190 PRESENT STATUS OF THE CONCRETE SHIP. 



For the beams the load was applied at the center of the span upon the upper 

 flange. The beams were supported at each end on a steel plate girder. The beam 

 lo feet deep was first loaded forty times with 640,000 pounds, which v/as four times 

 as much as the maximum which the Standards of the Joint Committee on Concrete 

 and Reinforced Concrete would have allowed as its working load. The widest crack 

 at the first application of this load was thirteen one-thousandths inch, and with forty 

 repetitions of the load there was no appreciable increase in widths of cracks. The 

 beam was then inverted and load was applied in the opposite direction, causing 

 failure at 1,363,000 pounds or nine times as much as the Joint Committee standards 

 for reinforced concrete design would have allowed as a working load. 



Plate 104 shows this beam after it had been loaded from one direction. The 

 cracks were painted to make them visible. The holes and channels cut in the con- 

 crete exposed the reinforcement to allow measurements of change of length of the 

 bars to be made. Plate 105 shows the beam after completion of the test in an in- 

 verted position. The cracks formed in this test were approximately at right angles 

 to those due to the first test. This view also shows the manner of failure. 



The ship frames were tested by applying, first, only a vertical load and adding 

 later a horizontal load at the sides corresponding to the horizontal water pressure 

 on the sides of the ship. It was found that the strength here was about eight times 

 as great as the Joint Committee recommendations allowed for the working load, also 

 that the shear due to the horizontal forces reduced the stresses set up by the shear 

 due to the vertical forces ; in other words, that the horizontal water pressure would 

 reduce the stresses caused by the vertical shearing forces on the frame. The form 

 and size of the ship frame specimens are indicated in Plate 106, which was taken 

 before any load had been applied. Figs, i and 2, Plate 107, show opposite sides 

 of the same frame after failure. The cracking was about the same on both sides, 

 but in Fig. 2 the cracks had been painted to make them visible. This view shows also 

 the places where the reinforcing bars were uncovered for the purpose of measuring 

 elongations and shortening during testing. 



A larger series of beam tests is being conducted at Lehigh University. Plate 

 108, shows the reinforcement for a typical beam of this series. Plate 109 shows 

 a beam in the testing machine. These tests confirm conclusions based on the Pitts- 

 burgh tests and will afford much more complete information on which to base 

 design. 



These tests have made it possible to design with confidence, using working 

 shearing stresses much higher than those which are recognized by the Joint Com- 

 mittee on Reinforced Concrete for structural members of ordinary design and pro- 

 portions. However, it has not been necessary as yet to use working stresses as high 

 as appear from the tests to be justified. 



Tests are under way to determine the effect of rapidly repeated loads on a rein- 

 forced concrete beam. A beam supported in a frame has a motor operating a lever 

 in such a way as to apply a known load to the beam alternately upward and down- 



