The lead core seismic isolation rubber bearing(hereinafter as lead rubber bearing or LRB) is suitable for each kind of road and municipal bridges in earthquake intensity section with 8 degrees or below according to the existing transportation industry standard《Lead Rubber Bearing Isolator for Highway Bridge》（JT/T 822-2011)，national standard《Rubber Bearing □ Part 2:曰astomeric Seismic-protection Isolators for Bridges》（GB 20688.2-2006) and related industrial codes as well as isolation bridge component product researched according to the European standards.
The lead rubber bearing is divided into rectangular lead rubber bearing and circular lead rubber bearing according to the shape of the main body.
The vertical load transfer process of LRB is beam body—? upper embedded steel plate —?upper connecting steel plate—? upper sealing plate —? laminated structure composed by rubber, lead core, reinforced steel plates-^ lower sealing platen lower connecting steel plate —>? abutment.
The horizontal seismic load transfer process of LRB is abutment—? lower anchor components —?lower connecting steel platen shearing key, lower sealing plate—? laminated structure composed by rubber, lead core, reinforced steel plate ^ upper sealing plate, shearing key —? upper connecting steel plate —? upper embedded steel plate —? delivering to beam by upper anchor component.
The design shear modulus of the series bearings are 0.8MPa, 1 .OMPa, 1.2MPa.
Level equivalent stiffness
When in 175% of shearing strain, the maximum horizontal equivalent stiffness of the rectangular lead rubber bearing is 9.7kN/mm and the minimum horizontal equivalent stiffness is 1.3kN/mm; the maximum horizontal equivalent stiffness of the circular lead rubber bearing is 10.4kN/mm and the minimum horizontal equivalent stiffness is 1.1kN/mm. The horizontal equivalent stiffness of each specification series sees the design parameter table of the specification size of the bearing.
When in 175% of shearing strain, the maximum equivalent damping ratio of the rectangular lead rubber bearing is 22.7% and the minimum equivalent damping ratio is 14.4%; the maximum equivalent damping ratio of the circular lead rubber bearing is 20% and the minimum equivalent damping ratio is 13.5%. The equivalent damping ratio of each specification series sees the design parameter table of the specification size of the bearing.
The temperature range of the series bearing is -25t) – +60^.
Note: if the project has special demands, the above technical parameters of the series bearing can be customized.
8.1 When calculating the bearing, the tangent value of shear angle a of the bearing under the normal using state is calculated; when not counting the braking force, tana ^0.5; and when counting into the braking force, tana ^0.7.
8.2 When calculating the bearing, mechanical properties of the selected bearing shall be checked whether to meet the using requirement under the corresponding earthquake force; the structure form, technical property feature, requirement of construction process, cost and the like of the bridge must be comprehensively considered.
8.3 It is designed respectively according to different design shearing modulus G values of the rubber; the project technician shall select according to the actual condition of each bridge so as to optimize the stress and using condition of the structure.
Similarly, the horizontal stiffness of the bearing with the same vertical bearing capacity is correspondingly increased along the increased G value, but the suitable deformation ability is correspondingly reduced along the increased G value, so the project technician must select the model according to the specific condition or requirement of each bridge so as to optimize the stress and using performance of the structure.
8.4 Normal model selection process of LRB series lead rubber bearing
Confirm the shear modulus G of the rubber (G0.8, G1.0 and G1.2)^shape of bearing body (circular and rectangular)^ design vertical bearing capacity—?design shear displacement—verifying calculation or optimized design—?repeating;
8.5 The model is selected according to the seismic fortification intensity and field type in the bridge region. The model selection scheme of LRB series lead rubber bearing is listed in table 1; and it is for reference of project technician.
8.6 When selecting the model of the bearing, it must consider the matching adaptation of the bridge structure and meet the space position requirement of actual bridge structure. In addition, the design and selection of the accessories, such as sleeve, anchor bar and the like shall be safe, suitable, economic and rational, it must avoid the interference or conflict with the structure stressed rebar; and if necessary, it must be subjected to optimal design.
Table 1 Recommended selection table of shear modulus of lead rubber bearing
Seismic fortification intensity
NOTE: Cs means the field coefficient, G means design shear modulus of the bearing