how much weight can all thread support ?

This is a Question for you engineer type fellas out there ,.. my ceiling has settled about a half inch or more in a nice bow ,.20 yrs ago,when i knokt out a 14ft wall and built on to the girls bedroom ,. i supported the ceiling and everthing from the 1x12 maple fuff sawn sheathing that was nailed in the gable above the bedroom ,, Now I think i should at the least build a 2x 10 beam 14 ft long to support the sagging ceiling ,. but then got to thinkin about this problem while rakin today ,, i just dont care for those expensive wafer board manufactured joists that probably could clear span 14ft and do the job . instead of having a hum-drum heavy 6x12 beam up there,That In all Honesty would need a center post for support ,. why not put a suspension bow across the distance,.? , the center mite drop as much a 15 inches ,and i could roll or drape the beam in 2 nice arcs that would look sweet , To That end i will mortise my end supports at the floor and ceiling and use oak blox for tension boards to keep from sqishing and compressing at the tension points,.i would rather use unthreaded round bar steel and thread the ends ,. but then i wonder if simply getting 3/4 all thread ? But i want to know what the load values are , Would anyone know what is best to do the job? IMHO i think any threaded rod could stretch significately over time ?, , i honestly believe the existing roof and ceiling has been in this state for 18yrs and will never fail ,but i know it has settled ,because i can plumb across the roof and it shows a slight drop .///.20 yrs ago , What i built was a self supporting 16ft round turrent above the new section and feathered it into the existing gable roof , complete with 9 feet of bow window glass made from 4 windows , 2 panes are fixt , 2 are casement crankouts . inside i made a 8 ft circle dome rotunda that rises into the roof about 3 feet ,, the turrent over the girls room and the triangled cathedral roof over the boys room addition complemented one another really well ,. the house is BEAUTIFUL. but it has a engineering flaw that needs addressed,. thanx guys for your thoughts and ideas

Depends on the grade, all thread comes in grade 2-6-8.

I can't see the rod stretching over your grandkid's lifetimes if you use the stronger rod as per Jon. It is either up to the job or not.

Here's a safe load chart. Doesn't say what grade, but as you will see, the numbers are up there.

It won't stretch over time. The beam may sag, but the rod will stay the same length. I have stretched it, trying to use it for a puller, but that was extreme abuse, nothing that would ever happen in a structural load application.
All Thread Capicity

Just me but I would never use 1" material for a load carrying header, depending on length and load 2" X 8" would be a minimum.

(quoted from post at 12:05:26 09/27/17) Just me but I would never use 1" material for a load carrying header, depending on length and load 2" X 8" would be a minimum.

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Jim you may want to school yourself on engineered structural products. You may be surprised how many one inch or less structural elements are in buildings that you frequent.

Well I can Agree ,for most part ,.. But if You Could See How,this is built ,, You Would Agree That I was Only Asking The 1x12 to support itself,. 14 ft is a pretty good span,, even for maple,. so i am notreally suprised that it lowered somewhat ,. like i stated earlier, it probably moved in the 1st 2 yrs and has not moved since ..just never was a priority,and still is 'nt , i just want to build the the double arc beam with a center drop drape ,..and i should or MUST true and fix the sag while i am at it

Steve ,.. many THAnKS ,, That is exactly the chart i was looking for ,,. loox like 3/4 mite be the correct size ,.

Coil rod has much more strength. 1/2 coil rod has 9000 # tension strength, with a 2 to 1 safety factor. (less threads per inch means more metal) That oughta hold your ceiling. Available at concrete supply's.