I~&/VON/6O/GCZ UPGRADING OF EXISTING PEDESTRIAN ® SUSPENSION BRIDGES FOR LIGHT VEHICULAR TRAFFIC A thesis submitted for the partial fulfillment of the Degree of Master of Engineering in Structural Engineering Design Submitted by D.K.Rohitha Swarna February 2002 gwo Scales . § Supervised by Dr. M. T. R. Jayasinghe Senior Lecturer Department of Civil Engineering University of Moratuwa 074548 University of Moratuwa 74548 Abstract For the rapid economic development of rural villages in Sri Lanka, the transportation facilities should be upgraded to motorable level. In this context, one of the bottlenecks is the need of large number of bridges, which is a costly item. Therefore, the solution adopted by the relevant authorities to this problem is the construction of pedestrian suspension bridges at these locations. Suspension bridges that can allow light vehicular traffic could be much more beneficial than pedestrian suspension bridges, since those will allow more economic benefits by facilitating the transport of goods. However such bridges are still not available in Sri Lanka. Therefore, it is useful to develop suspension bridges for light vehicular traffic that could be constructed with locally available expertise in modular fashion. When suspension bridges are designed for light vehicular traffic, it is necessary to ensure that an accurate analysis and design techniques are used. In this study, it is shown that two dimensional and three dimensional computer modelling could be utilized to accurately determine various possible load conditions. The results of such analysis would facilitate the structural design engineer to perform the design with a lot of confidence. This is a much better situation than performing the design on the basis of approximate analysis. In order to show the possibility of using the above techniques, three case studies were conducted for 42 m, 60 m and 78 m long bridges. The structural concepts were developed with the aim of allowing unobstructed traffic foe single lane of light vehicles. The techniques for constructing the bridges with local expertise are also investigated. i Acknowledgements My sincere thanks to the project supervisor Dr. M. T. R. Jayasinghe for devoting his valuable time in guiding me to complete the research study. It is no doubt that without his interest and guidance this would not have been a success. I wish to thank the Vice Chancellor, Dean of the Faculty of Engineering and the Head, Department of Civil Engineering for allowing me to use the facilities available at the University of Moratuwa. I am grateful to the Road Development Authority for the financial assistance given to me to follow this postgraduate degree course. I wish to thank Dr (Mrs) M. T. P. Hettiarachchi, the course and research coordinator of the project for the encouragement given to me in completing this study, and all the lecturers of the postgraduate course on Structural Engineering Design who helped to enhance my knowledge. I would like to dedicate this hard work to my parents, wife and two daughters for their enormous support. Finally, I wish to thank everybody who helped me in numerous ways in completing my research study. D. K. Rohitha Swarna Road Development Authority. ii Contents Abstract Acknowledgements Contents List of Figures List of Tables Chapter - 1.0 1.1 1.2 1.3 1.4 1.5 Chapter - 2.0 2.1 2.2 2.3 Chapter - 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Introduction General The objectives of the study The Methodology The main findings of the project The arrangement of the thesis Literature review Historical development Wind induced behaviour Summary Development of a suspension bridge for light vehicular traffic General The cables The stiffening girder The towers The hangers The anchor block Summary iii Chapter - 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Chapter - 5.0 5.1 5.2 5.3 5.4 5.5 > 5.6 Chapter - 6.0 6.1 6.2 References Appendix - A A.l A.2 Appendix - B B.l B.2 Computer modelling of suspension bridges 28 The modelling techniques 28 Special features 29 Two dimensional modelling 32 Three dimensional modelling 32 The specified loads on the bridge 33 The method of analysis 3 5 Summary 35 Results and analysis for case studies 39 Results for the two dimensional analysis 39 Results for the three dimensional analysis 41 Comparison of two dimensional and three dimensional results 42 Analysis of results 43 The cost study 44 Summary 44 Conclusions and future work 45 Conclusions 45 Future work 46 47 Computer output results of 42 m main span suspension bridge 49 Two dimensional results 49 Three dimensional results 61 The cost study for a 42 m long bridge 83 Cost of the bridge with pretension beams 83 Cost of the bridge with a suspension bridge 84 iv List of Figures Figure 1.1 Suspension Bridge at Haloluwa over Mahaweli River Figure 1.2 Suspension Bridge at Digana Figure 1.3 Suspension Bridge at Botanical Gardens - Peradeniya Figure 1.4 Gampola - Nuwara Eliya Road Bridge opening in 1926 Figure 1.5 Old Suspension Bridge at Gampola over Mahaveli River (Artist's Impression) Figure 3.1 General arrangement of suspension bridge considered for case studies Figure 3.2 3D truss module used for the stiffening girder Figure 3.3 Precast concrete slab used for the deck Figure 3.4 Plan view of the deck slab Figure 3.5 Details at tower Figure 3.6 Proposed arrangement of anchor block Figure 3.7 Details of anchorage Figure 4.1 The cable arrangement of the tower with the use of a pin Figure 4.2 The cable arrangement used over the tower to allow movement Figure 4.3 2D model of suspension bridges Figure 4.4 3D model for the 42 m span List of Tables Table 3.1 The details of the suspension bridges already constructed in Sri Lanka Table 4.1 The details of the load cases Table 5.1 Results of the computer analysis for the bridge of main span length 42 m Table 5.2 Results of the computer analysis for the bridge of main span length 60 m Table 5.3 Results of the computer analysis for the bridge of main span length 78 m Table 5.4 Results of the 3D computer analysis for the bridge of main span length 42m Table 5.5 Comparison of the critical forces in members and the maximum deflections for the 42m bridge with 2D and 3D modeling Table B. 1 Summary of the total cost of the bridge Table B.2 The sizes of members used for the stiffening girder Table B.3 Summary of the total cost for 42 m main span bridge vi