32 BULLETIlsr 801;, U. S. DEPAETMENT OF AGEICULTUEE. 



6 inclies in 50 feet, the usual amount for the compartment 100 feet in 

 length between exterior walls. This slope will reduce damage to the 

 cotton and, in the case of elevated floors, will prevent possible over- 

 loading from an accumulation of water — such as might result from, 

 continued flow of sprinklers. 



ROOF AND SELF-SUPPORTING FLOORS. 



Designs and materials for fire-resistive roofs and self-supporting 

 floors have been tried in many forms. Many methods of construction 

 used in the early development of fire-resistive construction were 

 needlessly costly and afforded very poor protection. In fact, the 

 simplest and often comparatively inexpensive construction usually 

 has proven the best.^ This discussion of roof and floor designs will 

 be confined to constructions which is most suitable for. the warehouse. 

 For special conditions other types of construction possibly may be 

 suitable. 



Eeinforced concrete is preeminently suited for the requirements 

 of the cotton warehouse. This material consists of concrete com- 

 posed of Portland cement, sand, and crushed stone or similar ma- 

 terial, so strengthened or reinforced with steel rods as to secure tho 

 most economical use of the strength and fire-resistive qualities of 

 both materials.^ 



In this construction the tensile strength, or the capability to with- 

 stand a pulling force, is supplied by the steel rods which are pro- 

 tected from the action of fire by the surrounding concrete. The 

 compressive strength, or the capability to withstand a pushing 

 force, is supplied by the concrete. This action of the concrete is 

 sometimes supplemented by additional steel. The value of this con- 

 struction depends very largely on a proper proportionment and ar- 

 rangement of the concrete and the steel, A detailed discussion of 

 the engineering phase of the construction is scarcely within the 

 scope of this treatise, though it should be pointed out emphatically 

 that the design should be handled by a competent engineer experi- 

 enced in this character of work, while the construction should be 

 under careful supervision. The most dangerous construction has 

 been the result of builders having no laiowledge of the real principles 

 of engineering involved. The mere judgment of such builders is 

 worthless in this type of construction, even though they may be 

 successful in ordinary frame buildings. 



* Valuable information and result of fire tests is contained in a Report on a 

 Test of Floors in the United States, by Ira H. Woolson, E. M., consulting engi- 

 neer, National Board of Fire Underwriters and Eudolpli P. Miller, C. E., 

 superintendent of buildings, New York City. 



^ See U. S. Bureau of Standards, Technologic Paper No, 2 : The Strength 

 of Reinforced Concrete Beams; Results of Tests of 333 Beams, by Richard 

 L. Humphrey and Louis H. Losse, 1911. 



