not only bridges

What are the basic differences between ACI 318 and Eurocode 2?

Structural codes were created to guide the design process to ensure that the structure is safe under most conditions. ACI 318 is an American norm and EC2 is a European norm. As you can imagine, the epistemological approach is very different for historic reasons. I have used both reinforced concrete codes. ACI is basically an empirical code with traditional formulas that resemble rules of thumb. Eurocode 2 is based on a sound underlying theory of concrete mechanics (see Fédération Internationale du Béton and the Model Code 90) that then is adjusted to experimental results by means of coefficients. ACI is a pleasant piece to read, truth be said while teading the EC2 is like reading any bureaucratic EU law or any arid materials science paper.

For me the main resulting diferences are:

  • How the safety factors are applied. EC2 applies constant safety factors to the materials. Safety factors in ACI are not applied directly to the materials but to the reinforcement situation (tension, compression, shear or flexure). That is why interaction diagram in Europe is more like an oval but the American interaction diagram looks like a squid.

ACI interaction diagram

EC2 interaction diagram
  • Punching and shear approaches are very different in ACI 318 and in EC2. Both neglect variables that may be important for some beams and slabs, and both have scatter of results when compared to empirical tests. Results may be unconservative or overconservative in some cases, so I recommend to use and compare both codes in case of doubt.
  • Cracking estimation does not exist in ACI 318. Ok, there is a rule of thumb for the separation of reinforcement bars for 0.41 mm average crack. Calculation of crack widths under quasi-permanent loads is mandatory under EC2. This shows a more modern approach.
  • In my opinion, ACI underestimates the influence of creeping.
  • Minimum reinfocement of columns according to ACI is 1%, everywhere and in any case. Minimum reinfocement of columns in non-seismic areas according to EC2 is just 0.4%.

Why is the human spine considered a bad design from an engineering perspective?

When engineers design a structure they usually plan on a lifetime of 50 years with minor maintenance. Our spine shape, like everything in biology, was not designed on purpose but it came about through random mutation and natural selection. Natural selection works a a greedy algorithm, this is, biology cannot take a leap back to a complete redesign when one evolutionary path was chosen.

The main problem is that the spine has to accommodate bipedalism instabilities and that the spine we have evolved mainly when we were not bipedals. Humans started to walk on two legs a short while ago in evolutionary timescales, therefore the spine is forced to support loads for which was never optimized for, working as a curved cantilever beam, supporting a big heavy head at the end of the cantilever.

Besides, serious problems of the human spine are caused by the materials from which it is built. Those materials have very little resistance to fatigue damage caused by repetitive loads. Sometimes the head which sits on top of the spine leads the individual to mechanical overloading. Repetitive loading leads to endplate failure which leads to disc degeneration. What is more, When subject to low oxygen caused by cigarette abuse, the discs lose their ability for self reparation and start to degenerate. The spine has a pretty small section to distribute all that weight from the top of the body to the hip. The rate of degeneration due to dynamic loads is dependent on those repetitive loads and genetic factors that govern the dynamic characteristics of the connective tissue from which discs are made and the ability to repair microcracks.

In conclusion, our body spine is far from perfect. Mind that it is not structurally very sound to support extreme weights and cyclic loads. Take care of it.

What is it like to be a personal Spanish tutor for techies on Italki?

I have been teaching Spanish and Galician for engineers, techies and business people on Italki for the past year and it is very rewarding for me. If you do not know, Italki is the largest language learning social network with which you may find the partners and language teachers from around the world.

I enjoy the experience because I can share my knowledge and views about a wide variety of engineering and technology subjects such as writing good consulting reports, construction glossaries, architecture and building arts and techniques, entrepreneurship, agile project management and so on. As a tutor you can decide your students, your lesson plan and your schedule.

Unfortunately, incomes can fluctuate a lot. Spanish is one of the cheapest languages on the platform, so you have to be quite a skilled tutor with a strong profile and good reviews to command a good hourly rate. Besides, Spain is a relatively expensive country compared to the rest of Latin America and Italki can only be considered as a sideline.

The tree and the cow: what doesn't stop climate change and what stops it and people don't believe it?

There are two inconvenient climate truths about beef consumption and planting trees.

Many people tend to believe that planting trees can save us from rising temperatures, but climate science states something different. It is a myth that photosynthesis dramatically controls the amount of oxygen in the atmosphere. A massive reforestation is not a solution because trees also breathe and burn oxygen and release carbon dioxide back into the air. What is more, reforestation programs need to be carefully designed. For example, planting adequate trees in the tropics would lead to some kind of cooling, but in colder regions, particularly wrong species in boreal areas, could lead to more warming.

On the other side, beef consumption negatively affects climate disruption. It is bad because overpopulation of cows release more tons of methane (CH4), which is a greenhouse effect gas, and it is bad because meat has to be transported (realeasing CO2) in refrigerated trucks (realeasing fluorinated gases) from farms to slaughterhouses and then to processing centers and to local supermarkets.
Industrial cow meat is one of the least climate-friendly foods in terms of greenhouse gases and it is possible to do a lot for the planet simply by giving up beef.

Picture: cows and eucalyptus in Riotuerto (Cantabria, Spain).

Why has Spain produced few famous scientists over the last centuries?

Spain has had a complex history that shaped the lack of a solid scientific environment over the past centuries.

First, Spain had a much harder Renaissance than France, England, or the Italian city-states. Spain spent a good portion of the Renaissance period engaged in a religious war to kick the Arabs out and expelling the Jews. Moorish Andalusia is where an important transfer of knowledge occurred. Everything associated with Moors and Ancient philosophy was considered heresy by the Inquisition and this probably made Spanish society more conservative. The Spanish inquisition truly dampened free inquiry and scientific exploration while France, England and the Italian city-states were creating the culture that nurtured most of the later famous scientists.

Then, the strongest resistance to progress and modernisation was probably expressed in the antagonism between the Francophiles and their opponents. Francophiles were accused of all sorts of religious heterodoxy. The 2nd May is a absurd public holiday in Madrid that celebrates the rebellion by the people of Madrid against the occupation by French troops. In reality, the 2nd May was a disaster day beacause of the following counter-revolution and reactionary policies. The people, blaming the policies of the Francophiles for causing the Napoleonic occupation by allying Spain too closely to France, at first welcomed Ferdinand VII. Under his rule, liberal schools and libraries were closed down, the engineering school was closed down, part of the press was suppressed and many editors and many writers were imprisoned. Even the liberal members of the Catholic church became victims of prosecution and the most scientifically educated group -the Jesuits- were expelled from Spain in mid XVIII.

And, last but no less significant, the Spanish civil war and the subsequent ideological conservatism of the dictatorship were a total tragedy for Spanish science. A whole generation of promising scientists was exiled.