## Seismic Designvessel On Unbraced Legs [47

Notation

A = cross-sectional area, leg, in.2 V = base shear, lb W = operating weight, lb n = number of legs Cv = vertical seismic factor Ch - horizontal seismic factor y = static deflection, in. Fv = vertical seismic force, lb F), = horizontal seismic factor, see Procedure 3-3 F;l = allowable axial stress, psi F|, = allowable bending stress, psi F, - seismic force applied at top of vessel, lb F'. = Euler stress divided by safety factor, psi fi = maximum eccentric load, lb Vā = horizontal load on leg, lb Fn = maximum axial load, lb f., = axial stress, psi fh = bending stress, psi E = modulus of elasticity, psi g = acceleration due to gravity, 386in./sec2 e = eccentricity of legs, in. Mi, = overturning moment at base, in.-lb M, = overturning moment at tangent line, in.-lb M = bending moment in leg, in.-lb Y] h = summation of moments of inertias of all legs perpendicular to F]ā in4 Y] I2 = summation of moments of inertia of one leg perpendicular to Fh, in,4 I = moment of inertia of one leg perpendicular to Fh, in.4

C'i = distance from centroid to extreme fiber, in. C,ā = coefficient, 0.85 for compact members K, =end connection coefficient, 1.5-2.0 T= period of vibration, sec r = least radius of' gyration, in.

Figure 3-10. Typical dimensional data and forces for a vessel supported on unbraced legs.

Figure 3-10. Typical dimensional data and forces for a vessel supported on unbraced legs.

Angle legs

Beams, channels, and rectangular tubing

Figure 3-11. Various leg configurations.

Table