Dynamic Analysis In Earthquake

CHAPTER-1

INTRODUCTION

1.1 PREAMBLE Earthquake is a manifestation of rapid release of stress waves during a brittle rupture of rock. The complexity of earthquake ground motion is primarily due to factors such as source effect, path effect and local site effect. Earthquake causes ground to vibrate and structures supported on ground in turn are subjected to this motion. Thus the dynamic loading on the structure during an earthquake is not external loading, but due to motion of support. The various factors contributing to the structural damage during earthquake are vertical irregularities, irregularity in strength and stiffness, mass irregularity, torsional irregularity etc. The complexity of earthquake ground motion is primarily due to

In addition to structures present in zone V, it is also required for a large number of different types of structural systems that are constructed in seismic zones II, III and IV. In this method, the lateral force is found out by several methods that can be used to determine the distribution of seismic forces within a structure. The major advantage of using the forces obtained from a dynamic analysis as the basis for a structural design is that the vertical distribution of forces may be significantly different from the forces obtained from an equivalent static load analysis as dynamic analysis is more accurate than the static

In particular, the seismic rehabilitation of older concrete structures in high seismicity areas is a matter of growing concern, since structures vulnerable to damage must be identified and an acceptable level of safety must be determined. To make such assessment, simplified linear-elastic methods are not adequate. Thus, the structural engineering community has developed a new generation of design and seismic procedure that incorporates performance based design of structures and is moving away from simplified linear elastic methods and towards a more non linear technique. Recent interests in the development of performance based codes for the design or rehabilitation of buildings in seismic active areas show that an inelastic procedure commonly referred to as the pushover analysis is a viable method to assess damage vulnerability of buildings. Basically, a pushover analysis is a series of incremental static analysis carried out to develop a capacity curve for the building with increasing lateral load or displacement. Based on the capacity curve, a target displacement which is an estimate of the displacement that the design earthquake will produce on the building is determined. The extent of damage experienced by the structure at this target displacement is considered representative of the damage