Design of dowel bar

By the term design of dowel bar , it is meant to estimate the dowel bar diameter and spacing. One of them can be assumed as known or fixed, and the other is estimated. Dowel bars are generally designed from two considerations: (i) Bearing stress approach, where the developed bearing stress is set equal to or less than the allowable bearing stress, and (ii) Relative deflection approach, where the relative deflection of the joints is not allowed to exceed some maximum specified value.

Example design

An example on design of dowel bar system from bearing stress consideration is presented in the following.

Problem
A design wheel load of 65kN is applied on to the concrete pavement slab, and 50% of the load is assumed to be transmitted through the dowel bar system. Assume the characteristic compressive strength (f_ck) of concrete (used in the concrete pavement) is 40MPa, the transverse joint width ( z ) is 15 mm, radius of relative stiffness (l) of the concrete slab as 950mm, Elastic modulus of steel (E) as 2.0 x 10⁵ N/mm² and modulus of dowel support (k_d) as 415N/mm 3 . Design the dowel bar system.

Solution

Assume, 32mm diameter dowel bars are used.

The allowable bearing stress (σ_b^a ) can be obtained from Equation (28) as:
  =  29.23 MPa

Assume, dowel bar spacing as 300 mm center-to-center. Thus, in 950 mm of effective length (using Tabatabaie et al. criterion) , 4 dowel bars can be placed.

Assuming, the load carried by the dowel bar which is just below the wheel, is P_d, one can write the load distribution equation of the dowel bar system as:

or, P_d=15437.5 N

Now,

  0.0238 per mm

From Equation (27), the developed bearing stress in dowel bar

  =   N/mm²  = 27.20 MPa

It is noted that  < , thus the design is safe. Thus, dowel bar of 32 mm may be provided with 300mm center-to-center.