Zhi-Wei Chen

Dynamic Stress Analysis of Long Suspension Bridges under Wind, Railway, and Highway Loadings

Computation of the dynamic stress of long suspension bridges under multiloadings is essential for either the strength or fatigue assessment of the bridge. This paper presents a framework for dynamic stress analysis of long suspension bridges under wind, railway, and highway loadings. The bridge, trains, and road vehicles are respectively modeled using the finite-element method (FEM). The connections between the bridge and trains and between the bridge and road vehicles are respectively considered in terms of wheel-rail and tire-road surface contact conditions. The spatial distributions of both buffeting forces and self-excited forces over the bridge deck surface are considered. The Tsing Ma suspension bridge and the field measurement data recorded by awind and structural health monitoring system (WASHMS) installed in the bridge are utilized as a case study to examine the proposed framework. The information on the concerned loadings measured by the WASHMS is taken as inputs for the computation simulation, and the computed stress responses are compared with the measured ones. The results show that running trains play a predominant role in bridge stress responses compared with running road vehicles and fluctuating wind loading. DOI: 10.1061/(ASCE)BE.1943-5592.0000216.

Computer-aided Nonlinear Vehicle-bridge Interaction Analysis:

The interaction between railway vehicle and bridge is dynamic and nonlinear in nature. This paper aims to develop a computer-aided numerical method for analyzing coupled railway vehicle-bridge systems of nonlinear features. The finite element method is used to establish not only a bridge model (bridge subsystem) but also flexible vehicle models (vehicle subsystem). The connections between the two subsystems are considered through wheel-rail contact models with and without wheel jumps. All the nonlinear forces and concentrated damping forces in the two subsystems and the nonlinear contact forces at their interface are treated as pseudo forces to facilitate nonlinear analysis. The mode superposition method is then applied to the two subsystems, and both non-iterative and iterative computation schemes are utilized to find the best solution. The convergence of iterative computation schemes is investigated with and without wheel jumps. The explicit integration scheme is found to possess higher convergence than other schemes. The applicability and accuracy of the proposed numerical method are finally illustrated through numerical examples and comparisons with previous work.

Condition Assessment on Thermal Effects of a Suspension Bridge Based on SHM Oriented Model and Data

This paper aims to carry out the condition assessment on temperature distribution and thermal effects of a long span suspension bridge. The structural health monitoring (SHM) oriented data analysis is first performed and several indices are developed to process the time-varying temperature, displacement, and strain responses. An analytical procedure based on heat transfer theory is presented to determine the temperature distributions within the bridge. The fine finite element models of the deck plate, the cross frame, and the bridge tower are constructed for thermal analysis. A new approach to the thermal-structural coupling analysis of long span bridges is proposed to examine the structural thermal effects. The feasibility and validity of the proposed data process method and the new approach for thermal-structural coupling analysis are examined through detailed numerical simulation. The numerical results are compared with the field measurement data obtained from the long-term monitoring system of the bridge and they show a very good agreement, in terms of temperature distribution in different time and in different seasons. This exercise verifies the accuracy of the heat transfer analysis employed and the effectiveness and validity of the proposed approaches for data processing and thermal-structural coupling analysis.

Damage Detection in Long Suspension Bridges Using Stress Influence Lines

AbstractNumerous long-span cable-supported bridges have been built throughout the world in recent years. These bridges begin to deteriorate once built and continuously accumulate damage during their long service life. The growing popularity of comprehensive structural health monitoring systems (SHMSs) in recently built long-span bridges has started a new trend of integrating SHMS and damage detection technology for real-time condition assessment of these bridges. This paper explores a novel damage detection technique based on stress influence lines (SILs) of bridge components and validates the efficacy of the technique through a case study of the Tsing Ma suspension bridge. A mathematical regularization method is first introduced to identify SILs based on the in situ measurement of train information and train-induced stress responses in local bridge components. Good agreement between the identified and baseline SILs demonstrates the effectiveness of the proposed identification method. Damage indexes based...

Damage detection on sudden stiffness reduction based on discrete wavelet transform.

The sudden stiffness reduction in a structure may cause the signal discontinuity in the acceleration responses close to the damage location at the damage time instant. To this end, the damage detection on sudden stiffness reduction of building structures has been actively investigated in this study. The signal discontinuity of the structural acceleration responses of an example building is extracted based on the discrete wavelet transform. It is proved that the variation of the first level detail coefficients of the wavelet transform at damage instant is linearly proportional to the magnitude of the stiffness reduction. A new damage index is proposed and implemented to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. Numerical simulation using a five-story shear building under different types of excitation is carried out to assess the effectiveness and reliability of the proposed damage index for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also investigated. The made observations demonstrate that the proposed damage index can accurately identify the sudden damage events if the noise intensity is limited.

