huangyhg

structural use of chimney
we are designing a lodge that will have some large open areas. i would like to use the chimney for part of the lateral force resisting system. is this allowed by the ibc 2003...i can't find it...any comments on good idea or bad are appreciated thanks.

if the chimney is engineered to take the required lateral loads (as a shearwall type system) and you provide adequate collectors properly connected to the chimney, then i would say you could certainly use it.
most chimneys are either multi-wythe brick or block and brick so the appropriate design code provisions would be required (i.e. aci 530).
if you are in a seismic zone you may actually have a really good idea... if you're reinforcing the chimney and paying close attention to ductility and any potential incompatibility of deflections. normally chimneys are considered bad news in seismic zones, however i believe this to be a symptom of where and how they are normally found (ie: timber structures with unreinforced clay brick masonry chimneys). they are then very brittle elements which refuse to deflect, attract disproportionate amounts of load and fail with high cost damage and potential loss of life as a consequence.
if you are planning a reinforced concrete masonry unit (cmu) chimney with veneer to hide the true nature i believe you have a fairly good idea when including it in your lateral load system since nature will include it anyway whether or not you consider it in your calculations.
ductile, within 25% deflection compatibility with the rest of the system, and based on a full-rigidity calculation of the system to determine the forces it should carry. with that done i believe you are actually designing a better system then you would without the chimney included in your llrs.
additional comment: if your structure is anything other than symetrical with a centre of rigidity coincident with centre of mass you're going to need to calculate the actual torsional moment on your building. (rather than any code-base symplified approach like 10% of structure's width or length).
good luck,
ys
p.s. recall: wall rigidity = 1 over [1/(e·t)][4(h/d)^3 + 3(h/d)]
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
there are fire issues that need to be considered.
i don't think the fire issues should be too major... i might be convinced otherwise by a persuasive argument, however at sls the chimney should not crack or have any distress that would allow fire or smoke to excape, thus not of concern. at uls loads all that is really intended is that the building not collapse and people can make it out alive. short of collapsing (already out of the question for our uls load case), the chimney should not let any catastophic amount of fire or smoke out.
definately something to consider, but i don't think it's a no-go.
cheers,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...

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