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Optimization of Cable System for a Cable-stayed Suspension Bridge using a Simplified Analysis Model

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dc.contributor.advisor고현무-
dc.contributor.author최현석-
dc.date.accessioned2017-07-13T06:42:00Z-
dc.date.available2017-07-13T06:42:00Z-
dc.date.issued2017-02-
dc.identifier.other000000142480-
dc.identifier.urihttps://hdl.handle.net/10371/118754-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 건설환경공학부, 2017. 2. 고현무.-
dc.description.abstractA cable-stayed suspension bridge is a hybrid structural system that is a combination of a cable-stayed bridge and a suspension bridge. In the cable-stayed suspension bridge, the cable-stayed system is generally allocated near pylons to reduce the loads supported by the suspension cables and to improve the stiffness of the bridge. Therefore, the span length can be extended and the structural behavior can be improved. Since the suspension system and the cable-stayed system present different structural behaviors due to the discrepancy in their load carrying path and the structural discontinuity taking place at the border between both systems, the design of the cable system is a complex and time consuming work. Particularly, designers should deal with the design variables of both cable-stayed system and suspension system and analyze various combinations of the variables to secure safety, stability, and economic feasibility. However, there is no generally optimized cable system for such a structural type since a few projects have been just completed in the past century and because of the scarcity of related researches. Accordingly, in this study, an optimization procedure to find an optimal cable system with minimized construction cost of superstructure for a cable-stayed suspension bridge using Genetic Algorithm (GA) is presented, and the optimal cable systems for a roadway bridge and a railway bridge are proposed. The proposed optimal cable system is defined using several design variables including a side span length (Ls), a main span length (Lsp), an overlapping length (Lov), a cable sag (f), and a dead load distribution factor (r). The application of the proposed optimal cable system to the practical design can enhance the efficiency of the design process as well as reduce much time, cost and manpower for numerous iteration works.
Generally, the optimization procedure based on a GA dealing with several design variables necessitates a lot of iteration works mobilizing tremendous time, cost and manpower. This study proposes a new simplified analysis model enabling to analyze efficiently a cable-stayed suspension bridge. The proposed simplified analysis model uses the two-dimensional truss elements for all members, and the cables in the side spans are replaced with an equivalent horizontal cable spring at the pylon top. Through the comparison with FEM analysis using a commercial software, the applicability of the proposed model to the structural analysis of cable supported bridges is verified, and the simplified analysis model is employed to the proposed optimization procedure. As a result, time for assembling and analyzing a structural model for a cable-stayed suspension bridge is remarkably reduced.
Using the simplified analysis model, parametric investigations are performed to understand the effects of design modifications including the change of a side span length, the composition of a suspension section and an overlapping section, the cable sag, and the dead load distribution factor on the structural behavior under traffic load and rail load. The 3rd Bosphorus Bridge with a main span length of 1,408 m is adopted as example bridge. The results of the parametric investigations are applied to set the range of design variables in the proposed optimization procedure.
Finally, the optimization problem for the design of the cable system of a cable-stayed suspension bridge is defined as a cost optimization for finding the minimum construction cost of superstructures. GA is employed for the optimization, design criteria for stress and deformation from the design specification of KBDC and Eurocode are employed to examine the structural safety in the optimization procedure. The optimal cable systems are proposed for both roadway and railway bridges, and a sensitivity analysis is performed to investigate the effects of the change of design constraints and variables on the optimized result. It appears that the angular change of suspension cables among the constraints and the suspension section length among the design variables are very dominant on the optimal design of cable system.
The proposed optimization procedure to find an optimal cable system for a cable-stayed suspension bridge using the simplified analysis model is so reasonable and efficient that it can be applied to the practical design process with reduced time, cost and manpower for numerous iteration works. Also, the proposed optimal cable systems for a roadway bridge and a railway bridge help design engineers avoid heavy iteration works to find a conceptual design in the preliminary design stage.
