減震器外文翻譯-- 減震器對(duì)底部隔震結(jié)構(gòu)抗震反應(yīng)的作用

1、<p>　　中文7000字，英文3900單詞</p><p>　　出處：Matsagar V A, Jangid R S. Influence of isolator characteristics on the response of base-isolated structures[J]. Engineering Structures, 2004, 26(12):1735-1749.</p&g

2、t;<p>　　本科畢業(yè)設(shè)計(jì)（論文）外文翻譯譯文</p><p>　　學(xué)生姓名： </p><p>　　院 （系）： 機(jī)械工程學(xué)院 </p><p>　　專業(yè)班級(jí)： </p><p>　　指導(dǎo)教師：

3、 </p><p>　　完成日期： </p><p>　　Influence of isolator characteristics on the response</p><p>　　of base-isolated structure</p><

4、p>　　Vasant A. Matsaar 1Z.S. Janids</p><p><b>　　Abstract</b></p><p>　　The influence of isolator characteristics on the seismic response of multi-story base-isolated structure is in

5、vestigated. The isolated building is modeled as a shear type structure with lateral degree-of-freedom at each floor. The isolators are modeled by using two different mathematical models depicted by bi-linear hysteretic a

6、nd equivalent linear elastic-viscous behaviors. The coupled differential equations of motion for the isolated system are derived and solved in the incremental form using </p><p>　　ment of isolator (i.e. slid

7、ing type isolation systems) tends to increase the superstructure accelerations associated with high frequencies. Further, the superstructure acceleration also increases with the increase of the superstructure flexibility

8、.</p><p>　　keywords: Base isolation; Earthquake; Elastomtric bearing Sliding system; Bearing displacement; Superstructure acceleration; Bi-linear hysteresis; Equivalent linear.</p><p>　　1 Introd

9、uction</p><p>　　Seismic isolation, which is now recognized as a mature and efficient technology, can be adopted to improve the seismic performance of strategically important buildings such as schools, h

10、ospitals, industrial structures etc., in addition to the places where sensitive equipments are intended to protect from hazardous effects during earthquake [1-3]. Based on the extent of control to be achieved over the se

11、ismic response, the choice of the isolation system varies and thereupon its design is don</p><p>　　It is very essential to understand the different parameters affecting the response of base-isolated structur

12、e when used for seismic protection of the structures. Especially in case of the base-isolated structures, that houses sensitive equipments, determination of acceleration imparted and associated peak displacement are the

13、key issues for the design engineer [4]. Moreover, the pounding and structural impacts in case of baseisolated structures made upon the adjacent structures, when separation </p><p>　　catastrophic failures lea

14、ding to immense isolator damage. Such failures and damages can be avoided by properly estimating the peak isolator displacement and recommendation of appropriate isolation gap distances. In order to predict peak displace

15、ment and determine accurate separation gap distance requirement for a base-isolated structure, it is mandatory to know, in prior, the different parameters that affect the bearing displacement and its consequent effect on

16、 the</p><p>　　superstructure acceleration. The failures due to such impacts can be avoided by reducing the peak bearing displacement by compromising with increase in superstructure acceleration to an accepta

17、ble level i.e. tolerable reduction in effectiveness of isolation. Selection of different parameters characterizing an isolation system is important in view of keeping a control over response quantities especially the exc

18、essive bearing displacement at isolator level. </p><p>　　The behavior of isolation systems and the baseisolated structures is now well established and codes are developed for designing the base-isolated stru

19、ctures[5–9]. For non-linear isolation systems, the codes allow to use the equivalent linear model to permit the use of</p><p>　　response spectrum method for designing the isolated structures. The equivalent

20、linear models are based on the effective stiffness at the design displacement and the equivalent viscous damping is evaluated from the area of the hysteresis loop. The comparison of equivalent</p><p>　　linea

21、r and actual non-linear model for the response of isolated bridge structures had been demonstrated in thepast [10–13] and shown that the equivalent linear model can be used for predicting the actual non-linear response o

22、f the system. However, the above studies were restricted to the bridge idealized as a rigid body and the non-linear behavior of the isolator was limited to the lead–rubber bearings idealized by bi-linear characteristics.

