BadgerEngineer
Structural
- Sep 16, 2008
- 43
In a slab-beam-column type construction in multistory building the practice is to many times use higher strength concrete in columns as compared to beams and slabs. The concrete is placed in the following stages:
1. Column is cast up to bottom of beam using high stength concrete.
2. Beams and slabs (Including junction) is cast using lower strength concrete.
3. Column above slab is again cast with high strength.
This sequence results in lower strength concrete in the beam-column junction portion of the column compared to the rest of the column.
Is it ok to use this method? If not, is it typical to puddle high strength concrete in the areas around column junctions? Is this addressed in ACI anywhere?
My thoughts:
Beam is designed for forces at face of column. - Therefore, beam-column junction is a part of the column and not the beam. Therefore it should be high strength.
Beam-column junction is the weakest zone (especially in seismic loading) so this portion should always be detailed with caution.
ACI-318 stipulates strengthening the joint when stength of concrete in beam is lower than concrete in column by 40%. However, ACI has no special provisions when the difference in concrete strengths is less than 40%.
Please let me know your thoughts.
1. Column is cast up to bottom of beam using high stength concrete.
2. Beams and slabs (Including junction) is cast using lower strength concrete.
3. Column above slab is again cast with high strength.
This sequence results in lower strength concrete in the beam-column junction portion of the column compared to the rest of the column.
Is it ok to use this method? If not, is it typical to puddle high strength concrete in the areas around column junctions? Is this addressed in ACI anywhere?
My thoughts:
Beam is designed for forces at face of column. - Therefore, beam-column junction is a part of the column and not the beam. Therefore it should be high strength.
Beam-column junction is the weakest zone (especially in seismic loading) so this portion should always be detailed with caution.
ACI-318 stipulates strengthening the joint when stength of concrete in beam is lower than concrete in column by 40%. However, ACI has no special provisions when the difference in concrete strengths is less than 40%.
Please let me know your thoughts.
