A New Approach for Free Vibration Analysis of Thin-Walled Box Girder Considering Shear Lag Effect

The thin-walled box girder (T-WBG) is widely applied in the long-span bridge structures during the past decades due to its lighter self-weight and better mechanical properties. The shear lag effect (SLE), an essential aspect of T-WBG which governs the stress and the deformation, is rather necessary to be revealed properly. The extraordinary issue of T-WBG analysis nowadays is the SLE impact on its dynamical response to external load. This paper proposes an improved finite element method (FEM) to obtain the realistic vibration characteristics of the T-WBG considering the SLE by theory analysis and formula derivation. Firstly, based on the classical plate and shell theory as well as beam theory, the T-WBG was divided into shell subunit for the roof and beam subunit for web and floor, respectively. Secondly, a 3-order polynomial which is consistent with the experiment results was adopted as the axial-displacement interpolation function of the roof subunit, whose nodal displacements parameters were also taken as the basic. Thirdly, the nodal displacement parameters of the web subunit and floor subunit were deduced by the basic according to the principle of deflection consistency. It is shown through a numerical example that the proposed method is much more economical to achieve reasonable accuracy than traditional FEM analysis software when dealing with the free vibration problem of the T-WBG considering the SLE. Besides, it is also observed that the natural frequency values considering the SLE have a trend of decreasing markedly in general, and the influence of SLE on higher-order frequency is more significant than on the lower one under the boundary condition of cantilever supported, while a contrary effect under the boundary condition of simple supported

Weathering Process of In Situ Granite and Particle Breakage Characteristics of Compacted Weathered Granite

Quantificationally describing weathering process and characterizing particle breakage are important in predicting the behavior of coarse-grained soil (e.g., weathered granite). In order to comprehensively understand the mechanical properties of weathered granite and provide references for reasonable evaluation of the engineering properties of subgrade filling in mountains, a series of tests—X-ray diffraction, sieving, heavy compaction, large-scale triaxial, and field compaction tests—were carried out in this research. Based on the weathering process parameters (m and r) of in-situ granite samples at two typical sections of weathered granite mountains obtained by using previous grading equation, the mathematical model of weathering process with depth was proposed and the variation laws of weathering process with depth were described. The results show that, with an increase in burying depth of mountain profile (h) of weathered granite, the geological year’s parameter (m) decrease by power function, but the geometric progression constants (r) increase by power function. Some factors affecting the particle breakage properties of compacted weathered granite were evaluated by using relative breakage (Br). Especially, the effect of field compaction condition (such as thickness of loose paving layer and number of vibratory rolling passes) on particle breakage was analyzed creatively. Through laboratory and field tests, it was found that particle gradation, mineral composition, compaction effect, stress level, and number of rolling passes significantly affected the particle breakage characteristics of weathered granite. Furthermore, it is worthy of attention that the weathered granite in this paper showed obvious particle breakage characteristics under weak compaction effect and at low stress levels and over-compaction could result in a decrease in the degree of compaction of a certain thickness of loose paving layer filled with weathered granite. Findings in this research can provide a theoretical basis for evaluating the physical properties and mechanical behavior of weathered granite as subgrade fillings

Dynamic Coupling Analysis of Vehicle-Bridge System for Long-Span Suspension Bridge Based on Backpropagation Neural Network Method

As the suspension bridge structures become more flexible and the forms of the vehicle load become more diverse, the dynamic coupling problem of the vehicle-bridge system has become gradually prominent in long-span suspension bridges, resulting in an increase in accuracy and efficiency requirements for dynamic coupling analysis of the vehicle-bridge system. Conventional method such as finite element method (FEM) for dynamic coupling analysis of vehicle-bridge system often requires separate iteration of vehicle system and bridge system, and the contact and coupling interactions between them are used as the link for convergence inspection, which is too computationally intensive and time-consuming. In addition, the dynamic response of the vehicle-bridge coupling system obtained by FEM cannot be expressed explicitly, which is not convenient for engineering application. To overcome these drawbacks mentioned above, the backpropagation (BP) neural network technology is proposed to the dynamic coupling analysis of the vehicle-bridge system of long-span suspension bridges. Firstly, the BP neural network was used to approximate the dynamic response of the suspension bridge in the vehicle-bridge coupling system, and the complex finite element analysis results were thus explicitly displayed in the form of a mathematical analytical expression. And then the dynamic response of the suspension bridge under vehicle load was obtained by using a dynamic explicit analysis method. It is shown through a numerical example that, compared with FEM, the proposed method is much more economical to achieve reasonable accuracy when dealing with the dynamic coupling problem of the vehicle-bridge system. Finally, an engineering case involving a detailed finite element model of a long-span suspension bridge with a main span of 1688 m is presented to demonstrate the applicability and efficiency under the premise of ensuring the approximation accuracy, which indicates that the proposed method provides a new approach for dynamic coupling analysis of the vehicle-bridge system of long-span suspension bridges

