How can I increase a loading incrementally?

Answer

The "Incrementally Increasing Loading" function of load cases and load combinations can incrementally increase the assigned load level and find an equilibrium for each load increment. The reference level “Load Increment 1.0 = 100% of the defined load” is the defined loading for load cases and a modified set of loads with partial safety factors for the load combinations. The detail settings of the function define the initial load increment k0 , the quantity of load increment Δk, the refinement of the last load increment, the break-off criterion, and the statical initial load situation.
When defining the initial load step k0, the start of the process is specified. This input is independent of the simple input of the load case and load combination and can be greater than or less than 1.0. The program always displays all results on the basis of the load increment 1.0 within the regular calculation and carries out the additional analysis of the possible load increments by activating the “Incrementally Increasing Loading”.

The the incrementally increasing loading is specified by the load increment Δk. With each process loop, the program increases the load to be analyzed by adding the increment to the previously analyzed load increment. The increment is constant until the break criterion is reached.

Due to the constant increment size, it is not possible to determine an exact load factor according to the break criterion. Finally, the program shows the approximate load factor on the basis of the last load increment at which an equilibrium can be found for the model. After the calculation in Table “4.0 Results — Summary”, the load factor is displayed in the relevant load situation. By specifying a refinement of the last load increment, the initial increment Δk is divided by the refinement value after the break criterion is reached and the process is performed from the last functioning load increment until the new break-off again. Due to the smaller increment, the resulting load factor is more accurate.

The break-off criterion for the process is basically the point at which the program can no longer find an equilibrium for the applied load (second-order analysis). In addition, you can specify the break-off by activating a maximum deformation on a particular node.

Since certain force components remain constant in reality, regardless of the action (e.g. self-weight, prestress, etc.), the detail setting provides an option for the assignment of a fixed load component for the incrementally increasing load. The fixed load can either be a load case or a load combination. This load component is independent of the loading to be increased and is simply added to the variable component in the process.

If the intermediate results of the active load increments are of interest in addition to the final load factor, it is possible to use the load case and load combination function "Save the Results of Load Increments" to display the intermediate results. Corresponding options are available in the panel window and in the result tables.

In RSTAB, the activation for saving the intermediate results is coupled with the RSBUCK add-on module and in RFEM, the activation of the incrementally increasing load is coupled with the RF-STABILITY add-on module. In these cases, a license of the corresponding add-on module must be provided in addition to the licensing of the main program.

Keywords

Load increment Incrementally Fix Initial load Prestress Branch

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

Price of First License
3,540.00 USD
RSTAB Main Program
RSTAB 8.xx

Main Program

The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

Price of First License
2,550.00 USD