# Incrseased characteristic strength of confined lightweight aggregate concrete: the coefficient `k`

## Eurocode 2 part 1-1: Design of concrete structures 11.3.7 (1)

If more precise data are not available, the stress-strain relation shown in Figure 3.6 may be used, with increased characteristic strength according to:

f = _{lck,c}f (1,0 + _{lck}k σ / _{2}f) _{lk} | (11.3.24) |

where:

`f`_{lck,c}- the increased characteristic strength
`f`_{lck}- the characteristic strength of lightweight concrete, see Table 11.3.1
`σ`_{2}- (=
`σ`) the effective lateral compressive stress at the ULS due to confinement_{3} `k`- the coefficient depending on National Annex.

## Recommendation

The recommended value of `k` is:

- 1,1 for lightweight aggregate concrete with sand as the fine aggregate
- 1,0 for lightweight (both fine and coarse aggregate) concrete.