This blog post highlights the recent research developments in developing a machine-learning based finite element analysis for reinforced concrete structures. The focus of this blog post is on the first step towards such a framework for shell elements. The blog post will guide you through the setup of the framework for a simple linear elastic material model and its application to an example of a plate subjected to bending moments. The most important learnings will be highlighted throughout the blog post, including one of the most important concepts in machine learning: Any machine learning model is only as good as its underlying data.

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Across Europe and beyond, many bridges are nearing the end of their design lifespan, requiring urgent structural assessments. However, conventional structural assessment methods are time-consuming, costly, and difficult to scale across large infrastructure portfolios. In this blog post, we introduce a machine learning-based pre-assessment tool for reinforced concrete frame bridges – one of the most common bridge types in Switzerland. Developed in collaboration with the Swiss Federal Railways (SBB), this prototype allows for an efficient and accurate estimation of structural utilisation, providing valuable decision support. We demonstrate its application through a real bridge case study and discuss its potential for broader implementation in infrastructure management.

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Strut-and-tie models are a simplified, safe and typically manual design approach for reinforced concrete structures such as beams or walls. Current automated approaches (e.g. topology optimisation) struggle to generate practical strut-and-tie models. This blogpost elaborates on a recently published grammar-based approach which interprets the problem as a graph and attempts to incorporate engineering judgement into its rule set.

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Another milestone on the way to CFRP prestressed railway bridges in Switzerland: The project team consisting of SBB, alphabeton AG, HSLU, Empa and ETH has tested a prototype in the laboratory. The load-bearing behaviour of the 1.7 m x 6.5 m prototype was tested under various loading conditions in static and cyclic bending as well as in shear. It was shown that the composite material has a certain plastic deformation capacity despite its brittle CFR prestressing. This is due to the fact that the steel reinforcement starts yielding before rupture of the CFRP. The prestressing remained intact during the entire test campaign but, like the shear behaviour, needs to be investigated in more detail. This is the subject of ongoing experimental and theoretical work.

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This blog post introduces a new 3D- / AR-application for teaching structural concrete developed at our chair. The content is represented as a 3D model that can also be viewed in an Augmented Reality (AR) environment. A story-based approach was implemented to achieve a better user journey without overwhelming the students with the content. The first example presented in this blog post deals with the design of a wall connected to a hollow cross-section using strut-and-tie models.
Another focus of the work was to create the application using an easy-to-use pipeline, thereby allowing the creation of more examples based on standard software like rhino3D and Excel.

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Increasing the static efficiency of concrete floor slabs is a very impactful lever to reduce the negative impact of building construction in light of the climate crisis. However, designs are often not governed by the load-bearing capacity, but by requirements such as serviceability or sound insulation, limiting potential savings. This blog post investigates the impact of these requirements on concrete floor slab designs, using a newly developed data generation pipeline.

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In this blog post, I would like to share with you an exciting part of the research work: Conferences. My experience report of the conference in Budapest is intended to give students and people from practice an insight into these special working days.

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This blog post explores a simple approach to gain insight into an existing model using the machine learning algorithm “classification decision tree”. In the application example, the existing model is a mechanical model predicting the load-bearing capacity of a continuous reinforced slab strip. It is used to generate a data for training the decision tree. Observing the different partitions and the feature importance property can help understand which input parameters are most significant to the outcome of the existing model. As an added benefit, interpreting the different partitions with theoretical knowledge may spark new ideas or lead to a different way of thinking.

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This blog post briefly presents a novel approach for carrying out a computationally economical beam-element analysis that accounts for the nonlinear load-displacement and moment-rotation behavior of RHS/SHS (rectangular and squared hollow sections) of various local slenderness: the “DNN-DSM”, which makes use of machine learning techniques (deep neural networks – DNN) to predict the nonlinear stiffness matrix terms in a beam-element formulation for implementation in the Direct Stiffness Method (DSM). The whole idea is grounded on trained DNN models from an extensive pool of shell-based simulations including linear buckling analysis (LBA) and geometrically and materially nonlinear analysis with imperfections (GMNIA).

