410 research outputs found

    Analytical and Experimental Study of Horizontally Curved Steel Bridge Girders with Tubular Top Flanges

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    The use of steel I-shaped girders with tubular flanges (i.e., tubular flange girders or TFGs) has been proposed for curved highway bridges. Compared with conventional steel plate I-shaped girders (IGs), TFGs have substantially greater torsional stiffness and strength, which improves significantly the behavior of an individual curved TFG compared with a corresponding IG. One type of TFG with a rectangular tube as the top flange and a flat plate as the bottom flange (i.e., the TFG1 section) is studied in this research. Compared to the previously studied TFG with rectangular tubes as the top and bottom flanges (i.e., the TFG2 section), a TFG1 has the advantage of avoiding the need for concrete infill or an internal steel diaphragm in the tubular bottom flange at the bearings, but still has sufficient torsional stiffness and strength to perform well as a curved bridge girder. This research focuses on developing and validating the use of TFG1s for curved highway bridges.Simplified FE models for curved TFG1 bridges are developed for use in the design of these bridges. Detailed FE models are developed for use in validating the simplified FE models and in verifying that the response of curved TFG1 bridges to various loading conditions is as intended. Design guidelines for curved TFG1 bridges are presented. Eight curved TFG1 bridges are designed. Detailed FE models of these bridges are used to evaluate the effectiveness of the design guidelines. The results show that the design guidelines can be used to safely design curved TFG1 bridge systems. In addition, comparisons between curved TFG2 bridges and curved TFG1 bridges are made. A comprehensive study of the response of curved TFG1 bridge systems compared with corresponding curved IG bridge systems is conducted. All comparisons are based on bridges that satisfy the current U.S. design recommendations for steel curved highway bridge girders. A parametric study is conducted, where the parameters of the bridges that were varied include the span length, the horizontal curvature, number of interior cross frames, and other factors. 28 different curved TFG1 bridges were designed. These bridges were used with detailed FE models in a study of the effectiveness of the design guidelines. Again, the results show that the design guidelines can be used to safely design curved TFG1 bridge systems. The results comparing TFG1 systems with IG systems show that curved TFG1 bridge systems have more efficient (lighter) girder cross sections and/or require fewer interior cross frames than corresponding IG systems.Detailing of cross frames for curved TFG1 bridges is studied. Conventional no load fit (NLF), steel dead load fit (SDLF), total dead load fit (TDLF) detailing methods were studied. In addition, two new detailing methods for curved TFG1 bridges, individual steel dead load fit (ISDLF) and remaining dead load fit (RDLF) were studied. The responses of example bridges with different detailing methods are compared, and appropriate detailing methods for curved TFG1 bridges are recommended. ISDLF detailing is recommended for cross frames of curved TFG1 bridges with a short span (90 ft or less). For longer span bridges, NLF detailing is recommended. A two-thirds scale two-girder test specimen and corresponding full size bridge was designed using the design recommendations. The test specimen was fabricated and erected. The procedure to erect and assemble the test specimen was studied. Detailed FE models were used to simulate the assembly of the test specimen and the results were compared with test data. The observations and analyses show that it is feasible to install the interior diaphragms as the individual curved TFG1s carry their own weight across the span without shoring or other temporary supports within the span.The test specimen was tested up to and beyond the maximum load capacity. An updated FE model, including accurate material properties, geometric imperfections, and test boundary conditions, was used to analyze the test specimen and make comparisons with the test data. The FE results and test data show that the design recommendations can be used to safely design curved TFG1 bridges for construction conditions. The close agreement of the FE results with the test data indicates that the FE models can be used to accurately predicate the response of curved TFG1 bridges

    When Leibniz Bialgebras are Nijenhuis?

