¡¡
The existing types of overhead bridge
¡¡
Steel box beam is constructed on upper
column in a placed state as simply supported beam. (Fig. 1)
Because it is simply supported beam, the
steel box section is designed as maximum positive moment occured
at the middle of span. so depth of beam is very large and it is
unshapely.
It has so large deformation because simply
supported beam.
When the beam contract with column, it
is contracted through previousely boiled bolt hole at beam and column
after column is fixed at foundation. so it is cause of poor construction
that column leans or wide the bolt hole by oxygen.
fig. 1 Simply supported
overhead brige
The other structure of existing overhead
brigde is double steel box section and rahmen structure consist
of four column, it has two column at one side. (Fig. 2)
Because beam and column section are designed
as double steel box section, it is more disadvantageous then single
steel box section at material using and production.
When the beam contract with column, a upper
part of column and beam are combined and place it on column after
part of column is fixed at foundation. this method is completed
by welding so there are many poor construction cases that cutting
the column by error of placed in field.
It need more material and expensive than
simply supported beam.
Figure 2. Double
steel box rahmen overhread brigde
Characteristics
The side of mechanics
The specific character of this method
is unification of steel box beam and column by welding. The existing
method of simply suported overhead bridge structure is not.
The method, prestressed steel box
rahmen overhead bridge using temporary supporting point, reduce
a third of maximum positive moment compare with existing method
and two thirds of both side negative moment of steel box beam compare
with existing simply supported beam so the hight of middle span
section is reduced compare with existing that. This effect of decreasing
moment not only make it possible construction that is varied the
section at middle and end of span with linear and curvature but
reduce 30% in amount of steel compare with existing simply supported
beam.
In serviceabillity, because the
maximum deformation reduce 20% when use the same amount of steel
by existing method of simply supported beam, it is advantageous.
In construction, it is useful in problem in temperature by contract
beam and column.
The side of an outward form
Compare this method with existing
doube steel box rahmen overhead brigde, existing method is similar
to this new method in mechanics. Section of beam is double steel
box and there are two columns at the end of overhead bridge in existing
method. But this new method reduce the materials and advantageous
in construction by use the single steel box, reduce the number of
column to one and large variation at upper section of contract with
single steel box beam compare with lower section.
The side of structure
In this method, after steel box
beam is placed on column, the temporary column that can control
the hight as equal to both sides of beam and upper column is instituted
at 1/8¡1/6 point from end of both sides of beam. It make negative
moment so it have prestressing effect that reduce the positive moment
by dead load and live load after contract beam and column. In part
of beam, the effect of prestress is harmful but it is very short.
¡¡
Construction Method
Step of construction
STEP 1 : Camber and loading of self weight
of steel member
Sigle steel box beam is placed
on column as linear or curvature varied section |
(fig.
1) Shape diagram and bending moment diagram about the
set single box beam on the existing column |
¡¡
STEP 2 : Set the temporary supported point
and loading of upword load
Set the temporary column that
get the prestressed effect by control the hight and
loading of upword load |
(Fig.
2) Shape diagram and bending moment diagram about creat
the negative moment by temporary spported point |
¡¡
STEP 3 : Remove the temporary supported
point after contract beam and column
Remove the temporary supported
point(fig. 3) after contract beam and column by welding
and complet the construction of overhead bridge(Fig.
4) |
(Fig.
3) Shape diagram and bending moment diagram about remove
the temporary supported point after contract beam and
column by welding
(Fig.
3) Shape diagram and bending moment diagram about completed
prestressed steel box rahmen overhead bridge using temporary
support |
¡¡
|