Damage identification of frame structures with joint damage under earthquake excitation

Previous damage detection of frame structures mainly focuses on the detection of beam and column element damage. It has been shown that beam-column joints in frame structures are more susceptible to damage than the other members in the structure. Joint damage may be represented by the reduction of beam-column connection rigidity. Therefore, damage detection of a frame structure with joint damage includes the identification of joint connection stiffness in additional to those of beam and column stiffness, which involves the difficulty of identifying a large number of unknown structural parameters. In this paper, an algorithm based on a two-step Kalman filter approach is presented for the damage detection of frame structures with joint damage under earthquake excitation using partial measurements of structural acceleration responses. Recursive solutions for unknown structural parameters and structural state vector are derived by a two-step Kalman filter, respectively. Therefore, the number of unknown variables to be estimated in each step is reduced compared with the conventional Extended Kalman filter (EKF) approach. Structural damage is detected from the degradation of the identified stiffness values of joints, beam and column elements of frame structures. A numerical example and a lab experiment test data are used to validate the performances of the proposed algorithm for damage identification of various joint damage scenarios in frame structures under earthquake excitation.

Damage Identification and Optimal Sensor Placement for Structures under Unknown Traffic-Induced Vibrations

AbstractThis paper proposes a damage-identification and optimal sensor-placement approach for structures under unknown traffic-induced vibrations. Response reconstruction is performed for structures under traffic-induced vibrations to formulate the relationship between different sets of time-domain responses. Measured acceleration responses from a structure under traffic-induced ground motions are used for damage identification with a sensitivity-based iterative model updating method. Numerical simulations on a seven-story planar frame structure are conducted to verify the performance of the proposed approach. Damage identification is conducted based on the initial finite-element model of the structure and the measured responses from the damaged state under traffic-induced vibrations. Structural elemental stiffness factors are iteratively updated until the reconstructed responses match the measured ones as closely as possible. A two-phase optimal sensor-placement scheme is proposed for better response rec...

Locate Damage in Long-Span Bridges Based on Stress Influence Lines and Information Fusion Technique

To ensure bridge safety and functionality under in-service conditions, detecting local abnormalities of a long-span bridge at the early stage is always a desirable but challenging task. Stress influence lines (SIL) or its derivatives are recognized as very promising indices for damage detection. Compared with bridge global responses (such as displacement and acceleration), stress/strain can be more conveniently measured and is often more sensitive to local damages. This paper explores a novel damage localization approach by synthesizing SIL measurements from multiple locations, in which Dempster-Shafer data fusion technique is utilized. Compared with the measurement from a single sensor, more reliable damage-related information with the improved sensitivity and capability in damage localization can be obtained by synthesizing the measured SILs from a number of sensors. The effectiveness of the proposed method is validated through a numerical case study of the Tsing Ma Suspension Bridge. Different hypothetical scenarios, including single-damage case, double-damage, and no-damage cases, are considered in the validation. The comparison with the damage detection results using single-sensor data clearly indicates that the data fusion technique effectively enhance the consistency in the information (e.g., damage-induced structural change) and minimize non-consistent information (e.g. “noise” effect) from multiple sensors installed close to damage. The increasing number of sensors benefits the damage detection results. Excellent damage detection accuracy can be achieved, if different types of bridge components are properly selected for the monitoring. Therefore, it is promising to use the proposed approach in this study in the damage localization of real-world long-span bridges. Parametric studies are conducted to examine the effects of parameter selections and noise levels in this approach.

Stress influence line identification of long suspension bridges installed with structural health monitoring systems

Numerous long-span suspension bridges have been built worldwide over the past few decades. To ensure the safety of such bridges and their users during the bridge service life, several bridges have been equipped with Structural Health Monitoring Systems (SHMSs), which measure dynamic bridge responses and various loading types on-site. Integrating SHMS and damage detection technology for condition assessment of these bridges has become a new development trend. Recent studies have proven that stress influence line (SIL)-based damage indices achieve excellent damage detection performance for a long suspension bridge. However, an accurate and prompt manner of identifying the SIL of a long suspension bridge is important to facilitate the development of the SIL for an effective damage index. Identifying the SIL from field measurement data under in-service conditions has several advantages over the traditional static loading test. This study proposes and develops a new SIL identification method by integrating the least squares solution and Weighted Moving Average (WMA) based on the measured train information and the corresponding train-induced stress time history. The efficacy of the proposed method is validated through its application to Tsing Ma Bridge (TMB). The good agreement between the identified and baseline SILs for a typical diagonal truss member verifies the effectiveness of the proposed method. Furthermore, robustness testing is performed by identifying SIL on the basis of information on different trains and train-induced stress responses and by identifying the SIL of different types of bridge components. Results indicate the feasibility of the application of the proposed approach to SIL identification for long-span bridges.

A Multi-Scale Wavelet Finite Element Model for Damage Detection of Beams Under a Moving Load

The resolution of structural finite element model (FEM) determines the computation cost and accuracy in dynamic analysis. This study proposes a novel wavelet finite element model (WFEM), which faci...