AECbytes Product Review (November 14, 2007)
Tekla Structures is a BIM application for structural engineering that also includes comprehensive tools for detailers, fabricators, manufacturers, and constructors.
Pros: Extensive repertoire of modeling and detailing tools for both steel and concrete construction, allowing integration of processes from design to fabrication; centralized database which ensures that all drawings and reports stay coordinated with the model; innovative data structure that makes file sizes concise, even for large and complex projects; extensive library of parametric components that automate the tasks of creating details and connections; excellent viewing and model navigation capabilities; ability for clash detection with native objects and reference models; good interoperability with other design applications and downstream manufacturing and construction technologies; bidirectional link to several analysis tools; good support for multiple users working on a project; allows web models to be published that can be freely shared with others.
Cons: Complex application with a very overwhelming interface; entirely text-based documentation that does not support self-learning well, mandating the use of professional training to learn the application; poor interface for making adjustments to the analysis model; more expensive compared to other BIM applications for structural engineering; does not directly integrate with other architectural and MEP BIM applications.
Price: Exact price varies depending on configuration, but overall, it is almost twice the price of other BIM applications for structural engineering.
A couple of months ago, I reviewed the new version of Autodesk Revit Structure and followed it up with an overview of the BIM Fundamentals Seminar for Structural Engineers that was held in San Francisco in early October. Clearly, BIM for structural engineering has arrived and at this juncture, it seems pertinent to also take an in depth look at Tekla Structures, one of the leading BIM applications for structural engineering in addition to Revit Structure and Bentley Structural (which was reviewed in AECbytes last November).
Formerly known as XSteel, Tekla Structures has a long 40-year old history in the building industry, and now has users in more than 80 countries around the world. A new version, Tekla Structures 13, was released earlier this year. Since this is the first time it is being reviewed in AECbytes, I will focus on the product as a whole rather than on the features new to version 13. Let’s start with a broad overview to better understand the scope and functionality of the product.
Overview of Tekla Structures
The basic functionality of Tekla Structures is similar to that of other BIM applications for structural design: instead of drawing 2D structural plans, sections, and elevations, engineers can use Tekla Structures to create a complete digital model that simulates a real-world structure and combines both the physical model as well as the analytical model. It can then be used for the different types of structural analyses engineers need to perform to design their structures, as well as to derive the construction documentation needed to build the structure. Tekla Structures also goes well beyond basic BIM by providing comprehensive capabilities for steel, precast, and rebar detailing, which extends its target audience to include detailers, fabricators, manufacturers, and constructors in addition to structural engineers. Thus, the scope of Tekla Structures is the entire structural design process from conceptual design to construction. This makes it a particularly compelling choice for structural engineering firms who want to extend their range of services to include detailing as well, such as Gregory P. Luth and Associates, which showed at the BIM Fundamentals Seminar how it implements Tekla Structures to do analysis, design, drawings, and detailing in a single integrated process. Tekla Structures has been used on several “signature” projects around the world, two examples of which are illustrated in Figure 1.
Figure 1. The use of Tekla Structures for structural design and detailing in two large and complex projects: the Denver Art Museum, and the Willis Building in London. (Courtesy: Tekla).
Even though the full Tekla Structures package spans the entire structural design process from structural engineering to concrete and steel detailing, it is designed to be modular, so that users can choose the configuration that best suits their needs. The various configurations include Standard Design, Steel Detailing, Precast Concrete Detailing, Reinforced Concrete Detailing, and Full Detailing. The Standard Design configuration is the typical one for engineers—it includes the modeling of a structure; all general arrangement (GA) drawings, reports, and other output; analysis and design integration links to products such as SAP2000, Staad.Pro, S-FRAME, GTStrudl, Robot, and Dlubal RFEM and RSTAB; and built-in connection design calculations and links to Excel to perform component or connection design. The other configurations can be purchased and added to the base application as required, based on the type and extent of detailing a firm is interested in doing.
It is important to understand the unique manner in which a Tekla Structures model and associated information is organized to better appreciate how it works. Just like Revit, it works with a central database, which means that all drawings and reports are derived from and stay linked to the model, get updated automatically, and are never out of date regardless of changes in the model. However, at the same time, the file sizes of Tekla models are much smaller than that of Revit. For example, one of the largest Tekla models created in actual practice contains over 1 million objects, yet it is only 25 MB in size, compared to Revit, where file sizes of close to 200 MB are not uncommon. Tekla Structures achieves this file size economy by a highly efficient data structure and also by storing the drawings in separate files rather than within the model file itself, which only contains a list of the drawings. The drawings themselves have been optimized to only contain the information about their specific view of the model rather than all the individual geometry that they display. Taking again an example from actual practice, a drawing set of over 15,000 drawings derived from a model did not exceed a combined file size of 100 MB. The leanness of both the model and the drawings makes the application relatively fast, even for large and complex models. Instead of updating drawings on the fly, which is very slow, a drawing is updated only when it is opened, printed, or accessed in any other manner. Thus, drawings still stay in sync with the model but maintain a separation and do not encumber the model. This also helps from a collaboration standpoint—the model can be very efficiently shared with others because of its small size.
