Site classification using natural frequency base on seismic data and suggestions for application in Iranian Building Code. Case study Ardakan City

Summary Based on the results of the analysis of site effects, mostly those with shear wave velocity and the fundamental period chosen as the basis for classification. In revision of Earthquake resistant design regulations for buildings, classification of lands should be subject to the field conditions, geological, geotechnical, geophysical, and laboratory tests.In this context, the average shear wave velocity of the soil to a depth of 30 m and soil normal period are important ones. In Iran, earthquake design rules (Iran standard 2800) and the classification of Komak Panah et. al. (2002) for the terrains are used in practice. The Komak Panah classificationis the only which applied he ground normal period. In this paper, we identify the dynamic characteristics of the land within the city of Ardakan. Adjustment of land classification according to the studies on the site effect base on geotechnical data, geophysical, and microtremors with dynamic design codes for buildings are shown. Evaluation of seismic wave propagation and its changes from the bedrock surface to the bedrock to determine the movement of the soil profile is used. The seismic wave propagation from the bedrock to the surface, such as amplitude and frequency content of the seismic wave changed so that the soft sedimentary deposits, certain frequencies of the ground motion amplification and dynamic behavior of soil, damaging effects of the earthquake.
Regulations seismic design of buildings for a variety of land, measures considered. The Regulations, based on dynamic mechanical parameters of the soil, the Soil classification is the valid regulations as well as regulations for Euro Code (CEN, 2004) and US (ICC, 2006), the classification of the land and exercising their influence on the design spectrum, in order to achieve the above objectives walked. In these Regulations, in addition to conventional fields, categories for loose ground and in certain circumstances, such as liquefaction, is intended collapsible soils. Different methods estimate the parameters of geotechnical soil profile and map the dynamic and resonant, liquefaction and landslide hazards in different scales in the United States by (Street et al 1997, 2001; Bauer et al 2001; Broughton et al 2001; Rix et al 2001; Cramer et al 2004, 2006). ) Is used. Shear wave velocity, density, frequency, nature and thickness of the layers of soil determines the period of hard or poor quality of the land area.
Based on these characteristics, particularly shear wave velocity and the normal period, there have been many different categories. UBC classification of natural period as the basis for classification is used Uniform Building Code, 1979)). Classification) 1991, Seed et al) in addition to the parameters of the seismic bed rock, sex and severity of vibration as well as the parameters of the auxiliary materials used. (Bray and Abrahamson 1999) of the two main parameters period and other parameters, such as the site and the average shear wave velocity and strength properties of soil deposits have been used. Regulations designed to Earthquake in Iran (2800) and classification help shelter al 2002) Komak panah et al,) noted. The fourth edition rules of Earthquake in Iran, (2800) of three parameters characteristic of sediments, soil thickness and the average shear wave velocity in the upper 30 m was used to classify the land as the land into 4 groups less than 175, 375-175, 750-375 and more than 750 meters per second are separated.
Classification Komak panah, et al, 2002, the natural frequency of the structure as the main parameter, gender, interests and geological conditions as auxiliary parameter is used for classification. In Europe Regulations (CEN, 2004) describes the layering of soil and soil classification based on the average of the three parameters of shear wave velocity, untrained shear strength and the standard penetration from the surface to a depth of 30 meters down. In the Ardekan city to improve ground classification , shear wave velocity and soil profile of 5 boreholes in addition to Microtremor recorded data of 100 points analyzed based on H/V method (Nakamura, 1989 and 2000) of natural frequencies obtained in the matches Borehole with the natural frequency of the linear one-dimensional analysis of soil profiles were compared. According to the characteristics of geotechnical, geophysical, and the results of the analysis of the site effect and the natural frequency of the microtremors data in the holes, the terrain was determined. Finally, Iran standard 2800 classification was slightly modified using fundamental frequency. These changes may efficiently represent the ground situation and better using of Iran Standard 2800 classification in this area.