Deflection calculation method on GFRP-concrete-steel composite beam

Zhaojie Tong,Xiaodong Song,Qiao Huang 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.26 No.5

A calculation method was presented to calculate the deflection of GFRP-concrete-steel beams with full or partial shear connections. First, the sectional analysis method was improved by considering concrete nonlinearity and shear connection stiffness variation along the beam direction. Then the equivalent slip strain was used to take into consideration of variable crosssections. Experiments and nonlinear finite element analysis were performed to validate the calculation method. The experimental results showed the deflection of composite beams could be accurately predicted by using the theoretical model or the finite element simulation. Furthermore, more finite element models were established to verify the accuracy of the theoretical model, which included different GFRP plates and different numbers of shear connectors. The theoretical results agreed well with the numerical results. In addition, parametric studies using theoretical method were also performed to find out the effect of parameters on the deflection. Based on the parametric studies, a simplified calculation formula of GFRP-concrete-steel composite beam was exhibited. In general, the calculation method could provide a more accurate theoretical result without complex finite element simulation, and serve for the further study of continuous GFRP-concrete-steel composite beams.

Experimental and Theoretical Study on the Flexural Performance of GFRP-Concrete-Steel Composite Beams

Zhaojie Tong,Xiaodong Song,Qiao Huang 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.8

A novel GFRP (glass fiber-reinforced polymer)-concrete-steel composite beam bridge was proposed to prolong the service life of bridges. In order to investigate the flexural behavior of the composite beams, four-point bending tests and push-out tests were conducted. First, GFRP-concrete-steel composite beams with different interface types were fabricated and tested. Experimental results indicated the concrete ultimate strain and the ultimate deflection were increased because of the confining effect provided by GFRP plates. The GFRP-concrete interface had no obvious effect on flexural stiffness and flexural capacity. The slip effect of GFRPconcrete- steel beams was similar to that of steel-concrete beams. The failure process of GFRP-concrete-steel beams was different from that of steel-concrete beams due to the effect of the GFRP plate. Then, push-out specimens were tested to investigate the slip effect between GFRP-concrete decks and steel beams. The effect of GFRP plates on the studs was insignificant because of the large stud hole, and a regression formula of load-slip relationship was presented based on the experimental results. Finally, finite element model and theoretical model were employed to analyze the deflection calculation method and the flexural capacity calculation method, respectively.

Experimental and analytical study on continuous GFRP concrete decks with steel bars

Zhaojie Tong,Yiyan Chen,Qiao Huang,Xiaodong Song,Bingqing Luo,Xiang Xu 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.6

A hybrid bridge deck is proposed, which includes steel bars, concrete and glass-fiber-reinforced-polymer (GFRP) plates with channel sections. The steel bar in the negative moment region can increase the flexural stiffness, improve the ductility, and reduce the GFRP ratio. Three continuous decks with different steel bar ratios and a simply supported deck were fabricated and tested to study the mechanical performance. The failure mode, deflection, strain distribution, cracks and support reaction were tested and discussed. The steel bar improves the mechanical performance of continuous decks, and a theoretical method is proposed to predict the deformation and the shear capacity. The experimental results show that all specimens failed with shear failure in the positive moment region. The increase of steel bar ratio in the negative moment region can achieve an enhancement in the flexural stiffness and reduce the deflection without increasing GFRP. Moreover, the continuous deck can achieve a yield load, and the negative moment can be carried by GFRP plates after the steel bar yields. Finally, a nonlinear analytical method for the deflection calculation was proposed and verified, with considering the moment redistribution, non-cracked sections and nonlinearity of material. In addition, a simplified calculation method was proposed to predict the shear capacity of GFRP-concrete decks.

Unbalanced control strategy featuring inconsistent sub‑module voltage for modular multilevel converter–bidirectional DC–DC converter

Peng Chen,Fei Xiao,Jilong Liu,Zhichao Zhu,Zhaojie Huang 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.5

Modular multilevel converter–bidirectional DC–DC converter (MMC–BDC) is a prospective solution for the bidirectional DC–DC power conversion between medium-voltage DC (MVDC) bus and distributed energy storage system. Researchers have studied its application in the shipboard power system. In face of distributed energy storage devices with discrepant state of charge (SOC), the sub-modules (SMs) of MMC–BDC should work under inconsistent power to unify the SOC level. The existing unbalanced SM power control strategies fail to consider unbalanced operation range and efficiency. Therefore, this study proposes a novel unbalanced control strategy based on the feedforward compensation method, which is characterized by inconsistent SM voltage. Comparisons are made to demonstrate the advantages of the proposed strategy over traditional ones, and the dynamic characteristics are analyzed. Simulation and experiment results illustrate the effectiveness of the proposed unbalanced operation strategy.

Optimal modulation strategy based on fundamental reactive power for dual‑active‑bridge converters

Zhichao Zhu,Fei Xiao,Jilong Liu,Peng Chen,Zhaojie Huang,Qiang Ren 전력전자학회 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.12

Dual-active-bridge (DAB) converters are widely used in bidirectional power transmission and voltage conversion. At present, phase-shift (PS) control is one of the most common and mature control methods for DAB converters. To improve the efficiency and performance of DAB converters, the soft switching and current stress are optimized by increasing the inner phaseshift ratio. However, under different PS controls, it is difficult to establish a unified mathematical model using the traditional instantaneous integral method. To solve this problem, based on the approximate equivalence of the fundamental component of a high-frequency link decomposed by Fourier series, an optimal fundamental modulation strategy is proposed, which takes the fundamental reactive power as the objective of optimization. The trajectories for each of the electrical parameters are analyzed intuitively through a vector diagram of the phasor. A practical optimal control strategy scheme for engineering is obtained. Finally, the effectiveness of the theoretical analysis and the proposed method are verified by experimental results.

Control Strategy for Bidirectional DC-DC Converter Based on Cascade Connection of LC Filter and DAB Converter

Zhu Zhichao,Xiao Fei,Liu Jilong,Chen Peng,Ren Qiang,Huang Zhaojie 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.3

The dual active bridge (DAB) DC-DC converter has broad prospects for use, for example, energy-storage systems, electric vehicles, and DC distribution network. To improve the quality of bus current, researchers often cascade fi lter inductors to the DC port of DAB converter. If so, the system may be instable and oscillate because the converter is turned into a cascaded structure of LC fi lter and DAB converter. In addition, it is found that the output current is used as the feedback variable for closed-loop control in bidirectional transmission, which will increase the number of sensors. And, the current of the energy storage unit (ESU) cannot be directly controlled when the ESU discharges. To solve these problem, this paper proposes a control strategy based on notch fi lter (NF) regulator. Regardless of whether power fl ows in the forward or reverse direction, the fi lter inductor current is always regarded as control objectives. For this purpose, NF regulator is introduced into the forward path of the current loop to suppress the oscillation of the LC fi lter inductor current. Finally, the eff ectiveness of the theoretical analysis and proposed strategy are verifi ed by simulations and experiments.