Experimental and Numerical Studies on the Mechanical Performance of a Wall-beam-strut Joint with Mechanical Couplers for Prefabricated Underground Construction

Tingjin Liu,Jiandong Lu,Hongyuan Liu 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.5

This paper investigates the nonlinear behavior of wall-beam-strut joints with mechanical couplers, which are proposed for prefabricated underground constructions, under monotonic and cyclic loading conditions using full-scale experimental tests and three-dimensional finite element modelings. The nonlinear behavior of the joint is discussed in terms of the load–displacement curves, concrete cracking distributions, and strains in the reinforcements obtained from both the experimental tests and the numerical modeling. The comparison indicates that the trends of both load–displacement curves are similar, although the cracking, yield and ultimate loads of the joints determined by the numerical modeling are 2.5% lower, 2.6% higher and 3.8% higher, respectively, than those determined by the experimental tests. The numerical simulation can capture the concrete cracking process in the joint in the early loading stage but cannot accurately model the crack distribution in later stages. Moreover, the reinforcement strains and the skeleton curve from the numerical modeling show the same tendency as those from the experimental test, but it is difficult to compare their exact values, especially after yielding. The differences are believed due to the fact that the numerical modeling idealizes the materials and fails to model the slippage between the reinforcements and concrete after the concrete cracking. On the basis of the experimental and numerical investigations, it is concluded that the proposed wall-beam-strut joint has not only an ultimate bearing capacity that is at least 3 times higher than the design load but also a good ductility. Therefore, the design of the wall-beam-strut joint satisfies the requirements for the prefabricated underground construction.

Experimental Investigation of the Mechanical Behaviour of Wall-Beam-Strut Joints for Prefabricated Underground Construction

Tingjin Liu,Jiandong Lu,Di Wang,Hongyuan Liu 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.1

Prefabricated construction is becoming increasingly prevalent, however, it is rarely applied in underground constructions, except for tunnel linings, due to the difficulties that arise in jointing various prefabricated components in underground conditions. To solve the vertical location problem of embedded mechanical couplers during the construction of wall–beam–strut joints for a prefabricated metro station, a new connection using welded steel plates is proposed. In this paper, four full-scale specimens of wall–beam–strut joints connected using welded steel plates and mechanical couplers were experimentally tested under monotonic and low-reversed cyclic loading conditions. The testing results were analysed in terms of the ultimate bearing capacity, failure mode, hysteresis, skeleton curve, stiffness degradation, energy dissipation and strain of the reinforcement bars. Notably, the two kinds of joints had similar ultimate bearing capacities and failure modes, but the crack distributions on the tops of the waler beams were different. For the specimens with the welded steel plate connection, tensile horizontal cracks first appeared on the top surface of the beam, where the welded steel plate was located, and then coalesced gradually; however, this cracking pattern was not observed during the experimental test of the specimens connected with the mechanical couplers. Furthermore, it was determined that the energy dissipation and ductility of the welded steel plate connection were better than those of the mechanical coupler connected joint, because the steel plate could redistribute the internal force in the joint and increase the stiffness. It was concluded that the proposed welded steel plate connection could be more favourable than the mechanical coupler connection in the construction of a prefabricated metro station in Guangzhou. Moreover, the results obtained from these experiments could provide guidelines for the corresponding connections employed in underground-prefabricated structures.

Experimental Study on the Longitudinal Mechanical Behavior of Shield Tunnel in Soft-Hard Uneven Strata and the Reinforcement Effect of Longitudinal Channel Steel

Tingjin Liu,Shuyi Zhang,Yongfeng Tang,Zhenwei Ye 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.1

