Quantification of digital image correlation applicability related to in-situ proof load testing of bridges

I've been working closely together with my colleagues at the Danish University of Technology for quite a while, and am cosupervisor of Christian Christensen. The first paper of this collaboration and the PhD research of Christian was presented at SMAR 2019, the 5th international Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures. The title of the paper is: "Quantification of digital image correlation applicability related to in-situ proof load testing of bridges".

The abstract of the paper is:
Advanced crack monitoring is crucial for high precision response- and threshold evaluation when performing proof- and diagnostic load tests on existing concrete structures. Mostly, crack monitoring techniques involve one monitoring method, which provide thresholds with regard to stop criteria and characterization information. Such thresholds and related precision uncertainties are expected to be of significant importance in identifying stop criteria as well as deliver input for probabilistic models. In the ongoing Danish bridge testing research program, it is hypothesized that several independent monitoring techniques are needed to reduce uncertainties related to crack detection and categorization. A number of novel monitoring methods are used in the research project. A special focus is however dedicated to two promising crack-monitoring techniques suited for combined use: a) Two-dimensional digital image correlation (2D-DIC) and b) Acoustic emission (AE). The output is expected to provide a unique crack evaluation, for which limitations and uncertainties of the techniques should be quantified individually as well as in combination. This paper presents initial research concerning evaluations related to digital image correlation based on sub-component beam tests performed in the DTU CasMat laboratory facility. The tested beams were prefabricated as TT-elements with a length of 6.4 m and cut into two T-beam elements. The test matrix consisted of ten beams strengthened with carbon fiber reinforced polymer (CFRP) in different configurations with and without post-tensioning of the CFRP, thus resulting in different crack initiation behavior. The investigations in this paper include: (1) time of crack detection compared to visual detection, (2) time of crack detection compared to time of crack width threshold values, and (3) crack width evaluation using 2D-DIC strain correction for out-of-plane deflection. The results show that cracks can be detected prior to both visual detection and significant stiffness change. After detection, crack development can be monitored for crack width stop criteria. Crack widths can also be successfully monitored for surfaces subjected to out-of-plane movement using a geometric correction method. The methodology is hypothesized to be of significant importance in future testing of full-scale concrete slab bridges in the Danish bridge testing project.

Improvements of a Nonlinear Analysis Guideline for the Re-examination of Existing Urban Concrete Structures

My colleagues Ane de Boer and Max Hendriks and I recently sent a paper for presentation for the IABSE 2019 symposium in New York. Dr. De Boer presented our work at the conference. The title of the paper was "Improvements of a Nonlinear Analysis Guideline for the Re-examination of Existing Urban Concrete Structures".

Here's the abstract:

The Dutch Ministry of Infrastructure and the Environment is concerned with the safety of existing infrastructure and expected re-analysis of a large number of bridges and viaducts. Nonlinear finite element analysis can provide a tool to assess safety. A more realistic estimation of the existing safety can be obtained.
Guidelines, based on scientific research, general consensus among peers, and a long-term experience with nonlinear analysis, allow for a reduction of model and user factors and improve the robustness of nonlinear finite element analyses.
The 2017 version of the guidelines can be used for the finite element analysis of basic concrete structural elements like beams, girders and slabs, reinforced or prestressed. Existing structures, like box-girder structures, culverts and bridge decks with prestressed girders in composite structures can be analysed.
The guidelines have been developed with a two-fold purpose. First, to advice analysts on nonlinear finite element analysis of reinforced and pre-stressed concrete structures. Second, to explain the choices made and to educate analysts, related to the responsibility of limiting model uncertainty.
The paper will contain an overview of the latest version of the guideline and its latest validation extensions. Most important impact is the extended operational lifetime of an existing reinforced concrete slab structure.

Shear capacity of steel fibre reinforced concrete beams

My student Belkis Filian recently traveled to Poland to present her research at the fib symposium in Krakow.
The title of her work was: "Shear capacity of steel fibre reinforced concrete beams". We also worked with my TU Delft colleague Yuguang Yang for this paper, and looked at a simple way to incorporate the effect of steel fibers in the critical shear displacement theory (disclaimer: the crack kinematics are so complex that "simple" methods unfortunately are only very coarse approximations)

Here's the abstract:
The Critical Shear Displacement Theory (CSDT) was developed to determine the shear capacity of reinforced concrete beams based on the different shear-carrying mechanisms (concrete in the compression zone, aggregate interlock, and dowel action). This research aims at extending the CSDT to Steel Fibre Reinforced Concrete (SFRC) by adding the contribution of steel fibres. The model extension was developed based on formulations for the contribution of steel fibres to the shear capacity from the literature. With this extension to the CSDT, the shear strength of steel fibre reinforced concrete beams without stirrups could be estimated. An extensive database is developed from the literature in order to evaluate, compare, and analyse the shear capacity of SFRC beams. The analysis indicates that two models are capable of predicting the shear strength of SFRC beams with reasonable accuracy. The mean, standard deviation, and coefficient of variation are 0.9, 0.28, 0.31 and 1.1, 0.33 and 0.30 respectively. The main geometric variables of the steel fibres that influenced the shear strength are the length, diameter, and fibre type (hooked, crimped, and straight). From the comparison between the results in the database and the proposed extensions to the CSDT it is found that the critical shear displacement of Δcr = 0.025 mm, gives reasonable results for SFRC. As such, this proposed method can be used to estimate the shear strength of SDRC based on a mechanical model.

