The Viaduct Works' Handbook

45 throughout the height. Within this space, at the bottom of it, the main girders were built. They were of sufficient length to reach nearly from centre to centre of piers; and after they were lifted to top of piers, the distance girders bb were fixed with the bracing bars connected to them. The sectional area of acting metal in the columns of one pier is about 400 square inches, and the maximum strain on the iron under test load is less than 1% tons per inch. The advantages offered by iron piers over masonry are :— 1st. Simplicity in erection and construction, as all the materials can be prepared and fitted before they are brought to the spot, and no expensive scaffolding is required. They are so arranged that each length of columns can be completed, and a few planks laid upon them forms a good even floor, and convenient to proceed with the next length. The materials are drawn up by a common windlass, and, as the heaviest piece does not exceed one ton in weight, can be easily fixed by common sheer legs and pulleys. 2nd. The rapidity with which these iron piers can be built—a pier 200 feet high can be completed in ten or eleven weeks, while a masonry pier of the same dimensions about as many months. 3rd. The amount of pressure on the foundations in some situa- tions is an important consideration. Mr. Kennard’s iron pier is remarkable for its lightness, and consequently a small amount of pressure on the foundations. The following estimate shows the weight on the foundations of a pier of the Crumlin Viaduct, and what may be fairly calculated for a stone pier of suitable dimensions :— WEIGHT ON FOUNDATION OF IKON PIER. Tons. Iron . . . 200 Superstructure . 100 Passing load . . 300 600 WEIGHT ON FOUNDATION OF MASONRY PIER. Tons. Masonry . 2900 Girders, &c.. . 100 Passing load . 300 ------segn 3300 The base of the iron pier is about 40 feet by 30 feet, or 1,200 superficial feet, therefore the pressure on the foundation is about half a ton per superficial foot, while that of masonry pier must be at least five times as much. 4th. The saving in the cost of iron piers may be safely estimated