Data concerning the behavior of lightly reinforced, conventional slab-on-grade foundations have
also been included in Fig. 7.24. This data indicates that cracking of gypsum wallboard panels is likely
to occur if the angular distortion of the slab-on-grade foundation exceeds 1/300 (Day, 1990a). The
ratio of 1/300 appears to be useful for both wood-frame gypsum wallboard panels and the brick pan-els studied by Skempton and MacDonald (1956). The data plotted in Fig. 7.24 would indicate that
the relationship Δ=350 d/Lcan also be used for buildings supported by lightly reinforced slab-on-grade foundations. Using d/L=1/300 as the boundary where cracking of panels in wood-frame res-idences supported by concrete slab-on-grade is likely to occur and substituting this value into the
relationship Δ=350 d/L(Fig. 7.24), the calculated differential slab displacement is 1
1
/
4
in. (32 mm).
For buildings on lightly reinforced slabs-on-grade, cracking of gypsum wallboard panels is likely to
occur when the maximum slab differential exceeds 11
/
4
in. (32 mm).