Old Apartment Column Retrofit

This project delivers seismic and load-carrying capacity upgrade for rectangular reinforced concrete frame columns of an apartment building. As-built structural review revealed inadequate transverse steel confinement, insufficient shear resistance and poor ductility, exposing columns to brittle shear failure under factored gravity and seismic loads. 

Heavy conventional strengthening schemes, including concrete jacketing and steel encasement, were ruled out due to significant section enlargement, loss of clear space and prolonged disruption to residential occupancy. The project adopted a thin, externally bonded CFRP confinement solution, engineered specifically for rectangular-section constraints, to enhance concrete passive confinement, suppress concrete spalling and convert brittle failure mode to ductile behaviour.

Deficiencies identified: Inadequate transverse reinforcement, low deformation capacity, insufficient shear strength, non-compliance with updated seismic demand.

Design objective: Increase effective confining pressure on core concrete, raise axial and shear capacity, improve hysteretic energy dissipation, and achieve seismic ductility without altering column external dimension or reducing usable floor area.

Material & Specification

Reinforcement fabric: High tensile unidirectional carbon fibre sheet, oriented along hoop direction for confinement; multi-ply layout determined by confinement calculation.

Matrix: Two-component structural saturating epoxy, formulated for concrete substrate, providing full fibre impregnation and durable bond.

Strengthening Scheme

Full-height closed circumferential wrapping. Carbon fiber sheets were applied as continuous horizontal bands around the full height of each column, from the base to the beam-column joint. The closed loop develops hoop tension in the fabric, confining the concrete core and improving the column's axial capacity and ductility without altering the section geometry.

Higher axial capacity and ductility in the wrapped columns, with no change to the column section, which is the answer to a load path that has no redundancy. Essentially zero added weight, so the existing foundations were not loaded further. No loss of saleable floor area, protecting the owner's primary asset. Fast, quiet installation compatible with the ongoing fit-out and with tenants remaining in place. A consistent, uniform strengthening pattern across all columns of the building.