380 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



columns on a rock or masonry foundation, experiments were 

 made by American engineers to determine the value of Portland 

 cement as a holding material. 



For this purpose, fourteen holes were drilled in a ledge of 

 solid limestone, seven of them being If inch in diameter, and 

 seven of them If inch in diameter, all being 3J feet deep. 

 Seven |-inch and seven 1-inch bolts were prepared with thread 

 and nut on one end and plain at the other end, but ragged for 

 a length of 3J feet from the blank end. 



Four were anchored with sulphur, four with lead, and six 

 with cement mixed neat. Half of each were f-inch and half 

 1-inch bolts, and all of them were allowed to stand till the 

 cement was two weeks old. At the expiration of this time a 

 lever of sufficient power was rigged, and all the bolts were 

 pulled, with the following results : 



Sulphur. Three bolts out of four developed their full strength, 

 16,000 and 31,000 Ibs. One 1-inch bolt failed by drawing out 

 under 12,000 Ibs. 



Lead. Three bolts out of four developed their full strength, 

 as above ; one 1-inch bolt pulled out under 13,000 Ibs. 



Cement. Five of the bolts out of six broke without pulling 

 out ; one 1-inch bolt began to yield in the cement at 26,000 Ibs., 

 but sustained the load a few seconds before it broke. 



While this experiment demonstrated the superiority of 

 cement, both as to strength and ease of application, yet it did 

 not give the strength per square inch of area. To determine 

 this, four specimens of limestone were prepared, each 10 inches 

 wide, 18 inches long, and 12 inches thick, two of them having 

 1| inch holes, and two of them 2J inch holes drilled in them. 

 Into the small holes 1-inch bolts were cemented, one of them 

 being perfectly plain round iron, and the other having a thread 

 cut on the portion which was embedded in the cement. Into 

 the 2|-inch holes were cemented 2-inch bolts similarly treated, 

 and the four specimens were allowed to stand thirteen days 

 before completing the experiment. At the end of this time, 

 they were put into the standard testing machine and pulled. 

 The plain 1-inch bolt began to yield at 20,000 Ibs., and the 

 threaded one at 21,000 Ibs. The 2-inch plain bolt began to 

 yield at 34,000 Ibs., and the threaded one at 32,000 Ibs., the 

 strain in all cases being very slowly applied. The pump was 

 then run at a greater speed, and the stones holding the 2 -inch 



