minimum shear reinforcing - prestressed member

huangyhg

minimum shear reinforcing - prestressed member
folks,
i have a question pertaining to the minimum shear reinforcing requirements for prestressed concrete members with fse > 0.4 fpu.
section 11.5.6.4:
av,min shall not be less than the smaller value from eq. (11-13)and (11-14)
equation (11-13) is 0.75 sqrt(fc′) bws/fyt but not less than 50 (bw * s)/fyt.
assuming that 0.75*sqrt(fc') is more than 50, will the minimum be based on the min [ max(section 11.5.6.3), section 11.5.6.4]
in other words, if 0.75*sqrt(fc') > 50, then the minimum will not be based on 50 bw*s/fyt.
please clarify.
as per your exposition, so it is, since you have properly determined the value per (11-13). hence this value, whichever it is, is the one to be compared with that of (11-14) to get the lesser of both, whatever the value of any of them, to be used as minimum reinforcement.  
slickdeals,
what you are proposing seems to be correct. as long as 0.75*sqrt(f'c) is greater than 50 then the governing equation in 11-13 will be:
avmin=0.75*sqrt(f'c)*bw*s/fyt
this is compared with 11-14
avmin=aps*fpu*s/(80*fyt*d)*sqrt(d/bw)
so...
avmin=min(0.75*sqrt(f'c)*bw*s/fyt,50*bws*s/fyt,aps*fpu*s/(80*fyt*d)*sqrt(d/bw))
asisth...
your last equation seems still allowing 50*bws*s/fyt become the minimum, that for the case considered seems be the contrary in (11-13), that for some cases (that quoted here as of interest, is precluding such lower value in favour of a higher one. so i think as slickdeals proposes
min [ max(section 11.5.6.3), section 11.5.6.4]
is a better statement,
otherwise you may be meaning that the 50*bws*s/fyt ,is always to be available as the minimum code shear reinforcement for the case
correct, the equation should read...
avmin=max(0.75*sqrt(f'c)*bw*s/fyt,50*bws*s/fyt,aps*fpu*s/(80*fyt*d)*sqrt(d/bw))  
no, if we are all agreeing to my op, then the equation would be:
avmin=min[max(0.75*sqrt(f'c)*bw*s/fyt,50*bws*s/fyt),aps*fpu*s/(80*fyt*d)*sqrt(d/bw))]
there is an exception for min shear steel in precast members.  if the precaster has appropriate testing data, they can forgo some of the minimum shear reinforement per aci.  i have seen this testing data for double tee webs.