Digital Trends in Structural Analysis and Design

Technical Article

The construction industry is increasingly digitized. Structural engineers, a smaller group in the construction industry, are not always considered as engineers who immediately join the latest trends. Often for good reason. Many consider this to be the reason why topics such as utilizing the BIM method are not yet the standard in structural engineering. However, the past few years have shown that a process of rethinking has begun and new digital trends are picked up and applied.

Industry Get-Together: digitalBau

In February 2020, a new trade fair took place for the first time in Cologne on "Digitization in the Construction Industry". After many difficult years for typical construction software trade fairs, this is the first successful repositioning of a trade fair in this industry. It is also remarkable that the event focused exclusively on software and thus, as is often the case, this industry segment was not lost due to the presence of other manufacturers of construction products like bricks or gutters. It will be interesting to see if the successful start will continue in the next two years with an increasing number of exhibitors and visitors. It is already clear that it was a get-together for all well-known software manufacturers in the construction industry in general and for structural analysis and design in particular. If you closely follow the developments in recent years, you can see some trends and digitalBau was also a good opportunity to realize it.

Building Information Modeling is Becoming Increasingly Important

For more than 20 years, civil engineers have been studying how digital options can be used to represent the entire life cycle of buildings. But only now it seems that more than just a few pioneers deal with it. Even more, the structural engineers also recognize this topic as an opportunity to acquire new clients, work more effectively and present their engineering office as innovative and progressive. The latter is a point not to be underestimated when it comes to hiring hard-to-find specialist engineers and retaining them for longer.

New software versions include more tools to better deal with 3D data and to communicate digitally. This was preceded by several years in which the architects have come to appreciate the advantages of digital twins. They help to create attractive visualizations and perform cost estimates quickly and accurately. Once the 3D models have been created, you want to use them for other tasks such as structural analysis and design.

Image 01 - Building Model in Various BIM Applications and IFC Viewer as Well as Calculated Model in RFEM (Deformations, Bottom)

Why starting from the beginning again when you can import the models with the certified Open BIM interface? These were the ideas so far. However, by now  it's well known that a digital calculation model is fundamentally different from a 3D model created by the architect, even if it looks the same at first glance. Although it is based on the dimensions and model data of the digital twin, it does not necessarily contain the information about supports, hinges and, for example, the associated loads and load combinations that are essential for a calculation. In addition, the analysis model contains significant simplifications, without which no effective calculation would be possible even today. For example, in the BIM model, all structural components are described as solids.

In the structural analysis model, however, solid elements are rarely used in calculations. Instead, columns and beams are modeled as 1D finite elements, i.e. with a start and an end node and a line in between. The stiffness of the element is described by the cross-section values and the length of the line. Thus, 3D solid geometries degenerate to simple wireframe models. This in turn means that the center lines and surfaces of columns, beams, ceilings, or walls do not always meet in a node or a line and thus you can easily get to the mentioned wireframe model. Instead, the position of the structural lines of action must often be moved and defined more precisely in order to obtain a coherent, meshable analysis model.

Image 02 - Different Options of Deriving the Analysis Model for a Bolted Steel Connection (Red Lines and Nodes) for Structural Analysis and Design

Since this requires engineering knowledge, it cannot always be completely automated by software and can be extremely time-consuming. State-of-the-art BIM software displays this issue and both models - including the structural model - are available. Special tools lengthen, shorten or find nearby points and define them as structural nodes. If these structural models are transferred to the structural analysis software in the next step, a common exchange format is required. This does not necessarily have to be the manufacturer-independent IFC format. There are multiple ormats as well as direct interfaces between BIM and structural analysis software, where the data is imported directly from one program to another without an intermediate file.

New Digital Solutions for Wind Load Simulations

Once the model has been imported into the structural analysis software, you have to refine it further. In addition to supports, hinges and other mechanical parameters, applying the load is a big step. In the traditional approach, load assumptions are made and entered into the analytical model as member or surface loads. For regular building shapes, the load standards indicate which loads you have to apply. Applying loads from self-weight, imposed and snow loads usually causes only few problems. The situation is different for wind loads. Wind flows and turbulences are only regulated for simple building objects. Even the most common things such as dormers, eaves, canopies or partially open buildings can quickly lead to situations in which it is not clear whether suction or compression loads are present and how large they are. However, with the option to plan digitally, you might want to design architecturally sophisticated and extravagant building shapes. Even if load assumptions can be made here, it is very cumbersome and time-consuming to apply them. As with using structural analysis to simulate wind flows, you can also use FEM methods which is, for example, usually used in mechanical engineering for the analysis of flows. It is obvious to use digital simulations for wind flows and for determining wind pressures on buildings.

