| Structural Analysis of the Minami Bisan-Seto bridge( Suspension Bridge ) |
| 1. Author's investigations: other proceedings of JSCE annual meetings and papers edited by the corporation are omitted. |
| (1) Y. Hayashi, "Cable Analysis by Finite Deflection and Reduction Method (Japanese) ", Proceedings of 25th JSCE Annual Meeting, 1970.10.; Y. Hayashi, H. Kamikubo, "Cable Analysis by Finite Deflection and Reduction Method (Japanese) ", JSSC 5th Matrix Structural Analysis Symposium,1971. |
| This time was a period of development in the world of computers. Structural analyses by stiffness equations needed large computer capacity. I wanted a method which enabled structural analysis for suspension bridges with only a small computer capacity. I formulated one method for a cable structural analysis which utilized the reduction method and the Newton-Raphson method for a cable deformation problem. |
| (2) Y. Hayashi, " Analysis of Suspension Bridges (Japanese)", Bridges and Foundations, Vol.7, No.10, 1973, A technical journal. |
| Global investigations for structural analyses of the super-structures of suspension bridges, such as tower rigidity, torsional behavior of stiffening trusses, finite deformation theories including Japanese original investigations, before the construction of the Honshu-Shikoku root bridges, are described here. |
| (3) Y. Hayashi, M. Yasuda. T. Shinke, "Analysis and Estimation of the Secondary Stress in Parallel Wire Suspension Cables( English)", Proceedings of the Symposium on Analytical problems for Design of Structures.1973.11. |
| (4) Y. Hayashi, K. Higuchi, Y. Tanaka, "Three Dimensional Analysis of Truss Girders by the Thin Walled Elastic Beam Theory Considering Cross-Sectional Deformations (Japanese), (English synopsis is shown)", Transactions of JSCE,1976.5., |
| The Seto Ohashi suspension bridges have a four-lane highway over the stiffening trusses and 4 railway tracks (2 railway loads including the Shinkansen are loaded simultaneously) through the cross section of the trusses. The live loads are very large. A continuous stiffening truss type was adopted for railway trafficability. We have many earthquakes and typhoons in Japan. In these conditions, the torsional live loads effect for the strains of truss members and cross-sectional deformation of the bridge became important. Note that computer capacity was not so large in those days. Analytical methods to resolve such problems were desired. The author attempted to use a thin walled elastic beam theory to analyze the torsional load problem for trusses. A structural analysis method for a folded thin walled elastic beam was developed. The effectiveness of the theory was examined for a simple folded truss bridge model. |
| Minami Bisan-Seto Bridge |
| (5) Y. Hayashi, K.Tada, "Static Mechanism of a Cable Friction Type Splay Saddle", Proceedings of 31st JSCE Annual Meeting, 1976. |
| My revered senior associate at work in the Honshu Shikoku Bridge Authority, the late Takeshi Nakayama first contrived a basic principle of a cable friction type splay saddle on a tower top. I formulated its static mechanism equations. |
| (6) Y. Hayashi, "Linearized Finite Deformation Theory in Suspension Bridges( English)", Proc. of JSCE., No.257, Jan. 1977. |
| We have had the famous deflection theory called Mellan's equation as an analytical theory for suspension bridges. In those days when my paper was written, large deformation analysis methods with computers began to develop. The relationship between the deflection theory and the large deformation analysis methods are discussed in this paper. |
| (7) Y. Hayashi, M. Murata, "Torsional Oscillation Analysis of Suspension Bridges by a Displacement Method( English)", Trans. of JSCE., NO.258, Feb. 1977. |
| The method developed in the reference (4) was applied to a torsional, dynamic, structural analysis for suspension bridges. By this method, torsional, dynamic analysis of a suspension bridge, even at an erection stage, became possible. |
| (8) Y. Hayashi, Y. Tanaka, K. Higuchi, "Three Dimensional Oscillation Analysis of Truss Girders by the Thin Walled Elastic Beam Theory Considering Cross-Sectional Deformations (Japanese)", Transactions of JSCE,1977.5. |
| As described in the reference (4) , cross sectional deformation behavior of truss bridges at an earthquake( when trains might run) was important. Through a theory developed in this paper, the above-mentioned problem was investigated for the planned Seto truss bridges . |
| (9)Response of a Structure Subjected to
Two Inputs (Japanese), Mar. 1969.
http://repository.dl.itc.u-tokyo.ac.jp/dspace/bitstream/2261/32141/1/sk021003004.pdf |
| 2. Structural Design |
| (1) The Minami (South) Bisan Seto (strait) Bridge and the Kita (North ) Bisan Seto Bridge have one anchorage (center anchorage), at the center of them, which connect both cable tensions, and transmit the forces to the earth. One cable of the Minami Bisan Seto Bridge cable, per one side, consists of 271 parallel wire strands, each of which is fabricated with 127 wires (5.12φ/1-piece). The maximum tension of the Minami Bisan Seto Bridge is about 43,600t / one side of bridge. The center span of the Kita Bisan Seto Bridge is smaller than that of the former bridge, so both cable tensions are different from each other. We could not make both side span cable angles horizontal because of the substructure positions. Therefore, the center anchorage is forced to have both large horizontal shear force and an uplift force by the two side cables. |
| Several structural design plans for the center anchorage had remained to be examined when I participated in the new super-structure design section for the bridges over the Seto-Strait. We selected two plans. One plan was a triangle-plates type and another was a cable-crossing in the air type. The triangle plates type is as follows: some required triangle plates are put and set in the center of the anchorage; each plate is reinforced by rib members; at both upper edges of a triangle plate, the strands are anchored from the both cable sides; the bottom of the triangle plate is vertically pulled down and anchored by pre-stressed steel bars from the bottom of the anchorage. The difficulties in the plan were how we would design the triangle plate bottoms( a friction problem at a static or a dynamic condition) and whether we could assure the pre-stressed structure in the climate of the sea. |
| The cable crossing type is shown in the next figure. At the end of one strand, an anchoring socket is set. The biggest difficulty was how we could handle and set a strand at the air crossing part of the strands. In the area of the crossing part, the clearance between the strands are very small, so a worker can't approach the crossing part. Disposition of the strands would be very complicated. The advantage was that it was difficult to destroy the anchorage by cable tensions even under a dynamic condition, or after a long period of concrete degradation, because the tensions would be changed into compressive forces in the concrete body. I wanted a durable structure for 200 years in the climate of the sea. |
| I considered that we might possibly handle and anchor the strand sockets to anchor frames with a specially made hydraulic crane. A junior associate at work, Mr. Yukio Hukui, presented the idea that we could vertically separate strands into some vertical groups of strands for one cable, and anchor each group of the strands of both side cables to an anchor frame vertically and alternately. This center anchorage, in which the cable crossing type plan was adopted, was really constructed when I had already left the Honshu-Shikoku Bridge Authority. Now when I see a same type center-anchorage at the Kurushima bridges, it fills me with deep emotion. By the way, another anchorage( BB7A), in the sea, of the Minami Bisan Seto Bridge has a unique shape. This resulted naturally from a pursuit process of structural consideration for bedrock stresses at the end of the anchorage. |
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Reference: Y. Hayashi, Y. Hukui, S. Tsuyama, T. Sugita, "Strands erection method of suspension bridge cables", Japanese patent No.1302592, 14/2/1986. |
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Center anchorage |
| Last updated: 19/10/2004 |
| Structural analysis of the Minami Bisan-Seto bridge | |||
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