Creating a new Tekla Structures project creates not just a file, but a project folder that contains the model file and a sub-folder for the drawing files. It also contains various default settings for the application and how it operates, including object attributes and tool settings. These can also be stored in a common folder on a firm’s network, but Tekla has found that most of its users prefer to maintain these settings within the project folder. This makes the project folder appear quite full, even for a blank project (see Figure 2), and does add some measure of complexity to external collaboration. Thus, for instance, if a firm has to share its model with another engineering firm, not just for viewing but for possible editing and further design development, the entire project folder has to be sent, and not just the model file. However, subsequent exchanges of the model will usually not require the settings to be re-sent as the environment is already established; then, only the model and drawing files, if any, need to be sent.
Figure 2. The Project Folder for a new Tekla Structures project that is still empty.
Developing a Structural Model
The typical workflow in Tekla Structures would be to model the structure from scratch or import an architectural model or drawing (several different file formats are supported) to use as a reference for creating the model. You would start by editing the default grid that gets created for a new project and change its coordinates to match the bays and elevations of the proposed design. Figure 3-a shows the grid settings specified for a new project. Just as with other structural modeling applications, grids in Tekla Structures allow easy positioning of objects in models, as you can snap to grid lines and their intersections. Additionally, they are useful to create plan and elevation views in Tekla Structures. There is no concept of floor levels as such, which means that there are no plan views automatically associated with floor levels as in Revit Structure. Similarly, there are no elevation or section markers you can place on the plan views to generate the corresponding elevation or section views. However, once you define the grid, you can use them to create a series of “named views” (see Figure 3-b), from which you can then select the ones you want to make visible. You can also created views by defining 2 or 3 points, by selecting an object plane, or by typing in an elevation value. Figure 3-c shows two of the Named Views created using a grid that were selected and moved over to the Visible Views section, which already has the 3D view by default. The end result of the process is the window configuration shown in Figure 4, where the 3D view and the plan and elevation views are all visible and have been sized and positioned as required. The process is admittedly somewhat roundabout and takes a little time to understand and get used to.
Figure 3. Adjusting the default grid settings and then using the grid to generate multiple views along the grid lines, out of which any view can be selected to become visible.
Once you have your grid and views set up, you can start creating the model using the various tools for typical parts such as beams, columns, plates, slabs, walls, polygon beams, etc. Related tools are grouped together into toolbars: for example, the Steel toolbar contains tools for creating steel beams, columns, and plates; the Concrete toolbar contains tools for creating concrete parts and reinforcements; the Detailing toolbar contains tools for trimming parts; the Loads toolbar contains tools for creating loads, and viewing and editing load groups, etc. There are several additional toolbars containing tools for modeling connections, details, and other components, editing elements, creating and managing views and work planes, creating construction aids, and so on. By default, most of the these toolbars are open and displayed along the top and left of the modeling window, as shown in Figure 4, making for a somewhat overwhelming interface. A beginning user would need to spend some dedicated time to learn what the various tools are and how to use them.
However, once the initial learning curve has been surmounted, engineers can start to appreciate the power of the application. You can build the model quickly and accurately by placing components using the grid lines, as shown in Figure 4. In addition to grids, you can create construction points, lines, and planes that you can snap to for accuracy. The modeling can be done in any of the open views—the application automatically detects which view is current active. So, for instance, you can start a modeling operation in the 3D view and seamlessly continue it in one of the plan or elevation views, without needing to first activate the view. View-related tasks such as zoom, pan, and rotate are built into the middle-mouse button, allowing you to carry them out quickly without selecting tools.
You can define the properties of components before creating them or modify the properties after creation. An example of this is shown in Figure 4, where a beam is selected and its Properties dialog is opened. You can choose the profile from an extensive catalog of steel, concrete, and timber standard sections and likewise, select the material from a catalog of industry standard types. In addition to specifying various other properties needed for analysis and design including loads, support conditions, etc., you can also define your own attributes for any object which can be listed in reports or referenced into drawings. As you can see in Figure 4, this comprises a vast array of options under various categories such as Parameters, Project Status for fabrication, RFI’s, Issue Control, Workflow, IFC export, and so on.
