Daniele Pelessone

Lattice Discrete Particle Model for Fiber-Reinforced Concrete. II: Tensile Fracture and Multiaxial Loading Behavior

In Part I of this two-part study, a theory is provided for the extension of the lattice discrete particle model (LDPM) to include fiber reinforcing capability. The resulting model, LDPM-F, is calibrated and validated in the present paper by comparing numerical simulations with experimental data gathered from the literature. The analyzed experiments include direct tension, confined and unconfined compression, and notched three-point bending tests.

Simulation of reinforced concrete structures under blast and penetration through lattice discrete particle modeling

In this study, the Lattice Discrete Particle Model (LDPM), a recently developed three-dimensional meso-level model for concrete, is used to simulate the behavior of reinforced concrete under severe loading conditions. LDPM simulates concrete through an assemblage of particles (coarse aggregate pieces) connected through a lattice mesh. In order to simulate steel reinforcement, a mesh of plastic beams is embedded in the lattice system. Nonlinear concrete-reinforcement bond is also included in the formulation. The effectiveness of the approach is demonstrated through the simulation of projectile penetration into reinforced concrete slabs and blast spallation of dividing walls.

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 threedimensional 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’ pullout tests are presented.

Dynamics Simulations of Concrete and Concrete Structures through the Lattice Discrete Particle Model

The Lattice Discrete Particle Model (LDPM), a meso-scale model for concrete, was extensively calibrated and validated in previous research for quasi-static loading conditions. In this paper, LDPM is used to investigate the time-dependent behavior of concrete for high strain rates with the main objective of (1) assessing the role of apparent and intrinsic rate effect mechanisms on the macroscopic concrete response; and (2) demonstrating LDPM predictive capabilities under dynamic loading conditions. The LDPM formulation is extended to incorporate rate-dependent fracture mechanisms associated with the interpretation of fracture processes as thermally activated phenomena and governed by the classical Maxwell-Boltzmann theory. According to this approach, the LDPM meso-scale strength and toughness are assumed to be functions of the meso-scale strain rate. The model is calibrated and validated on the basis of experimental data available in the literature and obtained through (a) reinforced and unreinforced unconfined compression tests; and (b) Hopkinson bar tests in tension and compression. Analysis of the numerical results shows the ability of LDPM to simulate accurately the dynamic response of concrete under a large variety of loading conditions. Furthermore, in this study, LDPM is used to perform simulations of projectile impacts on regular strength concrete (RSC) and high strength concrete (HSC). Perforation and penetration experiments on RSC and HSC for varied impact velocities are carried out and the exit velocities are compared to available experimental data. In general, LDPM replicates successfully the behavior of concrete for penetration and perforation events and it is able to capture accurately the main features of concrete response in terms of projectile deceleration as well as fracture patterns.

Calibration and Validation of the Lattice Discrete Particle Model for Ultra High-Performance Fiber-Reinforced Concrete

This paper investigates the calibration and validation of a new ultra high performance concrete (UHPC) named Cortuf using LDPM-F, the Lattice Discrete Particle Model for fiber reinforced concrete. The LDPM-F is a discrete meso-scale model that can accurately describe the macroscopic behavior of concrete in elastic, fracturing, softening, and hardening regimes. LDPM-F has been verified extensively through the analysis of a variety of experimental tests and can reproduce with great accuracy the response of concrete under uniaxial and multiaxial stress states in compression and tension, and under both quasi-static and dynamic loading conditions. The model is calibrated herein by simulating: (1) unconfined and confined compression tests as well as 3-point bending tests on plain Cortuf and (2) single fiber pull-out tests. Afterward, quasi-static compression and tensile validation and prediction experiments were performed. The numerical results are compared to the experimental results both graphically and through failure modes.

Proper Orthogonal Decomposition Framework for the Explicit Solution of Discrete Systems with Softening Response

The application of explicit dynamics to simulate quasi-static events often becomes impractical in terms of computational cost. Different solutions have been investigated in the literature to decrease the simulation time and a family of interesting, increasingly adopted approaches are the ones based on the proper orthogonal decomposition (POD) as a model reduction technique. In this study, the algorithmic framework for the integration of the equation of motions through POD is proposed for discrete linear and nonlinear systems: a low dimensional approximation of the full order system is generated by the so-called proper orthogonal modes (POMs), computed with snapshots from the full order simulation. Aiming to a predictive tool, the POMs are updated in itinere alternating the integration in the complete system, for the snapshots collection, with the integration in the reduced system. The paper discusses details of the transition between the two systems and issues related to the application of essential and natural boundary conditions (BCs). Results show that, for one-dimensional (1D) cases, just few modes are capable of excellent approximation of the solution, even in the case of stress–strain softening behavior, allowing to conveniently increase the critical time-step of the simulation without significant loss in accuracy. For more general three-dimensional (3D) situations, the paper discusses the application of the developed algorithm to a discrete model called lattice discrete particle model (LDPM) formulated to simulate quasi-brittle materials characterized by a softening response. Efficiency and accuracy of the reduced order LDPM response are discussed with reference to both tensile and compressive loading conditions. [DOI: 10.1115/1.4038967]

Lattice discrete particle modeling (LDPM) of flexural size effect in over reinforced concrete beams

At the macroscopic scale, concrete can be approximated as statistically homogeneous. Nevertheless, its macroscopic behavior shows quasi-brittleness, strain softening, and size effects evidencing a strong influence of material heterogeneity. A model naturally accounting for material heterogeneity is the Lattice Discrete Particle Model (LDPM). LDPM replaces the actual concrete mesostructure by an assemblage of discrete particles interacting through nonlinear and fracturing lattice struts. Each particle represents one coarse aggregate piece. Since the initial development, LDPM has shown superior material modeling capabilities. In this research, LDPM is used to simulate the flexural failure of three groups of over reinforced concrete beams. The groups represent 1D, 2D and 3D geometric similarities. Geometry is generated based on concrete mix design. Then calibration was only guided by the experimentally provided compressive strength. In order to reduce the redundancy of the calibration process, the fracture properties of concrete were estimated using relevant literature. Finally, the rebar assembly was connected to the LDPM mesh using penalty type constraints and the rebars were modeled using 1D beam elements. Numerical results show excellent agreement with experimental data and clear capability of capturing size effects.