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Characteristic
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This method of the prestressed steelbox
rahmen overhead bridge using vertical loading equals to a form of
overhead bridge using temporary supporting point. We compare this
method of overhead bridge construction with the method of overhead
bridge construction using temporary supporting point in this chapter.
The side of mechanics
Steelbox beam isn't united column
in the existing style of structure of overhead bridge of style of
simple beam, but we unites steelbox beam with column by the welding.
so we solve problem of construction. A section of foundation becomes
large in the method of overhead bridge construction using temporary
supporting point, because many wrong negative bending moments result
from upward loading. So we prevent downward loading in the middle
span form negative bending moment. Though block of the positive
bending moment is disadvantageous by the downward loading, we can
design within allowable stress. because maximum bending moment of
block of the positive bending moment doesn't reach half of maximum
bending moment of block of the negative bending moment.
The side of an outward form
We can construct same section through
all the span in using this method, because reduced negative bending
moment by the downward loading results that section of column
is reduced remarkably. Therefore we can secure space of girder in
the block of the negative bending moment in using this method and
reduce height and length of stairs.
Theoretical background
Procedure of construction
STEP 1 :Camber and loading of self weight
of steel member
Steel column of circular
section enlarge reduction of material and mechanical
effect. after this column is fixed in the constructed
foundation like figure 1, steelbox beam that is made
of the same section through all the span is set simply
on the column. After that we calculate stress considering
self weight of steel. 
(fig
1) Shape diagram and bending moment diagram about the
set single box beam on the existing column 
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STEP 2 : Loading of vertical load
Many wrong negative
bending moments result from upward loading in the method
of overhead bridge construction using temporary supporting
point. So we prevent downward loading in the middle
span form negative bending moment. Therefore we can
reduce section of box beam and section of column in
the end of span, because of prestress effect from this
method. so we apply vertical load in the downward direction
and calculated stress before steelbox obtains prestress
effect like figure 2. 
(fig
2) Applied vertical loading diagram and bending moment
diagram 
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STEP 3 : Removing vertical load before
unity of column and beam
After unites beam with
column by the welding, we remove vertical load like
figure 3. So we can make overhead bridge like figure
4. If steelbox beam is reinforced with design and column
is made good mechanical circular shape, At this time
setting position of steel box beam on steel column can
allow to change within 1cm allowable error, according
temperature influences on shrinkage, expansion because
of that, the method is economical on the side of reduction
of material. 
(fig 3) After steelbox is
united beam with column by the welding, remove vertical
load. At this time diagram and bending moment diagram
(fig 4) Prestressed steel
box rahmen overhead bridge using vertical loading diagram
and bending moment on live load. 
