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# Period Ts of the Design Response Spectrum

## Period Ts of the Design Response Spectrum

(OP)
What is the explanation for the unit of Ts being in second when Ts is equal to Sds/Sd1 both (Sds &Sd1)being spectrum response acceleration values having the same units?

### RE: Period Ts of the Design Response Spectrum

Your question isn't clear. Seismic acceleration is a function dependent on period. Can you cite an equation number or section in the code that is in question?

### RE: Period Ts of the Design Response Spectrum

(OP)
Sure, ASCE7-12, paragraph 11.4.5, item 4 under equation 11.4-7, Ts = Sds/Sd1.

### RE: Period Ts of the Design Response Spectrum

Now, I understand. ASCE should explicitly define the units in the definition of the symbols, section 11.3 and where they are defined below the equations (T in seconds and the accelerations with g). But, if you look at figure 11.4-1, the Design Response Spectrum figure has the units.

### RE: Period Ts of the Design Response Spectrum

(OP)
But Sds/Sd1 units would cancel each other out, therefore Ts would be unitless. There must be something else at work

### RE: Period Ts of the Design Response Spectrum

In the response spectrum (Figure 11.4-1 in ASCE 7-05, for example), the accelerations are discussed as functions of Period T, but they treat T as a number rather than a dimension. So where the curve is labeled Sa = SD1/T, they are neglecting the units of time there. So more properly, they should include some inverse-second units or define a unitless time parameter.

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