The protection of the columns, especially in a very high building, should be considered as the most important portion of the fireproofing, although in too many cases it is slighted even to a dangerous extent. The Chicago building ordinance is quite explicit in its requirements for the protection of columns, and forms a good guide for architects elsewhere to follow. These requirements are as follows:
Sec 108. In the case of buildings of Class I. the coverings for columns shall be, if of brick, not less than 8 inches thick; if of hollow tile, these coverings shall be in two consecutive layers, each not less than 2½ inches thick. If the fireproof covering is made of porous terra cotta, it shall consist of at least two layers not less than 2 inches thick each. Whether hollow tile or porous terra cotta is used, the two con-secutive layers shall be so applied that neither the vertical nor the horizontal joints in the same shall be opposite each other, and each course shall be so anchored and bonded within itself as to form an independent and stable structure.
Sec. 109. In places where there is trucking or wheeling or other handling of packages of any kind, the lower 5 feet of the fireproofing of such pillars shall be encased in a protective covering either of sheet iron or oak plank, which covering shall be kept continually in good repair.
Sec. III. In buildings belonging to Class II. the fireproof covering for internal columns is to be made the same as specified for the buildings of Classes I. and IV., excepting only that but one covering of hollow tile or porous terra cotta, and but two layers of any covering made of plastering on metallic lath, are to be used.
The most common and cheapest method of fireproofing interior columns has been through the use of shells of dense terra cotta surrounding the column, the separate tiles being usually clamped or hooked together, but not to the metal work. This method has not proved altogether successful. "The use of dense tiles is only to be recommended when such tiles are hollow, with a proper air space around the metal column, and even then experience seems to show that the hard tile is in no way as satisfactory under great heat as the more porous kinds."*
Solid blocks of porous tiling at least 2 inches thick, well bedded against the metal column and secured by copper wire wound around the column outside of the casing, seems to be the most approved method of insulation.
The custom has been quite general of running the water and gas pipes beside the metal columns and inside the fireproof casing. When this is done the protection at the floors is often very imperfectly made, and the custom is not now approved.
The best method of running and concealing the pipes is that shown in Fig. 199, which represents the fireproofing of the columns in the first eight stories of the newer portion of the Monadnock Building in Chicago.
Fig. 200 shows a few of the best shapes of dense tile covering. The tile shown at A may be used for any size or shape (except round) of column by varying the width of filling pieces a.
*Joseph K. Freitag, C E , in Architectural Engineering.
Columns are also occasionally protected by surrounding them with a thick coating of concrete. When the concrete is formed in place so as to make a monolithic shell, extending 3 or 4 inches beyond the metal, this should make a very efficient protection.