Connection Design - Multiple members framing in a single joint

[harlemshake]

For example, moment connections framing to the column web and flange at the same joint. Let's say the column flange connection requires stiffeners, do we really need to design the stiffeners and its welds for the max loads for both the moment connections? In the past, I assumed only the maximum, not additive, since I assumed max loads won't occur at the same time.

Another example is a post sitting on top of a girder support at the same time there's a beam framing to the girder support where the beam single plate connection also acts as a post stiffener. Do we need to design the stiffener/single plate for the max loads of the post and the beam?

Please give me your thoughts.

Thanks.

 

[CANPRO]

Whatever code you're designing to will give you the load combinations you need to consider.

In your first example with the beams framing into column web and flange - if both maximum moments occur under uniform loading of the floor/roof, I think you better consider them acting concurrently in the connection design.

Same for the second example - maybe you could make an argument for some sort of live load reduction due to the multiple sources of live load. But considering the cost of the connection, the fact you have to put a stiffener there in the first place is most of the cost...changing the thickness of the plate +/- a 1/4" or so isn't going to make that much of a difference.

 

[harlemshake]

I don't actually see all the load combinations. I work in a delegated connection design firm. We are only given max envelope loads by the EOR.

 

[TLHS]

Unless you know otherwise, you have to design to both. It seems unlikely that they both happen at once, but that's not your call to make. If you want to assume something else, you'd need to get it signed off on.

 

[CANPRO]

Ah, I get it, often in the same boat myself. Similar response though...I’ll take a look at the structure and see if it’s reasonable to consider concurrent loading. If it’s questionable, and makes a big difference in the design, I’ve gone back to the EOR for more detailed loading. Sometimes the EOR is helpful, others I feel often will tell you to design to the max for all elements without really giving it honest consideration.

A situation I find it can make a big difference is in braced bays. If the brace connects to the beam and the column, you need to consider interaction between gravity loads and lateral loads in the beam/column connection. Often you’re given some blanket requirement for shear connections and a factored axial load from the brace. Using 100% of both requirements concurrently is essentially using some extreme load case where your live load and wind are both your primary load i.e. 1.25D+1.5L+1.4W