifications" 2nd Edition

"Foundation and Anchor Design Guide for Metal Building Systems" 1st Edition

John Southard, M.S., P.E.

https://www.pdhlibrary.com/

 

[Ron247]

Ditto on getting the books by Alexander Newman. Both of them directly address PEMBs and are well-written.

As far as you current situation, it should be easy to contact PEMB suppliers and get what they call Preliminary Anchor Bolts and Reactions fairly quick. Be sure to let them know you also need member sizes or frame geometry.

The architect probably wants to know what clearances he has left more than actual member sizes. This is highly dependent on 1) Roof Live/Snow 2) whether you have an interior column or is it clearspan 3)lateral drift criteria 4) Bay spacing.

If they cannot get more accurate information from a supplier, consider this: I recently did the foundation for a 110'x25' clearspan in a 20 psf RLL, 5 psf Snow and light wind load. It was a 25' bay space. The loadings don't get much less than that. The clearance under the rafter was 20.5' near the edge of the building (more as you move from edge). The column was 12" at the base and about 36" at the top (knee). The columns set back 8" from the edge of the building. As a close approximation, on a clearspan with a tapered exterior column (not a straight column), the rafter depth at the knee is fairly close to the column depth at the knee. If your loadings are light like mine, these dimensions may give you some idea of what yours would be. Your vertical clear would be 21' to 21.5' etc.

 

[Ron247]

I need to make one correction to previous post. The building I did was 24' tall, not 25'.

 

[TEDstruc]

I'm not sure the reason you are needing preliminary member sizes, but a lot of PEMB manufacturers don't give that much detailed information with their bids, especially if it is at a preliminary/budgetary level, and not a bid for a real project. They will however usually give you a price to supply the design and building materials. They may even be willing to give you some preliminary foundation loads.

In a former role, I wrote many bid specs for PEMB's. I always requested preliminary general arrangement drawings and preliminary foundation loads be submitted with bids. I would guess 50% of the bidders provided some type of prelimary general arrangement and 25% supplied preliminary foundation loads.

After you do enough PEMBs you can get pretty good at coming up with your own general arrangements and estimating preliminary foundation loads.

 

[diegotorres1]

Hey everyone, thank you for the information and guidance. It was very useful and i was lucky to get a very understanding Manufacturer. The person i spoke clearly understood that this was for preliminary design and was nice enough to send out a "typical" structure" as this is a rectangular building with 24' bays and clear span with no additional loading to the roof or walls. I have a meeting with the architects this Friday and we will continue discussing the design. It didn't turn out to be as complicated as i had previously envisioned. Thanks again!