Tekla Structural DesignerAECbytes Review (February 15, 2018)

Tekla is one of the earliest and most established names in AEC technology, synonymous with structural engineering. Tekla Corporation was founded all the way back in 1966, and its flagship Tekla Structures product was, and continues to be, the premier application for structural design and detailing. With the introduction of the “building information modeling” concept, Tekla Structures was eventually developed into a full-fledged BIM application and remains, to this day, the only stand-alone BIM application focused entirely on structural engineering rather than becoming part of a multi-disciplinary suite.

Subsequent to its acquisition by the leading technology company, Trimble, in 2012, Tekla has gained both in stability as well as momentum, adding several additional products to its structural design and engineering suite including Tekla Structural Designer for the analysis and design of both concrete and steel structures; Tekla Tedds for automating repetitive structural calculations; Tekla BIMsight for BIM project collaboration; and Tekla Model Sharing, which allows Tekla Structures project teams to work efficiently together. While AECbytes has reviewed Tekla Structures several times over the years (with the most recent review being Tekla Structures 16), this review takes a detailed look at the capabilities of Tekla Structural Designer to see how it can complement the use of a structural BIM application such as Tekla Structures or Revit Structure.

Structural Engineering Applications

Similar to how an architectural BIM application lets you create a detailed physical model of the building that can be used for visualization, estimation, construction, documentation, and other additional tasks that rely on the geometry of the physical elements of the building, a structural BIM application lets you create a detailed physical model of the structural elements of the building, often in conjunction or coordination with other disciplinary models including architecture and MEP. However, unlike an architectural BIM model where the design and the modeling are happening simultaneously—i.e., the model is the design—this is not the case for structure. In structural engineering, the real “engineering” is happening in a separate “analysis and design” process, for which there is typically a separate specialized application. In the case of Tekla, this specialized application is Tekla Structural Designer, which is distinct from its structural BIM application, Tekla Structures.

Structural engineers have been relying on such structural analysis and design tools for decades, starting with simple calculators to assist with hand calculations to more structure-specific analysis tools to determine values such as stresses, forces, deflections, bending moments, shear, load resistance, load dispersal, etc., for the individual elements of the structure as well as the structure as a whole (Figure 1). The process is iterative, where you start with a tentative structural design based on the architectural design, determine the loads it will be subjected to, analyze the design, and based on the results of the analysis, re-design the individual elements and perhaps the structure as a whole to ensure that it will work as required. More rounds of analysis and design would typically be needed to fine-tune the structure. The finalized design becomes part of the multi-disciplinary model in the BIM workflow.

Figure 1. Structural engineering calculations to compute the bending moment and shear force on a beam. (Image courtesy: http://constructioncivilengineering.com)

Another important aspect to note is that structural analysis calculations are typically performed on what is commonly referred to as a “stick figure” of the model, where elements such as beams and columns are represented as lines (as shown in Figure 1) and the connections between them are represented as nodes. This is why all structural BIM applications generate an analytical model underlying the physical model of the structure, and it is this analytical model that is used by the structural analysis and design tool.  

Overview of Tekla Structural Designer

The analysis and design that needs to be done in structural engineering is so specialized and so dependent upon the type of structure that it is not uncommon for an engineer to use as many as five analysis and design tools on a single project—one for steel frame design, another for concrete slab design, a separate one for foundations, and so on. These individual models then have to be combined into a consolidated structural BIM model, which in turn has then to be coordinated with the architecture and MEP BIM models, a process that is long drawn out, inefficient, and error-prone. 

Tekla Structural Designer (TSD) addresses these problems by providing analysis and design capabilities for both concrete and steel design, along with additional smarts including automated load calculations, optimization, and checking for code compliance to make the engineering process faster and more efficient (Figure 2). In addition to bi-directional BIM integration with Revit Structure and Tekla Structures (along with IFC support for interoperability with other applications), it also includes a full-fledged modeling interface, allowing a structural model to be created from scratch within the application. Other key features includes a sophisticated FE (finite analysis) engine for calculations, quick comparison of alternative design schemes, transparency in analysis results so that they can be reviewed, and the automatic production of  accurate and detailed documentation including calculation reports, material take offs and drawings.

