Retrofitting / Renovation of existing RC beam/column

[Enhineyero]

Hi all. Does anybody know if there is a code restriction regarding re-construction of a RC beam. For example i have a RC beam carrying roof trusses, but the owner wanted to renovate the house and install a RC slab instead of a steel trusses. lets say the existing RC columns and Beams are adequate to carry the change in load (also no seismic load is req'd, the governing load is gravity loads).

Now the existing beam will have to carry the new slab. Can i partially remove the top concrete of the beam and recast it together with the new slab (existing beam and new slab will have the same grade of concrete and the existing rebars will not be removed or touched)? or is there something in the ACI or Euro code that will prevent me from doing this.

thanks for any information

 

[JAE]

To get the slab to work compositely with the beam so you have a flanged beam (instead of a rectangular beam) you would need to ensure that the slab and beam work compositely together so that horizontal shear slippage will not occur at the joint between slab and beam.

This would require vertical dowels, or stirrup legs, that would engage the two parts. In the ACI, this would be a horizontal shear dealt with via shear friction (chapter 11). The connecting reinforcement would have to be fully developed on both sides of the joint. This can be difficult to do as you typically don't have enough distance to develop the bars.