ASCE 7-05 Possible Typo 1

[swearingen]

I've stumbled on something that I'd like to run past some seasoned earthquake structural engineers:

In ASCE 7-05, equations 15.4-2 and 15.4-4, the variable S1 is used. It seems to me an SM1 or SD1 should be there because S1 is not adjusted for soil type or spectral response. Is this a typo or was it really intended to be this way?

My case is for soil class D and the S1 numbers on the map are based on soil class B. The Fv and Fa site coefficients are pretty substantial to make soil type changes (Tables 11.4-1 and 11.4-2). If S1 is used and it is supposed to be SM1 or SD1, the result would be very unconservative.

 

[dcm125]

While I do not claim to be a seasoned EQ engineer, I looked at this, and while it is hard to follow since ASCE 7-05 is in a new format, I believe that Eq.15.4-4 is intended to replace the Cs min equations 12.8-5 and 12.8-6, which also use S1. I believe that the R values from Table 15.4-2 are to be used in the Chapter 12.8 Cs equations, where Eqs.12.8-2, -3, and -4 use either Sds or Sd1.

In short, I don't think that this is a typo and it probably isn't unconservative because it defines the lower bound, and 15.4-1 and 15.4-2 is more severe than the minimums in 12.8.

 

[swearingen]

That makes perfect sense, and after re-reading the associated sections, I think you're right.

If anyone has hard knowledge of this being the case, please weigh in.

Thanks