CAMBRIA STEEL. 63 



BEARING PLATES FOR SHAPES USED AS 

 BEAMS. 



Shapes used as beams resting on masonry walls or piers will generally require 

 bearing plates of steel or their equivalents, set in or upon the masonry to prop- 

 erly distribute the load thereon with due regard to the allowable safe pressures 

 for the class of stonework or brickwork in question. 



A table of bearing plates is given on page 65, which gives the bearing values 

 in pounds for plates of various sizes based on the safe unit pressure allowable for 

 different classes of masonry. As the strength of masonry varies largely accord- 

 ing to the qualities of the material used, the workmanship and age, it is impossi- 

 ble to give absolute figures for safe unit pressures for all classes of work, but the 

 values given on page 64 are believed to fairly represent these for the usual kinds 

 of ordinary architectural masonry. The strength of ordinary masonry generally 

 depends upon the crushing value of the mortar or cement used and does not 

 bear any fixed relation to the ultimate strength of the brick or stone entering 

 into the construction. 



The table of bearing plates gives the bearing values of various sizes of plates 

 when used with different classes of masonry, but the thickness of the plate 

 should be computed for each case. 



For a plate of given length and breadth the thickness depends upon the 

 allowable load and unit stress, and the width of the flange of the beam or 

 channel resting upon it. 



The thickness may be determined by the following formula 



t = thickness of plate in inches. 



1 = length of plate in inches, in a direction perpendicular to the axis of the 



beam or channel. 



b = width of flange of beam or channel in inches. 

 R = reaction at point of support in pounds. 

 For uniformly distributed loads, R = one-half of the load given in Tables of Safe 



Loads, pages 106 to 123 inclusive. 



p = allowable stress in pounds per square inch on extreme fibre of plate. 

 u = width of plate in the direction of the axis of the beam or channel; *'. e., 



bearing on wall in inches. 



If p = 16 ooo Ibs. for steel we have 



EXAMPLE. 



What is the proper size of steel bearing plate to be used in a wall of brick laid 

 in cement mortar to support the end of a 10-inch standard I- Beam, weighing 40 

 pounds per foot, of 10 foot span, subjected to its safe load uniformly distributed? 



On page 109 in the Table of Safe Loads Uniformly Distributed for Cambria 

 I-Beams, the total load is found to be 33 850 pounds, and half of this, or 16 925 

 pounds, will be the reaction at each end. 



On referring to the Table of Bearing Plates, on page 65, the proper size for 

 this load on the class of masonry in question is found to be 6" x 10". The 

 width of flange of a 10-inch 40 Ib. standard beam is 5.10 inches. 



Substituting these values in the formula for thickness gives 



.00685 (10 - 5.10) - ~ = .562 



The nearest commercial size above this is & inch, which is the thickness 

 required. 



If a shorter plate would suit the location better it may be seen from the table 

 that a plate 8" x 8" will give the necessary bearing value and the thickness of 

 this would be 



t = .00685 (8 - 5.10) -J ~^ = .323 



\ O X O 



and the nearest commercial size above this is %," ', which is the thickness required. 



