PT Slab - Column Joint Rebar Details

[Murali27]

Dear All

In one of my project, the support moments on column-PT slab joint are governed by ultimate Dead & Live Load case compared to lateral load combinations.

Is there any additional steel required on account of lateral load effect alone i.e at top & bottom. Though the lateral loads are reversal, with the D +/- E & 1.2D + L +/- E load combinations, there is no need of additional bottom/top steel at support.

Am i missing anything?

Thanks
Murali

 

[rapt]

Murali,

Depends on the design code and the building type.

Normally there is a requirement for a minimum reversal capacity at supports and a minimum capacity anywhere in the member, top or bottom. These are related to the maximum moment at the supports.

 

[Murali27]

Thanks Rapt

Design Code: UBC 1997

Building Type:

Primary Lateral system: Shear wall (Core walls)
Height of the building : 150m
Primary Gravity system: Column + PT slab

The support moments are primarily governing for ultimate dead & live load case. i.e 1.4D+1.6L

The support moments are less for other lateral load combinations.

My question, as per analysis, we don't require any additional steel for lateral effect. Is it correct?

Is there any special requirement for PT slab + Column frame against seismic force.

Here, approving authorities are asking to have rebars at top & bottom near the column + slab joint so as to conform the deformation compatibility. Is this correct?

Thanks
Murali

 

[rapt]

Not sure what UBC says but normally for a fully braced frame, no. But normally the shear walls do not take everything and there is some frame action involved from the floors and columns and then there is a need for it.

It is a good idea in my opinion to make the joint dcutile like this.

 

[andiron]

Murali.
YUp. You have to design the slab for compatibility even if your assumptions is core is taking lateral.
Check capacity for different combo.

 

[Murali27]

Thanks, Andiron

Out of all load combinations, gravity load case is governing with respect to the support moments (Negative moment).

PT slab will be designed for this maximum moment out of gravity load combo

-Murali