not only bridges

How to build a gas processing plant

This is an award winning short film for its educational value to the oil and gas industry. It is a pity that the video does not come with music. Included are construction methods, sequence, resources and timelines. Activities covered in the video are earthworks, pipe racks, slugcatcher, steel tanks, heavy lifts, welding & spool fabrication, pavements and fencing.


In the past two years, David H Moloney, an Irish engineer, has made and uploaded short films like this one onto YouTube showing us how civil projects are constructed. These projects range from airports, seaports, motorways and railways to oil and gas pipelines, metros, in-situ piles, bridge construction, post-tensioning, precast yard, quarry, roofing and more. I strongly recommend to visit his channel.

The theories of everything

When you try to be all things to all people, you end up being nothing
(common saying  popularized by Robin Sharma)

I have recently finished watching The Theory of Everything. If you are interested in the borders of science, it is a must see. As Hawking admits, cosmology was thought of as a pseudoscience given that wild speculation was unconstrained due to the lack observations.

More examples of the difficult birth of a new science: the government of the Soviet Union declared that Mendelian genetics or plate tectonics (continental drift) were pseudo-science. Artificial intelligence has been considered as hype and junk science by many. Dijkstra considered software engineering to be a pseudoscience.

On the other hand, there are disciplines that were abandoned. For example, I have been taught elements of NLP - a debunked psycologic theory - many times on prestigious management courses. Why? Because although NLP is pseudoscience it brings under a single unique umbrella a host of useful good interpersonal and conversational techniques. Also, modern city planning has been called pseudoscience by Jane Jacobs and others.

What are the borders between mainstream science, fringe science, junk science, heuristics, useful pseudoscience, science fiction and fraud?

When materials are getting tired

Fatigue might be the the key of Germanwings accident. Fatigue is still nowadays an endemic structural problem of fuselage and specially of the rear portion of the cabin.

Low cost airlines usually fly short and more than 5 times a day. Each takeoff and landing cycle and the pressurization, ice forming on the wings and depressurization associated with it adds stress and damage to the skin of the plane.

Todd Curtis, a former Boeing safety engineer who is now director of the Foundation said  to US News "if you see a wing here and three miles later you see a fuselage, one doesn't have to be an expert to speculate that it didn't happen on the ground — that something happened before it impacted".

The rant of a senior engineer

One of my experienced colleagues made a blunt rant about what he felt were problems within the energy&engineering sector nowadays. Apart from the political views, which I do not totally share, it is an honest, clear, and frank writing for insight about engineering, management and factors that make talented engineers to get totally bummed out. 

"I am at home not working because of sanctions imposed on the Russians and indecision of whether we want to break up UK and Europe into small units. Scotland to break with what is the UK has caused a lot of problem to Oil & Gas and destabilized businesses and prices. Delayed projects that should be happening now. And Catalonia will cause problem for Spain. 
It is my belief more experienced people are sitting at home because they have been forced to continue doing nuts and bolts. The average younger engineers want to be project engineers and project managers only without practicing the core skills properly. It is the people on the shop floor which should be promoted to be managers they have clearer for sight. Consequence is energy will cost us a lot more until we re-address who are the decision makers."

The design of skew reinforcement revisited

Reinforcement that is not orthogonal or that is arranged in more than two directions occurs quite frequently in concrete slabs. In such cases, ultimate strength can be calculated from an equivalent distribution of orthogonal reinforcement.

Given n arbitrarily oriented groups of parallel bars with corresponding reinforcement ratios A(1), A(2),…, A(i),…, A(n), the equivalent reinforcement ratios Ax, Ay, Axy for the structural model axis XY can be obtained from the following equations

Where a(i) is the angle between the group of parallel bars “i” and X axis.

These values of reinforcement are then transformed into the equivalent reinforcement ratios in the principal directions p and q.

Where angle b can be obtained as

A model of shells of the slab in axis XY can provide axial forces Nx, Ny, Nxy and bending moments Mx, My, Mxy.

When reinforcement is arranged non-orthogonally or in more than two directions the design moments must be obtained in the principal directions of the reinforcement p and q, this is, we need to obtain from our FE software Np, Nq, Npq and Mp, Mq, Mpq before applying Wood and Armer rule or any similar rule.

In 1968, Wood and Armer proposed a popular design method that explicitly incorporates shell twisting moments. The Canadian code allows a simplified version of the Wood and Armer method that I assume here for the sake here of simplicity and safety.

Moment design rule can be stated as follows

All plus signs apply only to bottom reinforcement and all minus signs apply only to top reinforcement. Mpd and Mqd will be negative for tension in the top reinforcement and positive for tension in the bottom reinforcement. In the Canadian simplification, when the assumed-to-be-negative design moment is positive (adds compression) that moment is taken as zero. When the assumed-to-be-positive design moment is negative (adds compression) that moment is taken as zero.

Axial design rule can be stated as follows

It is generally assumed that tension (positive axial force) governs the reinforcement design of the slab and the plus sign generally applies. When the assumed-to-be-tension design axial force is a compression the axial force can be taken as zero.

After this step, the reinforcement Apd can be checked with the design forces Npd and Mpd; and the reinforcement Aqd  can be checked with the desing forces Nqd and Mqd.

Some final clarifications:

- When the slab is very thin the effective depth difference between different groups of reinforcement may be important. In the case of simple bending this can be taken into account simply by using capacities rather than ratios, but if there is bending and axial forces the formulation becomes slightly messy. In commons slabs it is usually considered an average depth since the error is small and the Wood& Armer rule tends to overestimate the necessary reinforcement. An alternative simple and conservative approach is to consider the least effective depth.

- The rule of Wood and Armer presented colloquially here is a simplified version. Full version and its variations as implemented in well known software packages are much longer algorithms. Also, mind that Wood and Armer rule was derived for ULS reinforcement design. For SLS, cracking or fatigue analysis other rules and other methods may be more appropriate.

- The current post has been written as a revision of my former post and it is not intended to be published as a peer reviewed paper. Avelino Samartin and other researchers have more rigorous procedures based on generating and rotating a tensor of resistances.

Part I

Part II

Unfortunately, I have not had time to apply those procedures in my professional practice.

- Spanish version of this post has been gently published by J. A. Agudelo in