126 ANNUAL REPORT 
the flexibility was 0.023 and 0.016 inch, respectively. “It thus appears 
that reinforcing a beam with even I per cent. of steel gives it ten times 
its former flexibility and more than three times its former strength.” 
In plain foundations or heavy walls where concrete, is only used in 
compression, and no transverse or tensile strains are brought upon the 
structure, there is no need for reinforcing concrete, for it has such great 
resistance to compression that it is as strong as can be desired for such 
work. 
It is in beams, floors, light walls, roofs, bridges, arches, and a thou- 
sand other places where it is desirable to use concrete because of its 
many good qualities, but where it is placed in tension, that reinforcement 
becomes necessary. ‘The qualities for which concrete are sought are, non- ~ 
corrosion in moist places, non-rotting under any condition, resistance to 
fire, resistance to weathering, deadening of sound, ease of construction, 
especially by unskilled labor when directed by a few competent skilled 
men, cheapness compared with other stone of equal appearance, and its 
durability. 
There are nearly as many systems of steel reinforced concrete as 
there are men who have attempted that kind of construction. The general 
theory is the same in each system, namely, that all transverse or lateral 
strains affect the material the same as such strains affect a beam; that is, 
by placing the-fibres or material on the side from which the force is acting 
under compression and on the opposite side under tension. 
As the concrete is an exceptionally good material for compression 
it needs no reinforcing upon the compression side, but as it is a poor 
material for tension, metal tension members are inserted upon the tension 
side. The systems fall into three classes, those that use expanded metal, 
those that use wire mesh and those that use iron or steel bars in some one 
of the various forms. Of the latter class, nearly every conceivable 
shaped bar is used—flat, round, square, twisted and special rolled shapes. 
DANGERS FROM CORROSION. 
One of the questions that the advocate of reinforced concrete must 
meet satisfactorily is, “Will your iron or steel members remain safe from 
corrosion and consequent weakening for an indefinitely extended time 
under all conditions?’ There seems to be little doubt among cement users 
that when neat cement mortar or a sand mortar rich in cement is used 
there will be no danger from rust, but when cinders or open material or 
lean concrete is used they fear there will be corrosion. Stone, Carpenter 
and Willson, architects of Providence, R. I., are quoted as having in- 
spected a five story steel skeleton building which was torn down after 
five years’ service. The outside columns were surrounded with brick, the 
interior columns protected with wire lathing and hard plaster. The 
floors were of expanded metal and cinder concrete. Before destruction, 
