Cultural relics are precious properties of all humankind, the damage of which is nonresilient. In previous earthquakes, stored cultural relics have shown poor seismic performance, so effective seismic methods are urgently needed. However, due to various restrictions, traditional damping methods are not suitable for the cultural relics stored in the Palace Museum. An efficient damping method, composed of silicone damper and connecting elements, is proposed to protect these stored cultural relics. This novel damping device is very convenient to install and no change or move for the original structures is needed. It is suitable for various kinds of new and existing relic cabinets. In order to validate the effectiveness of this novel damping method, both numerical simulation and shaking table tests are carried out. Results show that this method can effectively enhance the seismic performance of relic cabinet itself and the internal cultural relics. Relic cabinets with damping devices deform significantly less than noncontrol cabinets while the inside relics also have less sliding or overturning. Overall, a damping method, designed for seismic protection of cabinet stored cultural relics, is proposed and its effectiveness has been successfully demonstrated.
Situated in the heart of Beijing, the Palace Museum is one of the most prestigious museums in China and the world at large. Over 1.8 million pieces of cultural relics are stored in the Palace Museum, including paintings, calligraphy, ceramics, and antiquities of the imperial collections, which are priceless treasures to all humankind. Relics in museum are either being displayed or stored in storehouse. For better display effect and easier access, relics under both circumstances are typically unanchored. Stored relics, such as porcelains and jadeites, are typically stored in floating cabinets. Most of these relic cabinets lack proper seismic protection measures. Because of these relics’ high value, fragility, and nonreproducibility, once strong earthquakes happen, the adverse consequences would be tremendous and unacceptable [
Damage of cabinet stored relics in Wenchuan earthquake.
Finding proper methods to protect relics is important and inevitable [
Based on the above reasons, a damping control system based on viscous dampers is advocated. Cabinets are connected to each other at the top through viscous dampers and connecting elements. No move or change of the cabinets as well as the inside relics is needed. Besides, this damping system is fast and convenient to install and is environmental friendly.
In order to validate the effectiveness and robustness of this damping method, shaking table tests and finite element analyses are carried out. The design and configuration of damping system are given in Section
Viscous damper is developed based on the principle of fluid motion, especially the throttling resistance produced when the fluid gets through the throttling orifice, which is associated with the piston motion velocity. Viscous damper is widely used in high-rise buildings, bridges, seismic retrofitting of building structures, vibration resistance of industrial pipeline equipment, and military industry [
Viscous damper is usually composed of cylinder, piston, viscous fluid, and guide rod, the basic construction of which is shown in Figure
Basic construction of viscous damper.
In practical application, the mechanical characteristic of viscous damper is decided by viscous fluid property and damper construction. General expression of damping force is seen in (
For cultural relics stored in cabinets, the preservation conditions such as the humidity and temperature environment of the storehouse are extremely strict, which must be satisfied with the specific requirements. Therefore, the damper used in storehouse must ensure two aspects:
There are two configurations of silicone damper chosen in the damping device, named damper I and damper II [
Specifications of silicone dampers [
Parameters | Damper I | Damper II |
---|---|---|
Damper configuration | Double acting | Double acting |
Damping mechanism | Viscous fluid | Viscous fluid |
Characteristic equation | | |
Damping factor | 5.65 kN(s/m) | 2.75 kN(s/m) |
Velocity index | 0.25 | 0.15 |
Max force | 5.5 kN | 2.7 kN |
Nominal design frequency | 2.0 Hz | 2.0 Hz |
Max piston velocity | 0.90 m/s | 0.90 m/s |
Total stroke | 212 mm | 212 mm |
Force-velocity curves and force-displacement curves (under the max velocity) of silicone dampers [
Damper I
Damper II
In the design of connecting elements, the following requirements need to be satisfied:
The designed connecting elements are made up by six kinds of components: triangle piece, T-type piece, cross-type piece, L-type piece, plate piece, and sleeve. As the spaces between relic cabinets are different, while the length of the damper is fixed, the connection requirements between cabinets can be met by designing and changing the length of the sleeve. The damping device assembled by the silicone dampers and connecting elements is shown in Figure
Assembled damping device.
