James T. Baylot

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.

Quarter-Scale Building/Column Experiments

Terrorist-bombing events throughout the world have demonstrated the vulnerability of conventional reinforced-concrete buildings to blast effects. Typical columns and floor slab systems are not designed to resist the complex blast loading, such as uplift or reverse loading of floor slabs and combined lateral and tensile loading of columns. Two-story, quarter-scale reinforced-concrete models were used to investigate the blast response of a typical flat-plate structural system in support of the Technical Support Working Group (TSWG), Blast Mitigation of Structures research program. Experiments were conducted on five models, allowing a variation in explosives standoff and cladding configuration. The High-Performance Computing facilities available at the US Army Engineer Research and Development Center (ERDC) Major Shared Resource Center were used to perform analyses to support the TSWG quarter-scale experiments. Analyses were performed to predict the response of the exterior column for different ranges and exterior wall conditions.

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.

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.

Expedient FE analysis of concrete masonry walls subjected to blast loads

Publisher Summary In this chapter, concrete masonry unit (CMU) walls subjected to blast pressure are analyzed with the finite element method, with the goal of developing a computationally efficient and accurate model. Computational results are compared in the chapter to high-speed video images and debris velocities obtained from experimental data. It is found that the model has the ability to reproduce experimental results with good agreement. It is also found that wall behavior is sensitive to material properties. The exterior frames of buildings are commonly in-filled with CMU blocks. In a typical high-energy blast in close proximity to this type of wall, the CMUs may break apart and enter the structure as projectiles, potentially injuring building occupants. The accurate prediction of this behavior is a subject of great interest in protective technology research to evaluate the performance of existing structures and to suggest appropriate retrofit options or designs for new structures. A number of researchers have modeled CMU wall behavior, typically with the finite element (FE) method.

Vulnerability of Structures to Weapons Effects

The Geotechnical and Structures Laboratory (GSL) has a number of funded research efforts to support Department of Defense (DoD) requirements for understanding the response of structures to explosives/weapons. These efforts are all heavily dependent on high performance computing (HPC) simulations to meet research needs. The research efforts to be supported include Force Protection, Military Operations in Urban Terrain, and Homeland Defense. HPC simulations are used to enhance ongoing experimental programs. The simulations are used to assist in designing experiments, to aid in understanding the experiments, to extend the knowledge beyond the limitations of the experiments, and to develop numerical databases. High priority HPC hours available through the High Performance Computing Modernization Program (HPCMP) Challenge Project were used to perform these simulations. Simulation results are compared with experimental results when available.