Mechanical behaviors of air spring-FPS three-dimensional isolation bearing and isolation performance analysis
Introduction
With the continuous improvement of seismic performance requirements of large-span spatial structures in the past decades, the application of basic isolation technology has become increasingly widespread. Common horizontal isolation bearings, such as lead rubber bearings and friction pendulum systems [1,2], have been proven to effectively improve the seismic performance of large-span spatial structures. However, it is known from the seismic damage data obtained from the Northridge earthquake, the Chi-Chi earthquake [3], and the Lushan Earthquake [4], especially in the near-fault areas, the vertical component of the ground motions exceeds the horizontal component and has significant low-frequency characteristics [5]. Previous studies have shown that the phenomenon of resonance characterized by the coincidence of the predominant period of long-period ground motions with the fundamental natural period of buildings will have more adverse effects on long-period structures [[6], [7], [8]], and the horizontal isolation bearing can even amplify the vertical seismic response of long-period base-isolated structures [[9], [10], [11]]. Therefore, it is necessary to develop three-dimensional isolation bearings for large-span spatial structures, which can simultaneously isolate horizontal and vertical accelerations, and effectively reduce the structural response under long-period ground motions.
At present, several scholars have carried out much investigation on the mechanical behavior of three-dimensional isolation bearings. Three-dimensional isolation bearings can be divided into two types: independent and combined. The independent three-dimensional isolation bearings, such as thick rubber bearings, will not be divided into a horizontal isolation device and a vertical isolation device [12]. However, the thick rubber bearings are prone to be unstable vertically when the shear deformation is large and cannot resist the uplift. In addition to thick rubber bearings, some scholars have put forward the cable reinforced air spring three-dimensional isolation device with a large volume [13]. The above bearings are currently mainly used in the isolation of nuclear power plants [14].
The combined three-dimensional isolation bearing is composed of a horizontal isolation device and a vertical isolation device sequentially or in parallel. For example, a variety of combined three-dimensional isolation bearings using disc springs as the vertical isolation device have been developed [[15], [16], [17]]. To effectively avoid the resonance effect with the input ground motions, the isolation period is usually more than three times the natural vibration period of the superstructure, and the vertical stiffness of the bearing decreases with the extension of the isolation period. However, the natural vibration period of a large-span spatial structure is relatively long. Taking a single-layer spherical reticulated shell with a span of 60 m as an example, to meet the requirement of extending the vertical natural vibration period by three times, the height of the disc spring should be greater than 1500 mm to achieve the required lower vertical stiffness [18]. In addition to the disc spring, there are high-damping rubber three-dimensional isolation bearings in parallel with the viscoelastic core bearing and viscoelastic dampers [19], tension-resistant lead plug rubber bearing consists of a common lead plug rubber bearing (LRB) and several helical springs [20], inclined rotational three-dimensional isolation bearings composed of a lead rubber bearing with various inclined angles [21], hybrid isolation bearings, which include the viscous damper component and the triple friction pendulum component [22,23], and vertical variable stiffness three-dimensional isolation bearings composed of a horizontal rubber bearing and multiple hydraulic cylinders [18]. The above bearings have the characteristics of large vertical stiffness and poor deformability, and thus it is difficult to effectively control the influence of long-period ground motion on a large-span spatial structure. Most of the existing three-dimensional isolation bearings are suitable for nuclear power plants [24] or multistory buildings. These isolation bearings require complex construction, have high vertical isolation frequency, and cannot resist uplift and rotation. It is difficult to meet the requirements of three-dimensional seismic isolation bearings for large-span spatial structures.
To solve the above problems, a novel three-dimensional isolation bearing combining the air spring with a friction pendulum system is developed, which can isolate horizontal and vertical ground motions simultaneously for large-span spatial structures. Then, the mechanical model of the three-dimensional isolation bearing is established, and the design method of this isolation bearing in the large-span spatial structure is also proposed. Mechanical behavior tests on the air spring and the three-dimensional isolation bearing are also conducted. Finally, the vibration control effect of the three-dimensional isolation bearing under long-period ground motions is explored taking a large-span steel tubular truss structure as an example.
Section snippets
The construction of air spring-FPS three-dimensional isolation bearing
The air spring-FPS three-dimensional isolation bearing is composed of a friction pendulum system for horizontal isolation and an air spring for vertical isolation, as shown in Fig. 1. The vertical isolation air spring has low stiffness and low isolation frequency. It has an excellent isolation effect under long-period ground motions. To ensure the bearing capacity and reliability of the three-dimensional isolation bearing, the air spring rubber capsule is reinforced with double-layer
Theoretical mechanical model of air spring
An air spring is a nonmetallic spring that utilizes the restoring force of high-pressure compressed gas in a sealed capsule to isolate vibration. Air springs are mainly divided into three types: diaphragm-type air springs, bellow-type air springs, and hybrid-type air springs. The single-capsule bellow-type air spring has the advantages of simple construction, long service life, relatively large vertical stiffness, and low vibration frequency with a limited vertical bearing displacement response.
General
To investigate the mechanical behavior of the three-dimensional isolation bearing, static compression tests and hysteresis performance tests are carried out using an electrohydraulic compression-shear machine in Fengze Intelligent Equipment Co., Ltd. of Hebei Province, China, see Fig. 7. The maximum load and stroke in the vertical direction are 1000 t and 1000 mm with the vertical speed range of 0–200 mm/min, and the maximum load and stroke in the horizontal direction are 70 t and 800 mm with
Design method of air spring-FPS three-dimensional isolation bearing
The vertical stiffness of the FPS in the three-dimensional isolation bearing is far greater than the vertical stiffness of the air spring, and the mutual extrusion of the vertical ball bearings makes the horizontal stiffness of the air spring vertical isolation device far greater than that of the FPS. The horizontal and vertical stiffness of the three-dimensional isolation bearing are decoupled, so the horizontal and vertical isolation devices can be designed separately.
FE model of the steel tubular truss structure
The large-span inverted triangle steel tubular truss structure has dimensions of 128 m × 73.3 m with 17 spans in total. The steel model is Q355 and the ideal elastic-plastic constitutive model is adopted with the yield strength of 355 MPa. The chord members are Φ (180–299) × (8–12), and the web members are Φ (133–180) × (5–8). The height of the columns is 30 m, and 2000 mm × 2000 mm × 50 mm × 50 mm box section steel columns is adopted. The steel truss is hinged to the bottom columns. The
Conclusion
This paper presents an air spring-friction pendulum system (air spring-FPS) three-dimensional isolation bearing for large-span spatial structures. The construction and working principle are described. The mechanical behaviors of the bearing are explored through theoretical and experimental analysis. Then, the design method of the three-dimensional isolation bearing is proposed and applied to conduct vibration control analysis for a steel tubular truss structure. The isolation performance of the
Author statement
Qinghua Han: Conceptualization, Methodology, Investigation, Supervision, Writing-Reviewing and Editing. Ming Jing: Investigation, Methodology, Writing-Original draft. Yan Lu: Conceptualization, Methodology, Writing-Reviewing and Editing. Mingjie Liu: Methodology, Writing-Reviewing and Editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This material is based upon work supported by the National Key Research and Development Plan of China under Grant No.2016YFC0701103, the National Natural Science Foundation of China under Grant No. U1939208 and No. 51778411. Support from the funding agency above is gratefully acknowledged.
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