Chapter 2 – Advanced Introduction (Part 1 of 2)
Table of Contents
2.1 The Usual and The Unusual
2.2 Shall We Aim High?
2.3 Do We Really Know That Much?
2.4 Twist of Fate – A Nominal Structural Past Tense
2.5 Time History of A Crane Runway Girder
2.6 The Attitude of Knowing Nothing
2.7 Structure-Load Relationship
2.8 The Art of Crane Runway Girders, There Is?
2.9 Beware of Out-of-norm Effects
2.10 What Separates Unsymmetrical Section from Symmetrical Section?
2.11 Nothing Is Perfect After All
2.12 Pay Due Respect To The Nontrivial Shear Center
2.13 Imperfection – A Nonlinear Progression
2.14 An In-depth Looking Into P and Delta
2.15 What Controls How CRG Is Loaded?
2.16 The Faux Location of Shear Center
2.17 What Happens If the Shear Center Is Off?
2.18 How Does CRG Behave Under Its Own Deal Load?
John Fong (馮永康) . Bill Vanni
Structural Design Corporation
1133 Claridge Dr., Libertyville, IL 60048
©March 2010 − October 2021, 2023
“Every now and then” we might be stumbling upon obstacles or disorders while fulfilling our Structural Engineering Obligations. Technical roadblocks affecting advancement of production progress could be of intricate varieties or of other natures depending on many factors. Whether of usual or unusual trait, stagnations impacting productivity could come to light during a major crisis or that of minor scale while breaking through a marginal bottleneck.
We can always try labelling whatever issues that led us into a weaker position of any significance in any ways by any means; but of Crane Runway Girder importance, a good number of issues can be normalized to either conceptual or numerical in nature.
Basically any engineering process could be off pace out of wide range of reasons, explicit or implicit, which in turn might cause a minor delay in progress or incite a major setback affecting the entire project. These issues could turn up from misunderstanding (conceptual) at inception or from miscalculation (numerical) that could come about at any stage of a project.
Miscalculated result can always be corrected by recalculation in general – on paper, at least − so long as it had been caught promptly; but misunderstanding structural behaviors or design concept would have been far more punishing if not fixed up in time.
The worst outcome owing to misunderstanding of structural behaviors or design concept should be those exposed many years after the project had closed out long ago. Therefore the incident phasing or timing span of the so called “every now and then” in terms of a specific structure’s existence should cover as many periods as thereof “before and after.”
2.1 The Usual and the Unusual
The issues that may affect Structural Engineering Undertaking − whether of technical or non-technical in
essence − could be (1) those out of usual yet widely recognized reasons that kept repeating again and again showing same characteristics ranging from chronic shortage in resources, deficiency in problem-solving know-how to poor choice of tools, etc. or be (2) those of unusual causes never encountered before or (3) that simply the spontaneous up-to-the-minute types, etc.; with which how familiar to us would depend on what we do and how experienced/inexperienced we are.
Undue surprises or disruptions to project progress are not uncommon; which could occur during qualifying or re-qualifying structures of any configurations of any ranks of any classifications.
Usually frustration and deadlock draw much closer at us when dealing with structures of unusual
configuration commanding unusual behaviors and unusual structural responses linking with
unusual loading events derived from meeting unusual design requirement accommodating unusual
functional and/or operational needs, and so on.
Approaching setbacks or deadlocks with a positive attitude by accepting unusual challenges with intent of prevailing over all that comes is a good inspiration to draw on in order for Crane Runway Girder to have a better life in this context.
The only negative part being, one might not be fully geared up to take on qualification of structures besieged by so many unusual elements; it could turn out to be more demanding to deal with if the structure was already strained under ongoing distress that as if extra add-ons were piled up on top of so many innate obstacles to be overcome in the first place.
Often times when locked into a disadvantaged situation from (1) misjudging the extent of inherent difficulties and (2) devoid of thorough understanding of the problems’ nature, meanwhile (3) if not well-equipped in taking on the technical complications prescribed in these unusual circumstances, we might take in certain familiar or unfamiliar strategies, rules, fixes or shortcuts close at hand aptly out of usual convenience – that’s when trouble starts.
