Rehabilitation of Reinforced Concrete Beams Using Carbon Fiber

The adopted solution combines externally bonded steel plates (for primary beams with significant strength deficit) and carbon fiber reinforced polymer (CFRP) sheets (for secondary beams, joint zones, and shear-critical regions).

Project Overview

This project involves the structural rehabilitation of an existing multi-story reinforced concrete (RC) frame building. The structure consists of RC columns, primary and secondary beams, and cast-in-place reinforced concrete slabs — a typical cast-in-situ RC frame system common in university buildings from the late 20th and early 21st centuries.

Rehabilitation of Reinforced Concrete Beams Using Carbon Fiber

Problems

Change of building function — lab equipment, library stacks, or new functional requirements may exceed the original live load capacity

Member deterioration — long-term environmental exposure, concrete degradation, or reinforcement corrosion

Deficiency identified in assessment — structural audit revealing insufficient shear or flexural capacity in key members

Rehabilitation of Reinforced Concrete Beams Using Carbon Fiber

Solution

1. Primary Beams — Externally Bonded Steel Plates (Flexural rehabilitation)

Application method: Steel plates are epoxy-bonded to the soffit (bottom face) of primary beams, oriented along the longitudinal span direction.

2. Secondary Beams — CFRP Sheets (Flexural rehabilitation)

Application method: Unidirectional CFRP sheets are impregnated with epoxy resin and bonded to the soffit of secondary beams, with fiber direction aligned parallel to the beam span.

3. Beam-Column Joints — CFRP U-Wraps (Shear rehabilitation)

Application method: CFRP sheets are applied in a U-shaped configuration around the beam cross-section at supports and joint regions, with fibers oriented perpendicular to the beam axis (vertical direction on the web faces).

4. Beam Intersection Zones — CFRP Cross Sheet

Application method: CFRP sheets are applied in a cross-pattern at primary-to-secondary beam intersections, addressing the complex stress state at member junctions.

Advantages of the Combined Approach

Design Aspect	Steel Plates	CFRP Sheets	Combined Benefit
Strength gain magnitude	High — ideal for heavily loaded primary beams	Moderate to high — efficient for secondary members	Optimized per member requirement
Stiffness contribution	Very high — reduces deflection significantly	Lower modulus than steel per unit thickness	Steel handles stiffness-critical members
Added dead load	Moderate — steel is heavy	Near zero — critical for existing structures	CFRP limits overall weight increase
Installation speed	Slower — heavy plates, mechanical anchors	Fast — lightweight, hand-layup	Parallel installation on different members
Corrosion resistance	Requires protective coating	Inherently corrosion-resistant	CFRP preferred in aggressive environments
Cost per unit strength	Generally lower for large gains	Higher per kg but less material needed	Cost-optimized by member type