FIRE-PROOF BUILDING CONSTRUCTION. 615 



The proportions of cement and coarse beach-sand and gravel, used 

 in re-enforcing iron beams for floors and roof-supports, were one part 

 of cement to two parts of sand and gravel. The size of the iron beam, 

 selected for an experimental test, was a four-inch I-beam of lightest 

 pattern, twelve feet long, weighing thirty pounds to the yard, and its 

 safety load was limited to eleven hundred and fifty pounds. A plank 

 mold was made the length of the iron beam, twelve inches deep by 

 five inches wide, in the bottom of which a layer of beton was first 

 moderately tamped down to an inch in thickness ; then the iron beam 

 was laid on the course at equal distances from each side of the mold, 

 and settled down on the surface of the course of b6ton to a good bear- 

 ing. This brought the top surface of the beam seven inches below 

 the top of the mold. The work of filling and tamping the courses 

 was then continued until the mold was filled. 



The reason for placing the iron beam so near the bottom of the 

 mold was to utilize its tensile quality for resisting the strain below 

 the neutral axis when this composite beam was exposed to heavy 

 loads, while the beton above this line was relied on for resisting com- 

 pression from load-strain. The beton became thoroughly hardened in 

 about thirty days, when the following tests of transverse strength 

 were made : It was placed upon suitable supports, with a bearing 

 of three inches at each end. A lever was adjusted so as to bring 

 the testing-load on a knife-edge bearing at the center of the beam. 

 Weight was then applied to the long end of the lever, until the stress 

 on the center of the beam reached nine thousand five hundred pounds. 

 Under this load there was a deflection at the center of the beam of 

 seven sixteenths of an inch, but not a sign of rupture appeared at any 

 point. 



The load was then removed, and the beam returned to the original 

 line it occupied before the test, showing that the combination pos- 

 sesses the essential quality of elasticity in addition to the enormous 

 increase of capacity to resist strain over that which was possible for 

 either material to sustain if used separately, and in the same quantity. 



It is suggested that for future construction an inverted x-beam 

 would furnish a more preferable distribution of iron in the composite 

 beams than the I-beams which were used. 



The result of this experiment demonstrated the reliability of the 

 composite beam of iron and beton, and showed that the adhesion of 

 the cement to the iron could be depended on under heavy strains. This 

 warranted the adoption of beton, re-enforced with small rods, for the 

 floors and roofs. 



The beams for supporting the floors throughout the house were 

 placed at such convenient distances apart as to insure perfect safety 

 to the floors, and at the same time afford ample opportunities for 

 producing the best effects in deep, paneled ceilings. 



All the beams were molded in the positions where they belonged, 