A method for the robustness evaluation of cable-stayed bridges with steel truss girders under different reinforcement cases

Structural robustness, an index for structural geometrical agreement, is used to assess the alternative load paths of structures subjected to loads. Therefore, robustness can be extended to evaluate the robustness of bridges with local failure in individual members. In this work, a method that includes the use of a radar chart is proposed to assess the robustness of cable-stayed bridges by considering the mechanical performance of bridges with local failure in the cables and chords. Four plans regarding the truss girder and cables are designed to reinforce a damaged bridge. The results indicate that these two alternative path plans disperse the stress in the members in the truss girder, and the reduction of alternative path plan 2 (AP2) is greater than that of alternative path plan 1 (AP1). Similarly, the two plans regarding the cables are found to decrease the vertical displacement of the truss girder under gravity, and the reduction of the first plan is slightly greater than that of the second plan. Consequently, the two alternative load path plans improve the indexes of the truss girder, leading to an increase in the value of ''IRob'' to 0.74. Moreover, regarding the truss girder, the two alternative cable plans are used to increase the indexes, and the values are all found to be larger than the corresponding values of the intact cable-stayed bridge. The proposed method including the use of a radar chart, which is associated with several indexes, can be used to assess the structural robustness of intact and damaged bridges, thereby allowing for the development of reinforcement plans

TLR3 Signaling in Macrophages Is Indispensable for the Protective Immunity of Invariant Natural Killer T Cells against Enterovirus 71 Infection

<div><p>Enterovirus 71 (EV71) is the most virulent pathogen among enteroviruses that cause hand, foot and mouth disease in children but rarely in adults. The mechanisms that determine the age-dependent susceptibility remain largely unclear. Here, we found that the paucity of invariant natural killer T (iNKT) cells together with immaturity of the immune system was related to the susceptibility of neonatal mice to EV71 infection. iNKT cells were crucial antiviral effector cells to protect young mice from EV71 infection before their adaptive immune systems were fully mature. EV71 infection led to activation of iNKT cells depending on signaling through TLR3 but not other TLRs. Surprisingly, iNKT cell activation during EV71 infection required TLR3 signaling in macrophages, but not in dendritic cells (DCs). Mechanistically, interleukin (IL)-12 and endogenous CD1d-restricted antigens were both required for full activation of iNKT cells. Furthermore, CD1d-deficiency led to dramatically increased viral loads in central nervous system and more severe disease in EV71-infected mice. Altogether, our results suggest that iNKT cells may be involved in controlling EV71 infection in children when their adaptive immune systems are not fully developed, and also imply that iNKT cells might be an intervention target for treating EV71-infected patients.</p></div

IL-12 and endogenous CD1d antigens are both required for full iNKT cell activation in EV71 infection.

