Seismic Retrofitting

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Let us talk about Seismic Retrofitting today. Retrofitting can be broadly classified into Conventional methods and non-conventional methods

Conventional Methods are methodologies adopted to increase the strength of structure either globally or locally.

Non-Conventional Methods are methodologies adopted reduce seismic force into the system.

All the methods can be suitably adopted under the guidance of an experienced Structural Auditor, Structural Steel and RCC Designers who are already experienced in stability checks, retrofitting etc.

All of these should include site quality check, should check the level of capacity of the existing building, should check the condition of rebar’s, corrosion level, condition of concrete.

All possible solutions can be checked out by modelling it in a suitable software. We can make use of latest 3D BIM Modelling techniques. We can make use of modelling software like ETABS, STAAD, TEKLA Modelling etc to check effectiveness of various methods by modelling the existing structure with the retrofitting methodology adopted.

CONVENTIONAL METHODS adopted include addition of shear walls, infill walls, jacketing of members locally, steel bracings

Adding of shear walls, infill walls, steel bracings are good way to increase the lateral strength.

The problem with this is there can be architectural utility issue that can arise due to the construction of these walls, more than that the forces including the moments are bound to increase in the foundation due to increase in stiffness on the account of addition of these walls and bracings So this can be quite challenging and may not be easily adapted to the system.

Jacketing of mainly columns are done to improve the ductility of the system. The concept here is to add a layer of confinement around the columns to confine the concrete. The act of confinement improves the ductility, shear strength and flexural strength of the columns making it capable of absorbing more energy under a seismic tremor. Different methods of jacketing can be used including use of steel jackets, fibre reinforced polymer composite etc. around the column. This technique would require a good workmanship skill.

NON CONVENTIONAL METHODS method involved addition of damping to the system by means of different types of dampers, seismic base isolation.

The concept here is it to increase the time period of the existing structure which in general reduce seismic force in the building due to flexibility of building. But this again need a careful technical study considering the site specific spectra to achieve maximum efficiency.

Base isolators are fixed at the base and will lengthen the time period of the structure, hence reduce the force in the system. Dampers are fixed at specific locations to improve the damping capacity of building so that it absorbs the extra energy.

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