Dowel bars design and Expansion joint in Concrete pave.
Just read carefully and you will understand :-
Dowel bars are inserted and kept fixed at one end and other end in adjacent slab is kept free to expand or contract due to temperature variation by providing a thin coating of bitumen on bars and metallic cap (partly filled with cotton) is provided to allow a free space of 2.5-3cm for expansion, hence bars do not destroy concrete from inside. Closing and opening of joints depends on dowel bars. We generally use steel reinforcement bars as dowel bars. The resistance to bending in bar and bearing on concrete depends on the total length of embedment of dowel bar in slab.
Points to remember while designing dowel bars are:-
- they must be easy to install at site
- should not be provided in slabs less than 150mm thickness
- bars must be corrosion resistant i.e.painted or galvanised from the free end
- bars must easily distribute load stresses in adjacent slab without exceeding permissible stresses.
The dowel bars may be designed on the basis of Bradbury’s analysis for load transfer capacity of a single dowel bar in shear, bending and bearing in concrete.
Expansion joint in Concrete pavement: As the name indicates that the joint for expanding concrete pavement due to rise in slab temperature. These joints are mainly provided at 50m interval of 20mm width.
Hence by providing such width the continuity of slab breaks and forms a weaker plane in cement concrete pavement, so the stresses due to wheel loads at such joints is very high and to resist such stresses at edge and corner regions we generally adopt dowel bars projecting in longitudinal direction.