H.—2l.

8. Annealing. —Excepting minor details, steel which has been partially heated shall be properly annealed. 9. Burning.—The use of a burning-torch is permissible if the burned metal is not carrying stress during the burning. Stresses shall not be transmitted into metal through a burned surface. 10. Gleaning and Painting.—All iron and steel surfaces, except such as are to be encased in concrete with a hard aggregate (not breeze or pumice) mixed, in the proportion of one to two and a half to five (1.: 2§: 5), or a richer mix, shall be painted. All surfaces, before painting or enclosing in concrete, shall be thoroughly scraped and cleaned of rust, scale, and dirt, either with sand-blast, steel scrapers, or stiff wire brashes ; finally, surfaces to be painted shall be dusted off with stiff bristle brushes. Oil, paraffin, and grease shall be removed by wiping with benzine or petrol. All painted work, including rivet-heads, shall receive at least two coats all over. Part II. —Working Stresses. 1. Subject to the provisions of Sections 2, 3, and 4, the working unit stresses shall not exceed the following per square inch : — lb. (a) Tension on net section .. .. .. .. .. .. 18,000 (b) Compression on net section .. .. .. .. .. 18,000 (c) Compression on columns, struts, pillars. (See Section 4.) (d) Bending on extreme fibres of— Rolled shapes, built-up sections, and girders (net section) .. .. 18,000 Compression side of built-up section (gross section) .. .. 15,000 Pins .. .. .. .. .. .. .. 27,000 Steel castings .. .. .. .. .. .. 12,000 Iron castings —tension .. .. .. .. .. 3,000 Iron castings—compression . . .. .. .. .. 10,000 (e) Shearing on — Pins and power-driven shop rivets .. .. .. .. 13,500 Gun-driven field rivets .. .. .. .. .. 12,000 Turned bolts in reamed holes .. .. .. .. .. 12,000 Sledge-driven field rivets .. .. .. .. . . 10,000 Unfinished bolts .. .. .. .. .. .. 8,000 The strength of rivets and bolts in double shear is to be taken as twice that for single shear. The shear area for rivets and bolts shall be estimated on the nominal diameter. (/) Bearing on — Pins and power-driven shop rivets .. .. . . 27,000 Gun-driven field rivets . . .. .. .. 24,000 Turned bolts in reamed holes .. .. .. .. .. 24,000 Sledge-driven field rivets .. .. .. .. .. 20,000 Unfinished bolts .. .. .. .. .. .. 16,000 The bearing stress in holes for the central thickness of metal where rivets are in double shear may be increased by 25 per cent. (g) The allowable unit shearing stresses in webs of rolled sections or in plate girder webs for buildings shall not exceed that given by the formula— 12,000 bS = 1 1 h ~ 1 3,0001 2 where Ss is the allowable unit shearing stress in pounds per square inch, t is the thickness of the web, and h is the vertical distance between flanges of beams of rolled section, and for plate girders the horizontal distance between stiffeners or vertical distance between flanges, whichever is the smaller. All dimensions are in inches.

Allowable Unit Shearing Stresses, in Pounds per Square Inch, in Webs of Rolled Section or Plate Girders for Buildings.

2. If the unsupported length I of the flange of a beam is greater than twenty times the breadth b of the flange, the maximum fibre compression stress on the net area shall not exceed<^2s, j* lb. per square inch.

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h Ss h Ss * Ss - Ss h Ss t t t t t 10 11,610 20 10,590 30 9,230 40 7,830 50 6,550 12 11,450 22 10,330 32 8,950 42 7,560 52 6,310 14 11,260 24 10,070 34 8,660 44 7,290 54 ■ 6,090 16 11,060 26 9,790 36 8,380 46 7.040 56 5..870 18 10,830 28 9,510 38 8,100 48 6,790 58 5,660