Seismic strengthening techniques for masonry buildings

Strengthening of existing masonry aims at (i) restoring strength after damage (repair), and (ii) improving the strength, ductility and integrity of the building (retrofitting).

1. Repair of cracks

• Grouting of cement–sand or epoxy grout into cracks and voids in rubble walls restores continuity.
• Stitching (staples or bars across cracks) and re-pointing of joints with stronger mortar.

2. Jacketing of walls

• Ferrocement or wire-mesh jacketing: welded wire mesh fixed on one or both faces with anchors through the wall, covered by 25–40 mm cement mortar. It increases shear and flexural capacity and out-of-plane strength.
• Reinforced concrete jacket or FRP (fibre-reinforced polymer) strips and sheets on the face for greater strength with little added weight.

3. Adding bands and vertical elements

• External or internal RC bands (plinth, lintel, roof) and vertical bars at corners and jambs, added to existing walls to give box action.
• Corner stitching with steel or timber ties.

4. Connection improvement

• Anchoring floor and roof to walls with steel angles or through bolts; tie rods or cables across rooms to tie parallel walls.
• Adding cross-walls or buttresses to limit out-of-plane bending.

5. Modifying the structure

• Replacing heavy roofs with lighter ones.
• Closing unnecessary or weakening openings by infilling, or lining openings with frames.
• Adding new shear walls or RC frames to share the load.

6. Foundation improvement

Underpinning, plinth beams or foundation grouting.

The retrofitting scheme should follow a prior assessment: survey, material tests (see non-destructive tests), and analysis of the weakest link.