# Steel frame connection

this is a steel frame , top beams sitting on top of column with steel plate cantilever at both sides (one side longer than the other) , so there will be hogging moment at the center support. However, the top steel beam is one whole piece, does the connection between the steel beam and column need to take the moment ? Or the hogging moment will be taken by the steel beam itself ? Connection need not design to take the moment ??

If the connection need to take moment , then which moment value shall I use to design the connection between the steel plate and the steel beam ?

• Make a prototype out of lollipop sticks and attach them with a single drawing pin - you'll soon find out if the connection needs to take any moment... Commented Feb 7, 2021 at 12:47

In any "static" structure composed of different members, if a bending moment develops at a certain point then connection between two members needs to be able to resist that moment. Otherwise the two members will start to rotate relative to each other.

The key thing is if a bending moment develops, because depending on how the members are arranged and supported, different forces and moments can and will develop.

• The beam is whole piece sitting on top of the column with baseplate underneath, so the connection doesnt need to take moment ? the moment is resisted by the top beam itself ? Commented Feb 7, 2021 at 15:02
• The beam is whole piece sitting on top of the column with baseplate underneath, so the connection doesnt need to take moment ? the moment is resisted by the top beam itself ? Commented Feb 13, 2021 at 11:39
• Your question does not contain enough implementation details, to make me feel confident to confer an answer. If its just sitting (i.e. there is no weld, or fasteners) then I don't see how it can transfer that moment safely.
– NMech
Commented Feb 13, 2021 at 12:49
• I am just asking here. FYI, there will be welding (at both sides) between the side flange and the plate, I know the beam itself need to take the moment. Just unsure whether connection between the plate and the beam need to sustain moment or not Commented Feb 13, 2021 at 13:09
• Even if there is welding there are too many factors (thickness of flanges), type of welding, length of weld seams... In any case, your original post stated "does the connection between the steel beam and column need to take the moment *", "*If the connection need to take moment", so the part I am answering is that. Regarding the second part, what value do you need to use, I can't tell unless I carefully audit the assumptions/parameters in your model and the results. I am not willing to do it from the printscreen of an unknown model.
– NMech
Commented Feb 13, 2021 at 13:16

What you have is like a cantilever beam supported by a post, very similar to a traffic light structure situation.

your beam-column connection must be designed for the tributary moment multiplied by required factors,

• w = uniform load on the beam

• L1 and L2 are the long and short span of the beam.

$$M = w*L_1^2/2-w*L_2^2/2$$

And your column and the column to foundation connection has to be designed for a large overturning momentum plus dynamic loading due to wind and lateral loads.

The lesson to learn here is that you need to design your structure such that it matches your analytical model.

Does your model have a transfer of moment between the beam and the column? Then you need to make sure that you design your beam and column such that this moment can actually be transferred.

Does your model assume no transfer of moment? Well, then you also need to make sure to design your structure such that no moment transfer actually occurs.

In your case, you have a cantilever beam supported by a post. This can only be achieved by having the post absorb the bending moment (as happens in your analytical model). So yes, you need to make sure the connection between beam and post can ensure and withstand the forces generated by that bending moment transfer.

• Yes, I will design the welding between the plate and the column to take the moment, I am just not sure whether the connection between the beam and the plate need to withstand moment or not . Since the beam above is whole piece spanning across 2 cantilever span. Commented Feb 8, 2021 at 2:30
• @kitzlong: The answer still applies: you need to design the beam-plate interface in such a way that it can transfer the load from the beam to the plate. Otherwise the beam will simply slip off the plate.
– Wasabi
Commented Feb 8, 2021 at 19:55
• So, the connection between the plate need to design for the moment of 20kNm or 2kNm, i guess it shall be 20kNm ( the larger moment ) ? Correct me if I am wrong. Commented Feb 9, 2021 at 23:43
• @kitzlong: Once again, remember this is about transferring forces from the beam to the column. How much moment are you transferring to the column? The beam has 20kNm before the post and then 2kNm after it. Therefore you've transferred 18kNm to the post.
– Wasabi
Commented Feb 10, 2021 at 1:41
• Ok, so for the connection between the column and the plate shall be designed to take 18knm, while the connection between the beam and the plate shall take 20knm, correct me if I am wrong Commented Feb 10, 2021 at 4:34