Research Areas

1. Bayesian Model Updating

An efficient and robust Bayesian probabilistic approach was developed for FEM updating that accounts for various uncertainties and utilizes incomplete modal data (modal frequencies and partial mode shapes) identified by a limited number of sensors. A new objective function was introduced for Bayesian model updating that does not require any scaling or normalization of mode shapes because the likelihood function for mode shapes is formulated based on the cosine of the angle between the analytical and experimentally identified mode shapes. To validate the proposed approach, an initial MATLAB-based FEM of an existing steel truss bridge was updated using the identified modal parameters from the measured vibration data. The proposed framework was also found to be robust against measurement errors. The damage-detection capability of the proposed model-updating framework was then investigated by considering the data from a simulated damaged bridge and the experimental data from a damaged span of the same bridge with partial fractures on one of the diagonal members. 

    Link: https://doi.org/10.1061/(ASCE)BE.1943-5592.0001044

2. Vibration-based Structural Health Monitoring (SHM)

An analytical framework for vibration-based SHM was introduced using an energy-based damping evaluation (EBDE). The damage detection by the proposed EBDE was carried out by estimating the contribution of modal damping ratios from different structural elements utilizing experimentally identified modal damping ratios, and estimating modal strain and modal potential energies from an updated finite-element (FE) model of the structure under consideration. Model updating was performed using modal frequencies and mode shapes that are generally not sensitive to local damage. The advantage of using damping as a damage indicator is that the damping change in global modes affected by the local damage can be identified with a small number of sensors. A previous study reported that the studied bridge with damage at the local diagonal member showed a significant increase in the damping of global vibration mode of the structure. The proposed vibration-based SHM approach could be promising in detecting damage at the local level when the problem related to low sensitivity of frequencies and mode shapes due to local damage remains a concern, and damage detection by change in stiffness parameters using FE model updating utilizing data from a large number of sensors is not practically feasible due to the limitation of budget and time.

Link: https://doi.org/10.1061/(ASCE)BE.1943-5592.0001159

3. Monitoring System for Seismic Damage Detection

A methodology for the selection of sensors and their arrangement was developed for detecting seismic damage in an in-service steel plate girder bridge system. In this study, a detailed span-based model was developed for the finite element simulation including the effect of the rubber bearing and piers, and the damage control by the side blocks. The finite element dynamic simulation was carried out with input earthquake acceleration to investigate the seismic behavior and grasp the damageable parts during an earthquake. Based on the results of finite element dynamic simulation, a fault tree analysis was carried out to reveal more about the bridge behavior, the failure modes, and the occurrence of damage. It was found that the side block, the bearing stiffener, and the horizontal bracing on the fixed side of the bridge are most important to be monitored for the evaluation of soundness of a plate girder bridge immediately after an earthquake. Finally, a sensor arrangement for the bridge was proposed based on the analysis results. In this monitoring system, the optical time-domain reflectometer (OTDR) is placed in all bearings which are fixed in the transverse direction by the side blocks to measure the relative displacement between the superstructure and the substructure. 

Link: https://doi.org/10.1177/1077546320905176

4. Bridge Weigh-In-Motion (BWIM)

An iterative linear optimization problem (ILOP) was proposed to accurately identify the individual axle weights and GVWs of vehicles traversing a bridge. The proposed method used the bridge displacement responses as the measured responses which were determined from the recorded acceleration data. The information about the vehicle speed, number of axles and axle spacings were obtained by identifying the peaks in the recorded acceleration data. The effectiveness and accuracy of the proposed method were demonstrated through field tests using the four-axle test vehicles with closely spaced axles. The results showed that the axle weights of vehicles with closely spaced axles could be identified with much better accuracy by the proposed method as compared to classic BWIM systems which are based on Moses’ original algorithm.

Link: https://doi.org/10.1061/AJRUA6.0001118

5. Retrofitting

Orthotropic steel decks (OSDs) are being used increasingly to replace old deteriorated reinforced concrete decks (RCDs). A numerical investigation was carried out to examine the effect of reduction in superstructure weight on the seismic resistance of the bridges when an existing RCD was being replaced by an OSD. Firstly, a detailed FE-model of a plate girder bridge with RCD was developed and then, another FE-model was constructed by replacing the RCD with the model of an OSD. Then, an eigenvalue analysis was carried out for each FE-model and their natural frequencies and the mode shapes were compared in order to understand the influence of deck replacement on the global vibrational characteristics of the bridge. After that, the effects of deck replacement on the seismic performance of the whole bridge system was investigated by performing a series of non-linear dynamic analysis with input earthquake data in the longitudinal and transverse directions separately and simultaneously. Based on the results of seismic response analysis, the differences in response behavior and damage level due to the replacement of deck were evaluated. 

Link: https://link.springer.com/article/10.1007/s13296-020-00370-0

6. Distributed Optical Fiber Sensing

To investigate the optimal embedment depth for DOFS for pavement monitoring, a series of field tests was conducted by considering three embedment depths (10, 30, and 40 mm) and three moving loads (pedestrian, car and truck). The main objectives were to examine the performance of DOFS embedded in the pavement and investigate its suitability and sensitivity for obtaining information about moving loads at various depths from the road surface. Among the existing backscattering light technology, Rayleigh scattering-based Optical Frequency Domain Reflectometry (OFDR) was chosen in order to achieve a measurement of high-speed, high range, and good repeatability with a very high spatial resolution of 2.56 mm, all of which are necessary for monitoring dynamic responses due to moving loads. In addition, a data-processing method was developed based on a combination of a Hampel identifier and a low-pass filter, which proved to be effective in removing outliers and high-frequency noise from the raw measurement data, respectively. The results showed that it is not only possible to detect a moving load on a road, but that a wide range of information can also be obtained from the strains measured by DOFS, including the type of load, its speed, its weight, the number of axles, the axle spacings (in the case of a vehicle) and the traffic flow. With low maintenance costs, DOFS based on Rayleigh scattering OFDR could be used for collection of accurate and reliable traffic data when embedded in a pavement.

Link: https://doi.org/10.1016/j.yofte.2021.102705

7. Bridge Influence Line Identification and Damage Detection

The method to obtain an accurate influence line (IL) from the direct measurement is an important research topic for structural condition assessment, model correction and bridge weigh-in-motion (BWIM) system. The two most common approaches used for the identification of IL are the time-domain (TD) method and the frequency-domain (FD) method. Despite having a similar mathematical framework, the TD and the FD methods are treated as two different methods by the researchers working on this field. This paper presents a detailed theoretical demonstration to show that the two methods discussed above are nothing but the same. The two methods were compared experimentally by using field measurement data on an existing steel girder bridge which were obtained by using three calibration trucks (CTs) with different axle weights and axle configurations. Although the ILs identified by the two methods were apparently different, but a theoretical insight into the frameworks revealed that the TD and FD methods are basically the same and a seeming difference between the two methods is due to the inherent assumptions involved in the discrete Fourier transform (DFT) such as the assumption of cyclic nature of analysis interval. Finally, a method to obtain an accurate influence line has been outlined. 

Link: https://doi.org/10.1016/j.istruc.2021.05.082