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1.
Ambient accelerations due to dynamic excitation by wind and traffic were measured on the deck, towers, cables and hangers of the Fatih suspension bridge. From these measurements it was possible to obtain natural frequencies, mode shapes and damping ratios for vertical, lateral, torsional and associated modes in the deck and tower up to a maximum of 2 Hz. The objective of the test was to validate the mathematical modelling used in seismic analyses of the bridge. The agreement between the experimental and theoretical modes was acceptable for vertical modes below 1 Hz, and for torsional modes, but it was difficult to identify the lateral modes due to low levels of response. The dynamic behaviour of this bridge and two other major European suspension bridges is discussed in relation to the differences in loading and structural design. 相似文献
2.
本文考虑曲线梁桥在竖直方向的弯扭耦合以及水平方向的弯曲、轴向变形,导出了曲线梁单元竖直方向和水平方向的传递矩阵.给出了用传递矩阵法计算曲线梁桥竖直方向和水平方向的振动频率、振型、地震内力和变形的计算公式和步骤,并运用传递矩阵法对单跨简支桥进行了地震反应分析.算例表明,本文方法简单、具有较高精度和效率,可用于曲线梁桥抗震设计. 相似文献
3.
An approximate analytical solution is presented for torsional vibrations of footings partially embedded into a semi-infinite medium or a stratum. Simple formulas derived for pure torsional motion make it possible to apply a correction for the effect of embedment to the known solutions of surface footings. The solution completes an approach to the analysis of all modes of footing vibrations, including the coupled modes. The approach to coupled modes is illustrated by the solution of coupled response involving horizontal translation, rocking and torsion. Formulas are presented for stiffness and damping coefficients that can be used in the analysis of embedded footings or structures supported by such footings Field experiments were conducted with concrete footings featuring circular, square and rectangular bases and variable embedment depths. The experimental results were compared with theoretical predictions of pure torsional vibrations. 相似文献
4.
Based on an asymmetric multistorey frame building model, this paper investigates the influence of a building's higher vibration modes on its inelastic torsional response and evaluates the adequacy of the provisions of current seismic building codes and the modal analysis procedure in accounting for increased ductility demand in frames situated at or near the stiff edge of such buildings. It is concluded that the influence of higher vibration modes on the response of the upper-storey columns of stiff-edge frames increases significantly with the building's fundamental uncoupled lateral period and the magnitude of the stiffness eccentricity. The application of the equivalent static torsional provisions of certain building codes may lead to non-conservative estimates of the peak ductility demand, particularly for structures with large stiffness eccentricity. In these cases, the critical elements are vulnerable to excessive additional ductility demand and, hence, may be subject to significantly more severe structural damage than in corresponding symmetric buildings. It is found that regularly asymmetric buildings excited well into the inelastic range may not be conservatively designed using linear elastic modal analysis theory. Particular caution is required when applying this method to the design of stiff-edge frame elements in highly asymmetric structures. 相似文献
5.
分析实际桥梁结构的各种损伤状况,采用矩阵摄动理论分析桥梁结构发生损伤时固有频率及振型向量的一阶、二阶摄动结果,并讨论了固有振动特性对结构单元损伤的灵敏性。在理论分析的基础上,编制桥梁结构固有振动特性及其在损伤下的摄动分析程序,并用以分析简支梁、连续梁及拱结构损伤引起的固有振动的摄动结果。分析结果表明:单一单元损伤引起固有频率的摄动结果很小;不同位置处单元损伤与固有频率摄动结果的关系曲线与对应振型曲线具有相似性,但在中间支承处或结构端部有扭转约束处单元损伤影响显著;而单元损伤对振型向量影响极小。 相似文献
6.
Due to the damage suffered by many skewed highway bridges during the San Fernando earthquake, 1971, a study is made on the dynamic response of this type of bridge. Using a beam model capable of flexural and torsional deformations, the mode shapes and frequency equations are presented. Due to the skewness of the intermediate supports, coupled flexural and torsional vibrations are shown to be excited by the vertical component of ground motion An analysis is carried out for the Foothill Boulevard Undercrossing, S.E. Bridge in the San Fernando Valley, California which suffered damage to the intermediate supports. The results of the analysis correlate well with the observed damage pattern of the bridge. 相似文献
7.