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    Leibniz algebras can be seen as a "non-commutative" analogue of Lie algebras. Nijenhuis operators on Leibniz algebras introduced by Cari\~{n}ena, Grabowski, and Marmo in [J. Phys. A: Math. Gen. 37(2004)] are (1, 1)-tensors with vanishing Nijenhuis torsion. Recently triangular Leibniz bialgebras were introduced by Tang and Sheng in [J. Noncommut. Geom. 16(2022)] via the twisting theory of twilled Leibniz algebras. In this paper we find that Leibniz algebras are very closely related to Nijenhuis operators, and prove that a triangular symplectic Leibniz bialgebra together with a dual triangular structure must possess Nijenhuis operators, which makes it possible to study Nijehhuis geometry from the perspective of Leibniz algebras. At the same time, we regain the classical Leibniz Yang-Baxter equation by using the tensor form of classical rr-matrics. At last we give the classification of triangular Leibniz bialgebras of low dimensions

    Research of Evolution Mechanism of Network Group Event Based on Grounded Theory under Micro-Blog Platform

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    Abstract At this stage, China society in conflict-prone period, the network group events developed rapidly. Network group events had a significant impact on society. The trend which the online group event evolved into the offline group incidents is becoming evident. In this paper, we used grounded theory to study the evolution and the development process of network group events under the micro-blog platform. We present an evolution mechanism model of network group event under micro-blog platform and find the formation mechanism of the network of public opinion, intrinsic motivation and the evolution of the network group events

    Spatial performance of skewed continuous rigid-frame bridges based on finite element analysis

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    Continuous rigid-frame bridges are usually symmetrically designed along the bridge center line for simplicity and clarity purposes. However, the skewed bridges are necessary in case of complex intersections with space constraint in highways. Previous research mainly focuses on the discussion of skewed angle and the interaction between girders and cross frames on I shape section. Box sections are also used for skewed bridge due to large torsion stiffness, which have many problems during service time. This paper analyzed coupled skew and bending effect for the bridge which combines the continuous rigid-frame system and skewed system. For skewed bridges, significant out-of-lane effect occurs in bridges, which is hard to be predicted through linear analysis. For continuous bridges, at the interior supports, negative bending moments exist. In addition, a part of each diaphragm of the bridge is connected to the main girder, and the rest part only carries its self-weight, which makes the girder behavior more complex in the transverse direction. Therefore, the spatial performance of the bridge is very complex. The design cannot only use simple two dimension analysis. In the paper the three dimensional finite element analysis was conducted to find the effect due to dead load, live load, temperature, and brake force to find critical position for monitoring and maintainance. Primary bending normal stress, warping normal stress, coefficient of shearing force lag and stress distribution of consolidation pier were analyzed and output. The behavior of both superstructure and sub structure were investigated. The effect of coupled bending and torsion is significant to the behavior of the bridge. Finally the design recommendations about the skew bridge are given. The critical positions for the further test and monitoring are found

    Generalized Composition Operators from ℬ

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    Let 0<p<∞, let -2<q<∞, and let φ be an analytic self-map of and g∈H(). The boundedness and compactness of generalized composition operators (Cφgf)(z)=∫0z‍f'(φ(ξ))g(ξ)dξ, z∈, f∈H(), from ℬμ (ℬμ,0) spaces to QK,ω(p,q) spaces are investigated

    The Application of Three-Dimensional Collagen-Scaffolds Seeded with Myoblasts to Repair Skeletal Muscle Defects

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    Three-dimensional (3D) engineered tissue constructs are a novel and promising approach to tissue repair and regeneration. 3D tissue constructs have the ability to restore form and function to damaged soft tissue unlike previous methods, such as plastic surgery, which are able to restore only form, leaving the function of the soft tissue often compromised. In this study, we seeded murine myoblasts (C2C12) into a collagen composite scaffold and cultured the scaffold in a roller bottle cell culture system in order to create a 3D tissue graft in vitro. The 3D graft created in vitro was then utilized to investigate muscle tissue repair in vivo. The 3D muscle grafts were implanted into defect sites created in the skeletal muscles in mice. We detected that the scaffolds degraded slowly over time, and muscle healing was improved which was shown by an increased quantity of innervated and vascularized regenerated muscle fibers. Our results suggest that the collagen composite scaffold seeded with myoblasts can create a 3D muscle graft in vitro that can be employed for defect muscle tissue repair in vivo
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