81 



able difference In the strength of the slab, while an equal 

 displacement in a rod of a thicker beam as used in T 

 walls would not make such a difference in its strength. 

 The decreased dead load obtained by slab construction 

 does not give the advantage to retaining walls that it 

 does to floors of buildings or bridges, because the weight 

 of the beam itself, in the case of walls, is an aid to 

 stability. 



CONCRETE COLUMNS. 



Concrete columns can be designed according to the' 

 following formula based on the assumption that the load 

 is borne by the concrete and steel in a ratio depending 

 on the relative moduli of elasticity. Let 



C i total unit compression upon the concrete and steel, 

 (i. e. f the total load divided by the combined area of 

 concrete and steel) in Ibs. per sq. in. 



C = unit compression in concrete In Ibs. per sq. in. 



p ratio of cross-section of steel to total cross-section 

 of column. 



r= ^ratio of moduli of elasticity. 

 Then c l 



WEIGHTS OF POROUS OR DENSE TERRA COTTA 



PARTITIONS. (Kidder). 



In. in Lb. per 



Thickness. Sq. Ft. 



3 ........................................... 12 to 16 



4 ........................................... 13 to 19 



f. ........................................... 20 to 22 



6 ........................................... 22 to 23 



8 ........................................... 28 to 33 



Note. Plaster not included in the above. Will add 

 about 10 Ib. per sq. ft. for both sides. 



CRUSHING HEIGHT OF BRICK AND STONE. (Kidder). 



If we assume the weight of brick work to be 120 Ib. 



per cu. ft., and that it would commence to crush under 



luO Ib. per sq. in., then a wall of uniform thickness, would 



