Engineering Structures are designed to withstand all the anticipated loads without failure. Even after utmost care in assessing the expected loads as per the Codal provisions and field experience, modeling random loads like a seismic load is quite tedious and difficult. Performance based design using nonlinear pushover analysis is a highly iterative process aimed to control the structural damage under the action of earthquake forces based on precise estimation of proper response parameters. This paper reviews performance based design method using non-linear push over analysis and significant contributions published. Keywords: Seismic Load, Nonlinear static pushover analysis, Performance based design, Higher mode effects, Invariant load distributionINTRODUCTION Earthquake is one of the most destructive natural hazards. The primary objective of designer is to prevent the havoc of earthquakes and minimize the loss of life and property. Seismic loads are quite random in nature and are to be modelled carefully to assess the real time behaviour of the structure. Traditionally, the seismic design of structures has been based on strength criteria. In spite of the design using elastic codes, the quantum of damage was very high because the elastic method of seismic design has failed to provide insight into how the structure behaves during earthquakes. Realizing that increasing strength of structure may neither enhance safety, nor reduce damage, there is a gradual shift from "Strength orientation" to "Performance Based." Advantages in assessing the behavior of structure during strong ground motions to minimize property damage and loss of life has made Performance based design more popular choice among engineers. Structural behaviour during an earthquake of a given severity can be assessed using linear static, non-linear static, linear dynamic and non-linear dynamic analysis methods. The performance based seismic design process evaluates how a building is likely to perform under an earthquake of expected severity; considering uncertainties inherent in the quantification of potential risk and uncertainties in assessment of the actual building response. It is an iterative process that begins with the selection of performance objectives, followed by the development of a preliminary design, an assessment as to whether or not the design meets the performance objectives, and finally redesign and reassessment, if required, until the desired performance level is achieved. The most commonly adopted method is non-linear static analysis, popularly known as pushover analysis. The static pushover analysis is gaining significance as one of the popular tools for evaluating seismic performance of new and existing structures. The expectation is that the pushover analysis will provide adequate information on seismic demands imposed by the design ground motion on the structural system and its components (Krawinkler and Seneviratna, 1998).

Most of the existing low rise RCC buildings with 4 to 6 floors were constructed pursuant to the code provisions without detailed Earthquake analysis. To comply with the revised code provisions, it is essential to build up the seismic resistance of the existing buildings. International building safety agencies such as NEHRP, FEMA, and ATC etc., formulated the Performance-based design methods to verify the seismic resistance of the existing buildings and also recommend the retrofit the building to achieve the targeted performance. Pushover method (nonlinear static analysis) is one of the methods. This paper describes the increase of seismic capacity of structure with the additional steel contribution from 25 % to 75% increase in the beams near the beam-column joints. Moreover, this additional steel is placed up to 02.L, 0.25L and 0.3L of the beam span. To accomplish the above parameters, 4-storey, 5-storey and 6-storey rectangular framed structures are analyzed with the pushover analysis. The seismic capacity curves in terms of base shear versus displacement are illustrated. It is found that 10 to 25% of base shear is increased when beams are provided with additional reinforcement from 25% to 75% @0.2L. In this case of increasing the additional steel length from 0.20L to 0.3L, nearly 5% increase of the base shear is observed in width direction but no augmentation is observed in the length direction of the building.