The term dowel bar is not a new thing it’s just the normal steel which is using in reinforcement for the different purpose.
Dowel Bar – Scenario 1
The dowel bar is used in reinforcement to connecting the old and new concrete element.
You would see the reinforcement bars are extended in a column at over the slab level to connect the next slab.
You may aware that a steel rod has the maximum length is 12m but we cannot pour concrete up to 12m in a single moment.
So the concrete may pour to a certain length and the remaining portion will be poured after some time. Hence the steel bars are extended for joining the new and old concrete it is called dowel bar.
Where is it to be used?
Mostly those bars are provided in column, staircase, slab. Because these are the possible area may be extended in the future.
The dowel bar length will be in the range of 45d to 50d (d- Dia of the bar).
Dowel Bar – Scenario 2
In another scenario, a smooth round steel bar is provided between the two concrete elements to uniformly transfer the load without restricting the horizontal joint movement.
These bars can accommodate the expansion happening due to the horizontal movement.
The maximum length of the dowel bar is 500 mm and the diameter is 32mm and it will be placed in concrete at an equal spacing.
Another name of Dowel bar is Tie bar and mostly it was provided in the rigid pavement as above said to transfer the load.
You may interest to read the different types of joints used in construction.