Partial safety factor for concrete: the reduction based on assessment of concrete strength in finished structure, η and γC,red4
Eurocode 2 part 1-1: Design of concrete structures A.2.3 (1) - Annex A (informative)
For concrete strength values based on testing in a finished structure or element, cf. EN 13791 - Assessment of concrete compressive strength in structures or in structural elements, EN 206-1 and relevant product standards, the partial factor for concrete γC may be reduced by the conversion factor η.
The value of the partial factor for concrete γC to which this reduction is applied may already be reduced according to § A.2.1 (1), § A.2.1 (2) or § A.2.2 (1), § A.2.2 (2). However, the resulting value of the partial factor should not be taken less than γC,red4.
The recommended value of η is 0,85, of γC,red4 is 1,3.