150 PRACTICAL STRUCTURAL DESIGN 



Tables of sizes and weights of plates and bars for all the gauges 

 in use are given in all the steel handbooks. 



The areas of washers will be as follows, the cross bearing strength 



of the wood being 350 Ibs. per square inch; U 3 and L 3 = -^77 = 14.3 



ooU 



sq. ins. The washer should extend across the chord, which we will 

 assume is 8 ins. wide, so the width will be, - = 1.78 ins. Make 



o 



4 X (2 x 350) 

 it 2 ins. wide. The thickness = - - = 1400 in. Ibs. bend- 



z 



ing moment considering it to be two cantilever beams, one on either 

 side of the bolt extending to the edge of the chord. 



/6 M /14 000 x 6 



The thickness t = \f -=- = I/ - = 0.51 in. (make it 

 V jo V lb,000 X 2 



5 in.). Tables of standard square and round washers may be used, 

 if available, but the area must be sufficient to keep the stress on 

 the side of the wood down to the allowable limit. The washer may 

 be round or square, but it is best usually to have to go across the 

 width of the chord. If square the above washer will be 3.81 ins. 

 X 3.81 ins. If round the diameter will be 4| in. 

 The washers at Uz and L 2 will have the following area: 



1 ^ nnn 



' = 42.9 sq. ins. If extended across the chord the dimensions 

 o50 



will be 5| ins. X 8 ins. If square the dimensions will be 6.6 ins. X 6.6 

 ins. If round, the diameter will be 1\ ins. Assuming a washer of 

 steel with dimensions 5| ins. X 8 ins. the thickness will be obtained 

 by using the following formula: 



- 1.73' '~ W " r 



+ 



in which t = thickness in inches, 



W = total load centrally applied, 

 L = length of plate (width of chord) bolt hole, 

 6 = width of plate = bolt hole, 

 / = allowable unit fiber stress. 



The above formula is good also for cast iron, using for the fiber 

 stress a stress which is an average of the allowable tensile and com- 

 pressive stresses. With cast iron the thickness obtained will be 

 at the edge of the nut on the end of the bolt, and it may diminish 

 to one-half this thickness at the edges. For very large washers a 



