Two-dimensional design of post-tensioned concrete flat slab bridges

Abstract

A new procedure is described for design of flat-slab post- tensioned highway bridges. The goal is to provide a rational, sophisticated, and yet relatively facile method of design for this complex class of structures. One-dimensional strip analysis provides an estimated slab thickness, amount of steel reinforcement, and required longitudinal post- tensioning force. After adequate transverse post-tensioning is provided for dead load, finite element analysis computes deflections, strains, and stresses for both short- and long- term dead loads of the plate structure. The slab thickness is decreased in an iterative manner until deflections and stress levels are determined to be within an acceptable range of their target level. Several critical live load cases are applied to the slab and salient quantities are again checked for exceedence of specified bounds. A recommended approach for design of flat slab bridges is presented as a result of extensive experimental and analytical research. An example of a threespan bridge illustrates the design procedure. Details of calculations and -input preparation for the finite element code are included for this bridge. Results are compared with an actual bridge that has been constructed and monitored in the field for more than two years. The analysis takes into account losses due to creep, shrinkage, relaxation, friction, and cracking. Fringe plots of deflections and stresses show the graphical capabilities of the microcomputer software package used for this study.