End Anchorage

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.