Owing to special functional requirements of museum, such as great space and story height for exhibitions, large floor slab openings in plan and long span truss in elevation are becoming increasingly considered in museum design, which leads to challenges to structural safety. The aseismic performance of an isolated museum structure in high earthquake intensity regions was thus studied because of its complexity and irregularity. In order to observe the seismic characteristics and verify isolation effect, shaking table tests of a 1/30-scale structural model with and without base isolation bearings have been carried out under minor, moderate, and major earthquakes. The experimental results show that isolated structure dynamic characteristics and isolation effect are stable and storey peak acceleration responses of superstructure are less than that of fixed structure. Storey drifts of isolated structure meet required limits stipulated in Chinese design code and torsion responses of the bearings are not remarkable. It is suggested that seismic performances of complex museum structures have been effectively improved with isolation in use.
Seismic isolation using lead rubber bearings (LRBs) has been recognized as one of the most effective approaches to protect vulnerable buildings (e.g., historical buildings, hospitals, and computer facilities) from strong earthquakes. In the past decades, numerical analyses and experimental studies conducted by many researchers [
Museum is a kind of special functional public building, and its structural aseismic performances are always reduced by unique and complicated architectural design, such as large openings in floor slabs and long span truss in elevation. Structural safeties of these complex buildings are unable to realize by conventional structural design, especially in high earthquake intensity regions. The adoption of isolation could be an alternative choice for museums being capable of satisfying particular architectural functionality and structural aseismic requirements [
To examine the effectiveness of isolation for complicate museum, shaking table test is reliable choice, which has been increasingly used to study the dynamic responses of different types of structures in these decades [
As an important parameter in the shaking table tests, the scale factors of test model and prototype structure also have been studied by many researchers. Takaoka et al. ascertained the ultimate behavior of slender base-isolated steel framed buildings in response to buckling fracture in laminated rubber bearings based on 1/9 scaled model shaking table tests [
In recent studies, the aspect ratio effects on isolated structures have also been analyzed using shaking table tests. Chung et al. evaluated the effectiveness of base isolation systems for low-rise structure against severe seismic loads through the shaking table tests [
To achieve accurate seismic performances of isolated structure, some full-scale isolated models are used by researchers in the shaking table tests. Kasai et al. studied realistic 3D shaking table tests of full-scale building specimens utilizing the new schemes to assess performance of the building with passive control and base isolation schemes [
Besides common civil buildings, isolation bearings are also used to protect other constructions, such as industry facilities, liquid storage tanks, and some public buildings [
Shaking table test has become a powerful tool for researchers and designers to examine the dynamic performance of isolation systems of high-aspect-ratio buildings, irregular structures, and some crucial constructions. These years, growing amount of complex structures have been built in high intensity area, and their seismic safeties under severe earthquakes are hard to satisfy according to conventional structural design. As a functional public building, museum’s aseismic behaviors are always reduced by its large openings in floor slabs and long span truss in elevation. It is necessary for these complex structures taking shaking table tests to verify safety of conventional structural design and examine the effectiveness of isolation design. The objective of this paper is to assess seismic behaviors of such a seismically isolated museum structure called New Yunnan Provincial Museum, which has been attacked by Ludian earthquake in 2014. Brief introduction and primary achievements of the test has been summarized in [
The paper presents a shaking table test on a 1/30-scale model of 7-storey concrete-steel isolated structure with irregularities in both plan and elevation. A series of simulated ground motions, such as El Centro 1940, Tangshan 1976, Northridge 1940, and an artificial record, were included in test seismic loads. Dynamic properties, such as accelerations, displacements, and torsion responses, of the model were measured during the test.
New Yunnan Provincial Museum structure (as shown in Figure
Architectural rendering of museum structure.
There are three structure forms employed in the prototype structure: concrete filled steel tubular (CFST) in underground and first four layers, reinforced concrete (RC) in fifth layer, and steel truss in “Treasures fill the house,” as shown in Table
Details of the museum prototype structure.