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This blog post discusses ongoing collaborative research between the Universidad Politécnica de Madrid (UPM) and ACCIONA’s Construction Technology Centre on High-Performance Fibre Reinforced Concrete (HPFRC) in bridge design. HPFRC, with compressive strength of 100-120 MPa, offers elevated prestressing levels, reducing concrete volume and enabling larger spans in precast concrete bridges. Findings indicate reduced concrete consumption by 50%, mild reinforcement by 67%, with a 14% cost reduction compared to conventional material. This prompted a large experimental campaign in shear response. Despite difficulties, HPFRC presents a promising, cost-competitive alternative in bridge construction, with ongoing efforts to refine design models for wider industry adoption.

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To improve strategies for the design and verification of reinforced concrete structures, methodologies like non-linear finite element analyses should be taken advantage of. They allow for a more accurate understanding and a more detailed analysis of the highly non-linear behaviour of reinforced concrete and can thus lead to more resource-efficient designs. Such methods are however rarely utilised nowadays, partly because they are computationally much more time-consuming than linear elastic finite element analyses. Hence, it is difficult to carry out multiple design iterations. To overcome this limitation and generally explore the use of machine learning within the non-linear finite element method, the development of a new ML-FEA methodology is suggested.

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Have you ever struggled to find a suitable strut-and-tie model for the design of reinforced concrete dapped-ended beams or walls with multiple openings? We present the recent developments in automated strut-and-tie model generation and the challenges and limitations of two common optimisation-based approaches. Finally, we show the first step towards tackling our research question: How can we generate a range of strut-and-tie models using machine learning?

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The Brick Industry Switzerland supports establishing an inter-university masonry group with a generous donation to promote teaching and research in structural masonry. The masonry group is led by Dr. Marius Weber, with teaching and research activities being carried out simultaneously at the Chair of Concrete Structures and Bridge Design at ETHZ and at the Institute of Civil Engineering at Lucerne University of Applied Sciences and Arts. The research focuses on developing numerical simulation tools for solving practical design and verification problems for masonry structures. Our objectives include the development of open-source software packages for advanced masonry analysis and design, conducting lectures at both institutions, and actively engage in expert groups and standardization commissions. These efforts are aimed at effectively transferring our research findings and expertise into practical applications within the field of construction.

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The choice of efficient structural systems for floor slabs is an effective measure to make the currently very emission- and resource-intensive construction of buildings more environmentally friendly. Therefore, we established a new research project to explore how digital fabrication can enable the production of such efficient floor slab systems. Digital fabrication might be highly suitable as such systems have a higher geometric complexity than widely established flat slabs. It is essential to consider the numerous and diverse requirements that floor slabs must fulfil to ensure that the developed structural systems are not only low-emission but also suitable for the mass market.

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With the goal of establishing a CFRP-prestressed concrete railway bridge system, the project team consisting of SBB, alphabeton AG, HSLU, Empa and ETH has reached an important milestone: the production of a
1.7 m x 6.5 m biaxially CFRP-prestressed prototype. The longitudinal girders were cast first and provided with recesses for the steel-reinforcement and CFRP-prestressing of the transverse girders, which were cast in a second stage together with the bridge deck. To enable the production of this prototype, a 14 m long tensioning frame for pretensioning the longitudinal girders and three smaller steel frames for the transverse girders were built. Additionally, a wedge anchor system had to be developed at Empa to assure a reliable prestressing of the CFRP rods to 55 kN (1041 MPa).

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At the Chair of Structural Engineering – Concrete Structures and Bridge Design at ETH Zurich, we develop together with the Swiss Data Science Center an AI-augmented bridge design co-pilot in the form of a multi-modal variation of a conditional variational autoencoder (CVAE). The deep-learning-based software tool can be applied structure-agnosticly and will assist engineers as forward and inverse design models, combining AI’s computational capabilities and human intuition and knowledge in early design stages, to foster more sustainable, efficient, yet reliable structures of the future.

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This blog post is aimed at anyone who wants to know how a mechanically consistent, non-linear material model for Finite Element analyses of reinforced concrete structures can be developed and how it can be adapted for cyclic loading. Although this sounds like a particular topic, the blog post was written with the intention that also non-structural engineers should be able to follow the explanations to gain insight into the modelling of a material that is ubiquitous in the built environment and whose load-bearing behaviour is being further researched to optimise its use.

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Precast concrete tunnel lining segments are frequently used in tunnels built with a tunnel boring machine. The ring and longitudinal joints between the segments transfer the loads during construction and the service life and play a key role in the design of the tunnel lining segments. This blog post gives insight into a research project on tunnel lining joints, focusing on the longitudinal joints. Current design approaches of longitudinal tunnel lining joints and results of an experimental campaign on strip-loaded reinforced concrete blocks are presented. Furthermore, the Dual-Wedge stress field is introduced.