23、 The equivalent linear model may give different respons</p><p>　　isolator and the system parameters.</p><p>　　Here-in, the seismic response of multi-story structure supported on non-linear base

24、isolation systems is investigated. The specific objectives of the study are: </p><p>　　(i) to compare the seismic response of base-isolated flexible building obtained from various bi-linear hysteretic model

25、and its equivalent linear model; </p><p>　　(ii) to study the influence of shape of the isolator hysteresis loop and its parameters (i.e. yield displacement and force) on the effectiveness of the isolation sy

26、stem and (iii) to investigate the effects of superstructure flexibility on the response of base-isolated structures.</p><p>　　2. Structural model of base-isolated building</p><p>　　Fig. 1(a) sho

27、ws the idealized mathematical model of the N-story base-isolated building considered for the present study. The base-isolated building is modeled as a shear type structure mounted on isolation systems with one lateral de

28、gree-of-freedom at each floor.</p><p>　　Following assumptions are made for the structural system under consideration:</p><p>　　1. The superstructure is considered to remain within the elastic li

29、mit during the earthquake excitation. This is a reasonable assumption as the isolation attempts to reduce the earthquake response in such a way that the structure remains within the elastic range.</p><p>　　2

30、. The floors are assumed rigid in its own plane and the mass is supposed to be lumped at each floor level.</p><p>　　3. The columns are inextensible and weightless providing the lateral stiffness.</p>

31、<p>　　4. The system is subjected to single horizontal component of the earthquake ground motion.</p><p>　　5. The effects of soil–structure interaction are not taken into consideration.</p><p&

32、gt;　　For the system under consideration, the governing equations of motion are obtained by considering the equilibrium of forces at the location of each degrees of-freedom. The equations of motion for the superstructure

33、under earthquake ground acceleration are expressed in the matrix form as</p><p>　　where [Ms], [Cs] and [Ks] are the mass, damping and stiffness matrices of the superstructure, respectively; </p><p

34、>　　are the unknown relative floor displacement, velocity and acceleration vectors, respectively; and are the relative acceleration of base mass and earthquake ground acceleration, respectively; and {r} is the vector

35、 of influence</p><p>　　coefficients.</p><p>　　The corresponding equation of motion for the base mass under earthquake ground acceleration is expressed by</p><p>　　where mb and Fb ar

36、e the base mass and restoring force developed in the isolation system, respectively; k1 is the story stiffness of first floor; and c1 is the first story damping. The restoring force developed in the isolation system, Fb

37、depends upon the type of isolation system</p><p>　　considered and approximate numerical models shall be used.</p><p>　　3. Mathematical modeling of isolators</p><p>　　For the present

38、 study, the force-deformation behavior of the isolator is modeled as (i) non-linear hysteretic represented by the bi-linear model and (ii) the code specified equivalent linear elastic–viscous damping model for the non-li

39、near systems. A comparison of the </p><p>　　response of the isolated structure by using the above two models will be useful in establishing the validity of the code specified equivalent linear model.</p&g

40、t;<p>　　3.1. Bi-linear hysteretic model of isolators</p><p>　　The non-linear force-deformation behavior of the isolation system is modeled through the bi-linear hysteresis loop characterized by three

41、parameters namely:</p><p>　　(i) characteristic strength, Q (ii) post-yield stiffness, kb and (iii) yield displacement, q (refer Fig. 1(b)). The bi-linear behavior is selected because this model can be used f

42、or all isolation systems used in practice. The characteristic strength, Q is related to the yield strength</p><p>　　of the lead core in the elastomeric bearings and friction coefficient of the sliding type i

43、solation systems. The post-yield stiffness of the isolation system, kb is generally designed in such a way to provide the specific value of the isolation period, Tb expressed as:</p><p>　　where M＝（＋）is the t

44、otal mass of the base-isolated structure; and mj is the mass of jth floor of the superstructure.</p><p>　　Thus, the bi-linear hysteretic model of the base isolation system can be characterized by specifying

45、the three parameters namely Tb, Q and q. The characteristic strength, Q is normalized by the weight of the building, W=Mg (where g is the gravitational acceleration</p><p>　　3.2. Equivalent linear elastic–vi

46、scous damping model</p><p>　　of isolators </p><p>　　As per Uniform Building Code [8] and International Building Code [9], the non-linear force-deformation characteristic of the isolator can be r

47、eplaced by an equivalent linear model through effective elastic stiffness and effective viscous damping. The linear force developed in the isolation system can be expressed as :</p><p>　　where is the effecti

48、ve stiffness; c＝2 is the effective viscous damping constant; is the effective viscous damping ratio; ＝2=Teff is the effective isolation frequency; and T＝2 is the</p><p>　　effective isolation period.</p&g

49、t;<p>　　The equivalent linear elastic stiffness for each cycle of loading is calculated from experimentally obtained force-deformation curve of the isolator and expressed mathematically as:</p><p>　　w

50、here F+ and F_ are the positive and negative forces at test displacements D+ and D–, respectively. Thus, the keff is the slope of the peak-to-peak values of the hysteresis loop as shown in Fig. 1(c).</p><p>

51、　　The effective viscous damping of the isolator unit calculated for each cycle of loading is specified as </p><p>　　where E is the energy dissipation per cycle of loading.</p><p>　　At a specifie