This paper investigates the longitudinal behavior and failure pattern of shield tunnel, as well as the reinforcement mechanism of longitudinal channel steel, using reduced-scale tunnel models assembled with 24 lining rings. The longitudinal behavior of the shield tunnel and the reinforcement effect are discussed in terms of vertical deformation, joint deformation, and concrete cracking. The results indicate that the shield tunnel without reinforcement longitudinallydeforms in a “bending and dislocation” mode, with the failure pattern dominated by bending deformation. In contrast, the failure pattern of the shield tunnel reinforced by channel steels is characterized by brittle shearing dislocation fracture of the circumferential joint. The load at which damage occurs in the reinforced tunnel model is 1.74 times and 2.04 times that of the non-reinforced staggered and straight jointed tunnels. The reinforcement reduces the horizontal convergence discrepancy of lining rings above the soft foundation spring and the adjacent lining rings, which improves the overall integrity of the tunnel structure.

Tunnel Lining Segment Deformation and Cracking Mechanisms during Tunneling in Complex Mixed Grounds with the Combined Mining and Shield Tunneling Method

Tingjin Liu,Shuyi Zhang,Kepeng Yu,Hongyuan Liu 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.1

The combined mining and shield tunneling method solves the challenge that shield machine is slow to excavate hard rock formations during tunneling in complex mixed grounds such as soft soils mixed with hard rocks, which, however, causes the deformation and cracking of tunnel segments. Both in-situ field measurements and three-dimensional numerical simulations are conducted in this study to analyze the segment deformation and cracking mechanism of a tunnel excavated in complex mix grounds with the combined mining and shield tunneling method. It is concluded that the segment deformation and cracking are caused by insufficient pea-gravel fillings and uneven grouting pressures. To ensure the tunnel ovality satisfying standards and minimize the segment deformation and cracking, the angle range of the tunnel wrapped in the pea gravel should be greater than 180° and the resistance coefficient provided by the filling layer after grouting should be greater than 20 MPa/m. Moreover, it is found that the difference between the grouting pressures at the top and bottom of the tunnel has a significant impact on the overall deformation and opening amount of the joints between the segments.

Developmental Hypothyroidism Influences the Development of the Entorhinal-Dentate Gyrus Pathway of Rat Offspring

Ting Jin,Ranran Wang,Shiqiao Peng,Xin Liu,Hanyi Zhang,Xue He,Weiping Teng,Xiaochun Teng 대한내분비학회 2022 Endocrinology and metabolism Vol.37 No.2

Background: Developmental hypothyroidism impairs learning and memory in offspring, which depend on extensive neuronal circuits in the entorhinal cortex, together with the hippocampus and neocortex. The entorhinal-dentate gyrus pathway is the main entrance of memory circuits. We investigated whether developmental hypothyroidism impaired the morphological development of theentorhinal-dentate gyrus pathway. Methods: We examined the structure and function of the entorhinal-dentate gyrus pathway in response to developmental hypothyroidism induced using 2-mercapto-1-methylimidazole. Results: 1,1´-Dioctadecyl-3,3,3´,3´-tetramethylindocarbocyanine perchlorate tract tracing indicated that entorhinal axons showeddelayed growth in reaching the outer molecular layer of the dentate gyrus at postnatal days 2 and 4 in hypothyroid conditions. Theproportion of fibers in the outer molecular layer was significantly smaller in the hypothyroid group than in the euthyroid group atpostnatal day 4. At postnatal day 10, the pathway showed a layer-specific distribution in the outer molecular layer, similar to the euthyroid group. However, the projected area of entorhinal axons was smaller in the hypothyroid group than in the euthyroid group. Anelectrophysiological examination showed that hypothyroidism impaired the long-term potentiation of the perforant and the cornuammonis 3–cornu ammonis 1 pathways. Many repulsive axon guidance molecules were involved in the formation of the entorhinaldentate gyrus pathway. The hypothyroid group had higher levels of erythropoietin-producing hepatocyte ligand A3 and semaphorin3A than the euthyroid group. Conclusion: We demonstrated that developmental hypothyroidism might influence the development of the entorhinal-dentate gyruspathway, contributing to impaired long-term potentiation. These findings improve our understanding of neural mechanisms formemory function.