Determination of site period for NZS1170.5:2004
The fundamental site period, T, is a key parameter for site classification in NZS 1170.5:2004. Many sites in New Zealand will fall into site classes C and D, where the boundary between the site classes is T = 0.6 seconds. NZS 1170.5 offers several methods of determining site classification. The intent of this paper is to expand on NZS 1170.5 and guide practising engineers towards more accurate and efficient methods for determining site period. We review methods to calculate the shear-wave velocity, then give specific examples for calculating the site period for five types of soil profile (uniform layer, shear-wave velocity increasing as a power of depth, shear modulus increasing linearly with depth, two-layer profile and three-layer profile). We find that NZS 1170.5 clause 220.127.116.11 for calculating site period at layered sites is unconservative and inconsistent with two other well-accepted methods for calculating site period. We consider the most accurate and efficient method of calculating site period for layered sites is to represent the profile as a lumped mass system, then calculate the fundamental frequency from the eigenvalues of the system. The successive application of the two-layer closed form solution is also considered an acceptable method.
Standards New Zealand (2004) "NZS1170.5 Earthquake actions - New Zealand", Wellington, New Zealand.
Meyer, V. (1999) "Stress-strain and strength properties of an Auckland residual soil", PhD thesis, Faculty of Engineering, University of Auckland.
Weiler, W.A. (1988) "Small strain shear modulus of clay". Proc. ASCE Conference on Earthquake Engineering and Soil Dynamics II: Recent advances in ground motion evaluation, Geotechnical special publication 20, ASCE, New York, p. 331-335.
Mayne, P.W. and G.J. Rix (1993) "Gmax - qc relationship for clays". Geotechnical Testing Journal, 16(1): 757-774.
Richart, F.E., J.R. Hall and R.D. Woods (1970) "Vibrations of soils and foundations". Prentice Hall, Englewood Cliffs, New Jersey.
Baldi, G., R. Bellotti, V. Ghionna, M. Jamiolkowski and D.C.F. Lo Presti. (1989) "Modulus of Sands from CPTs and DMTs". Proc. 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, Brazil. p. 165-170.
Rix, G.J. and K.H. Stokoe. (1991) "Correlation of initial tangent modulus and cone penetration resistance". Proc. International Synopsium on Calibration Chamber Testing. Elsevier Publishing, New York. p. 351-362.
Seed, H.B., R.T. Wong, I.M. Idriss and K. Tokimatsu (1986) "Moduli and damping factors for dynamic analysis of cohesionless soils". Journal of Geotechnical Engineering, ASCE, 112(GT11): 1016-1032. DOI: https://doi.org/10.1061/(ASCE)0733-9410(1986)112:11(1016)
Sykora, D.W. and K.H. Stokoe (1983) "Correlations of in situ measurements in sands of shear wave velocity", Geotechnical engineering report GR83-33, University of Texas, Austin.
Imai, T. and K. Tonouchi. (1982) "Correlation of N-value with S-wave velocity and shear modulus". Proc. 2nd European Symposium on Penetration Testing, Amsterdam. p. 57-72.
Marks, S., T.J. Larkin and M.J. Pender (1998) "The dynamic properties of a pumiceous sand". Bulletin of the New Zealand Society for Earthquake Engineering, 31(2): 86-102.
Ohta, Y. and N. Goto (1978) "Empirical shear wave velocity equations in terms of characteristic soil indexes". Earthquake Engineering & Structural Dynamics, 6(2): 167-187. DOI: https://doi.org/10.1002/eqe.4290060205
McVerry, G.H. (2011) "Site-effect terms as continuous functions of site period and Vs30". Proc. Ninth Pacific Conference on Earthquake Engineering, Auckland, New Zealand.
Dobry, R., I. Oweis and A. Urzua (1976) "Simplified procedures for estimating the fundamental period of a soil site". Bulletin of the Seismological Society of America, 66(4): 1293-1321.
Idriss, I.M. and H.B. Seed (1968) "Seismic response of horizontal soil layers". Journal of Soil Mechanics and Foundation Engineering ASCE, 34: 1003-1031.
Dobry, R., R.V. Whitman and J.M. Roesset (1971) "Soil properties and the one dimensional theory of earthquake amplification", Research report R71-18, Department of Civil Engineering, MIT, Cambridge, Massachussetts.
Ambraseys, N.N. (1959) "A note on the elastic overburden of varying rigidity to an arbitrary ground motion". Bulletin of the Seismological Society of America, 49(3): 211-220.
Urzua, A. (1974) "Determinacion del periodo fundamental de vibracion del suelo", Masters thesis in soil mechanics, University of Chile, Santiago.
Madera, G.A. (1971) "Fundamental period and amplification of peak acceleration in layered systems", Research Report R70-37, Department of Civil Engineering, MIT, Cambridge, Massachusetts.
Chen, A.T.F. (1971) "Natural period of two-layered systems", Report No. USGS-GD-71-030, USGS, Menlo Park, California.
Nogoshi, M. and T. Igarashi (1971) "On the amplitude characteristics of microtremor (part 2)". Journal of the Seismological Society of Japan, 24(26-40). DOI: https://doi.org/10.4294/zisin1948.24.1_26
Nakamura, Y. (1989) "Method for dynamic characteristics estimation of subsurface using microtremor on the ground surface". Quarterly Report of RTRI (Railway Technical Research Institute) (Japan), 30(1): 25-33.
Acerra, C., G. Aguacil, A. Anastasiadis, K. Atakan, R. Azzara, P.-Y. Bard, R. Basili, E. Bertrand, B. Bettig, F. Blarel, ..., and B. Moreno (2004) "Guidelines for the implementation of the H/V spectral ratio technique on ambient vibrations measurements, processing and interpretation", SESAME European research project WP12 - Deliverable D23.12.
Lermo, J. and F.J. Chavez-Garcia (1993) "Site effect evaluation using spectral ratios with only one station". Bulletin of the Seismological Society of America, 83(5): 1574-1594.
Wessel, P. and W.H.F. Smith (1998) "New and improved version of the Generic Mapping Tools released". EOS Trans. AGU, 79(47): 579. DOI: https://doi.org/10.1029/98EO00426
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