Use of Bar joists in open structure canopies such as gas station 1

[HokieNation]

I am planning to use bar joists as roof framing members at open structure such as gas station canopy. Will there be any special connection requirements? Is it better to go with just steel beam framing?

 

[Ron]

An open web joist is like any other structural member....it can be part of your design. Here are a few considerations I would make....

1. In an open structure, your uplift might be higher so make sure your chord bracing accommodates this. The Steel Joist Institute provides recommendations for bottom chord bracing for uplift. If the structure is typical of gas station canopies, the upper structure will be exposed and a ceiling/soffit that looks nice will be used on the bottom of the structure. This requires bracing of the top chord as well since there will be no deck diaphragm.

2. Corrosion is an issue. There are lots of nooks and crannies in open web joists that do not get properly covered with protective coatings. Make sure the joists are properly protected from corrosion.

3. The connections can be either welded or bolted, depending on the way you want to design it. Either can work if properly designed.

4. Be aware of lateral loading. Most canopies have a reasonably large exposed face at the roof level. This presents relatively high lateral wind loads, inducing moment at the column bases unless you use knee braces. Keep in mind that the columns are also often used for drainage, so deterioration of the column cross-section can be expected unless proper methods are used to mitigate this.

 

[HokieNation]

Thanks Ron,

Appreciate your input. Yes, I did post it by mistake in the different forum and wanted to delete it but couldn't find anything to remove/delete posted thread.

Can you help me with that too? I am kind of new to posting threads.

Thanks a lot.

 

[Ron]

At the bottom of each post is an option to "Red Flag" the post. You can either "Like" a post or request that it be deleted by management. You cannot directly delete a post; however if you select the "Red Flag" option and put your valid reason in there, it will be deleted. Double posting is a valid reason for deletion!

Welcome to Eng-Tips. It's great, isn't it?

 

[HokieNation]

Thanks ron, I will red flag and have admin delete the post.

Yes, it is great place to share knowledge. As there are many different ways to approach engineering and this place provides kind of consensus and confidence

Just to read different threads gives tons of knowledge more importantly practicality of design.

Cheers!!

 

[cliff234]

I would tend to stay away from joists for this type of structure. Here are my reasons,

W shape framing will be cleaner. The fewer the number of pieces, the lower the cost (usually).
Joists will require uplift bridging. It will get pretty ugly. If you use W shape framing you can just design the beams as unbraced members resisting uplift forces.
I would think that it will be more difficult to keep the joists from corroding than it would to prevent corrosion of W shape framing. Lots of little crevices, etc. in joists where corrosion can start.
Are you going to specify that the joists be galvanized? I'm not even sure if joists can be galvanized. I would think that they might warp during the galvanizing process and it may be difficult to get a good galvanizing job with the nooks and crannies along the joist span.

 

[StructuralEd]

I've seen design drawings for a multitude of gas and convenience store canopies and have never seen bar joists used.
In addition to wind uplift, they usually only have centrally located columns so many cantilevers are involved, further complicating the potential loadings.
I would stick with rolled sections myself.