Aiqun Li

Comparative Study on Buffeting Performance of Sutong Bridge Based on Design and Measured Spectrum

The recent development in structural health monitoring (SHM) technology enables the buffeting responses of bridges to be evaluated in a more realistic manner. In this paper, the buffeting responses of the cable-stayed Sutong Bridge with a main span of 1,088 m is analyzed with the wind spectra used in the design phase and those obtained experimentally from a long-term SHM system to compare the actual buffeting response with design predictions. The autospectra of longitudinal and vertical fluctuating wind components are derived from the in situ strong wind data recorded by the monitoring system. The buffeting analysis is accomplished in the time domain with the aeroelastic effect included. Compared with the buffeting responses obtained from the measured spectrum, the girder responses from the design spectrum are larger in the horizontal direction and smaller in other directions, whereas the tower responses are larger and thus relatively conservative.

Comparison of Ambient Vibration Response of the Runyang Suspension Bridge under Skew Winds with Time-Domain Numerical Predictions

Existing buffeting theories and methods for dealing with skew winds are summarized. A modified version of the mean wind decomposition method is described that directly uses wind monitoring data from structural health monitoring systems. A method for time-domain buffeting analysis is presented and implemented in ANSYS, in which self-excited forces are modeled as elemental aeroelastic stiffness and damping matrices by element Matrix27. The entire numerical procedure is implemented in MATLAB and ANSYS, and the buffeting responses can be conveniently computed with very concise input data. This method is applied to the buffeting analysis of the Runyang Suspension Bridge during Typhoon Matsa. The measured data of wind characteristics are used to predict the buffeting responses of the bridge with a finite-element model. The predicted buffeting responses are compared with those from field measurements. A reasonably good agreement between the calculation and the measurement validates the effectiveness of the metho...

A Study on the WPT-based Structural Damage Alarming of the ASCE Benchmark Experiments

A workable realization procedure for damage alarming of frame structures is put forward based on energy variations of structural dynamic responses decomposed using wavelet packet transform in the paper. The WPT-based method consists of two steps: 1) calculation of the wavelet packet energy spectrum from the measured structural dynamic responses; 2) extraction of the damage alarming index ERVD from the wavelet packet energy spectrum, which is sensitive to structural local damage and insensitive to measurement noise. The ASCE benchmark experiments demonstrate the practicability of the damage alarming method for fame structures, which reveal that the WPT-based damage alarming index ERVD is a good candidate index that is sensitive to structural local damage affected by the actual measurement noise. Also, the experimental results reveal that the lower decomposition level and dominant frequency bands are sufficient for the detection of the damage occurrence using the index ERVD, which makes the proposed damage alarming procedure practical.

Finite Element Model Updating for the Runyang Cable-Stayed Bridge Tower Using Ambient Vibration Test Results

The finite element (FE) model updating method aims to fit the parameters of a given initial analytical model in such a way that the model behavior corresponds as closely as possible to the measured behavior. However, the success of applications of the method depends on the analytical conceptualization of complex civil engineering structures, a well-designed and controlled modal test and an integration of analytical and experimental arts. This paper presents a sensitivity-analysis-based FE model updating procedure for FE model updating of Runyang Cable-stayed Bridge tower based on ambient vibration measurements. The updated model results correlate well with the experimental data in both the active frequency range and the passive frequency range. Extensive comparisons are made among the results obtained from different model updating cases. It is found that the appropriate initial FE model and determination of updating parameters are very important for the FE model updating of Runyang Cable-stayed Bridge tower.

Accurate Stress Analysis on Steel Box Girder of Long Span Suspension Bridges Based on Multi-Scale Submodeling Method

The streamline flat steel box girder is broadly used in long span cable-supported bridges all over the world. As one of the most important part of the bridges, its stress level and distribution under various dynamic loads are especially concerned. However, it is difficult to obtain the accurate stress of the steel box girder by common finite element (FE) calculation. The Runyang Suspension Bridge (RSB) is taken as an example. To increase the accuracy of results, a 3-dimensional FE full model for the RSB is created by ANSYS and a spatial submodel of the steel box girder is particularly built with greater detail. Submodeling method is then employed as a connection technique to link different scale models. After the global analysis and connecting process, the local stress of the steel box girder under various vehicle loads is obtained by submodel analysis. The composite action between the full model and the submodel is analyzed, and the reasonable mesh size for the submodel is specially investigated. The numerical results are proved to be accurate by the field test results. This study demonstrates the reliability and efficiency of the submodeling method; and can provide references for accurately analyzing and designing the steel box girders of other long span bridges.

