huangyhg

analysis of two way slab
i need help with a two way slab problem. for some reason i just can't get started with this. i don't have much design and analysis experience and i need a starting point.
here's the problem. we have a two story building and there is a machine that weighs 5 kip currently in the basement, but they want it moved to the first floor. i need to see if the floor in that area can hold this weight. the floor has an 8" slab with colums spaced at 20' c/c both ways. the colums are 22" square. should i do a finite element analysis? if so, are there any good free ones available for download? any help getting started with this is greatly appreciated, i seem to be over thinking this and confusing myself! thanks!
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i think you should look at a concrete textbook (my favorite is wang and salmon's reinforced concrete design) and read the chapter on design of two way floor systems. basically, there are two methods for design. the first is an approximate method known as the direct design method, and the second (which i prefer) is the equivalent frame method. the equivalent frame method requires computer analysis, but not finite element analysis. you basically design the two way slab as strips in each direction.
daveatkins
i don't think you can use the dd method for anything other than uniformly distributed loads. i couldn't find a similar requirement for the ef method, but take a look to be sure.
you should check out some books and start reading, and ask yourself do you really want to check a floor slab for a 5 kip machine load with freeware.
you may use my website for such designworks, which are prepared as ms excel spreadsheets. and free of charge.
thanks for the help. i'm starting to read up on the ef method.
fuatornarli - i tried to access the slab design spreadsheet but it's not letting me, i can access other ones.
also, that was a good point about the freeware, i just have access or the means to get a good program right now!
you most definitely want to use the equivalent frame method in chapter 13 of aci 318. this allows you to place concentrated loads on the slab in addition to uniform loads and analyze the floor.
a finite element analysis could be done, but takes special care and knowledge to interpret the results without getting in trouble. - you could do both and compare results which would be good too.
for this specific calculation case, computer modeling (with shell elements for slab and beam elements for columns) may give results (bending moments, etc) faster. we tend to have better feeling about the results from equivalent frame method. but it is a simplified approach especially for the point load case and you still rely on computer for calculation. i used to use a dos procedure to calculate flat plate with efm. there might be some widespread-used software using efm?
there's a good design example in nilsson and winter's concrete textbook.

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