Damage Plasticity Model Research Articles

An investigation and design of novel moment-resisting beam-column connections for precast concrete construction

This study investigates the behavior of hybrid beam-column connections with numerous detailing methods to be incorporated into precast concrete moment-resisting frames under simulated reversed cyclic loading, and ultimately develops a design procedure. Seismic performance of moment-resisting precast concrete beam-column connections was investigated through simulated reversed cyclic load tests. In addition, nonlinear finite element analysis (FEA) of typical monolithic and precast concrete connections was carried out using a modified concrete damage plasticity model. Good agreement was achieved between experimental and numerical results, which indicates that the FEA model is capable of capturing failure modes of the investigated precast concrete connections. Simple detailing modifications resulted in major improvements in the performance of connections in terms of load-displacement curves, stiffness, and energy dissipation. Finally, a design procedure was developed for the investigated connections based on failure modes and investigated limit states.

FURTHER DEVELOPMENT OF GDEM FOR THE MODELING OF MULTI-SCALE DYNAMIC RESPONSE OF ROCK SUBJECTED TO BLASTING AND IMPACT

The dynamical responses of rock subjected to blasting and impact have been of concern in most underground projects. Due to the size effects and strain-rate enhancement induced by inertial effects, the dynamic responses of rock and underground structures show multi-scale characteristics. Thus, in order to achieve better understanding of multi-scale dynamic responses of rocks, both computation accuracy and numerical efficiency have been taken into account. This is achieved by further development of a continuum-discontinuous element method code, called GDEM, with a new type of dynamic bounding-surface damage model being implemented, thus forming a bounding-surface dynamic plasticity damage-GDEM model (DB-GDEM). A dynamic bounding-surface damage model is adopted, with the strength surface of Holmquist-Johnson-Cook model being employed as bounding surface. The concept of critical state, strainrate hardening, and continuum damage evolution has been taken into account for both brittle and ductile responses of rock. The model performance has been demonstrated by a few numerical simulations, including the Landau blast model, explosions under various confinements, and trapezoidal impulse loading, etc. By comparing modeling results among DB-GDEM model, linear-elastic model in GDEM, and D-P model in GDEM, it is noted that the contribution of plasticity-damage can result in the decay of stress waves and deterioration of dynamic strength. Both continuous and discontinuous mechanical behaviors of rocks have been captured well by the newly developed DB-GDEM model. The main multi-scale dynamic characteristics of rock subjected to blasting and impact, including particle movement, fragmentation of rock mass, stress-wave propagation, and failure models, have been captured. The introduction of bounding-surface plasticity damage model in GDEM would reproduce a more realistic dynamic damage response of rock compared with the original GDEM model that embedded with conventional constitutive models.

Early age cracking relevant to mass concrete dam structures during the construction schedule

Managing the early-age thermal behavior of mass concrete structures like dams, dykes, bridge piers, thick raft foundations, etc., is the major concern during their construction. The heat of hydration (HOH) of the fresh concrete pour does not get easily dissipated to ambiance since concrete is predominantly a poor conductor of heat. Eventually, in the presence of external boundary conditions (thermal or mechanical), the slower rate of heat dissipation may at times induce a substantial thermal gradient within the mass concrete which further may induce thermal stresses leading to the formation of cracks. The article attempts to develop a thermo-mechanical numerical model based on the finite element (FE) methodology to mimic the early age behavior of mass concrete that accounts for time and temperature-dependent heat generation during the hydration process with the evolution of thermal and mechanical properties over time. A two-stage sequential thermo-mechanical model is developed consisting of a thermal model to assess the thermal history of a particular concrete mix which is experimentally validated by performing thermal monitoring of a fresh concrete pour for 10 days, and a mechanical model to assess the stress and the cracking states, the model utilizes the concrete damage plasticity (CDP) model based on the principle of continuum damage mechanics which is characterized by experimental results. Later on, the methodology so developed is employed over a practical scenario of the dam construction process considering the relevant boundary conditions to arrive at a suitable optimum lift height and pouring frequencies.

