Design and Detailing of RC Jacketting for Concrete Columns

Retrofitting is a technique to enhance the structural capacities including the strength, stiffness, ductility, stability, and integrity of a building that is found to be deficient or vulnerable. It can effectively raise the performance of a building against earthquake to a desired level, and to even satisfy the requirements of an upgraded design seismic code. The building need not be deteriorated or damaged. The retrofit is intended to mitigate the effect of a future earthquake. In this paper, an effort is made to elaborate the procedure of providing concrete jacketing to the column as per guidelines of IS 15988: 2013. It is seen that the overall performance of the column significantly improves after jacketing. Keywords - Concrete Jacketting, Ductility, Retrofitting, Stiffness, Structural Capacities. Retrofitting can generally be classified in two categories: Global and the local. The global retrofitting technique targets the seismic resistance of the building. It includes adding of infill wall, adding of shear wall, adding of steel bracings and base isolation. Adding of infill wall in the ground storey is a viable option to retrofit buildings with soft storey. Shear walls can be introduced in a building with flat slabs or flat plates. A new shear wall should be provided with an adequate foundation. Steel braces can be inserted in frames to provide lateral strength, stiffness, ductility, and to improve energy dissipation. These can be provided in the exterior frames with least disruption of the building use (2). Local retrofitting technique targets the seismic resistance of a member. The local retrofit technique includes the concrete, steel or Fibre reinforced polymer Jacketting to the structural members like beams, columns, beam column joint, foundation. Concrete jacketing involves adding a new layer of concrete with longitudional reinforcement and closely spaced ties. The jacket increases both the flexural strength and the shear strength of the beam or the column. The following are the advantages of retrofitting. It increases the seismic resistance of the building without any demolition. It increases the ductile behaviour and lateral load capability of the building Strength and stiffness of the building is also improved (3) II. Strengthening Of Existing Columns By Jacketting There are two main purpose of jacketing of columns. (i) To increase in shear capacity of columns (strong column-weak beam design) (ii) To improve the column's flexural strength. After carrying out the detailed analysis of the existing building, deficient members are identified. A list of provided and required reinforcements is tabulated and highlighted. All these members require strengthening in order to increase their ductile strength. Hence, retrofitting of these members is carried out using Jacketting.