Static Seismic Inertial Loads - CAESAR II - Help

CAESAR II Users Guide (2019 Service Pack 1)

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CAESAR II
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CAESAR II Version
11.0 (2019)

Static earthquake loads are applied in a manner very similar to static wind loads. The static loading magnitude is considered to be in direct proportion to the weight of the element. Express earthquake load magnitudes in terms of the gravitational acceleration constant g. If you model an earthquake with a 0.5-g load in the X direction, then half of the systems weight is turned into a uniform load and applied in the X direction.

You create earthquake static load cases the same way you create wind occasional load cases. Use the same load case, nonlinearity, and directional sensitivity logic. In some cases, the client specifies the magnitude of the earthquake loading in g's and the direction(s). In other cases, analysis is left to the discretion of the analyst. It is not unusual to see only X-Y or Z-Y components of an earthquake. It is also not uncommon to see X, Y, and Z simultaneous components.

Dynamic (response spectrum) evaluation of earthquake loads are discussed later in this section, in the dynamic analysis and output sections, and in the screen reference section.

The ASCE #7 method for determining earthquake coefficients is described below. After you calculate the earthquake coefficients, enter the g-factors as uniform loads on the piping spreadsheet.

Calculate the horizontal seismic design force using equation 13.3-1 from ASCE 7 (10):

Fp = [(0.4 ap SDS Wp) / (Rp / Ip)] (1 + 2 z / h)

But, because Wp is "component operating weight", Fp/Wp = calculated (horizontal) acceleration, aH, so;

aH = [(0.4 ap SDS) / ( Rp / Ip )] (1 + 2 z / h),

additionally;

aH £ 1.6 SDS Ip

and:

aH ³ 0.3 SDS Ip

Where:

ap = Component amplification factor, from Table 13.6-1

= 2.5 for "Piping"

SDS = Design elastic response acceleration at short period (0.2 sec), from Section 11.4.4

Rp = Component response modification factor, from Table 13.6-1

= 12.0 for "Piping in accordance with ASME B31... with joints made by welding or brazing"; values range as low as 3.0 for other joints and for less ductile materials.

Ip = Component importance factor, from Section 13.1.3

= 1.5 for life-safety components, components containing hazardous material, or components that are required for continuous operation; 1.0 for all others

z = Height in structure at point of attachment

h = Average roof height of structure