Floor | Structure form | Structure frame (mm) | Materials | ||||
---|---|---|---|---|---|---|---|
Floor number | Building height (m) | Column | Beam | Slab | Steel | Concrete | |
Roof | 37.4 | Steel truss | 390 × 300 × 10 × 16 | 500 × 200 × 10 × 16 | / | Q345B | / |
“Treasures fill the house” | 33.2 | Chords: 450 × 16; webs: 351 × 16; suspenders: 299 × 10 | |||||
5th F | 33.9 | Reinforced concrete (RC) | 700 × 700 | 800 × 600/800 × 500 | 150 | Q345B | C40 |
4th F | 30.4 | Concrete filled steel tubular (CFST) | 1500 × 1500 | 1400 × 1000/1200 × 800 | 120 | C45 | |
3rd F | 26.6 | ||||||
2nd F | 22.8 | C50 | |||||
1st F | 15.2 | 150 | |||||
−1st F | 7.6 | ||||||
−2nd F | / | / | 400 |
Note: (1) Concrete filled steel tubular sections: column:
Mechanical properties of materials used in museum prototype structure.
Materials | Mechanical properties (N/mm2) |
---|---|
Steel | |
Q345B | |
HRB335 | |
HRB400 | |
| |
Concrete | |
C40 | |
C45 | |
C50 | |
Note:
Sections of structural members used in the museum structure: (a) beam section of CFST; (b) column section of CFST; (c) beam section of RC; (d) column section of RC; (e) H-shaped steel member section; (f) sections of chords, webs, and suspenders used in steel truss.
Structural plan layout of typical floor (unit: mm).
According to the Chinese Code for Seismic Design of Buildings (CSDB, GB 50011-2010) [
According to the Chinese Code for Seismic Design of Buildings (CSDB) and Chinese Technical Specification for Concrete Structures of Tall Buildings (JGJ3-2010) [
(1) As shown in Figure
(2) In structural design, several frame columns at axes H and D are only located in first four layers and no upward extension to fifth and roof layer. Column underpin is used to transfer lateral internal forces to lower layers. These irregular characteristics are classified as “discontinuity in vertical anti-lateral-force members” in CSDB.
(3) As the navy blue parts shown in Figure
Structural profile (unit: mm).
“Treasures fill the house” model (unit: mm): (a) elevation view; (b) 3D model.
It is unable for the museum conventional design to satisfy the standard requirements, especially build in high intensity area. Adverse effects of these irregular characteristics on structure seismic performance also have been proved by numerical analysis for conventional structural design. Given the irregularities and complexity of the structure, isolation system is applied to improve seismic behavior of the museum under severe earthquake.
Compared to several isolation plans, lead rubber bearings and normal rubber bearings are chosen in the museum isolation system to protect superstructures. Total weight of the museum is 1069087 kN, and 166 bearings are placed between −2nd and −1st layer to support it. Details of isolation bearings in prototype structure are shown in Table
Details and mechanical properties of bearings used in prototype structure.
Bearing | Number | Bearing details | Mechanical properties | |||||
---|---|---|---|---|---|---|---|---|
| | | | | | | ||
LRB1000 | 93 | 1000 | 190.4 | 200 | 5221 | 1.892 | 252 | / |
LRB800 | 34 | 800 | 185.6 | 160 | 3270 | 1.242 | 161 | / |
RB1000 | 20 | 1000 | 190.4 | / | 4649 | / | / | 4.649 |
RB800 | 19 | 800 | 185.6 | / | 2885 | / | / | 2.885 |
Note:
The shaking table tests were conducted in the State Key Laboratory for Disaster Reduction in Civil Engineering at Tongji University. The shaking table used in this test has a table dimension of 4 m by 4 m, and the maximum payload is 250 kN. Its maximum accelerations in longitudinal, transverse, and vertical directions are 1.2 g, 0.8 g, and 0.7 g, respectively. Detailed parameters of this facility are present in [
Test model materials including microaggregate concrete, fine wires, and red copper were used to construct structure model. As shown in Table
Conversion principles of model materials.
