Fig. 289.—Molds for Ornamental Railing Posts for Concrete Facade for Bridge.
In constructing a concrete facade for a plate girder bridge at St. Louis. Mo., the railing above the base was constructed of separately molded blocks as follows: The balusters were cast in plaster molds. To make these molds a box square in plan and the height of the baluster was constructed of wood and cut vertically into three sections. The inside lateral dimensions of this box were made 6 ins. greater than the largest dimension of the baluster. A full size wooden pattern of the baluster was set up and the three sections of the box were set around it. Sheets of thin galvanized metal, with their inner edges cut to conform to the curves of the baluster, were inserted in the joints of the assembled box so as to divide the vacant space between the pattern and the box into vertical sections.
Fig. 290.—Railing for Arch Bridge.
Fig. 291.—Form for Lattice Panels Shown by Fig. 290.
A mixture of 1 part Portland cement and 1 part plaster of Paris, made wet, was then poured around the pattern until the box was filled. When this mixture had become hard, the box was taken down, leaving a plaster and cement casing separated into three parts by the sheets of galvanized metal. This casing was separated from the pattern and given a coat of shellac on the inside. Four or five molds of this description were cast. To cast a baluster, the sections were assembled and a ½-in. corrugated bar was set vertically in the center. A mixture of 1 part Portland cement and 3 parts sand was then poured into the mold and allowed to harden. The molds for the urns on the railing post and the balls on the end posts were made in exactly the same manner as the baluster molds. The construction of the railing posts is shown by the drawings of Fig. 289. Referring first to the end posts, it will be seen that they were molded in place in seven sections marked A, B, C, D, E, F and G. The construction of the mold for each section is shown by the correspondingly lettered detail. The intermediate posts were built up of the separately molded pieces I, K and H. The costs of molding the several parts were: Balusters, 60 cts. each; hand rail, 40 cts. per lin. ft. The six intermediate posts cost $12 each, and the four end or newel posts cost $75 each.
Fig. 292.—Form for Hand Rail Shown by Fig. 290.
In constructing the 72-ft. span-ribbed arch bridge over Deer Park Gorge, near La Salle, Ill., a hand railing of the design shown by Fig. 290, was used. In constructing this railing, the posts were molded in place, but the open work panels between posts and the hand rail proper were molded separately and set in place between the posts as indicated. For molding the panels a number of boxes constructed as shown by Fig. 291, were used. These were simple rectangular boxes on the bottom boards of which were nailed blocks of the proper shape and in the proper position to form the openings in the railing. The bottom of the form was first plastered with mortar, then the concrete was filled in and plastered on top. As soon as the concrete had begun to set the blocks were removed so that final setting could take place without danger of cracking. When the concrete had set so that the panel could be safely handled, it was removed from the form and stored until wanted. The hand rail for each side was molded in two pieces in forms constructed as shown by Fig. 292. The total cost of the railing in place was about $2 per lineal foot. The concrete was a 1-2-4 mixture of screenings and ⅞-in. broken stone.