Seismic Retrofit for Reinforced Concrete Structures

Seismic retrofitting is the modification of existing structures so as to improve the system behaviour or its components repair or strengthening up to the performance is expected. The retrofitting of a building requires an appreciation for the technical, economic and social aspects of the issue. Choosing the optimal solution depends on a large variety of criteria, the most important being the total cost, period of construction, the ease of technologies application etc. Furthermore, the seismic behaviour of the buildings is affected due to design efficiency, construction deficiency, additional loads, additional performance demand etc. A case study is conducted in Mani Mandir complex located in Gujarat, to find the impact of various retrofitting techniques. A comprehensive retrofit program was formulated. Conservative principles, minimum intervention and consonance with the heritage character of the building were important considerations in selecting the retrofit program. The retrofit measures include providing a rigid diaphragm behaviour mechanism in existing slabs, introducing stainless steel reinforcement bands in the existing masonry walls, cross pinning and end pinning in walls and pillars and strengthening of arches and elevation features.

Earthquake creates destruction in terms of life, property and failure of structures. In order to protect from the risk triggered by seismic disaster to the life and property, the performance of the structure must be improved and thus Seismic Retrofitting plays its role. Retrofit involves modifications to existing structures that may improve energy efficiency or decrease energy demand. Seismic retrofitting is the modification of existing structures so as to improve the seismic behaviour or its components repair or strengthening up to the performance it is expected. Retrofitting also proves to be a better option catering to the economic considerations and immediate shelter problems rather than replacement of seismic deficient buildings. Two alternative approaches are conceptually adopted and implemented in practice for seismic retrofitting. The first approach focusses on upgrading the structure to resist earthquake induced forces (i.e. modifying the capacity) and is called Conventional method of retrofitting. The second approach focusses on reduction of earthquake induced forces (i.e. modifying the demand) or Unconventional approach. Seismic retrofitting is the collection of modern techniques for earthquake resistant structure.

The presence of soft and weak storey at the open ground floor, in-plane discontinuity out-of- plane offset of the ground floor columns and eccentric mass are commonly observed irregularities in the studied buildings. In absence of collector elements in the slab and proper detailing of the connections with the building frame, there is lack of integral action of the lateral load resisting elements, techniques for earthquake resistant structure. The seismic performance of beam-column joints in an RC framed structure has long been recognized as a dominant factor that affects its overall behaviour when subjected to earthquake forces, as indicated in earlier version of design codes and standards. Unsafe designs and deficient detailing that does not conform to seismic codes within the joint region may result in extra inelastic story drift and excessive post-yield rotation, which likely causes local failure, and may even lead to progressive collapse. The potential problems associated with the design deficiencies of the beam-column joints have been identified in many catastrophic structural failures reported in past major earthquakes.

Four major objectives are identified to understand the feasibility of seismically retrofitting existing structures. The first objective is to investigate how building location affects the annual probability of attaining or exceeding specified performance levels. The second objective is to develop a framework to determine the economic feasibility of seismic retrofitting. The third objective is to study the effects that achievable loss reduction, investment return period and retrofitting. The final objective is to determine the impact of a modest retrofit strategy applied to identical example buildings.


To provide safety to the occupants by reducing the of structural collapse during severe earthquakes. This can be done by strengthening the columns and joints so that their flexural and shear capacities will be adequately stronger. Retrofit strategy refers to options of increasing the strength, stiffness and ductility of the elements or buildings as whole. Several retrofit strategies may be selected under a retrofit scheme of a building.

  1. Increasing the lateral strength and stiffness of the building.
  2. Increasing the ductility and enhancing the energy dissipation capacity.
  3. Giving unity to the structure.
  4. Eliminating sources of weakness or those that produce concentration of stresses.
  5. Enhancement of redundancy in the number of lateral load resisting elements
  6. The retrofit scheme should be cost effective.
  7. Each retrofit strategy should consistently achieve the performance objective