Figure 4. Quickly building up a simple model with beams and columns by using the grid lines across all three open views. The Beam Properties dialog for the selected beam is also shown, along with the dialog for user-defined attributes showing the extensive range of options.
There are various shortcuts for modeling repeating elements. Figure 5 shows a simple Copy operation where all the elements modeled in Figure 4 were selected and 4 copies were made at a recurring height of 20'. In addition, there is a Building Builder tool that allows the user to quickly build columns and beams using a predefined grid system or by picking points on a plane in the Tekla model. Another tool called Filler Beams is similar to the Beam System in Revit—it allows the user to model purlins at equal bay spacing within girder bay layouts. The beams are parametric to the girders they are connected to and adjust automatically to any changes in the size and location of the girders.
Figure 5. Using the Copy tool to quickly create a repeating multi-level structure.
While Tekla Structures does not have built-in associativity and connectivity between components to the extent that Revit, for example, does, it includes several ways to associate components geometrically so that they can maintain connectivity when moved. The simplest way is to select object handles together as a group and then move them. Another way is to make grids and user planes “magnetic,” so that when the grid or plane is moved, all the associated object handles move with them and do not have to be moved individually. Objects can also be bound to specific points on other objects. For example, a chevron brace can be bound to the beam centerline at half its depth, and it will maintain this relationship even when the beam is moved.
The upside to the lack of built-in connectivity and modeling constraints is that it allows Tekla Structures to have a relatively high degree of modeling freedom compared to other BIM applications. For example, walls can be tilted by simply rotating them—this is a feature an application like Revit is still missing. Curved elements can be created by cambering. The shape of any component can be modified and fine-tuned with a variety of editing operations without losing its “BIM” nature. While Tekla Structures does not go all the way in providing full freeform modeling to the extent that generic (non-BIM) 3D modeling applications like form·Z and Rhino allow, you can always import freeform objects into the application and use them as a reference to model the corresponding structural elements. A good example of this is the Velodrome in Athens designed for the 2004 Olympic Games by Santiago Calatrava, for which the structural engineering was done using Tekla Structures, as shown in Figure 6.
Figure 6. The Velodrome project in Athens is a good example of the ability of Tekla Structures to model structural systems that support complex architectural forms. (Courtesy: Tekla)
No BIM application is complete without a set of object libraries, and this is true for Tekla Structures as well. It has an extensive library of parametric components that automate the tasks of creating the details and connections after you have created the main parts of the model. The library even includes modeling tools for some complex components such as stairs, trusses, and towers. All of these can be browsed and managed using the Component catalog shown in Figure 7. If required, you can also create custom components (connections, details, parts and seams) by modifying existing ones or building your own, and then saving them for future use in a custom library. Library components are placed in the model by using the corresponding tools in the Components toolbar, visible below the modeling window in Figure 7. You can search the Component catalog, as shown in Figure 7, where the search results for “base plate” are displayed. The selected base plate was the one used in the model. Another powerful feature of Tekla Structures is its ability to immediately create a series of close-up views of a component. So, for example, selecting the “Component basic views” command for the selected base plate opens up the set of views shown in the lower image of Figure 7, with the 3D view being briefly animated before becoming static. This allows the user to immediately get close-up views of a component and speeds up the design and detailing process.
Figure 7. Using a base plate from the Component catalog in a model, and then generating close-up views of the selected component with a single command.
Analysis, Drawings, and Detailing
Similar to other BIM applications for structural design, Tekla Structures allows the structural model to be transferred to analysis tools. However, in Tekla Structures, the analysis model is not created by default, as it is in Revit Structure. Instead, the analysis model is generated once you start the analysis process after creating the physical model and the loads. This is because Tekla Structures allows you to create several analysis models from the same physical model for running different kinds of analysis. You can also define which objects should be included in the analysis model. (See Figure 8, which shows four separate analysis models, two with the entire structure and two with selected parts only.) Once an analysis model has been created, it can be viewed along with the physical model, allowing the engineer a chance to study the assumptions about load paths and constructibility within a real world 3D. The precise location of the analysis model with respect to the physical model can be defined using rules. For example, for a specific type of beam, you can specify whether the analysis member should be located at the top, centerline, or bottom of the physical model. The analysis model can also be manually tweaked as desired, although this process is not as easy as it requires adjusting values in a dialog (as shown in Figure 8, where the analysis model of a beam is set to 6" below the default height) rather than through interactive editing. The analysis model can include load definitions, boundary conditions, member releases and even some design parameters, all of which can be transferred to analytical tools such as SAP2000, GTStrudl, S-Frame and Staad.Pro. The link with these tools is bidirectional, which means that analysis results can be brought back and can automatically update member sizes and end forces.
