IIIT Hyderabad Publications 


EARTHQUAKE BEHAVIOUR OF BUILDINGS ON SLOPESAuthor: Ramya Gullapalli Date: 20190718 Report no: IIIT/TH/2019/90 Advisor:Pradeep Kumar Ramancharla AbstractThe construction in hilly regions is generally constrained by local topography resulting in vertical as well as horizontal irregularities in the buildings. These irregularities cause irregular distributions of mass and stiffness of the structures. As a result, the dynamic properties such as natural period and mode shape of such buildings vary significantly when compared to those constructed on the flat terrain. During past earthquakes like 2005 Kashmir earthquake, 2011 Sikkim earthquake, 2015 Nepal earthquake, severe damages were observed in such constructions on hill slopes. The damage attributed to these buildings was observed to be disproportionately higher when compared to those on a flat land, despite smaller intensity of shaking. This damage is attributed to several reasons viz.,a. Landslide issues, Natural period, Shear distribution in columns and Torsional effects. Therefore, there is an urgent need to understand the seismic behaviour of such buildings standing on hill slopes and include corresponding changes in codal provisions. In the current study, two important seismic parameters, Natural Period and Base Shear of the structure have been studied. Fundamental Natural Period of a building is one such important dynamic property which has its significant use especially during the design phase of the building i.e., while calculation of base shear. Hence, to understand the same the natural period study has been divided into two parts i.e., in first part, natural period of buildings constructed on hill slopes have been obtained and in the second part, parametric study was done to obtain the best fit curve. In the first part, Natural Period of nine buildings constructed on the hill slopes of Mussoorie were obtained using Ambient Vibration testing. From the recorded data, it has been observed that the existing code provisions for estimating the approximate natural period of a building are not efficient enough in the case of such buildings with a standard deviation of errors of 0.1. Since the available data is too less to derive any expression, in the second part, the data has been extrapolated by modelling 270 similar buildings in SAP 2000 by varying different parameters like angle of inclination (5o to 45o), base dimension (3x3 to 5x5) and height (3 to 7 stories). Regression Analysis has been performed on the above data to derive an Empirical Relation to estimate Fundamental Natural Period of buildings constructed on slopes. It has been observed that the standard deviation of errors of the proposed expression with respect to the recorded data has reduced to 0.05. Another major issue with the step back buildings constructed on hill slopes is the distribution of the total Base Shear acting on the structure among the respective columns. The irregular configurations of a step back building causes stiffness differences in the structure. This results in short column/uphill column attracting the maximum base shear causing severe damages to the corresponding short columns and hence the whole structure. For example, in a 3x3 bays building standing on 30o slope, it has been observed that all the short columns were attracting 118% of the total base shear acting on the structure whereas the largest ones were attracting only 1.5%. To understand and reduce these stiffness differences, different building configurations using strut elements were studied. And the configuration of struts which supports optimum distribution of stiffness differences has been identified. The short column of proposed model attracts only 38% of total base shear acting on the structure and hence reducing the design cost as well as damage vulnerability of the structure. Full thesis: pdf Centre for Earthquake Engineering 

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