TRUSS DETAILS. 15 



Calculations of a scries of simple Fink trusses resting on walls and having a uniform span 

 of 60 ft. and different sparing Ravr ilu 1< a^i weight \*T square foot of horizontal projection of 

 tin roof for a spacing of 18 ft., and the least wri^ht of trusses and purlins combined for a spacing 

 of 10 ft. The weight of trusses per square foot was, however, more for the lo-ft. spacing than 

 for the l8-ft. spacing, so that the actual cost of the steel in the roof was a minimum for a spacing 

 of about 1 6 ft.; the shop cost of the trusses per Ib. being several times that of the purlins. Local 

 conditions and requirements usually control the spacing of the trusses so that it is not necessary 

 that we know the economic spacing very definitely. 



For long spans the economic spacing can be increased by using rafters supported on heavy 

 purlins, placed at greater distances than would be required if the roof were carried directly by the 

 purlins. This method is frequently used in the design of train sheds and roofs of buildings where 

 plank sheathing is used to support slate or tile coverings, or where the tiles are supported by 

 angle sub-purlins spaced close together as shown in Fig. 13. 



Truss Details. Riveted trusses are commonly used for mill buildings and similar structures. 

 For ordinary loads the chord sections are commonly made of two angles, Fig. 10. For heavy 

 loads the chords may be made of two channels, Fig. 12. Where the purlins are not placed at the 

 panrl jxrints the upper chord must be designed for flexure as well as for direct stress. Two angles 

 with a vertical plate make an excellent section where the chord must take both direct and flexural 

 stress. Trusses supported on masonry walls should have one end supported on sliding plates 

 for spans up to 70 ft., for greater lengths of span rollers or a rocker should be used. Shop drawings 

 of a steel roof truss are given in Fig. 10. Details of the end connections of trusses resting on walls 

 and fastened to columns are given in Fig. 1 1. Details of truss joints are given in Fig. II. Wher- 

 ever possible, truss joints should be so designed that the joint will not be eccentric. 



Details of Roof Framing. Roof trusses and transverse bents should be braced transversely 

 with vertical framework and bracing to give the roof framing lateral stability. The bracing may 

 be placed in the center line of the building as in Fig. 12, or at the quarter points as in Fig. 4; 

 long span trusses should be braced at both the center and the quarter points. Details of roof 

 framing giving methods of bracing roof trusses and transverse bents are given in Fig. 4, Fig. 41, 

 and Fig. 42. 



Details of a roof truss and roof framing to carry a Ludowici tile roof without sheathing, are 

 shown in Fig. 13. The tiles are carried on sub-purlins, the sub-purlins are supported by rafters, 

 which are in turn supported by the purlins. 



Columns: The common forms of columns used in mill buildings are shown in Fig. 14. For 

 side columns with light loads column (g) composed of four angles laced is very satisfactory, while 

 for side columns that take bending and heavy loads column (/) composed of four angles and a 

 plate is the most satisfactory column. Columns (a), (b), (c), (d), (e) and (j) are used to carry 

 heavy loads. The I beam and the angle columns are used for end and corner columns, respec- 

 tively. Details of a four angle laced column and a four angle and plate column are shown in 

 Fig. 15. Details of a heavy column and a light column made of two channels laced are shown 

 in Fig. 1 6. 



CORRUGATED STEEL. Corrugated steel is rolled to U. S. standard gage. The weights 

 of flat steel and corrugated steel for different gages and thickness are given in Table I. Corru- 

 gated siding and roofing is rolled as shown in Fig. 17. The special corrugated steel in (b) Fig. 17 

 is commonly used for roofing, and the corrugated steel in (c) is used for siding. 



The standard stock lengths vary by single feet from 4 ft. to 10 ft. Sheets can be obtained 

 as long as 12 ft., but are special and cost 5 per cent extra and will delay the order. 



The purlins for corrugated steel without sheathing should be spaced for a load of 30 Ib. per 

 sq. ft. on the roof; and the girts for 25 Ib. per sq. ft. on the sides, as given in Fig. 18. 



The details of corrugated steel as given in Fig. 19 are standard with the McClintic-Marshall 

 Construction Company and the American Bridge Company. 



