Hi,

In the seismic load g-factor calculation,
I recognize that the eq. 13.3-1 is used for the horizontal seismic design force of B31 piping in ASCE 7-05 Code.

the eq. 13.3-1 is as following

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

where

Fp = seismic design force
SDS = spectral acceleration, short period, as determined from Section 11.4.4
ap = component amplification factor(selected as 2.5 for piping in accordance with B31)
Ip = component importance factor that varies from 1.00 to 1.50
Wp = component operating weight
Rp = component response modification factor(selected as 12 for piping in accordance with B31)
z/h = selected as 1 for all system components

in this manner, the g-factor could be expressed as following ;-

g(horizontal) = 0.4*ap*SDS*/(Rp/Ip)*(1+2(z/h))

Now my questions are here,

1. Is my understanding for g-factor calculation as per ASCE7-05 is right?

2. According to my comparison work for the g-factor calculation result between CAESAR II seismic wizard and hand calculation, the CAESAR II seismic wizard g-factor equals the 0.85 times hand calculated g-factor. Is there any additional coefficient mulpied to the eq. 13.3-1?

Please provide me any opinion on this subject.

Regards,

You do not state your value for Sds so I cannot run your numbers.

A few things...
There are upper and lower bounds for the horizontal acceleration (ah):
0.3(Sds)Ip<ah<1.6(Sds)Ip
For use in "Allowable Stress Design" (ASD) (as opposed to Load Resistance Factor Design (LRFD)), ASCE 7 states that 70% of this seismic acceleration should be used.

Apply these and you should get that 85%.

Also, yes, 12 for Rp is listed in ASCE 7 but that is large. And you imply that z/h "should" be 1, I see no reason for that.

These adjustments for ASD are good for evaluating pipe stress using Code-defined allowable limits but, if you are interested in structural response (displacements, forces, etc.), I suggest you use the full (LRFD) load.

Dave,

I appreciate your valuable advise.

Here are my values applied for g-factor calculation ;-

SDS = spectral acceleration, short period, as determined from Section 11.4.4 >> 0.2176(2/3 * Fa(1.6) * Ss(0.204)
ap = component amplification factor(selected as 2.5 for piping in accordance with B31) >> 2.5
Ip = component importance factor that varies from 1.00 to 1.50 >> 1.5
Rp = component response modification factor(selected as 12 for piping in accordance with B31) >> 12
z/h = selected as 1 for all system components >> 1

The hor. g-factor from manual calculation : 0.0816
The hor. g-factor from CAESAR II seismic wizard : 0.069(about 85% of the manual calculated g-factor)

Also I've calculated the upper/lower boundaries of g-factor ;-
lower - 0.3(Sds)Ip = 0.09792
upper - 1.6(Sds)Ip = 0.52224

So, I would use the 0.09792 for the static flexibility analysis...
Do you agree to the conclusion?

Please also let me know which written sentence could I refer to the lower & the upper bounderies.

Referring only to numerical results, as Mr. Diehl explained, the acceleration is taken as 70%*0.09792g=0.068544g.

In ASCE 7-10, your equation has number 13.3-1 and can be found under 13.3 SEISMIC DEMANDS ON NONSTRUCTURAL COMPONENTS, 13.3.1 Seismic Design Force

In the same paragraph is written that the horizontal seismic design force, "Fp is not required to be taken as greater than
Fp = 1.6 SDS Ip Wp (13.3-2)
and Fp shall not be taken as less than
Fp = 0.3 SDS Ip Wp (13.3-3)"

Best regards.

Thanks mariog & Dave,

Through some check for CAESAR II seismic wizard, I found that the CAESAR II wizard multiples the factor 0.7 to the larger of eq.13.3-1 and eq.13.3-2.

Regards,

With regards to the Importance Factor:

In section 13.1.1 it implies that IP is either 1.5 or 1.0: "The component importance factor, Ip, shall be taken as 1.5 if any of the following conditions apply: ... All other component shall be assigned a component importance factor, Ip, equal to 1.0"

In section 13.3.1 it says: "component importance factor that varies from 1.00 to 1.50(see Section 13.1.3)"

So is it a range or an either/or?

Or.

Regards,

My understanding for factor 0.7:
0.7 factor given in section 13.1.7 of ASCE-7 is for "earth-quake-resistant design" and is not meant to be used with piping.
"Earth-quake-resistant" design is as per FEMA P-749.
Please correct me if I am wrong.

There is a section in ASCE-7 (13.1.7) that discusses the application of this 0.7.
For position and load: use the "full" ASCE load
For stress evaluation: use 0.7 ASCE load

(B31E states that the full load be used but with higher allowable stress limits. This will eliminate the two separate analyses.)

Thanks Dave!

Thanks Dave for clarifying the ASCE-7 , section 13.1.7 (0.7 multiplication factor).