Overturning of a structure causes variations in the normal loads of the isolators supporting that structure. For frictional isolators, such variation leads to changes in the frictional forces developed and, hence, in the strength distribution in plan. For frictional pendulum system (FPS) isolators, it also causes changes in the pendular action, i.e. in the stiffness distribution of the isolation interface. Therefore, although the structure is nominally symmetric it develops lateral–torsional coupling when it is subjected to two horizontal components of ground motion. This coupling is denoted herein as accidental torsion due to overturning, and its effect in the earthquake response of nominally symmetric structures is evaluated. Several parameters are identified to control this coupling, but the most important are the slenderness of the structure and the aspect ratio of the building plan. Results are presented in terms of the torsional amplification of the deformations of the isolation base and the interstorey deformations of the superstructure. The FPS system is modelled accurately by including true large deformations and the potential uplift and impact of the isolators. Impulsive as well as subduction‐type ground motions are considered in the analysis, but results show small differences between them. An upper bound for the mean‐plus‐one standard deviation values of the torsional amplifications for the base due to this accidental torsion is 5%. This implies that for design purposes of the isolation system such increase in deformations could probably be neglected. However, the same amplification for the interstorey deformations may be as large as 50%, depending on the torsional stiffness and slenderness of the superstructure, and should be considered in design. In general, such amplification of deformations decreases for torsionally stiffer structures and smaller height‐to‐base aspect ratios. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
A study is presented of the influence of stiffness and strength eccentricities on the inelastic torsional response of buildings under the action of two simultaneous orthogonal horizontal ground motion components. Asymmetric buildings were obtained from their respective symmetric systems and were characterized by their stiffness and strength torsional eccentricities in both orthogonal directions. Based on the results of inelastic response of both building types (symmetric and asymmetric), the seismic reliability functions are determined for each system, and their forms of variation with different global system parameters are evaluated. Illustrative examples are presented about the use of this information for the formulation of seismic design criteria for in‐plan asymmetric multistory systems, in order to attain the same reliability levels implicit for symmetric systems designed in accordance with current seismic design codes. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
10.
Results of a parameter study on eccentric pounding of two symmetric single storey systems under seismic excitation are presented. Linear behaviour is assumed, and pounding effect is considered using the restitution coefficient approach. The effect of impact eccentricity is studied on two sets of symmetric models symmetrically and asymmetrically aligned with respect to each other for several gap widths, period dependent gaps and three values of the torsional-to-lateral frequency ratio. Two time histories are used for input. On the whole it was found that impact eccentricity amplifies the response relative to symmetric impact but the effect is not proportional to first impact eccentricity. Also, increasing gap width is likely to be effective when the separation is sufficiently wide practically to eliminate contact. Larger torsional rigidity tends to lower response amplification. SRSS code-type gaps appear to be adequate, or even excessive, when the design spectrum is compatible with the expected earthquake record at the site. 相似文献
11.
2008年汶川地震中江油市太白公园曲径桥上的石雕发生转动破坏现象,本文对这一转动现象进行了振动台模拟试验。模拟试验结果表明:① 在振动台三向加载1.5倍的汶川地震江油台记录的平动加速度后,模型的转动情况与实际观测的石雕转动情况比较一致;② 石雕的转动与石雕的非对称性、地震动输入角度和地震动的竖向作用有关;③ 加载竖向地震动作用后,石雕模型会发生摇摆现象,说明竖向地震动是造成模型扭转现象的重要原因,这也说明在分析相似震害现象时竖向地震动作用不可忽视。 相似文献
12.
