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![(a) LDPM simulation of projectile impact and penetration through fiber-reinforced concrete panels (Smith and Cusatis [58]); (b) RBSM simulation of tensile fracture of a concrete cylinder loaded in a split Hopkinson pressure bar apparatus and damage pattern within the physical specimen (Hwang et al. [39]).](profile/Jan-Elias/publication/354959072/figure/fig9/AS:1160456504901634@1653685799165/a-LDPM-simulation-of-projectile-impact-and-penetration-through-fiber-reinforced.png)
(a) LDPM simulation of projectile impact and penetration through fiber-reinforced concrete panels (Smith and Cusatis [58]); (b) RBSM simulation of tensile fracture of a concrete cylinder loaded in a split Hopkinson pressure bar apparatus and damage pattern within the physical specimen (Hwang et al. [39]).
Source publication
Discrete models of solids have been motivated, in large part, by the discontinuous and heterogeneous nature of material structure and its breakdown under loading. The capabilities of discrete models have evolved over the past several decades, offering novel means for investigating material structure–property relationships. However, lack of understa...
Contexts in source publication
Context 1
... effects, such as mass inertia and changes in crack patterns, appear naturally as part of the solution process. Smith and Cusatis [58] applied the LDPM to modeling the response of plain and steel fiber-reinforced concrete structures to impact loading. Fiber additions increased material toughness, leading to reduced size of the damage zones ( Fig. 9) and better performance under repeated impacts. In agreement with test observations, the fiber additions had only a secondary effect on reducing the exit velocity associated with strike velocities above the ballistic ...
Context 2
... strength at higher strain rates. Visco-elastic-plastic damage (or visco-plastic damage) units were introduced within the lattice elements to represent the material-intrinsic components (e.g., the influence of pore water viscosity on fracture) of strain rate dependency. As shown through comparisons with experimentally recorded damage patterns (Fig. 9), discrete models are adept at simulating distributed damage and fracture localization within concrete under dynamical ...
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Citations
... The 3D-RBSM has been acknowledged as an effective numerical method for quantitatively studying the concrete fracture behavior, especially the internal crack propagation. [42][43][44][45] The study first documents an overview of the coupled RBSM and solid FEM model and element definitions. Then, it confirms the implementation of the numerical model for the shear capacities and failure modes of the single PBL shear connector for different positions of the transverse rebar. ...
The perfobond (PBL) shear connector reinforced with transverse rebar effectively contributes to sufficient ductility, bearing capacity, and anti-fatigue behavior to hybrid structures. The construction practice involves the placement of the transverse rebar at the bottom position within the concrete dowel, whereas past studies employed transverse rebar in the center of the dowel; hence, there exists a gap between literature and design practices. Furthermore, there is no specific information in the design guidelines for hybrid structures on the influence of the position of the transverse rebar. Therefore, the current research deals with the analytical investigations employing the coupled Rigid Body Spring Model (RBSM) and the nonlinear solid Finite Element Method (FEM) that encompass the internal fracture behavior of concrete with the various parameters of transverse rebar, particularly the position and strength, to recognize the failure mechanism. It was determined that the numerical model accurately captured the test shear capacity and failure modes. The internal failure process of a specimen with transverse rebar at the bottom position, identical to actual field practice, revealed that as the height of the concrete region above the rebar rises, more compressive stresses in a trapezoidal manner are being generated, leading to an enhancement of the deformation capacity. Furthermore , it was confirmed that the specimen with the transverse rebar inserted at the bottom generates the greatest axial force, which is followed by the greatest shear capacity. K E Y W O R D S analytical evaluation, detailed cracking process, PBL shear connector, shear resistance mechanism, transverse reinforcement 1 | INTRODUCTION The concrete-steel composite construction has gained significant popularity and application recently due to its enhanced structural response, and ease of implementation for hybrid structures, and the mechanical behavior of the shear connector has a major effect on the composite action and longitudinal shear transfer between concrete and steel. 1 In this context, the perfobond shear connector (Perfobond Leiste in German [PBL]), developed by the
... DEM was used to represent the mechanical behavior of concrete specimens by using discrete spherical elements interacting locally through normal and tangential contacts that generate cracks during their failure. There are several different discrete models for concrete mechanical behavior developed in the literature, such as classical lattice models, rigid-body-spring models, lattice discrete particle models and discrete element methods [33]. We chose DEM since it realistically captures the fracture processes in concrete [34][35][36][37][38]. Additionally, it correctly depicts mesostructure and contact forces, using simple dynamic equations. ...
