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Study on Connection of Crossbeams in Rationalized Plate-Girder Bridges

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Study on Connection of Crossbeams in Rationalized Plate-Girder Bridges NIPPON STEEL TECHNICAL REPORT No. 87 JANUARY 2003 UDC 624 . 2 Study on Connection of Crossbeams in Rationalized Plate-Girder Bridges Nobuaki SAKURAI*1 Kouichi NAKAMURA*1 Atsuo OOTAKE*1 Yuuzou OKAMOTO*1 Abstract In Japan, many rationalized plate girders are constructed for the new Toumei/ Meishin Expressway Project and for others. They reduce the number of main gird- ers, using pre-stressed-concrete-slabs. The bending moment of the slabs, accord- ingly, is increased. Additionally, their reductions of diagonals and laterals cause stress concentration on the connection of cross-beams. Nippon Steel pursued ana- lytic studies and experiments on real bridges, in several projects contracted with Japan Highway Public Corp et al. garding the design of the joint yet. 1. Introduction Since 1999 Nippon Steel Corporation has been awarded construc- In rationalized plate-girder bridges (see Fig. 1), the span of floor tion orders of rationalized plate-girder bridges, from Takahari Via- slab support is made longer than conventional bridges (see Fig. 2) duct of Higashi-Meihan Expressway to Sakae Viaduct, which is now thanks to the application of pre-stressed concrete floor slabs and other in the fabrication stage. During the period, the company has focused technologies, which leads to a larger bending moment in the direc- attention on the issue of the joint design, and through analyses, meas- tion of the floor span. Further, since lateral and diagonal bracings urements on real bridges and so forth, carried out a series of studies are omitted, a floor slab works as a main load distribution member regarding the design of the connection of a crossbeam with a main not only for normal traffic loads but also for lateral loads caused by girder in the rationalized plate-girder bridges. This paper reports the winds and earthquakes. results of the studies. For this reason, the joint of a girder with a floor slab is important; Japan Highway Public Corp., in its design guideline, instructs con- 2. Past Studies structors to verify the tensile force on the joint in the design of shear- Among various study reports, Ohgaki et al. presented a paper on connectors, even in the case of a non-composite girder1). However, analyses and tests2,3), paying attention to the studs and vertical stiff- although various study reports have been presented from various re- eners at the connection of the crossbeam, and there is a report of a search/design institutes, no unified philosophy has been formed re- loading test carried out on Hibakaridaira Bridge4). The results of these reports are essentially as follows. · When studs are arranged immediately above a vertical stiffener to which an intermediate crossbeam (a crossbeam between piers) is connected, a large axial force is imposed on the studs and stress concentration occurs at the upper end of the vertical stiffener, and as a result, fatigue problems may occur. · When studs are not arranged immediately above such a vertical Fig. 1 Rationalized plate-girder Fig. 2 Conventional bridge stiffener, the axial force on the studs is relaxed, but on the other bridge hand, a large bending stress is imposed on the upper flange of the *1 Civil Engineering & Marine Construction Division - 75 - NIPPON STEEL TECHNICAL REPORT No. 87 JANUARY 2003 main girder and what is more, separation of the floor slab from the the above analysis. The bending and shearing composite stress on main girder or cracks between them may take place when the floor the studs was verified referring to the study of Hiraki et al.5) slab cannot follow deformation of the upper flange. · An X-shape section comprising a triangle rib, a main girder web Observations obtained through other studies are basically the and a vertical stiffener was examined as a member subjected to an same, despite the fact that numerical data are different to some ex- axial force and a bending force. Also examined was the bearing tent depending on conditions, such as the floor slab construction stress of the floor slab to which the X-shape section was to be sub- method (pre-cast or cast-in-place) and its structure (composite or jected. non-composite). The construction work of the Viaduct was completed in June 2002. No cracks have been found near the upper end of the vertical stiffen- 3. Nippon Steel’s Activities ers at the connections of crossbeams, and the structure is performing In the above situation, Nippon Steel took measures and conducted well. analyses and loading tests on real bridges as described hereinafter. 