A 3D finite element (FE) model for the Sutong cable-stayed bridge (SCB) is established based on ANSYS. The dynamic characteristics of the bridge are analyzed using a subspace iteration method. Based on recorded wind data, the measured spectra expression is presented using the nonlinear least-squares regression method. Turbulent winds at the bridge site are simulated based on the spectral representation method and the FFT technique. The influence of some key structural parameters and measures on the dynamic characteristics of the bridge are investigated. These parameters include dead load intensity, as well as vertical, lateral and torsional stiffness of the steel box girder. In addition, the influence of elastic stiffness of the connection device employed between the towers and the girder on the vibration mode of the steel box girder is investigated. The analysis shows that all of the vertical, lateral and torsional buffeting displacement responses reduce gradually as the dead load intensity increases. The dynamic characteristics and the structural buffeting displacement response of the SCB are only slightly affected by the vertical and torsional stiffness of the steel box girder, and the lateral and torsional buffeting displacement responses reduce gradually as the lateral stiffness increases. These results provide a reference for dynamic analysis and design of super-long-span cable-stayed bridges. 相似文献
13.
Traffic and wind excitation has been used to obtain the dynamic characteristics of the first Bosporus (Bogazici) Suspension Bridge. Structural symmetry and the absence of suspended side-spans allowed attention to be focused on the main span and the Asian tower. For the main span, 18 vertical and 20 lateral modes were obtained, including torsional modes. For the tower, 12 longitudinal and 12 lateral modes were identified. All these models lie in the range 0–1-1 Hz. A detailed comparison is given between these modes and corresponding calculated modes, obtained by use of a three-dimensional finite element model which includes a geometric stiffness matrix. Of particular interest is the validity of the theoretical model used for the box-deck, because of its subsequent use in response studies of asynchronous seismic excitation. Comparison with a more limited study made in 1973 shows that the bridge continues to behave as it was designed to behave, particularly with regard to the deck-tower interface. From natural frequency measurements of two hangers, the load which they carry was assessed. 相似文献
14.
The potential application of tuned liquid column damper (TLCD) for suppressing wind-induced vibration of long span bridges
is explored in this paper. By installing the TLCD in the bridge deck, a mathematical model for the bridge-TLCD system is established.
The governing equations of the system are developed by considering all three displacement components of the deck in vertical,
lateral, and torsional vibrations, in which the interactions between the bridge deck, the TLCD, the aeroelastic forces, and
the aerodynamic forces are fully reflected. Both buffeting and flutter analyses are carried out. The buffeting analysis is
performed through random vibration approach, and a critical flutter condition is identified from flutter analysis. A numerical
example is presented to demonstrate the control effectiveness of the damper and it is shown that the TLCD can be an effective
device for suppressing wind-induced vibration of long span bridges, either for reducing the buffeting response or increasing
the critical flutter wind velocity of the bridge. 相似文献
15.
J. C. Correnza G. L. Hutchinson
A. M. Chandler
《Soil Dynamics and Earthquake Engineering》1992,11(8):465-484This paper reviews the various forms of reference model adopted for studies that evaluate inelastic seismic torsional effects and assess their implications for building design. Both qualitative and quantitative comparisons are presented. The importance of selecting an appropriate reference model is in accordance with the above aims is emphasised. It is found that variations in the reference models adopted in analyses of inelastic seismic torsional effects may lead to significant differences in the results obtained and, hence, to the conclusions drawn from such studies. It is demonstrated that accidental torsional effects, as incorporated in code design provisions, result in significant changes to the distribution of element strengths and the inelastic response behaviour of symmetric and generalised torsionally balanced reference models. Such changes should be considered when employing such models to evaluate the ineslatic response of torsionally unbalanced building systems. 相似文献
16.
