Considering the large number of people, high fatality in RC buildings and volume of economic activities, the social risk involved in cities is also very high; the seismic retrofitting of the existing buildings has to be undertaken to make these unsafe houses safe to resist future earthquakes, thereby reducing the number of casualties significantly. However, government can take up retrofitting of its own buildings and some public utility buildings which are of post earthquake importance.
Seismic assessment and retrofit of reinforced concrete buildings
The deficiencies in buildings and structures against earthquake may arise at i planning stage with faulty configuration and irregularities, ii design stage due to inadequate strength and ductility, and iii construction stage due to faulty construction practices. Revision of design codes is a continuing process world over and usually results in up-gradation of seismic hazard and increase in design forces.
In India also several regions have been upgraded in terms of seismic zones thereby rendering buildings unsafe according to new code. All these factors make the retrofitting of existing structures necessary. The level of retrofitting of a building depends on the seismic zone in which building is situated and the level of performance desired from the building.
Retrofitting design of structures subjected to seismic loading
Important buildings are desired to have a higher performance level during future earthquakes. The seismic zone governs the design earthquake forces and the performance level governs the permissible damage or the permissible values of member actions due to earthquake forces.
Not only member forces and strength are important, the nonlinear deformations and ductile capacity of members are also important for seismic safety of building and need to be evaluated and examined. The aim of present Guidelines is to provide an overview of the available techniques for seismic evaluation and retrofitting of existing buildings.
The techniques have been presented for the type of construction prevailing in India. Emphasis has been on detailing the techniques with illustrations, so that these may be easily understood and applied by common engineers, architects and builders.
A need has been felt to provide adequate information about seismic retrofit design of masonry and RC buildings which can be easily understood and implemented. The Guidelines deal with important aspects of seismic hazard estimation, systematic inspection of existing buildings, tests for estimation of in-situ strength and extent of damage and deterioration in masonry and RC buildings, mathematical modeling of frames, frame-tubes, shear walls and frames with infills, and various methods of analysis for earthquake forces for seismic evaluation, seismic evaluation which requires knowledge of structural behaviour, materials of construction, principles of seismic intervention and behaviour of modified structure, and various retrofitting materials.
This includes performance levels of various types of buildings. Two checklists have been given for systematic inspection of masonry and RC frames. Besides the increment in stiffness of the structure, major repercussion in the conventional method of retrofitting could be the development of new load paths that may lead to concentration of loads at the foundation level.
Short Course on Seismic Assessment and Retrofit Strategies for Reinforced Concrete Buildings
This happens in reinforced concrete RC frame structures, where inclusion of concrete shear walls in between the columns is carried out as a retrofitting measure. In such, existing foundation of the adjoining columns is likely to get overstressed. Selection of the proper retrofitting technique shall be done by carrying out the detail analysis of the existing structure. Re-Analysis including Re-Design of the structure may be required after the introduction of retrofitting measures; so that the objective of Seismic Retrofitting is met.
Design principles, even in case of retrofitting, as in case of new construction shall follow several factors.
2 Techniques for Seismic Repair and Retrofit | FPrimeC Solutions
For instance in order to have a full advantage of the potential ductility of retrofitted RC members, it is desirable to ensure that flexure rather than shear govern ultimate strength. Shear failure is catastrophic and occurs with no advance warning of distress. Most of the existing RC Columns and Beams have been found deficient in shear strength and in need of strengthening.
Shear Deficiencies occur due to several reasons such as insufficient shear reinforcement or reduction in steel area due to corrosion, increased service load, design principles in older codes and construction defects. Building structures lying in acceleration sensitive region and velocity sensitive region of the spectrum may require different retrofitting measures.
Retrofitting option suitable for one structure may prove to be inefficient for another structure with different dynamic behavior. Also, after retrofitting, stiffness of a building structure may increase significantly; thereby increasing a load demand on the structure than before retrofitting. Increase in stiffness also depends on the type of the retrofitting measure carried out. In such, re-analysis of the retrofitted structure shall be carried out.
- Kants Lectures on Ethics: A Critical Guide (Cambridge Critical Guides)?
- The Cambridge History of Latin American Literature Vol. 1 Discovery to Modernism.
- General Perspectives on Seismic Retrofitting of Historical Masonry Structures.
Modern Jacketing technique such as Fibre Reinforced Polymer FRP wrapping could be the best way to strengthen the capacity of structures without altering stiffness. Besides the increment in stiffness of the structure, major repercussion in the conventional method of retrofitting could be the development of new load paths that may lead to concentration of loads at the foundation level. This happens in reinforced concrete RC frame structures, where inclusion of concrete shear walls in between the columns is carried out as a retrofitting measure.
In such, existing foundation of the adjoining columns is likely to get overstressed. Selection of the proper retrofitting technique shall be done by carrying out the detail analysis of the existing structure.