So often at weighing up an elected problem-solving strategy (rule, fix or shortcut) prior to solving an unusual problem involving a specific tactic, our follow-up approach and the way things turned out may come down to what attitude we have, how we feel and where we stand:
In hesitant mode:
We might be (1) in doubt of our own (outmoded) approach on whether it’s suitable for the given task, or (2) unsure of the adopted (traditional) scheme is adequate to accomplish our mission − ended up going nowhere?
Or else in overconfident mode − if merely trusting our usual instinct or self-approved ruling:
In the worst case scenario, we could easily succumb to a false sense of satisfaction on the assumption or misguidance into (1) reflecting that our chosen course of action is the “one of its kind” and must be better than other choices if not being the best, or simply (2) riding on a pretentious pride as if we could always manage to a better outcome than employing other means regardless if the judgements made were good or bad – still, in the worst case scenario ended up going nowhere.
Or prompted by pseudo-confidence driven from unsophisticated imprudence for simplicity’s sake,
We might fall for a handy hardy shortcut just for getting over the immediate impediment in a hasty. All appeared fine to start until, only if it didn’t work out in the end (usually uncovered many years later) or by then we might not be around to witness the thrashing moment of unusual aftermaths − more often than not the very costly kind, unfortunately.
For simplicity’s sake, engineering shortcuts confer many advantages, and disadvantages, too.
In some cases, taking that route seemed rewarding from zipping much faster through a less winding course. Yet the experience bestowing such optimistic result or pleasant feeling could be nothing but a flashy mistaken sensation on the downside.
The truth being, some of the usual/unusual shortcuts we took advantages of, of which if taken on inappropriately for unusually demanding situations, would likely credit up hefty unpaid tolls − usually unseen upfront. These tolls in real (structure’s) life must be paid up (with interest) later on; whatever the amount accrued if not being compensated in time out of our own pockets then, for sure would have to be reimbursed by our successors someday.
On one hand from being an unsullied object of convenience, a shortcut in essence could be looked on as equivalence of leftover chunks sieved off (whether carefully, conveniently, or else carelessly or poorly) from the balk of the real deal;
On the other hand from being some form of blanketed ways and means, depending on its applications and what purposes that are for, shortcut could be (1) an ideal timesaver at best or be (2) a convenient excuse for not doing what should have been done, or (3) pseudo-ideal as a complete/flawless process in disguise or (4) for the worst a totally wrong path.
In Structural Engineering as some of the must-do steps if left off naïvely in favor of taking it easy for certain chores then,
An unjustified and/or unjustifiable usage of shortcut (such as wrong shear center location) would impart undue side effects (serviceability issues) to the structure sooner or later, or even pass on unforgiving financial penalty (hefty repair cost) in due course.
Such concerns or the worse often seemed too farfetched to affect us right away − as if unlikely to take place in our own courtyard − but don’t be surprised should that actually come to pass someday, perhaps in time when we were no longer in the picture.
While solving Engineering Problems in general, certain procedural steps so simplified conditionally or being omitted fittingly might still work out quite well for the moment for selected applications, but only do so as (if) justified.
And yet that offers no guarantee of universal success. Since for any tedious tactic there is, if the earnest version of which were to be simplified purposely then the options of whether trimming it down cleverly or overly, or accepting everything unchanged as-is, etc. should be determined customarily on how unusual or how unforgiving the obstacles, clutters or bottlenecks was on hand.
Obviously, not all the usual rules or fixes (or certain traditional engineering/analytical approaches) were equally dependable or deemed appropriate in all situations. Just consider the reality that some of the well-liked schemes (or engineering approaches) might not work in our favor at all if blindly applied to certain unusual state of affairs. That is based on facts, regardless to the fixes were it taken either at full strength or in small dosages.
There are many good reasons to chime in a negative ambiance this early on than the other way around, all because it’s still a long way to go. But it should be quite palpable hitherto following the closure of Chapter One to a common accord that some of the underperforming rules or fixes (predicaments) in Structural Engineering were buried deep down in what it takes to truly apprehend one of these classic yet ever-so-technically-baffling structures:
Crane Runway Girders (CRG) especially those having Unsymmetrical Profile Geometry