Dynamic pull-out test simulations using the lattice discrete particle model (LDPM)

This paper presents a novel algorithm to simulate rebar-concrete interaction when concrete is modeled using the Lattice Discrete Particle Model (LDPM), a recently developed three-dimensional meso-mechanical model. In the LDPM formulation, the mesostructure of concrete is simulated by an assemblage of particles interacting through nonlinear springs. Each particle represents a coarse aggregate piece with its surrounding mortar. The rebar-concrete interaction algorithm consists of a constraint element that treats the interaction of discrete particles close to the rebar with adjacent rebar finite elements. Bond constitutive equations provide relationships for computing interface forces given the relative displacements between particles and rebars. These equations implement the complex physical mechanisms that take place in the thin concrete layer surrounding steel rebars, including the formation of oblique cracks, dilation due to slippage, friction, etc. The complete formulation (LDPM, rebars, and bond interaction) is implemented in the framework of the object oriented dynamic finite element code MARS. Calibration and validation activities are being performed using a series of pull-out experiments recently conducted at the US Army Engineer Research and Development Center (ERDC) in both quasi-static and dynamic regimes. Three examples consisting of highly dynamic 'impact' pull-out tests are presented.