Figure 2. Examples of TSD use on projects. Top image: Jimmy John’s Field, Utica, MI, by The S/L/A/M Collaborative. Lower image: Center Court Tennis Building, Cincinnati, OH, by Lawson Elser. (Image courtesy: Trimble).

Modeling

While TSD’s BIM integration allows a structural model created in a BIM application to be brought into the application, it also comes with a full-fledged modeling interface to create a structural model from scratch. In fact, since it is a dedicated application for structural engineering, it includes many domains-specific shortcuts that make it much quicker and easier to create a structural model in TSD as compared to a multi-disciplinary BIM application. For example, for a multistory building with a repetitive structure, you can define the different construction levels to be duplicates of a reference level (Figure 3a); then you just need to model one level and add loads to it, and the information is automatically copied to all the duplicated levels (Figure 3b). You can come back and change this at any time when you want to model something unique on a level.

Figure 3. Setting multiple levels as duplicates of one level; subsequently, all the elements created on the reference level are automatically copied to all the duplicate levels.

Other shortcuts that make modeling quicker and easier include the ability to place multiple columns and beams in one step by drawing a window to select all the gridlines where the elements are to be placed (Figure 4); placing multiple infill beams in a bay in one step by specifying their spacing or the number of beams (Figure 5); and interactively showing a number of key points on an element to snap to (Figure 6).

Figure 4. Modeling multiple beams in one step by drawing a selection window around all the gridlines where the beams are to be placed.

Figure 5. Creating multiple infill beams in selected bays in one step.

Figure 1. Intelligent snapping points are automatically generated when modeling. 

Needless to say, the application comes with an extensive library of elements (Figure 7), both for steel and concrete design, each with a large number of structural attributes for that element type that can be easily modified in the Properties palette when required. Additionally, an Autodesign option is available for each element that can be activated for the application to automatically choose its properties from a range of options to pass the design check when the structure is analyzed. TSD also includes common visualization aids such as cutting planes and walkthrough modes as well as a button to toggle between 2D and 3D for any view. The analytical model underlying the physical model can be viewed at any time. Overall, I found the interface very intuitive and easy to use, with a modern look and feel.

Figure 7. A Truss Wizard is available for quickly creating different kinds of trusses.

Analysis and Design

Of courses, the crux of the application is how well it enables structural engineers to do their core task of analysis and design, starting with the application of loads to the proposed structure. As shown in Figure 8, there is an entire ribbon of commands and options related to defining and applying different types of loads, load cases, and load combinations. You can first specify the design codes that will be used for the structure, and subsequently the load cases, several of which are included by default. The individual loads for each of these load cases can be created using the wide variety of load type options available.  It is also possible to import a DXF file to use as a reference for creating loads (Figure 8). Additionally, there are wizards to simply the creation of snow, wind, and seismic loads, based on the geometry of the building and the design codes that were specified. Once all the loads are defined, they can be grouped into different load combinations to run various types of analyses on the structure.  

Figure 8. Using a DXF of an architectural floor plan as a reference for defining loads. 

An extensive range of 1st and 2nd order analyses can be performed using the Analysis toolbar as shown in Figure 9, from where an analysis type can be selected for any specific load case or load combination. The analysis time will depend upon the size and complexity of the design, the analysis type, and the applied loads. A Show Process dialog can be opened to see the process and methods of the analysis.

Figure 9. Running an analysis with the Process window open to see all the steps.

Once the analysis process is complete, the ribbon automatically switches to the Results toolbar so that the analysis results can be reviewed in detail. The results for the structure as a whole are also shown graphically, as shown in Figure 10, where the individual elements of the design are color-coded based on the analysis results. This is the Review view, which has also been automatically activated after the analysis. At any time, you can switch the view back to the original structure, or set it to Results, where you can now select different options in the Results toolbar to better understand aspects of the structure such deflections, shear, moment, support reactions, etc., in more detail for a specific analysis type and loading condition (Figure 11). There is also the option to review the results in a table, if required.

Figure 10. The color-coded graphical view of the analysis results.

Figure 11. Reviewing different aspects of the analysis results by switching to the Results view.

You could also select an individual element of the structure to review its analysis results in more detail if required, including load analysis, force diagrams, deflections, moments, and other structural behavior (Figures 12 and 13). 

Figure 12. Selecting an individual element to review its analysis results in more detail. 