Through the inspection of storerooms in the Palace Museum, two typical layouts of relic cabinets are selected, named layout A and layout B, respectively (Figure
Two typical layouts of relic cabinets ((a) layout A, (b) layout B).
The numerical simulation of relic cabinets is conducted with finite element software ANSYS/LS DYNA. In order to study the seismic performance of the damping device, both the original cabinet model without any control measure and the model with damping device control are simulated. The dynamic time history responses of the models with and without control are both analyzed and compared. In addition, by comparing the damping effects of models that use different parameters of the damping device, the optimal parameters of the damper are designated.
In the finite element model, relic cabinet is simulated by shell element, damper is simulated by spring-damping element, connecting element is simulated by three-dimensional beam element, and the ground and wall are simulated by solid element. The connection of relic cabinet and damper is simplified as a hinge joint, and the connection of damper and sleeve is set rigid. According to the parameters of the actual dampers, the damping factor is 5.0 kN(s/m)
Numerical models of relic cabinets ((a) layout A, (b) layout B).
According to the site condition in the area where the Palace Museum is located, referring to China’s code for seismic design of buildings (GB50011-2010) [
Input levels.
Name | Ground motions | Input PGA/g |
---|---|---|
T01 | Synthetic motion | |
T02 | Tangshan | |
T03 | Wenchuan | |
| ||
T04 | Synthetic motion | |
T05 | Tangshan | |
T06 | Wenchuan | |
| ||
T07 | Synthetic motion | |
T08 | Tangshan | |
T09 | Wenchuan |
Synthetic ground motion.
Beijing hotel ground motion in Tangshan earthquake.
Wolong ground motion in Wenchuan earthquake.
Response spectra.
Through the finite element calculation, the acceleration and displacement results of the top of cabinets and the force and displacement results of the dampers are obtained, in order to analyze the seismic performance of the damping device and adjust the appropriate parameters of the dampers. The damping ratio is defined as the indicator to evaluate the damping effect, calculated by (
Due to the limited paper space, only the 4# relic cabinet in layout A and the 12# relic cabinet in layout B are taken as examples to illustrate the damping effect. The comparisons of acceleration time history curves of the relic cabinets with and without control are shown in Figures
Peak acceleration (g) and acceleration damping ratio (numerical).
Input levels | 4# cabinet in layout A | 12# cabinet in layout B | ||||
---|---|---|---|---|---|---|
| | | | | | |
T05 (0.40 g) | ||||||
Without control | 1.97 | 1.93 | 2.00 | 2.29 | 2.19 | 2.40 |
With control | 1.28 | 1.33 | 1.32 | 1.59 | 1.69 | 1.44 |
| | | | | | |
T06 (0.40 g) | ||||||
Without control | 2.00 | 1.90 | 1.90 | 2.59 | 2.26 | 2.27 |
With control | 1.40 | 1.25 | 1.24 | 1.46 | 1.45 | 1.58 |
| | | | | | |
T08 (0.62 g) | ||||||
Without control | 3.27 | 3.24 | 3.17 | 3.01 | 3.13 | 3.14 |
With control | 2.42 | 2.43 | 2.12 | 1.99 | 1.82 | 1.79 |
| | | | | | |
T09 (0.62 g) | ||||||
Without control | 3.26 | 3.14 | 2.98 | 2.96 | 3.22 | 3.08 |
With control | 2.25 | 2.42 | 2.21 | 1.81 | 1.90 | 2.03 |
| | | | | | |
Relative displacement (mm) and displacement damping ratio (numerical).
