Unity Checks

Requires: 2D Design Level

Unity Checks

A unity check is simply the ratio of the demand to the design capacity. The unity check allows the user to quickly identify if the element is passing (unity ≤ Unity Success Limit) or failing (unity > Unity Success Limit). The Unity Success Limit can be manually set in the preferences (e.g. setting the value to 1.02 will allow a slight overstress for the design checks before the program indicates a failure has occurred). The unity check can be a stress ratio, a force ratio, a deflection ratio, etc. All of the design load cases are checked for a member and the worst-case (largest value) for the unity check is displayed in the Design View or the Report View. The unity checks for a member vary base on the member type, material type, design specification, etc. Unity checks can also be viewed as a "percent material utilization" factor. Low unity check values (in the range of 0.01 to 0.25 for example) indicate that the elements are over-designed and there is a significant amount of wasted capacity. High unity check values (in the rage of 0.95 to 0.99 for example) indicate that the elements are optimized and the majority of the capacity is utilized.

Some design check produces unity checks with an arbitrary number greater than one. For example when concrete reinforcement detailing checks fail, the unity check value is set to 10.0. Unity check values, errors, and warnings are displayed in the Design View and the Find Tool. Hover over a member to see quick information in the Help pane or double-click a member in the Design View to get a detailed design report.

Checks vs. Design

In VisualAnalysis, there is a distinction between checks and design:

Checks: The model is checked "as is" using the Design Group's parameters. Each member in a Design Group may be a different shape and is checked using its individual shape. Checks are automatically produced when the analysis results are available.

Design: Using the Design the Group or Quick Design All buttons in the Design ribbon to search for a shape that works for all members in the group; all members are checked using the chosen shape. Designing a group causes all the members in the group to take on the same final shape.

Check Level

Each design group has a check-level setting that may be used to improve performance or to identify issues in a model.

To Failure: The design checks stop as soon as a failure is detected. This is the fastest option but produces the least amount of information. If an early limit states fails, subsequent limit states will not be checked. For example, if shear fails, bending check may not be performed. It is possible that a more significant failure would have been identified if the checks had continued.
Each Limit State: Checks each limit state even if a previous limit state failed. This level considers the controlling location and result case for each limit state and is appropriate for the majority of design scenarios.
All: Every point along the member and every result case is checked and reported (no attempt is made to search for extremes during the design checks). This is the slowest option and may lead to large reports.

The All check level is intended to be used only in rare circumstances to investigate a particular limit state at a particular location in the model. The Each Limit State check level produces the same design results as the All check level, but with much better performance since only stores the controlling design check for each limit state. Using the All check level to try and design an entire model or to design a large Design Group can significantly reduce the program’s performance. Explore the differences between the Each Limit State and All check levels in a simple model prior to using the All check level in a large or complex model.