willowman
Civil/Environmental
- Feb 22, 2020
- 25
Hi all,
I need to use steel dowel bars in a concrete column to provide additional axial compression capacity. A dowel bar is preferred to reinforcement as it can be made from higher strength steel. The axial force in the column is sufficiently high compared to the bending moment so that there is no tension across the joint between column and beam below.
My question is one of strain compatibility. As I understand, I need to convert the dowel bar area into an equivalent concrete area using the modular ratio i.e. m = Es/Ec. Once I have this equivalent area I can multiply this by the allowable concrete stress and this gives me a new overall axial capacity.
We have to do this conversion because if we simply assumed that the steel dowel accepts a maximum load equal to its cross-sectional area x yield strength then this would ignore the fact that both the steel and concrete have to deform the same amount under load i.e. have compatible strain. We have to have compatible strains because we are assuming that load is transferred from the concrete to the steel dowel bar (which doesn't run the full height of the column)through a bond between the two materials. If the two materials strained at different rates then by inspection they can't be bonded. If they are not bonded then no load is transferred from the concrete to the steel.
Have I understood this correctly?
On a side note, is anyone aware of the Eurocode 2 approach to use of dowel bars or steel reinforcing bar in general being used in compression?
Thanks,
I need to use steel dowel bars in a concrete column to provide additional axial compression capacity. A dowel bar is preferred to reinforcement as it can be made from higher strength steel. The axial force in the column is sufficiently high compared to the bending moment so that there is no tension across the joint between column and beam below.
My question is one of strain compatibility. As I understand, I need to convert the dowel bar area into an equivalent concrete area using the modular ratio i.e. m = Es/Ec. Once I have this equivalent area I can multiply this by the allowable concrete stress and this gives me a new overall axial capacity.
We have to do this conversion because if we simply assumed that the steel dowel accepts a maximum load equal to its cross-sectional area x yield strength then this would ignore the fact that both the steel and concrete have to deform the same amount under load i.e. have compatible strain. We have to have compatible strains because we are assuming that load is transferred from the concrete to the steel dowel bar (which doesn't run the full height of the column)through a bond between the two materials. If the two materials strained at different rates then by inspection they can't be bonded. If they are not bonded then no load is transferred from the concrete to the steel.
Have I understood this correctly?
On a side note, is anyone aware of the Eurocode 2 approach to use of dowel bars or steel reinforcing bar in general being used in compression?
Thanks,
