Am I Missing Something?
Am I Missing Something?
(OP)
I am trying to verify some masonry spreadsheets and I am having a hard time with some things.
If you have a section with axial load and moment, is it correct to assume that you can analyze the section for each individually and superimpose the results to get max stresses? This is reinforced masonry.
I got some results for the combined loading that surprised me a little, but I took the results blindly and verified them through mechanics, not design. Needless to say, it did work out. I then analyzed the section for axial load only, and for moment only. I thought I could superimpose the masonry stresses and the steel stresses to get the same stresses that I got when using the combined loading, but it isn't working out that way. Does anyone have an idea why?
Am I just completely missing something.
This is ASD, and I thought that for the elastic range of stresses (I know it's not really elastic if it cracks, but we assume so for design), that the principle of superposition applies.
If you have a section with axial load and moment, is it correct to assume that you can analyze the section for each individually and superimpose the results to get max stresses? This is reinforced masonry.
I got some results for the combined loading that surprised me a little, but I took the results blindly and verified them through mechanics, not design. Needless to say, it did work out. I then analyzed the section for axial load only, and for moment only. I thought I could superimpose the masonry stresses and the steel stresses to get the same stresses that I got when using the combined loading, but it isn't working out that way. Does anyone have an idea why?
Am I just completely missing something.
This is ASD, and I thought that for the elastic range of stresses (I know it's not really elastic if it cracks, but we assume so for design), that the principle of superposition applies.






RE: Am I Missing Something?
For axial load, it probably behaves elastically, but for bending, I would imagine that your masonry behaves as a non-tension material, i.e. non-linear behaviour.
RE: Am I Missing Something?
RE: Am I Missing Something?
RE: Am I Missing Something?
RE: Am I Missing Something?
What method are you comparing this to?
RE: Am I Missing Something?
I was using P/A+bending stress due to moment only. Since this already took n into account, I thought that should work. Am I thinking about it wrong?
RE: Am I Missing Something?
RE: Am I Missing Something?
RE: Am I Missing Something?
RE: Am I Missing Something?
Hmmm... something to think about next time I'm "sitting on the throne".
RE: Am I Missing Something?
RE: Am I Missing Something?
RE: Am I Missing Something?
In the case where the properties you are using are the same throughout, then I don't see why the results are different between applying the combined load versus adding the axial effects to the bending effects. Remember to also check as T-beam as required.
RE: Am I Missing Something?
RE: Am I Missing Something?
masonry due to flexure or due to flexure in combination
with axial load shall not exceed (1/3) f'm provided the
calculated compressive stress due to the axial load
component, fa , does not exceed the allowable stress, Fa ,
in Section 2.2.3.1.
RE: Am I Missing Something?
RE: Am I Missing Something?
applicable for reinforced masonry and is therefore not
included in Section 2.3.
RE: Am I Missing Something?
The axial stress, fa, doesn't change, and so it is correct to refer to it as an axial "component." The bending stress, fb, changes depending an the axial force. Notice there is no mention of a bending "component." I think the commentary to 2.3.3.2 is more clearly written than section 2.3.3.2.2, but that may be because it says what I believe.
The ACI publication (SP-3) that I referred to in my original post was for ASD of concrete under compression and bending. I believe the same approach is valid for masonry. However, my reinforced masonry textbook by Schneider and Dickey uses the unity equation, which, as you say, is clearly dismissed by the commentary 2.3.3.2.2.
RE: Am I Missing Something?
A side note, all my older examples use the unity equation.
RE: Am I Missing Something?
When set to UBC 97, it checks the interaction equation.
RE: Am I Missing Something?
From what I can tell, the unity equation is always conservative, if the axial force is compressive. It is not conservative if the axial force is tensile.
RE: Am I Missing Something?
This is what I have been saying, it seems you have to assume a cracked section the whole time to superimpose stresses in this way. There may be some approximation being allowed by ACI 530 to add the stresses directly as RISA is doing. I am not sure at this time what to do exactly, I am going to have to look more into all of this. But it is clear the interaction equation is not to be used for reinf. masonry per ACI 530 commentary.
RE: Am I Missing Something?
RE: Am I Missing Something?
RE: Am I Missing Something?
htt
RE: Am I Missing Something?
I don't think this is directly found in ACI 530, but the seminar they were giving was ACI 530 based.
RE: Am I Missing Something?
fa/Fa+fb/Fb < 1.0 or (fa+fb)/Fb < 1.0?
RE: Am I Missing Something?
RE: Am I Missing Something?
I am actually working on some heavily loaded cmu pilasters right now so I will be coming up with some myself based on ASD.
RE: Am I Missing Something?
http://www