Locking-free Finite Element Formulation for Steel-Concrete Composite Members

In the conventional displacement-based finite element analysis of composite beam-columns that consist of two Euler-Bernoulli beams juxtaposed with a deformable shear connection, the coupling of the transverse and longitudinal displacement fields may cause oscillations in interlayer slip field and reduction in optimal convergence rate, known as slip-locking. This locking phenomenon is typical of multi-field problems of this type, and is known to produce erroneous results for the displacement based finite element analysis of composite beam-columns based on cubic transverse and linear longitudinal interpolation fields. In this paper it will be shown that by simple change of the pair of dependent variables in the formulation the locking behaviour can be alleviated. An example is presented to illustrate the effects of connection stiffness on the behaviour of composite beams and the results show that the proposed approach is efficient in alleviating the locking behaviour.