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First Structural Design Question

First Structural Design Question

First Structural Design Question

I am assigned a design for a 32x44' all steel canopy including decking. I have never done a structural steel design before, what exactly do I need to present to my boss (a civil PE)? I have estimates for dead and live loads, as well as base shear and wind uplift via ASCE 7. I also obtained a moment/shear diagram of the beam I plan on using. I am planning on using gussets to connect beams to 4'' columns and attaching the roof via purlins.

How do I determine appropriate connections, foundation depth, and materials to use? How do I make sure they can withstand the acceleration of an earthquake? What are some good resources for this stuff?

RE: First Structural Design Question

If your boss can't provide the guidance you need, your company should not be undertaking structural design. We can't expect to impart a whole structural education here.

RE: First Structural Design Question

...or a good mentor at your job. Sounds like you are in a position where the "boss" doesn't teach. Not good.

RE: First Structural Design Question

Why are you being assigned this project if your area of concentration is civil/environmental? .

I once worked for a civil land development who felt that all areas of engineering could be performed using nomographs and charts because this is how they did all of their design (not all land development guys take this approach). But structural is not a field that lends itself to the lay person. All of us can figure it out, but it takes more than a one-time chance to pick up a book to figure it out. Your best bet is to kindly inform your boss that this is outside of your expertise and probably too complex to do on your own. Then go find a structural PE who can help you out. The size canopy you are talking about, the fee would be reasonable.

Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi

RE: First Structural Design Question

Don't be so harsh on the OP - a canopy would be what we consider to be a miscellaneous structure, and legally well within the jurisdiction of a civil engineer, however, realistically, most civil engineers practice only civil, and probably fewer practice primarily low-rise structures. Very few Civils are practicing in both civil and structural on a regular basis.

RE: First Structural Design Question

A bit of a checklist to help guide you (from a calc package I am currently throwing together for something similar)

Frame Geometry
Loads (Dead and Live), including wind (you'll need to research into wind loads on a canopy roof i.e. pressure coefficients)
Application of loads
Load combinations
Frame behavior i.e. deflections/bending moment diagrams/shear force diagrams
Member Analysis
Member Design
Support Reactions
Foundation Design (if applicable)

RE: First Structural Design Question

I mentor a lot of young engineers in my job. Don't be afraid to ask your boss questions and learn from him/her the specifics of what you are to do. Develope that line of communication. It is important. Don't expect them to give you the final answer and do the work for you but do ask questions.

RE: First Structural Design Question

Rikmayall that checklist is almost exactly what I ended up doing and almost exactly in the same order. My boss was surprised at its thoroughness; he just wanted me to have some insight into structural design as I am actually more involved with planning, utilities design and construction/M&O management.

RE: First Structural Design Question

funkyhunky -

It's okay to do your own research before asking questions to your boss. I did that when I was a young engineer and was commended for my initiative. I don't have the latest AISC manual yet. But, the older one (black cover) came with a CD that had example of a full building design. Also, browse through your company's project directory and do a quick search on "canopy". I am sure you will find one or two projects that have already been worked out. Review the calcs for those projects and if you can't find any...try to find the engineers responsible for those projects. They should be able to guide you. Once again...it's okay to try on your own and impress the boss. At the same time it is perfectly alright to seek help from him/her. All the very best!

RE: First Structural Design Question

Is it an open canopy? with no walls? if so, I would consider fixing the base if possible and a 32' x height portal frame at each end. The 44' span is a bit large for a single bay portal and I would break this into 2 - 22' ones with a continuous beam over. Apply your loads and analyse your portal frame. Likely use HSS tubes could be large depending on the lateral and vertical loading. Break the 32' span into 8 equal spaces so column can be braced with an OWSJ (maybe need a beam in the middle). 1-1/2" steel deck and you're nearly done... do foundation to suit...


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