Response Spectrum Analysis for Regular Multistory Structure in Seismic Zone III

An RCC framed structure is basically an assembly of slabs, beams, columns and foundation interconnected to each other as a unit. The load transfer, in such a structure takes place from the slabs to the beams, from the beams to the columns and then to the lower columns and finally to the foundation which in turn transfers it to the soil. The results of analysis are used to verify the structure fitness for use. Computer software’s are also being used for the calculation of forces, bending moment, stress, strain & deformation or deflection for a complex structural system. The principle objective of this project is “The Comparative Study on Analysis Results of Multistoried Commercial Building (G+15) by STAADPRO and ETABS”.STAADPRO is one of the leading software’s for the design of structures. In this project we had analyzed the G+15 building through response spectrum analysis to develop the economic design. ETABS is also leading design software in present days used by many structural designers. Here I have also analyzed the same structure using ETABS software for the design.IS: 1893 (Part I) for seismic design is utilized to perform the dynamic analysis. The results were observed that the multistoried buildings are stiff for earthquake excitation as modal participation factor is found to be more than 75 percent.

INTRODUCTION Earthquake causes the random ground motions in all directions, radiating from the epicenter. These ground motions causes structure to vibrate and induces inertia forces in them. For the structure to perform better during the earthquakes, it must be analyzed and designed as per the Indian seismic code IS 1893 (Part 1) 2002. In the past, several major earthquakes have exposed the shortcomings in buildings, which had caused them to damage or collapse. It has been found that regular shaped buildings perform better during earthquakes. Earthquakes causes ground to vibrate and structures supported on ground are subjected to this motion. Thus the dynamic loading on the structure during an earthquake is not an external loading, but due to motion of support. The building can be designed to resist earthquake with certain amount of damage, but without causing the collapse and affecting the livelihood. The response spectrum represents an interaction between ground acceleration and the structural system, by envelope of several different ground motion records. For the purpose of the seismic analysis the design spectrum given in fig.2

B. Response Spectrum Analysis
The response spectrum method (RSM) was introduced in 1932 in the doctoral dissertation of Maurice Anthony Biot at Caltech. It is an approach to finding earthquake response of structures using waves and vibration mode shapes. The concept of the "response spectrum" was applied in design requirements in the mid-20th century in building codes of various countries. The computational advantages in using the response spectrum method of seismic analysis are the prediction of displacements and member forces in structural systems. The method involves the calculation of only the maximum values of the displacements and member forces in each mode using smooth design spectra that are the average of several earthquake motions.

C. Necessity of seismic zoning in India
Seismic zonation is a process, which provided information about any decision making for urban regional planning or for earthquake design in earthquake areas. In principle, seismic zoning map is the main source of zoning, which is

International Journal of Engineering Research & Technology (IJERT)
ISSN: 2278-0181 http://www.ijert.org displaying quantities related to the expected frequency and intensity of shaking caused by earthquakes .The task of seismic zoning is multidisciplinary and involves the best of inputs from geologists, geotechnical, seismologists, earthquake and structural engineers .The rapid urbanization due to population outburst, coming up of mega cities in potential seismic zones is the main reason of the seismic hazard in India.
According to IS 1893 code, seismic zonation map of a country is a guide to the seismic status of a region and its susceptibility to earthquakes. India has been divided into four zones with respect to severity of earthquakes Zone factor (Z) given in table 4.1, is for the maximum considered earthquake (MCE) and service life of a structure in a zone. For design horizontal seismic coefficient Ah=(Z/2)(Sa/g)(I/R) factor 2 in the denominator of Z is used so as to reduce the Maximum Considered Earthquake zone factor to the factor for design basis earthquake (DBE).
For any structure with t<0.1 s, the value of Ah will not be taken less than Z/2 whatever be the value of I/R. II. METHODOLOGY III. PROBLEM STATEMENT Reinforced concrete moment resisting frame building of different story heights are considered. The bottom story height is kept 3m and a typical height of 3m is kept for the entire story in the building. The aim of the study is to find the difference of base reactions,modal participation factors and periods and frequencies using ETABS and STAADPRO.       Figure 8 Maximum story drift obtained from response spectrum in X direction Figure 9 Maximum story drift obtained from response spectrum in Y direction Figure 10 Maximum story shear obtained from response spectrum in X direction Figure 11 Maximum story shear obtained from response spectrum in Y direction IV CONCLUSIONS Based on the response spectra study on multi-story regular building, following points are concluded: 1. The dynamic analysis must be carried out for high rise structure with vertical regularities having height more than 40 m. 2. As the modal mass participating factor is more than 75% in the higher mode, the considered structure is stiff for earthquake excitation. 3. Response spectrum analysis was performed on the building, from this analysis it was concluded that the structure has good resistance to smaller earthquake of moderate magnitude and intensity. 4. The story displacement in X-direction is found more as compared to Y and due to the fact that the earthquake motion was applied in X-direction. 5. By the analysis results, we can find that the base reactions for the structure is coming little bit different from both the software's.