GLEN HELEN BRIDGE

by S.R. Arnold

Some little while ago I had occasion to take some relations, visitors to the Island, on a "Round the Island Tour" organised by a local coach operator. Passing through Glen Helen where the road runs alongside the River Neb the greater elevation above the road provided by the coach as distinct from a private car, brought near the Glen Helen Hotel, a bridge into view. Surprisingly it was a suspension bridge.

I am an engineer and look at bridges differently to other people who are blessed with artistic and legally analytical minds. To me a bridge appears as the cheapest and most satisfactory design to fulfil a certain definite need and a suspension bridge did not seem to be called for to span the 'Neb' at this point.

Given a bank seat on each side of a gully, dry or wet is unimportant, the designer cognisant of the fact that the deflection of his bridge under load varies as the cube of its length, the material of which it is made and its shape naturally keeps the length minimal. He is helped in this end by the shape of the banks, the nearer vertical they are the shorter the span, the more sloping the longer the span. In this latter case the designer may erect towers or masts rising from the start of the slope in order to shorten the span and this necessity did not seem to be present at Glen Helen.

Enquiry revealed that old guide books to the Island stated that Telford had built this bridge as a pilot design for his Menai Straits work. Research in the libraries of the Institution of Civil Engineers in Great George Street, London, would not confirm this. Nor would it confirm that Telford had ever visited the Island. An interesting diversion arose that Telford had in fact organised the construction of the Glen Helen Bridge after the Menai Straits one had been completed in order to try out various schemes for painting and maintaining the larger one. Further research refused to confirm that his foreman, Whitaker, had ever visited the Island either. The Glen Helen Bridge was not a copy of the welsh one, a cursory glance established that.

I do not know and cannot discover the load which the designer planned this bridge to carry and, in consequence, cannot calculate the deflection of it when carrying this load.

Mr.E.F.Ladds, the Douglas Librarian, combed his shelves further and found reference to a slate quarry some hundred yards on the centre massif side of the bridge. This quarry closed about 1900 but signs of the track to it may still be discerned.

There is evidence, strong evidence, that the bridge was built to the orders of a Glasgow Ironmaster, Mr. H.E.Peacock, purely as a decoration, There is further evidence that Mr.Peacock purchased land and had the buildings now in use as the Glen Helen Hotel constructed as a retirement messuage but no evidence seems forthcoming as to whether he ever lived there.

This is to me disappointing and I venture to make the suggestion that this facility forms no part of the Industrial Archaeology of the Island, it is in fact a garden ornament.

P.S. It has been pointed out to me that this Glen Helen Bridge duplicated a bridge over the River Kelvin in the Kelvinside (now, I think, Royal Botanical Gardens) at the Western End of Sauchiehall Street in Glasgow. That Mr.Peacock crossed this on his way to school or apprentice work daily is more than probable and will doubtless explain the whole edifice.

APPENDIX

GRID REFERENCE The grid reference of the bridge is [SC] 292850.

<------------------------------- 59' 10" ----------------------------->
31' 3" between centres of towers
Footings 5 sq ft

FOOTINGS

For obvious reasons it was not possible to excavate the footings and measurements; they are therefore shown on the drawing at a scale of 1/8" (one eighth inch) to the foot as they most probably are.

SUSPENSION CHAINS

The bridge is not a suspension bridge. The two (or six) chains hang free to the mathematical configuration of a chain hanging free. It will be noted that the bridge is not central to the stream, the central massif side being longer than the side toward the sea. The chains are of 0.5" (one half) circular cross-section welded up into oval links 3" long and 2.125" wide. The material is probably wrought-iron to B-S.S. 9C.

DECKING

The decking has recently been renewed and is of 7" x 2" Baltic Fir laid transversely; this is probably not the original arrangement. The beams upon which this flooring is laid are 6" x 3" rolled steel channels (R.S.C.) to B.S.S. 31E and are four in number. That R.S.Cs. of this length (60 ft. nominal) were available in one length at the time this bridge was built is surprising; I doubt whether they could be rolled today or rather an iron master could be found willing to roll them or a transport organisation to transport them. I could not see any longitudinal joints; to be sure would involve the erection of scaffolding costing some £500 and this could not be contemplated. Could two 30' channels have been welded locally; if this was done at the time when the bridge was built it would have been a metallurgical feat, but there are other places in the Island where rare skills of this nature appear. This feature alone jusitifies a place for this bridge in the Island records.

DEFLEXIONS

For 1" deflexion at mid-span, the bridge could carry a point load of 0.22 tons. This is an approximate figure, the main span of the bridge is offset to the centre line and neither Wilson's theory of 3 moments nor Mohrs theorem can be applied to its scantlings. Professor Haigh's theory of least resilience would be more accurate but has, to my knowledge, never been used on Manx slate or the blue lias mortar employed in the construction of the four towers of the bridge.

[Additional notes by FPC]

I cannot find any purchase of land by a Mr Peackcock however the ground for the quarry was purchased by Mr R. Bell a Glasgow merchant - the development of these quarries was apparently one reason why Wm Quine sold his stake in Glen Helen.