COLUMNS AND STRUCTURES 275 



The student should study the formation of the last three 

 formulas. *The first one means that a force H, acting with an 

 ami h, tends to overturn a body having a weight W. It is, 

 therefore, necessary to find the length of an arm x, through which 

 W acts to resist the overturning moment Hh. 



In the second the distance x cannot be greater than one-sixth 

 of B. The total weight is distributed over an area Bb. With 

 these hints the student should attempt to construct the formulas 

 as an exercise. 



Attaching Column Bases to Footings 



Column bases are attached to footings by bolts. A horizontal 

 force, such as wind, develops a bending moment in the column 

 where it is attached to the footing. Referring 

 to Fig. 177, divide the bending moment by 

 the distance x between the center lines of the 

 bolts in the direction of the force. This gives 

 the pull on the bolts. The distance is mea- 

 sured between centers of bolts instead of from 

 the leeward edge of the plate to the center 

 line of the windward bolts, to avoid bending 

 the edge of the plate. 



The pull in the bolts is divided by the allow- 

 able tensile fiber stress, to obtain the required bolt area. Divid- 

 ing this by two gives the area of one bolt, and the circumference 

 i dily found when the diameter is known. Dividing the cir- 

 cumference in inches by 50 Ibs. gives the total bond resistance per 

 lineal inch of bolt. Dividing the uplift on one bolt by this 

 amount, the length of bolt is obtained. 



The area of footing is determined by the bearing value of the 

 soil. The depth must be great enough to make the footing of 

 the weight required and also furnish area for embedment of 

 bolts. The weight of the footing is fixed by the requirement that 

 it be heavy enough to anchor the structure, or so much of the 

 structure as may be carried by the column which rests on the 

 footing. 



The horizontal force acting on the column is applied to the 

 column at the proper height. The force multiplied by the height 

 exerts an overturning moment. Dividing this moment by the 

 width of the building the weight of the foundation is obtained. 



