Development of Site Classification System and Seismic Site Coefficients for Korea

Phytosociology has advanced in various respects since the fundamental groundwork was laid, which was mainly concerned with developing a classification system of vegetation units. Current site classification methods for forests consider not only floristic aspects, but also pedological, topographic and structural characteristics of forest stands. During the summer of 2007, a site mapping was carried out in the ETH Research Forest near Sedrun (Switzerland). This paper describes the methods employed, and it evaluates the applicability thereof based on case studies. Site mapping is based on expert opinion, and as such it includes a certain degree of generalization and subjectivity in the evaluation of stands and their assignment to a site type. However, we propose that site classification constitutes a suitable tool for describing and characterizing the complexity of forest sites. The accurate description of site types strongly facilitates the interpretation and the applicability of a classification system in decision support for sustainable forest management.

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An Empirical Geotechnical Seismic Site Response Procedure

Earthquake Spectra ◽

10.1193/1.1586167 ◽

2001 ◽

Vol 17 (1) ◽

pp. 65-87 ◽

Cited By ~ 107

Author(s):

Adrián Rodríguez-Marek ◽

Jonathan D. Bray ◽

Norman A. Abrahamson

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Classification System ◽

Soil Depth ◽

Site Response ◽

Dynamic Stiffness ◽

Evaluation Procedure ◽

Site Classification ◽

Seismic Site Response

A simplified empirically based seismic site response evaluation procedure that includes measures of the dynamic stiffness of the surficial materials and the depth to bedrock as primary parameters is introduced. This geotechnical site classification scheme provides an alternative to geologic-based and shear wave velocity-based site classification schemes. The proposed scheme is used to analyze the ground motion data from the 1989 Loma Prieta and 1994 Northridge earthquakes. Period-dependent and intensity-dependent spectral acceleration amplification factors for different site conditions are presented. The proposed scheme results in a significant reduction in standard error when compared with a simpler “rock vs. soil” classification system. Moreover, results show that sites previously grouped as “rock” should be subdivided as competent rock sites and weathered soft rock/shallow stiff soil sites to reduce uncertainty in defining site-dependent ground motions. Results also show that soil depth is an important parameter in estimating seismic site response. The standard errors resulting from the proposed site classification system are comparable with those obtained using the more elaborate code-based average shear-wave velocity classification system.

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Development of Site Classification System and Modification of Design Response Spectra considering Geotechnical Site Characteristics in Korea (I) - Problem Statements of the Current Seismic Design Code

Journal of the Earthquake Engineering Society of Korea ◽

10.5000/eesk.2006.10.2.039 ◽

2006 ◽

Vol 10 (2) ◽

pp. 39-50 ◽

Cited By ~ 5

Keyword(s):

Seismic Design ◽

Classification System ◽

Response Spectra ◽

Site Classification ◽

Design Code ◽

Site Characteristics ◽

Seismic Design Code

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New Site Coefficients and Site Classification System Used in Recent Building Seismic Code Provisions

Earthquake Spectra ◽

10.1193/1.1586082 ◽

2000 ◽

Vol 16 (1) ◽

pp. 41-67 ◽

Cited By ~ 223

Author(s):

R. Dobry ◽

R. D. Borcherdt ◽

C. B. Crouse ◽

I. M. Idriss ◽

W. B. Joyner ◽

...

Keyword(s):

Seismic Hazard ◽

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Classification System ◽

Site Amplification ◽

Site Classification ◽

Site Class ◽

Site Classes ◽

Code Provisions

Recent code provisions for buildings and other structures (1994 and 1997 NEHRP Provisions, 1997 UBC) have adopted new site amplification factors and a new procedure for site classification. Two amplitude-dependent site amplification factors are specified: Fa for short periods and Fv for longer periods. Previous codes included only a long period factor S and did not provide for a short period amplification factor. The new site classification system is based on definitions of five site classes in terms of a representative average shear wave velocity to a depth of 30 m (V¯s). This definition permits sites to be classified unambiguously. When the shear wave velocity is not available, other soil properties such as standard penetration resistance or undrained shear strength can be used. The new site classes denoted by letters A - E, replace site classes in previous codes denoted by S1 - S4. Site classes A and B correspond to hard rock and rock, Site Class C corresponds to soft rock and very stiff / very dense soil, and Site Classes D and E correspond to stiff soil and soft soil. A sixth site class, F, is defined for soils requiring site-specific evaluations. Both Fa and Fv are functions of the site class, and also of the level of seismic hazard on rock, defined by parameters such as Aa and Av ( 1994 NEHRP Provisions), Ss and Sl ( 1997 NEHRP Provisions) or Z ( 1997 UBC). The values of Fa and Fv decrease as the seismic hazard on rock increases due to soil nonlinearity. The greatest impact of the new factors Fa and Fv as compared with the old S factors occurs in areas of low-to-medium seismic hazard. This paper summarizes the new site provisions, explains the basis for them, and discusses ongoing studies of site amplification in recent earthquakes that may influence future code developments.

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