桥梁支座的作用和要求（The role and requirements of bridge
support）
The role and requirements of bridge support
The support is set between the superstructure of the bridge and the abutment. Its function is:
reaction in the shaft
(1) the supporting counterforce of the superstructure, including the vertical force and horizontal force caused by the constant load and live load;
(2) the guarantee structure under live load, temperature change, shrinkage and creep of concrete under the action of the factors such as the free deformation, to make the upper and lower part of the structure of the actual stress distribution comply with the static schema structure.
The classification of bridge support
1. The possibility of changing position
Fixed support
Movable support
The vertical force and horizontal force of the fixed support can allow the upper structure to rotate freely but not horizontally in the support.
The movable support only passes the vertical force, allowing
the upper structure to move freely and horizontally at the base.
Movable support can be divided into multi-directional movable support (vertical, horizontal and free movement) and one-way movement support (only one direction can move freely). ,
2. According to material
Easy bearing
Steel support
Reinforced concrete support
Rubber bearing
Special support (such as damping bearing, tension support) The layout principle of bridge support
(1) for the cross-structure of the slope bridge, the fixed bearings are easy to be arranged on the low - elevation
(2) for the continuous beam bridge and the continuous beam bridge of the bridge, for the longitudinal deformation of the whole beam to disperse to the two ends of the beam, the fixed support setting shall be set at the center of the bridge near the bridge; However, if the bridge pier in the middle pivot point is high or because of the force of the foundation, it is very bad for the tolerance of the horizontal force, the fixed support can be arranged on the other abutment on the side
according to the specific situation
(3) for the girder bridge of special width, the movable support base along the longitudinal and transverse direction should be set. For curved Bridges, the possibility of movable support to move along the arc is considered. For the girder bridge in the earthquake area, its pedestal structure should also consider the bridge's shockproof facilities, which should generally ensure that the horizontal force is Shared by multiple piers.
The arrangement of fixed support and movable support should be based on the principle of conveying longitudinal horizontal force to the pier.
(1) for the span structure of the bridge, it is better to have the lower edge of the beam under the pressure of horizontal force, which can offset the tensile stress generated by some vertical loads on the lower edge of the beam.
(2) for the bridge pier, the horizontal force should be directed to the river bank as far as possible, so that the top of the pier can not be pulled by horizontal force.
(3) for the bridge deck, the horizontal force should be directed to the center of the pier to make the top of the bridge under pressure and to balance the pressure of some of the back earth.
4. Precautions for the positioning of bridge bearings
The arrangement of bridge support is mainly determined according to the structure of the bridge and the width of the
bridge.
One end simply supported girder bridge a fixed support, and other activities support. Railway bridge width is small, due to bridge bearing transverse deflection is small, generally only need to set up a one-way activity support (vertically movable support), highway T girder bridge due to the bridge deck is wide, and consider the possibility of moving to bearing transverse bridge; That is, a fixed support is set on the fixed pier, and the adjacent supports are set to the horizontal movable and longitudinal fixed one-way movable support.
A vertical movable pedestal (corresponding to the fixed support) is set on the active pier, and the rest is set to
multi-directional movable support.
Continuous girder Bridges only have one fixed support. In order to avoid the expansion of the movable end of the beam; The fixed support should be placed in the intermediate fulcrum of each link. However, if it is relatively high, it should be considered to avoid or take special measures to avoid the excessive force of the pier.
The bearing arrangement of the continuous beam bridge directly affects the internal force distribution of the beam. At the same time, the positioning of the pedestal should enable it to fully adapt to the verti
cal and lateral free rotation and movement of the curved beam, which is generally suitable for the use of spherical bearings and for multi-directional movable support; In addition, the curve box girder standing among single fulcrum bearing, only in a league of beam end (or abutment) set up double
support, to withstand torque, intended to make curved beam fulcrum to the curve of the lateral deviation, adjustable torque distribution of curved beam.
When the bridge on the ramp, fixed support should be located in the lower end, so that the beam body under the action of vertical load along the gradient direction component compression, so as to offset part of the edge of beam produced by the vertical load pull, when the bridge on a flat slope, fixed support should be located in the front of the main driving direction.
The use effect of Bridges and the bearing can be accurately play its function has the close relation, so the bearing was laid, should make the lower part of upper structure bearing position and structure of bearing center line, but has the absolute is hard to do, so attention should be paid to make possible bias in the allowed range, does not affect the normal work of the bearing.
It is important to determine the load and displacement of the support base and the service life of the support. In general, the fixed support in addition to the vertical pressure, must also be able to withstan
d horizontal force, including possible braking force, wind, activities bearing friction resistance, tensile strength of the girder elastic deflection of bearing, etc., the horizontal force should always slant the land use, and require support and supreme, bottom structure of anchoring or your pin. For bending, oblique and wide bridge, the stress of the bearing is more complex, need from three coordinate direction to study earnestly, even in the same position of

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