Fundamentals of Shear - Unified Theory of Concrete Structures - page 147

Figure 4.13(b) also shows that point C on the Mohr circle, which is 90 ◦ (2 α 1 ) from point

45 ◦ . Such a 45 ◦ A, represents a face normal to the 1-axis and inclined at the fixed angle α 1 =

12 . On the opposite side of
the Mohr circle, 180 ◦ away, point D represents a face normal to the 2-axis and inclined at a
fixed angle

1 and a shear stress

diagonal face is subjected to a tensile stress σ τ

135 ◦ . Such a diagonal face is subjected to a compressive stress

2 and a shear

α 1 = σ

12 . The stress state represented by points C and D is illustrated in Figure 4.14(a) and
serves as the basis of the fixed angle theory .
Figure 4.13(b) further shows that point E on the horizontal axis of the Mohr circle represents
a face normal to the r -axis and inclined at a rotating angle

stress − τ

α r . This inclined face is subjected

σ r (assumed to be zero at cracked sections) and a zero shear stress.
On the opposite side of the Mohr circle, 180 ◦ away, point F represents a face normal to the
d -axis and inclined at a rotation angle 90 ◦ + α r . This inclined face is subjected to a principal
compressive stress

to a principal tensile stress

σ d and a zero shear stress. The stress state represented by points E and F is
illustrated in Figure 4.14(b) and serves as the basis of the rotating angle theory .
The rotating angle theory will be studied in Chapter 5, and the fixed angle theory in
Chapter 6.