Design of Steel Structure for canopies of large area 4

[anonymous119]

Dear all I have a task to design a steel structure for 3 canopies with the following specifications
1. 25x15 meters
2. 75x8 meters &
3. 700 Sq. meters (Overall)

The design is relatively in the initial stage and its just been demanded by our estimation section in order to give price of an inquiry. I am relatively fresh in steel structures but I am aware of AISC code and software tools like STAAD Pro. I have designed steel structures before for supporting architectural works, but such a structure is quiet bigger for me than the earlier ones. I have already design the 3 structures and send the steel detail to the estimation section. But the problem still remains there, that how come I be sure about the structures' safety because I don't fully believe on the software's result. Also there is an issue that I am the only Engineer who can do the structural design in my company. Please I need valuable information that how to proceed in future if our company gets the project.

Note: In my design I used trusses made up from equal angle section, I thought to use tapered section but later on abandoned the idea because of the bracing requirement for such a large structure.

 

[structSU10]

In order to be comfortable with the results a hand calculation is the best way to veryify if software has given you a reasonable result.

As far as safety goes, as long as you meet the criteria in the AISC specification, the structure should be safe. Check for load carrying capacity, stability, and servicability.

If you are only aware of such design practices however, it might be prudent to get some help by hiring an engineer.

 

[anonymous119]

I forgot to mention that the structure has to carry load of 4mm composite aluminum cladding having a weight of 5.5 kg/m2 both top and bottom. The 1st canopy is supported by a column of 800x800mm, the second one is supported by cables of 24mm @ 8 meters apart and the 3rd one is fully cantilever. I have applied cladding dead load and self-weight dead load on the members including wind load. Seismic load hasn't been applied because the concerned structure is not in a seismic area.

Thanks structSU10 I think that critical members should be enough for manual check and there is no need for checking the whole members what do you think?

Also can I design structural members (angles) instead of a truss, as a laterally braced beams with brcing as both in top, bottom and sides while using the same section for design? (I have designed it in this fashion in staad and it gives safe results)

 

[MiketheEngineer]

You are asking questions that deem you get some local professional consult

 

[dik]

Is this a free standing canopy and is the aluminum cladding around a perimeter fascia? Cantilevered or moment frame columns and beam/truss over?

Also 4 mm cladding is a tad thick.

Dik

 

[JAE]

One thing you might do in your situation ("fresh in steel design" "depending on STAAD" "only engineer in office")
is to include in your companies work offer a separate peer review of your designs by a licensed professional engineer.

 

[anonymous119]

The structure has to carry the cladding load on it,the cladding has 0.5mm thick aluminum sheets between which an inert core is sandwiched. The client has mentioned that all the calculations has to be carried by the contractor. Our company is basically a Building Envelope fabrication and installation contractor.
Also I have designed only so that estimation guys have something to quote in the inquiry rathar than mere guess. I will definately insist that the design shall be checked by an external Pofessional Engineer if we get the project in hand before the design approval.

 

[JLNJ]

Be careful!

Canopies are the first things to blow over during an extreme wind event. Or at least it seems that way from the photos on the Weather Channel. This indicates to me that we don't fully understand the action of the wind and the pressures generated on these types of structures. Or that the people who design them are not qualified.

 

[Ron]

JLNJ is correct. I've designed over 700 canopies, most in aluminum, although I've done steel as well. Many were large with similar issues that you have. It is often difficult to get these to work using your first cut at a design. Refinement of the design is almost always necessary to comply with code provisions, mostly wind loading. For some, it is almost impossible to meet serviceability requirements (mostly deflection on the cantilevered canopies) without significant effort.

Be careful with preliminary designs for estimating purposes....you might get bitten in the a$$ unless you consider the entire design.

 

[anonymous119]

Yeah you are right Ron. I have made an effort to over design the structure so that if the structure needs any future changes in the design (which will definitely happen), there can be a compensation in the margin of economy relative to the initial design or simply we don't have to pay from our own pocket. But we have already forwarded our quotation so lets hope there couldn't be large differences in the money matters.

So, guys up til now I conclude from the discussion that if we get the project for execution first of all we have to make our design to be checked by the Qualified Structural Engineer while I will start giving it final touches to it so in order to make it to be approved by the P.eng.

 

[anonymous119]

Yeah you are right Ron. I have made an effort to over design the structure so that if the structure needs any future changes in the design (which will definitely happen), there can be a compensation in the margin of economy relative to the initial design or simply we don't have to pay from our own pocket. But we have already forwarded our quotation so lets hope there couldn't be large differences in the money matters.

So, guys up til now I conclude from the discussion that if we get the project for execution first of all we have to make our design to be checked by the Qualified Structural Engineer while I will start giving it final touches to it so in order to make it to be approved by the P.eng.

Please correct me if I am wrong.

 

[SteelPE]

I've done work with plenty of "design-build" contractors. I have always followed the rule "when in doubt make it stout". When under the gun by the client to push out a design quickly for estimating purposes I don't exactly go for economy. One thing a client hates is change orders.

Ron you would be surprised with some canopies that I have seen. About a year ago we had a very extreme weather event in the area. While surveying the damage I came across a newly constructed gas station canopy that was still in place and functioning while there was a path 2' diameter oak trees that were snapped off like twigs 20' above their base either side of the canopy. Quite amazing.... somebody did their job.

 

[anonymous119]

The contracting guys demand to do it fast where there is a narrow window of time pressed upon by the client. So, at that time I always want that the contracting section should be aware that this design could be economical if there would have been more time. Sometimes they understand but sometimes they don't. Even there have been cases where they have pressurized to provide the most safe and economical structural design in a very little time.