What are the design considerations for dowel bars in joints of concrete
carriageway?
My dear Dr Amjad
The behaviour of dowel bars resembles that of piles in soils subject to lateral loads. Failure of the joint occurs by yielding of steel under bending action or by crushing of concrete due to bearing stresses.
In general, the spacing of dowel bars should not be too close which may pose problems during construction. However, it should be not too wide to allow the occurrence of bending between the dowel bars. On the other hand, regarding the length of dowel bars, it should not be too long because the induced stress at the end of long dowel bars is insignificant and is not effective in transferring loads between adjacent concrete panels. However, if the dowel bars are too short, the stress at the face of joint is increased resulting in concrete crushing.
The purpose of the dowel bar is to effectively transfer the load between two concrete slabs and to keep the two slabs in same height. They are smooth steel bars installed across a transverse joint to provide a mechanical connection between slabs without restricting horizontal joint movements. Dowelled joints are required for major roads, main urban streets, industrial roads, airports and harbor pavements. The design of dowel bars is mostly based on experience. AASHTO (1993) recommended the use of dowel bars with diameter equal to 1/8 of the slab thickness. Most road agencies adopt the standard center to center spacing of 300mm (12 in.). The typical length of dowel bars is 460mm (18 in.). Corrosion of dowel bars may cause joints to lock up. Epoxy coated and stainless steel dowels have been used to prevent corrosion. The design considerations are:
Mild steel rounded bars,
Bonded on one side and free on other side.
Please check references below.. hope it will be helpful for you…
Regards…
http://plumconstructioninc.com/resources/jointdesign.pdf
http://www.acpa.org/wp-content/uploads/2017/11/Joints-1-3-Dowel-and-Tie-Bar-Design-Considerations-Part-1.pdf
There are alternative shear connector systems for slabs requiring two way movement.
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