MATERIALS.
Space does not permit of a discussion of the value of every conceivable variety of build ing material and attention must therefore be directed to those which are commonly used or are of especial importance and utility..
1. Wrought Iron, Steel and Cast Iron.— Wrought iron and steel are largely used as beams, girders, columns or trusses, supporting not merely their own weight but also bearing an additional load — often a very great one. Subjection to tests and the exacting conditions of conflagrations show that, unprotected, these materials are very unreliable. Unprotected Fireproofing of Steel Roof Trusses.
steel, for example, will expand with each 100 degrees Fahrenheit so as to increase one inch in each 125 feet of length, an expansion at times sufficient to overthrow masonry bearing-walls. Steel columns are estimated, as a result of tests, to yield at temperatures of from 1,000 to 1,200 degrees Fahrenheit. With efficient pro tection, however, the steel framework of modern construction has demonstrated its value. Under these conditions, the end of the San Francisco fire found it usually uninjured. Cast-iron is most frequently used for columns supporting light loads and for ornamental construction. In moderate fires it may stand unprotected with insignificant damage. Above 1,500 degree's, however, the limit of its endurance is reached, with the consequent possible collapse of struc tures. Unprotected steel and iron members bearing loads are therefore a source of con siderable uncertainty and danger.
2. Stone.— Granite, limestone, marble, sand stone and all other building stones may be briefly dismissed with the statement that they will, under the action of heat, crack, disinte grate into sand, decompose into lime and spell. They have not the value which cursory thought would indicate. A photograph of a public storehouse in Baltimore showed granite columns completely destroyed by the fire and the per centage of loss to value of stone fronts is very high. Beautiful ornamental masonry fronts emerged from the San Francisco fire as ruins. The use of stone should therefore be confined to situations where severe exposure to heat is not anticipated.
3. Brickwork.—The value of this material has been conclusively demonstrated by many fires and conflagrations, the degree of value depending principally upon the chemical com position of the clay. Sand-lime bricks are said to be of value at least equal to the ordinary type. Conflicting testimony makes a conclusion
as to pressed-brick difficult and glazed brick showed considerable scaling in the Baltimore and San Francisco conflagrations.
4. Terra-cotta.—This differs from brick in that it consists of two or more specially selected clays, used in definite proportions, with the addition of grit. Each piece is made, further more, according to design and is not of stock form. It is extremely durable and impervious to water. The results of architectural terra cotta were disappointing in the two great fires above mentioned, the loss of value being often 70 to 75 per cent. This was principally due, however, to mechanical damage caused by poor construction or the expansion of covered steel members)) Terra-cotta fronts suffered con siderable damage in San Francisco, although the material retained its form. Opinions re garding structural terra-cotta vary widely, the relative value of concrete and structural terra cotta being a question brought into prominence by the large conflagrations. Important uses of these materials are for floors and column pro tection. An intermediate opinion seems to be that porous and semi-porous tile withstands a reasonable test, if intelligently used in sufficient quantity — a condition, however, seldom ful filled in the past.
5. Concrete.—There are three primarily im portant uses of this material, which has been in the limelight of discussion for some time — (a) floor construction, (b) column protection and (c) reinforced concrete buildings. Broadly speaking, concrete is used for floor construction under two types of conditions; where steel columns, girders and beams furnish the support and where the entire construction is of concrete. From previous remarks it is evident that steel supports require protection and columns will be more fully discussed later. The applicability of concrete to floor and roof construction has largely been made possible by the introduction of forms of metal reinforcement, which on the one hand add tensile strength while on the other they reduce the thickness and weight. Tests show that concrete floors may be so constructed as to embody a high degree of fire resistance and great load-carrying ability under emer gencies. Opinions as to their value, emanating from authorities on the basis of actual condi tions in San Francisco, are divergent. Some, regarding it as a fireproofing material, are dis