db7
Structural
- Aug 22, 2006
- 8
I have a concrete flat slab building. A hole for a stair is to be placed such that part of the column strip is cut out. The loss of stiffness in adjacent bays is being addressed by adding FRP to the top and bottom of the slabs. Punching shear has been checked. Our problem is that right adjacent to the hole to be cut there is heavy conduit that cannot be moved, so we are planning to install an upturned concrete beam to take the load of the stair and the slab column strip that is being cut out. The existing slab would be doweled for connection to the new upturn beam.
We are considering how to design the connection of the upturned concrete beam to the existing column. ACI allows for a maximum 20% redistribution of negative moment, but we can't find guidance in the code that would allow us to only design for the shear friction connection only if the upturned concrete beam is designed as a simple span. I have seen some threads with engineers who suggest that as long as beam is designed as simple span, one need not consider the negative moment. Does anyone have an interpretation of the code that would address the latter? It seams inconsistent with the code limit on the redistribution of negative moment.
We are considering how to design the connection of the upturned concrete beam to the existing column. ACI allows for a maximum 20% redistribution of negative moment, but we can't find guidance in the code that would allow us to only design for the shear friction connection only if the upturned concrete beam is designed as a simple span. I have seen some threads with engineers who suggest that as long as beam is designed as simple span, one need not consider the negative moment. Does anyone have an interpretation of the code that would address the latter? It seams inconsistent with the code limit on the redistribution of negative moment.
