Safety format

The checks performed by the program follow the partial factor method (semi-probabilistic limit state method) of EN 1990 and EN 1992-1-1 (EC2). For every section, and for each relevant action combination, the safety verification consists of satisfying the symbolic condition:

\[E_d \le R_d\]

where:

• \(E_d\) is the design value of the effect of the actions (e.g. a design bending moment, shear force or torsional moment) produced by the design actions \(F_d\) acting on the structure;
• \(R_d\) is the design value of the corresponding resistance developed by the materials of the section.

Design values of actions

The design value of an action is obtained from its representative value through the relevant partial factor for actions \(\gamma_F\):

\[F_d = \gamma_F \, F_{rep} \qquad F_{rep} = \psi \, F_k\]

where \(F_k\) is the characteristic value and \(\psi\) the combination factor (equal to \(1.0\) for the leading action). The partial factors \(\gamma_F\) and the combination factors \(\psi\) depend on the limit state and on the combination considered — see Design actions and combinations.

Design values of material strengths

The design strengths are obtained from the characteristic strengths by dividing by the partial factors for materials \(\gamma_M\):

\[f_{cd} = \alpha_{cc}\,\frac{f_{ck}}{\gamma_C} \qquad f_{yd} = \frac{f_{yk}}{\gamma_S}\]

The recommended partial factors for materials (EC2 Table 2.1N, persistent and transient design situations) are \(\gamma_C = 1.5\) for concrete and \(\gamma_S = 1.15\) for reinforcing steel; \(\alpha_{cc}\) accounts for long-term effects on the compressive strength (recommended value \(1.0\), see the National Annex). The constitutive laws derived from these design strengths are described in Assumptions.

Design internal forces

Once the actions and their combinations have been established, the structure (here assumed to be made of linear reinforced-concrete members) is analysed to obtain the corresponding design internal forces \(E_d\). EN 1992-1-1 allows different methods of analysis:

• linear elastic analysis;
• linear elastic analysis with limited redistribution;
• plastic analysis;
• non-linear analysis.

Whatever method is used, second-order effects must be included when they are significant (they may be neglected only when they are lower than about 10 % of the corresponding first-order effects — EC2 §5.8.2).

RC-SEC-EN receives the design internal forces \(E_d\) as input, from an external structural analysis, and performs the section checks; see Forces.