# Anchorage of longitudinal reinforcement: the ultimate bond stress `f`_{bd}

_{bd}

## Eurocode 2 part 1-1: Design of concrete structures 8.4.2 (2)

The design value of the ultimate bond stress for ribbed bars may be calculated as:

f = 2,25 _{bd}η _{1}η _{2}f _{ctd} | (8.2) |

where:

`f`_{ctd}- is the design value of concrete tensile strength
`f`=_{ctd}`α`_{ct}`f`/_{ctk,0,05}`γ`_{C}(3.16) with

`f`_{ctk,0,05}- the characteristic (5% fractile) axial tensile strength of concrete, see Table 3.1
`γ`_{C}- the partial safety factor for concrete, see § 2.4.2.4 (1), § 2.4.2.4 (2), and § 2.4.2.4 (3)
`α`_{ct}- a Nationally Determined Parameter, see § 3.1.6 (2)P.

`η`_{1}- is related to the quality of the bond condition and the position of the bar during concreting (cf. Figure 8.2):

`η`= 1,0 for "good" conditions,_{1}

`η`= 0,7 for other cases._{1} `η`_{2}- is related to the bar diameter:

`η`= 1,0 for_{2}`Φ`≤ 32 mm,

`η`= (132 -_{2}`Φ`)/100 for`Φ`> 32 mm.

This application calculates
the ultimate bond stress `f _{bd}`
from your inputs.
Intermediate results will also be given.