INELASTIC RESPONSE OF 3D RC FRAMES OF AN URBAN VIADUCT CONSIDERING THE URBAN VIADUCT CONSIDERING THE I S-S IIINTERACTION SOIL-STRUCTURE EFFECT BY EFFECT BY NUMERICAL SIMULATION H. Sánchez Sánchez & E. Lugo Espino SEPI ESIA Instituto Politécnico Nacional, México C. Cortés Salas Instituto Mexicano del Petróleo, México SUMMARY: Bridges and viaducts are subjected to considerable forces during strong ground motions that might cause major structural failures, damage and, in some cases they can lead to the collapse of the structure; for example the Loma Prieta, Northridge, Kobe and Chile earthquakes. Therefore, the performance of the viaducts has a particular interest of the structural behaviour, response, bridge design and retrofit. Then this research is focused to study the non- linear behaviour and structural response of a viaducts type frame of concrete placed in the soft soil of the Mexico Valley. To determine the response, the seismic simulation was done by numerical modelling with 3D non-linear analysis taking into account: the geometrical characteristics of the structure and non-linear behaviour of the material, as well as the soil-structure interaction effect is incorporated, using real and synthetic acceleration records. Finally, these numerical results show a behaviour and response expected according to the Mexican codes. Keywords: bridges, non-linear behaviour of frames, inelastic response, structural behaviour, numerical modelling, interaction soil- structure 1. INTRODUCTION The vehicular transportation has been increased in the Mexico City in the last two decades. Then additional transportation lines have been created how one alternative to solve the traffic problem in the city. As result of this solution the bridges and viaducts were adopted, these types of structures represent complex structural systems. Those systems choose for the structural characteristics are constituted by concrete rigid frames of two levels. The structures are placed in high or moderate seismic areas, because they restrict the lateral displacement. 1.1. Problem statement The San Antonio Viaduct is part of elevated roadway systems linking Miguel Alemán Viaduct with the south Periférico. It is located in south-west of the Mexico City. The double-deck viaduct carried four lanes of southbound traffic on the lower level and three lanes of southbound traffic on the upper level see figures 1.1 to 1.4. The upper and lower level box girder roadway deck were supported by structure system of reinforced concrete. This viaduct has three different configurations such as, a. isolated column, b. high frame and c. double frame. In this study, only c. the double frame is considered to be studied in this work. The frames studied are structure with circle columns for both levels and different box beams at each level. 1.2. Objective and scope This study investigates the potential damage that they could suffer during strong motions. Then to known the inelastic damage of the structure the ANSYS program was used for this study. The structures were analyzed by step-by-step methods. The requirements of RCDF and NTC-2004 were used for the