Feel free to write me if you want a copy of the paper!

PhD Talk for AcademicTransfer: How to select the right journal for your work

This post is part of the series PhD Talk for AcademicTransfer: posts written for the Dutch academic career network AcademicTransfer, your go-to resource for all research positions in the Netherlands.

These posts are sponsored by AcademicTransfer, and tailored to those of you interested in pursuing a research position in the Netherlands.

If these posts raise your interest in working as a researcher in the Netherlands, even better - and feel free to fire away any questions you might have on this topic!

If you are at the point during your PhD trajectory or beyond when you feel ready to start preparing your first journal article, you need to select the right venue to submit your work to.

Editors comment that a lot of desk rejections can be avoided by properly selecting a journal. Today, therefore, we will focus on the topic of selecting the right journal for your work.

When should you select where to submit your work? Ideally, before you start writing your article. As such, you can tailor your article to the audience of the journal, write directly into the right template, and keep the word count limitations of the journal in mind when outlining and preparing your work.

So, what should you consider when you select your target journal? Here are a few elements to consider:

1. Scope
First of all, you should always check the scope and aims of the journal. If your work doesn't fit the scope of the journal, you're headed for a straight desk rejection. If you're not sure if your work would fit the journal, then check a few back issues to see which topics are typically covered by the journal. If you don't know which journals to check first, start with the journals you read and in which work similar to yours has been published. As such, you'll get a pointer on where to start.

2. Audience
Another important topic to keep in mind when you select a journal, is the audience. When the journal is printed and managed by a learned society, the audience will be members of this society. For journals in the hands of commercial publishers, the audience may be a bit more difficult to determine. Try to learn who reads the journal: only academics, or practitioners as well? Is it read internationally, or is it oriented towards a specific region? A number of journals in my field are US-oriented, whereas others may be more European or international. When you know the audience, you need to write for your audience. For example, when the audience of the journal includes practitioners, include recommendations for practice.

3. Review timing
Do you need a journal paper in review or accepted as a requirement for graduation? In that case, it may not be a good idea to submit to a journal that has a very slow review process. Some journals take up to a year to return review reports. Check the time to review on the journal website - most journals nowadays display this information on their website. If the information is not available, ask your senior colleagues about their experiences with this journal.

4. Reputation
I don't subscribe to the idea that publishing in a high impact journal says anything about the quality of your work. Moreover, the impact factors depends on your field of study, so it does not create a level playing field. For example, the impact factor of journals in concrete material engineering tend to be higher than those of structural concrete. Saying that one field is more important or better than the other, of course, is utter nonsense.
However, when I mention reputation here, it is closely related to the audience: who reads the journal? Do people get the journal ever (other) month by mail? Or do people tend to read the articles online, and only the articles of interest?

5. Open access
Are there requirements from your funding body to publish all your work open access? Are there initiatives at your university that support open access publishing? If you have identified an open access journal, what is the APC (article processing charge)? Who pays for it - you, your funder, or your university? If not your funder or your university, can you apply for a waiver with the publisher? Can you do something else to reduce the APC? Some journals give vouchers to reviewers to get a discount on the APC.

6. Beware of predatory or hijacked journals
In the dark underside of academia sit predatory and hijacked journals. Have you ever received an email of a journal that says they want to publish your work? Sometimes even an email from a field completely different to yours, and maybe an email with spelling errors (or comic sans ms as their font)? Red flags to identify a predatory journal. Hijacked journals are even more sneaky - they tend to use a name that is almost the same as the name of reputable journal, and their only goal is to cash in on the APC.

Optimizing Finite Element Models for Concrete Bridge Assessment With Proof Load Testing

My colleagues and I recently published a paper "Optimizing Finite Element Models for Concrete Bridge Assessment With Proof Load Testing" in Frontiers in the Built Environment - Bridge Engineering for the Research Topic Diagnostic and Proof Load Testing on Bridges.

The paper is Open Access and can be accessed here.

The abstract is
Proof load testing of existing reinforced concrete bridges is becoming increasingly important as the current bridge stock is aging. In a proof load test, a load that corresponds to the factored live load is applied to a bridge structure, to directly demonstrate that a bridge fulfills the code requirements. To optimize the procedures used in proof load tests, it can be interesting to combine field testing and finite element modeling. Finite element models can for example be used to assess a tested structure after the test when the critical position could not be loaded. In this paper, the case of viaduct De Beek, a four-span reinforced concrete slab bridge, is studied. Upon assessment, it was found that the requirements for bending moment are not fulfilled for this structure. This viaduct was proof load tested in the end span. However, the middle spans are the critical spans of this structure. The initial assessment of this viaduct was carried out with increasingly refined linear finite element models. To further study the behavior of this bridge, a non-linear finite element model is used. The data from the field test (measured strains on the bottom of the concrete cross-section, as well as measured deflection profiles) are used to update the non-linear finite element model for the end span, and to improve the modeling and assessment of the critical middle spans of the structure. Similarly, an improved assessment based on a linear finite element model is carried out. The approaches shown for viaduct De Beek should be applied for other case studies before recommendations for practice can be formulated. Eventually, an optimized combination of field testing and finite element modeling will result in an approach that potentially reduces the cost of field testing.