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On the occasion of the fifth “Betontag”, that took place at the Fribourg School of Engineering and Architecture HTA-FR, the current blog post is dedicated to the Swiss delegation of the Fédération internationale du béton (fib-CH). In an interview, we talked to Thierry Delémont, head of the fib-CH delegation, and Dr Patrick Valeri, who has also recently become a member of the delegation and head of the fib-CH Young Members Group. They present to us the organisation, its tasks, and goals.

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The fabrication of the formwork is one of the major challenges when facing the difficult task of balancing efficiency, sustainability and economy in constructing an optimised concrete floor slab. A look into the past reveals how ancient master builders invented innovative formwork systems to achieve economic structures like, for example, the use of the traditional tile vaulting technique as integrated formwork for concrete shells. Researchers nowadays can learn valuable lessons from this legacy and combine them with the currently available digital tools for design, analysis and fabrication to explore context-aware construction systems that are able to produce a positive environmental impact in places where construction will dramatically increase in the following decades.

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In the last few decades, the Finite-Element-Method (FEM) has become an indispensable tool in structural engineering. In addition to the automation of common calculation procedures and routine tasks, more complex structures can be designed more efficiently with the FEM compared to conventional hand calculations while in addition the load-bearing reserves of existing structures can be exploited using nonlinear material models. The engineer’s task has shifted from the pure “calculator” to modelling, whereby the underlying models and their limits should be well understood. Our task as a teaching and research institute is to convey these model concepts and theories and the engineering-like handling of the FEM. This blog post gives a brief overview of the basic principles and the historical development of the FEM and introduces the FEM tools available at the Chair of Concrete Structures and Bridge Design and how we prepare future structural engineers for responsible use of the FEM.

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The influence of long-term effects (shrinkage and creep) to calculate the internal forces in piers monolithically connected to a prestressed girder or slab is discussed. Despite the availability of powerful structural analysis software, analysing statically indeterminate structures subjected to long-term effects remains a challenge. Therefore, simplified equations for estimating the time-dependent bending moments caused by shrinkage and prestressing at the pier heads are presented. They are useful in engineering practice, allow a simple yet accurate long-term analysis, facilitating the analysis of long jointless structures with monolithically connected piers.

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This blog post gives insight into why ductility is so essential in the design of concrete structures. It shows how modern codes deal with the topic, namely by construction measures or by conducting a check of the rotation capacity. Two simple methods to determine the rotation capacity are compared for that purpose. While these methods are valuable, they are limited to proven materials and one-way carrying structures. Current research at our chair, in particular an extensive experimental series on two-span slab strips, should fill some of these knowledge gaps.

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Extreme restraint actions and corresponding redistributions of forces and bending moments occur on restrained beams and slabs in the event of a fire. As experimental and numerical studies on statically indeterminate members under fire conditions show, sufficient rotation capacity may not be taken for granted, especially if no axial restraint can be mobilised (e.g. for two-span tunnel ceilings) nor two-way load carrying conditions prevail (many precast slab solutions). Within the framework of revising the EN 1992-1-2, we reviewed and studied force and bending moment redistributions under fire conditions. We found that the design rules given in the EN 1992-1-2 are overall reasonably safe and easily applicable to cover most continuous members of current practice, even though the rules do not cover all eventualities such as large redistributions of shear forces towards intermediate slab supports.

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Structural concrete design lectures are a central part of the education in every civil engineering curriculum. Advanced analytical thinking and abstraction skills are essential for understanding the content. Our research shows that the use of digital tools with spatial representation can support students in this process and increase their motivation. This blog presents the design, workflow, deployment, and evaluation of augmented and mixed reality demonstrators for practice exercises and colloquia on typical but geometrically complex structural concrete components (reinforced concrete corbel and torsion beam). Study participants had the opportunity to test the applications on their devices or watch pre-recorded videos. The feedback received underlines the great interest and potential, but also shows the obstacles for the implementation of digital teaching in structural engineering in the near future.

