Chapter 4 – Ready, Set, Prepare To Go Yet?
Table of Contents
4.1 Who Is To Blame?
4.2 Design Loose Ends, Are There or Were There?
4.3 Engineering Oversight?
4.4 Before The Other Means, What Does It Really Mean?
4.5 Facing the Challenge
4.6 New and Used, Experienced and Inexperienced
4.7 Scope of Coverage
4.8 LRFD and ASD
4.9 Sourcing the Design Basis
4.10 Site Visits
4.11 Crane Runway Alignment Survey
4.12 Runway Structural Inspection
4.13 Crane Wheel Loads
4.14 Lateral Thrust – The Probable Control Source
4.15 Lateral Thrust – The Certainty of Uncertainty
4.16 Lateral Thrust – The Ground Zero
John Fong (馮永康) . Bill Vanni
Structural Design Corporation
1133 Claridge Dr., Libertyville, IL 60048
©July 2018 – Oct 2019, 2022, 2024
If someone decided that Open Sectioned Crane Runway Girders (CRGs) should be given a special rank of their own then those having unsymmetrical sectioned profile should deserve much more, because they stood out for plenty of good reasons, in particular by traits of:
- The applied load resultant is consistently at offset from the Shear Center
- The applied load resultant is at skew from the Elastic Principal Axes on regular basis
- And above all, the location of Elastic Centroid never concur with the Shear Center
Those listed are not complete by all means, but we see the issues and can readily decode much of the complexity embroiled in the handling of structures of this caliber − having unsymmetrical sectioned profiles − was embedded deeply in the atypical relationship between the applied loads and the profile geometric features.
4.1 Who Is To Blame?
No one is to be blamed yet,
Despite our obligatory acceptance of (1) the non-modifiable way of how crane loads were applied and (2) the innate irregularity in the profile geometry, even though rationally we might be readied to take on the unavoidable challenge and to endure through the burdensome workout, but situation could change once we started “playing” with those issues; because various technical adversities concealed behind the planning and execution of Engineering Qualification Process could break loose in multiple passes, one after another
On the whole, each CRG project is unique in its own way. Albeit one project could be different from another in certain aspects, but it is quite common when running typical CRG Engineering Errands during the structural analysis and design qualification sessions, we might encounter numerical–data-nurtured inconvenience, surprise or disarray that could drop in on us following several paths:
- As in (1) making sense of the never-again-simple-bending- privileged structural behaviors attributed to loads off shear center and in (2) allocating, extracting and backtracking of extreme effects duly enveloped from all probable moving load scenarios
- And to great extent in establishing an effective strategy tending to the massive amount of information cropped up throughout the process
While meeting design qualification mandates and getting by with less frustration – as to minimizing the run-in with numerical disarray − as design process progresses, quite noticeably rather trendy these days that many CRGs were configured with symmetrical sectioned profile appeasing both practical and sensible causes. That is by choice a much wiser preference and resolve contrasting those with no better options yet caught up with much less privileged configuration involving unsymmetrical sectioned members – an inevitable must-be-dealt-with condition inbuilt in many forensic and upgrading projects.
In retrospect, quite plausibly that – when opined at sophistication level from a Fabrication Detailers’ perspective rather than Engineering-Mechanics’ standpoint − unsymmetrical-sectioned girders were widely accepted once upon a thought that they were much more practical in their own right.
Thereby so many not-so-regularly-shaped members were so intuitively configured, so inadequately qualified yet so consciously implemented all along in so many facilities in the Industry worldwide
The catch:
What was popular back in those days now bequeaths an everlasting speculation becoming rather unfavorable to so many Facility Owners’ Maintenance/Operation teams of late for the least; the come-to-be compensations they’ve gotten or have troubled to put up with, if at all, could be flip-flopping from (1) what at best a seemingly no-fault sense of security, yet still toiling behind an insecure sensation wondering whether if all girders on hand could survive till the end to (2) what at worst a high and dry certainty, yet still battling with an ambiguous outlook whether some of the girders could ever live up to their useful life
Quite visibly from here on out, we can’t let the ongoing downhearted issue quietly slip through right behind (or right in front of) us as if nothing had happened:
From a subjective viewpoint not so much of conceptual measures but by looking closely at those gloomy track records gathered from (latest or historical) field monitoring and inspection proceedings, as the range of these not-so-optimistic findings became more and more widespread, and the count of unfavorable rulings kept mounting at each pass, so, wouldn’t it be more pressing now than ever (1) to reconnect our general awareness toward such concern and (2) to contrive from our ingenuity into truly practical means aiming to prolong, salvage and revitalize those CRGs in need?
The scapegoats, if at all not too many to place blame on but then:
- Was it the fault of loads being applied too unconventionally?
- Or was it the fault of cross sectional geometry being too unsymmetrical?
- Or were there any loose ends in how these structures were qualified and detailed, after all?
What is to blame based solely on the above is not important for the moment but we shall see. Granted we all knew the fault is not the loads, neither is the section geometry.