La Junta tribune., 1912-06-08

tNespOndinS boa0a th1l Will be cDfyieh
safely That h. the stm,ae hean u
inches By !? inchea square aud ~ fess
between pointa Of support will carr
safely com entrsted iond Of one ana
one half tons II its center. while II the
u me beam b~ made INTO Z King pos,
beam BY passing underneath the beam
4 one inch steel rod. which II made
fas; at either eud Of the t,..am. and In.
seriinS y single r0xt under the l0sid ai
Me center Of the beam. then such .
beam will carry about two and three
quarter times a. much. or a load Of
three and three-Vuarter tons. safely.
while II the same b~.s IN BE- buiis into
a King truss b.xm the load concen,
.ra,ei ut the center nAy then be 10.
creased To nine tOin
The best culverts and smaller bridges
nre built Of re-enforcsd concrete The
cost /, greni ter than for wu.tieu or pir,e
constructions In the FIRST instance. but
II well built there should In. no fur.
ther cost for reimirs. That Il. the firxt
cost Is the last cO~,. while durability
and safety are secured from the out.
set.
Good materials. consisting Of crush.
ei stone or gravel. sand and portland
cemen, and water. are required for con.
crete DefOrmcd steel rods irnbs-id.si
In the concrete nrr used for strength.
'enne the cover spans The mixing Of
these materials into concrete and plac.
ins II in the forms are extremely sim.
pie matters after they are once well
understood, but nevertheless should not
b. undertaken by one who Is uufamil
lar With the use OF concrete
There are three general Kinds Of con.
crete cuiverfs. which are known as th,.
concrete box tyre They are built for
the smaller sizes W to such ns have an
opening about four feet by six fee,
vide For siz.~ above that the floor Is
usually left out where II is not needed
10 project the foundation. or paving
may bc substituted for II The floor
'nl side walls are const rucie1 Of con.
rrrte With or without metal r--enforce
ment, usually without such re-enforce-
a. ~ Nv VI
used for the floor and side walls are
usually. I. 3. G-that is one part by
measure Of portland cement. three
parts los measure NJ sand and six parts
by measure ~ crushed stone or gravel
For spans aboN. ten or Twelve feet the
cover nc.-ls 10 h~ strengthened with
rOncrct. beams. This type Is known
As lb. concret. r beam from its resem
b.ance TO the capital letter They are
placed adjacent t. each other. the dis
lance from center to center depending
upon the load which, the bridge Is eI.
Pc ted to carry
The best typ" of concrete cuiverts for
-pans from ten f,,f up TO thirty feet is
the steel bs~m inca~ed In concrete. ~
.ho wn iu Fig I. Here the concrete
door Il designed to carry the load
,rroas TIE spas sroo QUE bsam to a.
the loud from one abutment to the 9th
~ Il often happens that the culv-rts
are built on yielding foundations and
that the abutmenis sometimes settle
causing cracks that would be danger
oas In sOsn. tyie- Of cuiveSta. but II b
the stA,ity ~ the steel I beam type TO
Withstand such conditions - these Just
oentioned that makes II the be.t type
10 build. The bea are incssed In
coocrets to protect them from rusting
Sometimes they nre simply painted or
more often not painted At all. and what
would b~ \ permanent bridge II al
lowed To rust out for lack of proper
care
For details In regard to the methods
Of Designing and building concrete
bridges attention 10 called to bulletin
No. N. Highway Brtdse~ and CuI
verts." issued by the once Of public
roads. Uui,~d States department Of
agriculture
No road can he called good rOad
that h dated with broken. w"euout
and unsafe wooden culverts and
brsdRea. such as arr en~s'unsered "p