Honolulu star-bulletin. [volume] (Honolulu [Oahu, Hawaii]) 1912-2010, 1912-08-22

De strengthened and states the cor
responding loads THAI will be carried
safely. That "a, the simple beam L.
inches by l. inches square and "a feet
between points Of support will carry
safely a concentrated load Of one and
one half tons at its center, while II the
same beam be made into King post
beam by passing underneath the beam
q one inch steel rod. which is made
fast at either end Of the beam. and In
serting a single post under the load at
the center Of the beam. then such a
beam will carry about two and three
quarter times as much. or q load OF
three and three-Quarter tons. safely,
while If the same beam be built into
King truss beam the load concen-
tra;ed at the center may then be ill.,
creased to nine tons.
The best Culvprts and smaller bridges
are built Of REINFORCED concrete. The
cost is greater than for wooden or pipe
constructions in the first instance, but
II we'll built there should be no fur
ther cost for repairs. That is. the first
cost is the last cost. while durability
and safety are secured from the out
set.
Good materials. consisting Of crush
ed stone or gravel. sand and portland
cenIcDt 3nd water, are required for con-
crete DefOrmCd steel rods imbedded
In the concrete are used for strength
tning the cover spans. The mixing of
these materials into. concrete and plac-
ing It in the forms are extremely sim
pie matters after they are once we'll
understood. but nevertheless should not
be undertaken by one who is unfanil-
lar with the nse Of concrete.
There are three general kinds Of con-
crete culvprtS. which are known as the
concrete box type They are built for
the smaller sizes up to such as have an
opening about four feet by six feet
wide. For sizes above that the floor is
usually left out where it is not needed
to protect the foundation. or paving
may he substituted for it. The floor
and side walls are constructed Of con-
crete with or without metal reinforce
ment usually without such REINFORCE
mCntS. The proportions of concrete
used for the floor and side walls are
usually. l, ). G-that is. one part by
measure Of portland cement, three
parts 10y measure Of sand and six parts
by measure OF CRUSHED StoDp or gravel.
For spans above ten or twelve feet the
cover needs to W. strengthened with
concrete beams. This type is known
blancc to the capital rrt+or. They are
placed adjacent t. each other. the dis
lance from center to center depending
upon the load which the bridge is ex-
pected to carry.
The best type Of concrete cuIverts for
spans from ten feet up to thirty feet is
the steel beam incascd in concrete. as
shown in Zig. l. Here the concrete
floor Is designed to carry the load
across the span from one beam to an
other, while tls steel beams carry
the load from one abutment to the 9TH
er. 1t often happens that the culverts
are built on yielding foundations and
that the abutmentS sometimes settle.
causing cracks that would he danger
GUS in some types of culverts, but 1t is
the ability Of the steel 1 beam type to
withstand such conditions as these just
mentioned that makes 1t the best type
to build. The + beams are incased in
concrete to protect them from rusting.
Sometimes they are simply painted or
more often not painted at all, and what
Would be a permanent bridge IS al
lowed to rust out for lack Of proper
care.
For details in regard to the methods
of designing and building concrete
bridges attention is called to bulletin
No. 80, "Highway Bridges and Cul-
verts," issued by the office Of public
roads, United States department Of
agriculture
No road can be called q good road
that is dotted with broken. vermont
and unsafe wooden culverts and
bridges. such as are encountered on
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