Input levels | 4# cabinet in layout A | 12# cabinet in layout B | ||
---|---|---|---|---|
| | | | |
T05 (0.40 g) | ||||
Without control | 30.10 | 14.10 | 8.04 | 20.30 |
With control | 19.40 | 10.10 | 3.62 | 6.37 |
| | | | |
T06 (0.40 g) | ||||
Without control | 4.80 | 0.70 | 5.18 | 0.77 |
With control | 3.10 | 0.50 | 2.33 | 0.47 |
| | | | |
T08 (0.62 g) | ||||
Without control | overturn | overturn | 24.80 | 32.50 |
With control | 3.40 | 4.30 | 11.40 | 7.20 |
| / | / | | |
T09 (0.62 g) | ||||
Without control | 6.20 | 1.30 | 12.60 | 1.00 |
With control | 4.00 | 0.90 | 2.60 | 1.00 |
| | | | |
Acceleration time history curves of 4# cabinet in layout A-T05 (0.40 g) (numerical).
Acceleration time history curves of 12# cabinet in layout B-T09 (0.62 g) (numerical).
Force time history curves of the dampers (numerical).
1# damper in layout A
2# damper in layout B
The results show that the optimal acceleration damping ratio is 0.56 and the average acceleration damping ratio is 0.67; the optimal displacement damping ratio is 0.22 and the average displacement damping ratio is 0.48. The range of the damping force is about 1.3 kN to 4.3 kN, and the maximum relative displacement of the damper is about 50 mm. Therefore, the parameters of the damper can be designated as follows: damping index is 0.2, damping force is 2.7 kN–5.5 kN, and maximum stroke is ±100 mm.
Through further analysis of the results, the following conclusions can be summarized.
In order to verify the actual damping effect of the damping device for the relic cabinets, the shaking table tests are carried out at the Key Laboratory of Earthquake Engineering and Engineering Vibration of China Earthquake Administration. The maximum load of the 5 m × 5 m triaxial shaking table is 30 t, and the maximum accelerations under the full load are 2.04 g in
Text models ((a) layout A, (b) layout B).
As the test phenomenon can directly reflect the seismic damping effect, by observing the test phenomena of layout A and the layout B both without and with control (Figure
Test phenomenon comparison (left: without control; right: with control).
Layout A-PGA 0.20 g
Layout A-PGA 0.40 g
Layout A-PGA 0.62 g
Layout B-PGA 0.20 g
Layout B-PGA 0.40 g
Layout B-PGA 0.62 g
In the cases without control, under PGA 0.20 g level, the slipping of relics in the cabinet is obvious; under PGA 0.40 g level, some cabinet doors are opened, the cabinet appears slipping, and the slipping of the relics is obvious; under PGA 0.62 g level, the cabinet doors are almost all opened, all cabinets slip obviously, and several cabinets collide with each other.
In the cases with control, under PGA 0.20 g level, there is nearly none slipping of the relics; under PGA 0.40 g level, the cabinet doors are locked well, the cabinets do not slip, and only the inside relics slip slightly; under PGA 0.62 g level, several cabinet doors are opened, and several cabinets slip slightly.
Compared to the two different layouts, it can be found that, in the cases without control, under the same level, the seismic damage of layout A (with the short sides of most relic cabinets being against the wall) is lighter, while the damage of layout B (with the long sides of most relic cabinets being against the wall) is heavier, with cabinet doors opening, cabinet sliding earlier, and collision between cabinets. In the cases with control, both of the two layouts have obvious damping effect, and the damping effect of layout A is better than that of layout B.
Taking the 4# relic cabinet in layout A as an example, under T02 (0.20 g) and T08 (0.62 g) levels, the peak accelerations and acceleration damping ratios of 4# cabinet with and without control are shown in Table
Peak accelerations (g) and acceleration damping ratios of 4# cabinet in layout A (experimental).
Input levels | 4# cabinet | | | |
---|---|---|---|---|
T02 (0.20 g) | Without control | 0.60 | 0.58 | 0.42 |
With control | 0.29 | 0.23 | 0.33 | |
| | | | |
| ||||
T08 (0.62 g) | Without control | 2.02 | 2.44 | 1.56 |
With control | 1.71 | 1.26 | 1.08 | |
| | | |
Acceleration time history curves of 4# cabinet in layout A-T02 (0.20 g) (experimental).