Structural members | Prototype structure | Test model | Conversion relations | Equivalent principle | Note | |
---|---|---|---|---|---|---|
Column/beam | Section steel | Flange | Red copper | | Strength | |
Web | ||||||
Reinforcing bar | Fine wires | | | |||
Concrete (C40/C45/C50) | Microaggregate concrete | | Area | / | ||
| ||||||
Floor slab | Reinforcing bar | Fine wires | | Strength | | |
Concrete | Microaggregate concrete | Prototype: 100/120/150 mm | Area | / | ||
| ||||||
Steel truss | Circular steel tube | Copper tube | | Strength | / |
Note:
According to the dynamic similitude theory, there are three independent controlling scaling factors, and other subordinate scaling factors are derived from them. The purpose of the museum shaking table test is to examine seismic responses of test model with and without isolation bearings, and the use of large scale model in test is the best way to grasp seismic performance of isolated structure. However, it is often practically impossible to conduct testing at full scale and at the proper conditions of loading and history of motion. Given the bearing capacity and the size of the shaking table, the dimension scaling factor (
Main similitude relationships.
Item | Model/prototype |
---|---|
Time | 0.133 |
Acceleration | 1.888 |
Velocity | 0.251 |
Displacement | |
Force | 1/3600 |
Stiffness | 1/120 |
Stress | 1/4 |
Strain | 1 |
Weight of prototype and scale model.
Dead weight | Additional weight | Total weight | ||
---|---|---|---|---|
Floor | “Treasures fill the home” III | 0.20 | 1.19 | 1.39 |
“Treasures fill the home” II | — | 0.24 | 0.24 | |
“Treasures fill the home” I | — | 0.25 | 0.25 | |
6 | 1.36 | 11.09 | 12.45 | |
5 | 1.12 | 7.41 | 8.53 | |
4 | 3.36 | 21.15 | 24.51 | |
3 | 3.04 | 19.97 | 23.01 | |
2 | 3.57 | 24.45 | 28.02 | |
1 | 4.09 | 32.06 | 36.14 | |
ISO | 64.24 | 0.00 | 64.24 | |
| ||||
Total weight | 80.98 | 117.81 | 198.78 |
Based on general principle of dynamic similarity, isolation period scaling factor (
According to the test results of model materials, the elastic scaling factor
Theoretically, if
Moreover, due to the small size of the bearings in test, no remarkable reduction of the yield force was observed with the cyclic deformation increases, which should be much more remarkable for large size bearings [
The base-isolated museum structure with a 4 m by 4 m floor plan for shaking table tests is shown in Figures
Shaking table test model for the isolated structure (unit: mm).
Photograph of shaking table test setup for isolated structure.
Overview and structural components of “Treasures fill the house”: (a) specimen; (b) joints.
The bearings (as shown in Figure
LRB100 bearing used in test: (a) specimen; (b) profile.
For reasonable bearings used in test model, dynamic similitude of isolation performance was proposed to keep design parameters of isolation layer, such as horizontal stiffness and yielding force, to be consistent with the bearings in prototype model. Considering similitude law, nine lead rubber bearings with 100 mm diameter were designed in the isolated model, which could well simulate the performance and deformation requirements of the prototype bearings. Major properties of the base isolators are shown in Tables
Fundamental mechanical and material properties of base isolation devices.
Diameter/mm | Thickness of rubber/mm | Primary shape factor | Secondary shape factor | Shear stiffness/kN⋅m−1 | Yield force/kN | Vertical modulus/kN⋅m−1 |
---|---|---|---|---|---|---|
100 | 14.3 | 19.23 | 6.99 | 302 | 1.23 | 374200 |
Comparison of isolated structure parameters at 100% shear strain.
