Finite element formulations of one-dimensional elements with bond-slip

This paper presents two general formulations of one-dimensional structural members with deformable interfaces. The interface accounts for the bond-slip between the element components. The first formulation is the classical displacement-based formulation; the second one is a novel force-based approach. The two formulations are derived from the equilibrium and compatibility differential equations of the problem. A special force recovery procedure, based on residual deformations, is presented for the force-based formulation. Two applications are used to illustrate the two formulations: the first is a reinforcing bar with bond slip, the second is a steel–concrete composite beam with partial interaction between the steel beam and the concrete slab. Examples of a bar with bond failure and of a composite beam with weak connection show the precision of the force-based element and its capability to trace the complex response of softening members with a limited number of elements.