Fig. 164 shows the Penn Mutual Building of Boston, during construction, of which Messrs. F. C. Roberts & Co., and Mr. Edgar V. Seder of Philadelphia were the architects and engineers. This photograph shows the deep girders at each floor level which serve not only to carry the loads but as wind bracing.
The student should also notice the method of supporting staging independently from any floor, and the masonry supported independently at each floor, as shown at the fourth floor.
Figs. 165, 166, and 167 give interior views of the same building. The floor system was put in by the Eastern Expanded Metal Co. and consisted, in general, of a slab 7 inches thick re enforced continuously at the bottom. by 3-inch No. 10 expanded metal, and also at the top for about four feet from the ends. There were also 4-inch round rods bent over the tops of the girders and running down to the bottom of the slab at the center ; these rods were used every six inches.
The span. of these floor slabs is 17' — 6." These views show also the method of wrapping the columns and flanges of beams with metal lath and plastering.
The student should note, also, the appearance of the center ing shown by Figs. 166 and 167, and of the concrete where the centers are removed; the grain of the wood is shown clearly marked in the concrete.
Fig. 168 shows the Oliver Building, Boston, during construc tion, of which Mr. Paul Starrett was the architect.
This photograph shows clearly the practice of leaving the masonry down for one or more stories and building the stories above. It also shows the iron fascias set in place in the upper stories ; this is clone in advance of the masonry so that the masonry will fit more accurately and neatly around them.
The cornice brackets and framing are shown in place ready for the cornice when the building shall have reached this stage.
Mil. BUILDING CONSTRUCTION.
This term must not he confused with " mill construction." The latter term applies to what is sometimes called "slow burning construction." This is a construction which is the result of the standardizing of requirements and recommendations of the Insur ance Underwriters. It applies to a construction in which the walls are of brick, the interior posts of hardwood and of a size generally not less than 8 inches, the floor of heavy wooden girders with hard-wood floor timbers spaced about 5' 0" center to center and 3" or 4" of hard-wood floor planks ; while this con .
struction is largely of wood the size of the timbers makes them slow burning to a certain degree. Modifications of this construc
tion in varying degrees exist, in which steel replaces some of the wooden members, and from this to the all steel and brick construc tion. ' In some cases the spacing of columns and required floor loads make it desirable to use steel or iron columns and steel girders, the floor beams remaining wood, however. In other cases crane loads and other special requirements make steel mem bers more advantageous than the wood. The possibility of reduc ing the brickwork to a minimum, by carrying all loads on a steel frame, and thus giving large window areas, caused a further development of the steel mill construction. Underwriters object to steel framed mills where the steel is left unprotected and thus exposed to speedy collapse in case of fire. The additional cost of fire-proofing generally results in its omission, however.
Where the building is of the shed construction, that is, with no floors or a very high first story, special provision for strains must be made. Trusses are generally connected rigidly through their whole depth and also by knee braces to the columns. Wind struts at the eaves and at intervals between these and ground are provided. A continuous brace at the ridge, and diagonal bracing in certain bays between the trusses is required. With certain types of buildings, longitudinal trusses or braces between the main braces are also required. Before details of the different con nections met with in this class of construction can be made, the student must become familiar with the general types of construc tion. While only a few of the more common forms can be given, they will serve as a basis for more complete study of the different types.