Structural Engineering (owsj design)

[JahmaiS_]

I am a civil engineer intern working at a contracting company. 1 was tasked to design a open web steel joist roof
containers. The the webs will be prevent ponding.
system for 2 bay areas, made from 3
dimension for the two bays are 40 ft x 20ft and 40 ft x 40 ft. The joists will be made from 2 x 2 angle irons for the top and bottom chord and made from 1 inch rebars. A joist girder will be at the midpoint of the the span. A valley gutter is should be incorporated in the design to Snow loads will not have to be accounted for. Below is a picture of a similar joist system already constructed. I am asking for some guidance with the structural analysis however I have done drawing in AutoCAD based on calculations I have done myself.

 

[JahmaiS_]

In the picture, the height of the bay is two containers high, however the one I have been asked to design will only use one container. Attached is the drawing I came up with.

 

[DaveAtkins]

I recommend off the shelf open web steel joists. I have never heard of someone fabricating steel joists for a roof.

I would ask for drawings for the containers. Your structural analysis needs to include an analysis of them as well.

DaveAtkins

 

[kipfoot]

A few thoughts:
1) you're doing the right thing by asking for help. I think you also need a structural engineer in your location who can guide you and ideally do the analysis for you;
2) Look up Howe Truss and configure your web members like that;
3) configure the trusses so that a vertical member aligns over the bearing point;
4) make the longer truss deeper; If you already know what steel shapes you have available, then the truss will need to be proportioned based on these shapes;
5) your purlins should align over panel points (i.e. where the web members connect to the top chord);
6) consider how the loads will be carried into the containers. Typically, these are designed to carry the load at the corners;
7) Consider the effect of wind induced uplift. (the roof in the photo is a very light system. would it lift off in monsoon winds?)
8) I'm not sure what you consider to be a truss girder, but I think what you need may be better described as bracing between trusses.

 

[BAretired]

I am a civil engineer intern working at a contracting company. 1 was tasked to design a open web steel joist roof
containers. The the webs will be prevent ponding.
system for 2 bay areas, made from 3
dimension for the two bays are 40 ft x 20ft and 40 ft x 40 ft. The joists will be made from 2 x 2 angle irons for the top and bottom chord and made from 1 inch rebars.
A joist girder will be at the midpoint of the the span. A valley gutter is should be incorporated in the design to Snow loads will not have to be accounted for. Below is a picture of a similar joist system already constructed. I am asking for some guidance with the structural analysis however I have done drawing in AutoCAD based on calculations I have done myself.

1. Please edit the above text so that it makes sense.
2. Do not include the same thread in more than one forum within Eng-Tips.
3. Panel points of your truss do not appear to align with the supports.
4. Location of the joist girder is not clear on the framing plan.
5. Use simple spans for trusses, with a more conventional shape.

 

[JoshPlumSE]

I recommend off the shelf open web steel joists. I have never heard of someone fabricating steel joists for a roof.

I was going to ask you if you really wanted to design it yourself or if you were just planning on spec'ing it out for a joist fabricator. If the spans are something that joist manufacturers will do (and 40 ft seems perfectly reasonable), then it will almost always be cheaper to go through them.

The ponding should only occur at the midpoint where the trusses slope down. My belief is you'd have to specify some minimum stiffness for the joist girder to prevent significant ponding. Maybe add on an extra distributed load on the sloped joists to account for them seeing the ponding as well.

 

[BAretired]

For simplicity, use simple spans throughout for the joists (or trusses). Below is my suggestion. I am assuming the containers are capable of carrying roof joists, and that they are each 8' wide. I don't believe you need a joist girder running perpendicular to the joists.

For the 8' spans, I suggest Beam B1. You don't need a joist for such a short span. And making the joists continuous is unnecessarily complicating the structure, as well as adding reactions where you don't want them.

T1 and T2 are OWSJs or trusses spaced at 8'-0" o/c according to your plan. Hint: depending on snow load, 8' may be a bit too long for 1.5" 22 ga. steel deck, so I suggest a 6'-8" spacing, which is modular with 40'-0". I tend to agree with those who suggest using prefabricated trusses or joists in lieu of designing them yourself.