Structure | Weight (kN) | Effective stiffness (kN/mm) | Yield force (kN) | Isolation period (s) | Yield force |
---|---|---|---|---|---|
Prototype model | 1069087 | 260.38 | 28838.1 | 4.026 | 2.70% |
Design model | 199 | 2.713 | 9.65 | 0.538 | 4.95% |
Test model | 199 | 2.673 | 7.20 | 0.542 | 3.62% |
Three types of sensors, including accelerometers, displacement transducers, and 3-directional force sensors, were installed on the model so that both the global and bearing responses could be measured. Totally, there were 39 piezoelectric acceleration sensors including 23 laboratory shaking table system sensors and 16 external acceleration sensors used to monitor the acceleration responses of test model. The acceleration sensors were located on the shaking table, isolation layer, and each storey of superstructure and steel truss. 15 ASM drawing displacement sensors with ranges of 0~±375 mm were located on the isolation layer and each storey of superstructure. Seven 3-directional force sensors including three ESM-100 kN type sensors and four YBY type pressure sensors were employed to measure mechanism properties of bearings and analyze horizontal hysteresis performance and vertical force. Distributions of some accelerometers and 3-directional force sensors are shown in Figure
Arrangement diagram of sensors: (a) acceleration sensors; (b) three-directional force sensors.
The New Yunnan Provincial Museum was located in the city of Kunming, Yunnan Province. According to the CSDB, the site soil in this city belongs to type III, which is an important factor for selecting earthquake waves in dynamic tests. Considering the definition of type III site soil in the CSDB, the overlaying thickness of the site is no less than 50 m, and average velocity of shear wave in the soil layer is between 150 m/s and 250 m/s. Then three different ground motions (as shown in Table
Parameters of original ground motions selected.
Records | Magnitude | Date | Site class | Peak acceleration of original waves/g | Predominate period of response spectrum/s |
---|---|---|---|---|---|
El | 6.7 | 1940.5.18 | II-III | 0.3417 | 0.55 |
LWD | 6.7 | 1994.01.17 | II | 0.207 | 0.120 |
TJ | 7.6 | 1976.7.28 | III-IV | / | 1.04 |
Acceleration response spectrums of four waves used in test and the design response spectra specified in the CSDB.
Details of the waves attacked the test model in the tests are also important parameters for shaking table tests. Figure
Time histories and Fourier amplitude spectra of input ground motion acceleration from shaking table surface.
EL wave
LWD wave
TJ wave
ART wave
According to the CSDB, three earthquake input levels, including minor, moderate, and major earthquakes, should be considered in shaking table tests. As Kunming belongs to the seismic zone of intensity 8, the peak ground accelerations (PGAs) for isolated structure design corresponding to the three different levels are specified as 0.132 g, 0.378 g, and 0.755 g, respectively. In the seismic response analysis for the prototype structure with and without isolation, seismic-reduced factor (max ratio of structures storey shear forces with and without isolation) is less than 0.4, and the superstructure supported by isolation bearings could be designed as intensity 7 due to the CSDB. The peak ground accelerations (PGAs) for superstructure corresponding to the three input levels are specified as 0.092 g, 0.264 g, and 0.581 g, respectively. There were unidirectional and three-dimensional inputs used in the shaking table tests. As stipulated for three-dimensional inputs by CSDB, the PGA ratio of the principal direction to the other direction should be 1 : 0.85 : 0.65.
The objective of the white noise excitation tests is to measure the dynamic properties of the model structure and investigate the variations of dynamic characteristics of model structures with and without isolation. A total of 74 cases were conducted in test, and a summary of the inputs used for each case is presented in Tables
Test program for the isolated structure.
