Recalc > Dynamics/Iterations
Dynamics
Definition of the relevant parameters for dynamic calculations. Reasonable default values are defined for all parameters, except damping parameters which must essentially be defined by the user (otherwise damping is zero).
Setting | Description |
---|---|
g | Gravity constant (acceleration of gravity) in internal database units (independent from the selected unit system always in m/s2). The constant is used for computing the actual mass values from defined equivalent forces. |
dt | Time step length for the dynamic time history
calculation (schedule action Tint).
Tip: For
required time step length, the Newmark method is a numerically unconditionally
stable integrations method. However, in order to avoid numerical damping of
vibrations with higher frequency, the highest considered vibration period shall
be divided into at least 10 time steps. I.e. the default value of 0.01 sec
allows for sufficiently accurate consideration of vibration frequencies of up
to 10 Hz (period 0.1 sec).
|
c1 | Integration constant 'Delta' for NEWMARK time integration (see relevant textbooks) |
c2 | Constant 'Alpha' for NEWMARK time integration (see relevant textbooks) |
Alfa | Mass coefficient for calculating the damping matrix [C] = Alfa*[M] + Beta*[K] |
Beta | Stiffness coefficient for calculating the damping
matrix [C] = Alfa*[M] + Beta*[K]
Default: Beta = 0 = no stiffness dependent damping Note: The effective
damping percentage of Rayleigh damping is dependent on the frequency. Design
codes and guidelines usually define damping as damping ratio in %of the
critical damping and Rayleigh coefficients are usually not known. Therefore,
they commonly recalculated from damping ratios given for 2 relevant
frequencies. RmBridge offers a respective subfunction when pressing the arrow
button on the right. (see
Subfunction > Rayleigh coefficients )
|
Xsi | Global damping ratio (actual to critical) for the modal superposition. The value is for instance used for calculating the correlation coefficients of the CQC superposition, if no other value is defined for the respective earthquake event (absolute value, not in percent!). |
Tol(mi/ki) | Mass tolerance for calculation of natural modes (schedule action Eigen). Small, irrelevant masses are eliminated in order to make the subspace iteration stable and reliable. For each DOF the ratio of the diagonal terms of the mass and stiffness matrices is checked against the defined tolerance value (mii/kii .lt. Tol). The respective DOF will be eliminated from the subspace if the condition is true. |
Iteration control
Definition of the convergence parameters for non-linear iterative structural deformation analysis. The default values ensure in general a fast and sure convergence to an extremely accurate solution. Variation of the values is recommended only in special cases where convergence problems arise.
Cross Section Integration
Definition of governing parameters for calculation functions on cross-section level. The default values are set such that a stable and quick solution is provided in general. In critical situations the values can be adapted to achieve an improvement of the calculation procedure to get the required solution.
Setting | Description |
---|---|
Iteration | Max. number of iterations determination of position and angles of the neutral axes. Used for calculating cross-section values in in the ultimate capacity check (UltChk). |
Recurs.level | Maximum number of recursions. Only used in reinforcement design (UltChk/Rein). The increasing factor is further reduced if no equilibrium is found. |
Increasing factor | Used in the ultmate capacity check (UltChk). The program first calculates the strain plane for a partial load and increases the load in steps. The position of the neutral axis of the previous step is the iteration start for the next step. |
Relax.factor | Only used in reinforcement design (UltChk/Rein). Theoretically required increments of reinforcement area are in the iteration process reduced by this factor. |
Tolerance | Calculation toleranz related to the norm N(F) of force vector F [abs(N(Fi)-N(F))/N(F)] |
Check-button: Try with best reinforcement | Optimization function - Additional variation of distribution of the total reinforcement to different reinforcement groups to get minimum total amount |
Check-button: Try to reduce small values | The program checks, whether omitting reinforcement groups with small area is possible by a reasonable increase of the amount of other groups. |
Eigen Solver | There are two options available: Skyline and Parallel Sparse (INTEL). The new Parallel Sparse solver improves the calculation speed for dynamic analysis in bigger models. |
Modal Analysis | There are two options available: Eigen and Ritz. The load dependent Ritz vector analysis provides faster extraction of more relevant modes for response spectra modal superposition analysis. |