determination of "c" of Boundary Element from ACI
determination of "c" of Boundary Element from ACI
(OP)
Good day everyone,
this topic is a big question for me for so long
its all about the ACI 318-08 Section 21.7.6.2 on how to know if a certain shear wall needs a boundary element
the formula is ok, but I still dont get how some examples I see in the internet is solving the neutral depth "c" in this computation. Those examples are already uses a value of "c" thAt is already coming from an "in house" computer program.
how did they determine the "c" value?
and it will be a big help also if there's a reference regarding any manual calculation regarding "c"
thank you in advance!!!!
this topic is a big question for me for so long
its all about the ACI 318-08 Section 21.7.6.2 on how to know if a certain shear wall needs a boundary element
the formula is ok, but I still dont get how some examples I see in the internet is solving the neutral depth "c" in this computation. Those examples are already uses a value of "c" thAt is already coming from an "in house" computer program.
how did they determine the "c" value?
and it will be a big help also if there's a reference regarding any manual calculation regarding "c"
thank you in advance!!!!
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RE: determination of "c" of Boundary Element from ACI
RE: determination of "c" of Boundary Element from ACI
Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds
RE: determination of "c" of Boundary Element from ACI
Seeing that the code says that
"c in Eq. (21-8) corresponds to the largest neutral
axis depth calculated for the factored axial force and
nominal moment strength consistent with the design
displacement δu. Ratio δu /hw in Eq. (21-8) shall not
be taken less than 0.007"
it is clear it is a (factored) flexo-compression loadcase producing δu, then look within it for the section producing the highest c anywhere in the height of the shearwall for such hypothesis.
So you need a mathcad worksheet or excel sheet or any other tool doing the referred sectional analysis for the P-M solicitations at the investigated sections. The simplest (but only approximate) way is to assume a rectangular ACI stress block satisfying the P-M equilibrium, and if only considering tension steel compression-tension equilibrium can be established even by hand; otherwise it is better to use one of the referred tools.
RE: determination of "c" of Boundary Element from ACI
To make it simple you can assume that only the tension chord steel yields and add that to the applied compression force Pu also assume that the compression steel does not contribute to the compression force. From the way I am reading that section if your "c" is small enough you don't need a special boundary element. Once you have that number use the expression above and that will get you a "c" that is a good guess.
I am not very familiar with Chapter 21 as I don't do much seismic stuff, but I would think that you could get a good idea if you need this element from the numbers above.