Figure 13. The detailed load analysis view of the beam selected in Figure 12. 

You could skip the stand-alone analysis process and go straight to the Design toolbar, which allows combined analysis and design to be performed in different ways: for steel, concrete, or both types of elements; and for gravity loads only or all loads. There are also dedicated design tools for slabs which require some amount of user interaction. The analysis engine is the same, and the progress of the analysis can be seen by opening up the Process window as was shown earlier in Figure 9. If the analysis process highlighted some elements that did not pass the checks, more information about the exact cause of the failure can be reviewed, as shown in Figure 14.  You can also choose to automatically design the element to resolve any fixable issues, as shown for the beam in Figure 15, by selecting the element and choosing the “Design Member” option.

Figure 14. Checking the analysis results in detail for an element. This is done by selecting the Check Member option from the sub-menu shown in Figure 12.

Figure 15. Running the Check Design option for the failed element automatically designs its reinforcement so that it passes the analysis.

Other important aspects about TSD’s analysis and design toolset are that in addition to a graphical display of the analysis results as shown in the preceding illustrations, it is also possible to see the ratio by which elements have passed the analysis, which makes it easier to identify elements that are over-designed (Figure 16). And in addition to the Autodesign capability, there is an Interactive Design option for concrete elements to view and modify the reinforcement that was automatically designed for them (Figure 17).

Figure 16. The color-coded display of the analysis results showing the design ratio of each element.

Figure 17. Using the Interactive Design option to view and modify the reinforcement that was automatically added to the beam.

Bi-directional BIM Integration

With the growing use of BIM on AEC projects, it is likely that most structural engineers have to use a BIM application for creating a structural model as part of a multi-disciplinary coordinated BIM workflow. To this end, TSD includes not just the ability to import a structural model created in any BIM application in the IFC format—which applies to most of the applications—but deeper API-integration with two of the most popular structural BIM applications—Revit Structure and Tekla Structures. The integration is bi-directional, allowing not just the BIM model to be imported to TSD but also pushing out any changes made in TSD back to the model, so that they are available when the model is re-opened in Revit Structure or Tekla Structures.

The round-trip integration happens through a free plug-in for both applications. Figure 18 shows the process for Revit Structure, enabled through a TSD Integrator add-in that is available on the TSD website and which does not require the Revit user to have a copy of TSD. In this example, the model is first created in TSD, exported as an integration file (in the CXL format), and then imported into Revit using the TSD Integrator add-in. The import can create a new model or update an existing model, which would be the choice if the integration was being performed iteratively.  The engineer can continue working on the model in Revit Structure and can send it back to TSD at any time for analysis and design through the same add-in. The model can now be brought back into TSD as an update and any changes to the model that are made in Revit Structure, including property information, can be visually reviewed as they are displayed in different colors. This round-tripping between Revit Structure and TSD can be repeated as many times as needed during the design process.

Figure 18. Bringing a structural model created in TSD into Revit Structure using the Integrator plug-in. The import could require some mappings to be specified between TSD elements and Revit elements, which can be saved in a custom mapping file for re-use.

The integration between TSD and Tekla Structures works in a similar fashion. For both types of integrations, TSD allows a visual representation of what has been added, changed or deleted when an existing model is updated with a new integration file (Figure 19), making it easier to audit the changes as the design progresses. 

Figure 19. The changes to a model made in Tekla Structures are highlighted when it is brought back to TSD.

Conclusions

In addition to the features described above, TSD includes full-fledged documentation and reporting capabilities, and these, along with its ability to work with both concrete and steel structures, extensive analysis and design capabilities, a Finite Element engine that enables it to perform complex and accurate analyses, the ease of creating loads and combining them into load cases and combinations, the automated design capabilities, and the ability to review analysis results in detail to fix errors and over-design all add up to a structural analysis and design application that is top of its class. The interface is modern and easy to navigate, and there are abundant resources to learn the application in depth including video tutorials, a getting started guide, and a comprehensive Help documentation. In addition, the bidirectional BIM integration with Revit Structure and Tekla Structures allows the structural analysis and design to be done in tandem with the modeling, which is already an important need in the AEC industry and is only going to get more critical as BIM implementation ramps up.

About the Author

Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at lachmi@aecbytes.com.


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