In flat slab system, say that the t 1

[dccd]

In flat slab system, say that the total length is 48m x 24m, column with drop panel with spacing of 6m... In this case , main bar outermost top bar (T1) and outermost bottom bar (B1) should be parallel to the 24m , right?

I came across an example that main bar T1 & B1 is parallel to 48m... Which one is correct ?

Or it doesnt matter that whether mian bar is parallel to shorter / longer dimension of the overall flat slab system ?

 

[jayrod12]

I usually design as if the bar is always the inside layer, that way I stop caring on site so much when they inevitably screw it up. Since your spans are evenly 6m, does it matter what direction it goes?

 

[dccd]

Thanks, so when the spacing of column is equally spaced in both direction, so the main bar direction doesnt matter?

How if the at the intersection of 2 slab, at the continuous part , slab 1 main bar direction is horizontal (T1), whereas for slab 2 , slab 2 secondary bar direction is horizontal T2...

In such case , I shall label the extra contionous top bar RED in horizontal direction as T1 or T2 ? Main bar direction labelled in blue ...

 

[KootK]

The outer bars will act over the greatest cross sectional lever arm and thus generate the most moment resistance per unit area of reinforcing provided. Consequently, if the loads and layout are such that design strips in one direction generally have greater moment demand, then the outer rebar will be specified to run in that direction. That's the general principle and it's nothing more than trying to match the most advantageous flexural capacity per unit reinforcing with the greatest flexural demand.

 

[KootK]

With regard to your L-shaped plan example:

1) I'd normally make the lower primary / secondary bar order the same for both slabs. Otherwise, where the bottom steel is continuous across the boundary, you'd great an offet lap splice condition that is undesirable.'

2) I'd normally make the upper primary / secondary bar order the same for both slabs for the sake of simplicity. That said, if there were a compelling reason to switch it up, that could be done since top steel is usually not continuous. That said, I'd be very careful about calling this up clearly unless I was following jayrod12's conservative, fool proof approach.

 

[dccd]

Say that I have a basic T10-200 bar top and bottom for both slab aforementioned. However, there’s extra T10-300 top horizontal top bar needed at the junction. In such case, extra T10-300 is added at the outermost top (T1) or inner top (T2) ? How can this extra T10-300 lap with existing rebar from the left and right ?

 

[dccd]

With regard to your L-shaped plan example:

1) I'd normally make the lower primary / secondary bar order the same for both slabs. Otherwise, where the bottom steel is continuous across the boundary, you'd great an offet lap splice condition that is undesirable.'

2) I'd normally make the upper primary / secondary bar order the same for both slabs for the sake of simplicity. That said, if there were a compelling reason to switch it up, that could be done since top steel is usually not continuous. That said, I'd be very careful about calling this up clearly unless I was following jayrod12's conservative, fool proof approach.

In this case, I shall add the extra rebar [highlight #4E9A06]T10-300[/highlight] in which case ? Which case is more appropriate ?

 

[jayrod12]

That is precisely why I wouldn't be designing or detailing it such that this scenario exists. Why flip the top bars at the junction? It just makes for these undesirable options.

 

[dccd]

Can you provide a sketch that how's its down at construction site usually? Extra horizontal top rebar with lap with which one? I have no idea at all... Thanks for your help

 

[jayrod12]

I would be doing it this way. Even if it means that the bars aren't as optimized in one wing of the L-shape. It makes everything so much easier to deal with on site. As I indicated, I would be designing the reinforcing as if they are always in the least optimal location. Because then when they screw it up on site, you do not care. A little bit of extra steel where I practice is far less costly than reworking the steel once tied.

 

[dccd]

I would be doing it this way. Even if it means that the bars aren't as optimized in one wing of the L-shape. It makes everything so much easier to deal with on site. As I indicated, I would be designing the reinforcing as if they are always in the least optimal location. Because then when they screw it up on site, you do not care. A little bit of extra steel where I practice is far less costly than reworking the steel once tied.

1.) Since you made the horizontal rebar as main rebar at top for both slab, For slab at the right, when you design the slab top bar , do you make the effective depth (center of rebar to base of concrete) shallower ? This will result in higher amount of rebar necessary ?

2.) I might as well design the vertical top rebar as the main bar (placing it at outer layer) ? In such case, the extra horizontal rebar it tied on top of the vertical top rebar ? Or at the lower top rebar (tied to the side of lower top rebar) ?

3.) For the slab at the left, the main rebar supposed to be in horizontal direction, for the slab at the right, the main rebar supposed to be in vertical direction... In such case, if we are going to make the main rebar and secondary rebar for both slab in the same direction only, main rebar spanning horizontal /vertical direction is more benificial and what's the reason behind ? Would youi mind to explain further ?

 

[jayrod12]

The answer to all your questions is, I would design my slab in all cases as if the reinforcing were the inside layer, therefore requiring more reinforcing than optimal, but allowing me to care less whether it is tied exactly as I showed it or not. The additional cost of reinforcing is far less than the cost and pain of reworking the reinforcing when they inevitably tie it in the wrong orientation.