Bridge pedestal grit blasted

The bridge reopened on the 17th July to some small fanfare. This was after the council’s appointed engineers had blast cleaned the cast iron pedestals so that they could be fully examined for cracks, and the case for continued safe operation could be made. 

There are cracks evident in all pedestals to a lesser or greater degree, but they are now assessed as not being critical to structural integrity, provided that the pedestals are not overstressed, which means minimising the movement of the chains that run over them.

Chain heating arrangement (pedestal within housing)

Bridge Chain heater

The temporary solution, which allows the current limited use by pedestrians and bikes, is to heat or cool the chains that run over the pedestals to maintain temperature, so as to keep them in approximately the same place avoiding excess pedestal stress.  This is obviously a 24×7 energy-intensive business, a least-worst solution for the time-being.  It’s worth noting that even with only pedestrians and bikes crossing, the bridge still sways a little, it is very much a live structure.  The current and much reduced-cost proposal for shoring up the bearings on top of the pedestals (“stabilisation works”) is to replace them with elastomeric sliding bearings, at a total cost of around £6m as widely reported, a figure that doesn’t seem unreasonable.  Others can judge whether this is a good enough solution for the long term.  We’d prefer to be without the nagging doubts of the hidden cast iron bolted-in parts in critical structural positions, to allow the engineering of a robust 100-year + solution using easily replaceable bearings. This wouldn’t be expensive in the scale of the total repair bill, and as we described early this year, fixing the recurring problem effectively for good.

Without going into further exhaustive detail, which can be found in the references listed below, the main issue remains who will pay for the repairs. The most sensible option is to substantially dismantle the existing bridge with the COWI-Foster structure, or other temporary bridge in place for the duration. This would allow it to be properly repaired to a higher quality than can be achieved onsite, including replacing the troublesome cast iron, and might be quicker overall.  Consideration should also be given to lightening the structure via a lighter/improved roadway as we’ve mentioned before, so as to lower bridge loadings, potentially raise capacity a little, and we’d very much like to see wider pathways for pedestrians & bikes.

The latest update from the Task Force shows that our council leader and the newly re-appointed government minister responsible, Baroness Vere, are again at loggerheads, this time over the relatively small sum of £6m for stabilisation works, which is why they haven’t started.  If they can’t agree on this, how ever will they agree on the £100m+ full repair bill ?  We call for a ceasefire and end to hostilities by letter.

References

• Bridge Task Force documents
• New Civil Engineer – bridge reopening 
• H&F Bridge page including letters to and fro.
• Barnes Village Bugle (August) with significant detail and discussion of the proposed ferry, now mothballed.