684 EXPERIMENT STATION KECORD. [Vol.36 



described for conducting wear tests on concrete blocks 8 in. square and 5 in. 

 thick by means of the Talbot-Jones rattler. 



The strength of clamped splices in concrete reinforcement bars, E. L. 

 Lasier {Avier. Soc. Testing Materials Proc., 16 (1916), pt. 2, pp. 209-238, figs. 

 12; abs. in Engin. and Contract., 45 {1916), No. 26, pp. 518, 519, fig. 1; Engin. 

 Rec., 74 {1916), No. 2, pp. 48, 49). — " U-bolt clamped splices of both 17- and 

 21-in. lengths of splice were tested to determine the load at first slip and the 

 maximum load the splice would resist. Three different classes of splices were 

 thus tested, (1) lap splices not embedded in concrete, (2) butt splices not 

 embedded in concrete, and (3) lap splices embedded in concrete. The rein- 

 forcement steel in all cases consisted of 1-iu. square cold twisted bars. 



" The loads necessary to produce first slip had a range of from 7,000 to 

 50,000 lbs. The maximum loads which the splices withstood varied from 23,000 

 to 69,000 lbs. The ratios of load at first slip to yield point of bar for clamped 

 splices not embedded in concrete varied from 12 to 21 per cent, and for splices 

 embedded in concrete from 53 to 83 per cent. Ratios of maximum load to 

 tensile strength of bar ranged from 31 to 61 per cent for unembedded splices, 

 and from 79 to 95 per cent for embedded splices. The conclusions which may 

 be drawn from the tests are as follows : 



" The 4-in. difference in lengths of lap tested, of one bar upon the other, 

 apparently does not affect the rigidity or strength of the splice. The clamped 

 lap splices not embedded in concrete sustain, on the average, a slightly greater 

 load before first slip, and a larger maximum load, than the clamped butt 

 splices. Splices consisting of two bars of opposite twist probably sustain a 

 greater load before first slip, and a larger maximum load, than do splices in 

 which the bars have like twist. 



" When U-bolt clamped lap splices (of the type, size, and lengths reported 

 upon) are embedded in masses of concrete similar to those of the test speci- 

 mens, the splices may be expected to withstand a stress before first slip equal 

 to at least one-half the yield point stress of the continuous reinforcement bar. 

 Also, the maximum strength of such splices is probably equal to at least three- 

 fourths of the tensile strength of the bar. When U-bolt clamped lap splices 

 (of the type and lengths reported upon) are embedded in relatively large 

 masses of concrete, It is reasonable to suppose that first slip would not occur, 

 or the splice would not completely fail, before the yield point or tensile strength, 

 respectively, of the reinforcement steel had been reached ; for in such cases the 

 splices would undoubtedly fail only by the pulling out of the bars along the 

 grooves (either through untwisting or through direct shear), and not by 

 splitting of the surrounding concrete. In either case, unlike the results in the 

 tests, the clamps would remain embedded in the concrete, unless the concrete 

 prism directly compressed by the area of the upper or lower clamps were pulled 

 out also, a condition which is not in the least likely to occur \vith a relatively 

 large mass of concrete. Hence for purposes of design, it is probable that such 

 U-bolt clamped lap splices, embedded in concrete under conditions ordinarily 

 obtaining in actual practice, could safely withstand a unit load equal to the 

 allowable unit stress in the steel reinforcement bars." 



An apparatus for determining soil pressures, A. T. Goldbeck and E. B. 

 Smith {Amer. Soc. Testing Materials Proc, 16 {1916), pt. 2, pp. S09-319, figs. 

 5; abs. in Engin. News, 16 {1916), No. 8, p. 339, fig. 1; Engin. Rec, 74 {1916), 

 No. 2, p. 48, fig- 1). — This paper describes an apparatus for measuring the 

 pressure under earth fill or against walls. A small cell having a thin brass 

 annular diaphragm is buried at the desired position with pipe and electrical 

 connections to an air supply and electrical equipment. Air pressure within the 

 cell equilibrates the external soil pressure as indicated by breaking the elec- 



