Predicting the Shear Capacity of Reinforced Concrete Slabs subjected to Concentrated Loads close to Supports with the Modified Bond Model

For IABSE 2014, I published the first paper about the theoretical work about the Modified Bond Model from my dissertation.

The abstract of the paper is:

The shear problem is typically studied by testing small, heavily reinforced, slender beams subjected to concentrated loads, resulting in a beam shear failure, or by testing slab-column connections, resulting in a punching shear failure. Slabs subjected to concentrated loads close to supports, as occurring when truck loads are placed on slab bridges, are much less studied. For this purpose, the Bond Model for concentric punching shear was studied at first. Then, modifications were made, resulting in the Modified Bond Model. The Modified Bond Model takes into account the enhanced capacity resulting from the direct strut that forms between the load and the support. Moreover, the Modified Bond Model is able to deal with moment changes between the support and the span, as occurs near continuous supports, and can take into account the reduction in capacity when the load is placed near to the edge. The resulting Modified Bond Model is compared to the results of experiments that were carried out at the Stevin laboratory. As compared to the Eurocodes (NEN-EN 1992-1-1:2005) and the ACI code (ACI 318-11), the Modified Bond Model leads to a better prediction.

Predicting the Shear Capacity of Reinforced Concrete Slabs subjected to Concentrated Loads close to Supports with the Modified Bond Model from Eva Lantsoght

Practical Application of Transverse Load Redistribution in Reinforced Concrete Solid Slab Bridges

I recently presented a paper titled "Practical Application of Transverse Load Redistribution in Reinforced Concrete Solid Slab Bridges" at the 9th conference on Short and Medium Span Bridges in Calgary.

The abstract of the paper is the following:

For an initial design or assessment of a reinforced concrete solid slab bridge, spreadsheet-based or hand calculations are typically used. The shear stress is compared to the shear capacity as prescribed by the code. The distributed loads result in a uniform shear stress at the support. Concentrated loads are less straightforward to take into account. It is known that transverse load redistribution occurs in slabs. To explore the topic of transverse load redistribution, experiments on elements subjected to a concentrated load close to the support were carried out. These elements had an increasing width, starting at 0.5 m and increasing with steps of 0.5 m up to 2.5 m, so that the effect of transverse load redistribution could be studied. The threshold effective width resulting from the experiments was then compared to load spreading methods, in order to give recommendations for the practical use with concentrated loads. It was found that the load spreading method as used in French practice is to be preferred. As compared to load spreading methods that were used previously, the French load spreading method results in smaller shear stresses at the support. This result allows for more economic designs and provides a better assessment tool.

The slides of the presentation are given below:

Practical Application of Transverse Load Redistribution in Reinforced Concrete Solid Slab Bridges from Eva Lantsoght

Recommendations for the Shear Assessment of Reinforced Concrete Solid Slab Bridges

At IABMAS 2014 in Shanghai, I presented a paper titled "Recommendations for the Shear Assessment of Reinforced Concrete Solid Slab Bridges".

The abstract of the paper is:

As a result of the heavier live load models and more conservative shear approaches prescribed by the recently implemented Eurocodes, a large number of existing reinforced concrete solid slab bridges in the Netherlands were found to be shear-critical. The beneficial effect of the transverse load redistribution in slabs under concentrated loads is not taken into account. To quantify this effect, a comprehensive number of experiments was carried out. These results are used to formulate recommendations for the assessment practice for the case of solid slab bridges. The recommendations focus on the effective width over which the axle load can be distributed and its lower bound, the beneficial effect of transverse load redistribution and the influence of the yield strength of the reinforcement on the lower bound of the shear capacity. These recommendations are implemented in the “Quick Scan” method, leading to a significant reduction of the shear stresses.

