One of the most serious problems in the construction of concrete-steel buildings is the designing of the forms. They must be as light as is consistent with strength to facilitate handling. They should be of simple construction so that they may be set up and removed without too much supervision, and they should be so assembled with bolts and screws that they may be used repeatedly. In erecting a large building sufficient forms are usually provided to set up one floor complete, including columns, beams, girders and floor slabs. After placing the reinforcement, the concrete is filled in as rapidly as possible, making the slabs, girders and columns practically monolithic.
The forms for the girders usually rest upon the column molds and are supported at intermediate points by posts resting on the completed floor below. While column molds are sometimes filled from the top, better work is assured by having one side of the mold built up as the concrete is filled in from the side.
The mold to receive the concrete forming the floor slab is either a part of, or is supported by, the pieces forming the sides of the girders and beams. Provision is sometimes made for leaving supports at intervals under the completed beams and girders after removing the forms from the sides of the beams and the bottom of floor slabs. This is done by making the bottom piece of the girder mold separate, and attaching the side pieces to it by screws which may be removed without disturbing the bottom. The caps of the supporting posts are then made long enough to permit the lower edges of the side pieces to rest directly on them. This method was adopted in building the Central Felt and Paper Company's factory at Long Island City.1
1 Wight-Easton-Townsend Company, Contractors, Engineering Record, Jan. 16, 1904.
625. In the same building the walls were built with molds three feet high and sixteen feet long, placed in pairs on opposite sides of the wall. When one section was completed, the molds were " lifted until the lower edges were two inches below the top of the concrete. In the new position they were supported by horizontal bolts through their lower edges, across the top of the concrete; the upper edges were tied together by transverse wooden strips nailed to them about three feet apart, and they were braced to the false work supporting the roof and column molds." "The bolts passed through sleeves which were left permanently embedded in the walls. At first, iron pipes were used for this purpose, but afterwards it was discovered that pasteboard tubes were equally efficient and much easier to trim and point after the molds were removed".
626. An excellent system of molds was used in the con" struction of the Kelley and Jones Company's factory at Greens-burg, Pa.1 The floor molds were especially convenient, being made collapsible by a hinge joint at the top along the longitudinal center line. . These floor molds were in reality cores between adjacent floor beams; when in place the top surface was horizontal, to form the under side of the floor slab, and the vertical side pieces formed the sides of the floor beams. When the concrete had set sufficiently, the lower edges of the form were made to approach each other, thus coming away from the concrete gradually. A special light wooden framework or tower, with a working platform six feet below the floor, and a rope sling to receive and lower the floor mold, permitted of removing the molds rapidly and without injury. A special truck was also used for moving the floor molds about the building.
627. A convenient adjunct for the construction of concrete wall forms consists of a short section of I-beam having a width between flanges equal to the thickness of the plank to be used. These plank holders are laid in pairs, with web horizontal, one on either side of the wall, and connected by a bolt passing through them and through the wall.2 Two rows of planks on edge are first placed around the building so as to inclose the proposed wall. At the upper side of each junction between two planks in the same horizontal row is placed one of these plank holders. Another horizontal row of planks may now be placed, with the iron plank holders at the joints as before. As the wall is built up, the lower planks and holders may be removed and placed on top, and thus few forms are required. Tees and L-forms are provided for partition walls and corners.
1 Mr. E. L. Ransome, Architect and Engineer, Engineering Record, Feb. 6 and 13, 1904.
2 Patented by Thomas G. Farrell, Washington, N. J.
When an air space is desired in a wall a special terra cotta tile or building block may be built into the wall, but this is quite expensive, and an interior collapsible form may be made of timber by the use of two planks held apart by a wooden brace which may be knocked out. Special means of handling the interior plank should be provided, and the building of a high wall cannot be continuous with this method.