Effect of different configurations of end stirrups on the seismic performance of RC columns

To improve the seismic performance of reinforced concrete (RC) columns, this paper establishes the equations for the theoretical relationship of bending-shear resistance of RC columns based on the theory of truss and arch. Tests and finite element simulations are carried out on six groups of specimens with the same main reinforcement but different stirrup configurations and stirrup ratios. Based on theoretical calculations, test data, and simulation results, the hysteresis curves, failure modes, compressive deformations, main reinforcement deformations, and deformations at the ultimate limit state of carrying capacity of the RC columns are investigated. Moreover, the feasibility of adjusting the stirrup configurations and stirrup ratio for controlling the damage location at the end of the column is discussed. The comparison of the results shows that the hysteresis curves obtained from the tests and the finite element simulations are in general agreement, verifying the correctness of using the concrete plastic damage model for modeling. In addition, the theoretical results based on the theory of truss and arch are closer to the test results, which also proves the reliability of the theory. By analyzing the results, the relationship between the ratio of the test and theoretical values (Z) and the stirrup ratio (ρw) is summarized through fitting. Under the ultimate limit state of carrying capacity, it can be concluded that the encryption of the stirrup reinforcement at the end of the column can retard the crack development and reduce the shear deformation. Overall, the computational method proposed in this paper has high accuracy in predicting column cracks and detecting the ultimate load-carrying capacity.

An Advanced Formulation for Rehabilitating Shear Strength in Deep Beams with Shear Openings through Integration of Varied Steel Configurations for Utility Provisions

In the contemporary urban landscape, rapid technological advancements necessitate adaptations in industrial and residential structures to accommodate new utilities such as ducts, pipes, and passages. This study focuses on formulating a design methodology and aid for recovering shear capacity losses resulting from openings in existing solid deep beams. A novel design approach involves the implementation of steel elementary configurations around the openings in deep beams, enhancing their shear resistance. The study employs a systematic investigation, integrating simulation through the ABAQUS program, to assess the effectiveness of the proposed steel configurations in restoring shear capacity. The research explores three distinct steel configurations, emphasizing the synergy between concrete and steel materials. Concrete Damage Plasticity models, incorporated within ABAQUS, enable detailed quasi-static analysis to unravel the intricate behaviour of deep beams subjected to shear openings and strengthened with proposed steel formations. Specifically, a deep beam model featuring a combination of a full-length steel plate welded with a steel cylinder around the opening (EDSBPD) exhibited full capacity restoration, achieving an efficiency of 1.0064 compared to solid deep beams. Leveraging ABAQUS simulations and adhering to ACI 318-14 specifications, a parametric study was conducted to investigate the EDSBPD for design assistance. This study led to the development of a dimensionless equation that calculates the shear strength of deep beams, accounting for the impact of the thickness-to-width ratio of the steel configuration around the opening. This equation provides a valuable tool for incorporating openings into solid deep beams without compromising shear strength.

Compressive and tensile behaviour of alkali‐activated slag‐based concrete incorporating single hooked‐end steel fibres

AbstractThe effect of single hooked‐end steel fibres, namely Dramix® 3D, on the mechanical performance of alkali‐activated slag‐based concrete (AASC) and Portland cement concrete (PCC) has been investigated. Compressive strength, modulus of elasticity, stress‐strain response under uniaxial compression and tension, splitting tensile strength and flexural strength have been evaluated. The experimental results show that AASC incorporating 3D fibres in a volume fraction of 0.75% exhibits an enhanced behaviour, under both compression and tension, in comparison to PCC incorporating the same fibre type and dosage. Although the reference mixes show similar compressive strength, 3D fibres enhance the modulus of elasticity, splitting tensile strength and flexural strength of AASC of 8.6%, 61.7% and 12.8%, respectively, while for PCC 1.1%, 42.2% and 16.1%, respectively. Three‐point bending tests show the effect of 3D fibres on the response of AASC and PCC under flexural loading. Although fibres have a limited effect on the strength corresponding to the limit of proportionality (LOP), they enhance the post‐peak behaviour, increasing the residual flexural strength and the material ductility. Finite element analysis has been performed to predict the flexural behaviour of steel fibre‐reinforced AASC (FRAASC) under flexural loading. The Concrete Damage Plasticity (CDP) model implemented in ABAQUS software can predict the flexural response of FRAASC quite accurately, although additional experimental data are needed to calibrate the model for different alkali‐activated matrix types.

