An anchorage is generally provided in the form of
1. A semicircular
hook
2. A 90 –
degree bend
3. A 45 –
degree bend
SEMI-CIRCULAR HOOK
RIGHT ANGLE BEND
45-DEGREE BEND
The hook or bend allowance
depends on the grade of steel governed by the value of the constant K. The
value of K is taken as 2 for ordinary mild steel (140 N/mm2) for
above three cases. For the case of medium tensile steel (190 N/mm2)
K is taken as 3. In the case of cold twisted bars K is taken as 4. In the case
of bars above 25 mm diameter it is desirable to increase the value of K to 3, 4
and 6 respectively. For a plain mild steel bar, the bond – resistance value of
an anchorage is assumed as 16d for a semicircular hook, 8d for a 90 – degree bend
and 12d for a 45 – degree bend. The length of the straight portion of the bar
beyond the end of the curve is 4d. ‘d’ is the diameter of the bar in mm. A
semicircular hook and A 90 – degree bend are fully dimensioned, with respect to
a factor K. The best form is a semi – circular hook as this has greatest bond
resistance value. In the case of deformed bars of the those which are not
circular in cross-section, the diameter can be assumed as their nominal size.
In case of deformed bars, the
value of bond stress for various grades of concrete is greater than 40% than
the plain bars. Hence deformed bars may be used without hook and anchorage provide
development length is satisfied. In practical field there may be shortage of
space to provided the requisite
development length at the ends and simultaneously hard labour requires to form
a semicircular hook. In this case a 90 – degree or 45 – degree bend may be
found suitable provided the bond value can be satisfied.
