huangyhg

n.a. location, doubly reinforced beam
any body has any step by step guide for it. i know the formula.
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i made a spreadsheet for this. you have to assume a na location and it checks out if t=c. if it doesn't, you adjust your na location until it does.
you have to make a spreadsheet for this or you'll drive yourself crazy going through the iterations. are you just trying to get the moment capacity of a doubly reinforced beam? i will typically use pcacol (but you can use any concrete column software that gives you an interaction diagram) and just pick off the pure moment value.
i need this to find icr. u mind uploading your spedad sheet if it is in excel. mathcad i do not know.
i'll do you one better. here is a spreadsheet that will find icr and ieff directly. i developed this for input into ram advanse for the ie/ig factor.
i developed it for t-beams, but if you have a rectangular beam, just use b=0. the top part of the spreadsheet is for a quick strength check. the bottom is what you're interested in. only input the boxes shaded yellow.
file has an extension xlsx.
cannot open it ms excel 97
try this one.
iterations can be very simple when using goal seek to solve for t=c. i would ignore the extra capacity that you get for beams reinforced near the compression face. basically all that steel is going to do is raise your neutral axis but i would not include it in the design.
your depth of compression has to be below the top layer of reinforcement or the top steel does nothing for moment capacity.
same basic procedure as a concrete column in bending, effectively having both tension and compressive steel.
mike mccann
mmc engineering
structaco-
it has to be a fairly good distance above the na to do anything for the moment capacity, not just above it. more importantly, however, is it's role in deflections, specifically long-term deflections. i've rarely had a situation where i needed compression steel for strength, but often need it for deflections.

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