Test case | Input signal | Peak value of input acceleration(g) | Note | ||
---|---|---|---|---|---|
| | | |||
1 | | | | | — |
2 | EL(NS)- | 0.132 | Minor 8 | ||
3 | LWD(EW)- | 0.132 | Minor 8 | ||
4 | TJ(EW)- | 0.132 | Minor 8 | ||
5 | ART- | 0.132 | Minor 8 | ||
6 | EL(NS)- | 0.132 | Minor 8 | ||
7 | LWD(EW)- | 0.132 | Minor 8 | ||
8 | TJ(EW)- | 0.132 | Minor 8 | ||
9 | ART- | 0.132 | Minor 8 | ||
10 | EL- | 0.132 | 0.112 | 0.086 | Minor 8 |
11 | LWD- | 0.132 | 0.112 | 0.086 | Minor 8 |
12 | TJ- | 0.132 | 0.112 | 0.086 | Minor 8 |
13 | | | | | — |
14 | EL(NS)- | 0.378 | Moderate 8 | ||
15 | LWD(EW)- | 0.378 | Moderate 8 | ||
16 | TJ(EW)- | 0.378 | Moderate 8 | ||
17 | ART- | 0.378 | Moderate 8 | ||
18 | EL(NS)- | 0.378 | Moderate 8 | ||
19 | LWD(EW)- | 0.378 | Moderate 8 | ||
20 | TJ(EW)- | 0.378 | Moderate 8 | ||
21 | ART- | 0.378 | Moderate 8 | ||
22 | EL- | 0.378 | 0.321 | 0.245 | Moderate 8 |
23 | LWD- | 0.378 | 0.321 | 0.245 | Moderate 8 |
24 | TJ- | 0.378 | 0.321 | 0.245 | Moderate 8 |
25 | | | | | — |
26 | El(NS)- | 0.755 | Major 8 | ||
27 | LWD(EW)- | 0.755 | Major 8 | ||
28 | TJ(EW)- | 0.755 | Major 8 | ||
29 | ART- | 0.755 | Major 8 | ||
30 | El(NS)- | 0.755 | Major 8 | ||
31 | LWD(EW)- | 0.755 | Major 8 | ||
32 | TJ(EW)- | 0.755 | Major 8 | ||
33 | ART- | 0.755 | Major 8 | ||
34 | El- | 0.755 | 0.642 | 0.491 | Major 8 |
35 | LWD- | 0.755 | 0.642 | 0.491 | Major 8 |
36 | TJ- | 0.755 | 0.642 | 0.491 | Major 8 |
37 | | | | | — |
Test program for the base-fixed structure.
Test case | Input signal | Peak value of input acceleration(g) | Note | ||
---|---|---|---|---|---|
| | | |||
1 | | | | | — |
2 | El(NS)- | 0.092 | Minor 7 | ||
3 | LWD(EW)- | 0.092 | Minor 7 | ||
4 | TJ(EW)- | 0.092 | Minor 7 | ||
5 | ART- | 0.092 | Minor 7 | ||
6 | El(NS)- | 0.092 | Minor 7 | ||
7 | LWD(EW)- | 0.092 | Minor 7 | ||
8 | TJ(EW)- | 0.092 | Minor 7 | ||
9 | ART- | 0.092 | Minor 7 | ||
10 | El- | 0.092 | 0.078 | 0.060 | Minor 7 |
11 | LWD- | 0.092 | 0.078 | 0.060 | Minor 7 |
12 | TJ- | 0.092 | 0.078 | 0.060 | Minor 7 |
13 | | | | | — |
14 | EL(NS)- | 0.264 | Moderate 7 | ||
15 | LWD(EW)- | 0.264 | Moderate 7 | ||
16 | TJ(EW)- | 0.264 | Moderate 7 | ||
17 | ART- | 0.264 | Moderate 7 | ||
18 | EL(NS)- | 0.264 | Moderate 7 | ||
19 | LWD(EW)- | 0.264 | Moderate 7 | ||
20 | TJ(EW)- | 0.264 | Moderate 7 | ||
21 | ART- | 0.264 | Moderate 7 | ||
22 | EL- | 0.264 | 0.224 | 0.171 | Moderate 7 |
23 | LWD- | 0.264 | 0.224 | 0.171 | Moderate 7 |
24 | TJ- | 0.264 | 0.224 | 0.171 | Moderate 7 |
25 | | | | | — |
26 | EL(NS)- | 0.581 | Major 7 | ||
27 | LWD(EW)- | 0.581 | Major 7 | ||
28 | TJ(EW)- | 0.581 | Major 7 | ||
29 | ART- | 0.581 | Major 7 | ||
30 | EL(NS)- | 0.581 | Major 7 | ||
31 | LWD(EW)- | 0.581 | Major 7 | ||
32 | TJ(EW)- | 0.581 | Major 7 | ||
33 | ART- | 0.581 | Major 7 | ||
34 | EL- | 0.581 | 0.494 | 0.378 | Major 7 |
35 | LWD- | 0.581 | 0.494 | 0.378 | Major 7 |
36 | TJ- | 0.581 | 0.494 | 0.378 | Major 7 |
37 | | | | | — |
Before and after each test phase, as mentioned in Section
Dynamic characteristics test results of isolated structure model.
