Retrofitting Concrete Walls

Project Background

The BTCL (Bangladesh Telecommunications Company Limited) Headquarters required structural upgrading after years of service. A comprehensive structural assessment revealed that certain reinforced concrete walls on the 3rd floor and 4th floor — no longer met current lateral load and flexural capacity requirements under the Bangladesh National Building Code (BNBC). Key issues identified included:

• Insufficient shear capacity under seismic and wind lateral loads

• Reduced out-of-plane bending resistance due to concrete carbonization and reinforcement corrosion

• Crack development in wall panels indicating progressive deterioration

• Functional changes in certain zones increasing structural demand beyond original design

To minimize disruption to building operations and avoid the weight penalty of traditional strengthening methods, the engineer specified CFRP (Carbon Fiber Reinforced Polymer) plate bonding — a proven, lightweight solution for concrete wall strengthening.

3rd Floor

4th Floor

Why CFRP Plate Bonding for Concrete Walls?

CFRP plate bonding is particularly effective for RC wall strengthening in the following scenarios:

• In-plane shear strengthening: Increases shear capacity under lateral (seismic/wind) loads — critical for RC shear walls

• Out-of-plane bending resistance: Enhances wall stability under eccentric loading and boundary conditions

• Crack control and confinement: Carbon plates bridge existing cracks and confine concrete to prevent progressive failure

• Minimal intervention: CFRP plates are thin (~1.2–1.4mm), preserving floor space and architectural finishes

• Speed and ease of installation: Significantly faster than traditional concrete jacketing or steel plate bonding

• Corrosion resistance: Unlike steel, CFRP does not corrode — ideal for humid environments

Material Specifications

• Carbon plate type: Unidirectional (UD) CFRP plate, Class I

• Tensile strength: ≥ 2,400 MPa

• Elastic modulus: ≥ 160 GPa

• Plate thickness: 1.4mm

• Bonding agent: High-modulus CFRP saturating resin, compatible with concrete substrate

Results 

• Shear capacity of strengthened RC walls increased by approximately 40%

• Out-of-plane bending resistance significantly enhanced, reducing risk of wall failure under lateral loading

• Minimal disruption to operations — work confined to designated zones (SW-03, SW-04)

• Negligible added weight — CFRP plates add less than 3 kg/m² to the wall surface

• Corrosion-resistant system, providing long-term durability in Bangladesh's humid climate