Figure 8. Creating multiple analysis models of the same physical structure. The currently selected model is displayed in the window. The analysis model of a beam has been tweaked by adjusting settings in its Attributes dialog.
For creating drawings, Tekla Structures has a dedicated drawing interface that is directly linked and updated from the model. The automation and extent of information shown on the drawing derived from the model is extensive due to Tekla's positioning between engineering and detailing. Various drawing wizards can be used to create different types of drawings. Figure 9 shows an example of plan views collected onto a drawing sheet. As mentioned earlier, drawings are created in a separate folder but stay linked to the model, so that changes made to the model are merged with the drawings when they are opened or printed. However, changes made to the drawings will not update the model, mandating that the user really work on the model if any changes have to be made. As described in the Overview section, this connection between the model and the drawings allows both of them to be lean and is much faster as drawings are not updated continuously but only when they are accessed. Schedules work in conjunction with the drawings, and use templates to show different kinds of data from views in the drawings. Examples include column, strip footing, pad footing, and concrete pilaster schedules. Essentially, anything in the model can be scheduled using templates.
Figure 9. The drawing list for a model with one of the drawings opened for viewing.
As mentioned earlier, Tekla Structures includes comprehensive detailing capabilities, both for steel as well as concrete. Engineering details can be created in 2D or in 3D. The 2D approach involves adding lines, shapes and text to structural model views in a drawing, importing 2D DWG blocks and text as required for reference. The 3D approach involves deriving live text and data from the model rather than drawing them. Tekla Structures also automates the creation of shop drawings for structural steel, precast contractors, rebar detailers, and so on. A key strength of the application in comparison to other structural BIM applications is rebar modeling and detailing in precast concrete or cast-in-place concrete projects. These can contain literally hundreds of thousands of reinforcement objects, all of which can be comfortably handled by the application and can also be easily visualized in 3D, as shown in Figure 10.
Figure 10. Visualization of rebar details in a concrete structure. (Courtesy: Tekla)
Internal and External Collaboration
For multiple team members working on the same model, Tekla Structures has a very simple transaction-based model sharing concept, which was developed close to 10 years ago in the application and is still working well for its users. When you first create a project, you can specify whether it is a single-user or multi-user project. Designating a project as multi-user allow multiple users to work on it at the same time and save back or synchronize their work with the main model. No part of the model, however, is locked down; instead, conflicts are resolved on a “first come first served” basis. So, for example, if two users are working on an operation related to the same beam element at the same time, priority is given to the action of the last one who saved the beam object and the other user is informed about a conflict. This is very different from the “lock down” approaches of worksharing in other BIM applications, which can become quite restrictive. What Tekla Structures does not yet have is an offline capability that will allow users to work on their models even when they are not connected to the server and then synchronize their work with the central model once they are connected. But this capability is in development and should be available in a future release.
Because Tekla Structures is a stand-alone application for structural engineering and detailing rather than part of an integrated suite of BIM solutions such as Revit and Bentley, it has invested significant effort into providing good interoperability with other design applications as well as downstream manufacturing and construction technologies, so that the structural data created in Tekla Structures can be easily shared. It support various neutral file formats such as IFC, SDNF, CIS/2, and DXF, and also provides an API (application programming interface) built using .NET standards for easy access to both 3D geometry and project data. Tekla Structures can import model geometry from RISA, ETABS and RAMSteel through the CIS/2 format as well as exchange steel profile geometry. An Excel plug-in allows users to link in their existing Excel calculation sheets into the Tekla model. For interoperability with architectural and MEP design applications, IFC is the most common data exchange method. A Tekla model can be exported as an IFC file and opened in other BIM applications, while IFC files can be exported from those applications and imported as reference models in Tekla Structures, as shown in Figure 11.
Figure 11. Importing an IFC model in Tekla Structures as a reference.
With regard to coordination and conflict detection, Tekla Structures allows clash detection of its own native objects and offers more clash prevention capabilities with external models imported as references. To facilitate visual coordination, Tekla includes several features for easier viewing of large, complex 3D models including point and zoom, clip planes, pivot point for rotation, pan, fly, and close-ups of components as shown in Figure 7. External collaboration is also facilitated by the ability to publish web models that can be shared with other project team members for free. Several examples of web models can be found on the Tekla website, one of which is shown in Figure 12. As you can see, in addition to navigating through the model, you can also get some basic information about the different components of the structure by holding the cursor over an object.