Full-Scale Measurements and System Identification on Sutong Cable-Stayed Bridge during Typhoon Fung-Wong

The structural health monitoring system (SHMS) provides an effective tool to conduct full-scale measurements on existing bridges for essential research on bridge wind engineering. In July 2008, Typhoon Fung-Wong lashed China and hit Sutong cable-stayed bridge (SCB) in China. During typhoon period, full-scale measurements were conducted to record the wind data and the structural vibration responses were collected by the SHMS installed on SCB. Based on the statistical method and the spectral analysis technique, the measured data are analyzed to obtain the typical parameters and characteristics. Furthermore, this paper analyzed the measured structural vibration responses and indicated the vibration characteristics of the stay cable and the deck, the relationship between structural vibrations and wind speed, the comparison of upstream and downstream cable vibrations, the effectiveness of cable dampers, and so forth. Considering the significance of damping ratio in vibration mitigation, the modal damping ratios of the SCB are identified based on the Hilbert-Huang transform (HHT) combined with the random decrement technique (RDT). The analysis results can be used to validate the current dynamic characteristic analysis methods, buffeting calculation methods, and wind tunnel test results of the long-span cable-stayed bridges.

Experimental and Analytical Studies on Static and Dynamic Characteristics of Steel Box Girder for Runyang Cable-Stayed Bridge

In this study, a multi-scale computational model and methodology is presented for a comprehensive simulation of the static and dynamic characteristics of the steel box girder of Runyang Cable-stayed Bridge. The global-scale finite element model uses the shell elements with the equivalent orthotropic materials to simulate the top/bottom plate and its U-shape rib, which leads to accurate modeling of structural properties of the steel box girder in terms of vertical, lateral, torsional and warping stiffness. The local-scale finite element modeling of the girder is essentially a combination of fine finite element sub-models of selected details and the global-scale shell element model of the steel box girder by using the submodeling method. The developed three-dimensional global-scale and local-scale FE models have achieved a good correlation with the field load tests and ambient vibration tests. The static and dynamic characteristics of steel box girder of Runyang Cable-stayed Bridge under vehicle load tests and ambient vibration tests are further discussed.

Measurement study on wind characteristics of Typhoon Kalmaegi on the sutong bridge

The Sutong Bridge, a cable-stayed located in the southeast coastal area of China, is vulnerable to the Pacific typhoons. From the data measured by two 3D ultrasonic anemometers at the height of 76 m and 306 m, the wind characteristics (including 10-minute mean wind speed and direction, turbulence intensity and gust factor, power spectral density and integral scale of turbulence) of Typhoon Kalmaegi are analyzed The comparison of 10-minute mean wind velocity from the two anemometers validates the reliability of wind data. The turbulence intensities (Iu, Iv, and Iw) show the decreasing trend as the mean wind speed increases. The mean value of Iv/Iu is 0.94, while that of Iw/Iu is 0.90. Discrepancy exists between field-measured power spectra and code-suggested spectra. Those results can enlarge the wind database of the southeast coastal area of China, and provide references for wind resistance evaluation of the bridge.

Investigations on serviceability control of long-span structures under human-induced excitation

The increasing strength of new structural materials and the span of new structures, accompanied by aesthetic requirements for greater slenderness, are resulting in more applications of long-span structures. In this paper, serviceability control technology and its design theory are studied. First, a novel tuned mass damper (TMD) with controllable stiffness is developed. Second, methods for modeling human-induced loads are proposed, including standing up, walking, jumping and running, and an analysis method for long-span floor response is proposed based on a finite element model. Third, a design method for long-span floors installed with a multiple TMD (MTMD) system considering human comfort is introduced, largely based on a study of existing literature. Finally, a design, analysis and field test is conducted using several large scale buildings in China including the Beijing Olympic Park National Conference Center, Changsha New Railway Station and the Xi’an Northern Railway Station. The analytical and field test results show that the MTMD system designed using the proposed method is capable of effectively mitigating the vertical vibration of long-span floor structures. The study presented in this paper provides an important reference for the analysis of vibration serviceability of similar long-span floors and design of control system for these structures.