# Performing a calculation

Calculations are subdivided into the analysis part and the design part.

In the case of both analysis and design, calculations can be made at any point after configuring geometry and applying loads. In point of fact, it is possible to ask PRE-Stress to calculate before that point, but the result will not be very useful. In order to calculate, select the Calculate menu, which works as regular interface button. When PRE-Stress is in the analysis mode, this will bring up a dialog. When in design mode, clicking Calculate will cause PRE-Stress to perform the design with no dialog opening.

# Analysis

When in the Analysis context, left-clicking Calculate brings up the calculation dialog.

You may opt to calculate all elements by checking the All Prestressed Elements box. If it is unchecked, a project tree will fold out on the right-hand side of the dialog, allowing you to choose the element(s) to which you want to apply the calculation.

After configuring the dialog settings, simply press Calculate and the analysis will commence. The progress will be shown graphically. When the analysis is complete, the program will enter Results mode.

We discuss the results of an analysis in its own chapter.

# Design

In order to perform a design calculation, we must first have concluded a successful analysis.

The Input menu holds basic settings for the design. From here, the Deflection Check dialog allows the user to select whether to consider deflection during calculation.

Viewing the results of a design is covered here.

# Performance

The speed of a PRE-Stress calculation depends on the complexity of the calculation being performed. By default, PRE-Stress is set to provide a good balance between accuracy and speed, but these settings can be altered if desired.

To configure the amount and position of calculation sections, select the beam element in the project tree handler, then select the Calculation sections tab. This tab displays the calculation sections that the program uses for the calculation.

PRE-Stress performs its calculations by using the Finite Element Method in which the beam is subdivided. Upon calculation, an element is split into smaller calculation segments, and the calculation is performed on each segment in succession. Reinforcements and loads are also split. Should one of these segments be cracked, the program alters the stiffness of the segment before repeating the calculation by iterations, ending when a stable stiffness distribution has been reached.

The list of sections are default values given by the measurements of the beam, but you can easily remove sections (trading accuracy for calculation speed) as well as add them (improving accuracy at the risk of slower calculation). Numbers given in blue denote sections that can't be removed or altered.

Note that while the calculation sections may appear similar to the sections shown during presentation of results, they are not identical. For one, an increased number of calculation sections will not show a corresponding increase in number of sections in the result tables.

Not all tradeoffs are gainful. For instance, example four. mentions the option to increase the number of sides of the polygon representing the shape of the hole. By raising the value, the polygon progressively approaches a circular shape, but each successive increase will provide a smaller increase in precision while linearly increasing calculation time.