The form shown by Fig. 199 was used in constructing a factory building in Long Island City, N. Y., and it is given here chiefly for the purpose of exhibiting the unnecessary complexity of form work. Comparing this form with that of nearly any of the preceding designs will bring out the point. The design, however, was one of the earlier ones to recognize the advantage of stripping the slab centers and the sides of the girder boxes without disturbing the bottom plank of the boxes or the staging. The drawing shows the independent support of the bottom board and side pieces of the girder mold on the transverse caps of the staging posts. These posts are 6×8 ins. in section and are spaced from 6 to 8 ft. apart. Briefly described the bottom board is a single plank from 1 to 3 ins. thick, to which the side pieces are lag-screwed at the bottom. The side pieces are panels composed of 4×⅞-in. vertical boards nailed to top and bottom 2×4-in. horizontal timbers. A third horizontal timber near the top serves as a seat for the ends of the joists carrying the slab lagging and is braced from the bottom horizontal by vertical stiffeners. The edge boards of the slab lagging are nailed to the top edges of the side pieces of the girder mold and the tops of these side pieces are connected across the trough by strips of board; all the slab lagging boards except those at the edges of the girder molds are laid loose. In the building referred to, after the floor concrete had set about seven days the joists carrying the slab lagging were turned a quarter over thus dropping the slab form about 2 ins. A few days later the joists and lagging were taken down and the side pieces of the girder mold were unscrewed and removed. The bottom board and staging posts were left in position about three weeks longer and then dropped about 1 in. by removing fillers from the staging post caps. In another week the bottom boards and staging posts were taken down. This construction of form and method of removing it permitted the concrete to be stripped so that the air could get at it as fast as it was safe to take the support from any part and at the same time kept the supports in such position that they form a safety platform in case of collapse. A more important advantage is that the form timber can be removed as fast as any part of it is free and used again. Thus the lagging boards and joists and the side pieces for the girder molds were free for use again about every two weeks and yet the main supports of the girders were undisturbed until they were fully a month old.
Other examples of girder and slab forms are shown in the succeeding sections describing the construction of a six-story building and of a garage constructed at Philadelphia, Pa.
Fig. 200.—Collapsible Core Forms for Girder and Slab Floors.
Another type of slab and girder form construction that deserves brief mention because of its variation from usual practice and also because of its extensive use by one prominent builder is shown by Fig. 200. Cores, or inverted boxes, with four vertical sides and rounded corners, are set side by side, with ends on stringers carried by the column forms, at intervals wide enough to enable the beam to be molded between. A plank resting on cleats on the sides of the cores forms the bottom of the beam mold. The main girders are molded in similar spaces between the ends of the cores in one panel and of those in the next panel. To permit the core to be loosened readily it is hinged; when in place spacers inside the core keep the sides from closing. These are knocked out, the core sides close together and the core is removed for use in another place. Cores similar to these were used in molding the ribbed floor for the Bush terminal factory building described in a succeeding section. These cores are capable of repeated use so that while they are somewhat expensive to frame they give a very low cost of form work when the beam and girder spacing is arranged largely in duplicate from floor to floor. It will ordinarily be cheaper to have these cores made to pattern by regular woodworking shops, and shipped to the building ready to erect.
WALL FORMS.—Wall work in modern commercial and manufacturing buildings, when we come to eliminate windows and wall columns and girders, is confined very largely to isolated curtain wall panels between windows and framework. In such buildings, therefore, wall forms consist merely of wooden panels, one for each face of the wall, constructed to fit the spaces to be walled up. Where these spaces are duplicated from bay to bay or story to story the same form panels will serve repeatedly. For residences and other buildings having greater proportionate area of blank wall the builder has a choice between continuous forms carried by staging and movable panel forms.
Fig. 201.—Continuous Form for Wall Construction.
For one and two-story buildings, with the usual variation in architectural detail, panel work and window work, the continuous form has many advantages, and the superior economy of movable panels in retaining and other plain wall work is by no means always true here. One good type of continuous wall form construction is shown by Fig. 201. The gallows frames are spaced about 6 ft. apart along the wall and connected by horizontal stringers nailed to the uprights or by diagonal bracing. Each frame may be made up of 6×6-in. posts connected by 2×4-in. cross-struts and diagonals with bolted connections so that the frame can be taken down and put together easily and so that the bracing can be removed as the wall is built upward. The other details of the form work are shown by the drawing. This construction leaves a clear space for placing the concrete and the cross pieces give support to runways; it has been successfully used in a large amount of low building work.
