Dowel bars are placed at the transverse joints of concrete pavement and they take part in partial wheel load transfer from one slab to its adjacent slab. The dowel bars also allow axial thermal expansion and contraction of the concrete slab along the axis of the dowel.
Dowel bars are Mild Steel bars 30–38 mm diameter and 450 or 500 mm length. They are spaced at 300 mm centre to centre.
Tie bars are deformed rebars or connectors used for holding faces of rigid slabs in contact to maintain aggregate interlock. Tie bars are not load transferring device. For instance, tie bars are used in longitudinal joints in concrete pavement.
Tie Bars are TOR Steel bars 12 or 16 mm in Diameter (12 is common, 16 is not) of around 640 mm length. Their spacing is variable since it depends upon thickness of concrete surface and width of slab, though typically it varies between 550–640 mm.
Difference between dowel bars and tie bars