Page 105 - Marine Structural Design

Chapter 4 Scantling of Ship's Hulls by Rules 81

p.s.E2
SM =- (4.15)
120
The classification rules contain this kind of equations for design of beams under lateral
pressure.
Girders
Girders are to comply with the same scantling criteria as stiffeners with respect to the section
modulus. In addition, shear force should be considered due to the height of girder. The
following equation represents the scantling criterion in terms of the cross sectional area of
girders:

T S T

Figure 4.10 Girder

Q
r=- (4.16)
A
where, r , is the shear stress at the girder end in N / m2 and A, is the cross sectional area at the
girder end in m2. If the load is equally distributed, with each end of the girder carrying half
the load, Q is defined to be:
Q = 0.5. p * b- S (4.17)

),
where p and b denote the design pressure acting on the girder (in N / mz and the loading
breadth (in m). The girder span is denoted as S (in m). Substituting Eq.(4.17) into Eq.(4.16),
the following equation is obtained:
Q-0.5.p.b-S
r=-- (4.18)
A A
From Eq. (4.18), the required sectional area is derived as the following:

(4.19)

The allowable shear stress z,,,, depends on the girder. In addition, girders are to satisfy the
requirements of the web plate thickness, the girder web area, and the ratio of the girder flange
thickness to flange width.