FLAT SLAB DESIGN OF UNDERGROUND STATION BUILDINGS USING 3D FEM TOOLS

Abstract

 A joint venture (SFTE-JV) led by Shimizu Corporation is currently conducting the detailed design and construction of underground station box culverts for the first subway project in the Republic of the Philippines, the Metropolitan Manila Subway Project (MMSP), Section CP101. In Japan, where earthquakes are common, underground stations are generally constructed with rigid-frame structure which consist of beams for earthquake resistance, but in the project site of MMSP, the ground has good quality and the underground stations are all contained in solid soft rock layers, thus making the effects of earthquake minimal. Therefore, a simpler flat-slab structure was adopted to improve workability and ensure quality, and at the same time, make effective use of the interior space. Conventional 2D frame analysis is a simplified method in which cross-sectional forces obtained from 2D analysis are redistributed in a certain ratio for verification. In this design, 3D FEM analysis was used to verify stress development in every detail of the station structures, aiming for a rational design that provides the necessary amount of reinforcing steel bars in the critical areas.