METHOD OF RECORDING CHARACTER OF REINFORCED-CONCRETE BEAM FAILURES. a, c, Typical failures by steel reaching elastic limit; b, typical failure by diagonal tension and stripping of rods. MAXIMUM LOAD 21870 00081 14000 14000 12000 16000 14000 20000 20 20000 +12.000 00000000 00091-00021 0006 +14000 12000 18000 14000 12000 412000 12000 GOOD 00000000 0008 0006 0009 00091 0009 00002 DOOR 20000 22120 +22120 -22120 22120 21280 21280 021324 2/280 00002 000900040000 000 线 3000 2000 244 243 beams would fail in the same manner, since the gain in strength of the concrete rendered it less likely to fail. Consequently, when the older beams were tested, the cracks were marked out for the increments of 1,000 pounds for the first beam only of each set of three. The other two were tested to failure; at the maximum load the cracks were marked out as before. A group of three beams treated in this manner is shown in Pl. XVII, c, the bottom beam being the one first tested. Slipping of the rods with reference to the adjacent concrete at the ends of the beam is determined by means of a micrometer reading to one ten-thousandth of an inch, shown at the extreme right end of the beam illustrated in Pls. XV, B, and XVI, A. The micrometer is clamped to the end of the beam, from which a small portion of concrete has been removed, exposing the end of one of the reinforcing rods. The micrometer screw is adjusted to touch the end of the exposed rod. No electric contact is used with the micrometer since the least slipping of the rods may be detected by touch. This same instrument is used to detect the slipping of the rods in the bond tests. Form L is used for recording the results of the tests on reinforced concrete beams. Beam Reg. No. UNITED STATES GEOLOGICAL SURVEY. ....... Lab. No. Age points spaced ...... inches apart. Weight of beam inches. Span ...... REINFORCED inches. Contact feet inches. Rods: days. Gage length pounds. Length of beam ...... feet...... inches. Cross section at center...... inches by Number........; size...... .........; kind................ Reg. No. of steel...... For distribution of steel, see diagram No.... For information regarding concrete and corresponding test pieces, see Batch report Bm.... Deformeter No. Weight of deformeter Applied inches from center. inches from center. pounds. Load applied at pounds. Position of crack feet ..... ...... load at first observed crack time; test completed at due to....... COMPUTATIONS. The forms of batch report for both the plain and reinforced beams (Form F, p. 40) are identical except that for the reinforced beams the number, size, position, and form of rods are also given. For these beams the percentage of reinforcement is computed and the yielding point of the steel is found from tests on short pieces cut from the reinforcing rods before being placed in the beams. In order to make clear the methods used in obtaining some of these values a short statement of the theory will be given. The method of finding the necessary decrease in the reactions in order that the total deformation within the gage length will be zero will be given first. This method is used in order to obtain a greater number of readings of the micrometers during the test and therefore more points on the deformation-bending moment curves. |