Acceleration time history curves of 4# cabinet in layout A-T08 (0.62 g) (experimental).
Taking the 12# relic cabinet in layout B as an example, under T02 (0.20 g) and T08 (0.62 g) levels, the displacements (relative to the input) and displacement damping ratios of 12# cabinet with and without control are shown in Table
Relative displacements (mm) and displacement damping ratios of 12# cabinet in layout B (experimental).
Input levels | 12# cabinet | | |
---|---|---|---|
T02 (0.20 g) | Without control | 13.38 | 14.53 |
With control | 1.69 | 0.66 | |
| | | |
| |||
T08 (0.62 g) | Without control | 273.96 | 79.61 |
With control | 40.41 | 13.06 | |
| | |
Displacement time history curves of 12# cabinet in layout B-T02 (0.20 g) (experimental).
Displacement time history curves of 12# cabinet in layout B-T08 (0.62 g) (experimental).
The force and displacement of each damper in layout A and layout B are shown in Tables
Force and displacement of each damper in layout A (experimental).
Input levels | 1# damper | 2# damper | 3# damper | 1# damper | 2# damper | 3# damper |
---|---|---|---|---|---|---|
Force/kN | Force/kN | Force/kN | Displacement/mm | Displacement/mm | Displacement/mm | |
T01 (0.20 g) | 0.32 | 0.09 | 0.13 | 0.07 | / | 0.15 |
T02 (0.20 g) | 0.34 | 0.06 | 0.08 | 0.07 | / | 0.04 |
T03 (0.20 g) | 0.28 | 0.11 | 0.13 | 0.06 | / | 0.15 |
| ||||||
T04 (0.40 g) | 0.85 | 0.20 | 0.41 | 0.17 | / | 0.34 |
T05 (0.40 g) | 0.96 | 0.18 | 0.13 | 0.32 | / | 0.14 |
T06 (0.40 g) | 0.58 | 0.22 | 0.26 | 0.24 | / | 0.23 |
| ||||||
T07 (0.20 g) | 2.23 | 0.99 | 1.09 | 1.61 | / | 0.60 |
T08 (0.62 g) | 2.39 | 0.74 | 1.04 | 2.69 | / | 0.99 |
T09 (0.62 g) | 0.81 | 0.61 | 0.32 | 0.38 | / | 1.27 |
Force and displacement of each damper in layout B (experimental).
Input levels | 1# damper | 2# damper | 3# damper | 1# damper | 2# damper | 3# damper |
---|---|---|---|---|---|---|
Force/kN | Force/kN | Force/kN | Displacement/mm | Displacement/mm | Displacement/mm | |
T01 (0.20 g) | 0.47 | 0.28 | 0.10 | 0.65 | 0.61 | 0.42 |
T02 (0.20 g) | 0.43 | 0.23 | 0.08 | 0.45 | 0.13 | 0.20 |
T03 (0.20 g) | 0.53 | 0.30 | 0.12 | 3.99 | 1.14 | 0.18 |
| ||||||
T04 (0.40 g) | 1.35 | 0.75 | 0.86 | 3.62 | 1.58 | 0.76 |
T05 (0.40 g) | 0.80 | 0.31 | 0.27 | 1.07 | 0.81 | 0.78 |
T06 (0.40 g) | 0.54 | 0.58 | 0.74 | 1.26 | 1.85 | 0.84 |
| ||||||
T07 (0.20 g) | 1.66 | 0.89 | 1.37 | 6.32 | 2.26 | 2.51 |
T08 (0.62 g) | 2.26 | 0.79 | 0.83 | 5.46 | 2.75 | 1.18 |
T09 (0.62 g) | 1.11 | 0.97 | 0.74 | 9.29 | 2.31 | 2.07 |
Force and relative displacement time history curves of 1# damper in layout A (experimental).
Force and relative displacement time history curves of 1# damper in layout B (experimental).
