How to Make your Process Pipework Earthquake–Proof

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• Step 9: With SDS and SD1 values response spectrum can be built as follows:

• ● Period Sa less than T0, straight line Sa

• ● Flat Sa between Sa between T0 and Ts.

• ● Sa curve about Ts.

Sa = SDS [0.4+0.6 T / T0] …… for period < T0Sa = SDS …………………… for T0 <=T<=TsSa = SD1 / T ………………… for T> Ts

• Step 10: Calculate seismic response coefficient Cs as Cs = SDS / (R/I).

Where, R is the response modification co-efficient and can be obtained as minimum value (conservative approach) from the ASCE 7 (Table 12.2-1 or Table 13.6-1). The typical value for structural support, R = 3. (Note: More accurate values can be selected on the basis of structural properties). I is the occupancy importance factor which can be obtained from ASCE 7 (Table 11.5-1).

I will vary from 1 to 1.5. Selecting I = 1.5, Cs can be calculated as Cs = 0.74 / (3/ 1.5). Therefore, Cs = 0.37.

Example for Designing a Pipe

Consider a straight pipe subjected to spectral acceleration as per Table 1. The pipe data given is as follows. The outer diameter of the pipe is 8.625 inches, its thickness is 0.322 inches, with a corrosion allowance of 0.125 inches, and the material used is A106 B. The weight of the pipe is 28.5lb/ft.

Simple beam calculation provides the vertical dead weight on support number 20 = 228 lb (refer Figure 2). The seismic force acting at each support location can be calculated as (Fseismic) 20 = 0.37 * 627 = 232 lb acting in the lateral direction.

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