Modeling for Design
Requires: Design Level
- Choosing a Structure Type
- Member Elements vs Combined Members
- Pick Good Preliminary Sizes: Also size 'constraints'
- Design Tapered Members
- Plate Design Limitations
Choosing A Structure Type
IES strongly recommends using Space Frame structural models for design purposes.
When running the design software, the stresses, forces, or deflections that are checked come directly from VisualAnalysis. (There is no way to just "design" something, without first building a model, applying loads, and analyzing.) The design will automatically check all of the forces or 'behaviors' present in the model.
This means if you wish to check bending in members you need to create your model as a frame rather than a truss. Plane models are simply ancient tools to minimize computer hardware resources or for academic simplicity..
Members Elements vs Combined Members
As you create models in VisualAnalysis, you should be aware of the design ramifications. In most cases, you will model a beam as a single member element. With girders, columns, and other types of frame elements, you will need to use multiple member elements in order to provide connection nodes. This introduces a complexity in design.
The design software looks primarily at member elements. The software is not smart enough to see the big picture, so when beams, columns, or other frame members are split, you may need to adjust the design options for span length, bracing, deflection limits, and other parameters that may assume an element is the entire member.
VisualAnalysis has a feature that can be used to simplify your work and make the design software see the whole member at one time. This feature does not make everything automatic though! The unbraced length of a combined member defaults to the total length, even if you have other members or plates framing into it, because the software currently is not 'smart' enough to distinguish which connections may or may not be actual braces--there are simply too many possibilities. You will need to explicitly specify where lateral bracing exists along a member.
Pick Good Preliminary Sizes
Design is usually an iterative process. As you make design changes you change the stiffness and therefore the moment distribution in your model, causing the design checks to become invalid. By selecting reasonable preliminary sizes before you run the design software you can save time.
The design software allows you to limit the depth of beams, or the size of columns using Size Constraints. This can have two benefits: The software will not 'design' members that fall outside of these boundaries (or will warn you if you model members outside these boundaries). This can also dramatically reduce the "design' performance when searching for a size that works, because many shapes in the database can be skipped! Note that setting beam width constraint is only available in the 'Advanced' level of VisualAnalysis.
Design Tapered Members?
Although tapered members are supported in VisualAnalysis for analysis, there is no 'design' support for them. If you attempt to design a tapered member, you will get unpredictable results. At best, the member will be sized as a prismatic member; at worst, you will get garbage design results. For steel and wood members, you will now see an error message in the Design View "tips" to indicate this condition.
Plate Design Limitations
The only support for plate element design is in the concrete wall/slab component.
If you are looking for design help with circular structures, or in materials other than concrete, you will not find it in VisualAnalysis—yet. For these types of problems, you will be able to get analysis results (stresses, deflections) and then you may perform your design manually or with non-IES tools (such as a spreadsheet) using this information.