Chapter 7 – Special Subjects, Rare or Inconspicuous
Table of Contents
7.1 Looking Back At Business as Usual
7.2 Maybe Business Is Not as Usual
7.3 Looking Beyond Business as Usual
7.4 The Risk of Doing Nothing or Not Enough
7.5 Top Flange Local Bending Stress – Derivation
7.6 Top Flange Local Bending Stress – Numerical Example
7.7 Top Flange Local Bending Stress – Potential Problem
7.8 Permanent Warps or Tilts – The Phenomenon
7.9 Permanent Warps or Tilts – The Implication
7.10 Variable Sectioned Members – Atypical But Not To Be Ignored
7.11 Variable Sectioned Members – Limitation of Classic Treatment
7.12 Variable Sectioned Members – Beyond Simple Bending
7.13 Variable Sectioned Members – The Need of an Out-o-the-box Approach
7.14 Variable Sectioned Members – Development of Equivalent Section Properties
7.15 Variable Sectioned Members – An Application Example
7.16 Chapter Conclusion
John Fong (馮永康) . Bill Vanni
Structural Design Corporation
1133 Claridge Dr., Libertyville, IL 60048
©May 2018, 2022, December, 2025
As in so many cases of conducting business as usual, when solving Familiar Structural Engineering Problems by “widely received” approaches ‒ including those not necessarily the best suited or that entirely error-free ‒ but in the end, most of us are OK to proffer credence to an illusory wisdom, that is to trust whatever and however we had done, it would always turn out satisfactory results.
On occasions, when the engineered outcome isn’t as rewarding as expected then, we must be curious to find out what happened; perhaps (1) the problem being solved is not an ordinary one after all ‒ although it may look so recognizable ‒ or else (2) we might have misapplied our die-hard personal-professional understanding of the algorithm and approach used in solving the given problem in the first place
To list a few to that effect, it could be as simple or as serious as:
- Not realizing the “widely received” approach is not suitable or inadequate for the task,
- Miscalculation in section properties, load magnitudes or load effects,
- Error or omission in definition of basic loading cases or load effects or
- From making unjustifiable assumptions, etc.
Many of us might have similar experience, not all our engineered results were one-hundred percent satisfactory every time, the depth of our disappointment from which usually hinges on how on track (or off track) we had comprehended and assimilated to what were passed on to us from the beginning
In normal practice, all elements and articles as-mandated or as-specified in the problem/project definition should have been taken in as part of our engineering deliberation. And sometimes the initiative thereof to our cognizance are not always so clear-cut or as being one-hundred percent conventional. How things turn out with that in the end may vary with how thorough and how accurate we had deciphered the given information
Incidentally, we should have accepted it by now and by heart, in the realm of proper engineering of Crane Runway Girders (CRG) – based on their behavior – there is no such thing as Simple-bending.
So before we press the enter key or click that magic button for a quick solution, always check to see what is missing first. The biggest fallacy in it is, many of us don’t know what to check or aware of what is missing. There are subtle CRG-unique situations we have to pay extra attention to, not only the discernible issues but also certain subtle elements that were not so well-defined or well-understood
Or even when we “fantasized” that all the “issues” were resolved during and after the CRG engineering process, sure we can claim we did it all, but if so then on the other hand, how come there is cracked weld and sheared bolt? For that we must give honest answers when being asked;
Had we mistreated torsion?
Had we forgotten about fatigue?
Regardless to what kind of response, yet besides professing the verity perhaps there is incorrectness in torsion treatment and inadequate provision of strength against metal fatigue, what else is missing? Had we failed to subjugate all the other “must-get-it-done issues” under our belt? When in doubt, shall we take a closer look if we have missed any supplementary constrains with concealed characteristics that are unique to CRG?