8. Design of Coastal Structures
267
Compute,
± = *| = 0.8l8,
± = i| = 1.80>,0
yc
5.5
yt
2.5
From Fig. 8.9, the réduction factors, rf and rm for b/yc = 0.818 are found as,
rr = 0.968 and rm = 0.912, and — > 1.0
yt
Reduced forces and moments are calculated as
F' = rf F, M' = rmM
Use appropriate rf and rm corresponding to crest or trough
At crest,
Fc' = 0.968Fc and M'c = 0.912Mc
where Fc and Mc are the forces and moments including that due to hydrostatic component owing to the non-breaking waves. The horizontal wave
forces may be evaluated using Fig. 8.5. The value of F/'fd2 above F/^d2 — 0
will be the dimensionless force when the crest is at the wall: Fc/^d2, the
lower family of curves (below F/^d2 = 0) gives dimensionless forces when
the trough is at the wall: Ft/^d2.
H
H
F
F
with —h = 0.0043, -/■ = 0.5, —= 0.63,
= -0.31 for T = 6 sec
gF
d
ydz
ydz
Assuming 7 = 10 kN/m3,
Fc = 56.7 kN/m or 5781 kg/m
Ft = -27.9 kN/m
Total forces including hydrostatic component can be established from
Eqs. (8.2) and (8.3).
yd2
^c(totai) = 56.7 +
= 101.7 kN/m
'yd2
■^t(totai) = -27.9-1—— = 17.1 kN/m
The total force acts against the seaward side of the structure, and the
resulting net force will be determined by considération of static loads (e.g.
weight of structure), earth loads (e.g. soil pressure behind a seawall) and
any other static or dynamic loading which may occur.