Littérature scientifique sur le sujet « Tapered box girder »

Traditionally, bridge bearings supporting steel trapezoidal box girders (tub girders) consist of fabricator-designed mechanical devices, such as pot or disc bearings, that may be guided or unguided and are expensive to fabricate and place. Performance of these bearings has been mixed: some are maintenance-free and others require significant maintenance, repair, or replacement. In Texas, bridge bearings supporting concrete and steel superstructure types are typically steel-laminated elastomeric bearings that are tapered or have a constant thickness. Recently, the Texas Department of Transportation has used these structurally engineered elastomeric bearings for tub girders in place of mechanically engineered pot or disc bearings. This paper describes the rationale for the application of elastomeric bearings to tub girders and outlines design recommendations that are based on the use of elastomeric bearings for the tub girder direct connectors of the interchange of US-290 and I-35 built in Austin in the late 1990s and placed in service in 2001.

Hefei Xinqiao International Airport Terminal is a steel structure consisting of long-span rigid frames, with 804m in length and about 161m in width at the widest part. The long-span frame consists of box columns, large curvature beams, tapered box beams and space trusses. The joints between space trusses and box beams named truss-to-box beam connections are the critical parts of the whole structure, because of the discontinuity in geometries and stiffness which result in high stress concentrations and complicated mechanical properties. GJ3-6, GJ3-5 and GJ3-1 of the airport terminal are modeled by ABAQUS. Structure internal forces at six load combinations of bearing capacity limit state are calculated. Lower chords of the landside connections sustain large tensions, while web members of the airside connections sustain large pressures. Since these truss bars are directly connected to cover plate of the box beam, better design details are recommended to reduce the stress concentrations caused by geometrical discontinuity.

Boxwoods (Buxus spp.) are common woody ornamental hedging plants in Europe and North America, typically propagated by cuttings. In October 2011, shoot dieback and defoliation was observed on Buxus sempervirens ‘Suffruticosa’ (dwarf English boxwood) and ‘Green Balloon’ in outdoor, 10-cm pots at a wholesale nursery in Chilliwack, British Columbia. Circular leaf spots with black rings occurred on leaves and black, water-soaked, cankers girdled the stems and petioles. Leaf and stem samples were collected on November 21, 2011, and incubated for 48 h in a moist chamber at room temperature. In addition to Volutella buxi, a Cylindrocladium species producing conidia on white sporodochia was observed on host tissue under the microscope. Leaves with lesions were surface-sterilized in 10% bleach for 30 to 60 s, rinsed in sterile water, and lesions were cut out and plated on PDA and carnation leaf media. The species was identified as Cylindrocladium pseudonaviculatum Crous, J.Z. Groenew. & C.F. Hill 2002 by comparison of conidia and phialide morphology to published descriptions. Conidia were hyaline, one-septate, cylindrical with rounded ends and 38 to 76 μm (mean 51 μm) × 4 to 6 μm on carnation leaf media and 41 to 66 μm (mean 52 μm) × 4 to 6 μm on B. sempervirens ‘Suffruticosa’ leaves, comparable to the reported range of 40 to 75 × 4 to 6 μm (1,2,3,4). Conidia were produced in clusters on terminal, ellipsoid vesicles at the tips of penicillate conidiophores. Vesicles were 10.2 (7.6 to 12.8 μm) at the widest point, consistent with the 6 to 11 μm reported in (2,3) and tapered to a rounded point; stipe extensions were septate and measured an average of 130 μm (107 to 163 μm) in length to the tip of the vesicle, consistent with the 95 to 155 μm reported in (1), 89 to 170 μm reported in (2), and 95 to 165 μm in (3). Chlamydospores were not observed on host tissue but appeared in older PDA cultures as dark brown microsclerotia. DNA was extracted from single-spore colonies on PDA and the internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1 and ITS4. The ITS sequence (GenBank Accession No. KC291613) was 100% identical to C. buxicola strain CB-KR001 (HM749646.1) and Calonectria pseudonaviculata strain ATCC MYA-4891 (JX174050.1). In early December 2011, box blight was identified on container-grown B. sinica var. insularis × B. sempervirens ‘Green Velvet,’ ‘Green Gem’, and ‘Green Mountain’ and B. sempervirens L. (common or American boxwood). The pathogen was identified by microscopic examination at three wholesale nurseries in the eastern Fraser Valley and one landscape planting. The isolate has been deposited in the Canadian Collection of Fungal Cultures in Ottawa, Canada (DAOM 242242). References: (1) B. Henricot and A. Culham. Mycologia 94:980, 2002. (2) K. L. Ivors, et al. Plant Dis. 96:1070, 2012. (3) C. Pintos Varela, et al. Plant Dis. 93:670, 2009. (4) M. Saracchi, et al. J. Plant Pathol. 90:581, 2008.

The thesis aims at shedding light on the difference in the stress distribution between prismatic and non-prismatic beams. The approach strategy has being that of drastically simplifying the initial problem in the attempt to identify the relevant governing parameters. The geometry of a real wind turbine blade has been first drastically simplified: from the multi-cellular airfoil to a box girder and to a single web panel. Once solved the simplest problems, the intention has been to gradually reintegrate the complexity of the problem with the aim of applying the obtained results to a real wind turbine blade. The thesis consists of three parts. In the first part some brief information on the technology of wind energy and wind turbines are given. Also, the state of the art of the modeling of non-prismatic beams is discussed, with a particular focus on tapered beams. After some first remarkable results obtained at the beginning of the 20th century, the literature survey shows that only in recent years it has been an increase of interest on the subject. In the second part all the theoretical details that lead to the approach that is subject of the present thesis are deepened. In the third part the results of the application of the strategy proposed to both elementary and more complex geometries are shown, and the final remarks on the 10MW wind turbine blade are discussed.

<p>Bru over Otra is a newly constructed pedestrian bridge located in the Norwegian city of Kristiansand. The bridge has an overall length of 180m and provides a 4m clear width route for both pedestrian and cycle traffic over the Otra River.</p><p>The bridge is made up of six spans (25m+5x32m+25m) with four piers located within the river and one located in a public park. The bridge is curved in plan and elevation, allowing for the change in level between both embankments.</p><p>The deck structure is a multicell continuous steel box girder. The maximum deck depth of 0.9m is constant all long the bridge, although the transversal section is tapered at the edges.</p><p>In the case of the substructure, the challenging conditions related to ice loads and the construction of the foundations and columns inside the river flow were crucial to establish their design.</p>