Locking-free Exact Finite Element for Beams with Bond-slip
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The consideration of bond-slip in reinforced beam elements improves the accuracy and robustness of the finite element simulation. Typically one considers additional degrees of freedom to take into account the relative displacements at the interface between matrix and reinforcement, along with a bond-slip constitutive relation . Classic displacement-based finite element formulations eventually present locking phenomena, including shear and slip locking caused by the different interpolations of the bond-slip expression, in Euler as well as in Timoshenko beam models. Exact finite elements based on the analytical solution of the differential equations are important for novel element solution assessment and development of closed-form analysis or design formulae, providing solutions with very few elements and free of locking. The purpose of this work is to present an exact finite element formulation for beams with embedded bars, for which bond-slip between the matrix and the bars is taken into account. These FE solutions reproduce the analytical response employing a single element per member. Departing from a system of equations where the slips are the sole variables, the beam element flexibility matrix in a system free of rigid body modes is deduced. Next, the stiffness matrix of the general beam coordinate system is obtained for direct stiffness analysis by trivial operations. The exact load vector including loads along the member is also developed. The proposed finite element formulation is applicable to relevant engineering beam-column problems, and numerical examples are provided to show the excellent properties of the proposed scheme.
