コンクリート下路箱げた鉄道橋の設計法に関する研究
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概要
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Prestressed concrete through box girder bridges were constructed as snowshed structures in the moutainous regions of heavy snow and snowslide on the Jyoetsu Shinkansen. The new-type box girder is different from the conventional one of deck type in the following points : (1) it has a large cross section of about lO m by lOm for its short span ranging from 15m to 45m, resulting in its span-depth ratio and span-width ratio less than 4.5; (2) there is no diaphragm fitted inside the cell. An experimental study has been conducted on a reinforced concrete model with a span-depth ratio of about 3,but it has not established the design method of the structure yet. This paper presents the design method of concrete through box girder railway bridges which is chiefly based on the experimental results of acrylic resin models. Chapter 1 presents the introduction, the discussion on the theories of concrete box girders and past studies, and the objective and scope of this study. Chapter 2 presents the outline of the tests conducted on the 1/40-scale acrylic resin models and the discussions on the elastic behavior of the through box girders under the action of vertical or lateral loads and on the applicability of various theories. Among the test results, those which were described in the Proceedings of the Faculty of Engineering (Tokai University) Vol.26 (1986) No.2,are omitted here, and the distribution of principal stresses in web, the effect of support condition (point support or continuous support), local stresses near supports in bottom slab and the applicability of deep beam theory (Schleeh's method) are discussed. Chapter 3 presents a practical design method of the concrete through box girder railway bridges which is based on the test results. The test results agreed well with the theoretical values calculated by the finite element method, but this method does not give satisfactory results for the longitudinal tensile stresses at bottom of web and for the local stresses near the supports and the loading points. In order to obtain satisfactory results by the method, it is necessary to divide the elements more finely near the supports as well as the loading points and to carry out the three-dimensional analysis near the bottom of web. It seemed to be time-consuming and expensive to adopt the method in the practical design, so that a practical design method based on the simplest 'ordinary method' was adopted. According to this method, each bridge is firstly analyzed as a box-section beam in the longitudinal direction and as a rigid frame simply supported under the webs in the transverse direction. Secondly, in the longitudinal design, deep-beam stresses are added to the in-plane stresses in the webs within the range of about the girder depth from the supports; out-of-plane stresses due to the longitudinal moments are also considered for each plate composing a box girder. After examining how to calculate the effective widths of top and bottom flanges in the beam theory, the deep-beam stresses in the webs, the longitudinal effective width in the frame analysis and the longitudinal moments of each plate, the author proposes a practical design method of prestressed concrete through box girder railway bridges. Chapter 4 deals with two types of prestressed concrete through box girder bridges designed by the method proposed in Chapter 3. Chapter 5 summarizes the discussions on the test results and the practical design method.
- 東海大学の論文