span to depth ratio

huangyhg

span to depth ratio
i was asked to make a quick analysis of  a small single storey structure to ascertain if a second floor could be constructed on top of it.
however i found that the span to depth ratio of one of the panels was slightly greater than the limit.
can you offer me some advice as to whether this is significant or what can be done to rectify this problem?
(other elements in the stucture seem  adequate.)
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the span/depth ratio limit is primarily set to limit deflection under serviceability loads.  if you exceed the limit by too much then walking across the floor would be like walking on a trampoline (extreme case).  the other problem you are more likely to encounter is cracking of any floor finishes or partition walls which are connected to the floor.
you need to look at the structure and its usage in this light before accepting a floor whose span/depth ratio is too large.
andy machon


could you describe what you mean by "panels"?  are these concrete precast planks?
is this a concrete beam and slab system? if so there are usually modification factors for tension steel and again for compression steel. presumably you have the reinforcement drawings and so can assess what these are. it may be that there is compression steel just for anticrack measures which you can then use to help you with your span/depth ratio. if all that fails then you will need strengthening measures which could vary. you could add a column (a bit intrusive usually and needs another footing). you could also use externally bonded reinforcement under the slab. i don't know much about this technique but i'm sure some of the other engineers on this forum could help there.
carl bauer