The slides of the presentation are uploaded here as well:

Recommendations for the Shear Assessment of Reinforced Concrete Solid Slab Bridges from Eva Lantsoght

How to present your proposal

Continuing with the pile of questions that I have which deserve a spot in the Q&A series, I would like to expand on the following question, which I got through Twitter:

I have presentation on my proposal, please help me with details I should include on my slides @evalantsoght @PhDForum @phdchats
— Vke Ziglone (@ziglone) October 1, 2013

First of all, you might like to think about the outline of your presentation. Don't just throw information randomly at your listeners. Instead, follow a logic. Essentially, there are two outlines you can use:
1. Deduction of results from experiments
- Introduction / Motivation of the research
- Literature review / background info
- Experiments
- Analysis of the experiments
- Results
- Conclusions
2. QOD approach
- Introduction / Motivation of the research
- Literature review / background info
- Proposition
- Proof (this can be based on experiments)
- QOD / Conclusions

With that said, we are talking here about a proposal, so the research is just starting, and you are mostly focusing on the value of your research.
Since the goal of your proposal presentation is to convince your committee that your line of research is worth leading to a doctoral dissertation, you need use a persuasive presentation rather than an informative presentation.
Moreover, since you are defending your proposal, you probably only have a vague idea yet of the direction in which your data analysis will lead you. You can't promise certain results in your presentation, so you should focus on the motivation of the research.

If you want to take that focus on your motivation one step farther, you can dedicate one slide to the greater impact of this research. Will it have an influence on the (local) economy? Will your results be valuable for the industry? Will your research fit somewhere in the cure for a disease? Try to get a helicopter overview of how your research would fit into your field, and then into the world.

Come prepared as well: have an idea of the methods that you will be using, have a good understanding of the literature in this field, and do a careful estimate of what your research results might look like. For example: will you be gathering data on a certain topic, or will you develop software or a tech tool? Have an idea of the direction where you want to go.

Which other elements should this reader add to the slides of his proposal presentation? Share your thoughts and suggestions in the comments below!

Effective Width in Shear of Reinforced Concrete Solid Slab Bridges under Wheel Loads

Just like last year, I've given a presentation at the Annual Meeting of the Transportation Research Board. Last year, I wrote as well about navigating TRB for the first time, and how I enjoyed using the conference app.


Like last year, my presentation was in the section about Concrete Bridges. Here is the abstract of the corresponding paper, that is published in the Annual Compendium of Papers:

For the assessment of reinforced concrete slab bridges in the Netherlands, the shear stress resulting from the dead loads and live loads is determined in a spreadsheet or from a finite element model. In a spreadsheet-based approach, an assumption for the distribution of the loads from the wheel prints is necessary. When finite element methods are used, it is necessary to determine over which length (a multiple of the effective depth) the peak shear stress can be distributed for comparison to the design shear capacity.
To recommend a load-spreading method, experiments were executed on slab strips of increasing widths. The shear capacity did not increase with the increasing width upon passing a threshold. This threshold is compared to different load spreading methods, indicating that a distribution from the far side of the wheel print is to be preferred. This recommendation is also supported by the results of a statistical analysis and the stress distribution in nonlinear finite element models.
To find the distribution width in a finite element method, a numerical model is compared to an experiment on a slab subjected to a concentrated load in which the support consists of a line of 7 bearings equipped with load cells measuring the reaction forces. These measurements were compared to the stress profile at the support from the model, showing that the peak can be distributed over 4 times the effective depth.
These recommendations for the effective width and distribution width are research-based tools that replace the previously used rules of thumb resulting from engineering judgement.

Effective Width in Shear of Reinforced Concrete Solid Slab Bridges under Wheel Loads from Eva Lantsoght

Applying Experimental Results to the Shear Assessment Method for Solid Slab Bridges

I recently presented a overview of the recommendations for shear assessment from my PhD research at Concrete 2013 in Gold Coast, Australia. In this paper and presentation, we looked at the our experiments, and how these led to the recommendations for shear assessment.

The abstract of the paper is the following:

"The combination of increased live loads and a more conservative shear capacity in the recently implemented Eurocodes, resulted in a large number of existing solid slab bridges in the Netherlands being shear-critical upon assessment. However, an enhancement of the shear capacity can occur in slabs under concentrated wheel loads due to transverse load redistribution. To quantify this effect, a comprehensive series of experiments on slabs and slabs strips under a concentrated load near to the support and under a combination of a concentrated and a line load was carried out. The experiments show the difference in behaviour for slabs, carrying the load in a two-dimensional way, as compared to beams in shear. The results from the laboratory research are used to develop recommendations, that are easily used in combination with the codes. These recommendations are implemented in a spreadsheet-based first-level assessment tool, the Quick Scan method. The assessment with this tool of selected cases of existing solid slab bridges shows that applying the experimental results into the assessment practice leads to an improved selection ability of the Quick Scan method."

