1 overview

When installing the bridge, it is required that the beam should be in close contact with the support and should not be empty.
But because of the construction and various aspects of reasons, the phenomenon of support emptying occurs from time to time, in the inspection of Bridges, many plate Bridges have problems such as support emptying, deviation, some of which are quite serious.
Bearing the basis is a serious problem in the bridge construction, after bearing the basis, increase the local pressure, under repeated load bridge will produce vibration, influence on the performance of the bridge use, at the same time for bearing the basis will reduce the stability of plate, can quickly reduce the service life of bearing, and even make the plate girder damage, so bearing road.the must handle in time.
At present, there is no unified method to solve the support emptying in China.

2. Causes and analysis of abutment emptying

Support emptying is generally caused by construction, nothing more than the following reasons:
(1) the construction process control is not strict, does not meet the standard requirements, and the plate and beam installation is relatively careless.
(2) the board beam is not integrated in time after installation, and the bridge deck is not constructed in time, resulting in too large arch back, which makes the support empty, especially in the inclined bridge. Under the action of prestress, the short side tends to become warped upward.
Under the action of prestress, obtuse angles of skew Bridges tend to warp.
When the plate is integrated, it can be regarded as an inclined plate when the bridge deck paving and vehicle load are acted upon.
Under the action of load, the load has a tendency to transfer to the shortest distance of the two supporting edges, and at the same time, the bearing has a certain compression deformation.

3. Treatment method -- lifting bag method of integral lifting

Lifting air bag is made of wear-resistant, aging resistant, fatigue resistant high-quality rubber and bending strength steel cord cloth through special processing, its requirements of the operating space is very small, only 3cm, small pressure, lifting force, easy to use and operate.
In the treatment of support emptying, the use of lifting air bag, can be very smooth overall lifting half of the bridge or the whole bridge, so that the support adjustment is simple and convenient.
(1) applicable conditions
A. The lifting weight of the whole or half of the plate girder bridge is not greater than the comprehensive lifting capacity of lifting air bag. Considering the friction force at the end of the beam, the lifting capacity is generally 1.2 times of lifting weight.
B. The gap between the plate beam and the abutment or cover beam is greater than 3cm, and the lifting air bag and the load contact area is guaranteed to be greater than two-thirds of the lifting bag area.
C. The bridge is lifted as a whole, and the support adjustment is convenient and safe.
(2) construction tools
A. Lifting bag: according to the conditions of the bridge, generally cq-24 type can be used to lift the prestressed plate beam with a span of 13-20cm.
B. Inflating equipment: air compressor and high-pressure gas cylinder can be used.
C. Connection system: it mainly ensures that the lifting bags under the beam are simultaneously aerated and simultaneously deflated, and there must be a master valve and a deflated valve, which can be made of steel pipe.
D. Square wood and leveling board, adjusting steel plate, feeler gauge, epoxy resin, adjusting steel bar hooks for support, etc.
(3) construction
A. Check the deviation of the support, and measure the height of the disengagement with the feeler after the disengagement, calculate the compression amount of the support, and prepare steel plate.
B. Remove sundries on the abutment, no pebbles, steel bars and other sharp objects. When the beam has a large self-weight, the expansion joints should be cleaned to reduce resistance.
C. One lifting air bag shall be placed for each beam, and the position shall be accurate.
When the action space is larger, the lower part of the application of wood pad height, should ensure that the working space in about 5cm.
D. Connect lifting air bag and inflating equipment, try to inflate and check whether the system is normal.
E. Inflating and pressurizing. When the pressure reaches 0.5mpa, it shall be stopped for a period of time to observe the working condition of the air bag and the system.
Then add it to full pressure and stabilize.
F. Bridge jacking in place, plug into the square wood, such as uneven flat leveling.
At this time, slowly release the air from the lifting bag, take out the air bag, so that each piece of beam falls on the square wood, with tools to adjust the problem of the support, when using the adjustment steel plate to increase the height of the empty support, the application of epoxy resin will be glued to the steel plate on the abutment.
G. After adjusting the support, re-insert it into the air bag, take out the wood block after inflation, and slowly release the air, so that the beam falls on the support slowly.

4 conclusion

(1) after the beam body is prefabricated, the storage time shall not be too long.
After the beam body is installed, it should be integrated in time and the bridge deck pavement construction, in order to prevent the back arch into the support empty.
(2) it is a better method to adopt the lifting bag method of integral lifting to deal with the lifting of the support, which is simple and economical to construct and can solve the problems such as the replacement of the support at the same time.
(3) when the bridge deck pavement is not constructed, wedge tightening method is more suitable to solve the support emptying of small span Bridges.

Key words: bridge support emptying treatment bridge support replacement