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At the Chair of Concrete Structures and Bridge Design, a project starts intending to design a bridge system for short (2-10m) single-span bridges for the SBB. The materialisation is tailored to durability and efficient installation (prefabrication): ultra-high performance concrete with corrosion – and fatigue resistant CFRP prestressing combined with conventional steel reinforcement. A large experimental series in collaboration with Empa, the Lucerne University of Applied Sciences and Arts, SBB and alphabeton AG over almost three years aims to answer the main scientific questions raised concerning material behaviour. Based on analytical and numerical parameter studies, the designs for bridges with variable spans (2 – 10m), different widths (one or two lanes) and type of crossing (orthogonal or skew) will be developed and implemented into a design and dimensioning tool for applications in engineering practice.

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Digital fabrication with concrete is growing at a fast pace. More and more projects worldwide are produced with these new technologies. But what exactly is it all about, and where do these technologies go next? These technologies promise to revolutionise the construction industry. Can they hold what they promise? Many researchers worldwide address different aspects of these technologies, and industry tries to find the best applications.

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Conceptual structural design today relies heavily on the intuition and experience of the structural engineer, often includes an investigation of similar reference projects, and is mostly a time-consuming and demanding task that is characterized by many iteration steps. On the other hand, Generative Design (GD) allows for exploration of high-dimensional design spaces and has been applied successfully to design tasks in mechanical and space engineering. In addition to GD, augmenting structural design as we know it today by modern machine learning (ML) algorithms might further accelerate the design workflow. This blog post discusses a multi-step ML approach, currently under development at ETH Zurich, to improve the design and optimization process of network tied-arch bridges and discusses as well as exemplifies the wide potential of applying ML algorithms to the conceptional structural design phase.

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Reinforced concrete structures exhibit a favourable behaviour in case of fire with the cross-sectional dimensions and concrete covers currently adopted. The fire resistance of reinforced concrete structures is easily ensured in most cases by conceptual decisions and quick checks with the help of tabulated design data. Nevertheless, there are essential structures or sensitive structural members for which in-depth fire resistance verifications are necessary. Correspondingly, knowledge of the behaviour of reinforced concrete under fire exposure and application limits of the relevant standards is indispensable. This article discusses the fire behaviour of reinforced concrete structures and the relevant competencies taught to students in civil engineering education at ETH Zurich.

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On 14 August 2018, an approximately 250 m long section of the Polcevera Viaduct in Genoa collapsed, claiming the lives of 43 people. Following this tragedy, a number of professionals heavily criticised the concept of the bridge and its renowned designer Riccardo Morandi. While some of the points of criticism raised are simply wrong, the bridge’s structural concept indeed did not comply with today’s state of the art in various respects.

Hence, was Morandi no pioneer of bridge design but rather a bad engineer – as claimed by some critics? Or is it unfair to measure a structure built more than half a century ago against today’s standards?

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There are many benefits that the presence of exchange researchers within our group can bring. According to Dr. Jaime Mata Falcón, working every day with foreign researchers is the best way to keep our minds and research horizons open. An international exchange of research ideas and methodologies also provides a huge potential for synergies and progress. Unfortunately, the ongoing COVID-19 pandemic has difficulted the interaction with foreign researchers spending some time with us. To get more insight into this topic, three exchange researchers share in this post their professional and personal experiences and how both have been affected by the pandemic.

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Almost five years ago, as part of a Master’s project thesis, I received the opportunity to develop first methods for a crack measurement tool for the evaluation of concrete tests. The aim was to automatically detect cracks and measure their width and slip from the surface deformation measurements obtained by digital image correlation. My supervisors Prof. Dr. Walter Kaufmann and Dr. Jaime Mata-Falcón had already worked out the first ideas and concepts at this point and some test data were also available. After completing the project thesis, the tool was continuously refined and increasingly used in the analysis of our experiments. The procedure showed great potential, so that today it is freely available as open-source software under the name ACDM (for “automated crack detection and measurement”). The graphical user interface allows an easy application and also other research institutes have started using this tool. This blog post is about the process leading to today’s ACDM, its importance in experimental research and the most important elements that helped the tool to leverage.

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In developed countries, a huge number of ageing infrastructure objects need to be reassessed to ensure their structural safety. However, current assessment methods for analysing the load-carrying capacity of existing structures are in many cases not sufficient as they are typically based on the same models as the methods used in the design codes for new structures. In particular the estimation of the shear strength is often deficient due to low transverse reinforcement ratios which were possible due to the ancient code provisions. In my dissertation, which I successfully defended in February, I tried to improve the comprehension of the load-deformation behaviour of reinforced concrete membrane elements with very low amounts of and without vertical reinforcement subjected to in-plane shear and normal forces.

