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- Recorded
Dipl.-Ing. (FH) Adrian Langhammer
Product Engineering & Customer Support
Mr. Langhammer is responsible for development in the area of reinforced concrete structures, and provides technical support to our customers.
Dipl.-Ing. (FH) Adrian Langhammer
Product Engineering & Customer Support
Mr. Langhammer is responsible for development in the area of reinforced concrete structures, and provides technical support to our customers.
The nonlinear calculation is activated by selecting the design method of the serviceability limit state. You can individually select the analyses to be performed as well as the stress-strain diagrams for concrete and reinforcing steel. The iteration process can be influenced by these control parameters: convergence accuracy, maximum number of iterations, arrangement of layers over cross-section depth, and damping factor.
You can set the limit values in the serviceability limit state individually for each surface or surface group. Allowable limit values are defined by the maximum deformation, the maximum stresses, or the maximum crack widths. The definition of the maximum deformation requires additional specification as to whether the non-deformed or the deformed system should be used for the design.
The nonlinear calculation can be applied to the ultimate and the serviceability limit state designs. In addition, you can specify the concrete tensile strength or the tension stiffening between the cracks. The iteration process can be influenced by these control parameters: convergence accuracy, maximum number of iterations, and damping factor.
The deformation analysis according to the approximation method defined in standards (for example, deformation analysis according to EN 1992‑1‑1, 7.4.3) applies to the calculation of "effective stiffnesses" in the finite elements in accordance with the existing limit state of the concrete with or without cracks. These stiffnesses are used to determine the surface deformation by repeated FEM calculation.
The effective stiffness calculation of finite elements takes into account a reinforced concrete cross-section. Based on the internal forces determined for the serviceability limit state in RFEM, the program classifies the reinforced concrete cross-section as 'cracked' or 'uncracked'. If the tension stiffening at a section should be considered as well, a distribution coefficient (according to EN 1992-1-1, Eq. 7.19, for example) is used. The material behavior for the concrete is assumed to be linear-elastic in the compression and tension zone until the concrete tensile strength is reached. This is reached exactly in the serviceability limit state.
When determining the effective stiffnesses, creep and shrinkage are taken into account at the "cross-section level". The influence of shrinkage and creep in statically indeterminate systems is not taken into account in this approximation method (for example, tensile forces from shrinkage strain in systems restrained on all sides are not determined and must be considered separately). In summary, RF-CONCRETE Deflect calculates deformations in two steps:
For a response spectrum analysis of building models, you can display the sensitivity coefficients for the horizontal directions by story.
These key figures allow you to interpret the sensitivity to stability effects.
The modal relevance factor (MRF) can help you to assess to which extent specific elements participate in a specific mode shape. The calculation is based on the relative elastic deformation energy of each individual member.
The MRF can be used to distinguish between local and global mode shapes. If multiple individual members show significant MRF (for example, > 20%), the instability of the entire structure or a substructure is very likely. On the other hand, if the sum of all MRFs for an eigenmode is around 100%, a local stability phenomenon (for example, buckling of a single bar) can be expected.
Furthermore, the MRF can be used to determine critical loads and equivalent buckling lengths of certain members (for example, for stability design). Mode shapes for which a specific member has small MRF values (for example, < 20%) can be neglected in this context.
The MRF is displayed by mode shape in the result table under Stability Analysis → Results by Members → Effective Lengths and Critical Loads.