Movement limiting device for bridge bearing

Details Movement limiting device for bridge bearing Movement limiting device for bridge bearing

1998-12-09

2001-01-30

Kent, Christopher T. (Department: 3635)

Static structures (e.g., buildings)

Means compensating earth-transmitted force

C014S073500, C014S077100, C052S573100

Reexamination Certificate

active

06178706

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a movement limiting device which limits the movement of a superstructure (bridge girder) in a bearing portion of a bridge in a horizontal direction.
BACK GROUND OF THE INVENTION
A bridge girder of a bridge may be caused deflection, expansion or contraction in the longitudinal direction of the girder (the direction along the longitudinal axis of the bridge, hereinafter referred to as “bridge longitudinal direction”) due to creep of concrete, drying shrinkage, or prestress. A movable bearing has been employed which has a mechanism to support the bridge girder so as to allow horizontal movement of the bridge girder in the bridge longitudinal direction. The movable bearing is provided with a movement limiting device for preventing an upper shoe from deviating from a lower shoe in the event of an earthquake.
FIG. 2
is a schematic perspective view showing a conventional bearing device with a movement limiting device. The movement limiting device comprises an upper shoe plate
10
made of steel, which is provided with a notch
12
formed in a side thereof (extending in the bridge longitudinal direction), and a side block
14
which is secured such that the side block
14
is positioned in the notch
12
. There are spaces
13
S between the side block
14
and both ends of the notch
12
respectively for allowing limited movement. An anti-floating member
16
is disposed on the side block
14
for preventing the upper shoe
10
from moving upwardly.
This movement limiting device has been employed in various kinds of bearings including a line bearing, a plate bearing, a roller bearing, a locking pier pivot tearing, a rocker bearing, and a rubber bearing).
FIG. 3
is a perspective view of a roller bearing with plural rollers having a movement limiting device. An upper shoe
20
is pivotally mounted to a lower shoe
26
through a pin
22
and caps
24
. The lower shoe
26
is supported to a bottom plate
30
through rollers
28
in such a manner that the lower shoe
26
is movable in the bridge longitudinal direction. The lower shoe
26
is provided with notches
32
formed in sides thereof. Upper portions of side blocks
34
secured to the bottom plate
30
are positioned in the notches
32
, respectively. A numeral
36
designates an anchor bolt,
38
designates a side block bolt.
FIG. 4
is an exploded perspective view showing a plate bearing with high strength brass bearing plate having a movement limiting device. A bearing plate
44
is interposed between an upper shoe
40
and a lower shoe
42
. Disposed around the bearing plate
44
is a seal ring
46
.
The upper shoe
40
is provided with notches
48
formed in sides thereof. The lower shoe
42
has integrally formed side blocks
52
of which upper portions are positioned in the notches
48
, respectively. Anti-floating members
53
are attached to the side blocks
52
by bolts
50
. A numeral
54
designates an anchor bolt.
There is a possibility of a bridge pier fracturing when extremely large force is exerted on a bridge girder in a horizontal direction and a movement limiting device still restrains the bridge girder. Accordingly, there are some movement limiting devices which are designed to cancel the restraint of the bridge girder in such a case. It should be noted that, in this case, an aseismatic connector is further provided besides the movement limiting device.
In the conventional examples as shown in
FIGS. 2 through 4
, for canceling the restraint of the bridge girder by the movement limiting device, the side blocks
14
,
34
,
52
are structured to be sheared when the horizontal force exerted on the bridge girder exceeds a predetermined value.
As mentioned above, according to current design of bearings, side blocks are structured to be broken when large horizontal force of such a magnitude as to fracture a bridge pier is exerted on a bridge girder, for ensuring safety in the event of earthquake. This prevents extremely large force from being exerted on bridge piers.
This structure is called the knock-off structure. It is necessary to balance the strength of the side blocks
14
,
34
,
52
in the bridge longitudinal direction and a direction perpendicular to the bridge longitudinal direction (hereinafter, referred to as “the bridge perpendicular direction”) in such a manner that the side blocks can be broken when a horizontal force exceeding the corresponding predetermined value is exerted in the bridge longitudinal direction or the bridge perpendicular direction.
However, nearly all side blocks should have a thinner thickness in the bridge perpendicular direction and a longer length in the bridge longitudinal direction for the structural reason. Accordingly, the strength in the bridge longitudinal direction should be too large relative to the strength in the bridge perpendicular direction.
To balance the strength in the bridge longitudinal direction and the strength in the bridge perpendicular direction of the side blocks
14
,
34
,
52
, for example, portions of the side blocks where positioned in the notches
12
,
32
,
48
may be set to have reduced length in the bridge longitudinal direction and increased thickness in the bridge perpendicular direction. In this case, however, the whole size of the bearing becomes larger, so it is diseconomy.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to solve the problems as mentioned above and to provide a movement limiting device of a bridge bearing in which horizontal strength in the bridge longitudinal direction and horizontal strength in the bridge perpendicular direction when the movement limitation is cancelled are properly set respectively.
A movement limiting device of a bridge bearing of the present invention comprises an upper member movable in a horizontal direction, a lower member which is fixedly installed to confront the upper member, a notch which is formed in one of the upper and lower members to extend in a bridge longitudinal direction, and a plurality of stoppers which are fixed to the other one of the upper and lower members such that the stoppers are positioned in the notch and spaced apart from each other. When the upper member moves in the bridge longitudinal direction, one of the stoppers comes in contact with a corresponding end of the notch to limit the movement of the upper member. When a horizontal force exceeding a predetermined value is exerted to the upper member, the end of the notch pushes and thus shears the stopper so as to cancel the limitation in the movement of the upper member.
In the movement limiting device of the bridge bearing, when the upper member moves in the bridge longitudinal direction and its travel distance reaches its limit, one of the ends of the notch comes in contact with the corresponding stopper so as to limit the further movement of the upper member. In this case, when the horizontal force is too large, the stopper is sheared, thereby canceling the limitation in the movement of the upper member.
In the present invention, a plurality of (for example, two) stoppers are arranged to be spaced apart from each other in the bridge longitudinal direction, thereby enabling the stoppers to be selectively formed in various configurations to properly set the shearing strength in the bridge longitudinal direction and the shearing strength in the bridge perpendicular direction of the stoppers.
In the present invention, a block confronting the notch and extending in the bridge longitudinal direction may be fixedly disposed, and the stoppers are projections formed on the block. In this case, the notch may be formed in the upper member and the block may be fixed to the lower member by bolts, which are arranged in portions on the end sides of the projections of the block in a longitudinal direction of the block and in a portion between the projections.
In the movement limiting device of the bridge bearing, the block can be fixed by the bolts not only in both sides of the block but also in the center thereof, thereby increasing the strength for f

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