Monthly Archives: April 2021

Queensferry Crossing stay cable strands – insulating timetable

Transport Scotland’s recent release to me 😀 of the details of the number of strands in each stay cable of the Queensferry Crossing allows me now to update my “Restranding Timetable” to allow the strands to be electrically insulated so as to carry a heating current for de-icing purposes.

The number of strands in the bridge 21,186    100%
To be replaced with a new longer strand 440 2%
Replace with an old strand from a longer cable 7,764 37%
To be left as now 12,982 61%

Insulating Timetable South Tower Stay Cables

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Insulating Timetable Centre Tower Stay Cables

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Insulating Timetable North Tower Stay Cables

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Note that the south and north towers stay cables would take longer to insulate / re-strand because the bridge designers apparently specified that those towers’ shortest, most vertical, most efficient cables with the easiest work-load should paradoxically use the strongest of the bridge’s stay cables.

Being shorter those cables are better re-stranded last so that they may re-use strands replaced from longer cables.

The centre tower stay cables seem to be designed more as expected from a structural engineering science point of view. I’m curious as to why the discrepancy?

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Bridge Stay Cable Electrical-Heating Strand Calculator

I’ve written this spreadsheet to calculate the specifications for the electrical power supplies to heat the strands of stay cables of the Queensferry Crossing or of other bridges prone to icing with similar cables of an arbitrary number of strands up to 109 strands.
This is a screenshot – click to view a high-resolution image.

Download QFC Electrically-heated Cables. It’s an Excel .xlsx file but it was developed in Google Sheets (for free!). I don’t have Excel on my computer so it has never been tested in Excel. If it doesn’t work on Excel then try uploading it to Google sheets. That should work but any problems let me know

Email: peterdowaberdeen@gm…….

and if necessary I can let you share my Google sheets version with viewer access which I can authorise to any Gmail account and then you can copy it directly into your Google sheets file space.

Instructions

Select a strands sheet with the closest number of strands to the cable you want to calculate for, choosing between 45, 55, 73, 91 or 109 strands. Best to duplicate the sheet for back-ups.

The strands arrangement is represented by coloured cells where the cell formula calculates that strand’s heating capacity.

To re-arrange and / or change the number of strands, first drag off the strand circles overlay image then add strands by selecting an existing strand cell, Edit Copy (ctrl-C) then select another coloured cell for the new strand and Edit – Paste special – Paste formula only. To remove a strand just delete the formula from its coloured cell.

To use the Strands calculator spreadsheet with data for another bridge, you will have to edit or create a new “Cable Data” sheet with the new data and modify the strands calculator sheets’ (hidden) cell X61 so that it fetches the cable data from the new sheet with the appropriate table range.

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