The work aims to numerically investigate the quasi-static response of partially fluid-saturated concrete under two-dimensional uniaxial compression at the mesoscale. We investigated how the impact of free pore fluid content (water and gas) affected the quasi-static strength of concrete. The totally and partially fluid-saturated concrete behavior was simulated using an improved pore-scale hydro-mechanical model based on DEM/CFD. The fluid flow concept was based on a fluid flow network made up of channels in a continuous region between discrete elements. A two-phase laminar fluid flow was postulated in partially saturated porous concrete with very low porosity. Position and volumes of pores/cracks were considered to correctly track the liquid/gas content. In both dry and wet conditions, a series of numerical simulations were performed on bonded granular specimens of a simplified spherical mesostructure that mimicked concrete. The effects of fluid saturation and fluid viscosity on concrete strength and fracture, and fluid pore pressures were investigated. It was found that each of those effects significantly impacted the hydro-mechanical behavior of concrete. Due to the rising fluid pressure in pores during initial specimen compaction under compressive loading that promoted a cracking process, the compressive strength increased as fluid saturation and fluid viscosity decreased.
Graphical abstract
DEM-CFD results for fully saturated specimen: evolution of maximum pore water pressure against vertical normal strain during uniaxial compression (from zero up to peak stress for).
... These models offer the capability not only to simulate macroscale fractures and cracks but also to capture lower-scale crack propagation, including mesoscale and microscale phenomena. Among the diverse range of discrete models, classical particle discrete models such as the discrete element method [2], discrete lattice element method [1], and finite discrete element method [3] have proven particularly effective in various fields of engineering failure analysis of concrete, rocks, and other materials [4][5][6][7]. ...
... Discrete lattice models generally use one-dimensional lattice elements to transmit forces between material particles or distinct portions of the material (grains), which is efficient in simulations of crack and fracture growth. The lattice element models can be represented by truss bars, Euler-Bernoulli beams, or Timoshenko beams [1], or, alternatively, the models may use springs, giving rise to a rigid-body spring model [2]. The unstructured lattice configuration possesses structural randomness, resulting in efficiency in capturing cracks and fractures, which is very beneficial in simulations of failure at lower scales. ...
This research presents a novel approach to modeling fracture propagation using a discrete lattice element model with embedded strong discontinuities. The focus is on enhancing the linear elastic response within the model followed by propagation of fractures until total failure. To achieve this, a generalized beam lattice element with an embedded strong discontinuity based on the kinematics of a rigid-body spring model is formulated. The linear elastic regime is refined by correcting the stress tensor at nodes within the domain based on the internal forces present in lattice elements, which is achieved by introducing fictitious forces into the standard internal force vectors to predict the right elastic response of the model related to Poisson’s effect. Upon initiation of the first fractures, the procedure for the computation of the fictitious stress tensor is terminated, and the embedded strong discontinuities are activated in the lattice elements for obtaining an objective fracture and failure response. This transition ensures a shift from the elastic phase to the fracture propagation phase, enhancing the predictive capabilities in capturing the full fracture processes.
... In the last decades, Lattice Discrete Models (LDM) have been proposed in which each aggregate is idealized as a single rigid body. The main advantage of the LDM models is the significantly lower modeling complexity [109][110][111][112] compared to tensorial macroscopic models. The LDM approach has been used to study the crack propagation under lateral compressive cyclic loading. ...
The limited understanding of the fatigue behavior of reinforced and prestressed concrete members is one of the reasons why many structures do not reach their expected service life. Without a deeper theoretical understanding of the fatigue phenomena in the various fatigue process zones, reliable fatigue life predictions are not possible. This paper provides a classification of the major fatigue process zones and mechanisms in reinforced and prestressed concrete members, accompanied by a brief review of recent developments in design rules, experimental characterization, and modeling approaches specific to each fatigue process zone and mechanism. The limitations of current approaches to fatigue characterization and modeling are also discussed, highlighting the need for further research in this area.
... Our research group has eectively simulated the dynamic ailure o concrete by introducing an explicit time integration method and a rheological model within 2-dimensional [39,40] and 3-dimensional [41,42] lattice-based models, which are composed o rigid-body-spring elements. These discrete element approaches can accommodate the modeling o aggregates, steel rebars, and bers within the concrete [43][44][45][46][47]. ...
... Continuum models, in contrast, are based on homogenized material behavior and lead to an element size-dependency of strength and fracture toughness predictions, stress-locking problems, and difficulties to capture multiple growing cracks. 3,6 Over the past decades the approach of using lattice networks to study numerically quasi-brittle materials such as concrete has been continuously improved by inelastic damage behavior of the spring elements connecting the particles as well as friction between them. 7,8 Discrete lattice networks have also been applied to study fracture behavior of cortical bovine bone 9 or textiles and woven fabrics. ...
