THEOKY AND PRACTICE OF CONCRETE-IRON CONSTRUCTIONS. 105 



Notes on the THEORY and PRACTICE op CONCRETE- 

 IRON CONSTRUCTIONS. 



By F. M. GUMMOW, M.C.E., Assoc. M. Inst. O.E. 

 [With Plates III. -VI] 



[Bead before the Royal Society of N. 8. Wales, September 7, 1904.^ 



In presenting the following notes on concrete-iron con- 

 struction, the author's object is to place before you a digest 

 of the opinions of leading authorities on the subject, 

 moulded together to represent a correct view from the pre- 

 sent standpoint of scientific research on this subject. As 

 the constant mentioning of the authorities from whom data 

 have been obtained would become tedious, the author has 

 abstained from quoting tliem, and it is to be understood 

 that the general term "concrete-iron " includes " concrete- 

 steel," the word iron being used in its generic sense. 



"Concrete-iron" is the designation applied to those con- 

 structions which consist of Portland cement concrete and 

 iron insertions, both so intimately united that the construc- 

 tions act as homogeneous bodies when taking up stresses, 

 and at the same time allow the utilisation of each material 

 to its utmost limit. The great success of this combination 

 is due to the following characteristics, five in number, 

 which may be called the fundamental and essential prin- 

 ciples : — 



1. The thermal coefficients of expansion and contraction 

 of the two materials are nearly equal. 



The coefficient of expansion and contraction for cement 

 concrete for each degree Celsius (1° C.) may be taken as 

 0*0000137, and for iron as 0*00001235. These differences of 

 the coefficients although so small nevertheless set up 



