Rebar bending

Reinforcement bars are being bent either in order to follow the stresses developed in the mem-ber 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 bend of the bar where large forces appear. The smaller the mandrel diameter is, the larger these forces are and con-sequently the concrete may fail thus leading to the disintegration of the cross-section.

Anchorage with bends and hooks

Forming the right mandrel diameter has no additional cost since bending machines have ap-propriate rings for changes in the rolls diameter.

Practically, the minimum bend diameters Øm are:

• Bending Pin Øm=4Ø for Ø≤16 mm

• Bending Pin Øm=7Ø for Ø>16 mm

Minimum bending pin diameter for wired meshes

In wired meshes:

(a) The anchor should be at least 5Ø (Thus for a wired mesh with Ø10 bars, 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 bar is external and in distance ≤3Ø (thus, in the ex-ample 30 mm), where the pin should be 20Ø! (Thus, in the example Øm=200 mm!!!)

Simple hook anchorage

Anchorage with drum

In columns that have a small dimension in the anchorage direction, (see the table below) the bending is implemented with the use of a large diameter drum.

The minimum diameter of the drum is inversely proportional to the strength of the concrete and proportional to the steel strength.

For grade C30/37 concrete and B500 steel, for various bar diameters, the minimum bending drum diameter and the minimum column dimension are displayed in the following table.