Title:

Shear strength of reinforced concrete beams

The investigation reported in this thesis is concerned with
the general subject of the shear resistance of reinforced
concrete beams and the findings are applicable to rectangular,
T and Isections.
To assist the theoretical analysis, tests of 75 normal sized
beams, in which the parameters affecting shear varied systematically,
were carried out. Concentrating on the types of
members where lack of sufficient experimental data existed, all
but 10 of the beams contained shear reinforcement and 45 had
compression flanges.
Virtually all the beams, having high strength longitudinal
reinforcement with good bond quality, failed in shear in one
of the following modes
1) Diagonal Tension
2) Shearing (Shearing of concrete above a shear crack)
3) Shear Compression
4) Web Crushing
The theoretical analysis is to a large extent based on
observations of the behaviour of these beams during the tests
and at failure. As a result equations are presented representing
each mode of failure. If the strengths corresponding to modes
2, 3, and 4 are greater than the diagonal tension load, the
final solution is given by the mode of failure equation predicting
the least strength; in other cases failure is by diagonal
tension. In this manner not only is an adequate numerical
prediction of the failure load obtained, but a comparison of
the results pertaining to the various modes provides a good
indication of the actual typo of failure that is likely to
take place.
Intrinsic to this approach is a rational solution of the
problem of compression reinforcement and its influence or lack
of influence on the ultimate shear strength of rectangular
beams. The increased strength of Tbeams over that of rectangles
composed of their webs is also adequately reflected in the
proposed theory.
To establish the equation for the shearing mode of failure
a new adaption of a Coulomb type "plastic shear" failure criterion
for concrete is presented.
Since collapse loads are not the only design criteria, in
addition to the equations for the four modes of failure mentioned,
formulae are also developed, substantiated by test results,
to cover two other possible criteria
1) Shearing off of flanges in Tbeams
2) Shear crack widths
The various equations put forward in this thesis show
adequate correlation with test results, giving on average a
10% safety margin at a coefficient of variation of loss than
0.10.