You can find the slides here:

Applying Experimental Results to the Shear Assessment Method for Solid Slab Bridges from Eva Lantsoght

Lecture at Vrije Universiteit Brussel

On September 10th 2013, I gave a lecture about my PhD research at my alma mater, the Vrije Universiteit Brussel in Brussels, Belgium.

Even though I graduated from Brussels in 2008, I have kept in touch every now and then with my former adviser and one of my former professors. When they invited me to give a lecture to their research group about my doctoral dissertation, I was more than delighted.

The abstract of the lecture was the following:

The capacity of existing reinforced concrete slab bridges in the Netherlands is subject to discussion for two reasons: 1) the increase in traffic loads and volumes and 2) the fact that the majority of the bridges was built before 1976, and these structures are reaching the end of their service life. Upon assessment according to the governing codes, a large number of slab bridges are found to be shear-critical. The shear capacity from the codes, however, is the result of experiments on beam in shear. Slabs subjected to concentrated loads (such as wheel loads of a truck) are expected to have a larger bearing capacity as a result of the transverse distribution capacity.

In this research, the capacity of slabs subjected to concentrated loads close to supports is studied. A literature review, resulting in a database of 215 experiments from the literature, is used to study the mechanisms that occur in one-way shear (beam shear) and two-way shear (punching shear). For this research, 156 experiments on 38 scale models (scale 1:2) of slab bridges are executed. The experimental results are analyzed in a parameter study.

Two methods are proposed to determine the shear capacity of slabs subjected to concentrated loads close to supports: 1) the Modified Bond Model, a new theory; and 2) an extension of the Eurocode provisions based on a probabilistic analysis according to the safety philosophy of the Eurocodes.

Finally, the connection to the assessment practice is made by means of recommendations, by improving the Quick Scan tool of the Ministry of Infrastructure and the Environment, and then applying this method to existing slab bridges.

You can find the slides of this lecture here:

The Essential Conference Clothes

As I started to travel to conferences, I often found myself faced with the "What should I wear?" dilemma. Being in my mid twenties, I didn't want to give off the impression of being the "lost student" out there without any authority on the topic, nor did I want to dress like someone in their forties - and certainly I didn't want to wrong type of attention you might get as a women in a men's world.

While most advice online on what to wear to conferences and/or as a starting professor seems to focus on being neutral, I'm not too convinced about all the black, navy and grey that is being advised*. It's not because you decided to be a scientist, that you should adhere to society's impression that equates being a scientist to being boring!

Therefore, by all accounts, start from what you like wearing. Are you more comfortable in pants or do you prefer skirts and dresses? What colors do you naturally gravitate towards? I like wearing dresses, if necessary layered over long-sleeved t-shirts. As a result my natural choice would be a dress with a jacket. I prefer clothes with a lot of red and purple, so by no means I'd force myself to wear just navy, grey and black.

If you aren't sure about what style would work for you, borrow some items from a friend, a parent or a sibling. If nobody is willing to send you off with their best clothes to a conference, then go and weed through thrift stores to look for items that you want to try out.

Over time, and after visiting a large number of conferences, I've come up with the following list of essential clothes for conferences:

1. Comfortable shoes

Aerosoles Roler Derby Pump (see more short heel shoes)

An obvious choice - you don't want to be limping around because you can't walk around an entire day on those heels. I swear by a pair of Naturalizer shoes and a pair of Aerosoles that I scored for about 30 bucks at DSW.

2. A white blouse

Alexander Wang Combo Blouse (see more white sleeveless blouses)

A staple in every wardrobe: try to find a blouse that fits well at the shoulders, the arms, the waist and -please- does not bulge at the buttons.

3. A suit

BOSS Black Melange Jacket (see more BOSS Black)

An easy option if you want to test the waters at a conference. Comfortable, and it gives you so many options: you can dress it up and down with accessories, your choice of shirt and you can wear the separates too in different combinations.

4. Good jackets

Banana Republic Metallic Sweater Blazer - New sly stone (see more banana republic jackets)

Whatever you wear, it looks instantly more dressed up if you add a jacket. Take enough time to find a few jackets that fit well and that are versatile, then start combining.