Stress-strain models and numerical simulations of steel headed studs at low temperatures

Headed studs are commonly used in steel–concrete composite (SCC) structures. To promote the application of SCC structures in cold regions, this study first developed prediction equations for key indexes in temperatures ranging from 20 to −80 °C. Then, full-range stress–strain (σ–ε) models of headed studs considering low temperatures were proposed. Validations against 56 tensile test results confirmed that the developed constitutive models accurately estimated the stress–strain behaviour of headed studs at low temperatures. Subsequently, finite element models along with the continuum damage plasticity model (CDM) and proposed σ–ε models were developed for headed studs at varying temperatures. Using the test results combined with finite element analyses, the true stress–strain curve and stress-modified critical strain model were calibrated for headed studs at low temperatures. Finally, the reliability of the developed CDM and σ–ε models were validated by applying them to finite element models of six pull-out and eight push-out specimens.

Fragility evaluation of nuclear containment structure subjected to earthquake and subsequent internal pressure

Strong earthquake may lead to the rupture of pipeline inside the nuclear containment structure, which leads to overpressure of the nuclear containment structure. Therefore, nuclear containment structure suffers from the risk of subjected to earthquake and internal pressure sequence. However, studies on the performance evaluation of the nuclear containment structure subjected to earthquake and subsequent internal pressure sequence is very rare. This study presents fragility evaluation of the nuclear containment structure subjected to earthquake and subsequent internal pressure sequence. Firstly, detailed nonlinear finite element model of the nuclear containment structure is developed with layered shell element and concrete damage plasticity model. Then, 20 far-fault ground motion records are selected and scaled to different intensity levels to simulate different damage states of the nuclear containment structure. Nonlinear response of maximum strain, displacement and fragility of the nuclear containment structure subjected to earthquake and subsequent internal pressure sequence is analyzed. Results reveal that distribution of maximum strain and displacement of the nuclear containment structure subjected to earthquake and subsequent internal pressure are significantly different. Maximum displacement distribution of the nuclear containment structure subjected to earthquake is related to the ground motion intensity level. The variation of the median pressure capacity and logarithmic standard deviation presents a quadratic form with the increase of ground motion intensity level.

An energy-based chemo-thermo-mechanical damage model for early-age concrete

Cracking prediction and control in hydration process of mass concrete and structures has always been a challenging task. In this work, an energy-based chemo-thermo-mechanical damage model for early-age concrete is well established within the framework of thermodynamics and continuum damage mechanics. The evolution laws for the mechanical damage are driven by the work conjugate elastoplastic damage energy release rates to fully represent the microcracks closure-reopening effect, the anisotropy, and the aging effect of concrete relating to the degree of hydration. A formulation fitted from a large number of test data is introduced to simulate the thermal evolution during hydration process, resulting in an excellent approximation of the degree of hydration. When the degree of hydration is 1, the model is degenerated into the classical plastic damage model. The presented model is thus able to simulate the hydration process of early-age concrete and mechanical responses of concrete as well as reinforced concrete structures at any age. The model is implemented by user defined subroutine in Abaqus, in which a sequential coupling method is established. Several benchmark tests are successfully reproduced, indicating that the proposed model is capable of predicting the damage evolution and typical nonlinear behavior of early-age concrete and hardened concrete. The computational efficiency of the model is significantly improved compared to the classical ones due to the introduction of the fitting formulation of the thermal evolution and the sequential coupling method to reduce the nonlinearity of the system. The strategy allows the model to be applied in massive concrete structures during construction and provide valuable prediction as well as guidance for large scale engineering structures.

