Moment Connection at Beam pockets in Foundation Wall 5

[Vrpps EIT]

If a steel beam is placed in a beam pocket in a foundation wall and then grouted solid completely around the beam pocket, is this connection considered as a fixed connection?

 

[BridgeSmith]

Fixed? Definitely not. Partially restrained and transferring a substantial amount of moment to the wall? Maybe. How much moment is transferred to the wall depends on the stiffness of the connection and the stiffness of the wall, relative to the stiffness of the beam. The stiffness of the connection depends on the configuration and development of the reinforcement around the beam. The stiffness of the foundation wall depends on the configuration of the wall and its reinforcement.

Generally, a concrete or CMU wall isn't stiff enough to restrain a steel beam in any substantial way.

 

[Vrpps EIT]

@HotRod10

In that case what type of connection is to be considered when a steel beam with a bearing plate (2holes) is completed with 2 J anchor bolts into the beam pocket in the foundation wall?

 

[swearingen]

In a word, pinned.


-5^2 = -25 ;-)

http://www.eng-tips.com/supportus.cfm

 

[MotorCity]

I would say the beam is torsionally fixed by grouting the beam pocket solid, as it would not be able to twist within the pocket. However, in considering the beam to be fixed for flexure, you would be relying on the bond between the grout and beam and the bond between the grout and concrete. Difficult to quantify and questionable at best.

Now, if the pocket was in the middle height of the wall, such that there is wall above the pocket, then I would say you could make a case for the beam being fixed as long as the beam was in contact with the wall above.

 

[MIStructE_IRE]

I wouldn’t like to rely on it for fixity... I would be calling this a pinned connection in reality.

 

[Ron247]

It would be difficult to fix-end the steel beam. I do not know how much moment you would have in the steel beam calculation but the wall may not be able to accommodate that magnitude. The thicker the wall the better chance you have but you still have to check the "couple" in the wall pocket. The top flange of the end of the steel beam is pushing up on the foundation wall while the bottom flange is pushing down on the inside face of wall. The thicker the wall, the lower the force in the couple is. Is the foundation wall concrete or masonry?. If there is very little foundation wall above the pocket, you may crack/split your wall and lose any fixity there was.

It is doubtful you can prevent rotation at the wall.

 

[BridgeSmith]

I'm not a 'buildings' guy - I'm a bridge guy, so I could be completely wrong, but I'll throw in my 2 cents worth. If the beam has any significant end rotation (deflection) and the pocket will be fully grouted, you'll need to isolate the beam from the surrounding grout. Otherwise, you'll have spalling grout around the beam or cracking in the wall, or both.

Especially if you do as I suggest above, the beam should be designed assuming a pinned end condition. Even if it's directly embedded, it would take significant analysis to put a number on the end restraint that you could confidently assume. Unless this is a large project with many such beams, it's unlikely to be worth the time to properly analyze the connection and wall system.

 

[CANPRO]

If you were in a pinch and had to justify some fixity at the end of the beam you could install a short knee brace between the beam and the wall.

If I ever question the fixity of a connection, I put it to a simple test - I imagine the beam in question cantilevering over my head supported only by the connection I'm considering - If the imaginary version of myself starts sweating bullets standing under this beam then I call it a pin and move on. There is not a chance I would stand under a cantilevered beam supported by the connection you describe.