Cost-based design and renewal strategy for long-life structures

T = (h/ϕ)2 (4) This corresponds to Eq. (3) with m = 2; the layer thickness h characterises the protective ability of the structure against corrosion of the rebars (h2 corresponds to B in Eq. 3), and ϕ characterises the intensity of chemical attack. The rate of deterioration in actual structure can vary due to varying temperature, air humidity and other factors, and a more general value of exponent m instead of 2 may sometimes be more appropriate, similarly to Eq. (3).