Seismic pot type rubber bearings are based on the transportation industry standard of the People's Republic of China, " pot rubber bearings for highway bridges" (standard number JT391-1999) and the seismic design code for highway engineering (JTJ004-89). Energy dissipation and damping measures are added to the pot type rubber bearings.
Anti seismic pot rubber bearings include two types: fixed bearings and guided movable bearings, and are used in conjunction with bidirectional movable bearings. The vertical design bearing capacity, bearing angle, friction coefficient, and displacement of the support are all designed according to the standard requirements. The horizontal force of fixed bearings in all directions and unidirectional movable bearings in non sliding directions has been increased from 10% of the original bearing capacity design to 20%.
Both rigid seismic method and flexible seismic reduction method are adopted domestically and internationally. Rigid seismic reduction requires an increase in the size of the structure (including the foundation structure and seismic support structure). The characteristics of flexible seismic reduction are: good seismic performance with low stiffness, and the possibility of damage in the event of large seismic waves. This series of bearings adopts effective seismic measures such as a combination of rigidity and flexibility, increasing the energy dissipation capacity of the bearings and greatly improving their seismic performance. Therefore, when an earthquake occurs, the seismic capacity of the bridge can be improved, limiting the relative displacement between the upper and lower structures of the bridge to the maximum extent, and reducing the amplification coefficient of seismic force. It is equivalent to using general basin type rubber bearings during non earthquake situations.
The principle of shock absorption is mainly that when the horizontal force of the support is greater than 20% of the designed vertical bearing capacity of the support, the energy dissipation plate begins to slip, playing the first isolation effect; Then the damping ring exerts the second damping effect, and the support plays a seismic role; When the seismic shock wave exceeds a certain limit, the rigid seismic resistance of this series plays a third seismic effect.
Matters Needing Attention
1. It is recommended to install supporting pad stones on the top surface of piers and abutments. The height of the support pad stone should consider the convenience of maintenance and inspection of the support, as well as the possibility of replacing the top beam when replacing the support. It is best to set a certain slope on the edge of the pad stone outside the base plate of the support to facilitate drainage.
Due to the different heights of supports with the same specifications and types, attention should be paid to adjusting the elevation of the top surface of the pad stone.
2. The concrete carried by the top and bottom plates of pot rubber bearings should be equipped with steel mesh in accordance with the relevant requirements for local pressure bearing in the design specifications of highway bridges and culverts.
3. The specifications of rubber bearings can be selected from the nearby specification series table based on the sum of the calculated dead load, live load, and eccentric load effects of the upper structure. Due to the certain safety factor of the support, there is no need to artificially increase the size of the support during selection. When choosing a normal temperature bearing or a cold resistant bearing, it is advisable to determine based on the monthly average minimum temperature in the area where the bridge is located. If the monthly average minimum temperature of the bridge location is lower than -25 ℃, cold resistant bearings should be selected. The monthly average minimum temperature should not be lower than -25 ℃, and room temperature bearings can be selected at this time.
4. When the displacement required for the design of movable supports is not the value listed in the specification series table, attention should be paid to adjusting the spacing of reserved holes accordingly.
5. When the bridge is a sea crossing or coastal bridge, it should be marked in an appropriate position on the design drawing, and the manufacturer can choose corrosion-resistant stainless steel plates to improve the service life of the support.