3.2 Nobuno viaduct 3.1 Takabari viaduct Nobuno viaduct is a continuous non-composite two plate-girder Takabari Viaduct is a continuous non-composite two plate-girder bridge having cast-in-place PC floor slabs, located in the western bridge having pre-cast PC floor slabs, located in an eastern suburb of part of Shimane Prefecture forming a part of Cross-Chugoku Ex- Nagoya forming a part of Higashi-Meihan Expressway (between pressway, and its order was placed by Matsue Construction Office of Osaka and Nagoya), and its order was placed by Higashi-Nagoya Japan Highway Public Corp. In this bridge, the triangle ribs intro- Construction Office of Japan Highway Public Corp. In this bridge, duced in Takahari Viaduct were arranged also on both the sides of studs were arranged immediately above a vertical stiffener to which the vertical stiffeners for the purpose of relaxing the bending stress an intermediate crossbeam was connected and, in addition, for the on the main girder upper flange (see Fig. 5). Usefulness of these purpose of relaxing the stress on the vertical stiffener, stiffening ribs triangle ribs was confirmed through an analysis by the three-dimen- called triangle ribs (see Fig. 3) were fitted to the upper flange and sional finite element method (FEM), and the result of the analysis web of main girders. The design of the portion is explained below. was verified through measurements on the real bridge. · An analysis was made on a frame (rahmen) model consisting of 3.2.1 Analysis by three-dimensional FEM main girders, a floor slab and crossbeams on two cases: Case-1 in The model for the three-dimensional FEM analysis was defined which live loads were imposed on the extended portions of a floor as shown in Figs. 6 and 7 to cover the entire bridge. The floor slab, slab and Case-2 in which live loads were imposed on the center of main girder webs, their flanges, crossbeam above a pier, vertical stiff- the floor slab support span (see Fig. 4). eners and triangle ribs were regarded as shell elements in the model, · The arrangement and number of the studs were determined based and all the other members as beam elements. Two cases, with and on the stress resultant (M: bending moment, S: shearing force, N: without the triangle ribs, were analyzed so as to evaluate their ef- axial force) at the upper end of the main girder web obtained from fects, and these two cases were combined with a case with a dead 55 55 200 55 55 load and another with a live load. Figs. 8 to 11 show the results of the analysis. The figures show the force in the axial direction of the studs, from the position of an Stud 250 intermediate crossbeam (shown as 0 m) to the center of the distance Upper flange to an adjacent crossbeam. The analysis made it clear that the tri- 350 23 300 50 Vertical stiffener Triangle rib Triangle rib 350 16 350 (mm) 370 320 Fig. 3 Connection of intermediate crossbeam Outside face of (mm) Inside face of main girder main girder 1) Dead load + Live load (Case 1) Concrete barrier curb P PPPPaving Concrete C24 C24 Noise barrier Haunch Haunch barrier curb Floor slab Fig. 5 Detail of upper end of vertical stiffener at crossbeam connection Floor slab (shell element) 12 4 5678910 11 12 13 14 1618 3 1517 Member 101Member Member 102 310 Upper flange dummy member (beam element) 95 19 20 Upper flange (beam element) 100kN × 1.333 = 133.3kN Web (shell element) 3,000 3,000 250 2) Dead load + Live load (Case 2) Concrete barrier Lower flange (beam element) curb PPPaving P P Concrete barrier curb Noise barrie HaunchFloor slab Haunch Upper flange (beam element) Web (shell element) 12 4 5678910 11 12 13 14 1618 Crossbeam near vertical stiffener (stiff member) 3 1517 Intermediate crossbeam (beam element) 101Member Member 102 Crossbeam near vertical stiffener (stiff member) 19 20 Lower flange (beam element) 100kN × 1.333 = 133.3kN Fig. 4 Frame (rahmen) model Fig. 6 Analysis model (1) - 76 - NIPPON STEEL TECHNICAL REPORT No. 87 JANUARY 2003 Inc: 0 Time: 0.000e+00 Z X Y rib-death.dat 1 Fig. 7 Analysis model (2) 50 48.52 Between girders 40 Center 30 Outside girders Fig. 12Stress on vertical stiffener (without triangle ribs, under dead 20 load) 10 6.26 –0.68 2.46 1.69 0.61 0 –0.95 –0.98 –5.57 –0.25 –7.72 –11.85 –6.47 –10 –9.2 –17.31 –14.35 Axial force (kN) –20 –24.29 –19.99 –30 –40 –50 012345 Distance from crossbeam (m) Fig. 8 Axial force on studs (without triangle ribs, under dead load) 50 Between girders 40 34.91 Center 30 Outside girders 20 10 5.01 1.41 1.32 0.88 –5.65 0 –1.7 –5.39 –0.74 –6.83 –2.77 –10.54 –10 –6.45 –12.46 –13.34 –9.47 Fig. 13 Stress on vertical stiffener (with triangle ribs, under dead load) Axial force (kN) –20 –19.77 –19.9 –30 angle ribs reduced the force in the axial direction of studs and the –40 fluctuation of the axial force by 30% or so.
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