From 2019 to 2022, SCE produced 8 Jiangsu Province Excellent Master's Dissertations and 3 Jiangsu Province Excellent Doctoral Dissertations. On average, SCE produced about three excellent Master's dissertations and one excellent Doctoral dissertation each year. The lists of excellent Master's (Academic and Professional) dissertations and Doctoral dissertations (from 2019 to 2022) are shown below.

List of Excellent Master's Dissertations of Jiangsu Province from SCE (2019-2022)

List of Excellent Doctoral Dissertations of Jiangsu Province from SCE (2019-2022)

Below are the abstracts of some award-winning Master's and Doctoral dissertations:

(1) Study on reasonable structure system and wind resistance performance of three-tower suspension bridge with unequal-length main spans

MSc. candidate: Yang Chaoyu

Supervisor: Professor Zhang Wenming

ABSTRACT

Multi-tower suspension bridges have extraordinary spanning capacity and excellent economy. Several multi-tower suspension bridges with equal-length main spans have been built in China. If unequal-length main spans are adopted, this bridge type will have better terrain adaptability and wider application scope. Due to the loss of symmetry, the reasonable structural system and wind resistance performance of multi-tower suspension bridge with unequal-length main spans are different from those of multi-tower suspension bridges with equal-length main spans. In this study, a three-tower suspension bridge with unequal-length main spans is taken as the research object, and the following prospective works are carried out by employing theoretical analysis and numerical simulation methods:

(1) Based on the theory of segmented catenary, shape finding of the main cable of three tower suspension bridge with unequal-length main spans is studied. According to the principle that the length of the shortest suspender in the main span is equal to that in the secondary main span, the tower top elevation of the secondary main span side tower is determined, the thermal effect on the main cable shape, tower displacement and rotating momentum of splay saddle are calculated.

(2) By calculating the main cable shape under live load, combined with the two conditions of limit value of deflection to span ratio and limit value of anti-sliding between main cable and saddle, the analytical formula of reasonable stiffness interval of central tower is derived. The influences of dead to live load ratio and friction coefficient between main cable and saddle on reasonable stiffness interval of central tower are studied.

(3) Based on the method of segmented catenary, the analytical algorithm of main cable shape in three states of double-cable suspension bridge (completed bridge state, live load action and free cable state) is derived. Meanwhile, the key construction parameters are obtained, such as the saddle pre-offset and the installation positions of the cable clamps. Finally, the influence of bridge tower stiffness on live load effect of three-tower double-cable suspension bridge and the longitudinal restraint effect of double cables on the central tower are analyzed.

(4) Based on the theory of equivalent elastic support, the model of three-tower suspension bridge is simplified to two-tower suspension bridge. Based on the theory of equivalent simply supported beam, the analytical algorithm of gravity stiffness of three-tower suspension bridge is derived considering the central tower stiffness. The influence of rise span ratio, central tower stiffness and cross-sectional area of main cable on gravity stiffness is analyzed and verified by the finite element method.

(5) Based on the finite element method, the wind-resistance performance of three-tower suspension bridge with unequal-length main spans is studied. The critical wind speed and instability mode of aerostatic stability are calculated by the incremental double iteration method, with optimum iteration. The critical flutter wind speed and the flutter mode are calculated by the full mode method. The wind-resistance performance of the bridge is compared with that of the three-tower suspension bridge with equal-length main spans.

Key words: three-tower suspension bridge; unequal-length main spans; analytical method; segmented catenary; main cable shape; central tower stiffness; gravity stiffness; double main cables; wind resistance performance

(2) Study on Seismic Performance of Self-centering CLB Rocking Coupled Wall with Additional Damping System

M.Sc. candidate: Wang Weiyang

Supervisor: Professor Lyu Qingfang

ABSTRACT

To make the rocking structure suitable for wall with large opening (coupled shear wall), a self centering CLB (Cross Laminated Bamboo) rocking coupled wall with an additional damping system is proposed in this study. The rocking coupled wall consists of two CLB rocking walls and a steel truss energy-dissipating coupling beam located between the two walls. Among them, the steel truss energy-dissipating coupling beam is composed of two chords and two dampers as diagonal webs. The dampers adopt a novel buckling-restrained damper with friction energy dissipation. The hysteretic performance and failure mode of the damper and the energy-dissipating coupling beam are studied through quasi-static tests. In addition, a predictive model of the self-centering CLB rocking coupled wall with a steel truss energy-dissipating coupling beam is established based on the finite element models of the damper, energy-dissipating coupling beam and CLB rocking wall, and a series of parametric analyses is conducted. Finally, theoretical analysis of the working mechanism of the rocking coupled wall is carried out, and the theoretical skeleton curve is proposed. The main research contents and conclusions of this paper are as follows:

(1) Low cycle loading tests are carried out on the buckling-restrained damper with friction energy dissipation (BFD), and the influences of different variables and different loading protocols on the hysteretic performance, failure mode, ductility and energy consumption of the BFD are studied. The results show that the hysteretic curve of the BFD is stable. When the stopper mechanism of the BFD is activated, the axial deformation of the small plastic segment is limited, and the large plastic segment can continue to deform to provide additional strength and stiffness for the damper. By analyzing the single loading cycle’s energy dissipation of BFDs with different bolt torques, it is found that the energy consumption ratio of the large plastic segment, small plastic segment and friction energy dissipation mechanism in Specimen L100S10-V is 0.455: 0.398: 0.106, respectively. As the strain amplitude of the constant amplitude loading protocol increases, the failure mode of the BFD will change, from failure of the small plastic segment first to failure of the large plastic segment first. Besides, the cumulative ductility index and compression-strength adjustment factor of the BFD can meet the relevant requirements of AISC 341-16.

