Development trend of expansion joint
At present, expansion joints series products have been widely used in highway bridges and other aspects, and on the basis of the original has a more clear improvement.
Expansion joints generally have docking type, steel support, combined shear type (plate type), modular support and elastic device.
Docking type expansion joint device, according to its structural style and stress characteristics of different, can be divided into filling butt type and embedded type packing. Two kinds of butt butt type expansion device is to asphalt, wood, rubber and other materials caulk oakum, are under pressure, flexible body state in any case. This kind of telescopic device commonly used in conventional bridge engineering scale below 40mm, but has not seen. Embedded devices use different forms of butt joints of steel rubber strip with different shapes (with) embedded firmly, and the rubber strip (belt) tension and compression deformation to absorb the deformation of the girder the telescopic body can, in a compressed state. You can also place .
(2) modular support
When the bridge telescopic deformation of more than 50mm, often using a steel telescopic device. The telescopic device when the vehicle passing due to beam end rotation or bending deformation caused by noise, rattling effect, and easy to make structural damage. Therefore, the device is provided with a spring bolt to fix the sliding plate, to reduce rattling and noise the structure is relatively complex, the expansion joint.
(3) shear type
The device is a rubber band as a filling material expansion device using a variety of different shapes. The rubber elastic, easy to paste, and can meet the requirement of deformation and waterproof. In China, has been widely used in bridge engineering.
(4) steel support
This type of plate rubber expansion device, it is difficult to meet the requirements of large displacement expansion device; the steel type, it is difficult to achieve a water tight seal, and easy to cause the impact of vehicle impact on vehicle. Therefore, the use of absorbing the shock performance and easy rubber sealing material. With high strength and good performance of special-shaped steel combination, various types of modules supported can withstand the vehicle load in large displacement condition (Modular) series of bridge expansion device.
Elastic expansion device consists of zinc iron joints and TST gravel elastic joints, elastic expansion device is a simple expansion joint device for small and medium span bridge, when the expansion joint device can adopt TST gravel elastic expansion is less than 20mm-40mm, is a special plastic material after heating and melting of TST after cleaning, poured into the heated gravel, which formed the TST gravel flexible joints, gravel to support vehicle load, TST elastic plastic body can meet the requirements of the expansion amount in a 25 to 60 DEG C conditions.
Setting requirements for expansion joint
According to the length of the building, structure type and the rigidity of the house and roof have set the temperature or heat insulation layer to consider. Among them, the building length is mainly related to the temperature stress accumulation size; structure type and roof stiffness is mainly related to temperature stress effect on other parts of the structure is easy to transfer and whether or not. Set the temperature or the heat insulation layer is related to the structure directly affected by the influence of temperature stress.
Spacing of expansion joints
(1) the distance between the frame and the expansion joint of the frame shear wall can be based on the numerical value of the frame structure and the shear wall structure in the concrete layout of the structure.
(2) when the roof has no heat preservation or heat insulation measures, the shrinkage of concrete is larger or the distance between the expansion joints should be reduced due to the longer construction exposure time.
(3) in the climate dry region, the structure of the hot and heavy rain in summer, the distance between the expansion joints is reduced.
To increase the maximum distance of the expansion joints, or even without expansion joints, the key is how to reduce the temperature stress and concrete shrinkage stress, as well as how to improve the crack resistance of concrete components.
Construction measures and construction measures for the appropriate distance between the expa
1, the top, bottom, side gable and longitudinal wall temperature variation of large parts of the increase of reinforcement ratio;
2, the top layer of insulation measures to strengthen the external thermal insulation layer;
3, each 30-40M spacing set aside after the construction of the pouring belt, bandwidth 800 - 1000MM, reinforced with lap joints, after pouring concrete should be poured two months after;
4, the top floor of the structure with a small stiffness or the top of the structure of the local temperature, the structure is divided into a short length of section;
5, the use of small shrinkage of cement, reduce the amount of cement, adding a suitable admixture in the concrete;
6, to improve the structure of the floor of each floor reinforcement ratio or the use of partially prestressed.