This paper presents an efficient computer-based method for optimal
criteria design of composite girder under biaxial bending. The width,
depth for concrete slab and steel section are taken as the design
variables. The strength constraints for the design are formulated using
the finite element method. The method solves composite girders taking
into consideration the material non-linearity due to the change in stressstrain
curves of steel and concrete, and geometric non-linearity due to
the change of the path of the composite girder during deformation. The
formulation depends on the principle of Virtual Work. An optimality
criteria method is applied to minimize the cost of concrete slab, steel, and
form subject to constraints on strength and stiffness. Four full composite
girder examples are presented to illustrate the features of the design
optimization method.
It is shown that the design method provides an effective iterative
optimization strategy that converges in relatively few cycles to a leastcost
design of reinforced concrete element satisfying all relevant
requirements of the governing design code. The iterative process is
insensitive to the selected initial design and converges smoothly to a final
design involving concrete slab dimensions and steel section consistent
with usual design practice. A complete computer program has been
developed to solve the problem of full composite-beams under biaxial
bending.