LIFE-CYCLE COST OPTIMIZATION OF PRESTRESSED SIMPLE-SPAN CONCRETE BRIDGES WITH SIMPLE AND SPLICED GIRDERS

In  this  paper,  determination  of  the  design  variable  optimum  values  of  simple  and spliced pre-tensioned girders in bridges is addressed by considering the life cycle cost of the whole structure.  To  this  end,  a  program  called  OBPG is  written  with  FORTRAN,  consisting  of  the analysis,  design  and  optimization  subroutines  based  on  the  feasible  direction  method.  AASHTO principles are used, assuming initial values for the design variables such as the dimensions of the girders and the deck, and the strands number. Then, using the analysis outcomes and considering the design criteria, the total cost of the structure, including that of the girders and slabs concreting, pre-tensioning cables performance, reinforcement and frameworks, are minimized as functions of the  design  variables.  Although  the  initial  optimization  cost  using  life  cycle  cost  is  slightly  more than that using the initial cost, optimization of the life cycle cost proves to be more economical. Ultimately,  a  program  capable  of  analyzing  simple  and  spliced  pre-tensioned  bridge  girders  is developed which calculates the life cycle and gives an optimum design.