#
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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(last
update 12th January 1998)