Continuous Beam Thru Column

[mkrei]

I have a situation where I need the column to not be interupted but I also need to make the beams framing into the web of the column behave like they are continuous. This is a elevated walkway with 14' cantilever on one end, 88' center span and 8' cantilever on the other end. The columns need to be continuous through the floor and roof to create a moment frame for lateral resistance of wind blowing perp to long axis of the walkway. The beams need to think they are continous to create the cantilvers on each end. I detailed stiffeners in the beam web to match the thickness of the flanges. These stiffeners were to be partial penetration welded to the column web and flanges. In turn the "simple span" beam and the "cantilever" beams flanges were to be full penetration welded to the stiffeners to transfer the tension and compression forces through the top and bottom. The contractor has requested instead of a full penetration weld that splice plates be used that are welded to the top flanges of the beams and to the web and flanges of the column. Will the deflection of the cantilever be adversly impacted by using the thinner splice plate versus welding the flanges to the stifferers. The flange/and stiffeners are 2" thick.

Thanks for the input in advance. This is a good web page to discuss these types of things.

 

[jike]

Use whatever size flange plate you need to carry the stress. With splice plates smaller than the beam flanges you will get more rotation at the column and thus more deflection on the end of the cantilever. If you can model it on the computer, input a short section of beam to model the thinner flanges over the column area to see what affect it has on the end deflection of the cantilever. I would suspect not much, but let us know what you find.

 

[hokie66]

I would not make a cantilevered connection with less capacity than the member. Introducing the weakest link in a cantilever at the fixed end doesn't seem right to me. What happens if you want to hang something off the cantilever in the future but can't because of the connection? If you don't need the member with 2" thick flanges in the cantilever, why not use a lighter section?

 

[civilperson]

Perhaps you could support the beam off a bracket on the side of the column, using the full section of the beam continuous throughout the beam's length. Might be cheaper than an elaborate welded connection with an added moment to the column.

 

[jike]

I assume the center span controls the design and not the cantilevered end. Is this correct, mkrei?

 

[mkrei]

Center spann controls design.

 

[civilperson]

Fixed-end moment will exceed center span moment.

 

[csd72]

Alternatively make it a double channel one each side of the column.

 

[mkrei]

It is not a fixed end as the column is flexible so it acts some place between a beam with simple supports and a cantilever on each end and a beam with the ends fixed. The center span has a higher moment than the moment over the support.

 

[csd72]

mkrei is right,

to get the real deflection and bending, this needs to be analysed as a frame.

 

[mkrei]

I ran it in Risa originally so it was run as a frame.