52、d design isolation displacement, D, the effective stiffness and damping ratio for a bi-linear system are expressed as:</p><p>　　4. Solution of equations of motion</p><p>　　Classical modal superp

53、osition technique cannot be employed in the solution of equations of motion here because (i) the system is non-classically damped because of the difference in the damping in isolation system compared to the damping in th

54、e superstructure </p><p>　　and (ii) the force-deformation behavior for the isolation systems considered is non-linear. Therefore, the equations of motion are solved numerically using Newmark’s method of step

55、-by-step integration; adopting linear variation of acceleration over a small time</p><p>　　interval of Dt. The time interval for solving the quations of motion is taken as 0.02/200 s (i.e. =0:0001 s).</p&

56、gt;<p>　　5. Numerical study</p><p>　　Seismic response of a multi-story base-isolated building is investigated under various real earthquake ground motions for bi-linear and equivalent linear isolator

57、characteristics. The earthquake motions selected for the study are N00E component of 1989 Loma</p><p>　　Prieta earthquake recorded at Los Gatos Presentation Center, N90S component of 1994 Northridge earthqua

58、ke recorded at Sylmar Station and N00S component of 1995 Kobe earthquake recorded at JMA. The peak ground acceleration (PGA) of Loma Prieta, Northridge and Kobe earthquake motions are 0.57, 0.60 and 0.86 g, respectively.

59、 The displacement and acceleration spectra of the above ground motions for 2% of the critical damping are shown in Fig. 2. The maximum ordinates of the pseudo-acceleration are 3</p><p>　　soil or rocky terrai

60、n. The response quantities of interest are the top floor absolute acceleration and relative bearing displacement. The above response quantities are of importance because floor accelerations developed in the superstructur

61、e are proportional to the forces exerted because of earthquake ground motion. On the other</p><p>　　hand, the bearing displacements are crucial in the design of isolation systems. For the present study, the

62、mass matrix of the superstructure [Ms] is a diagonal matrix and characterized by the mass of each floor,</p><p>　　which is kept constant. Further, the base raft of the isolated structure is considered such t

63、hat the mass ratio, mb/m=1. The damping matrix of the superstructure, [Cs], is not known explicitly. It is constructed by assuming the modal damping ratio in each mode of vibration for superstructure, which is kept cons

64、tant. The damping ratio of the superstructure, ns, is taken as 0.02 and kept constant for all modes of vibration. The inter-story stiffness of the superstructure is adjusted such that a s</p><p>　　5.1. Compa

65、rison of response for bi-linear and equivalent</p><p>　　linear model</p><p>　　In this section, a comparison of earthquake response of base-isolated structure is made for bi-linear and equivalent

66、 linear model of isolation systems. The bilinear behavior is selected in a way to represent the force-deformation behavior of the commonly used isolation systems such as elastomeric (i.e. lead–rubber bearings) and slidin

67、g systems (i.e. friction pendulum system). The equivalent linear behavior is considered by selecting the appropriate values of the effective isolation time period, </p><p>　　loop are derived such that it has

68、 an effective time period as Teff and damping ratio beff from Eqs. (7) and (8), respectively, at the design displacement D. The values of design displacement, D, used for such transformation are 53.61, 34.06 and 32.58 cm

69、 under Loma Prieta, Northridge and Kobe earthquake ground motions, respectively, obtained from equivalent linear model with T＝2s and =0.1.</p><p>　　In Fig. 3, time variation of top floor absolute acceleratio

70、n</p><p>　　and bearing displacement of a five-story building is plotted for linear and bi-linear isolator models under Loma Prieta, 1989 earthquake motion. The parameters of the equivalent linear system cons

71、idered</p><p>　　are: T＝2s and =0.1. For the bi-linear system, two values of yield displacement i.e. 0.0001 cm and 2.5 cm are considered which corresponds to friction pendulum system and lead–rubber bearing i

72、solators, respectively. The peak superstructure acceleration obtained by bi-linear hysteretic model are 0.665 and 0.701 g for the yield displacement of 2.5 and 10_4 cm, respectively. The corresponding peak superstructure

73、 acceleration obtained from the equivalent linear model is 0.582 g. This implies that the</p><p>　　Fig. 7 shows the comparison of corresponding FFT amplitude spectra (for both equivalent linear and bilinear

74、hysteretic models) of the top floor acceleration for five-story non-isolated and isolated structures under different earthquake motions (refer Figs. 3–5 for the time history of top floor acceleration). There is a signifi

75、cant difference between the FFT spectra of the top floor acceleration obtained from the equivalent linear and bi-linear models. The equivalent linear model shows the peak o</p><p>　　frequencies. These effect

