[Univ of Cambridge][Dept of Engineering]

The shear of concrete with elastic FRP reinforcement

by T.J. Stratford

This thesis describes a fundamental review of shear in concrete reinforced with Fibre-Reinforced-Plastics (FRPs).  Current descriptions of shear in concrete were developed using steel reinforcement, and rely on lower-bound plasticity theory.  Plasticity theory cannot be applied to FRP-reinforced concrete.  An elastic analysis is required that considers equilibrium, compatibility and constitutive relationships.

By detailed consideration of the load-carrying mechanisms within a beam, a crack-equilibrium model is developed.  The model assumes that the deflection of the beam can be described by rigid body rotations at cracked sections.  Equilibrium of the cracked section is satisfied by adjusting the crack opening angles and crack lengths.  Constitutive relationships are required for each element of the beam:  the compression-zone concrete, the tension-zone concrete, the flexural reinforcement, and the web reinforcement.

The compression-zone concrete is modelled using a simple model describing strain-localisation.  Only the axial response of the compression-zone is considered in detail, but the effects of a compression-zone shear force are discussed.  Tension-zone concrete is included to allow size effects to be investigated.

A long-embedded-length analysis of the bond between the reinforcement and the concrete is developed, by extending existing short-embedded-length models.  This is used to study both the web and flexural reinforcement in a beam.

It is also necessary to predict the shape of the cracks.  The direction of crack propagation is determined by examining the crack tip stress concentration using linear-elastic fracture-mechanics.  Global effects such as crack interaction are separated from the detailed local analysis.

The crack-equilibrium model uses an incremental solution procedure.  During solution, checks are made to predict the formation of new cracks, and simple failure criteria are applied to each of the beam's components.

Examples analyses are presented and discussed.  These show that the crack-equilibrium model provides a framework for shear analysis in FRP-reinforced concrete, and highlights subjects that require further research.

[Cambridge University | CUED | Division D | Structures Group
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