The concrete cover is the distance between the surface of the reinforcement closest the nearest concrete surface (including link and stirrups and surface reinforcement where relevant) and the nearest concrete surface. The nominal cover cnom shall be specified on the design drawings. It is defined a minimum cover, cmin (see §4.4.1.2), plus an allowance in design for tolerance, Δcdev (see §4.4.1.3):
cnom = cmin + Δcdev
The evaluation of the nominal cover is preliminary to the checks of any section once established concrete data, the environmental conditions and the diameter of longitudinal bars and stirrups.
The cover to assign to longitudinal bars in the input windows of this program is the above nominal cover value plus half diameter of bars.
The calculation of the concrete cover to be performed two times: first with reference to the stirrups, the second to that of the longitudinal bars. The concrete cover more restrictive of the two affects the value of the other concrete cover.
In the Example 4.1 in ref./4/ are given:
- Φ20 as diameter of longitudinal bars
- Φ8 as diameter of stirrups
- XC1 as exposure class
- ds=20 mm as max aggregate size (<32 mm)
- 50 years as design working life of structure
- S4 as Structural class
- 10 mm as Δcdev
- Normal quality control is put in place.
For stirrups the calculation leads to: cmin = 15 mm then cnom = cmin + Δcdev = 15+10 = 25 mm
For long. bars the calculation leads to: cmin = 20 mm then cnom = cmin + Δcdev = 20+10 = 35 mm
The concrete cover for the stirrups is "dominant". In this case, the concrete cover for longitudinal bars is increased to: 25+8 = 33 mm
The same result is shown in the below window that you can open from "Run" drop-down menu or directly from the pertinent command (the last one) in the principal Tab bar of the program. Note that the last result is the cover value to assign in the input windows of the present program. Results can also be printed on paper.
The correspondences between the symbols used in this sub-program and those in §4.4.1 EC2 are:
Cmin,dur = cmin,dur minimum cover due to environmental conditions
dCdur,st = Δcdur,st reduction of minimum cover for use of stainless steel
dCdur,add= Δcdur,add reduction of minimum cover for use of additional protection
dCdur,g = Δcdur,γ additive safety element