(2) Quasi-static loading tests are conducted on the steel truss energy-dissipating coupling beam, which shows that the cumulative energy consumption of the energy-dissipating coupling beam decreases with increase of the height of the coupling beam. The force-displacement responses of the energy-dissipating coupling beams using the BFD with the same sectional areas of large and small plastic segments and using the conventional buckling-restrained damper (CBD) are similar, while the energy-dissipating coupling beam using the BFD with different sectional areas of the large and small plastic segments has a better low-cycle fatigue life. Besides, failure mode of the articulated damper in the steel truss energy-dissipating coupling beam is a little different from failure mode that occurred in the BFD tests. A new failure mode is added, that is, the end of the outer tube of the damper broke. Finally, theoretical analysis of the force on the end of the articulated damper is carried out, and an equation for computing fracture of the end of the outer tube is given.

(3) Based on the above test results and test results of CLB rocking walls by the research team, the validity and accuracy of the finite element models of the BFD, steel truss energy-dissipating coupling beam, and the CLB rocking wall are verified, and a predictive model of the self-centering CLB rocking coupled wall with a steel truss energy-dissipating coupling beam is established. A series of parametric analysis is carried out for this model, and the results show that increasing the wall width can significantly increase the strength, initial stiffness and second stiffness of the rocking coupled wall. Increasing the initial stress ratio of prestressed tendons or increasing the number of prestressed tendons can increase the strength of the rocking coupled wall, but increasing the number of prestressed tendons is more effective, and increasing the number of prestressed tendons can increase the second stiffness of the rocking coupled wall. The energy dissipation capacity of the rocking coupled wall can be effectively adjusted by changing the width of the opening, the inclination angle of the damper and the sectional area of the damper. In addition, a theoretical model of the rocking coupled wall is established and verified by comparison with the numerical results. Finally, the design process of the rocking coupled wall is proposed.

Keywords: cross-laminated bamboo; self-centering rocking wall; coupled wall; coupling beam; buckling restrained damper; hysteretic performance

(3) Prediction approaches with applications of multi-source structural health monitoring data for long-span bridges

Ph.D. candidate: Zhang Yiming

Supervisor: Professor Wang Hao

ABSTRACT

Rational interpretation of massive structural health monitoring (SHM) data is critical to ensuring the safety and operation efficiency of significant infrastructures, which has attracted increasing attention in civil engineering. This research aims to develop prediction approaches of multi-source data collected from long-span bridges. The main contents of this thesis are presented as follows.

(1) Modeling and forecasting the strain of a long-span bridge using an improved Bayesian dynamic linear model (BDLM). An improved BDLM, which considers an auto-regressive (AR) component in addition to the trend, seasonal and regression components, is presented in this thesis to improve the computational accuracy. The model parameters are estimated by combing the expectation-maximization (EM) with Kalman filter algorithms. The order of the BDLM is determined by the measure criteria of Akaike information criterion (AIC) and root mean squared error (RMSE). The real-time monitoring data collected from a long-span cable-stayed bridge is utilized to demonstrate the feasibility of the improved BDLM. Its performance is compared with the AR model, multiple linear regression model and BDLM without the AR component.

(2) Anomaly detection of SHM data using the improved BDLM. The sub-space identification method is introduced to overcome the initialization issue of the EM algorithm. The log-likelihood difference of consecutive time steps is then used to determine the thresholds without introducing extra anomaly detectors. The proposed BDLM-based approach is first verified by the simulation data and then applied to the SHM data collected from two long-span bridges.

(3) BDLM with switching for performance alarm of bridge expansion joints using SHM data. An approach based on the BDLM and Markov-switching theory is presented for bridge response alarm of bridge expansion joints. A weighted combination of BDLMs is employed to estimate the real state of the expansion joint displacement. The EM algorithm initialized by the sub-space method is utilized to optimize the parameters of switching BDLM. Then, the EM algorithm is compared with the Newton-Raphson approach in terms of computational accuracy and efficiency. The present approach is validated through the simulated data and then applied to the expansion joint of a long-span bridge.

(4) Bayesian dynamic regression for reconstruction of missing data in SHM. To address issue that static regression model fails to accurately capture the relationship in related variables, this study presents a Bayesian dynamic regression (BDR) method to reconstruct the missing SHM data. The Kalman filter and EM algorithms are employed to estimate the state variables (regressors) and parameters. The moving window strategy is introduced to reduce the computational expense of the BDR model. Two cases, including a laboratory building model and a long-span cable-stayed bridge, are utilized to examine the reconstruction performance of the multivariate BDR method.

(5) A probabilistic approach for short-term prediction of wind gust speed using ensemble learning. As an efficient strategy to improve the performance of a single model, the ensemble model including random forest (RF), long-short term memory (LSTM) and Gaussian process regression (GPR) models, is presented in this research. The outputs of RF and LSTM are set as inputs of the GPR model to perform probabilistic prediction. The performance of the present methodology is compared with the persistence model (PM), RF, LSTM, GPR, averaging and gradient boosting regression decision tree (GBDT) model.

(6) A probabilistic framework for predicting typhoon-induced dynamic responses of a long-span bridge. As opposed to the conventional model-based analysis involving low efficiency, TIR prediction is performed from a data-driven perspective. The quantile random forest (QRF) with Bayesian optimization is presented for probabilistic prediction. The predictor variables are obtained from parameters related to typhoon characteristics. In particular, QRF can be utilized to rank the relative importance of the predictor variables. To illustrate the superiority of the QRF with Bayesian optimization, it is compared with various optimization algorithms and models. The SCB is used as a test bed to illustrate the effectiveness of the present method.

Keywords: long-span bridges; structural health monitoring; multi-source data; probabilistic prediction; anomaly detection; data reconstruction.