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STATE GEOLOGIST. 135 
Thacher rolled bar, (a later design) does not have the first two advantages 
named. Illustrations of Thacher’s original method of reinforcement will 
be given later under the head of bridges. 
Hennebique System.—The Hennebique system gives the effect of a 
trussed concrete beam by the use of two sets of round iron bars. One 
set is straight and laid near the lower edge of the beam, the other 1s 
bent upward at the ends, approaching the upper part of the beam. Besides 
these, vertical U-irons, or stirrups, are used to assist in resisting both 
shear and bending. Application of this system to columns and other 
forms of construction is quite as simple. In the column four or more 
round iron rods are used, bound together at frequent intervals with iron 
plates through which they pass, or they are bound together by being 
heavily wired. These rods give the tensile resistance required while the 
concrete gives the compressive resistance and rigidity to the structure. 
The Hennebique system has been used in every form of construction in 
which armored concrete can be used—tanks, stairways, floors, walls, 
bridges, piles, etc. Figures 70 and 71 show its detail for floors and beams. 
Contrary, also, to usual practice, Hennebique prefers the steel or 
iron to be “covered with rust to facilitate the foundation of an extra 
hard coat of ferro-concrete, which prevents the penetration of moisture 
and air to the metal.” 
Ransome System.—The Ransome construction “consists in the use 
of iron bars, cold twisted, so as to form a continuous bond with the con- 
. . ’ . 
crete, in which they are permanently imbedded.” 
“The basis of the system is the method of introducing iron with con- 
crete in such a manner as to give to the concrete beam or girder the 
power to resist tensile stresses, as 1f the beam were of a fibrous or homo- 
geneous material, like iron or wood. In such a construction it is essential : 
First, that the iron and the concrete be so united as to enable each to 
act immediately with the other in resisting stresses. Second, that the 
bond between the two should be continuous and equal from one end of the 
beam to the other. Third, that the elastic limit of elongation of the two 
should be made as nearly equal as possible.” 
Ransome claims for his system of cold twisted bars, increased elastic 
limit, decreased elongation under strain, the detection of all serious imper- 
fections in the iron before it is put into use, and a more secure union of 
the metal and concrete. He does not attempt the trussing effect, but 
allows the concrete to form its own truss, depending upon the iron to 
supply the tension member. It costs about one dollar per ton to twist the 
iron so that if all is gained that is claimed, the twisting certainly pays. In 
floor or surface construction, auxiliary bars are used running at right 
angles to the main system of bars. 