Mode | Description | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | AVE |
---|---|---|---|---|---|---|---|---|---|---|
Isolated structure model | Initial (Hz) | 3.89 | 3.89 | 4.25 | 19.11 | 21.94 | 42.81 | 57.32 | 69.00 | |
Minor 8 (Hz) | 3.89 | 3.89 | 4.25 | 19.11 | 21.94 | 42.81 | 57.32 | 69.00 | ||
Variation (%) | | | | | | | | | | |
Moderate 8 (Hz) | 3.89 | 3.89 | 4.25 | 18.40 | 21.05 | 42.81 | 57.32 | 68.64 | ||
Variation (%) | | | | | | | | | | |
Major 8 (Hz) | 3.89 | 3.89 | 4.25 | 18.40 | 21.05 | 42.28 | 57.32 | 68.64 | ||
Variation (%) | | | | | | | | | | |
| ||||||||||
Base | Initial (Hz) | 8.49 | 9.91 | 10.97 | 14.86 | 15.21 | 47.06 | 33.79 | 39.81 | |
Minor 8 (Hz) | 8.14 | 9.55 | 10.97 | 14.15 | 14.51 | 46.23 | 31.84 | 38.92 | ||
Variation (%) | | | | | | | | | | |
Moderate 8 (Hz) | 7.07 | 9.20 | 10.26 | 13.8 | 14.51 | 45.29 | 30.78 | 37.51 | ||
Variation (%) | | | | | | | | | | |
Major 8 (Hz) | 6.02 | 7.08 | 8.49 | 11.68 | 12.03 | 42.64 | 27.95 | 33.61 | ||
Variation (%) | | | | | | | | | |
The variations of average frequency (variation of frequency = (frequency after shaking table tests original frequency)/original frequency) values for each mode have been also listed in Table
For the fixed model, the average variation values are −3.4%, −7.60%, and −20.60% after the minor, moderate, and major level earthquake inputs. Although the natural frequency of base-fixed structure decreased a little after minor earthquake, it was still much more than that of the isolated structure under moderate and major earthquake. The base-fixed structure has even more serious damage than the isolated structure after major earthquake. Besides, the first torsion frequency of the isolated structure is 4.25 Hz after different levels earthquake input. However, the values for the base-fixed structure are 10.97 Hz, 10.26 Hz, and 7.08 Hz after minor 7, moderate 7, and major 7 tests, implying that serve damage has taken place in the model due to the reduction of torsion stiffness.
Acceleration responses were measured directly by mounted accelerometers on the model. The acceleration amplification factor (AAF) which is usually defined as the ratio of the peak value of floor accelerations response to the PGA of input waves is used to evaluate acceleration vibration amplification effects at different floor of the New Yunnan Provincial Museum structure with and without isolation bearings.
The profiles of acceleration amplification factor (AAF) for the isolated model (ISO) and fixed model (FIX) are shown in Figures
Comparisons of AAF for the isolated and fixed structures under minor earthquakes: (a) direction
Comparisons of AAF for the isolated and fixed structures under moderate earthquakes: (a) direction
Comparisons of AAF for the isolated and fixed structures under major earthquakes: (a) direction
The storey distributions for the isolated structure are close to a linear characteristic, and whip effects have been effectively controlled. With arising of seismic inputs, the decreases of superstructure acceleration responses are increasingly obvious. Figures
Comparisons on roof acceleration time history of the isolated and fixed structure under major earthquake in direction
EL
LWD
TJ
ART
Comparisons on Fourier amplitude spectra of roof acceleration time history of the isolated and fixed structure under major earthquake in direction
EL
LWD
TJ
ART
For architectural aesthetics and large exhibition space of the museum, the “Treasures fill the house” system composed of steel trusses and suspension layers hanging below was designed in the atrium. As an additional system of the whole structure, it arises construction clearance and reduces cross-section of steel beam at same time.
