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 where,
vtu
=
nominal torsional stress, psi
Tu
=
total torsional moment at critical section, in-lb
[phi]
=
capacity reduction factor equal to 0.85
b
=
width of beam, in
h
=
overall depth of beam, in
The critical section for torsion is taken at the same location as diagonal
tension. It should be noted that the torsion stress in the vertical face of
the beam (along h) is maximum when b is less than h, whereas the torsion
stress along the horizontal face of the beam (along b) is maximum when b is
greater than h.
(5) For a beam subjected to combined shear (diagonal tension) and
torsion, the shear stress and the torsion stress permitted on an
unreinforced section are reduced by the presence of the other. The shear
stress permitted on an unreinforced web is limited to:
2[phi] (f'c)1/2
EQUATION:
vc =
(48)
[1 + (vtu/1.2vu)2]1/2
while the torsion stress taken by the concrete of the same section is
limited to:
2.4 [phi] (f'c)1/2
EQUATION:
vtc =
(49)
[1 + (1.2vu/vtu)2]1/2
where,
vc
=
maximum shear capacity of an unreinforced web, psi
vtc
=
maximum torsion capacity of an unreinforced web, psi
[phi]
=
capacity reduction factor equal to 0.85
vu
=
nominal shear stress, psi
vtu
=
nominal torsion stress in the direction of vu, psi
It should be noted that the shear stress permitted on an unreinforced web of
a beam subjected to shear only is given by Equation (44). Whereas, the
torsion stress permitted on an unreinforced web of a beam subjected to
torsion only is given by:
EQUATION:
vtc = 2.4 [phi] (f'c)1/2
(50)
2.08-76
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