Heng Lin

To adapt to harsh engineering environments, the use of structural components with fiber-reinforced polymer (FRP) grid-reinforced ultra-high-performance concrete (UHPC) is considered a new development trend. Twelve FRP grid-reinforced UHPC I-beams are fabricated to investigate the effects of the thicknesses of FRP grids (0 mm, 1 mm, 3 mm, and 5 mm) and the steel fiber contents of UHPC (0%, 1%, and 2%) on their flexural performance. Four-point bending tests are conducted to obtain the failure modes, load-deflection characteristics, and strain responses of each testing beam, and a simplified calculation method for cracking loading and flexural bearing capacity is proposed. The results reveal that the increase in FRP grid thickness, the ultimate load bearing capacity of FRP grid-reinforced UHPC structural beams increases and the ductility also can be enhanced. The presence of steel fiber effectively inhibits the cracking and increases the first cracking load of the beam during the test process, although its influence on the ultimate bearing capacity is limited. Besides, until to the cracking stage, there is no noticeable change in the tensile strain of the FRP grids as the applied load increases. It has been used to simplify theoretical calculations, which shows good agreement with the experimental results.

Submerged floating tunnel (SFT) is an innovative traffic structure for crossing long waterway or deep straits. To investigate the hydrodynamic pressure acting on the SFT under coaction of seismic SV wave and ocean wave, a theoretical model is developed for considering the effect of marine sediment. According to the displacement potential functions and linear wave theory, the reflection and refraction coefficients of wave action in different media are derived. Numerical examples are illustrated to analyze the hydrodynamic pressure distribution. The results show that the hydrodynamic pressure has a spatial difference along the SFT longitudinal direction when the structure operating in the water subjects different incident phase ocean wave. Wave incidence frequency not only changes the loading action mode but also affects the amplitude of the hydrodynamic pressure. Besides, due to the ocean wave loading combined, the effect of saturation on the hydrodynamic pressure load on the structure is not obvious. And the dense arrangement of tethers is recommended to the structure construction.

Submerged floating tunnel (SFT) is an innovative underwater structure for crossing long straits, which withstands the effects of water wave and current throughout its lifecycle. This paper proposes a theoretical approach to investigate the nonlinear dynamic response of the SFT tube-cable system under combined parametric excitation and hydrodynamic forcing excitations (i.e., wave and vortex-induced loading). Firstly, the governing equations of the SFT system considering the coupled degrees of freedom in the tube and cable are established based on the Hamilton principle and are solved numerically. Then, several representative cases are analyzed to reveal the dynamic characteristics of the SFT. Finally, some key parameters are discussed, such as the wave and current conditions and the structural parameters. The results show that when the flow velocity reaches a certain value, the vortex-induced vibration (VIV) of the anchor-cables will excite a strong resonance in the structure. The displacement amplitude of the SFT increases with the increase of the wave height. Gravity-buoyance ratio (GBR) of the tube and the inclined mooring angle (IMA) of the cables jointly determine the natural vibration frequency of the SFT. The influence of the wave force on the tube is limited when the installation depth of SFT is more than 40 m.