Hampstead Road Bridge (Regent's Canal)
This road bridge, Regent's Canal Bridge No. 24, is also called Camden High Street Bridge and Chalk Farm Road Bridge, is constructed from riveted wrought iron plate, with cast iron capping on parapet and restrained cast iron decorative panels on the girder faces.
1876 'THE CHALK FARM BRIDGE. .....
The old brick bridge was built in the year 1815. It was of the type known as a hyperbolic curve arch bridge. It had some peculiarities in its construction, noticeable in the disposition of the buttresses and counterforts, the variation of the several thicknesses of the half-brick rings forming the arch, in the introduction of iron clamps, ties, and heavy blocks of stone, and in having an insert [invert?] of solid brickwork under the bed of the canal throughout its entire length. It was remarkable that the centre of the crown at the arch was only nine inches in thickness, and it is a wonder that it stood so long . ....
Dimensions: width between parapets 33 ft; skewed at an angle of 78 degrees with the line of the canal; width of water between abutments 22 ft.....
'The new bridge will be a handsome iron structure, supported on massive brick abutments, wingwalls, counterforts, and concrete banking. .... The south abutment follows the same line of frontage as the south pier of the old bridge. ... Along the front of the north abutment is formed a new towpath ten feet wide, leaving a clear waterway of 43 feet Instead of 22 feet, as was originally the case. The towpath is continued round the south-west angle of the abutment, and by means of an inclined plane has its exit into the Chalk Farm road. .... The superstructure of the new bridge consists of five substantial wrought iron girders, bedded on Aberdeen granite bedstones. These girders have the peculiarity (for a roadbridge) of projecting above the level of the carriage and footway. One girder will divide the carriageway longitudinally. Two girders will separate the carriageway from the footways and the two outer girders will form the parapet. The platform of the roadway and footways will be built upon the flanges of these several girders. This exceptional mode of construction for a road bridge has been adopted in order to obtain the greatest possible improvement of the of the approaches to the bridge while maintaining the height of headway required for the passage of the barges. Another peculiarity of the bridge will the practical use to which two of the girders will be adopted. The Gas Company that supplies the district, north as well as south of the canal, have hitherto had considerable difficulty in crossing over or under the canal with mains of sufficient capacity to supply the rapidly and constantly increasing demand for gas in the district on the north side of the canal. By arrangement with the Vestry two of the boxplate girders, those between the roadway and the footways, are to be utilised as gas mains, each girder giving a real capacity equal to three square feet. .... The total length of the new bridge will be sixty-three feet and the full width fifty-two feet. The five main girders are of the style known as box-plate girders, the top flange being level and the lower flange having a camber, or rise, of 12 inches to the middle, which gives an improved gradient of approach. The roadway will be supported by cross and longitudinal girders, well stiffened and braced, the whole being covered in by curved flooring plates, which will carry bituminous concrete, on which wood of the best description will be laid. The top flanges of the girders will be ornamented by cast iron capping, the ends being finished with stone pilasters supporting handsome lamp columns. Cast iron panelling, mouldings, flanges and rosettes will be introduced upon the bays of the girders, to give relief to the external elevation and to make the structure as handsome as the circumstances of the site will admit. The corner is laid in the north-east quoin of the bridge, and the following inscription ..... William Booth Scott, Member Institution Civil Engineers, engineer. Wall Brothers, contractors.
'In the west wing wall of the bridge, a little to the north of the north-west quoin, is inserted the builders' stone, bearing the monogram of the designer and engineer of the bridge. It is worked upon the keystone of the old bridge. This in its outline retains its original form, the apparent irregularity of which is due to its having been the key of an oblique arch. The sentiment of working the key of the old bridge into the fabric of the new structures as a connecting link between the work of the engineer of 1815 and of him of 1876, is pleasing, and, as far as we know, unprecedented, and the idea has been artistically carried out. On the upper port of the stone appears in relief as a countersunk face a key stone of true masonic form with lewis attached. On the face of this is a circle enclosing a triangle. The periphery of the circle displays the letters H.T.W.S.S.T.K.S., whatever they may mean, and we suppose free and accepted masons alone can understood their signification. The periphery is countersunk, the letters remaining in relief ; within the triangle is a circular piece of Sicilian marble bearing the autograph monogram of the engineer, "the Builder " of olden times. The initials will be recognised, becoming become pretty well known in the course of the last twenty years with a large and important district of the great metropolis of which district the bridge happens to be the centre point. The lowest part of the stone holds the following inscription : "This builder's stone was originally the key stone of the old bridge built 1815. removed 1878." '[1]
Note: HTWSSTKS stands for “Hiram, Tyrian, Widow’s Son, Sent To King Solomon” [2]
See here for photographs of the builder's stone and its location.
In 1881 some of the cast iron copings and masonry were damaged by a gas explosion, thought to be due to gas leaking into the coping and mixing with air.[3]