one-way slab

huangyhg

one-way slab
two questions about 1-way slabs.
1) when are 1-way slabs preferable to 2-way slabs? i can only think of the ease of design and perhaps the geometrical requirements of a particular project, i.e. column locations.
2) when calculating live load reduction based on floor (or flat roof) area, do you consider the total floor area or a single span of the one way slab? for example, think of a continuous 1-way slab spanning beams 20' o.c. in the short direction. for the purpose of live load reduction, do you consider a single span of slab (let's say, 20' x 40') or a total floor area consisting of several such spans (e.g. 100' x 80')?
1. it depends on what system you're using.  in some cases, you'll want beams and girders on a grid.  usually, the slab will naturally span between the beams because the beam spacing is much closer than the girder spacing, so it's more of a one-way situation.  if you have a flat slab or flat plate, then you obviously have a two-way slab.  of course, there are exceptions and some systems that don't neatly fit into one or the other category.
2. i don't have my asce 7 here, but i seem to re  
there are specific instances where it's worth the trouble to use a two way slab.  it's a pain to use and there's a certain amount of black magic inherent to the method.  you can use a lot less concrete (with higher reinforcement ratios), meaning less shoring, less dead load and more headroom.
slab aspect ratio will determine whether it is a one way or two way slab. i typically use 1.5:1 or 2: 1 or greater as a 2 way slab.

asce 7-05
limitations on one-way slabs:
the tributary area, at, for one-way slabs shall not exceed an area defined by the slab span times a width normal to the span on 1.5 times the slab span.

steelpe: thanks a lot.
little correction... sorry.
asce 7-05
limitations on one-way slabs:
the tributary area, at, for one-way slabs shall not exceed an area defined by the slab span times a width normal to the span offff"> 1.5 times the slab span

oops, i meant 1.5 to 1 or greater for one way slabs.