Escalator Span for existing beam to beam spacing 1

[ali07]

We have a situation where escalator supplier is asking for slicing 5" existing 24"x48" beam, so that he can fit his escalator. We asked to adjust his escalator, but he told that escalator cannot be changed.

My question is whether all escalator are too tight to some existing opening dimensions or this is the only case we are facing, Escalator supplier is OTIS.

Also suggest what would be the practical solution without disturbing existing beam.

 

[JAE]

Are these concrete beams?

I assume so.

And you need to cut 5" out of the width of the beam? If so you would probably be cutting the shear stirrups away on one side. Also cutting at least one top and bottom bar and eliminating required concrete cover over the reinforcement.

When you have existing conditions, the elevator supplier should adjust.

Othwerwise - you would have to demolish the entire beam and replace with new beam (concrete or steel) to provide the wider opening.

 

[ali07]

Yes, these are concrete beams and spanning 55 ft.

Is it possible to adjust escalator framing, or escalator guy is hesitating to change his escalator as it would involve more cost to the design.

 

[ali07]

Hi Jae,

Attached herewith is a sketch shows only for pocket.

 

[JAE]

ali07,

OK - so it is just a small pocket in the corner of the beam. This isn't so bad.

The consequences are that the top corner bar is damaged. If this is in a compression zone of the beam, then you've probably lost some continuity in the top bar, thus negating to some extent its ability to help minimize long term deflections.

If it is in a tension zone (i.e. near the beam ends) then you will have cut a top tension bar and reduced the beam's strength.

The stirrups at the pocket would also be cut at the ends, diminishing the developement of the stirrup to resist the shear forces.

I think you have a couple of options here:

1. Carefully analyze the beam to see what the cut bars are actually doing and where they are cut along the length of the beam will certainly matter a lot. It may be possible that at the pocket the stirrups are there as minimum reinforcing (and not substantially providing Vs for capacity. Also the top bar may not be a tension bar and the cut may not significantly affect the beam capacity.

2. Alternatively, could you install a bolted bracket to the side of the beam to support the escalator without a pocket?

3. Or, see if the escalator supplier can indeed alter the framing to bolt directly to the sides of the beam instead of making a seat for the top of the escalator. Yes, they are trying to avoid re-engineering their product, which is totally understandable.

 

[hokie66]

JAE is correct, you have to analyze the beam to determine if removing the reiforcement at the pocket is acceptable.

 

[ali07]

This pocket required is 5.5ft in length of beam and located at about 5ft from support. This part of the beam is in negative region, that means the bar to be cut is in tension.

What about long term deflection if beam was cast about 40 years before.

 

[hokie66]

I wouldn't worry about deflection. If the beam is strong enough without the removed bars, I would allow it.

 

[JAE]

But 5.5 ft. from end means the bar being cut is in tension and this will certainly reduce negative moment strength. You would then have to see about whether positive moment capacity will work with a "pin" on one end - or at least some reduction in stiffness.

Also - the shear capacity should be carefully studied. How much extra capacity do you have to work with once the escalator is in place? It might be MORE shear than was originally designed for.

 

[ali07]

There is 80,000 lbs concrete stairs at this location which is going to be replaced with this 45000 lbs escalator, i'll check the difference.