Feasibility of Collapse Test on Nieuwklap Bridge

My colleagues and I published a paper in the BEI (Bridge Engineering Institute) Conference proceedings. In the end, none of us could make the trip to the conference, even though I had originally co-organized a mini symposium in this conference about field testing. I couldn't figure out childcare, my colleague didn't receive his visa, so in the end we couldn't give our presentation.

Nevertheless, here is the abstract of our paper:

The Nieuwklap Bridge is a 7-span reinforced concrete slab bridge that is scheduled for demolition. Since a large number of reinforced concrete slab bridges in the Netherlands are found to have insufficient shear capacity upon assessment, such bridges have been studied extensively over the past decade. To better evaluate the structural behavior and ultimate capacity of slab bridges, it was suggested to test the Nieuwklap Bridge to collapse. Since collapse tests are expensive and involve large risks, an extensive feasibility study is necessary. Testing of the Nieuwklap Bridge would be interesting if the assessment shows that the bridge is representative for the shear-critical slab bridges in the Netherlands, and if the test can be carried out safely. An assessment of the bridge in an end span and middle span at two levels of approximation is carried out, and the maximum load required to cause collapse is estimated. The outcome of the feasibility study is that the required loads for collapse are large when a plasticity-based model is used. Furthermore, the Nieuwklap Bridge is not shear-critical and thus not representative of the shear-critical slab bridges in the Netherlands. As such, collapse testing is recommended against.

Two books on Load Testing of Bridges

I published two books as an editor on the topic of Load Testing of Bridges: Load Testing of Bridges: Current Practice and Diagnostic Load Testing and Load Testing of Bridges: Proof Load Testing and the Future of Load Testing.

Besides the work involved with contacting all authors and making sure everything gets submitted on time, I also contributed as an author to about half of all chapters in these two books. It's been a long process (three years in total!), but I'm quite happy with the final product - and extremely grateful to all authors who dedicated time and effort to writing their chapters!

To give you an idea of the breadth of these volumes, I am sharing here the table of contents of the two books:
Part I Background to Bridge Load Testing

Chapter 1 Introduction
Eva O. L. Lantsoght
1.1 Background
1.2 Scope of application
1.3 Aim of this book
1.4 Outline of this book

Chapter 2 History of Load Testing of Bridges
Mohamed K. ElBatanouny, Gregor Schacht and Guido Bolle
2.1 Introduction
2.2 Bridge load testing in Europe
2.3 Bridge load testing in North America
2.4 The potential of load testing for the evaluation of existing structures
2.5 Summary and conclusions
References

Chapter 3 Current Codes and Guidelines
Eva O. L. Lantsoght
3.1 Introduction
3.2 German guidelines
3.3 British guidelines
3.4 Irish guidelines
3.5 Guidelines in the United States
3.6 French guidelines
3.7 Czech Republic and Slovakia
3.8 Spanish guidelines
3.9 Other countries
3.10 Current developments
3.11 Discussion
3.12 Summary
References

Part II Preparation, Execution, and Post-Processing of Load Tests on Bridges

Chapter 4 General Considerations
Eva O. L. Lantsoght and Jacob W. Schmidt
4.1 Initial considerations
4.2 Types of load tests, and which type of load test to select
4.3 When to load test a bridge, and when not to load test
4.4 Structure type considerations
4.5 Safety requirements during load testing
4.6 Summary and conclusions
References

Chapter 5 Preparation of Load Tests
Eva O. L. Lantsoght and Jacob W. Schmidt
5.1 Introduction
5.2 Determination of test objectives
5.3 Bridge inspection
5.4 Preliminary calculations and development of finite element model
5.5 Planning and preparation of load test
5.6 Summary and conclusions
References

Chapter 6 General Considerations for the Execution of Load Tests
Eva O. L. Lantsoght and Jacob W. Schmidt
6.1 Introduction
6.2 Loading equipment
6.3 Measurement equipment
6.4 Practical aspects of execution
6.5 Summary and conclusions
References

Chapter 7 Post-Processing and Bridge Assessment
Eva O. L. Lantsoght and Jacob W. Schmidt
7.1 Introduction
7.2 Post-processing of measurement data
7.3 Updating finite element model with measurement data
7.4 Bridge assessment
7.5 Formulation of recommendations for maintenance or operation
7.6 Recommendations for reporting of load tests
7.7 Summary and conclusions
References 151

Part III Diagnostic Load Testing of Bridges

Chapter 8 Methodology for Diagnostic Load Testing
Eva O. L. Lantsoght, Jonathan Bonifaz, Telmo A. Sanchez and Devin K. Harris
8.1 Introduction
8.2 Preparation of diagnostic load tests
8.3 Procedures for the execution of diagnostic load testing
8.4 Processing diagnostic load testing results
8.5 Evaluation of diagnostic load testing results
8.6 Summary and conclusions
References
Appendix: Determination of Experimental Rating Factor According to Barker

Chapter 9 Example Field Test to Load Rate a Prestressed Concrete Bridge
Eli S. Hernandez and John J. Myers
9.1 Introduction
9.2 Sample bridge description
9.3 Bridge instrumentation plan
9.4 Diagnostic load test program
9.5 Test results
9.6 Girder distribution factors
9.7 Load rating of Bridge A7957 by field load testing
9.8 Recommendations
9.9 Summary
References