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Resource consumption and greenhouse gas emissions of concrete construction are very high worldwide. In the light of the climate crisis, a replacement by other construction methods appears to be the obvious solution. However, this is not expedient: The problem is not concrete per se but the high level of construction activity as a whole. Limiting this activity is hardly appropriate, especially in emerging and developing countries.

Instead, we must reduce resource consumption and emissions of concrete construction. With structurally efficient buildings, we structural engineers can make a significant contribution to climate protection here. We should see this as an opportunity to focus on one of our very own competencies and to grant structural efficiency the importance it deserves.

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Teaching in structural concrete has always been characterised by frontal lecturing for the entire class. However, this only fosters the critical discussion of the subject matter and the students’ self-initiative to a limited extent. As part of an Innovedum-funded teaching project, we looked at approaches for fostering students’ curiosity about the complex non-linear behaviour of reinforced concrete structures. This resulted in a collection of digital learning applications. In this blog entry, you may read about our motivation to discover new teaching methods, the improved interaction with students through digital apps, and the challenges in developing and implementing them into the existing curriculum.

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Many ageing reinforced concrete structures are affected by local reinforcement corrosion. One example is the corroding flexural reinforcement of many cantilever retaining walls along railways and motorways. But what are the effects of local corrosion, resulting from e.g. chloride ingress, from a structural point of view? This question shall be answered with various tests on locally damaged reinforcing bars and large-scale experiments on retaining wall sections. The results of these experiments show a severe reduction of the load-bearing and deformation capacity of affected structures. Read in this blog post what the reasons and consequences are.

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Building concrete structures of customised complex geometries requires very expensive, one-of-a kind formwork, which can often not be reused or even recycled. Hence, such structures are far from being economically and ecologically sustainable. Unfortunately, this has led to the abandonment of very efficient structural systems used in the past for the sake of construction efficiency. In this post, we will present how digital fabrication processes can get rid of conventional formworks to allow fabricating material optimised concrete structures in a sustainable manner. We will discuss more in detail the Mesh Mould Prefabrication technology we are developing in cooperation with industrial partners to combine formwork and structural reinforcement into one robotically fabricated construction system.

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Last year, four weeks into the Spring Semester 2020, ETH Zurich suspended classroom teaching due to the Covid-19 pandemic, forcing us to switch online teaching within a few days. What we then thought would last a few months has kept stretching, and we still have not yet returned to the classrooms. This blog gives a personal review of our teaching activities during this special year, the challenges posed by the pandemic, and what we could learn from it.

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The combined loading of in-plane shear and transverse bending is an important load case that needs to be considered in the assessment of the structural safety of webs of concrete box-girder bridges. As developed countries are faced with the challenge of ageing infrastructure, such assesments are ever frequently required. In order to make maximum use of the load carrying capacity of an existing structure, an engineer requires reliable and experimentally verified methods that enable her/him to determine the structural member’s response while respecting the limits of deformation capacity. This blog post discusses the latest experimental and analytical results obtained in the frame of research on this particular load combination.

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Truss models and stress fields are extremely powerful tools for design in structural concrete. They make it possible to consistently follow the flow of forces and to largely control how the structure should transfer the loads.

As manual calculations, however, they hardly meet the demands of today’s professional practice, which is why they are increasingly being replaced by FE analyses. In order to promote the use of stress fields in the future, we have implemented them, in cooperation with an industrial partner, as compatible stress fields in a user-friendly commercial software. In addition to structural safety, as with conventional truss models, this allows the behaviour in service condition to be investigated without sacrificing the advantages of transparency and control over the design.

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Welcome to the new blog of the Chair of Concrete Structures and Bridge Design at ETH Zurich! We are a passionate team of structural engineers dedicated to teaching and research. This year, we are starting this blog to provide a platform for exchange in our domain. Soon, you will find posts on a variety of topics here, such as recent findings and publications, activities in commissions, ongoing experimental research, new teaching content or reviews of exams. We will also share our thoughts and opinions on current and relevant topics, including guest contributions. After this bilingual introduction, the posts will generally be published either in English or German, depending on the author’s preference and the target audience.

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