are taken for every 200 to 1,000 pounds of applied load. This method is used in order to obtain a complete record of the deformations, since in this way it is possible to take readings from the point of zero deformations instead of only for the applied loads. Readings are taken up to the point of failure, blocks being so arranged under the beam, as shown in Pl. XV, A, that it can not drop more than one-half inch at failure, thus never endangering the deformeters. After the beam breaks the larger of the two portions is tested on as great a span as its length will permit. The load is applied in the same way as with the long beams, the load points being each 2 feet from the center of the span. No attempt is made to suspend the beam for zero deformations, and only the outside set of deformeters is used. The beam deformeters are of two types; that shown in Pl. XV, A, attached to a beam, is of the electric contact type, the contact being noted by means of head-band telephone receivers; there is also another set used in which the indicator of the dial is moved by the movement of the rod. In Pl. XV, A, the micrometers on the outside set of deformeters are shown at the right; those on the inside set are shown at the left. In some recent tests the inside deformeters have been omitted, their only use having been to confirm the theory of the conservation of plane sections. The vertical deflections of unreinforced concrete beams are so slight that they are not recorded. Form K is used for recording the results of the tests of both full-length and short-length beams. The values entered are subsequently copied into tables for publication. All necessary computations for reducing the results to comparable figures are made by the computing division. applied load exclusive of weight of deformeters, from center. TEST OF PLAIN BEAM. feet...... inches. Age, inches apart. Weight of beam, pounds. Cross section at center, feet...... inches. For character of con Maximum inches pounds. Load applied at pounds. Beam broke feet ...... Unit elongation of lower fiber for weight of beam and attachments ......; modulus of rupture, ......; distance of neutral axis from top, inches. Beam brought from damp closet at......; placed on supports at .; test completed at ......; time ......; sheet given to office at due to Remarks. ....; test started at time REINFORCED BEAMS. A reinforced-concrete beam in the testing machine ready for testing is shown in Pl. XV, B. The support shown at d is the same as that used for plain beams. Addition of the part e gives a rocking motion perpendicular to the length of the beam. This insures an even distribution of the reaction over the width of the beam and also permits the lower part of the beam to elongate without restraint. The test is started by supporting the beam at the third points to get zero deformations; only one set of deformeters is used. The gage length is 29 inches, and the lower contact point is 1 inch above the bottom of the beam, except when the reinforcing rods are 1 inch or 1 inches in diameter, when the lower contact points are 11 inches from the bottom of the beam. The upper contact points are onehalf inch below the top of the beam in all cases. For the purpose of reading vertical deflections a steel piano wire is stretched tight from end to end of the beam and hangs from two clamps, being supported at each end by a projection near the bottom of the clamp directly over the supports. One of these clamps is shown in Pl. XV, B. Near the center of the span a steel scale is fastened to the side of the beam directly behind the piano wire, and the deflections are read on this scale. In order to avoid parallax a mirror is fastened beside the scale. After readings are taken at zero total deformations in the gage length and when the beam rests under its own weight the load is applied in increments which vary with the amount of reinforcement in such a way that as large a number of points as possible is obtained where there is an abrupt change of direction of the load-deformation curve. The first three increments in all cases are 1,000 pounds, after which they are usually 500 pounds each up to a total load of about 7,000 pounds. Between these limits it has been found the cracking of the concrete brings about a sharp change in the direction of the curve. Increments of 1,000 pounds are used from about 7,000 pounds up to nearly the maximum, after which 500-pound increments are again used. Great care is taken to discover the first crack and to locate and trace all the cracks that appear throughout the test. Three men examine one surface of the beam very carefully with reading glasses after each 1,000-pound increment of load. The directions of the cracks and the highest points to which they reach before they become invisible through the reading glasses are marked with a pencil on the concrete and the applied load on the beam is marked at the top of each crack. When the test is completed these pencil marks and numbers are painted on the concrete and the beams are photographed in sets of three. These photographs, two of which are shown in Pl. XVII, a, b, form chronological charts of the development of the cracks, giving their position, shape, and extent for each load. With the 28-day-old beams this method was strictly followed for each individual beam, but when three beams identical in construction and 28 days old failed by tension in the steel, it was safe to assume that the corresponding older |