Chapter 10 Example Load Test: Diagnostic Testing of a Concrete Bridge with a Large Skew Angle
Mauricio Diaz Arancibia and Pinar Okumus
10.1 Summary
10.2 Characteristics of the bridge tested
10.3 Goals of load testing
10.4 Preliminary analytical model
10.5 Coordination of the load test
10.6 Instrumentation plan
10.7 Data acquisition
10.8 Loading
10.9 Planning and scheduling
10.10 Redundancy and repeatability
10.11 Results
10.12 Conclusions and recommendations
Ackowledgements
References

Chapter 11 Diagnostic Load Testing of Bridges – Background and Examples of Application
Piotr Olaszek and Joan R. Casas
11.1 Background
11.2 Examples of diagnostic load testing
11.3 Conclusions and recommendations for practice
References

Chapter 12 Field Testing of Pedestrian Bridges
Darius Bačinskas, Ronaldas Jakubovskis and Arturas Kilikevičius
12.1 Introduction
12.2 Preparation for testing
12.3 Organization of the tests
12.4 Analysis of test results
12.5 Theoretical modeling of tested bridge
12.6 Concluding remarks
Acknowledgments
References

-----

Part I Proof Load Testing of Bridges

Chapter 1 Methodology for Proof Load Testing
Eva O. L. Lantsoght
1.1 Introduction
1.2 Determination of target proof load
1.3 Procedures for proof load testing
1.4 Processing of proof load testing results
1.5 Bridge assessment based on proof load tests
1.6 Summary and conclusions
References

Chapter 2 Load Rating of Prestressed Concrete Bridges without Design Plans by Nondestructive Field Testing
David V. Jauregui, Brad D. Weldon, and Carlos V. Aguilar
2.1 Introduction
2.2 Inspection and evaluation procedures
2.3 Case studies
2.4 Conclusions
References

Chapter 3 Example of Proof Load Testing from Europe
Eva O. L. Lantsoght, Dick A. Hordijk, Rutger T. Koekkoek, and Cor van der Veen
3.1 Introduction to viaduct Zijlweg
3.2 Preparation of proof load test
3.3 Execution of proof load test
3.4 Post-processing and rating
3.5 Summary and conclusions
Acknowledgments
References

Part II Testing of Buildings

Chapter 4 Load Testing of Concrete Building Constructions
Gregor Schacht, Guido Bolle, and Steffen Marx
4.1 Historical development of load testing in Europe
4.2 Load testing of existing concrete building constructions
4.3 New developments
4.4 Practical recommendations
4.5 Summary and conclusions
References

Part III Advances in Measurement Techniques for Load Testing

Chapter 5 Digital Image and Video-Based Measurements
Mohamad Alipour, Ali Shariati, Thomas Schumacher, Devin K. Harris, and C. J. Riley
5.1 Introduction
5.2 Digital image correlation (DIC) for deformation measurements
5.3 Eulerian virtual visual sensors (VVS) for natural frequency measurements
5.4 Recommendations for practice
5.5 Summary and conclusions
5.6 Outlook and future trends
Acknowledgments
References

Chapter 6 Acoustic Emission Measurements for Load Testing
Mohamed ElBatanouny, Rafal Anay, Marwa A. Abdelrahman, and Paul Ziehl
6.1 Introduction
6.2 Acoustic emission–based damage identification
6.3 Source location during load tests
6.4 Discussion and recommendations for field applications
References

Chapter 7 Fiber Optics for Load Testing
Joan R. Casas, António Barrias, Gerardo Rodriguez Gutiérrez, and Sergi Villalba
7.1 Introduction
7.2 Distributed optical fibers in load testing
7.3 Conclusions
Acknowledgments
References

Chapter 8 Deflection Measurement on Bridges by Radar Techniques
Carmelo Gentile
8.1 Introduction
8.2 Radar technology and the microwave interferometer
8.3 Accuracy and validation of the radar technique
8.4 Static and dynamic tests of a steel-composite bridge
8.5 A challenging application: structural health monitoring of stay cables
8.6 Summary
Acknowledgments
References

Part IV Load Testing in the Framework of Reliability-Based Decision-Making and Bridge Management Decisions

Chapter 9 Reliability-Based Analysis and Life-Cycle Management of Load Tests
Dan M. Frangopol, David Y. Yang, Eva O. L. Lantsoght, and Raphael D. J. M. Steenbergen
9.1 Introduction
9.2 Influence of load testing on reliability index
9.3 Required target load for updating reliability index
9.4 Systems reliability considerations
9.5 Life-cycle cost considerations
9.6 Summary and conclusions
References

Chapter 10 Determination of Remaining Service Life of Reinforced Concrete Bridge Structures in Corrosive Environments after Load Testing
Dimitri V. Val and Mark G. Stewart
10.1 Introduction
10.2 Deterioration of RC structures in corrosive environments
10.3 Reliability-based approach to structural assessment
10.4 Corrosion initiation modeling
10.5 Corrosion propagation modeling
10.6 Effect of spatial variability on corrosion initiation and propagation
10.7 Influence of climate change
10.8 Illustrative examples
10.9 Summary
References 328

Chapter 11 Load Testing as Part of Bridge Management in Sweden
Lennart Elfgren, Bjorn Täljsten, and Thomas Blanksvärd
11.1 Introduction
11.2 History
11.3 Present practice
11.4 Future
11.5 Conclusions
Acknowledgments
References

Chapter 12 Load Testing as Part of Bridge Management in the Netherlands
Ane de Boer
12.1 Introduction
12.2 Overview of load tests on existing structures
12.3 Inspections and re-examination
12.4 Conclusions and outlook
References

Part V Conclusions and Outlook

Chaper 13 Conclusions and Outlook
Eva O. L. Lantsoght
13.1 Current body of knowledge on load testing
13.2 Current research and open research questions
13.3 Conclusions and practical recommendations

How do steel fibers improve the shear capacity of reinforced concrete beams without stirrups?

