326 STEEL GRAIN ELEVATORS. CHAP. IX. 



2. The lateral pressure of grain on bin walls is less than the vertical pressure (0.3 to 0.6 of 

 the vertical pressure, depending on the grain, etc.), and increases very little after a depth of 2\ 

 to 3 times the width or diameter of the bin is reached. 



3. The ratio of lateral to vertical pressures, k, is not a constant, but varies with different grains 

 and bins. The value of k can only be determined by experiment. 



4. The pressure of moving grain is very slightly greater than the pressure of grain at rest 

 (maximum variation for ordinary conditions is, probably, IO per cent). 



5. Discharge gates in bins should be located at or near the center of the bin. 



6. If the discharge gates are located in the sides of the bins, the lateral pressure due to moving 

 grain is decreased near the discharge gate and is materially increased on the side opposite the 

 gate (for common conditions this increased pressure may be two to four times the lateral pressure 

 of grain at rest). 



7. Tie rods decrease the flow but do not materially affect the pressure. 



8. The maximum lateral pressures occur immediately after filling, and are slightly greater 

 in a bin filled rapidly than in a bin filled slowly. Maximum lateral pressures occur in deep bins 

 during filling. 



9. The calculated pressures by either Janssen's or Airy's formulas agree very closely with 

 actual pressures. 



10. The unit pressures determined on small surfaces agree very closely with unit pressures 

 on large surfaces. 



11. Grain bins designed by the fluid theory are in many cases unsafe as no provision is made 

 for the side walls to carry the weight of the grain, and the walls are crippled. 



12. Calculation of the strength of wooden bins that have been in successful operation shows 

 that the fluid theory is untenable, while steel bins designed according to the fluid theory have 

 failed by crippling the side plates. 



RECTANGULAR STEEL BINS. For the calculation of the stresses in and the design of 

 rectangular steel bins, see the author's " The Design of Walls, Bins and Grain Elevators," 

 Second Edition. 



CIRCULAR STEEL BINS. In the designing of steel grain bins particular attention should 

 be given to the horizontal joints, and to the strength of the bin to act as a column to support the 

 grain. To calculate the thickness of the metal the horizontal pressure L is obtained from Jan- 

 ssen's formula, and then the thickness may be found by the formula 



L-d 



1 = ^ ( <4 } 



where / = thickness of the plate in in. ; 



L = horizontal pressure in Ib. per sq. in.; 

 d = diameter of bin in in.; 

 S = working stress in steel in Ib. per sq. in.; 

 / = efficiency of the joint. 



The unit stress S may be taken at 16,000 Ib. per sq. in., and / will be about 57 per cent for a 

 single riveted lap joint, 73 per cent for a double riveted lap joint, and 80 per cent for double 

 riveted double strap butt joints. For the efficiency of riveted joints, see Table I la, Chapter XI. 

 The allowable stresses given for the design of steel mill buildings should be used in design. 

 These allowable stresses are as follows: Tension on net section 16,000 Ib. per sq. in.; shear on 

 cross-section of rivets 11,000 Ib. per sq. in.; bearing on the projection of rivets (diameter X thick- 

 ness of plate) 22,000 Ib. per sq. in. Compression in columns P = 16,000 "joljr where P = unit 

 stress in Ib. per sq. in. , / = length of member and r = radius of gyration of the member, both in inches. 

 Rivets in Horizontal Joints. The side walls carry a large part of the weight of the grain in 

 the bin and this should be considered in designing the horizontal joints. The weight of the 

 grain supported by the bin above any horizontal joint can be calculated as shown in the following 

 example. Assume a steel plate bin 25 ft. in diameter, and it is required to calculate the grain 





