STATE GEOLOGIST. 139 
DeMan’s System.—DeMan uses a flat steel bar with quarter twists 
put into the bar, alternately to the right and left, at intervals of two to 
four inches, according to the size and depth of bar. These bars are shaped 
so as to hook over the I-beams and are straight longitudinally except 
for the twists. This system is designed principally for floors. A specially 
designed concrete floor block is made which is cast at central manufac- 
turing plants and shipped to the building, ready to slip into place between 
the floor girders. This block is as deep or deeper than the I-beam and 
rests upon the lower flange. The DeMan steel bars being special shapes 
are not as readily obtained as standard forms and consequently are ob- 
jectionable for that reason. 
Luten’s System.—Lutin’s system pertains more especially to bridges 
and culverts and is particularly an application of any system of re- 
inforced concrete, to a certain method of building rigid structures. 
Instead of allowing the thrust of the arches to be taken up by abutments, 
and embankments, a steel concrete tie is inserted from the base ends of 
the arches, making a monolithic complete structure, capable of sustaining 
all the varying stresses within itself. The advantages secured are: Pre- 
vention from arch rupture due to settlement, the possibility of flatter 
arches, a more rigid resistance to action of floods and possibly a slightly 
less amount of material necessary in construction. Figures 76 and 77 
show a section and view of bridges illustrating this method. 
It will be seen from the preceding discussion and descriptions that re- 
inforced concrete gains its marked pre-eminence over plain concrete in 
such structures as bridges, girdérs, beams, floors, roofs, thin walls, chim- 
neys, piles, etc., structures where great tensile strains enter into portions 
of the building. Again, in localities where both stone and gravel are 
scarce, reinforced concrete, because of the reduced amount of material re- 
quired, is very economical. In describing the uses of reinforced concrete, 
but brief attention will be given to such structures as are commonly built 
with plain concrete, except, perhaps, to occasionally compare the results 
obtained by the two methods. The various methods of building beams and 
girders have been so well illustrated in describing the various systems of 
reinforcing, that they will not again be mentioned. 
STEEL CONCRETE FOOTINGS. 
The soil in Chicago is especially noted for its instability. This con- 
dition requires the highest engineerng skill to be used in designing rigid, 
firm foundations for the “skyscrapers.” The old form for foundations 
was of stone or immense blocks of concrete, taking up the room which 
Should be given to basements and adding so much extra weight to the 
total load which the foundation soil had to sustain. To obviate these 
objections, the first combination of steel with concrete for heavy founda- 
