F. K. Kong MA, MSc, PhD, CEng, FICE, FIStructE, R. H. Evans CBE, DSc, D ès Sc, DTech, PhD, CEng, FICE, FIMechE, FIStructE (auth.)-Reinforced and Prestressed Concrete-Springer US (1987)

Chapter6
Shear, bond and torsion
Preliminary note: Readers interested only in structural design to BS 8110
may concentrate on the following sections:
(a) Section 6.4: Shear design (BS 8110).
(b) Section 6.6: Bond and anchorage (BS 8110).
(c) Section 6.11: Torsion design (BS 8110).
(d) Section 6.12: Design and detailing example.
6.1 Shear
Shear is an important but controversial topic in structural concrete [1-11].
In design, it is generally desirable to ensure that ultimate strengths are
governed by ftexure rather than by shear [1, 2]. Shear failures, which in
reality are failures under combined shear forces and bending moments, are
characterized by small deftections and lack of ductility. There is sometimes
little warning before failure occurs, and this makes shear failures
particularly objectionable.
It was stated in Section 3.4 that the effect ofaxialload on short columns
need not be considered for the serviceability limit states; similarly, shear in
beams is normally to be considered for the ultimate limit state only.
6.2 Shear failure of beams without shear
reinforcement
Figure 6.2-1(a) shows half of a reinforced concrete beam acted on by a
shear force V. An element in the beam would be subjected to shear stresses
v, as in Fig. 6.2-1(b), and to horizontal normal stresses due to bending. It
the element is ne ar the neutral axis or within a ftexurally cracked region,
the bending stresses are comparatively small and may be neglected without
serious loss in accuracy. The shear stresses in Fig. 6.2-1(b) are then
equivalent to the principal stresses in Fig. 6.2-1(c), in which the principal
tensile stresses are traditionally called the diagonal-tension stresses. It can
be seen that (see Failure criteria in Section 2.S(f» when the diagonal
ten sion stresses reach the tensile strength of the concrete, a diagonal crack
will develop. The preceding description, though convenient as an
F . K .K o n g e t a l., Reinforced and Prestressed Concrete
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