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Driving velocity, natural frequency of vehicle and natural frequency of bridge are the main contributing factors to vibration of a vehicle when passing a bridge. By separating contributions of the first two factors, one can estimate the natural frequency of a bridge indirectly from vehicle acceleration response when it crosses a bridge. In this paper, we apply this concept to estimate the bridge fundamental frequency indirectly using the response of a passing instrumented vehicle. The paper first describes analytical formulation and finite element simulation to demonstrate the feasibility of the method. Afterwards, it describes an experimental verification as a proof-of-concept of the method on a full-scale simply-supported short span bridge by using a light commercial vehicle instrumented with accelerometer. Dynamic responses of the vehicle while passing the bridge are recorded and analyzed. Spectra analysis of the vehicle responses reveal that the first natural frequency of the bridge can be estimated with reasonable accuracy when the vehicle moves with constant velocity. The concept of indirect frequency estimation is useful for assessment of short and medium span bridges where permanent instrumentation and routine visual inspection can be too costly. In this method, one can use inspection vehicle instrumented with vibration sensor to conduct periodic measurements by passing the vehicle over several monitored bridges and estimate their fundamental frequencies. When significant change in frequency is detected, detail inspections can be further conducted to investigate the possible damage on the bridge.

Strong motion data acquired from instrumented bridges during seismic events provides an excellent opportunity to gain insight into the behaviour of bridges and performance of their components. Using system identification, modal parameters of bridges can be estimated and the performance during various level of earthquake can be studied. In this study dynamic behaviour of Yokohama-Bay Bridge is investigated using seismic response recorded from six earthquakes. Modal parameters of the structure are estimated using system realization of state-space model. The realization method used here is based on the system realization using information matrix (SRIM), which makes use of the correlations between earthquake input and output data to identify the coefficient matrices of state-space model. Identification results from six earthquakes show that the system identification can be used to capture global behaviour of the bridge by estimating modal parameters and also to explain local behaviour of its component such as performance of link-bearing connections during earthquake. of the early studies on this was made by Beck and Jennings [1] that uses the output-error minimization method for linear, time-invariant structural systems with classical damping. In the same approach, but using frequency domain McVerry [2] utilizes a transfer function to minimize the objective function of output error. Chaudhary et al. [3] improves it for a more general problem of non-classical damping which includes the structural model in addition to the modal model. The last method, while powerful and significantly insightful into the structural model, requires prior information of structural properties that are typically unavailable and difficult to obtain, especially for large and complex structures. Most approaches are developed in the frequency domain, which is mainly due to the tradition of experienced personnel and vast application of instrument for measurement. These approaches offer advantages in incorporating soil-structure interaction into analysis, but suffer when closely spaced modes are present or high frequency resolution and non-linear identification is required [4]. Other considerable effort and discussion on system identification of civil structures can be found in the works by Masry [5,6], Udwadia [7], Safak [8,9] and Beck and Katafygiotis [10,11].Recent advances in the study of state-space models for modal parameter identification have led to the development of a new technique in time domain. This technique makes use of an input-output mapping technique to determine the impulse response histories which is also known as Markov parameter of linear system. The methodology, referred to as observer/Kalman filter identification algorithm (OKID) [12], is formulated entirely in the time-domain and does not require any prior knowledge of structural properties. This algorithm has shown its high capability in identifying structural modal parameters when it is used in conjunction with eigensystem realization algorithm (ERA) [13] or eigensystem...

Dynamic performance is an important consideration in long-span bridge design. Owing to its flexibility an d low damping, various types of vibration from different sources of excitation could occur during the lifetime of a long-span bridg e. This paper reviews important studies and developments on long-span bridge vibration mechanism an d control under wind, seismic,traffic and human-motion excit ations. Types of vibration commonly observed on the long-span bridge are discussed from the viewpoint of structure engineering. Discussion for each subject is commenced by describing the vibration mechanism followed by the survey on observed phenomena in many long-spa n bridges associated with the type of vibration. The paper also describes the engineering solutions adopted as countermeasures for each type of bridge vibration problem.

A system that uses ambient vibration and two laser Doppler vibrometer (LDV) is developed for noncontact operational modal analysis of structural members. The system employs natural excitation technique (NExT) to generate the cross-correlation functions from laser signals, and the eigensystem realization algorithm (ERA) to identify modal parameters of structural members. To facilitate simultaneous modal identification, time-synchronization technique and construction of cross-correlation functions from ambient response of laser signals are proposed. Performance of the proposed system is verified experimentally by evaluating the consistency and accuracy of identification results in different measurement conditions. The work presented here is an extension of the previous study, where a modal-based damage detection method using LDV was formulated. In the present study, application of LDV for structural parameters identification of a combined dynamical system is proposed. A model that represents the connection properties in terms of additional stiffness and damping is developed, and its importance for structural damage detection is discussed. The study shows that the presence of simulated damage in a steel connection can be detected by tracking the modal phase difference and by quantifying the additional stiffness and damping.