590 THE DESIGN OF STEEL DETAILS. CHAP. XVII. 



The stress due to bending moment due to wind loads in the leeward end-post will be, 



M-c 

 /. = p^ (27) 



I ?; 



_ 240,000 X 7 



= ^8 (90,000 + 5.060 + 7,000)2582 = 6 ' 73 lb> *** Sq ' m ' 



10 X 30,000,000 



The total stress due to direct wind load will be f w = (5060 + 7ooo)/i3.3O = + 910 Ib. per 

 sq. in. The total maximum wind load stress will come on the windward fiber of the leeward 

 end-post, and will bef w " = + 6,370 + 910 = + 7,280 Ib. per sq in. 



The maximum stress due to direct dead and live loads (not including impact) and wind load 

 stresses will be 



/ = 90,000 -5- 13.30 + 7,280 



= 6,770 + 7,280 = 14,050 Ib. per sq. in. 



From 46 in the specifications the allowable stress may be increased 50 per cent when direct 

 and flexural wind stresses are considered. 



The allowable stress when both direct and flexural wind stress are considered is then 



f e = 9,400 X 1.50 = 14,000 Ib. per sq. in. 



The stresses in the windward post will be less than in the leeward end-post calculated above. 



While the section assumed appeared to be excessive, the additional area and the width of 

 plate .are required to take the flexure due to wind loads. 



For the method used by the C. M. & St. P. Ry. for the design of an end-post, see p. 222. 



Column of a Transverse Bent. Design a column similar to that of the transverse bent shown 

 in Fig. 3, Chapter XVI, but having column length of 25' 6" and being hinged at the base. Direct 

 stress = + 12,800 Ib., bending moment at foot of knee brace = 181,250 ft.-lb. Shear = H 

 = 13,500 Ib. 



References. 34 and 38, p. 57; 79, 80 and 84, p. 60; 94, 97, 98 and 100, p. 61. 



Solution. A section composed of four angles and a plate will be used. The column will be 

 supported laterally by the girts so the length in that direction will be taken as % X 25' 6" = 12.75 

 ft. 



Try 4 angles 5" X Z 1 A" X 1 A", long legs out, 18^ in. back to back and one web plate 18 in. 

 X % in. Distance between rivet lines = i8J^ 2X2 = 14^2 in. Maximum allowable 

 distance for % in. plate = 40 X % = 15 in. 



Using method at bottom of Table 69, A = 22.75 in- 2 ; I A I.3H m - 4 ; IB = 94-6 in. 4 ; 

 r A ~ 7-59 in-; ?B = 2 -4 in. The greatest value of / -r- r 12.75 X 12 -j- 2.04 = 75.0. The 

 maximum allowable value of I -r- r = 125. The allowable unit stress is: 



1.50(16,000 70 Ijr) = 1.50(16,000 70 X 75.0) = 16,100 Ib. per sq. in. 

 The actual unit stress is: 



S 



I2JOO __ 181,250 X 13X9.25 = I6>ooolb . 



__ 

 A T - P ' P 22 -75 _ I2 ' 8o x 2 5-5 x 



10 X 30,000,000 



Floorbeam. Floorbeams are designed in the same way as other plate girders. The section 

 cut away for clearance at the joint must be strengthened by means of plates as shown in Fig. 13. 

 To determine the strength at the weakest section, A-A, the following method is used. 



The floorbeam is drawn to scale in Fig. 13, so that distances can be scaled and the maximum 

 floorbeam reaction 189,980 Ib. be resolved graphically, in the center line of the post, into 80,000 

 Ib. normal to A-A, which produces direct tension on the section A-A, and 173,000 Ib. parallel 

 to A-A, which produces shear and flexural stress. 