5. Tops

Jane Norman Floral Peplum Top (see more long peplum tops)

At my age, I think it's OK to wear a more casual top combined with a suit or jacket, instead of opting for a blouse. I usually add a flowery top to a suit, to keep everything light and to add a bit of my liking and young age.

6. Conference dinner dress

Essentiel Candle Leaf Printed Silk Dress (see more floral print dresses)

Unless your conference is super-formal, I think that it's acceptable to show a little more of your personal taste in the choice of your conference dinner dress. I typically opt for a printed dress, or an all-red dress - because that is what I like. And often the choice is a dress by Essentiel (a mildly affordable Belgian label).

7. Opaque tights

Wolford Individual 100 Leg Support Tights (see more wolford hosieries)

If you go for dresses or skirts, tights are still a must at conferences. You might opt for bare legs, but I never do so, also because I like how tights flatten bumps and streamline everything.

8. A big purse

Village Convertible Leather Tote Bag, Brown - Cole Haan (see more cole haan purses)

Unless you want to drag the conference bag around the entire time, you need a large purse that can fit the conference program, notes, preparation material and whatever you like to have with you. I use an over-sized dark brown leather bag that I've had for many years, but I like how the leather is weathering.

If you want some inspiration, this post on My Laser Boyfriend has a lot of information, and great looks too.

*I might be biased as I was spent too much time wearing a grey - blue - white uniform during my schooldays.

What are your essential conference clothes? Do you have your favorites already, or are you still searching?

Peak shear stress distribution in finite element models of concrete slabs

On September 2nd, I gave a presentation with the title: "Peak shear stress distribution in finite element models of concrete slabs" at the Fifth International Conference on Structural Engineering, Mechanics and Computation in Cape Town, South Africa.

What I presented at this conference was not part of my PhD research, but related to a side project that we did together with the Dutch Ministry of Infrastructure and the Environment.

The abstract of the paper associated with this presentation is the following:
For the evaluation of existing slab bridges in the Netherlands, the governing shear stress resulting from composite dead load and live loads is determined from a finite element model. It is necessary to determine over which length (expressed as a multiple of the effective depth) the peak shear stress can be distributed for comparison to the design shear capacity. To answer this question, a numerical model is compared to an experiment. A continuous reinforced concrete slab, representing a half-scale slab bridge, is tested under a concentrated load. The support consists of 7 bearings equipped with load cells, measuring the reaction force profile, that can be compared to the stress profile determined in the finite element model. The comparison of measured reaction force profiles over the support to finite element models results in a research-based distribution width that replaces the rules of thumb that were used until now.

Peak shear stress distribution in finite element models of concrete slabs from Eva Lantsoght

Presentation of my PhD Defense, "Lekenpraatje"

On June 14th 2013, I defended my doctoral dissertation at Delft University of Technology.
As I wrote before, the defense itself was the very end of the entire process of writing, editing, re-editing, publishing and finally defending my doctoral dissertation.

One of the elements of the defense at TU Delft itself is the so-called "lekenpraatje" - a presentation for the laymen.

For my "Lekenpraatje" I decided to touch upon a few elements of my dissertation:

• the background: why was this research necessary, and what has been (or has not been) done previously
• an overview of the experiments: because all my friends and family know is that I spent crawling around on a dusty laboratory floor for a little less than 3 years, resulting in my ever-white-dusted appearance at random events, or my needing to wash my labjeans at high temperatures to get the cement dust out.
• beams versus slabs: or something that I have been trying to repeat over and over again: slabs in one-way shear behave differently than beams!
• Modified Bond Model: the theory that I worked on, and I tried to explain it as graphically as I could.
• Application to practice: What have we won by investing in experiments? We found that we can decrease the loads for calculation with almost 20% as a result of the recommendations that we formulated from our experiments. That does NOT mean we've "won" 20%, as the shear provisions in the current code result in lower shear capacities. Overall, we did see a modest improvement based on our recommendations and the Eurocodes as compared to the previously used national code.

All in all, I had about 20 minutes' worth of time allotted for the presentation - and it was a little on the short side. 30 minutes would have been more comfortable to stop and expand on a few topics along the way, but I think (and hope) it gave my friends and family an idea of what I worked on for the past few years.

