Equilibrium-serviceability design of hyperstatic P.C. beams

A practical flexural design procedure for continuous prestressed concrete girders based on simulataneously ensuring specified margins of safety against both limit states of section and structural failures is presented. The problem formulation consists of expressing the appropriate limit equilibrium, serviceability and ductility constraints. Solutions are found by solving sets of linear equations whose unknowns are reduction factors of the elastic moment envelope for the structure and the secondary moments at critical sections. As such the efficiency of the solution can readily be related to code-permissible moment redistributions. A numerical example for a continuous bridge girder allows a comparison with solutions based on the ACI Code and illustrates the application of the method for three different cracking limitations at service conditions.