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ructures shall bedesigned for the following dynamic forces in addition tothe static pressures: (a) inertia forces P w and P r ; (b)hydrodynamic impulsive pressure P i from the containedliquid; (c) hydrodynamic convective pressure P cfrom the contained liquid; (d) dynamic earth pressure

from saturated and unsaturated soils against the buriedportion of the wall; and (e) the effects of verticalacceleration.4.1.1 Dynamic lateral forcesThe dynamic lateral forces above the base shall bedetermined as follows:(4-1)(4-1a)(4-2)(4-3)(4-4)Where applicable, the lateral forces due to thedynamic earth and ground water pressures against the

buried portion of the walls shall be computed in accordancewith the provisions of Chapter 8 .4.1.2 Total base shear, general equationThe base shear due to seismic forces applied at thebottom of the tank wall shall be determined by the followingequation:(4-5)P w ZSIC i

e W wR w i

= ------------P w ZSIC ie W w R w i

= --------------Pr ZSICi

W r

R w i

= ---------P i ZSIC i

W i

R w i

= ---------P c ZSIC c

W c

R w c

= ------------V P i + P w + P r 2 P c= + 2R4.1 Earthquake pressures above baseThe general equation for the total base shear normallyencountered in the earthquake-design sections of governing

building codesis modified in Eq. (4-1) through (4-4) byreplacing the term W with the four effective masses: theeffective mass of the tank wall, e W w , and roof, W r ; theimpulsive component of the liquid mass W i ; and the convectivecomponent W c . Because the impulsive and convectivecomponents are not in phase with each other, normal practiceis to combine them using the square root of the sum ofthe squares method (Eq. (4-5)).The general equation for base shear is also modified in Eq.(4-1) through (4-4) by the soil profile coefficient S in accordance

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