I've recently published a review paper in the journal Composites Part B: Engineering titled "How do steel fibers improve the shear capacity of reinforced concrete beams without stirrups?".

The paper addresses the different shear-carrying mechanisms, and the effect of adding steel fibers to a concrete mix on these shear-carrying mechanisms in specimens with steel tension reinforcement. This review paper is the result of my Poligrant 2017-2018, continued as a Poligrant 2018-2019. While originally I started the research to find a way to extend to Critical Shear Displacement Theory with an extra term that takes the contribution of the fibers into account, reading on the topic and understanding the mechanics further led me to the insight that the simple solution of adding an extra term is insufficient. This paper shows how all shear-carrying mechanisms are influenced by the presence of fibers.

The abstract is:
Even though the structural behavior steel fiber reinforced concrete (SFRC) has been extensively researched, structural applications are still limited. One barrier to its implementation is the lack of mechanical models that describe the behaviour of SFRC members failing in shear. This paper reviews the effect of steel fibers on the different mechanisms of shear transfer and combines the observations from the literature regarding the parameters that affect the shear capacity of SFRC. Additionally, a selection of currently available expressions for the shear capacity of SFRC is presented. This paper reviews the current state-of-the-art on the shear capacity of SFRC elements without shear reinforcement, shows the lacks in our current understanding on the shear behaviour of SFRC elements without shear reinforcement, and outlines the steps necessary to address these lacks. The presented work aims to be a framework for (experimental) efforts addressing the shear capacity of SFRC members without shear reinforcement.

You can access the article here.

Fatigue Assessment of Prestressed Concrete Slab-Between-Girder Bridges

My colleagues and I recently published a paper in Applied Sciences, Special Issue Fatigue and Fracture of Non-metallic Materials and Structures titled "Fatigue Assessment of Prestressed Concrete Slab-Between-Girder Bridges".

You can download the open access paper here. If you're interested in it, the preprint is also publicly available.

This paper is the last journal paper in the suite of papers that deal with fatigue in slab-between-girder bridges. In this paper, we went one step further than in the previous ones, which dealt with the experiments only. Here, we developed a method to assess existing slab-between-girder bridges based on the experimental results. It's a rather practical and practice-oriented paper.

The abstract is:
In the Netherlands, the assessment of existing prestressed concrete slab-between-girder bridges has revealed that the thin, transversely prestressed slabs may be critical for static and fatigue punching when evaluated using the recently introduced Eurocodes. On the other hand, compressive membrane action increases the capacity of these slabs, and it changes the failure mode from bending to punching shear. To improve the assessment of the existing prestressed slab-between-girder bridges in the Netherlands, two 1:2 scale models of an existing bridge, i.e., the Van Brienenoord Bridge, were built in the laboratory and tested monotonically, as well as under cycles of loading. The result of these experiments revealed: (1) the static strength of the decks, which showed that compressive membrane action significantly enhanced the punching capacity, and (2) the Wöhler curve of the decks, showed that the compressive membrane action remains under fatigue loading. The experimental results could then be used in the assessment of the most critical existing slab-between-girder bridges. The outcome was that the bridge had sufficient punching capacity for static and fatigue loads and, therefore, the existing slab-between-girder bridges in the Netherlands fulfilled the code requirements for static and fatigue punching.

Two papers from the ACI Structural Journal

My collaborators and I recently published two papers related to the topic of fatigue in slab-between-girder bridges. These paper are published in the ACI Structural Journal, Vol 116 nr 4. The two papers deal with two series of experiments: the first series had transversely prestressed decks between prestressed T-girders, and the second series had transversely prestressed decks between inverted T-girders / bulb T-girders. I worked on part of the analysis of the test results, and reporting the results in journal papers during the summer of 2018.

The abstract of the first paper is:
In the Netherlands, slab-between-girder bridges with prestressed girders and transversely prestressed decks in between the girders require assessment. Static testing showed that compressive membrane action increases the capacity of these structures and that the decks fail in punching shear. The next question is if compressive membrane action also increases the capacity of these decks under repeated loads. Therefore, the same half-scale bridge structure as used for the static tests was subjected to repeated loads at different fractions of the maximum static load, different loading sequences, and for single and double concentrated loads. A relationship between the load level and number of cycles at failure (S-N curve) for the assessment of these bridges is proposed, but the influence of the loading sequence was not successfully quantified yet. The conclusion of the experiments is that compressive membrane action enhances the punching capacity of transversely prestressed thin decks subjected to repeated loads. 



The abstract of the second paper is:
Previous research showed that the capacity of existing slab-between-girder bridges is larger than expected based on the punching shear capacity prescribed by the governing codes, as a result of compressive membrane action. A first series of fatigue tests confirmed that compressive membrane action also acts under cycles of loading. However, a single experiment in which first a number of cycles with a higher load level and then with a lower load level were applied, seemed to indicate that this loading sequence shortens the fatigue life. This topic was further investigated in a second series of fatigue tests with three static tests and ten fatigue tests. The parameters that were varied are the sequence of loading and the effect of a single or a double wheel print. The results show that the sequence of load levels does not influence the fatigue life.