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dc.description.tableofcontents1. INTRODUCTION 1
1.1 Background 1
1.2 Literature Review 8
1.3 Research Objective and Scope 12
1.4 Overview of Dissertation 14
2. A PROPOSED SIMPLIFIED ANALYSIS MODEL FOR A CABLE-STAYED SUSPENSION BRIDGE 16
2.1 Structural Analysis Model of a Combined System 16
2.2 Design Variables 20
2.2.1 Design variables for a cable-stayed suspension bridge 20
2.2.2 Variables for a material property 23
2.2.3 Principal design variables for a combined system 23
2.3 A Proposed Simplified Structural Analysis Model 26
2.3.1 A simplified analysis model 27
2.3.2 Initial equilibrium configuration analysis 35
2.3.3 Live load analysis 43
2.3.4 Algorithm of structural analysis 46
2.4 Verification of the Simplified Analysis Model 46
2.4.1 Application to a suspension bridge 47
2.4.2 Application to a cable-stayed suspension bridge 50
2.4.3 Summary of the verification 56
3. PARAMETRIC INVESTIGATION OF EFFECTS OF DESIGN VARIATIONS ON A STRUCTURAL BEHAVIOR UNDER LIVE LOADS 57
3.1 Effects of the Side Span Length 60
3.1.1 Effects on the cables 62
3.1.2 Effects on the deck 66
3.1.3 Effects on the pylon 68
3.2 Effects of the Suspension Section Length 69
3.2.1 Effects on the cables 71
3.2.2 Effects on the deck 75
3.2.3 Effects on the pylon 77
3.3 Effects of the Overlapping Length 78
3.3.1 Effects on the cables 80
3.3.2 Effects on the deck 84
3.3.3 Effects on the pylon 86
3.4 Effects of the Cable Sag 87
3.4.1 Effects on the cables 89
3.4.2 Effects on the deck 93
3.4.3 Effects on the pylon 95
3.5 Effects of the Dead Load Distribution Factor 96
3.5.1 Effects on the cables 98
3.5.2 Effects on the deck 102
3.5.3 Effects on the pylon 104
3.6 Summary of Parametric Investigations 105
3.6.1 Effects of the variation of Ls 106
3.6.2 Effects of the variation of Lsp 107
3.6.3 Effects of the variation of Lov 108
3.6.4 Effects of the variation of f 109
3.6.5 Effects of the variation of r 110
4. OPTIMIZATION OF CABLE SYSTEM USING THE PROPOSED SIMPLIFIED MODEL AND GENETIC ALGORITHM 111
4.1 Optimization Problem of Cable System 111
4.1.1 Definition of an optimization problem 111
4.1.2 Objective function for cost optimization 112
4.1.3 Genetic algorithm for optimization 115
4.2 Design Variables 116
4.2.1 Design variables of cable system 116
4.2.2 Live load 120
4.3 Design Constraints 122
4.3.1 Constraints on cables 122
4.3.2 Constraints on decks 125
4.4 Cost Optimization Procedure 128
4.4.1 Optimization procedure 128
4.4.2 Penalty in the objective function 129
4.5 Optimal Cable System for a Road-railway Bridge 131
4.5.1 Design conditions 131
4.5.2 Optimal cable system 134
4.5.3 Sensitivity analysis 141
4.6 Optimal Cable System for a Roadway Bridge 143
4.6.1 Design conditions 143
4.6.2 Optimal cable system 144
4.6.3 Sensitivity analysis 147
5. CONCLUSIONS 149
References 153
초 록 159
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dc.formatapplication/pdf-
dc.format.extent10039324 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoen-
dc.publisher서울대학교 대학원-
dc.subjectCable system-
dc.subjectcable-stayed suspension bridge-
dc.subjectcost optimization-
dc.subjectsimplified analysis model-
dc.subjectparametric investigation-
dc.subjectgenetic algorithm-
dc.subjectsensitivity analysis-
dc.subject.ddc624-
dc.titleOptimization of Cable System for a Cable-stayed Suspension Bridge using a Simplified Analysis Model-
dc.typeThesis-
dc.description.degreeDoctor-
dc.citation.pages160-
dc.contributor.affiliation공과대학 건설환경공학부-
dc.date.awarded2017-02-
Appears in Collections:
College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Civil & Environmental Engineering (건설환경공학부)Theses (Ph.D. / Sc.D._건설환경공학부)
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