For structural design, it is essential to analyze the seismic responses of this suspension system because of its weakening in lateral stiffness. The distributions of “Treasures fill the house” AAFs under the three level earthquakes are presented in Figures
Comparisons on profiles of “Treasures fill the house” AAFs for the isolated and fixed structure under minor earthquake: (a) direction
Comparisons on profiles of “Treasures fill the house” AAFs for the isolated and fixed structure under moderate earthquake: (a) direction
Comparisons on profiles of “Treasures fill the house” AAFs for the isolated and fixed structure under major earthquake: (a) direction
The max displacement responses of isolated model with different intensity earthquakes input are shown in Figures
Profiles of maximum storey displacements of isolated structure under minor earthquakes: (a) direction
Profiles of maximum storey displacements of isolated structure under moderate earthquakes: (a) direction
Profiles of maximum storey displacements of isolated structure under major earthquakes: (a) direction
The peak interstorey drift ratios (defined as the ratio of the peak interstorey drift and storey height) for isolated and fixed structures subjected to three level excitations are plotted in Figure
Story drift ratios of superstructure under earthquakes of different intensities: (a) minor earthquake; (b) moderate earthquake; and (c) major earthquake.
In the test, the input earthquake level for isolated model was designed as intensity 8 and the earthquake for fixed model was designed as intensity 7 according to the CSDB. As shown, the interstorey drift ratios of isolated model are still less than that of fixed model, which are much more obvious with moderate and major earthquake input. With minor earthquake input, the storey drift ratios of both models are much less than the elastic limit value, which indicates that both models are in elastic condition and no damage happened. As input earthquake increases, the differences of storey drift ratios become much more notable. For major earthquake, the storey drift ratios of both models are still less than the elastoplastic limit value and no severe damage occurred in the structure. It could be found that, under major earthquake, the storey drift ratio of isolated model is still less than the limit value of elastic story drift, and the isolation effect is remarkable.
A series of bearing force-displacement curves under different level intensity ground motions are shown in Figure
Typical hysteretic curves of LRB: (a) EL wave, (b) LWD wave, (c) TJ wave, and (d) ART wave.
As shown in Table
Isolation layer torsion angle under different intensities.
Direction | Case | Minor | Moderate | Major |
---|---|---|---|---|
| EL | 1/7704 | 1/4897 | 1/3625 |
LWD | 1/5942 | 1/3635 | 1/3698 | |
TJ | 1/4390 | 1/3372 | 1/4355 | |
ART | 1/8496 | 1/5724 | 1/1817 | |
| ||||
AVE | 1/6215 | 1/4208 | 1/3016 | |
| ||||
| EL | 1/6698 | 1/3731 | 1/1915 |
LWD | 1/4651 | 1/1991 | 1/1991 | |
TJ | 1/5147 | 1/2235 | 1/1773 | |
ART | 1/6983 | 1/2189 | 1/900 | |
| ||||
AVE | 1/5700 | 1/2389 | 1/1482 |
Shaking table tests for the New Yunnan Provincial Museum with and without base isolators were conducted and the model was subjected to earthquake actions representing minor, moderate, and major earthquakes for a region of moderate seismicity, with basic seismic intensity at the 8 degrees. From the test results the following conclusions can be drawn: The interstorey drift ratios of isolated structure are all less than the elastic and elastoplastic limits specified in the CSDB. The museum isolated model remains in elastic state without any damage occurring under minor earthquake and no severe damage happened with major earthquake input. Compared with the test results of isolated and base-fixed structures, significant differences are experimentally observed in the acceleration and story drift responses. The acceleration amplification factors (AAFs) for the isolated structure under three level ground motions are all less than 1. Acceleration responses of the “Treasures fill the house,” composed of steel truss and suspension system, are effectively reduced by isolation bearings. The isolation bearings exhibit full hysteretic curves and the input seismic energy is well dissipated. The efficiency of the isolation system varies with different earthquakes, which is better for high-frequency waves such as EL wave. Base isolation provides outstanding seismic performances for this complex museum structure under different level earthquakes.
The authors declare that they have no competing interests.
The writers gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grant nos. 51478257, 51308331, and 51508414), Natural Science Foundation of Shanghai (Grant no. 15ZR1416200), and Research Fund for the Doctoral Program of Higher Education of China (Grant no. 20133108110024).