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INTRODUCTION
Earthquakes are the natural hazards with high damage potential. However, by utilizing several principles, it is possible to identify and minimise the resulting social and economic losses, which mainly involve loss of human lives, damage to major industrial facilities, civil engineering structures and lifelines.
In the last decades many methodologies on seismic hazard analysis and damage prediction are developed. In recent years, the development of structural design criteria for new structures and renewed importance of the assessment of seismic vulnerability of existing under-designed buildings have broadened the objectives of seismic design. While safety against collapse is still the main goal, performances in terms of functionality and economy assumed a central role in the design criteria. Hence, a great effort has been made to improve the current earthquake resistant design methods in order not only to avoid collapse under a destructive earthquake but also to limit the damage under moderate earthquakes. Furthermore, the new design philosophy is tending to multi-level probabilistic structural performance criteria, replacing completely the simple force strength approach. However; the implementation of all these new concepts requires the definition of qualitative damage index and measure.
1.1 TYPES OF DAMAGE:-
There are two types of damage in reinforce concrete structures.
a) Structural Damage
The RCC element may suffer a minor to severe level damage. The beams, columns, slabs and RCC walls may get cracks. In some cases there may be partial failure or collapse of local elements.
b) Non – Structural Element Damage
Though damages to the non-structural elements do not pose a threat to stability of structures. It may affect the functioning, movements, services and aesthetics. Failure of non-structural elements may cause loss of life or injury or damage to equipment etc. The non-structural damages such as misalignment of lifts, damage of plumbing work, especially damages to the concealed pipes will lead to leakage and electric wiring.
1.2 EFFECTS OF DAMAGE ON A STRUCTURE:-
The effects of damage on a structure can be classified as linear or nonlinear. A linear damage situation is defined as the case when the initially linear elastic structure remains linear elastic after damage. The change in modal properties are a result of changes in the geometry and / or the material properties of the structure, but the structural response can still be modelled using a linear equation of motion. Non-linear damage is defined as the case when the initially linear-elastic structure behaves in a non-linear manner after the damage has been introduced.
1.3 RESEARCH METHODOLOGY:-
The concept of damage identification is outlined from review of the available literature. The approach, which has been used in the present study, is based upon Push–Over Analysis of the structures. For the formulation of the present work a twenty five storey 3-D building frame has been taken. Seismic analysis of the frame was done using computer software (SAP Advanced 14.0.0) in repetitive manner applying IS earthquake spectra, consequently changing the monitored displacements i.e. the target displacement of the structure as per FEMA 356. Finally the input and output of above-mentioned analysis is used for prediction of damage in the RCC framed building based on stiffness degradation.
1.4 SCOPE OF THESIS:-
Most of the structures are severely damaged during an earthquake event. The degree of damage depends upon the earthquake magnitude, type of system, foundation condition etc. IS1893-2002 speaks no word on this issue since; the quantification of damage is complex. Various methods for assessing the damage index have been proposed by researchers in last decade and each one described with varied approach in turn, it observed that different strategies has resulted different correlation between damage state and damage index hence study is required to present simple approach.
1.5 ORGANIZATION OF THESIS:-
Chapter 1 of this thesis contains introductory information on Damage identification for reinforced concrete structures. It covers scope, limitations and methodology used in developing this study. A brief description of the following chapters is given in the following paragraphs.
Chapter 2 deals with detailed literature review of various methods for the quantification of damage.
Chapter 3 deals with the seismic evaluation methods
In chapter 4 frequency and mode shape based damage indices and energy based damage indices have been discussed in more detail.
Chapter 5 deals with the development of model for the identification of damage using the approach of push – over analysis.
Chapter 6 is dedicated to discussion and conclusions drawn from above study.
CHAPTER 2
LITERATURE REVIEW
2.1 “A story Damage Index of Seismically-Excited Buildings Based on Modal Frequency and Mode Shape” Jer-Fu Wang, Chi-chang Lin, Shih-Min Yen (1):
In this paper, dynamic and characteristic equations are developed for a planer shear building frame and expressed as a simple formula based on modal frequency and mode shape obtained from real earthquake records. The approximate SDI, called ASDI, is also applied without the floor mass information.
In this paper a general expression for lth storey stiffness is formulated using the famous characteristics equation for an undammed system considering an N floor planer shear building frame without damping and damping parameter. Based on above equation the storey damage index for that storey is calculated. As most of the buildings have uniform floor mass distribution a new approximate method is invented called ASDI i.e. approximate storey damage index. It takes into account only one set of modal parameters which is beneficial for practical applications.
Finally for the validations of SDI and ASDI a five storey shear building with varying stiffness reductions in the first and third stories are considered looking towards the variation based on the modal frequency and mode shape of a particular mode. Further these methods are practically employed to investigate the damage assessment of a 7 -storey reinforced concrete building in Van Nuys, California undergone severe damages during the 1994 Northridge earthquake.