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Floor Beam supported at one end with Bottom Flange of the Girder

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NC_EIT

NC_EIT

Civil/Environmental
Feb 1, 2023
7
I have come across an existing detail where the floor is supported on a beam that is welded to a girder bottom flange at one end. Note that the girder beam sticks above the floor to form a "curb." To the right of the existing floor beam, the client is changing the use of the floor and I have two intermediate members aligned with the "dropped" beam. I am thinking of connecting the new beam with the existing one via a shear connection and just confirm the capacity of the existing welded connection without making a lot of changes to the existing system. 

Do you see any concerns with the welded connection between the top flange of the floor beam and the bottom flange of the girder? Based on the capacity of the weld (force will be perpendicular to weld), my d/c is well below 50%. I want to confirm if there is anything else I should be considering for this detail. 

Beam_Supported_with_Bottom_Flange_of_Girder_brm1em.png
 
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OP said:
1. Is this type of connection between the beam and girder with the beam's top flange welded to the girder's bottom flange acceptable? considering the factored load of around 850 PLF.
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Such a connection will have some capacity but that will be limited by the highly non-uniform -- and difficult to predict -- weld stresses owing to the the flexibility of both the beam and girder flanges. Is the girder existing or new? Either way, I'd seek to install stiffeners on the beam that are aligned with, and connected to, the girder flange right below the girder web. That will yield a connection of far greater capacity and reliability.

OP said:
2. Due to increased lead on the right span, I need to add new beams/joists on the right span(these new beams will help reduce the deck span). Is the detail attached for the connection acceptable?
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It is acceptable. It may not be preferable however. In retrofit applications, it's often more economical to use welded joints rather than bolted. bolt holes can be difficult to position accurately and the mag drills that are used to create the holes can sometimes be a problem to fit into tight spaces.
 
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I might be able to get behind this too. You want to limit the flex in the girder flanges lest that manifest longitudinal bending in the fillet welds. I do like the previous version better.

C01_yi075u.png
 
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One more time for the beam - girder connection.
C01_yeldnm.png
 
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Everything drawn in "RED" is existing and only "GREEN" is new. And, we do not believe that there are stiffeners at the connection location. This detail was installed back in 1989.

 
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Existing deck is steel. New deck is wood. If a wood nailer is bolted to the new beam to attach the deck, the top of the new beam will be 1.5" lower than the existing. May be better to continue with steel deck.

 
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NC01 said:
Everything drawn in "RED" is existing and only "GREEN" is new. And, we do not believe that there are stiffeners at the connection location. This detail was installed back in 1989.
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Because of the rather extreme potential for weld unzipping with the original connection, I'd be looking at reinforcing the connection as shown in my details above. All but the first detail could be brought to bear on a condition where both the beam and girder are existing members. Frankly, I don't actually know of a valid way to assess the capacity of the existing connection. And I'd not be in a hurry to green light somebody else's detailing error.
 
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