Bracket Plate to Existing Retaining Wall 1

[jreit]

I have a new bracket plate connecting a beam to an existing retaining wall. I'm trying to understand how the new loads on the wall will act.

It is a fixed connection at the end of the gantry which imparts a moment and shear. The moment is resolved into a tension couple between the top and bottom anchors going into the concrete.

I'm not sure how to treat the vertical reaction at the end though. Do I just translate that into an additional moment that acts together with the fixed end moment on the wall?

Is there any shear force that acts on the wall? Both faces of the wall have rebar perpendicular to the anchors so it might translate as shear in the concrete but I'm not sure.

 

[BAretired]

If the load is vertical, say 'P', the moment applied to the wall is P*e where e is the distance from the center of wall to the point of application of P.

The moment gets into the wall via the fasteners, but it is not an additional moment. The fasteners would feel a moment of P(e-t/2) where t is the wall thickness.

A wall with an applied moment at the top has a shear force equal to M/h where h is the height of wall. If there is a horizontal force 'H' applied in addition to P, that would add to the shear.

BA

 

[JAE]

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[JAE]

An applied moment near the very top of the wall could be a problem - on the tension side of the wall at the top - your vertical reinforcement doesn't have a chance to be developed at the very top of the wall between the upper bolt line and the lower bolt line where the moment gets to its maximum.

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[Ron247]

I guess I am confused. How do you get a fastener to go into compression without double nutting it and leaving a gap between the plate and the wall at that fastener? Seems the lower part of the steel plate is in compression and the lower fastener may be doing nothing or it may be in minor tension.

 

[JAE]

Ron247 - I think technically you are correct - the lower fasteners don't really impart compression on the wall, but rather just serve to take some vertical shear.

The lower portion of the plate is the actual element that imparts compression on the wall. It is just sometimes convenient to assume the C force is aligned with the lower bolts.
That isn't always perfectly the case, though. The compressive force probably works more like a standard Whitney stress block as in reinforced concrete design.



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[Ron247]

Thanks JAE. I have used the same method as a quick approximation. When the plate dips a good bit below the bottom fastener, it is fairly conservative ball-park estimate.

 

[BAretired]

Another point to consider is whether or not the beam acts as a lateral prop for the top of the retaining wall. If it does, the wall is not exactly a cantilever but is fixed at the bottom and hinged at the top.

If the beam is connected to the bracket, even by friction, temperature change or vibration could impart horizontal force from beam to existing wall.

BA

 

[BAretired]

It is a fixed connection at the end of the gantry which imparts a moment and shear.

If the beam is bolted or welded to the bracket, the possibility exists that a horizontal force 'H' exists at the connection in question, either from temperature change in the beam, impact loading from the gantry or change in lateral soil pressure on the wall.

If the wall is truly pinned at the top and fixed at the bottom, then there should be a point of inflection between top and bottom, or a reversal of moment. The moment at the bottom would be M/2 where M is the applied moment at the top.

In actuality, the top is not truly pinned and the bottom is not truly fixed but restrained against rotation. In any case, there should be a reversal of moment as opposed to the constant moment below the lower bolts shown by JAE.

I don't know why a bracket was selected to support the beam. It appears from the sketch that the beam could be extended over the wall to provide direct bearing. The issue of a horizontal force H still exists, but a sliding connection could be devised to limit the magnitude of H.

I have a new bracket plate connecting a beam to an existing retaining wall. I'm trying to understand how the new loads on the wall will act.

Me too!!



BA

 

[BAretired]

@jreit,

No comment? What do you mean by a "fixed connection"? How is the other end of the beam supported?

BA