Presentation about Load Testing of Structures

The ACI USFQ Student Chapter organized a session with presentations last October. I gave a general introduction to the session, as well as an overview of load testing of structures. You can find my slides here:

Load testing of structures from Eva Lantsoght

Stop Criteria for Flexure for Proof Load Testing of Reinforced Concrete Structures

My collaborators and myself recently published a paper titled "Stop Criteria for Flexure for Proof Load Testing of Reinforced Concrete Structures" in Frontiers in Built Environment - Bridge Engineering.

The work in this paper was sponsored by my Chancellor grant of 2016. Three years later, and I finally managed to wrap my head around the topic. Sometimes, we need to let our ideas stew for a while and revisit them every now and then until I have a good idea - this paper was such a situation.

The abstract is as follows:
Existing bridges with large uncertainties can be assessed with a proof load test. In a proof load test, a load representative of the factored live load is applied to the bridge at the critical position. If the bridge can carry this load without distress, the proof load test shows experimentally that the bridge fulfills the requirements of the code. Because large loads are applied during proof load tests, the structure or element that is tested needs to be carefully monitored during the test. The monitored structural responses are interpreted in terms of stop criteria. Existing stop criteria for flexure in reinforced concrete can be extended with theoretical considerations. These proposed stop criteria are then verified with experimental results: reinforced concrete beams failing in flexure and tested in the laboratory, a collapse test on an existing reinforced concrete slab bridge that reached flexural distress, and the pilot proof load tests that were carried out in the Netherlands and in which no distress was observed. The tests in which failure was obtained are used to evaluate the margin of safety provided by the proposed stop criteria. The available pilot proof load tests are analyzed to see if the proposed stop criteria are not overly conservative. The result of this comparison is that the stop criteria are never exceeded. Therefore, the proposed stop criteria can be used for proof load tests for the failure mode of bending moment in reinforced concrete structures.

Database of Shear Experiments on Steel Fiber Reinforced Concrete Beams without Stirrups

I recently published a paper in Materials titled "Database of Shear Experiments on Steel Fiber Reinforced Concrete Beams without Stirrups". This is my first paper as a single author, of one of my new research projects in Ecuador related to the shear capacity of steel fiber reinforced concrete.

The abstract is as follows:

Adding steel fibers to concrete improves the capacity in tension-driven failure modes. An example is the shear capacity in steel fiber reinforced concrete (SFRC) beams with longitudinal reinforcement and without shear reinforcement. Since no mechanical models exist that can fully describe the behavior of SFRC beams without shear reinforcement failing in shear, a number of empirical equations have been suggested in the past. This paper compiles the existing empirical equations and code provisions for the prediction of the shear capacity of SFRC beams failing in shear as well as a database of 488 experiments reported in the literature. The experimental shear capacities from the database are then compared to the prediction equations. This comparison shows a large scatter on the ratio of experimental to predicted values. The practice of defining the tensile strength of SFRC based on different experiments internationally makes the comparison difficult. For design purposes, the code prediction methods based on the Eurocode shear expression provide reasonable results (with coefficients of variation on the ratio tested/predicted shear capacities of 27–29%). None of the currently available methods properly describe the behavior of SFRC beams failing in shear. As such, this work shows the need for studies that address the different shear-carrying mechanisms in SFRC and its crack kinematics.

10 Planning Concepts I Wish I'd known Before my PhD

On March 14th, I gave a presentation for the opening of the academic year as part of the XV week of Postgraduate Studies for the School of Engineering at Universidade de Sao Paolo in Sao Carlos. The topic of this presentation was time management for graduate students.

I couldn't make the trip to Brazil (the Toddler Empress did not approve), but I gave the presentation by videoconference. I'm grateful to USP - Sao Carlos for hosting me.

Here are the slides of my presentation:

10 Planning Concepts I wish I'd known Before my PhD from Eva Lantsoght

The recording of the presentation is on YouTube:

Publication metrics

I recently ran a poll on Twitter on which platform is most used for publication metrics. While in my field it seems to be Scopus, the consensus of the poll is clear: Google Scholar!

Here's the wake of the poll

Proof load testing of viaduct De Beek

I recently gave a presentation about a case study of a proof load test at the IABSE event organized by the national groups of Belgium and the Netherlands.

You can find the slides of the presentation here:

Proof load testing of viaduct De Beek from Eva Lantsoght

Two papers on the arched strut

In 2018, I was co-author of two papers on the topic of the arched strut - both were presented by my colleague Dr. Alexander.

The first paper, presented at the conference on Short and Medium Span Bridges in Quebec City, looks at the use of the arched strut for approach slabs of bridges and considers the effect of fatigue. The abstract is as follows:

Strut-and-tie models (STM) are appropriate for analyzing and designing disturbed regions in a reinforced concrete structure. The arched strut is an addition to the STM tool kit. It models the combination of disturbed behavior in one direction with slender behavior in the perpendicular direction. The arched strut is part of the Strip Model, originally developed to model load transfer between a two-way slab and its supporting column.
It is difficult to define the geometry of conventional STM in a slab. One end of the strut is connected to the concentrated load but there is no similar feature to define the position of the other end. The arched strut is a means of addressing this difficulty. The method does not model a failure criterion; rather, it defines an acceptable load path that meets static and material constraints.
This paper summarizes the technique in the context of column-slab connections, develops the modifications needed to model conventional punching of an approach slab under a patch load, and proposes additional modifications to adapt the analysis to fatigue loading.
The principal findings are that, while the analysis for two-way shear given in S6-14 are deficient, the punching strength of a typical approach slab under both static and fatigue loading from a CL-W truck should not be a concern.


