Laminated rubber bearing Main materials used—— steel plate It is similar to rubber at home and abroad, including neoprene, natural rubber and EPDM. The three kinds of rubber have their own advantages and disadvantages. The choice of rubber is mainly based on the temperature conditions of the bearing. Generally speaking, in cold regions, such as Northeast China and Inner Mongolia, EPDM can be used as the raw material for the bearing; In North China, natural rubber can be used as the raw material for bearings; Neoprene bearings can be used in central and southern China. Plate rubber bearings are usually composed of several layers of rubber sheets and steel plates (with steel plates as rigid stiffeners). Each layer of rubber is firmly bonded with its upper and lower steel plates through pressure vulcanization. Under the vertical load P, the steel plate embedded between the rubber sheets will limit the lateral deformation of the rubber, and the vertical deformation will be reduced accordingly, which can greatly improve the vertical stiffness (compressive stiffness) of the bearing. At this time, the total vertical deformation of the bearing will be the total deformation of each layer of rubber sheet. The steel plate embedded between the rubber sheets of the highway plate rubber bearing has little effect on the shear stiffness of the rubber bearing while preventing the lateral expansion of the rubber layer. Under the action of horizontal force H, the horizontal displacement Δ generated by the stiffened rubber bearing depends on the net thickness of the rubber sheet. (Figure 1) In order to prevent the stiffening steel plate from rusting, the upper, lower and four periphery of the plate rubber bearing are protected by rubber. The structure of plate bearing is shown in Figure 2.
The plate rubber bearing has the following advantages: simple structure, easy manufacture, low cost and steel saving. The material source is sufficient and suitable for mass production. Rubber has excellent elasticity and damping, so the rubber bearing has good shock absorption performance, which can reduce the impact of dynamic load on the bridge span structure and pier, thus improving the stress condition of the bridge. During the use of the plate rubber bearing, the maintenance work is less. Low building height and simple installation can save construction labor and time. It is easy to replace, and the bearing can also be replaced on the bridge in operation. The plate rubber bearing only produces very small elastic deformation under the vertical force, while the shear deformation under the horizontal force can occur in any direction in the horizontal plane, so it has a wide range of applications and can adapt to wide bridges, curved bridges, skew bridges, etc. The working performance of plate rubber bearing is reliable. According to the analysis and comparison test of bearings that have been used for more than 10 years on domestic bridges, and the reports of relevant tests and practical data abroad, the service life of rubber bearings can reach at least 50 years, which is completely possible to reach the same life as the bridge.
The construction quality of rubber bearings, and the convenience of installation, adjustment, observation and replacement of bearings; It is necessary to set bearing pad stones on the top of piers and abutments no matter what type of plate rubber bearings are installed, whether cast-in-place beams or precast beams are used for construction. The plane size of the bearing pad stone used for the plate rubber bearing should be able to bear the load of the superstructure, and the general length and width should be about 10cm larger than that of the rubber bearing. The height of the pad stone shall be more than 6cm to ensure that there is enough space from the bottom of the beam to the top of the pier and abutment for placement lifting jack , for support replacement. The construction sequence of rubber bearing installation on the poured beam is as follows: first remove the floating sand from the top surface of the pier pad stone, and the surface should be clean, flat and free of oil stain. If the elevation difference of pier pad stone is too large cement mortar Adjustment. The center line of bearing position shall be marked on the bearing pad stone according to the design drawing, and the cross center line shall also be marked on the rubber bearing. Place the rubber bearing on the bearing pad stone, so that the center line of the bearing coincides with the center of the design position on the pier and abutment, and the rubber bearing is in place accurately. Two or four supports of the same beam shall be on the same plane. To facilitate leveling, a layer of cement mortar can be paved between the rubber support and the pad stone before pouring, so that the support can be automatically leveled under gravity. Before pouring the concrete beam body, a supporting steel plate slightly larger than the bearing plane shall be added on the rubber bearing, and the steel plate shall be welded with anchor reinforcement to connect with the beam body. The supporting steel plate shall be cast as part of the cast-in-place beam formwork. In order to prevent slurry leakage, yarn, putty or soft board Filling. In the future, when removing the formwork, the filler shall be removed, and the above construction can make the upper and lower parts of the support closely stick to the top surface of the steel plate at the beam bottom and the pad stone. Installation of prefabricated beam rubber bearing. The reinforcement mesh shall be arranged in the bearing pad stone, and the vertical reinforcement shall be connected with the reinforcement in the pier. The concrete grade of the pad stone shall not be lower than C30 or the design grade. The top surface of the pad stone concrete shall be calibrated with a level in advance to make it flat and not smooth. The elevation force of the top surface of the bearing pad stone shall be accurate and consistent. In particular, the top surface of the bearing pad stone of two or four bearings of a beam should be in the same plane to avoid bias, initial shear and uneven stress.
The key to installing the rubber bearing of the precast beam is to ensure that the beam bottom and the top surface of the pad stone are parallel and flat as far as possible, so that they are closely attached to the upper and lower parts of the rubber bearing, and avoid the occurrence of eccentric pressure, void and uneven bearing. The construction sequence is as follows: first, treat the bearing pad stone according to the cast-in-place beam (1). The bottom plane of the precast beam in contact with the support shall be horizontal and flat. In case of honeycomb or inclination, cement mortar shall be used for tamping and leveling in advance. Correct positioning of rubber bearing. First, place the rubber bearing on the pier pad stone according to the design center according to the cast-in-place beam (2). The longitudinal axis of the T-beam shall coincide with the center line of the support; The longitudinal axis of plate beam and box beam shall be parallel to the center line of support. In order to drop the beam accurately, when erecting the front span plate beam or box beam, the cross position centerline of the two supports can be marked on the bottom of the beam, and the straight line along the centerline of the two support positions can be marked on the elevation of the beam end; The beam falling shall be consistent with the center line of the pier and abutment. The beam can be dropped on the basis of the front span beam for the following several spans. The beam shall fall steadily to prevent eccentric compression of the support or initial shear deformation.
