Westergaard solutions for maximum bending stress and deflection are de
rived by assuming infinite slab width and length, and ignoring possibl
e thick-plate behavior of slab under loading. This paper examines the
effects of these two factors on Westergaard solutions by comparing wit
h thick-plate solutions for rectangular slabs derived by the writers.
The infinite slab assumption is found valid if the slab length is more
than four times the radius of relative stiffness. However, because of
thick-plate action, not all solutions for slab responses converge to
Westergaard values when slab sizes are large. For large slabs where th
e effect of slab dimensions is negligible, the difference of thick-pla
te solutions and Westergaard solutions for maximum bending a;tress are
less than 15% for square slabs, and less than 20% for 3.66 m (12 ft)
wide rectangular slabs. For these large slabs, the values of maximum d
eflection obtained from the two solutions show good agreement in the c
ase of square slabs. However, for 3.66 m wide rectangular slabs, Weste
rgaard solutions underestimate maximum deflection by 10-70%, depending
on the value of radius of relative stiffness of the slab-on-grade sys
tem.