design of one way reinforced slabs

huangyhg

design of one way reinforced slabs
at some places i found the practice of designing small span slabs say  upto 3.2m in residential apartment type buildings as one way reinforced slabs irrespective of their ly/lx ratio.(even it is <2) is it a correct way to design a slab?
thanks
mvk
it may be acceptable practice, as long normally you will be providing one mechanism for thransfer of the loads, the one-way parallel beams. it may also be convenint in simplicity for some cases. since normally transversal steel is required by any modern code, no special problem should develop if the design as beams covers the necessary requirements, whath will be easy for so small spans.
whenever mass-production is involved i suggest detailed evaluation for economy.
when designing in reinforced concrete keep in mind one thing: where you put reinforcement is where the load path will be, so there's no problem if you design a one-way slap even its span ratio less than 2, but keep in mind that you will spend more on reinforcement this way, because you could take more advantage of the two-way action.
hope this helps you
ngedm
there is one more aspect to be kept in mind. it is true that the load flows through the stiffer path. however, in a slab with a two way geometry (lx/ly<2),the initial load distribution will tend to be in both the directions as per the two way action.it is only after a certan amount of yielding along the weaker direction, the load will get redistributed and flow through the stronger path. in other words, the slab will crack in the weaker direction before the one way action is realised. of course, the slab will not collapse since, the slab is designed for one way action for the total load.
so it is desirable to design the slab as one way or two way as per the geometry and allow the load flow consistent with the geometry to avoid such cracking.
also realize that significant cracking, deflections, or other serviceability problems may occur in order for the chosen load path to become effective.
bear in mind that for such small spans you will probably have minimum reinforcement and for practicality it will probably be the same in both directions (probably 10mm bars at 200mm spacing in both directions). so if you find that you want to use this reinforcement and find that with a one way span this is adequate then there is no need to calculate the reinf for a two way span
carl bauer
thanks all for reply
as mentioned by trilinga initial load distribution will be in both directions then it will get redistributed in the direction of stronger path, then what loads shall be considered to be taken by beams in parellel direction to one way action? at least for this initial load distribution phase
mvk
since the weaker direction has very less moment capacity, it will not transfer the proportion of the load expected to flow during two way action ( such as the load defined by the yield lines). the extent of load transfer in the weaker direction could be as much as the load carried upto the yielding in the weaker direction. if the reinforcement along the direction is nominal, the load transfered may be negligible. the total load shall be applied on the two beams supporting the one way span. the beams at the ends of the weaker span can be designed for their own weight and a nominal additional load.
i understand -or if not is my opinion-, you design then simply as one way (if such is your approach). that the corner effects and other cause some damage will depend much on the total thickness, and should be despicable if your slabs are thick enough.
note however that these corner effects sum sometimes at corners with the parallel effects of dishing action at the foundation affecting the whole building.