COMPARISON OF STATIC AND LINEAR DYNAMIC METHODS OF ANALYSIS IN CONTEXT OF IS1893:2016 AND EUROCODE 8.

Abstract

Earthquake motion causes a vibration of the structure leading to inertia forces. Thus a structure must be able to safely transmit the horizontal and the vertical inertia forces generated in the superstructure through the foundation to the ground. In earthquake-resistant design, it is required that the response of the structures to induced seismic forces is within the acceptable limit. In Indian IS1893:2016 standard, the regulations are not intended that no structure shall suffer any damage during the earthquake of all magnitudes. It has been endeavored to ensure that, as far as possible, structures are able to respond, without structural damage, to shocks of 'moderate intensities and without total collapse to shocks of heavy intensities.

The analysis of earthquake resistant design of structure can be done either by a linear or non-linear method [1]. In this paperwork, a comparative study has been conducted on four different frames using linear static and linear dynamic methods of analysis. In each frame, the response quantities have been determined for the 3-an increment of story number started with the one of three up to twenty-seven story framed buildings. This means that for each frame, nine different building having the same materials and the same loading conditions but different height have been analyzed. The responses quantities for these buildings are determined by taking the application guidance provided in IS1893: 2016 and that of the EUROCODE 8.

In applying the Indian code of standard, IS1893:2016, it has been observed that as the number of story increases, the seismic weight keep increasing. The natural period for the first mode becomes longer as the number of the story increases. This

vi

means that for 3 story frame, the natural periods can be shorter than that of 6 stories framed building for the first mode in each orthogonal direction. This has a tremendous effect on the values of shear forces. It has observed that when the Natural period is in the interval of (0-0.55) the shear values increase as the number of story increase, but when it is in the interval of (0.55-4) the shear values decrease as the number of story increases. This phenomenon has been observed for medium soil type. It has been observed that the linear dynamic method produce higher response values than that of the linear static method. Furthermore, the mode shapes have been determined for 9 stories framed building using both EXCEL and ETABS and the variation of the results is not that much.

In applying the Eurocode 8, the seismic weight and natural period, show the same pattern as observed in the Indian code of standard. The base shear values decrease as the number of story increase when the natural period is less than 4Tc or 2. It increases for both linear static and linear dynamic method as the number of story increase whenever the natural period is greater that 4Tc or 2. For a building with less story number, the linear dynamic methods of analysis procedure higher response values than that of the linear static method. As the number of story increase, the linear static method resulted in an excessive response value than that of the linear dynamic methods. The axial, shear and bending moment for a column of 3 stories and that of 27 stories has been determined. It turns out that, for 3 stories framed building, the linear dynamic analysis produces a higher response value. But for that of 27 stories framed building, the reverse is true. It has been observed that the two codes show different response patterns.