Optimization of Buildings with Scia Engineer

Mark Flamer, P.E., M.I. Flamer & Associates

Astrid Bastiaens, Product Engineer, Nemetschek Scia

One of the benefits of Structural Analysis and Design software is the ability to optimize the members in a structure.

Optimizing single members is easy. The challenge is that structures are rarely made up of one member. Structures typically include various profiles and materials. After an engineer optimizes one member, the stiffness matrix of the entire structure changes, which forces another optimization run followed by a check. So optimization is really an iterative process, not a single check.

Scia Engineer and its Auto Design feature makes this iterative optimization process easy.

Here are a few ways that Scia Engineer can help optimize a structure:

• Minimizing the weight of a steel structure for a previously defined type of frame
• Searching the optimal definition of bridge spans
• Finding a maximum carrying load for a crane under various geometrical positions
• Searching the optimal relation between stiffness of beams and columns
• Finding the optimal thickness of concrete slabs
• Determining the optimal dimensions of concrete beams
• Optimization of the position of foundation piles
• Sensitivity analysis of the subsoil parameters

… and so on.

With this in mind, let’s take a closer look at Scia’s optimization capabilities. In this article, we will look at two levels of optimization: Parametric design and Auto design. In a subsequent article, we will look at some additional optimization capabilities of Scia including Esa XML solver, Input/Output interface, and Batch optimizer.

Parametric Design

A Parameter is simply an object property. In Scia Engineer, parameters can be dimensions, cross-sections (including built-up sections), materials, loads, etc. With parameters, users can define relationships between members and use those parameters to create and drive changes in more complex structural systems or even entire buildings.

The picture below shows the list of parameters in Scia Engineer. As you can see, almost every property of an object can be defined as a parameter: 

Take, for example, a steel hall. If we create a parameter that automatically changes the heights of all the eaves, the only thing we need to do is define the type of parameter and a default value for the parameter. In the case of the eave height, the parameter is the Z-coordinate of the nodes which represent the height of the eave, and the height value.

In the next step, the value of the parameter can be adapted in what is called the Template dialog. This dialog provides an easy interface for sharing parametric objects.

You can create relationships between objects to drive the change of more complex structural systems or even entire buildings. 

For example, you can use a simple formula in which the span S1 is related to the height of the top H17. Therefore, now a change to the span will automatically change the height.

Thus, you can optimize the modeling of any structural system or entire buildings with Scia Engineer by simply defining and entering a few parameters.

Auto Design  

In Scia Engineer, optimization goes beyond steel-cross sections to include:

• Reinforcement for concrete beams
• Standard steel code check
• Fire resistance steel check
• Timber code check
• Bolted diagonal check
• Pad foundations

Let’s first look at Auto Design for concrete. During the automatic reinforcement design (AMRD), several checks are performed.

The output of this Auto Design is a scheme of reinforcement which satisfies the performed checks and several detailing provisions.

Turning to Auto Design for steel, here are some aspects to note:

• Auto Design is a tool that searches for the optimal member cross section within a given criteria.
• It can be used on one member or a group of members.
• It works for standard profiles as well as built-up sections.

Let’s look at a new examples of Auto Design.

Example 1: Auto Design of a Single Member

This simple example shows the basic principles of the Auto Design functionality.  A simply supported beam is loaded with a concentrated load of 200kN at the middle. The section selected is HP8x36.

After analyzing the structure and performing a code check, we find that the section has a maximum unity check value of 2.37.

Since the unity check fails (result > 1), it’s obvious that this member is not optimal. The Autodesign dialog shows a display of the selected cross-section, which in this case is the HP profile.

Several optimization options are available for the user:

• Input of the Maximal check
• Direction: Up & down or only Up
• Choice limited to list of profiles
• Sort by properties of the cross-section (H, A, Iy)

If you now click the Search for optimal button, Scia Engineer searches for a more optimal profile sorted by the dimension H.  A new profile HP12 x 63 is proposed.

