Why Do (Young) Structural Engineers Tend to Believe Whatsoever The “Magic” Numbers/Outputs Given by The Software?

By Chanthoeun Chiv

My mentor/senior always keeps reminding me about utilizing one’s engineering sense to judge the results from the analysis. After pushing the “run” button, the first thing you should do is not about rushing to play with “design” option to obtain the amount of the reinforcement, but to look at the deformed shape of your structure, does it deform the way it should be? Are there any nodes floating alone like a roller coaster? Do the time periods of the building make any sense to you? How about checking the reaction due to dead load only to see whether the selfweights are actually transferred to the foundation? SFD and BMD for specific case? These are the fundamental questions you should be asking yourself prior to jumping to use the analysis results directly from the commercial softwares without careful discretion, otherwise you will be just a software operator or a robot who just knows how to throw garbage in and wait for the garbage out. If you keep doing so, you will be putting your career on the line and can’t inevitably avoid facing the worst disasters afterwards if something really bad happens.

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Structural engineers are explicitly responsible for the buildings he/she has designed, one needs to be able to read the analysis results and interpret them professionally. But why most of the time, we are usually perceived by the supervisors/mentors that we are lack of engineering sense/judgement? Is it fully our fault? Is there probably any hidden reason behind it?

I believe it’s of paramount significance to inject novel content and creative methodology into the conventional and out-of-dated learning methods student used to be taught at school particularly for structural engineering curriculum. Why I say so?

Base on Dr.Graham H.Powell, Professor Emeritus of Structural Engineering from UC Berkeley, there are three distinct phases in structural analysis such as:

1) Modeling

2) Computation

3) Interpretation

Prof.Graham H.Powell believes (and you may want to argue later) that the most important phases are No.1 and No.3, and the least important one is No.2. However, what we have been taught extensively at school was how to do “computation”, but giving little attention to “modeling” and “interpretation”. The skills being needed and useful the most are not taught while the skill with the least importance level has been inherited down in the exact same old way like it used to be decades ago. So I think something should be done, a reform must be implemented to promote these two needed skills. By doing so, the young engineer could be exposed to the most important skills early and they could enhance and/or improve their skills accordingly in order to fulfill the gaps left out from school.

1) Modeling
The structural analysis is carried out on the “model” of the actual structure, not on the actual structure itself. There are a number of key points need to be addressed as follows:

  1. What you draw in the software is just an “approximated” model of the real structure, it does not necessarily represent the “exact” behavior of the actual one, but it should capture the crucial “aspects” of the real structure’s behavior.
  2.  Always employ “node-element” model
  3.  Choosing appropriate element, assigning with corresponding properties like stiffness and strength
  4.  Choosing the appropriate demand/capacity measure for performance evaluation.
  5.  3D model may looks splendidly appealing with colorful rendering. However, it doesn’t mean it has the exact same behavior as the real structure, keep that in mind!


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3) Interpretation
After finishing modeling of your structure, computation of the model will be taken care by the computer. At the end of the computation phase, a set of “results” will be provided and that is the time the structural engineers start using their hard-earned skills from school to “interpret” these “results”. There are a number of key points need to be addressed as follows:

  1. There is no one-size-fits-all procedure for interpreting the analysis result.
  2. Use demand/capacity ratios (DCR) to help make design decisions.
  3. Always being skeptical about your analysis results.
  4. The results from your analysis model isn’t for the actual structure, it doesn’t have to be, and it will never be. However, as a structural engineer, our job is to look for the results that are close enough for practical purposes.

2) Computation
Anything that is neither included in “Modeling” nor “Interpretation” is to be coined as “Computation”. A number of key points are to be addressed as follows:

  1. For current scenario, almost every structural engineers are using computers to do the “computation” part.
  2. Basic understanding of the computation phase like equilibrium equations, compatibility and the boundary condition is necessarily needed. Even the structural engineers rely heavily on the skill and expertise of computer program developers, they can’t go away from these fundamental knowledge in structural engineering.
  3. Only those who write the computer programs require an in-depth knowledge about the computation phase. We, the users of the program, do not need that skill.

Long story short, it’s easy to be seduced into believing that what we draw in the model is an exact representation of the real structure. Therefore, we need to be skeptical about the outputs obtained from the software. We need to know what we throw into the computer with acceptable understanding of the assumption inside the software, and remember this old saying: “garbage in, garbage out”. Indeed, for the time being, “modeling” and “interpretation” are archived from hands-on experience as well as merely from the job training. However, what if students/young engineers could get exposed to these two needed skills since they are at school, it would be extremely helpful for their work in the future. The least/minimal supervision for the freshers will be able to be implemented effectively and economically.

Related post: https://www.linkedin.com/pulse/garbage-out-chanthoeun-chiv/

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