The second paper, presented at IABSE Nantes in September 2018, describes the arched strut from a more general perspective and shows how the arched strut can be used as a tool in the strut-and-tie models toolkit. The abstract is as follows:

The arched strut is an addition to the strut-and-tie (STM) tool kit. It models the combination of disturbed behavior in one direction with slender behavior in the perpendicular direction. Common applications for the arched strut are in the design of connections between a reinforced concrete slab and its supporting columns or punching of bridge decks.
The arched strut can be applied to any combination of shear and moment at a column-slab connection. The designer is given clear guidance on anchorage requirements for the flexural reinforcement and the expected ductility of the connection. The method does not model a particular failure criterion; rather, it defines an acceptable load path that meets design objectives.
The paper outlines the basis for the arched strut and presents examples illustrating its use in design.

Getting into the habit... A PhD student’s perspective on data management

Today's post is a guest post by Annemarie Hildegard Eckes. Annemarie is a PhD student in Biogeography at the department of Geography in Cambridge, working with all sorts of data and formats: Climate data in .netcdf, and .txt format. Tree growth dynamics data in .excel spreadsheets. Tree ring anatomical data as images, and later as .txt -files. Her project involves the development of a computer model that simulates how a tree stem grows in width, in response to the environment (temperature, precipitation etc..). The ultimate aim is for the final model to be used in the vegetation model HYBRID, developed by Andrew Friend, to help in projections on how vegetation will behave under climate change in the future.
All this data needed to be described and managed well, for example: who gave it to me? What did I do to it? How to make sure I don’t lose it? How do I version control and document the scripts that use the data and the model that I compare the data against? How will I make sure the data and scripts during my PhD will be shared with the community and what standards should I adhere to, to make reusability really easy? Annemarie didn’t feel that she had enough expertise in this, but wanted to do it right from the start. Before she started her PhD she worked with a database for crop data. That’s when she really learned how poorly documented and poorly organised research data can slow down a research project immensely and she did not want to make the same mistake which she has seen experienced researchers make. Her previous experience and motivation to acquire good habits right from the start got hervery interested in RDM and made me an advocate for it as Cambridge and JISC data champion.

A PhD project is a significant period in a researcher’s life. During the project, we generally must develop our own research question and methodology, generate data and publish our results in papers and as a final thesis. Such a project is meant to teach us how to conduct research. This is the crucial time in which we as early career researchers should pick up the right habits for our future as successful scientists.

Research Data Management (RDM) is an important day-to-day activity for Scientists. Research output, collaborations and productivity depend on it. No surprise, then, that the documentation of a project’s RDM has become a requirement for many grant applications. By writing a Data Management Plan as part of the PhD proposal, we students are not only confronted with the whole data lifecycle of our research data before it is even generated, but we also gain experience in how such a plan is written. Early career researchers such as us PhD students should not underestimate the importance of skills in RDM, which in my opinion are nowadays pretty essential for a good scientific career.

I think “data management” in its most basic form starts with managing your email inbox. To me, it often is simply the act of keeping all information that I deal with in order. We all do it more or less all the time. The tricky bit is how to deal with what we call research data the best way. As we may be new to the research subject of our PhD, we may not know how best to collect, document and manage the data we are dealing with.

PhD students and RDM training
The point of a PhD is to learn how to conduct research and RDM is part of that process. But sometimes it may be important to learn about good practices right from the beginning, rather than getting into bad habits that cause problems later in your research.

I think that training in RDM for us PhD students is useful for two reasons, firstly to learn the right habits and secondly to enhance productivity throughout the duration of the PhD.

Figure 1 RDM-smileys: In talks I give about research data management, I like to use these smileys in my presentations. The first row at the beginning and the second row at the end of the talk. The principle behind these smileys is based on a presentation by the Cambridge office for Scholarly communication.

I conducted a survey and interviews at our department, asking fellow PhD students about their data management practices, the data types they collected and their training needs. Participants at the end of their PhD indicated that they generally felt prepared to conduct data management in their coming research career, while they also say that they would have benefited from training at the beginning of their PhD. In one interview, this came out especially, with one interviewee stating that “the lack of training in research data management slowed me down”. This shows that while we PhD students have ourselves learned more on the aspects of data management during our PhD, early training would have made us more productive - and certainly more happy ( see figure 1)! Please check this blog entry where I discuss some of the survey results.

PhD students and the data tree training platform
An online platform that provides training on RDM for PhD students is in my opinion a much needed resource! I think that at the beginning of my PhD, I would have been happy if Data Tree had existed to provide me with a good overview of RDM.

As an online course it is accessible to all PhD students at any time. And with some of us having crazy schedules and weird working and sleeping habits, doing such training in our own time might help us remain flexible. It’s my experience that people do not spend the time to come to talks or workshops. While my survey showed clearly that PhD students do think RDM is important, the turnout to stand-alone talks, workshops and other events I have organised has been rather low. I hope that such a continuously accessible platform would decrease the barrier to learning more about RDM.