If we agree with the proposed profile, Scia Engineer will re-run the calculation and steel code check.  Here, we can see that the unity check is satisfied (unity check = 0,92 < 1)

The Auto Design also works for built up (welded) sections, as shown below.

The Autodesign dialog shows a list of parameters that can be used for Auto Design. One of the options is Advanced Autodesign.

Choosing this option opens up the dialog shown below:

This means that the user can choose which dimensions need to be taken into account in the optimization routine. Moreover, relations between the dimensions can be defined.

Example 2: Auto Design of a Structure with Multiple Section Types

In this example, we will Auto Design a structure with three types of sections. The Auto Design process will be set considering each section separately.

First, a code check is carried out for the section of type UC152/152/23. We notice that a number of members are failing. The maximum utilization factor is 1.68 here. So, Auto Design is performed for this type of cross-section.

Then, the same is repeated for the section of type RSJ75/75/13. Also here, we notice that a number of members do not satisfy the code check. So, the Auto Design for this cross-section type is carried out.

Using this iterative process, we can easily re-analyze the modified cross-sections until the optimal design is achieved.

Example 3: Overall Auto Design of a Steel Structure

Scia Engineer’s overall Auto Design function offers:

• The ability to Auto Design entire structures at one time
• The ability to run more than one type of Auto Design at one time (steel, timber, concrete, aluminum, etc.)
• The ability to use an iterative optimization

To illustrate the overall Auto Design capabilities in Scia Engineer, we will use the same structure as in Example 2. The overall Autodesign can be found in the Main tree of Scia Engineer, under Calculation, mesh.

In the Overall Auto Design dialogue, you can see that different optimization types are available:

In this case, we will optimize the “cross-section steel check.” Once selected, a list of the cross sections used in the structure appears. Next, we will select which sections we want to include in the Auto Design. In this case, all cross-sections are selected.

Once the cross-sections are selected, they are added to the Overall Autodesign window.

By clicking on any section name, the Auto Design parameters and section shape appear.

In this example, we’ll sort Cross-section by Area (A), and Maximal check values of 0.9.

Next, the calculation is performed. This dialog closes, and the Overall Autodesign database window appears. Here, all the Auto Design parameter groups appear. In this example, only Cross-sections steel check was defined.

There are a group of buttons on the lower right corner edge of the window:

• Optimization Routine: performs an iterative Auto Design on all items in the database.
• Autodesign all: performs an Auto Design on all items in the database.
• Calculate: performs a calculation to update the analysis results.

The profiles in the database may be of different types. So, if we select the Optim. Routine button, the Automatic Autodesign routine window opens:

Here we can set a number of iterations for the optimization, or we can let Scia Engineer iterate until an optimum solution is reached.  In this example, we will limit the number of iterations to 3. 

Conclusion

Within Scia Engineer, there are different possibilities that guide you through the optimization process. The most basic option is the use of parameters. Again, almost each entity in Scia Engineer can be covered by a parameter. Once this project is defined and analyzed, the user can always save the project as a template for reuse on a new project.

A more general and very useful tool is the Auto Design tool. This allows the user to optimize different parts of the structure. With the sensitivity optimization, one has the option to define relations between the dimensions and to define the iteration steps. Last but not least, the defined optimization groups can be combined in the Overall Auto Design in order to optimize multiple types of members or entire structures.

In the next article, we will look at the more advanced optimization capabilities of Scia Engineer.

For more information on Scia Engineer, please visit www.scia-online.com.

About the Authors

Mark Flamer, P.E, of M.I. Flamer & Associates, is a registered engineer in California and an early adopter of 3D and BIM technologies. He has successfully completed over 15 BIM projects. Mark consults with leading software developers on BIM technologies and is a member of the SEI-CASE BIM committee.

Astrid Bastiaens is a Product Engineer at Nemetschek Scia. She graduated with a degree in Civil Engineering from Katholieke University, Leuven, Belgium and has worked at Nemetschek Scia since 2006 .

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