Prokon Frame offers a comprehensive suite of advanced structural analysis types tailored for engineers tackling complex projects. These encompass both Static and Dynamic analyses, ensuring accurate modelling and design of structures under various loading conditions.
Advanced Static Analysis Types
- Second-Order Analysis
Second order analysis is an iterative analysis that accounts for the effect of sway. By considering deformation under loading, it ensures a more accurate distribution of internal forces within a structure. This analysis is also necessary for analyzing compression/tension-only members in Frame.
In the second order parameters dialogue, one would need to enter the solution tolerance as the static setting.
- Buckling Analysis
Buckling analysis is used to determine the overall stability of a structure, Buckling Factors for different mode shapes. Buckling analysis goes together with the Second-Order analysis.
In the buckling analysis parameters dialogue, enter the number of mode shapes to be calculated and the solution tolerance.
- Non-Linear Analysis
Non-linear analysis is more accurate and considers the effect of large displacements and material nonlinearity, amongst others. Like second order analysis, this analysis type is also necessary for analyzing compression/tension-only members in Frame.
In the nonlinear analysis parameters dialogue, enter the number of load steps (minimum 2), loads are divided into equal steps and applied to the structure incrementally making it to respond more accurately.
Comparative Analysis Insight
In many cases, results from linear analysis can be used for design purposes. However, structures subjected to lateral loads and those approaching their elastic buckling limits, require second order analysis.
In this example, for a frame subjected to vertical and lateral loads, we need to determine the elastic stability and a suitable section size.
Recorded results:
Observation:
- As the section size decreases, the Buckling Factor (BF) approaches 1.0.
- If the buckling factor is less than 1 (0<BF<1) The structure is unstable, and a larger section size must be used.
- The % Variance is inversely proportional to the Buckling Factor.
- A greater variance indicates that linear analysis is less suitable for the scenario.
- In this example, iteration number 3 (203x203x60) provides the optimum section because the buckling factor is closest to, but not less than 1.0.
Advanced Dynamic Analysis Types
- Modal Analysis
Modal analysis is used to determines natural frequencies and mode shapes. Critical for evaluating seismic and vibration-sensitive structures (e.g., towers, industrial platforms).
The following parameters are typically used for Modal Analysis:
- Number of mode shapes (500max)- Number of mode shapes calculated. Must be less than or equal to the number of unrestrained translational degree of freedom.
- Add axial force effects to stiffness (Y/N)- Compressive forces in the member reduce the effective stiffness of the structure. Select Yes to reduce stiffness.
- Damping Ratio (%) – The average damping ratio depends on the type and condition of the structure.
- Including torsional modelling – This applies to beam elements. If included, the torsional modes of the beam will also be included.
- Solution tolerance (%) – The analysis is deemed to have converged once the total strain energies of two sequential iterations differ by less than the specified tolerance.
- Include own weight in static analysis- If axial forces effects are considered, a static analysis is performed first to determine the axial forces.
- Load cases included as weight – indicate which unfactored load cases must be added as weight.
- Seismic Analysis
Seismic Analysis determines Natural Frequency for different mode shapes, inclusive of seismic effects and Force effects of seismic effects.
Earthquake Analysis Parameters
The following earthquake analysis parameters are typical entered for seismic analysis
- Ground acceleration (g) – Specify the maximum ground acceleration in the X-,Y-, and Z-directions. These values are code dependent.
- ULS Load factor for seismic action – Load Factor applied to moments and forces caused by seismic action.
- Spectrum reduction factor in Y-direction – Enter a reduction factor if the effects of vertical seismic motions are to be considered.
Response Spectrum
Select a response spectrum from the listed design codes. The input parameters will change depending on the selected design code.
Combination Method
Select the combination method. The combination methods have to do with how the program analysis the acceleration in different direction and combine the effects using these methods
- SRSS – Square Root Of the sum of the squares
- CQC – Complete quadratic combinations (is better suited for closely spaced modes of vibration)
- Harmonic Analysis
Harmonic Analysis determines effects of harmonic (cyclic) loading and allows for phase angle inputs.
Dynamic parameters and load cases included as weight are defined in a manner like modal analysis.
The following additional Harmonic loading parameters are typical entered:
- Load cases – Load cases name are automatically displayed, based on load cases that are defined in the input tab.
- Loading Frequency Hz – Enter the cycle per second. A machine’s rotational speed (rpm) must be concerted to loading frequency (Hz).
- Phase Angle°- Enter the phase angle, in degrees, a phrase angle represents the angular difference between two or more loading frequencies at a given point in time. There are three angle scenarios:
- In-phase – A phase angle of 0°(loading frequencies aligned) resulting in a greater effect on the structure.
- Out-of-phase – A phase angle 180°(loading frequencies exactly opposite) resulting in a reduced effect on the structure.
- Intermediate phase – a phase between 0°and 180°(varying loading frequencies) resulting in a mix of greater or reduced effects on the structure.
