not only bridges

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 http://notonlybridges.blogspot.com.es/2009/05/skew-or-non-orthogonal-reinforcement.html 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 http://estructurando.net/2014/09/29/el-problema-del-diseno-de-armado-oblicuo-no-perpendicular/

Can social media help structural engineers?

Written by Ms. Minara El-Rahman at http://seblog.strongtie.com/

Here are some tips for any structural engineer looking to grow his/her online presence:

Map out your social media strategy

Think about where you want to be in terms of online presence. It is important to be where your clients are online. 

Do your potential clients have a page on Facebook? 
Do they gather and share industry news from LinkedIn? 

Once you decide where your clients are, start listening to their conversations, reading their posts and following them on their social media accounts so you can determine where you should be online and start to build your presence.  Try to narrow it down to a few social media platforms at first so that you can devote your time and resources to growing your social media presence. This is especially true if you are managing your social media content yourself, or requesting someone on staff to do it for you part time.
Make sure to take the time to think about how you define social media success at this stage. 

Is social media success a lift in brand/company awareness? 
Is it an increase in your social media fan base, number of retweets or traffic to your site? 

Once you have figured out what success looks like to you, write it down and craft your strategy and content around that criteria.

Create engaging content

Offer content that is informative and interesting to the audience you want to reach. For structural engineers, content that explains concepts such as the importance of a continuous load path in structures in high wind or seismic areas may show potential clients the value in working with a professional engineer. Whether you are writing a blog post, or sharing an image on Pinterest, content should improve knowledge, help to solve problems and spark conversation.

Map out your content ahead of time in a content calendar. It could be as basic as writing down your posts in a Word document and setting reminders in Outlook. Planning keeps you consistent and accountable. Consistency is key when it comes to engaging with clients on social media.

Think about creating content specific to the platform. 
Pinterest and Houzz are social media platforms that rely heavily on visuals, so content such as infographics, photos and BIMs are appropriate. 
For LinkedIn, in-depth articles about your industry tend to perform very well. Craft content around the platform so it appeals to who you want to reach.

Measure successes

Don’t forget to check in on your measures of success on a monthly basis. This will help you gauge whether your social media efforts are paying off. If you are doing well, that’s great! If you notice that you are not quite hitting your goals, look at the numbers and adjust your strategy. 

Are you posting at a time when no one is looking at your content?
There are a number of articles that recommend the best time to post content so that it will be seen. 

Is your content not resonating with readers? 
Try to change it up so that it really connects your readers with what they want to know.

And one final tip: be committed. Posting every once in a while or not responding quickly to readers’ comments and questions can negatively impact a firm’s brand and reputation. However, those that are active on social media and post regularly are able to build stronger relationships with clients, demonstrate their expertise and ultimately grow their business.


Flood simulations and actual flood risk

Looking at the maps in the article http://www.theatlanticcities.com/neighborhoods/2013/05/way-we-build-cities-making-them-flood/5590/  I found a report by the Chicago-based Center for Neighborhood Technology based on 177000 local flood insurance claims that found no correlation between damage and floodplains, as this graph shows: 


http://cdn.theatlanticcities.com/img/upload/2013/05/14/Screen%20Shot%202013-05-14%20at%202.06.51%20PM.png

It is a completely counter-intuitive result: are flood plains not always a good indicator of flood risk?

The main problem is that the flood decisions that local governments are making today not only determine how much damage future floods will cause locally, but also how healthy the community’s river and coastal areas will be. Chicago and its surrounding cities, for example, have artificially created flood-prone places simply by paving over the region's natural ability to manage excess water.

Impervious surface creates risk over a much wider area, and it is impossible to say that just because you are locally above the 100 year flood, flooding is not a risk.

Tips for importing CAD into Abaqus or similar FEM software

Frames:
1) Create geometry in AutoCAD or free alternatives (Draftsight, Nanocad,...). Explode entities if necesary to obtain only lines and save as Frames.DXF
2) Use gCAD3D (it is a free and open software http://www.gcad3d.org/), import Frames.DXF and save as Frames.IGS
3) Import parts as wires with Abaqus/CAE

Planar shells:

1) Create geometry in AutoCAD or similar. Explode entities if necesary to obtain only lines. Separate and save as Contour.DXF and Partitions.DXF
2) Import Contour.DXF as sketch in Abaqus/CAE
3) Create part form sketch called Contour
4) Tools> Partition>Face>Sketch and use the sketch called Partitions

3D Shells and solids:
1) Create regions (command REGION of AutoCAD) and solids in AutoCAD and export as SAT (ACIS) file
2) Import parts as shells and solids with Abaqus/CAE

The latest procedure also works for planar shells but it is less precise.