While time and timing might be a barrier to learning about and performing RDM, I wonder whether the main reason PhD for students not attending training courses is the lack of priority. For many busy PhD students, RDM never seems to be a priority- and neither does RDM training. Therefore, PhD students will probably need to be encouraged in some ways to make use of this online platform. One option could be that Universities make this online course count in their PhD training logs.

It will be interesting to see how the platform is taken up and what strategies are used to encourage us busy PhD students to do this online course. I wish this platform a good start, a lot of users and that it makes a significant contribution to PhD students’ success in RDM!

Moving towards more Open Access publishing?

Eleven countries in Europe formed cOAlition-S, with as its basic principle:

"After 1 January 2020 scientific publications on the results from research funded by public grants provided by national and European research councils and funding bodies, must be published in compliant Open Access Journals or on compliant Open Access Platforms.”

I wondered if researchers are planning to move more towards open access, and ran a poll on the topic.

Here are the poll and its wake:

PhD Talk for AcademicTransfer: Activism in academia

This post is part of the series PhD Talk for AcademicTransfer: posts written for the Dutch academic career network AcademicTransfer, your go-to resource for all research positions in the Netherlands.

These posts are sponsored by AcademicTransfer, and tailored to those of you interested in pursuing a research position in the Netherlands.

If these posts raise your interest in working as a researcher in the Netherlands, even better - and feel free to fire away any questions you might have on this topic!

Activism in academia is a hot topic. Some argue that our only responsibility is to do the research, and publish our results - and the rest will sort itself out: the right people will pick up on our conclusions and turn this into policies and actionable items. Some go even further, and say that activism is a threat to carrying out research in a neutral environment.

I beg to differ - with more and more voices trying to persuade that science is something almost like a religion (you believe in it or not), I feel compelled to roll up my sleeves and turn my work into more practical and actionable items. The wake-up call for me was the latest IPCC report and the loud and clear alarm bells our fellow scientists are ringing. I spent quite some time wondering how I can contribute. While I'm only exploring these options recently, I wanted to share these with you, and get your feedback on this!

Here are some of the ideas that I collected:

1. Develop case studies
Think about how your cause of interest is affected by your field. For example, in my case, the cement used for building concrete structures is a large contributor to the world's CO2 emissions. Since a while, I've been adding calculations of carbon footprint and driver delays (as a measure of social cost) when I want to estimate the cost of a certain decision (replacement, testing, maintenance...) of an existing bridge. Presenting the results in such a format can shine a different light on the choices we make.

Another example could be that you want to see more gender balance in your field and/or institution. A first step could be to simply gather data: which % of students are female? Which % of faculty members, deans, etc?

2. Use speaking opportunities
When you are invited to give a presentation, and depending on the audience, take the chance to talk about how your cause of interest is related to your field. In the past, I've been taking the opportunity to talk about maintenance of existing structures when invited to speak to a general audience of the construction industry in Ecuador, since I feel that all attention here goes to building new structures, after which we just turn our back to this structure and never give it the maintenance it needs to thrive. At a next opportunity, I would like to talk about steps the construction industry can take to be more climate-conscious and eventually CO2-neutral.

3. Volunteer your free time
If you feel that in your professional life, it is difficult to link your cause of interest and your work, then you can consider volunteering some of your time to contribute to your cause. You can also pledge to give a certain percentage of your income every month to a charity that fights for your cause.

I must say that, even though I would love to go out and do volunteering work in the Amazon, my current family situation is not very compatible with this (my toddler would probably run off into the jungle or eat a poisonous bug). I've been thinking about this option, but haven't been able to realize it yet - nor have I been able to pledge part of my income constantly to a cause; I chip in when I can for now.

4. Take on a side research project that is related to your cause of interest
Sometimes, I feel like I am not doing research in the field that matters most for the future of humanity. I wonder if I could do more if I had been a researcher studying, for example, infectious diseases or climate change directly. For now though, I want to see if I can volunteer some of my research time to developing recommendations for the local construction industry, so that they can reduce their carbon footprint and fresh water use. Once I have these recommendations ready, I need to see how I can communicate these effectively - not with a boring report, but perhaps through infographics and lots of visuals.

5. Lead by example
I once read (and unfortunately forgot where) that as university professors, we have a responsibility to lead by example. Driving to work in a SUV and then talking about carbon footprints sends conflicting messages to our students. In our daily choices, we should show to way forward. I try to set an example by walking my commute (for now, I still live close to campus), eating no animal products, and trying as much as possible to sort out my trash and recycle. I'm also much more conscious about my conference travel, and reducing this as much as possible to limit my CO2 emissions related to air travel (and also because my daughter doesn't do well when I'm away from home).

6. Teach students how to read science
If we want people to make informed decisions, they need to learn how to interpret and analyze information. In the era of fake news, there are sadly predatory journals that have been publishing bogus science (for example, studies supporting antivaxxer claims), which gives even more fuel to those who say that "scientists are in disagreement" on topics such as vaccinations and global warming. It's important we teach our students where to find peer-reviewed articles (and certainly, post-publication peer review and "endorsements" of researchers for published articles can be an extra confirmation of quality), and teach them the basics of the scientific methods, so that they can check if the presented methods are valid. I am even leaning towards saying that this skill should be part of the high school curriculum.