Reinforcement bars are being bent either in order to follow the stresses developed in the member or to get properly anchored.
The minimum diameter Øm (mandrel diameter) to which a bar is bent shall be such to avoid bending cracks to the bar and ensure the integrity of concrete inside the bent of the bar where large forces appear. The smaller the mandrel diameter is, the larger these forces are and consequently, the concrete may fail thus leading to the disintegration of the cross-section.
Practically, the minimum bend diameters are:
Bending Pin Øm=4Ø για Ø≤16 mm Bending Pin Øm=7Ø για Ø>16 mm
In wired meshes:
(a) The anchor should be at least 5Ø (Thus for a wired mesh with Ø10 wires, at least 50 mm)
(b) The bending pin should be at least 5Ø (Thus, in the example is Øm=50 mm) for all cases except when the transverse reinforcement wire is external and in distance ≤3Ø (thus, in example 30 mm), where the pin should be 20Ø! (Thus, in the example Øm=200 mm!!!)