FRP-encased concrete as a structural material

TLDR

Plastics reinforced with continuous glass fibres have high tensile strength and corrosion resistance but low modulus and compressive strength, and their weathering and fire resistance are limited, requiring improvement measures. The study proposes developing composite members where a prefabricated FRP casing serves first as a form for casting concrete and then as confinement, tensile reinforcement, and corrosion protection. The authors conduct experimental tests on FRP‑encased concrete cylinders under axial compression and rectangular beams under bending, and analytically model circular beam‑column behaviour with moment‑axial‑load and ductility‑axial‑load interaction diagrams and moment‑curvature relations. The results show significant cost savings, particularly for exposed structures such as bridges, and demonstrate that FRP‑encased members exhibit excellent strength and ductility.

Abstract

Synopsis Plastics reinforced with continuous glass fibres have outstanding tensile strength in the fibre direction and excellent corrosion resistance, but are characterized by low modulus and low compressive strength. It is proposed to develop composite members in which a prefabricated FRP (fibreglass-reinforced-plastic) casing is used initially as the form to cast plain concrete, and thereafter to confine the concrete, act as tensile reinforcement and provide corrosion protection. Significant cost savings are possible with the proposed combination of materials, especially in exposed structures, such as bridges. An experimental investigation of FRP-encased concrete cylinders in axial compression and of rectangular FRP-encased beams in bending is presented. The results demonstrate the excellent strength and ductility characteristics of FRP-encased members. The behaviour of circular FRP-encased concrete beam-columns is described also, in terms of analytically obtained moment-axial-load and ductility-axial-load interaction diagrams and moment-curvature relations. The weathering characteristics and the fire resistance of the FRP are discussed, and measures to improve these environmental properties are reviewed.