If you are interested in the slides of this presentation, you can find them here:

Lekenpraatje from Eva Lantsoght

Quick Scan Method - Presentation at the International Bridge Conference

I recently presented in a technical session of the International Bridge Conference in Pittsburgh - a great venue for practitioners and researchers that work on practical applications for the bridge engineering field.

The proceedings will be published over the summer, and the abstract of my paper is the following:

To assess a large number of reinforced concrete slab bridges for shear, recommendations based on experimental research are implemented in a spreadsheet-based “Quick Scan” method. In particular, transverse load redistribution is studied. The resulting method is used to study cases of existing slab bridges in The Netherlands, indicating the benefits of the proposed method as compared to previous “Quick Scan” approaches.

You can see my slides here:

Quick Scan Method from Eva Lantsoght

Prolonging the service life of existing reinforced concrete slab bridges

I recently presented a paper at the 1st International Conference on Concrete Sustainability in Tokyo, Japan. The next edition will be in Madrid, in 2016.

The abstract of my paper is:

A large number of existing reinforced concrete slab bridges are found to be insufficient for shear when calculated according to the governing codes. Seeking improved methods, for example, based on new experimental evidence, to assess the residual shear capacity and prolonging their service life can avoid large economic, environmental and social costs. Experimental results are combined with Monte Carlo simulations to quantify the increase in shear capacity in slabs as a result of transverse load redistribution. As a result, a larger number of slab bridges can remain in service.

You can find the slides here:

Prolonging the service life of existing reinforced concrete slab bridges from Eva Lantsoght

Presentation from ACI Fall Convention 2011

For those ACI members out there, I recently discovered that my lecture in the session on "Recent Developments in Reinforced Concrete Slab Analysis, Design and Serviceability" is available online.

If you're a student in structural engineering, you should consider becoming an ACI student member. It's free, and gives you access to the archives of the publications, presentations, and some additional documents.

Hope you enjoy watching the presentation, and, as always, feel free to get in touch with me when you have more questions!

IABSE presentation on slabs subjected to a combination of loads

At the IABSE spring conference in Rotterdam, I've presented a paper on slabs subjected to a combination of loads.

The abstract is as follows:

Previous experimental research at Delft University of Technology indicated an increased shear capacity of slabs under concentrated loads as a function of decreasing distance to the adjacent line support. Expressions have been derived for this increase, including the definition of an appropriate effective width. However, it is unknown if the uniformly distributed loads on solid slab bridges, e.g. due to dead loads, that act over the full width can be combined with the effects of concentrated loads acting only over the associated effective width at the support. To study this problem, additional experiments have been carried out at Delft University of Technology, in which a combination of loads consisting of a concentrated load close to the support and a line load over the full slab width are applied. The experimental results prove that the superposition principle applies to combinations of concentrated loads and distributed loads.

You can view the slides here:

Concrete slabs under a combination of loads from Eva Lantsoght

Presentation on Shear Assessment of Solid Slab Bridges

At the IABSE spring conference in Rotterdam, I've presented a paper on the shear assessment of solid slab bridges.

The abstract is as follows:

The capacity of reinforced concrete solid slab bridges in shear is assessed by comparing the design beam shear resistance to the design value of the applied shear force due to the permanent actions and live loads. Results from experiments on half-scale continuous slab bridges are used to develop a set of recommendations for the assessment of slab bridges in shear. A method is proposed allowing to take the transverse force redistribution in slabs under concentrated loads into account, as well as a horizontal load spreading method for the concentrated loads. For selected cases of existing straight solid slab bridges, a comparison is made between the results based on the shear capacity according to the Dutch Code NEN 6720 and from the combination of the Eurocode (EN 1992-1-1:2005) with the recommendations, showing an improved agreement.

You can view the slides here:

Shear Assessment of Slab Bridges from Eva Lantsoght

Presentation at fib Symposium 2013

Last April, I gave a presentation at the fib Symposium in Tel Aviv. The abstract of the paper and presentation is the following:

Existing solid slab bridges under a combination of wheel loads and distributed traffic loads sometimes do not fulfil the code requirements for shear. However, reinforced concrete slabs loaded close to the support are subjected to shear stresses which might result in a failure mode of combined punching and shear. This behaviour is studied in a first series of experiments on slabs under a concentrated load close to the support, and these experiments resulted in a set of recommendations. To verify if these recommendations can be used when assessing solid slab bridges under distributed and concentrated loads, slabs under a combination of a line load, representing the dead weight, and a concentrated load, representing a wheel load, are tested up to failure. The experimental results are used to assess the ultimate shear which can be carried at the support and the influence of the varied parameters is discussed. The results demonstrate how different types of loading such as dead loads and live loads can be superposed and how a stress check at the support can be carried out.