Figure 12. An example of a web model published from Tekla Structures that can be freely viewed by anyone who has access to the Internet.
Analysis and Conclusions
Tekla Structures is a very powerful, sophisticated, and comprehensive application for any kind of structural engineering. Its 3D modeling capabilities were first introduced 10 years ago and have continued to be developed and refined, making the application able to handle projects of any complexity. Its extensive detailing capabilities make it possible to create detailed BIM models representing true "as-built" conditions, helping the engineer make better decisions about constructibility, and integrate processes from early concept phase planning, design development, through to fabrication and installation. A wide variety of analysis tools are supported. Drawing production can be fast and efficient with features such as automated dimensioning and detail creation that meet the requirements of the detailing industry. It also comes with an extensive library of parametric connections for both steel and concrete. It boasts of excellent viewing and model navigation capabilities, and features such as the automatic generation of close-up views of a component can be a tremendous time-saver for the engineer. On the collaboration front, it also scores by providing good support for multiple users working on a project, allows web models to be published that can be freely shared with clients and other project team members, and includes clash detection capabilities with imported reference models.
The innovative data organization of a Tekla Structures project, which separates the model from the drawings but still makes them part of one central database so that they always stay in sync, is a very clever solution to the file size problem that bogs down other centralized BIM applications. Even for complex models with large amounts of geometrical and analytical data, the file sizes are concise and there is no significant slowing down of the application. In short, Tekla Structures enjoys all the benefits of a single database solution such as automatic coordination of all drawings and reports with the model, but nicely avoids the problem of huge file sizes that slow down other BIM applications and makes model sharing difficult.
Given the power and sophistication of the application, one would hardly expect it to be easy to learn. I also found that with Tekla Structures, all of the power and complexity is “in your face,” so to say—there is no attempt to hide the complexity in layers that can be gradually opened when the user has mastered one level and is ready to move on to the next. It starts right with first opening the application—there are literally hundreds of tools in the interface and as the icons are not accompanied by text labels, it takes a while to figure out what each one does. You can turn on a Tool Tips option, but that still does not allow you to get a quick visual overview of the tools. There is no concept of a Project Browser or Project Navigator as in other BIM applications; even setting up a plan or elevation view is not intuitive and needs to be learned. All the tool dialogs are packed with options and settings, making the interface very overwhelming. Overall, it is a very complex application, and requires at least two days of training to even make a start. Apart from the online Help and a Getting Started guide, several tutorials are available in PDF format, but these are not accompanied by any sample files and are quite laborious to go through. There are no video tutorials, which would have helped enormously and speeded up the learning process. Hopefully, some of these shortcomings will be addressed in future releases and will make this very powerful application easier to approach and master.
Another aspect of Tekla Structures that has both a plus side and a down side is the relative lack of modeling constraints. While this does allow the user a free hand in modeling, it doesn’t provide all the connectivity and associativity benefits that a stricter parametric application like Revit can provide when it comes to editing and maintaining model integrity. Engineers will have to follow some modeling guidelines, and Tekla provides a detailed document on how to maintain model discipline in the application. If the integrity of the physical model cannot be guaranteed, the analysis model may also require relatively more adjustments before it can be sent to analysis tools. As we have seen, the current user interface for tweaking the analysis model relies solely on dialogs to do the tweaking and needs to be overhauled so that the modifications can be made directly to the model graphically.
Looking at the application from a cost perspective, Tekla Structures is almost twice the price of other BIM applications for structural engineering, which is understandable given its extensive detailing capabilities. However, this puts it at a disadvantage for those firms who are not interested in going beyond design to detailing. It would be tremendously helpful for the industry if there was a more competitively priced version of Tekla Structures that did not include all of its powerful detailing capabilities but would at least put its excellent design and analysis tools within the reach of more engineers. This might also help to simplify the interface of the application and make it easier to learn and use.
From a broader multi-disciplinary perspective, Tekla Structures is very strong on interoperability, but it is still missing out on the benefits of integration that multi-disciplinary BIM applications built on the same platform such as Revit and Bentley inherently have. The AEC industry is increasingly moving towards more integrated design teams, which calls for tighter coordination between architects and engineering consultants. While it is probably not feasible for Tekla to start developing architectural and MEP BIM applications at this point, I think it would do well to explore much closer integration with other existing single-disciplinary BIM applications such as ArchiCAD rather than simply rely on IFC-enabled interoperability to make the connection. It can then become a much more mainstream BIM application for structural engineering, rather than be seen only as a best-of-breed application—which it clearly is!—that “power users” will adopt.
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
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