International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 04 Issue: 11 | Nov -2017 www.irjet.net p-ISSN: 2395-0072 © 2017, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 2037 Three Dimensional Non-Linear Seismic Analysis of a Cable Stayed Bridge Using ANSYS Muhammad Habib 1, 2, Lifei Yang 3 , Nawaz Ali 4 , Shuang Liu 5 , Zhijun Chen 6, 7 1, 3, 5, 6 School of Civil Engineering and Mechanics, Huazhong University of Science and Technology, Wuhan, China 2, 4 Civil Engineering Department, Balochistan University of Information Technology, Engineering and Management Sciences, Quetta, Pakistan Abstract - The dynamic behavior of a cable stayed bridge is studied. The response of the cable stayed bridge is examined by carrying out non-linear static and dynamic (earthquake) analyses. Modes and the natural frequency of the bridge is studied by Modal analysis based on the Block Lanczos method. ANSYS is used to simulate the 3D model based on the Finite Element Method (FEM) .Cables are modeled by single element approach instead of multiple elements to reduce the data usage and computational time. The displacement convergence approach is used to avoid the convergence problems as cable stayed bridges are complex structures. The result shows that the bridge has complex modes due to the coupling effects for the free vibrations and it is more flexible in vertical direction than in transverse and longitudinal directions. Response of the bridge under earthquake loads is also studied. Transient analysis was performed for EI-Centro 1940 ground motion data of 10 second with a time interval of 0.0001 seconds. Important sections of girder and tower were carefully observed. Key Words: Dynamic Behaviour, Single-tower Cable Stayed Bridge, Modal Analysis, Time History Analysis, ANSYS 1. INTRODUCTION Due to their efficient, economically viable, faster construction and aesthetically attractive looks have made cable stayed bridges as one of the most widely used bridge system for medium to long span bridges. At present these bridges have the ability to cover a span length from 200 m to 1200 m or even more. Of all the long span bridges being constructed nowadays, almost 90 percent are cable supported bridges [1].Recent development in the analysis and design of cable stayed bridges ensure to build this type of bridges with relatively small size of the sub structural elements. Rapid and efficient construction techniques also add to its popularity. With the advancement in design techniques, material properties and qualities and good construction techniques enable to achieve long spans with slender elements. To achieve slim, shallower and long span bridges, more advance and accurate techniques need to be developed in order to predict the structural response due to the earthquake and wind loadings. During the last 70 years, since the collapse of the first Tocoma Narrows Bridge, dynamic study of the cable stayed bridges has become very important. A lot of research works both experimental and theoretical has been carried out to understand the behavior of the cable stayed bridges under the wind and earthquake loadings [2, 3]. Fleming and Egesli [4] proposed that the linear dynamic analyses were accurate enough to design a cable stayed bridge by studying a 2-D bridge model. Abdel Ghaffar and Nazmy [5] give motion equations for some 3-D hypothetical models by considering some of the nonlinear behaviors also. Abdul Ghaffar and khalifa [6] also consider the effect of vibration of the cables on the dynamic behavior of the cable stayed bridges. A lot of work related to earthquake effects is also done. Jamuna Bridge was studied for the earthquake effects on the basis of spectrum analysis and found that cable stayed bridges can withstand an earthquake acceleration up to 0.216g [7]. To save time and storage modal analysis is mostly performed. It is used to obtain information about the frequencies, mode shapes and modal participation factors. With increasing span, slim cross sections, low damping and high flexibility cable stayed bridges are more vulnerable to the earthquake and wind loadings. Major source of damping is greatly reduced in the cable stayed bridges as compared to conventional bridges. Cable stayed bridges have very low damping which is not even sufficient to overcome its own vibrations. To increase the damping of the system external damping devices are extensively used in nowadays cable supported bridges. But a lot of research is needed to be investigated the damping problems of the modern bridges and its economy [8]. Since 80’s a lot of work is being done focusing the seismic response of the cable stayed bridges [9- 13]. Nonlinear behavior, supports condition role, cable vibrations and spatial variability were also studied. Some dynamic characteristics of interest of this study are frequencies, mode shapes, modal participation factor and effective modal masses. Vertical and transverse and torsional behavior is studied separately. 7 Professor, School of Civil Engineering and Mechanics, Huazhong University of Science and Technology, Wuhan, China ---------------------------------------------------------------------***---------------------------------------------------------------------