This term must not be 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 Insurance 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 construe-tion in varying degrees exist, in which steel replaces some of the wooden members, and from this to the all steel and brick construction. 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 members more advantageous than the wood. The possibility of reducing 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.

Special Features. Mill building, and by this term is included machine shops and all classes of manufacturing buildings, must always be treated according to the requirements and conditions peculiar to the case. Details and capacities cannot be as well standardized as in the case of other classes of buildings, because there are generally features or combinations of features peculiar to the case. For this reason, the required loading should be accurately determined and the details carefully studied. Heavy loads should be brought directly on columns or over girders if possible, rather than supported by shelf or side connections.

Hill Building Construction 0500187

Fig. 168.

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 connections met with in this class of construction can be made, the student must become familiar with the general types of construction. 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.

Figs. 169 to 174 show general features and details of a building of the shed type.

Fig. 169 shows the side framing, the openings, diagonal bracing, eave strut and columns.

Fig. 170 shows a plan of the columns and trusses, and the bracing between. Fig. 172 shows the end-wall framing, and Fig. 171 is a cross-section showing the type of trusses and the bracing to the columns.

Fig. 173 shows a detail of the walls and the columns. These •walls are for protection against weather only, and are not designed to stiffen the steel frame which is sufficiently braced together itself.

Fig. 174 shows the anchorage of the ends of the trusses if solid walls were used in place of the steel wall columns.

Figs. 175 to 177 show a machine shop steel frame with pin connected trusses. Generally trusses of this character are riveted, but occasionally they are pin connected.

Fig. 175 shows the cross-section with low wings along the side walls and a high central portion to provide room for a travelling crane. This central portion is lighted by a monitor at the top as shown; the windows in the end walls are also indicated.

The columns are braced together and to the trusses and the whole frame is self-supporting. The crane runs on a track girder which is supported by a separate column. This is of advantage because it allows the column to be placed directly under the load instead of on a bracket which would cause heavy eccentric loading.

Hill Building Construction 0500188

Fig. 173.

Hill Building Construction 0500189

Fig 171.

Hill Building Construction 0500190

Fig. 169.

Hill Building Construction 0500191

Fig. 174.

Hill Building Construction 0500192

Fie. 172.

Hill Building Construction 0500193

Fig. 170.

Hill Building Construction 0500194

Fig. 176 shows a partial elevation of the side. The columns are placed under every other truss only; the intermediate cross trusses are therefore supported by longitudinal trusses shown by Fig. 176. These trusses serve also to give the necessary lateral stiffness to the frame.

Hill Building Construction 0500195

Fig. 177 shows a detail of the ends of these trusses and the connection to the columns and of the bracing to the columns and trusses.

Figs. 178 to 183 show the outlines and some details of a light mill building having a double pitched roof as shown by the elevation, Fig. 178. This elevation has letters indicating the positions of the different types of purlins shown by Figs. 179 to 182.

Hill Building Construction 0500196

Fig. 183.

As there are skylights on this roof, purlins "B" have special framing. The regular purlin is "A," and "D" shows the wind struts between the columns; there is also a wind strut at the ridge.

OFFICE BUILDING FOR THE CHICAGO & NORTHWESTERN RAILWAY COMPANY, CHICAGO, ILL., JACKSON BOULEVARD SIDE

OFFICE BUILDING FOR THE CHICAGO & NORTHWESTERN RAILWAY COMPANY, CHICAGO, ILL., JACKSON BOULEVARD SIDE.

Frost & Granger, Architects; E. C. & R. M. Shankland, Engineers. This Illustration shows the Modern Steel Column and the Greek Doric Column - the Structural Column and the Applied Classic Column - Side by Side, the Former being Used Solely for Structural Purposes, the Latter being Used Structurally in the Facing of Granite, and also Decoratively to Mark the Entrance to the Building. For Plan, See Page 138.

OFFICE BUILDING FOR CHICAGO & NORTHWESTERN RAILWAY COMPANY, CHICAGO

OFFICE BUILDING FOR CHICAGO & NORTHWESTERN RAILWAY COMPANY, CHICAGO.

Details of wind-bracing construction in basement. Note connection of beams to girders, also girder connection to column. Note that all connections are riveted.

Hill Building Construction 0500199detail of Main Column Fig. 186.

detail of Main Column Fig. 186.

Detail of Connection of Floor Girders to Wing Columns. Fig. 187.

Detail of Connection of Floor Girders to Wing Columns. Fig. 187.

Fig. 183 is a detailed elevation of one-half of the main truss, and of the connection of the purlins to the truss.

Figs. 184 to 187 show general features and details of a combined wood and steel frame mill building. This form is used quite extensively. The main columns, trusses and girders are of steel; the roof purlins and floor beams of wood, and the walls of brick.

Fig. 185 shows the detail for securing the wood purlins to the trusses.

Fig. 186 shows the main column which carries a bracket for a light crane. This column, on account of the eccentric crane connection, is made of the two channels latticed as shown; in order to get a stiff connection of roof truss to the upper section of column, and also, because of the light load, a column of four angles and a web was desirable. This upper column, therefore, sets down inside of the channel column and is riveted to it as shown by the details.

Fig. 187 shows the connection of the girders in the wings to the columns; the double beams coming at right angles to the web made it necessary to use deep shear plates across the flanges of the column in order to give support to the bracket and provide for the eccentric strains.

OFFICE BUILDING FOR CHICAGO & NORTHWESTERN RAILWAY COMPANY, CHICAGO

OFFICE BUILDING FOR CHICAGO & NORTHWESTERN RAILWAY COMPANY, CHICAGO.

Girder connection to column on first floor. Note method of temporary bolts in connections. These are bolted up temporarily until the steel frame is plumbed up; then the connections are made with rivets. In good practice, about one-half of the holes are bolted up. Note knee-bracing of girders to columns. Note stiffened angles on girders fitted to top and bottom flange.