huangyhg

load bearing concrete ring design
i am looking for some design references for circular concrete rings. i need to determine the gravity load that rings of a certain configuration can carry. i am familiar with the astm reference c 478-08, but that does not really address the design approach. it just seems to set forth minimum reinforcing requirements. the rings will be precast and in this situation i will be stacking about 4 ring segments on top of each other vertically to get the necessary height. any reference suggestions?
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used these quite a bit, cant you ask the maufacturer. they are used for tunnel shafts so id imagine they can have a fair few stacked on top. check as plain concrete wall?
if the ring is to be used for vertical tunnel shaft, the gravity load capacity usually would be controlled by the friction developed in between the lowest ring surface and the surrounding soil/backfill. what is your application?
the rings are being used to carry the precast roof wedges in a circular tank. the outer part of the roof wedges are carried by the wall of the tank and the inner is carried by these precast ring sections. the rings do have small openings to allow the water into the inside of the rings so there will not be an external hydrostatic pressure load on the walls of the tank solely the vertical load from the dead weight of the precast roof sections and snow load. the rings will be sitting on a concrete mat foundation which will be keyed to accept them and prevent horizontal movement.
for this case, your load capacity is controlled by concrete bearing strength, which is a fraction of the nominal compressive strength (fc'). you can check aci-318, or pci design manual to find how much is allowed.
i would say you have a large column-like object (hollow circular column), with low slenderness. i would check it as a short column for axial compression capacity.
just out of curiosity, what is the height to od for these rings?
i would probably also check it based on wall compression requirements from aci. but likely they will kick you back to the column compression equations.
you could break your rings into discreet elements, say 1 foot wide, and find the capacity of each element individually, assumed fully braced. then multiply that by the number of elements.

if you have access to pca-column software, you could enter your geometry and have it calculate the compression capacity. this would be pretty straight forward for it i think.
the fact that they are precast rings really doesn't change things, as long as there is no loss in strength at the joints. are the rings connected together at all, or just sit together with some keyed interface? as long as the rings can't shift or distort relative to each other, i think you are ok.
thank you everyone for the input.
the outer diameter of the rings is 9'-6". the ring sections are 6' tall with a total stacked height of 21'. the top ring is shorter than the rest and they all have a ship-lap joint to lock the top and bottom rings together. preliminarily i have the walls of the rings as 9" thick.
would you consider the 1 foot wide element fully braced in both directions or just in the direction of the adjacent elements?
~waytsh

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