TranSystems Corporation - LGM Construction

ASCE 7-05 chapter 20.3.1.1 guidelines indicate that a “Stiff Soil Profile” Site Class ‘D’ is
appropriate for use for liquefiable sites with short period structures ( ≤ 0.5 seconds). We
expect the period of vibration for the proposed development is less than 0.5 seconds. If
this period is larger than 0.5 seconds, we should be contacted to review our
recommendations presented herein and recommend adjustments as necessary.
Based on the above, we recommend that the site be classified as a Site Class ‘D’ for
seismic response purposes and development of ground motion parameters according to
ASCE 7-05 and CBC 2007 as presented in Table 1613A.5.2 and Section 1613A.5.5 of
the 2007 CBC. Site Class D is defined as Stiff Soil profile with average properties (in
the top 100 feet) of shear wave velocities between 600 and 1200 feet/sec, SPT-N
between 15 and 50 blows/foot, or Su (undrained shear strength) between 1,000 and
2,000 pounds per square foot (psf).
1. SPT-N refers to the standard penetration test blows
2. Su refers to undrained shear strength
8.3.2 2007 CBC Code Values
For seismic design purposes, the 2007 CBC code enforced as of January 2008 is based
on 2006 IBC and ASCE 7-05. The seismic design parameters provided are for the
Maximum Considered Earthquake (MCE). The MCE mapped spectral accelerations
values for 0.2 second and 1 second periods (SS and S1) were calculated using the
online Java calculator at the USGS website
(http://earthquake.usgs.gov/research/hazmaps/design/) for Site Class D. The mapped
acceleration values and associated soil amplification factors (Fa and Fv) based on 2007
CBC are presented in Table 1 below. The SDS and SD1 values were computed as
follows.
SDS = 2/3 SMS
SD1 = 2/3 SM1
SMS = Fa SS
SM1 = Fv S1
SS = mapped acceleration value at 0.2 sec
S1 = mapped acceleration value at 1.0 sec
94240/1(OAK8R061)/es Page 23 of 29 June 13, 2008
© 2008 Kleinfelder