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What is retrofitting; why it is necessary

Short answer

Retrofitting is strengthening an existing building to improve its seismic resistance beyond the original design. It is necessary because many older buildings lack seismic design, codes are updated, use changes or deterioration reduces capacity, and it saves lives at a fraction (10–30%) of reconstruction cost.

What is retrofitting of a building? Why is it necessary?

Retrofitting

Retrofitting is the strengthening or modification of an existing building so that it can resist earthquake forces better than it was originally designed to. It improves strength, stiffness, ductility and load path of the existing structure without rebuilding it.

It is done after a structural assessment (condition survey, NDT, calculation of the capacity versus demand) that identifies weak points. The common methods are jacketing, adding shear walls/bracing, strengthening of connections and foundation, wall plastering with mesh, and use of FRP.

Why it is necessary

  • Many older buildings in Nepal were built without engineering design or seismic code (NBC 105), so they can collapse in a moderate earthquake (as in Gorkha 2015).
  • Retrofitting saves lives and property at a cost much lower than demolition and reconstruction (typically 10-30% of new construction cost).
  • Seismic codes are revised; buildings built to old codes become deficient.
  • Change of use, added floors, or deterioration (corrosion, cracks, aging) reduces capacity.
  • Heritage and important buildings (hospitals, schools, temples) must be preserved.
  • Damage from a past earthquake must be repaired and the building made safe against the next one.

✓ Answer checked by Claude Opus 5.5 (high effort)

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