Therefore, the simulation of wind loads was a major topic at the booth of the structural analysis and design software company Dlubal at the digitalBau in Cologne. The corresponding program with the name RWIND Simulation can be interpreted as a digital wind tunnel. What is otherwise analyzed on replica models in one of the few wind tunnels in Germany in a time-consuming and expensive way can now be analyzed much more quickly. Digital models, as they are already available when using the BIM method, are imported into the software and can thus be displayed with a high detail level. In addition, the topography of the surroundings and the adjacent buildings are important in wind simulations. These can also be additionally imported and aligned in relation to the building. The relevant standards specify the basic wind speeds and turbulences to be applied in diagrams. You can define them in the software as a vertical wind profile depending on the standard. With these specifications, the simulation of wind flows from different directions starts. As a result, we obtain animated visualizations of wind flows and speeds as well as the resulting pressures on the structure surface, which can then be used as a strutural load.

Image 03 - Wind Load Simulation of CIMU - ILE DE SEGUIN, Paris, in the Digital Wind Tunnel in RWIND Simulation (© www.bouygues.com)

The digital wind tunnel can be used even more effectively in combination with the structural analysis software RFEM. 3D analysis models can be transferred directly to the digital wind tunnel. After the simulation is completed, loads are automatically transferred as a structural load case. By using CFD software such as RWIND Simulation, a significant part of the structural analysis is lifted to a completely different level. Load assumptions based on CFD provide the opportunity to determine more realistic and possibly more economical and safer load actions for the supporting structures. Utilizing 3D models in structural analysis and wind simulation also saves time when entering wind loads. On the other hand, there is the discrepancy that load applications that are based on load standards do not correspond to the numerically determined loads from the CFD analysis. This raises doubts, especially if the load level is lower. Reference calculations and validating numerical results against known benchmarks are necessary here.

However, it can also be argued that real wind tunnel tests only represent the reality approximately because of the very scaled-down models, measurement errors, and the distribution of the sensors. In addition, it is difficult to determine the elasticity of buildings in an real wind tunnel test. Numerical solutions offer great potential here. Moreover, the load standards are very simplified methods, which are usually considered as a safe tool. Both methods of load determination - real wind tunnel test and simplified methods of the load standard - thus only represent approximations of the reality. Therefore, loads determined by means of CFD and RWIND are at least a good alternative and help to understand the actual conditions. This is a good example of how the construction industry can benefit from digitization, BIM as well as innovative and new products. In addition to the architecture and analysis model, a digital wind model is also required. Let's hope that the legal circumstances and the methods of checking structural analysis will be adapted to the new possibilities and actively shape the technical progress.

Image 04 - Pressure Distribution of Residential Building With Garage in the Digital Wind Tunnel by RWIND Simulation

Cloud-Based Services

Another much discussed topic is utilizing cloud-based services for structural analysis and design. However, it is not only about saving data on servers, but also about providing information on the web and its automated use. Related to structural analysis, there are already many examples where calculations can be carried out on the web. An example of how structural planning can benefit from cloud-based services is the Geo Zone Tool by Dlubal Software. This service includes zoning maps to quickly determine snow loads, wind speeds as well as seismic and tornado data for many countries worldwide. Actions from tsunamis, temperature, rain or icing is currently in development. The zoning maps are based on digital maps of online map services like Google Maps or OpenStreetMap. For each country, the respective standards are available. A limited number of requests is available at no cost. Your access is activated to all zoning maps after having logged in. An additional web application is available for automated data transfer from third-party websites for any location. In this way, the service can also be included in other applications.

Image 05 - Dlubal Online Service to Determine Wind Loads Based on Cloud-Based Map Services

Furthermore, you can utilize Cross-Section Properties online. Previously, you had to update documents or obtain cross-section properties in printed form regularly, but now you can access the latest versions online. Not only standard cross-sections are available, but also cross-section shapes that you can enter by means of dimensions. Thus, the online service provides much more than an unchangeable printed table book.

Image 06 - Dlubal Online Service With Comprehensive Cross-Section Libraries and Determination of Cross-Section Values for Structural Analysis and Design

FEA programs and the projects calculated with them are sometimes so complex that in some cases, an intensive contact with the software manufacturer is necessary. Again, there is a trend towards more spontaneous online training and support meetings. As in private life, the support team and users can be contacted directly, at least for initial simple questions. Now, this goes far beyond the usual email request and you can use the comment functions in social media channels such as Facebook or Instagram to contact the company. Some manufacturers also offer chat functions on their websites, which automatically search for possible answers to the questions asked by using artificial intelligence. If you used to book a training including a multiday trip, you can now expand your knowledge on the Youtube channel with a recorded webinar or customer event.

Image 07 - Dlubal Youtube Channel with Detailed Ttechnical Webinars on Various Structural Topics

The web pages, for example by Dlubal Software, have been developed into a comprehensive structural analysis portal. In addition to a traditional forum, there are numerous frequently asked questions (FAQs) that help solve problems outside office hours. Expertise on specific topics is provided by technical articles. All content is available at no cost and additionally, take advantage of the extensive search options to find your relevant article.

Image 08 - Dlubal Website with Technical Articles and Calculation Examples

Keywords

BIM Building Information Modeling RWIND Wind load Wind load simulation CFD Structural analysis and design

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  • Updated 25 January 2021

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