IES VisualAnalysis User's Guide
Cold Formed Steel Design
VisualAnalysis performs the design of light-gauge cold-formed steel members (beams, columns, braces, wall components, headers, etc.) according to the following design specifications:
Cold-formed members in VisualAnalysis are designed with a built-in version of CFS by RSG Software, Inc. Listed below is the version of CFS that is used within VisualAnalysis.
Cold-formed members are designed for flexure (strong axis and weak axis), shear, tension, and compression to resist the varying demands along the length of the member. When necessary, the interaction of these loads are accounted for in the design checks per the selected design specification. The maximum unity value (demand to capacity ratio) for the member is shown in both the Design View and in the Report View, allowing the user to quickly identify if the member is passing (unity ≤ Unity Success Limit) or failing (unity > Unity Success Limit). In addition to checking the capacity for cold-formed members, VisualAnalysis can check the deflection limits for the members based on the deflection limits set by the user and the Deflection Check load combinations. The shapes for cold-formed members can be manually adjusted in the tab until a satisfactory design is reached or VisualAnalysis can automatically optimize the shape for the Design Group using the Design the Group button in the Design Ribbon.
VisualAnalysis can design custom cold-formed shapes that are not originally included in the IES Shape Database. The shapes must defined in a .scl or .cfsl file, which is a shape library file produced by the CFS program from RSG Software. The .scl or .cfsl file can be imported directly into the database using the . These custom shape library files need to be stored in specific locations with other IES data in order for VisualAnalysis to find use the files.
VisualAnalysis designs cold-formed members for flexure (strong axis and weak axis), shear, and axial load (tensions and compression) according to the provisions outlined in the chosen design specification. All member forces are with respect to the member's principle axes which may not align with the geometric axes (as is the case for asymmetric shapes like single angles). When the model is sufficiently supported, loaded, and has the appropriate load combinations, the cold-formed design checks are performed automatically. When necessary, members are checked for interaction of the combined loads according to the chosen design specification.
Several parameters must be defined to design cold-formed members in VisualAnalysis. The design parameters are set in the tab when the Design View is selected. After creating a Design Group, choose one of the members that belongs to the group in the Design View to set up the Design Group's Parameters. Since the design parameters apply to all members in the Design Group, it is often best to choose the most conservative condition that applies to any member in the group.
| Cold-Formed |
Specification - The Design Specification used to design the members in the Design Group. Strength Increase? - Allows higher stress values due to strain hardening effects in cold-worked steel. Overstrength? - Causes the Design Group to be designed using overstrength load combinations. Live Load Reduction - If specified, design checks will only consider result cases with the matching live load reduction. Combinations with live load reduction can be created in the . Disable Checks? - Causes selected Design Group to be omitted from design checks. This feature can be used to speed up design checks and focus on targeted areas of larger models. Check Level - Determines the level of detail reported from design checks. Options are: To Failure (Fastest), Each Limit State, and All (Slowest, but provides the most information). |
| Bracing |
Lateral Top (+y) - Lateral bracing at the top side of the member (+y). Choose a bracing arrangement. Lateral Bottom (-y) - Lateral bracing at the bottom side of the member (-y). Choose a bracing arrangement. Strong (z) - Brace against strong-axis buckling for columns. |
| Torsional Bracing |
Lateral Top (+y) - Do the specified braces on the top side of the member (+y) provide torsional restraint? This is used to determine the Torsional Unbraced Length. Lateral Bottom (-y) - Do the specified braces on the bottom side of the member (-y) provide torsional restraint? This is used to determine the Torsional Unbraced Length. Strong (z) - Do the specified braces for strong-axis buckling provide torsional restraint? This is used to determine the Torsional Unbraced Length. |
| Deflections |
Strong (dy) - Specify the type of limit for beam deflections in the y-direction. Use Total to include the displacements of the nodes at each end of the element. Weak (dz) - Specify the type of limit for beam deflections in the z-direction. Use Total to include the displacements of the nodes at each end of the element. |
| Axial |
Manual Kz/Ky - Allows the user to manually override the effective length factors for the strong/weak axis. Kz/Ky Sidesway? - Choose if the member is apart of a sway frame in the specified direction. |
| Size Constraints |
Limit Depth/Width? - Allows the design search to 'Fail' if the shape is outside the Min/Max range. |
| Overrides |
Override Cb? - Disable the automatic determination of Cb and allows a custom value to be used.