<p>(A) EV71M-infected or-uninfected WT macrophages (Mock) were co-cultured with purified iNKT cells in the presence of neutralizing anti-CD1d (αCD1d), isotype control antibodies (Iso) or medium alone (M). (B) EV71M-infected or –uninfected WT or CD1d-deficient (CD1d^-/-) macrophages were co-cultured with purified iNKT cells. (C) EV71-infected WT macrophages were co-cultured with purified iNKT cells in the presence of the lipid synthesis inhibitor NB-DGJ or medium alone. (D) Seven-day-old WT or CD1d^-/- neonates (n = 3–5) were adoptively transferred with 5×10⁵ purified iNKT cells or saline control intraperitoneally and infected with 2×10⁵ PFU of EV71M. After 16 hours, splenocytes of saline (mock)-treated or EV71M-infected WT or CD1d^-/- mice were stained with TCRβ, CD1d tetramer, CD69 and DAPI. The CD69 MFI levels on iNKT cells are shown. (E) EV71M-infected WT macrophages were co-cultured with purified iNKT cells in the presence of neutralizing anti-IL-12, anti-IL-18 or isotype control antibodies. The IFN-γ concentrations in the 24-hour culture supernatants were quantified by ELISA. (F) The IL-12 (p70) concentrations in the supernatants of WT or TLR3^-/- macrophages infected with 10 MOIs of EV71M. All results represent the mean ± SD. NS, not significant; *, <i>P</i><0.05; **, <i>P</i><0.01. Data are representative of three (A, B, C, E, F) or two (D) independent experiments.</p

TLR3 is indispensable for iNKT cell activation in EV71 infection.

<p>(A) TLR3 signaling is required for IFN-γ production by EV71-infected splenocytes. Splenocytes from WT, TLR3^-/-, TLR7^-/- and MyD88^-/- mice (n = 3–5) were cultured with EV71M or mock for 24 hours, and IFN-γ production was quantified by ELISA. (B) TLR3 deficiency dramatically reduced the IFN-γ production of iNKT cells. Splenocytes from CD1d-deficient or WT C57BL/6 mice (n = 3) were infected with EV71M for 24 hours and then stained with TCRβ, CD1d tetramer and IFN-γ. Splenocytes were stimulated with PMA and ionomycin (PMA/I) or mock treated (mock), which served as positive and negative controls, respectively. IFN-γ-producing cells are shown among CD1d tetramer⁺ TCR⁺-gated cells. (C) iNKT cell activation in EV71 infection is dependent on TLR3 signaling. Macrophages from WT or TLR3^-/- mice were cultured in the presence of EV71M for 24 hours. After extensive washing, macrophages were co-cultured for 48 hours with purified iNKT cells from WT mice, and cytokine production was quantified by ELISA. (D) TLR3 signaling is required for <i>in vivo</i> activation of iNKT cells upon EV71M infection. Six-8 week-old WT or TLR3^-/- mice (n = 3–6) were injected with 1×10⁵ PFU of EV71M or saline intraperitoneally. After 16 hours, splenocytes of mock (PBS) or EV71M-infected WT or TLR3^-/- mice were stained with TCRβ, CD1d tetramer, CD69 and DAPI. The mean fluorescent intensity (MFI) of CD69 expression on iNKT cells is shown. NS, not significant; **, <i>P</i><0.01. (E) TLR3 triggering in macrophages activated iNKT cells. BMDCs or macrophages were cultured with medium alone or pI:C for 24 hours and then co-cultured with purified iNKT cells from WT mice for 48 hours. Cytokine production was quantified by ELISA. All results represent the mean values of cultures of 5 mice ± SD. *, <i>P</i><0.05. (F) The survival rates of 7-day-old wild-type (WT) mice and TLR3-deficient (TLR3^-/-) mice (n = 6, per group) after infection by 1×10⁶ PFU of EV71M. Data are representative of three (A, C, E, F) or two (B. D) independent experiments.</p

CD1d is essential for the protection of young mice from EV71 infection.

<p>Seven-day-old WT and CD1d^-/- mice were infected intraperitoneally with a lower dose (A, 2×10⁴ PFU) or higher dose (B, 2×10⁵ PFU) of EV71M. The clinical score (A) and survival (B, Kaplan-Meier curve) were monitored for the indicated period (n ≥ 10 per group). (C) Kaplan-Meier survival curves for 7-day-old WT and Jα18^-/- mice (n ≥ 5 per group) that were infected intraperitoneally with 2×10⁵ PFU of EV71M. The viral loads in each organ were examined by quantitative PCR on days 2 (D) and 4 (E) after the high dose of EV71M infection. Data are shown as the mean ± SD of three independent samples. NS, not significant; **, <i>P</i><0.01. Data are representative of two independent experiments.</p