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The serviceability limit state design (SLS) is generally divided into the three following groups:
- Stress limitation (EN 1992-1-1, clause 7.2)
- Crack control (EN 1992-1-1, clause 7.3)
- Deflection control (EN 1992-1-1, clause 7.4)
The design of reinforced concrete structures is generally based on linear structural analyses: To determine the reinforcement including the serviceability limit state design, the internal forces are determined linearly; afterwards the cross-section analysis is performed. However, this procedure considers the cracking typical for reinforced concrete with the corresponding nonlinear material rules of reinforced concrete only at the cross-section level.
By including the nonlinear behavior of reinforced concrete in the determination of internal forces, you get realistic states of stresses and therefore distributions of internal forces that, in statically indeterminate systems, differ significantly from the linearly determined internal forces due to stiffness redistributions. For the serviceability limit state design, this means that the nonlinear material behavior of the reinforced concrete must be taken into account to realistically calculate deformations, stresses, and crack widths.
If the crack formation is not taken into account in the deformation calculation, the occurring deformations are underestimated. By considering creeping and shrinkage, the deformation may be 3 to 8 times larger, depending on the stress and boundary conditions. The add-on module RF-CONCRETE NL allows for a realistic calculation of the deformations, crack widths, and stresses of reinforced concrete surfaces by considering the nonlinear material behavior when determining internal forces.