Lattice networks are indispensable to study heterogeneous materials such as concrete or rock as well as textiles and woven fabrics. Due to the discrete character of lattices, they quickly become computationally intensive. The QuasiContinuum (QC) Method resolves this challenge by interpolating the displacement of the underlying lattice with a coarser finite element mesh and sampling strategies to accelerate the assembly of the resulting system of governing equations. In lattices with complex heterogeneous microstructures with a high number of randomly shaped inclusions the QC leads to an almost fully-resolved system due to the many interfaces. In the present study the QC Method is expanded with enrichment strategies from the eXtended Finite Element Method (XFEM) to resolve material interfaces using nonconforming meshes. The goal of this contribution is to bridge this gap and improve the computational efficiency of the method. To this end, four different enrichment strategies are compared in terms of their accuracy and convergence behavior. These include the Heaviside, absolute value, modified absolute value and the corrected XFEM enrichment. It is shown that the Heaviside enrichment is the most accurate and straightforward to implement. A first-order interaction based summation rule is applied and adapted for the extended QC for elements intersected by a material interface to complement the Heaviside enrichment. The developed methodology is demonstrated by three numerical examples in comparison with the standard QC and the full solution. The extended QC is also able to predict the results with 5% error compared to the full solution, while employing almost one order of magnitude fewer degrees of freedom than the standard QC and even more compared to the fully-resolved system.
... Several types of models have been proposed over the years to describe concrete fracture and size-effect. One can mention for instance the cohesive model [7], the crack-band model [8], non-local continuum damage models [9,10], and discrete models [11]. In all the aforementioned formulations, two features are essential in capturing size-effect in strain softening materials such as concrete: (i) crack localization and (ii) existence of an internal characteristic length related to the size of the heterogeneity. ...
... The scope of bonded-block models has extended outside rock mechanics to include the fracture of other geomaterials and structures, for example, in the detailed analysis of lab tests on masonry specimens, prisms and wallettes [54][55][56]. Concrete fracture has also been approached with bonded-block models [57] and related numerical techniques employing polygonal or polyhedral elements [58]. ...
... Thus, particle models may allow more refined analyses with reasonable run times. In summary, both types of modeling remain active fields of research and application in rock engineering, as discussed in various review articles [7,9,10,58]. ...
Discrete element models are being increasingly applied to model rock failure processes. Bonded-particle models, based on circular or spherical particle systems, have been successfully used for two decades. More recently, bonded-block models, using polygonal or polyhedral elements, have proven to be a powerful alternative. This paper describes the basis of the application of these models in the numerical simulation of failure in rock materials. The critical governing parameters are identified, and their influence is discussed. The model calibration procedure based on the analysis of laboratory tests is discussed. An application example of an underground excavation problem is presented using a simple bonded-block model employing rigid blocks and a bilinear softening contact model. The results show the capability of this approach to reproduce observed failure modes involving block fractures.
... On this basis, the mechanism of steel fiber-reinforced concrete has been explored more at home and abroad. From the structural level to fracture mechanics, there are many basic ideas so far, among which the use of composite mechanics (hybrid law) and the fracture mechanics-based fiber spacing theory are dominant [4]. The current research has gone further to the microstructural level and analyzed the strengthening mechanism at the tissue level. ...
Steel fiber reinforced concrete (SFRC) is a new type of composite material formed by dispersing discontinuous short steel fibers in a uniform and random direction throughout the concrete, which has excellent properties of tensile, shear and high toughness, can effectively improve the load-bearing capacity of arch bridges. In this paper, the mechanics of SFRP in the nodal structure of an arch bridge is initially explored by means of indoor model tests and numerical simulation studies. The results show that the maximum principal tensile stress occurs at the intersection of arch rib, arch foot and tie beam, and the maximum principal compressive stress occurs at the connection between arch rib and arch seat, which should be considered in the design. In this paper, we hope to understand the characteristics of the force and bearing capacity of this type of structure to provide a reference for similar projects.
... Still, as computing technology advances, such approaches become more applicable beyond the material level in the research domain. An overview of the application of discrete methods including the conceptualizations, model definition and application covering the limitations and merits of discrete mechanical models are provided by Bolander et al. [20]. The aforementioned article states that in the application of some discrete models, the discretized cells try to replicate the microstructure or morphology of the targeted material which is referred to as a physical discretization. ...
... In structural element scale, RBSM-based models are already utilized in the study of failure mechanisms of concrete members, effects of cyclic loads as well as failures at structural concrete connections. Such studies are closer to the latter group of discrete models that employ the so-called scalable non-physical discretization approach [20,[26][27][28]. ...
In this study, the cracking behavior of concrete-like materials in keyed shear joints of a structural member under the push-off test is investigated by employing discrete and continuum models. Initially, the behavior of the reinforced concrete member is simulated by a novel discrete element previously developed by the authors and referred to as the Rigid Body Coupled Spring model (RBCS). Shear key connections with different failure modes are modeled and compared to experimental observations. Following that, the numerical outcomes are discussed and compared with the outcome of Finite Element Method (FEM) models employing a continuum plasticity-based damage model. According to the obtained results, with the applied continuum method and constitutive model, unlike the experimental evidence, the modification of the shear key design did not have a significant effect on the failure mode of the modeled connection. On the other hand, the employed discrete element technique was able to represent the failure modes of the shear key connections. This study demonstrates the possibility of the application of discrete methods in studying the behavior of concrete in structural elements.