Here are the slides of my presentation:

Shear capacity of slabs under a combination of loads from Eva Lantsoght

Transportation Research Board (TRB) Annual Meeting: Presentation and Paper

At the 92nd Annual Meeting of the Transportation Research Board, I've presented in the session of "Topics in Concrete Bridges".

You can find the slides of my presentation here:

Assessment of the Shear Capacity of Existing Reinforced Concrete Solid Slab Bridges from elantsoght

The paper, published in the Annual Compendium of Papers, can be accessed online.

As always, if this topic is of your interest, give me a shout-out and let's exchange ideas!

Improve Your Public Speaking Skills

I'm not someone who naturally loves to go up on a stage and speak in public - and that's an understatement. One of my main challenges in 2012 was to deliver a talk for TEDx Delft Salon - and to my surprise, nobody ate me alive or ridiculed me.

When recently I came across Jenny Blake's brilliant article with 8 Ways to Practice and Improve your Public Speaking Skills, I found myself nodding along as I read.

In fact, I found so much value in Jenny's article that I revisited her list of 8 ways here, and gave them an academic twist. Here is my academic view on her list:

1. Download a free recording app on your phone. When you practice a presentation, record it. Not only will you get used to the cameras at conferences (sessions often are made available as a webinar or for members of the association that organized the conference). If you listen to your recording, pay special attention to your pauses. You need to understand that the pauses in your sentences give the listener the possibility to digest what he/she just heard.

2. Take three ujayii breaths before starting. Abdominal breathing for stress-reduction: we've discussed this topic previously, and this technique is my single most powerful too for centering before a stressful moment.

3. Make it a challenge for yourself to bring more awareness to your speech in every day interactions. Practice makes perfect - breathe from your abdomen, release the tension in your throat and practice continuously on speaking in a calm, composed way.

4. Give yourself a rating on scale of 1-5 after every class you teach (or training, or meeting you present at). Bonus: write a blog post or diary entry to reflect on how your (conference) presentation went. Also, if a recording is available, watch it in a non-judgmental way to see how you can improve.

5. Pretend you are speaking to a non-native English speaker or a five year old. The five year old might not apply to conferences, but keep in mind that you, and only you are the real expert in your field. Take enough time to introduce your topic, and avoid unnecessary jargon.

6. Channel/observe a speaker or teacher you really respect. At a conference, do not only pay attention to the contents of the speakers, but also to the way they have structured their presentation, how they talk and how they respond to questions.

7. Probably most important: ASK FOR FEEDBACK – often! If possible, have a trial run of a presentation with your supervisor, or for a small group of peer PhD students. They can help you improve before your real gig.

8. Clench and release a muscle several times before going up to speak. Jenny introduced this method to boost adrenaline and stop shaking. Along the same lines: practice powerposes!

How do you improve your public speaking skills? Share you experiences in the comments section!

Kick-off 3TU.Bouw

On Monday October 8th, I gave a short PhD pitch at the kick-off meeting for 3TU.Bouw Center for the Built Environment, which combines the four academic Built Environment faculties of the Netherlands. My PhD pitch (5 minutes presentation) represented the faculty of Civil Engineering and Geosciences of Delft University of Technology. The event also allowed for outreach to the public sector and the building industry of the Netherlands.

In my presentation, I gave a quick overview of the project on the capacity of existing concrete bridges and briefly discussed the research from the group of Concrete Structures, Structural Mechanics, and the cooperation with TNO and the Dutch Ministry of Infrastructure and the Environment. The end of the pitch focuses on the impact of the research: the (inter)national scientific impact of this project, as well as the broader impact on society showing how this project contributes to a more sustainable future.

I've shared my slides on SlideShare:

 

Bestaande betonnen bruggen from elantsoght

The recording of the presentation can be viewed here (at 48:30 my presentation starts):

Storify of 3TU.Bouw kickoff