Concrete Beam End Moments

[carnahanad]

Hello,

I'm evaluating an existing structure that has a 1-way slab supported by concrete beams and concrete walls. The existing documents indicate a Live Load for the room. I'm using the concrete beam reinforcement schedule to double check the beams for some new equipment in the room. I have a 3 span beam condition. Unfortunately, I don't meet the beam length or uniform loading requirements of 8.3 (ACI 318-08) to use the moment calcs in 8.33. I put my beams and loading into RISA to get load diagrams. From the reinforcement in my beam, which is an end beam, the only way I can get the positive moment reinforcement to work is if I fix the end of the beam at the wall. The reinforcement at the top of the beam at the end is hooked into the wall and there is enough reinforcement to develop the end moment assuming a fixed end. Is this a valid assumption, or do I need to determine the rigidity of the beam and use that for developing a moment at the end?

I look forward to the discussion.

 

[dhengr]

JAE:
Moonshine never lasted long enough to age, and I’m not that big a fan of wine, so I wouldn’t pay a great premium for some fancy aging, can’t taste the difference. Never did the moonshine thing myself, too young, but I did know where a couple old stills had been, out in the woods, where I grew up in northern Wisconsin. I did know a few older guys (born early 1900's) who did make moonshine though. Otherwise, I are damn near perfect, despite the aging, just ask me.

Acarnah2:
The original designer would have had a 100#/sf LL, or some such, where ever he didn’t have boilers and cooling towers on that mech. room floor. Obviously, the 100#/sf LL does not apply under the footprint of your new mech. equip., so the new added load is less than the total operating weight of the equip., maybe (100#/sf)(foot print) less. You could also put the new equip. on skids, or some such, which would apply the new load more favorably. The walls will take some end moment as a function of their stiffness and reinf’g., they are doing that now; otherwise I agree with Hokie, I probably would not have designed for a fixed end beam at the wall, but would have still shown some reinf’g. for an end moment, to avoid/minimize cracking. ASCE has pages and pages on this, but my 100#/sf LL is a transient LL, and is different than the fixed LL of a large piece of mech. equip. The Tee action of the slab and beam is also worth considering if needed. The original design was working so why are you concerned about that? Your last sentence sounds bass-acwords to me.