It has been nearly 20 years since CHINA applied seismic isolation technology to building structure engineering in 1992, although the seismic isolation technology contains laminated rubber
Seats, three-dimensional rubber isolation bearings, slide bearings and other technologies, more than 80% of the existing isolation buildings use laminated rubber isolation bearings.
The laminated rubber shock-absorbing bearing is composed of thin steel plates and thin rubber sheets. The rubber material is under the action of light, heat, oxygen, ozone and mechanical stress.
The molecular chain is broken, and the performance is reduced, showing aging. Since the rubber isolation bearing is placed at the bottom of the building, it is necessary to consider the difference in climate in each region
For example, heat resistance should be considered in the south, cold resistance should be considered in the north, and ultraviolet radiation resistance should be considered in the plateau area.
Conducted temperature dependence and thermal aging research. In this paper, 12 600-type rubber shock-isolating bearings were used as test bodies, and their performance and temperature,
According to the relationship between thermal aging, the thermal aging resistance of 60-100a is obtained, and the long-term aging resistance of rubber shock-isolating bearings is evaluated.
1 Experimental device and test body
The performance test device of the test body in the research is shown in Figure 1, Figure 1(a) is a 20 MN electro-hydraulic servo loading system, its vertical force reaches 20 MN, and its horizontal force reaches 2 MN; To maintain a constant pressure, the loading speed is 3-8 mm/s, the loading adopts sine wave, and the sampling frequency is 2 Hz. The size of the temperature control box is 2 m × 1. 5 m × 1. 8 m, and the temperature ranges from -22 ℃ to 42 ℃. The thermal aging test is completed in a thermostat with a controlled temperature of 100°C.
The test body is 12 600-type laminated rubber shock-isolation bearings, including 7 LRB-type and 5 RB-type. The support adopts rubber shear elastic modulus G =0. 39 N/mm 2 , the total thickness of the rubber layer T r =120 mm, and the total thickness of the steel plate T p =144 mm. The structure is shown in Figure 1(b).
2 Test content
2.1 Benchmark performance test
Before carrying out various tests, a benchmark performance test with a vertical design load of 15 MPa (4 241 kN) was carried out on 12 test bodies (LRB type and RB type).
The vertical pure compression test is to determine the vertical stiffness and vertical deformation of the isolation bearing, and the cycle is within ±30% of the design load, and the number of cycles is 4 times. The vertical load value is collected by the oil pressure sensor, and the vertical displacement is collected by the CLP50 displacement sensor, and the collection time interval is 0.5s.
The horizontal performance test is to determine the horizontal equivalent stiffness, post-yield stiffness, yield force and damping characteristics of the isolation bearing. In the research, a compressive stress of 15 MPa was applied vertically to the test body, and then a restoring force with a horizontal shear strain of 100% (±120 mm) was applied to it, and the frequency was 0.02 Hz for 4 reciprocating cycles.
2.2 Temperature-related performance test
For the 3 LRB-type and 3 RB-type test objects after the benchmark performance test, when the temperature is: -20 ℃, -10 ℃, 0 ℃, 5 ℃, 10 ℃, 22 ℃, 29 ℃, 40 ℃, The correlation test was carried out. In the test, a compressive stress of 15 MPa was applied vertically to the test body, and a shear strain was applied horizontally to 100% of the restoring force. The frequency was 0. 02 Hz and the reciprocating cycle was repeated 4 times.
2.3 Thermal aging performance test
After the benchmark performance test, the 6 (RB and LRB type) test bodies were subjected to heat aging tests at a temperature of 100 °C for 240 h and 336 h (20 °C × 60 a). After aging, the test bodies were all subjected to After parking for 72 h, conduct the benchmark performance test again. Before the aging test, the compressive stress correlation and shear strain correlation tests were carried out on the LRB-600-J bearing of the test body; after aging, the test with the same content and the unidirectional 350% ultimate deformation test Load 15 MPa, horizontal displacement -420 mm), see Table 1. At the same time, 120 repeated cyclic loading tests (vertical load: 15 MPa, horizontal strain: 100%) were carried out on the RIL-600-L bearing in the test body after the aging benchmark performance test.
