Determination of characteristic site period and preliminary ground responce analysis according to resonance by using GIS

Abstract

Ground response analyses are mostly used for the development of design response spectra in the modern earthquake engineering. After 1999 Marmara Earthquake, the damages were mostly related with unavailable soil conditions and this unavailability were analysed according to liquefaction analysis. The other analyses which cover the dynamic soil properties were not studied in detail. In this study, granular soil which the Eskisehir urban area is located has been studied according to vibration period. Eskisehir is the city, which would be influenced negatively by the earthquake due to unavailable soil conditions and uncontrolled constructions. Five different districts of the Eskisehir municipality were included in this studied area. Seismic conic penetration test (SCPT) which is known seismic down hole test results have been used for obtaining low-strain dynamic soil properties in the study. The geophone in the seismic penetrometer detects the travel time, depth and shear wave velocity (Vs) of the tested horizon have been obtained. The soil thickness of the studied area has been calculated from the seismic resistivity results of the State Hydraulic Works of Eskisehir. The raw 60 m seismic resistivity records have been evaluated by using 3 dimensional GIS and 3 dimensional alluvial thickness model have been created. Average shear wave velocity (Vsav) of each 32 SCPT test points have been calculated by taking average of each SCPT drill log. Characteristic site period (Ts), which is defined as the period of vibration corresponding to the fundamental frequency has been obtained for each 32 test points. GIS which is a powerful tool and technique for especially earth science, has been used for the preparation of characteristic site period map (Tf) of the studied area. After that, the number of story of each building has been determined by in-situ studies in the studied districts. Fundamental vibration period (Tf) of each building has been calculated with respect to number of story according to building codes. GIS overlapping analyse technique, has been used with characteristic site period (Ts) map layer and fundamental vibration period map layer of each building. Soil and structure relationship has been searched in this situation and close Ts and Tf values have been defined as critical values according to high resonance risk. It has been seen that, the number of critical buildings which are under the high resonance risk in the studied area are 63 and this covers approximately 5.4% of the total studied area. At the end, ground response of the soil according to resonance risk map has been prepared by GIS technique.