by hand while the concrete is tamped around it. The concrete is brought somewhat above the top of the mold; then the casting shown in Pl. XI, A, its surface having been oiled, is slipped down over the rod and twirled about on the surface of the concrete. After the concrete has set the casting is removed, leaving the upper surface of the test piece as a smooth plane perpendicular to the rod. The test pieces are stored in the moist room. The molding room is shown in Pl. XII. Three empty molds used in forming the beams are shown in the foreground. Each mold makes a beam 8 inches wide, 11 inches deep, and 13 feet long, and consists of five sections of steel channel bolted together. The two side channels and the two pieces closing the ends are placed with their flanges outward. The channel forming the bottom is placed with its flanges turned down. At the points where the beams are supported in moving them the webs of the bottom channels are cut away for a width of 1 inches. When the beam is being molded this slot is closed by a filler. When the beam is ready to be moved this filler is driven out and a slightly narrower piece which projects 11 inches beyond each side of the beam is substituted. A stirrup hanging from the chain blocks is hooked under these projecting ends. When the concrete is ready to be placed in the molds their inside surfaces are coated with oil. In molding the plain beams the concrete is deposited in three layers of approximately equal thickness and the layers are tamped by hand. Each layer is tamped three times with an iron tamper weighing 133 pounds and having a rectangular face, 1 by 34 inches. The following sequence of steps is strictly followed: Beginning at one end of one side of the beam the tamper is moved its own width at each stroke until it arrives at the opposite side. It is then moved forward and worked back across the beam. In this way every part of a layer, after the first tamping, has been struck once. This operation is then repeated. After each layer has been tamped twice the concrete is spaded back from the sides of the mold, the attempt being to reach down to the bottom at each spading. With the dry mix, however, it was found impossible to force the spade to the bottom after the top layer had been tamped. After each spading the layer is tamped a third time to force the concrete back against the sides of the mold. The tops of all beams are troweled to as smooth a surface as possible with a large bricklayer's trowel. In molding reinforced-concrete beams two methods are used, depending upon whether the steel is placed in one or in two layers. All the reinforced beams are tamped with a pneumatic tool working under 60-pound pressure and having a 3-inch by 3-inch rectangular head. The method of tamping described above for the plain beams is followed, except that each layer, after the first, is tamped but once before spading and once after. When the rods are in one layer their centers are placed 1 inch from the bottom, except for 1-inch and 14-inch rods, for which a distance of 14 inches was used. Sufficient concrete is placed in the bottom of the mold to bring the surface of the layer a little above the center of the rods. After this layer has been tamped twice the rods are laid upon it and held the proper distance apart and from the sides of the mold by slotted wooden templets. The rods are then tapped down into the concrete to the required depth; the distance down from the top being gaged by means of a T-shaped templet, the arms of which rest on the sides of the mold and the end of the leg on the rods. The concrete is then placed in three equal layers, tamped and spaded as described above, and the top troweled smooth. With those beams reinforced with two layers of rods the manner of placing the first layer of concrete and the bottom layer of rods is identical with that followed when there is but one layer of steel. When the lower rods have been placed a layer of concrete is added of such thickness that, when tamped, its surface comes about to the depth of the center of the upper layer of rods, which are placed 24 inches from the bottom of the beam. This layer of rods is then placed in the same manner as the first layer. The concrete in the remainder of the beam is placed in three layers in the usual manner and the top troweled. The accuracy with which the rods are spaced may be seen in Pl. XI, B, which shows a beam selected at random and cut open after testing. Three beams are molded in succession; the first three are molded on the floor and over these wooden horses are placed upon which to support another set of three beams. The molds are allowed to remain on the beams for twenty-four hours. The sides and ends are then removed for use in molding other beams. The beams remain on the bottom channels until lack of room on the molding floor makes it necessary to move them into the moist room. With the present accommodations the time that the beams are permitted to remain on the molding floor ranges from twelve to sixteen days. When the side channels are removed the beams are covered with burlap, which is kept wet by sprinkling with a hose at regular eight hour intervals. STORAGE. When it becomes necessary to move the beams they are lifted from the bottom channels, as described, by means of hoists. The 4-wheeled trolleys run on the bottom flanges of I beams that traverse the ceilings of the molding and storage rooms. A smooth motion, free from jolting, is obtained by the use of Yale & Towne triplechain blocks. The tracks are spaced such a distance apart that a 13-foot beam will be supported at those points which will cause a minimum bending moment. An interior view of the moist room for storing beams, cylinders, cubes, and bond test pieces is shown in Pl. XIII. A 13-foot beam, supported by the trolleys, is shown at the right. The cylinders are piled three high with three cubes at the top. The beams are piled six high and the piles are prevented from toppling over by the wooden racks shown at the left. Each beam rests on two small timbers placed at the points that give the smallest bending moment. The register numbers of the test pieces may be seen. Either steam or water may be sprayed into the moist room from the ordinary type of fire sprinklers near the ceiling. At the present time water is sprinkled in fine spray over the test pieces at regular eight-hour intervals. The waterproofing of this room for the purpose of making it steam tight was done without cost to the laboratories under the supervision of a representative of the Hydrex Felt and Engineering Company, through the courtesy of the manager, Mr. Edward De Knight. Both the molding and storage rooms have self-registering thermometers giving a seven days' continuous record, and the moist room is equipped with a hygroscope for determining the percentage of moisture in the air. Each day the beams that are to be tested are raised by means of the chain hoists, moved out into the molding room, and placed upon two trestles or upon the floor, whence they are taken to the testing room. BEAM TESTING. APPARATUS. The testing room is equipped with one 3-screw 100,000-pound testing machine, one 4-screw 200,000-pound testing machine, and one 3-screw 200,000-pound testing machine, as shown in Pl. XIV. A 600,000-pound machine for testing columns and large beams is being installed in this room. The machine ordinarily used for testing beams is shown in the center. The beams are raised and carried to the testing machine by means of a steel carriage shown in Pl. XVI, B. The carriage is pushed along the floor end first over the extension arm of the testing machine and one end of the beam is lowered to a dolly and rolled into place on the testing table. The beams are tested on a 12-foot span. The load is applied to the beams at the third points; that is, 4 feet from the ends and 4 feet apart. The apparatus through which the load is transmitted to the beams at two points consists of a steel box girder 4 feet long by 6 inches deep, built of two 6-inch channels and a 4-inch by 8-inch cover plate, top and bottom. 15767-Bull. 329-08-5 |