huangyhg

unstressed strands as reinforcing
i am researching the use of high strength unstressed wire strands, coiled together, as conventional reinforcing in concrete instead of rebar. i was looking for information on bond strengths, strain compatibility etc, but found nothing substantial as of yet. one bit of information i did find is the closed thread below from eng-tips forums web page.
do a strain analysis on it and see how close the strand it to yeilding or if it even comes close to 60 ksi.
note: the e, modulus of elasticity, is not 29000 ksi, varies from 25,500 to 27,000. use the calculated e from the strand steel report. if substituted for grade 60 reinforcement in a equal area exchange, the reinforced concrete will have very similar strengths if the bonding lengths are correctly proportioned. you can not say 270 ksi steel can substitute for 60 ksi steel in proportion to the yield strengths.
there are several issues to consider here. using strands as mild reinforcing will affect the ductility of the member. this could cause issues for you if you are in a seismic region. you should also consider the failure mode of the
markallan,
you will be wasting your time if you try to do any type of analysis. the whole reason we have prestressed concrete today is because of the use of high strength steel (250k, 270k). you cannot take advantage of the properties of hs steel if it is not pre/postensioned. the prestress phenomenon is a consequence of the tensioning of hs steel, and therefore we cannot ignore it; although it has many advantages.
markallan,
theoretically you can use un-tensioned strand in a concrete
thanks to all for your input. by way of experiment, i did an ultimate (uls) strength analysis on a 200mm wide x 500mm 30mpa beam with 2 x 16mm diameter deformed bars (fy = 450mpa, es = 200gpa), area of steel = 402mm2. i then did an equivalent area-force substitution with 1400mpa strand (es = 205gpa), and needed 129mm2 of strand to get same uls resistance as 2 x 16mm bars.
i then did a strain analysis with the 1400mpa strand, and crack widths were unaccepatable at service (sls) loads - about 70% greater than upper limit allowed, thus highlighting the serviceability concerns.
of course, i made some "dicey" assumptions for the purpose of this comparison, for example that stress-strain curves for rebar and strand are the same (which they are not), that bond strength for strand is same as rebar (which it is not) etc.
but it did show me the truth of the words from my pre-stress course notes concerning the use of unstressed high strength steels: "the strain required to develop the strength is so high that the concrete surrounding the steel would be severley cracked at the serviceability limit state."
so the conclusion of the matter...pre-stress high strength strands.
ma
whoa, what units are those?????
lololol
it seems to me that if you "coil" the strands your modulus of elasticity will be different than if the strands are "straight".
maybe you will be closer to the characteristics of wire rope when looking at strain compatibility.
swivel63
real logical computer input friendly units, not like ft, inch's and fractions of an inch.
didn't i tell you not to waste your time? consider precast concrete piles with prestressing strands. why are the strands tensioned if by doing this you are applying a prestressing force which reduces the capacity of the section to resist external loads? the answer is, because you have to tension prestressing strands. if you find a case where strands were used successfully as conventional reinforcement, please let us know. another thing you need to re

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]