The results show that, under all conditions, the values of damper forces are in the range of 0.1 kN to 2.4 kN, and the values of relative displacements are in the range of 0.1 mm to 10 mm, which do not exceed the max force and total stroke of the damper. When the input PGA is small, damper force is relatively small, with no obvious damping effect. When the input PGA increases, damper force also increases, which can give full play to the damping effect of the damper.
The acceleration amplification factor of relic cabinet
Average acceleration amplification factor of relic cabinets in layout A (experimental).
Average acceleration amplification factor of relic cabinets in layout B (experimental).
The results show that, without control, the acceleration amplification effect is very obvious, and the acceleration amplification factor increases with the increase of the input PGA. However, with control, the acceleration amplification factor of the cabinet is obviously reduced. Besides, compared with the two layouts, after installing the damping device, the acceleration amplification factor of the layout A decreases more, and the damping effect of layout A is better than that of layout B.
The acceleration damping ratio and displacement damping ratio of relic cabinets are defined correspondingly to the numerical simulation section, seen in Section
Average acceleration and displacement damping ratios of relic cabinets (experimental).
Input PGA levels | Average | Average | |||
---|---|---|---|---|---|
| | | | ||
Layout A | 0.20 g | 0.67 | 0.61 | 0.67 | 0.96 |
0.40 g | 0.50 | 0.37 | 0.56 | 0.34 | |
0.62 g | 0.58 | 0.45 | 0.58 | 0.35 | |
| | | | | |
| |||||
Layout B | 0.20 g | 0.73 | 0.78 | 0.38 | 0.34 |
0.40 g | 0.72 | 0.62 | 0.57 | 0.51 | |
0.62 g | 0.75 | 0.79 | 0.50 | 0.42 | |
| | | | | |
| |||||
| | |
The results show that the optimal acceleration damping ratio is 0.13 and the total average acceleration damping ratio is 0.63; the optimal displacement damping ratio is 0.01 and the total average displacement damping ratio is 0.51. The designed damping device performs obvious damping effect both in acceleration and displacement responses, which totally achieves the expected purpose of relic protection:
Due to the fact that almost no damping and isolation measure has been taken in most relic cabinets, the seismic risk of relic cabinets and the inside relics is very high. Corresponding study of the damping methods is urgently needed. There are many difficulties in the damping design of relic cabinets. Firstly, it is necessary to ensure the durability of the dampers and connections, which cannot be damaged for a long time and can maintain the working condition. Secondly, toxic and harmful gases and liquids should not be produced to avoid damaging the environment in the storehouse. Thirdly, when designing the connecting elements, it is important to ensure that the modular assembly method can be used without moving the relic cabinets, drilling holes, or using glue, which may damage the cabinets. At the same time, the construction should be simple and fast, so as to minimize the disturbance to the storage environment.
In order to solve these problems, a modular assembly damping device is designed with silicone damper as the key part. The finite element model is established and analyzed to determine the damper parameters, and through the shaking table tests it is proved that the damping device can effectively reduce relic cabinets’ acceleration and displacement responses under earthquakes, to achieve the purpose of relics protection.
The designed damping device has obvious damping effect and can effectively improve the seismic performance of the cultural relics. Meanwhile, the advantages of the device are as follows: the installation is simple and fast, with no need to move the relics in the cabinets and the minimal effect on the storehouse; the use of the top space of the cabinet does not affect daily work; it uses environmental protection material which is dust free with no vibration and no pollution; it is mechanically designed, passive damping, and maintenance-free; all the components can be manufactured in batches and connected only with bolts. As the adjustable components, the generalizability of the proposed damping method to another close situation is also good.
In conclusion, through numerical simulation and shaking table tests, the effectiveness of the modular damping method is demonstrated. Supreme seismic effectiveness and practical operability are proved. A positive reference for future study on seismic protection of cabinet stored cultural relics is offered.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors appreciate the financial support from the Basic Research Foundation of Institute of Engineering Mechanics, CEA (2017A01), the Earthquake Scientific Research Funds Program (201508023), and Program for Innovative Research Team in China Earthquake Administration.