76、s are found to be more pronounced for the bi-linear system with low isolator yield displacement (i.e. q=0.001cm representing sliding type isolation system). These higher frequency contributions in the superstructure acce

77、leration can be detrimental to</p><p>　　the sensitive equipments with high frequency placed within the base-isolated structures. Thus, the base isolation systems with very low yield displacement transmit mor

78、e acceleration in the superstructure associated with high frequencies and this phenomenon is not predicted by the equivalent linear models.</p><p>　　The comparison of the peak response of the isolated struct

79、ure for equivalent linear and bi-linear models is shown in Tables 1 and 2 for single and five-story structure, respectively. The response is compared for different values of effective isolation time period (i.e.</p>

80、;<p>　　T＝2, 2.5, 3 s), effective isolation damping (i.e. =0.1. 0:05, 0.1) and isolator yield displacement (i.e. q=0.001, 2.5, 5 cm) under three earthquake motions. As observed earlier, the peak top floor accelerat

81、ion for all earthquake ground motions is higher for bi-linear models in comparison to the equivalent linear for all combinations of system parameters. This confirms that the superstructure acceleration will be under esti

82、mated if the bi-linear force-deformation characteristic of the isolator is</p><p>　　model. On the other hand, the peak bearing displacements predicted by the equivalent linear model is higher than the corres

83、ponding bi-linear hysteretic model. In some cases under Kobe, 1995 earthquake motion, the peak bearing displacements estimated by</p><p>　　the equivalent linear model are less than the bi-linear model for q=

84、2:5 and 5 cm. This is attributed due to the typical variation of the spectral displacement of this earthquake motion, in which the peak displacement decreases with the increase of time period in the range</p><

85、p>　　from 1.5 to 3 s (refer Fig. 2). Thus, the equivalent linear model of hysteretic isolator system over-predicts the peak bearing displacements. </p><p>　　5.2. Effects of isolator yield displacement <

86、/p><p>　　In order to understand the influence of the shape of the bi-linear hysteresis loop of the isolator, the variation of peak top floor acceleration and bearing displacement of a five-story structure is pl

87、otted against yield displacement, q in Figs. 8–10 under Loma Prieta, 1989, Northridge, 1994 and Kobe, 1995 earthquakes, respectively. The responses are shown for three isolator characteristic strengths (i.e. Q/W = 0:05,

88、0.075 and 0.1) and three values of isolation time periods based on the post-yie</p><p>　　structure is not captured by an equivalent linear viscous model as the q had no effect on the effective stiffness and

89、a very little effect on the effective damping for large design displacement (refer Eqs. (7) and (8)). Further, it is also observed from Figs. 8–10 that with the increase in characteristic strength, Q, the top floor accel

90、eration increases and the bearing displacement decreases. This is expected because for higher isolator characteristic strengths, the isolation system remains much</p><p>　　base-isolated structure is signific

91、antly influenced by the shape and parameters of the bi-linear hysteresis loop of the isolator.</p><p>　　5.3. Effects of superstructure flexibility</p><p>　　The flexibility in the base-isolated s

92、tructure is mainly concentrated at the isolation level, as a result, the response of base-isolated structure can be investigated by modeling the superstructure as rigid [14–16].</p><p>　　However, it will be

93、interesting to compare the seismic response of a base-isolated structure with superstructure \odeled as rigid and flexible to study the influence of the superstructure flexibility. Fig. 11 shows the variation of top floo

94、r acceleration and bearing displacement of a five-story base-isolated structure against the superstructure fundamental time period, Ts. The isolation system parameters considered are isolation period, T=2 s, normalized c

95、haracteristics strength, Q/ W=0:05 and d</p><p>　　displacement values such as q 10_4, 2.4 and 5 cm. It is observed that there is significant difference in the top floor acceleration obtained when superstruct

96、ure is rigid (i.e. Ts =0s) and flexible (i.e. Ts > 0). There is substantial increase in the top floor acceleration as the</p><p>　　fundamental time period of superstructure increases. This implies that th

97、e superstructure accelerations will be under-estimated if thesuperstructure flexibility is ignored and it is modeled as a rigid body. The increase in the superstructure accelerations is found to be more pronounced for th

98、e isolation system with low value of yield displacement (i.e. sliding type systems). On the other hand, the bearing displacement is not much influenced with the increase in superstructure flexibility. Simila</p>&

99、lt;p>　　6. Conclusions</p><p>　　Influence of isolator characteristic parameters on the seismic response of multi-story base-isolated structures is investigated. A comparison of the response of the isolated

100、 structure for equivalent linear and bi-linear force-deformation behavior of the isolator is made. In addition, the effects of the shape of isolator loop and superstructure flexibility on the seismic response of the base