A reassessment of the dynamic characteristics of the 542 m cable‐stayed Bayview Bridge in Quincy, Illinois, is presented using a newly developed output‐only system identification technique. The technique is applied to an extensive set of ambient vibration response data acquired from the bridge in 1987. Vertical, torsional and transverse modal frequencies of the deck are identified, and uncertainty in damping values are estimated using an automated procedure on several redundant measurements at four locations. Important practical implementation issues associated with the implementation of the procedure and selection of algorithm design parameters for stochastic subspace identification techniques are discussed. An overall mean and standard deviation of damping of 1.0±0.8% is estimated considering all identified vertical, torsional and transverse modes in the 0–2 Hz band. The mean damping for the fundamental vertical mode (0.37 Hz) is identified as 1.4±0.5%, and for the first coupled torsion–transverse mode (0.56 Hz) is identified as 1.1±0.8%. Variability in the damping estimates is shown to decrease as estimated modal RMS acceleration levels increase. Standard deviations on estimated damping range from 0.05% to 2%. The results are shown to be a substantial improvement in the evaluation of damping compared to earlier spectral analysis conducted on the same data set. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
17.
This paper presents the results of a unique field test on a curved highway overpass. In the test, large horizontal loads were applied to the superstructure of the bridge and quickly released, causing the bridge to vibrate. The resulting large-amplitude vibrations were intended to be similar to the vibrations caused by earthquakes (horizontal accelerations of up to 25 per cent of gravity were measured on the bridge deck). Well-defined lateral, longitudinal, vertical and torsional vibration modes were identified from the test data. The vibration modes were used to verify an analytical model of the bridge's dynamic response. For this paper, the model was verified using only the fundamental vibration mode, which was primarily a horizontal vibration mode. Using a system identification procedure, the dynamic response model was adjusted until its frequency and mode shape matched the measured frequency and mode shape. Parameters in the verified model were compared with the same parameters calculated from information in the structural drawings. Because the fundamental mode represents a horizontal mode, the bridge parameters identified in this paper were those parameters which strongly influence the horizontal response of the bridge. 相似文献
18.
Study of the data from the extensively instrumented buildings in the 1987 Whittier Narrows earthquake suggests that torsional modes probably were excited in buildings that outwardly appear quite symmetric. Accordingly this study involves: (i) investigation of the observed response of two low-rise buildings in both the elastic and moderately inelastic domains, (ii) comparison of such behaviour with the results obtained from modelling studies, and (iii) examination of the possible effects arising from stronger shaking. The study was directed towards attempting to provide a partial answer to the critical question of whether or not the torsional response was important in the gross total response of these low-rise buildings, and to what extent torsional concepts should be considered in design. Also the numerical results were extrapolated to examine the survivability of the same buildings if subjected to a somewhat stronger earthquake. The ultimate goal was to contribute insight to the practical guidelines for design and analysis of low-rise buildings subjected to strong ground motion. 相似文献
19.
Fan Yang Qifeng Luo Wei Che Research Institute of Structural Engineering Disaster Reduction Tongji University Shanghai China 《地震学报(英文版)》2010,(1):79-85
It is well known that there are some torsional damages in earthquakes. In Taibai park, Jiangyou city, Sichuan province, most of the stone statues, which were placed upon the banisters of one zigzag bridge, exhibited different torsional phenomena in 2008 Wenchuan earthquake. This paper introduces the torsional phenomena of all the statues on the zigzag bridge firstly. Then one eccentricity model is established and the equivalent rotational accelerations are calculated in order to analyze the causes of the to... 相似文献
20.
Seismic Design of Symmetric Structures for Accidental Torsion 总被引：5，自引：0，他引：5
The paper presents an analytical estimation of the dynamic effects, caused by the shifting of the centre of mass with accidental
eccentricity in symmetric structures. The approximate analytical solution proves, that even under small accidental eccentricities
the symmetric structures exhibit “irregular behaviour” and the accidental torsional effects cannot be described properly by
static application of torsional moments. The prescribed application rule by Eurocode 8 for multimodal analysis underestimates
the accidental torsional effects up to 21% for 5% eccentricity for the structures considered in the paper. An expression for
the correction of member responses is derived. It is proved by numerical simulations of the dynamic response of three-dimensional
models of symmetric structures, that the proposed correction coefficient gives accurate results in cases of single-storey
and multi-storey structures. It gives a convenient way for the design practice to estimate accurately the accidental torsional
effects on planar and 3-D models of symmetric structures.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献