Retrofitting a brick masonry building

Importance of retrofitting

• 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.

Retrofitting a brick masonry building

Steps: (1) condition survey and NDT of the walls, mortar and foundation; (2) selection of method; (3) execution; (4) quality check.

1. Crack repair: inject cement or epoxy grout into cracks; stitch large cracks with steel dowels or staples.
2. Replace damaged parts: remove crushed bricks and re-lay in rich mortar (1:4).
3. Re-pointing: replace weak mud mortar with cement mortar to a depth of 20 mm.
4. Ferrocement / mesh jacketing: weld mesh or chicken mesh fixed on both faces of walls with through-wall ties at 450-600 mm, covered with 20-30 mm cement plaster (1:3). Improves in-plane strength and out-of-plane stability.
5. Adding RC bands: insert plinth, lintel and roof-level bands (in lengths) or provide external steel bands.
6. Vertical steel at corners and jambs: drill holes through walls, insert bars, and grout.
7. Strengthening openings: put RC frames or steel angles around large openings; close unnecessary openings.
8. Tying of floors and roof: anchor roof and floor to walls; provide diagonal bracing in flexible roofs; add an RC topping to make a rigid diaphragm.
9. Adding buttresses or shear walls at weak walls; replace heavy mud roof with a light roof.
10. Improving foundation: underpin or widen the foundation, add a plinth beam.

   mesh + plaster on both faces
   |#|   wall   |#|
   |#|----------|#|   <- through tie every 450-600 mm
   |#|          |#|