3 Test resultsanalyze
3.1 Benchmark performance
See Table 2 for the benchmark performance test results of 12 test bodies. Its vertical stiffness is K v = E cv ·A c /T c (1) In the formula, E cv is the modified compressive elastic modulus of the laminated rubber bearing, E cv= E c ·E v /(E c + E v ); among them, E v is the elastic modulus of volume constraint of rubber material; E c is the compressive elastic modulus of laminated rubber bearing, Ec = E(1 +2kS21 ); E is the standard elastic modulus of rubber material; k is the rubber Material hardness correction coefficient; S 1 is the first shape correction coefficient of the laminated rubber bearing. Data processing and analysis in the test takes the third cycle in the test data.
K v = (P 1 - P 2 )/(δ 1 - δ2 )(2)
Figure 2. Horizontal performance calculation and analysis method
Fig．2 Calculate analysis method of horizontal property
In the formula, P 1 = (1-30%)P; the corresponding vertical displacement is δ 1 ; P 2=(1 +30%)P, the corresponding vertical displacement is δ 2 ; P is the laminated rubber bearing The vertical design load.
The horizontal performance analysis adopts the bilinear model calculation and analysis, as shown in Fig. 2, K eq is the horizontal equivalent stiffness; H eq is the equivalent damping ratio; K d is the stiffness after yield; Q d is the yield force; Horizontal deformation displacement
K eq = (Q 1 - Q 2 )/(δ 1 - δ2 )
H eq =2·ΔW/[π·K eq(δ1－δ2 )2 ]
K d = {[(Q 1 - Q d1) /δ1 ] + [(Q 2 - Q d2 ) /δ 2 ]} /2
Qd = (Qd1－Qd2)/2
The curve in the figure is the characteristic of bilinear restoring force obtained from LRB bearing test.
Hysteresis curve, the dotted line is the characteristic curve of the restoring force of RB bearing. It is known from Table 2 that the vertical stiffness test values of the two types of bearings through the benchmark performance test are similar, and the change range is -21.1% to 3.3%; the horizontal equivalent stiffness of the RB type bearing is very close; The post-yield stiffness, equivalent stiffness, yield force, and damping ratio of the horizontal performance of LRB bearings are also classified similarly, and the deviation from the design value is within 15%.
3. 2 Temperature-dependent performance
Fig. 3 shows the temperature-dependent equivalent stiffness, post-yield stiffness, yield force and equivalent The test result curve of the damping ratio and the result curve of the vertical performance.
In the formula, T 0 is 20 ℃ under the standard normal temperature; T is the test temperature; K is the horizontal stiffness.
Figure 3(a) is the comparison between the equivalent stiffness of the test body (RB and LRB type) and the design formula, and it is known that the curve trend is similar to the design formula, and the RB type
支座 40 ℃时等效刚度偏离设计式为 5. 5%，温度 －20 ℃时偏离设计值为 －3. 2%;LRB 型支座 40 ℃时等效刚度偏离设计式达 2. 0%，温度 － 20 ℃ 时偏离设计值为 － 0. 9%，阻尼比在 40 ℃ 时偏离设计式为 －11. 5%，温度 －20 ℃时偏离设计值为 17. 8%． 反映出温度对支座的等效刚度及阻尼均具有不同程度的影响，低温使阻尼增大，支座耗能能力显著上升，高温则使其降低． 图 3(b)、3(c)为 LRB 型支座屈服后刚度、屈服力与设计式的对比，知屈服后刚度及屈服力曲线均与其设计式趋势相一致;40 ℃时其屈服后刚度与设计式偏离为 8. 5%，温度 －20 ℃时偏离为 10. 1%;而 40 ℃时其屈服后力与设计式偏离为 －5. 9%，温度 －20 ℃时偏离为 0. 4%;图 3(d)为 RB 和 LRB 型支座的竖向刚度与温度相关性曲线，低温使其刚度增大，高温则使其减小。
3. 3 热老化相关性能
试验体支座热空气加速老化试验理论According to Arrnenius 提出的反应速度论进行，其时间为
式中，t 0 、T 0 分别为设计基准期(d)和使用环境的绝对温度(K);t、T 分别为试验所需时间(天)和试验所需温度(K);R 为气体常数( =8. 31 J/mol·K);E 为橡胶活化能( =90. 4 KJ/mol)． According to式(5)可计算出相对于某一环境温度和设计使用年限的加速老化温度和时间．
