Experimental study on large-scale compression members strengthened with circumferential prestressed CFRP plate

Area of Science:

• Civil Engineering
• Materials Science
• Structural Engineering

Background:

• Limited research exists on reinforcing large-scale bridge columns (meters in cross-section) using prestressed carbon fiber-reinforced polymer (CFRP) materials, unlike smaller structural elements.
• Replacing traditional steel tendons with CFRP sheets in cable-stayed bridge tower columns offers potential benefits in construction, maintenance, and fatigue resistance.
• Large-sized tower columns in bridges require robust reinforcement solutions to ensure long-term structural performance and safety.

Purpose of the Study:

• To develop and evaluate a novel tensioning device for applying circumferential prestress using CFRP plates on large-scale composite compression components.
• To investigate the effectiveness of CFRP plate reinforcement in large bridge columns, specifically focusing on tower columns in cable-stayed bridges.
• To analyze prestress loss and stress distribution when using CFRP plates with different tensioning methods and interface materials.

Main Methods:

• Development of a specialized tensioning device and test pedestal utilizing wave-shaped-gear-grip (WSGG) anchor clamping for CFRP plates.
• Conducting circumferential tensioning tests on CFRP plates wrapped around a 2-m long composite compression component.
• Deriving and verifying a calculation formula for the constraint pressure exerted by circumferentially prestressed CFRP sheets.
• Measuring prestress loss in CFRP plates under single-end and double-end tensioning with an iron sheet as an interface medium.

Main Results:

• The developed device successfully achieved circumferential tensioning of single-layer CFRP plates to 0.5ftk, generating 60kN tensile force and effective restraint pressure on a 2-m component.
• The derived formula for constraint pressure showed a maximum error of 5% compared to experimental values, validating its accuracy.
• Prestress loss was significant (84% for single-end, 58%-60% for double-end tensioning with iron sheet), indicating limited effective prestress with this interface.
• Double-end tensioning proved more effective than single-end tensioning for CFRP plates with an iron sheet interface.
• Tensile stress in the CFRP plate along the member followed a cubic function, leading to a deduced quadratic function distribution for the constrained compressive stress on the member.

Conclusions:

• The developed WSGG-based tensioning device is effective for applying circumferential prestress to large composite components using CFRP plates.
• The derived formula accurately predicts the constraint pressure generated by prestressed CFRP sheets.
• Careful consideration of interface materials and tensioning methods is crucial to minimize prestress loss and maximize the effectiveness of CFRP reinforcement in large structural elements like bridge columns.