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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: For the determination of the reinforcement including serviceability limit state design, the internal forces are determined linearly; the cross-section analysis is performed subsequently. However, this procedure considers the cracking typical for reinforced concrete with the corresponding nonlinear material rules of reinforced concrete only on the cross-section level.
By including the nonlinear behavior of reinforced concrete in the determination of internal forces, we obtain realistic states of stresses and, therefore, distributions of internal forces that, in statically indeterminate systems, differ significantly from the linearly determined internal forces because of stiffness redistributions. For the serviceability limit state design, this means that we must take the nonlinear material behavior of reinforced concrete into account to obtain a realistic calculation of deformations, stresses, and crack widths.
If the cracking 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 the realistic calculation of the deformations, crack widths, and stresses of reinforced concrete surfaces by considering the nonlinear material behavior in the determination of internal forces.