本研究According to规程及现行行业标准 ［8］ 要求，在恒温箱中不仅连续进行 100 ℃ ×240 h 热老化试验，且完成100 ℃ ×336 h 的老化试验，可进一步确定6 个试验体在20 ℃ ×60 a 使用条件下力学性能的变化率。下述列出试验体热老化前后基准性能(竖向荷载15 MPa，水平剪应变100%)的对比率，知试验体支座竖向性能的变化率小相对稳定，
RB 型支座老化后等效刚度降低;LRB 型支座老化后屈服后刚度、等效刚度趋于降低，屈服力、等效阻
尼比呈上升趋势． 图 4、图5 分别给出试验体 LRB－600－J(100 ℃ ×336 h)老化前后竖向载荷为15 MPa，水平性能与压缩应力相关性和剪应变相关性的比较． 图 4 反应出试验体 LRB－600－J 老化前后随压缩应力的增加，其等效刚度、屈服后刚度变化趋势相近呈递减;而其等效阻尼比、屈服力呈递增趋势． 图 5 反应出。
试验体 LRB－600－J 老化前后随剪应变的增大，等效刚度、等效阻尼比及屈服后刚度均呈现减小趋势;其屈服力略显上升． 图 6 为试验体 LRB－600－J 支座老化后竖向载荷为 15 MPa，水平剪应变为 350%( －420mm)极限变形时水平力与水平位移的关系曲线，试验中未见试验体外观出现异常及龟裂现象。表 3 列出试验体 LRB－600－J(100 ℃ ×336 h)和 LRB－600－L(100 ℃ ×240 h)老化前后、经极限变形、120 次反复循环加载后基准性能对比，反应老化时间的不同，对试验体支座性能显现一定的差异． 试验体 LRB－600－J(经老化)极限变形后水平基准性能试验显示屈服后刚度、等效刚度要比之前小，降低 － 24. 4% 和－12. 96%;而屈服力、等效阻尼比上升分别为 2. 5%和 17. 9%． 试验体 LRB－600－L(经老化)120 次循环加载后的水平基准性能试验显示屈服后刚度、等效刚度、屈服力比之前减小，降低 －15. 7%、－11. 96% 和－8. 7%;等效阻尼比比之前提高了 5. 6%． 揭示了经不同时段的老化，试验体支座的等效阻尼比有不同程度增加，老化促使铅芯支座耗能性增强。
4 结论
1) 600 型(RB 和 LRB)叠层橡胶隔震支座温度在 －20 ℃ ～40 ℃内变化时，竖向刚度变化趋势具有相
The same sex, the stiffness decreases with the increase of temperature, and the stiffness at low temperature increases. The equivalent stiffness of the RB-type bearing is similar to the design formula; the stiffness and yield force of the LRB-type bearing after yielding are consistent with the trend of the design formula, and decrease with the increase of temperature; the damping ratio decreases with the increase of temperature, showing the low temperature damping Increased energy consumption characteristics are strong, high temperature energy consumption is reduced.
2) After aging of the 600-type (RB and LRB) test body supports, the benchmark performance test shows that the vertical stiffness change rate is small and stable. The equivalent stiffness of the RB bearing decreases after aging; the equivalent stiffness and post-yield stiffness of the LRB bearing tend to decrease after aging, while the yield force and equivalent damping ratio show an upward trend (increase in energy consumption).
3) The performance comparison test before and after aging (100 ℃ × 336 h) of the LRB-600 test body support shows that: with the increase of compressive stress, the equivalent stiffness and stiffness after yielding have a similar trend of decreasing; while the equivalent damping ratio, yield The force is increasing. With the increase of shear strain, the equivalent stiffness, equivalent damping ratio and post-yield stiffness all decreased, while the yield force increased slightly. After aging, no damage was observed in the ultimate deformation of the vertical load of 15 MPa and the horizontal shear strain of 350% (-420 mm).
4) The benchmark performance of the LRB-600 test body bearing after aging at 100 ℃ × 240 h and its benchmark performance before aging, after 120 repeated loading cycles, and before and after aging at 100 ℃ × 336 h, and after 350% ultimate deformation The benchmark performance comparison shows that the aging time has a considerable influence on the benchmark performance of the rubber bearing. Long-term aging leads to a decrease in the horizontal benchmark performance of the bearing, and an increase in the vertical performance; after 350% ultimate deformation and 120 cycles of the horizontal benchmark performance test, the stiffness decreases and the damping ratio increases.
