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I wrote: ↑Thu Aug 04, 2022 19:58
I would suggest that the load could however safely oversail the central reserve barrier with the columns taken down and then reinstated on the concrete barrier section.
Some pictures show the load travelling comfortably on a two-lane sliproad, so I'd be interested to know why it was necessary to span the whole width of the M53 when it could clearly have fitted onto one carriageway. Maybe this was for reasons of stability - a broader base for the longest part of the journey - or maybe to sit in the middle of the formation to avoid a camber?
My quick thoughts
There will probably have been a special assessment made of the underbridges (unless one has been done previously for a similar load) for the diferent possible locations of the load transmitted into the deck from the trailers - that might be the constraining factor - sharing the load between the (effectively) two different bridges (one for each carriageway) may have been necessary to avoid overstress of the deck.
For stability, having the trailers and load coplanar to the carriageway on a 2.5% crossfall over 14m would involve a level difference of 350mm which (although the trailers are height adjustable to mitigate) would be replicated in the vertical dimension. Keeping the load as horizontal and stable as possible may well be one of the drivers behind using both carriageways so reducing the vertical difference - assuming balanced carriageways.