Override Cm? - Disable the automatic determination of Cm and allows a custom value to be used. |
To achieve an adequate design, the section for the members in a Design Group can be manually chosen from the Database until all the design checks pass. Alternatively, the built in optimization feature in VisualAnalysis can be used to find an adequate shape for the members in a Design Group. The optimization feature can be used to search for adequate Database Shapes until an adequate shape is found.
1. Create the Members
In the Model View draw or create the cold-formed members.
2. Support and Load the Members
Define support conditions for the model and apply the service level loads to the members. Set the load combinations in the Load Case Manager.
3. Specify the Parameters
Select a preliminary cold-formed Database Shape or Standard Parametric Shape and set the material properties.
4. Analysis and Preliminary Design
VisualAnalysis will automatically analyze the model and perform the appropriate design checks. Simply click on the Results View tab to view the analysis results for the model or the Design View tab to see the design results.
5. Create/Modify Design Groups
VisualAnalysis will automatically create groups for members based on material, orientation, length, and/or cross-section. Alternatively, Design Groups can be created or modified manually as explained in the Groups Category.
6. Define the Parameters
For each Design Group, set the cold-formed parameters (design specification, strength increase, overstrength, etc.) in the in the tab in the Design View. Also, adjust the bracing, deflections, axial, size constraints, and overrides for the design group as needed.
8. Design the Group
After selecting a cold-formed design group, click the Design the Group button in the Design ribbon. In the Design Selection dialog box, choose the Database search type and set the number of shapes to be returned from the optimization. Choose which database is to be searched and the category of shapes that are to be searched within the database. Also, set the size constraints if needed. Parametric shapes are not supported for cold-formed design. Once the search parameters are set, click the Optimize Now button to search for various sections and display the unit value for each shape. If a warning stating "demands could not be satisfied" appears, then all the shapes within the search parameters have a unity value larger than the Unity Success Limit defined in the Preferences. Enabling the Return all Shapes feature will provide information on every considered section which may be useful for determining why a section failed or was not optimal.
9. Select a Section
Once the optimization is complete, select a section from the list and click the Accept Design button. Now the unity value for all members in the design group are displayed using the selected section. The tilde symbol (~) in front of the unity value indicates that the unity checks must be validated with another analysis since the member stiffness and resulting load distribution may have changed.
10. Synchronize Design Changes
Click the Synchronize Design button in the Design ribbon to automatically update the model with the new cross-section, re-analysis the model with the new member stiffness, and rerun the design checks with the updated analysis results.
11. Verify Unity Ratios
The final step in the design process is to verify that Unity Ratios in the Design View are less than the Unity Success Limit defined in the Preferences. If member sizes were drastically changed during the design process, final unity ratios can differ from predicted unity ratios because the analysis results may vary significantly.
The cold-formed design reports in VisualAnalysis are highly customizable. To control what is included in a report, simply click on a table in the report and adjust the settings in the tab. The Extreme Rows feature is particularly useful to produce concise reports of only the controlling cases or to produce detailed reports that display every design check that is made. When this feature is set to Show All, the reports may become excessively large which can be controlled by adjusting the Conciseness feature. The reports for cold-formed design include both a summary of the parameters input for the Design Group and tables that included the various design checks. These tables have the following columns:
| Column Name | Description |
|---|---|
| Member | The member's name. |
| Section | The member's cross-section (e.g. 10x2.0C12). |
| Offset |
This is the distance from the 'start' end of the member. The number and locations of offsets are as defined in the performance settings in VisualAnalysis. |
|
Result Case |
The result case that is used for the design check. |
| Demand/Capacity | These columns varies depending on the type of design check. In most cases these values are used directly in the unity check, but there are some special cases where the unity checks also include intermediate values or other values that not reported. |
| Code Reference | The controlling equations or provisions from the chosen design specification. |
| Unity Check | The unity check value for this particular member, load case, and offset. Unity checks are calculated as the absolute value of an actual force divided by an allowable strength [ASD] or as the ultimate force (factored) divided by the design strength (factored) [LRFD]. |
| Details | Intermediate values and other information which can be helpful for validating results. |