Due to the random nature of the quantities affecting the structural behaviour (e.g. actions, geometry, restraints, and strength of materials), the assessment of structural performance requires a probabilistic rather than a deterministic approach and an assessment of the reliability of design calculations, particularly under in-service conditions[1]. Indeed, probability-based limit-state design is accepted in codes for reinforced concrete design throughout the world. Structural safety and serviceability are two broad classifications of the performance requirements for structures. Structural safety is the ability to estimate the overall stability, ductility and ultimate bearing resistance corresponding to a set of assumed design actions with appropriate levels of reliability. Using probabilistic methods in conjunction with the finite element method (FEM), many reliability analyses have been proposed to deal with the ultimate limit state of RC structures [2–۹]. Compared to structural safety, the serviceability problem, relating to deflection, crack width, vibration, and degree of spalling [1], are much more difficult to define. Considerations of serviceability are based on subjective issues, such as human perception and tolerances, the importance of the structure and the consequences of serviceability problems and are more client-oriented [10]. Moreover, in modern times, the introduction of high-strength materials has led to more slender structural elements and has made serviceability issues of increasing importance. Under in-service conditions, reinforced concrete structural members are almost always cracked, as the tensile strength of the concrete is low. Cracking affects the stiffness of a RC member and hence its deflection. Therefore, it is important to assess RC-members after cracking in any serviceability analysis.