Experimental and numerical investigation of screw anchors in large crack width

In predicting the capacity of screw anchors under static tensile loading, the Concrete Capacity (CC) method is the state-of-the-art prediction model which covers concrete cone capacities in uncracked and cracked concrete up to 0.3 mm crack width. However, in seismic applications, anchors may be subjected to large crack widths of up to 0.8 mm. With large crack width, the behaviour of small-sized (typically 6 mm) screw anchors has not been studied. In this study, experimental investigations were conducted for a total of 29 anchors in uncracked and cracked concrete with large crack widths up to 0.8 mm. The experimental results showed that the load-carrying capacity of screw anchors significantly dropped resulting in a reduction factor of 0.13–0.47 for cracked concrete with 0.8 mm crack width (significantly lower than 0.7 assumed by the CC method for a crack width of up to 0.3 mm). This paper focused on developing modelling technique for predicting the performance of screw anchors in cracked concrete with a crack width of up to 0.8 mm since screw anchor in cracked concrete has not been studied using finite element analysis. Three-dimensional finite element models were developed for screw anchors in uncracked and cracked concrete and validated by the experimental results. Further, parametric analysis showed that dilation angle and shape factor are the two most influencing parameters among other of the concrete damage plasticity model.

Evaluation of the Dynamic Stability of Underground Structures Assuming a Hydrogen Gas Explosion Disaster in a Shallow Underground Hydrogen Storage Facility

Amid the ongoing global warming crisis, there has been growing interest in hydrogen energy as an environmentally friendly energy source to achieve carbon neutrality. A stable and large-scale hydrogen storage infrastructure is essential to satisfy the increasing demand for hydrogen energy. Particularly for hydrogen refueling stations located in urban areas, technological solutions are required to ensure the stability of adjacent civil structures in the event of hydrogen storage tank explosions. In this study, a numerical analysis using equivalent trinitrotoluene (TNT) and Concrete Damage Plasticity (CDP) models was employed to analyze the dynamic behavior of the ground in response to hydrogen gas explosions in shallow underground hydrogen storage facilities and to assess the stability of nearby structures against explosion effects. According to the simulation results, it was possible to ensure the structural stability of nearby buildings and tunnel structures by maintaining a minimum separation distance. In the case of nearby building structures, a distance of at least 6 to 7 m is needed to be maintained from the underground hydrogen storage facility to prevent explosion damage from a hydrogen gas explosion. For nearby tunnel structures, a distance of at least 10 m is required to ensure structural stability.

Retraction Note: Investigation of bond-slip in reinforced steel rebar using concrete damage-plastic model

Retraction Note: Investigation of bond-slip in reinforced steel rebar using concrete damage-plastic model

Numerical modelling of 3D concrete printing: material models, boundary conditions and failure identification

3D concrete printing (3DCP) attracts significant attention as an innovative manufacturing technology for the construction industry. As one of the challenges in 3DCP, failure mechanisms of 3D printed concrete structures were not well understood yet and hard to predict. The three-dimensional finite element (FE) method is an effective method to simulate such a layer-by-layer process. However, some existing technical issues in FE modelling, including additional initial deformations, failure identification, selection of material models, concrete foundation interactions and initial imperfections, need to be addressed for accurate simulation of 3DCP. In this study, FE models using a novel tracing element approach are developed to capture mechanical behaviours and failure modes of typical 3D printed concrete structures. The developed FE models was validated by comparing the obtained numerical results with those data available in literature. Furthermore, four material constitutive models are investigated analytically and numerically to compare their applicability in modelling 3D printed concrete structures. The obtained results show that the Mohr-Coulomb and Concrete Damage Plasticity (CDP) models can accurately predict failure behaviours of 3D printed concrete structures.

Numerical Analysis of Reinforced Concrete Corbels Using Concrete Damage Plasticity: Sensitivity to Material Parameters and Comparison with Analytical Models

The Concrete Damage Plasticity (CDP) model is a widely used constitutive model to represent the non-linear behavior of concrete in numerical analysis. However, a limited number of studies compared the level of accuracy of numerical models with the main code provisions from the literature. In addition, the influence of CDP material parameters on the structural behavior of corbels was scarcely studied. This study proposes to evaluate the ability of numerical models using CDP to represent the structural behavior of corbels regarding the ultimate load, reinforcement deformation and failure mechanism. In addition, we compared the predictions of the numerical models with the ones from design code expressions regarding the ultimate capacity. For this, three test results of corbels from the literature were evaluated with numerical models using the CDP, as well as with analytical models from different code provisions. A sensitivity analysis—by changing the dilation angle (ψ) and shape factor (Kc)—was performed. The comparison between tested and predicted resistances with the proposed numerical modeling choices was equal to 1.04 with a coefficient of variation of 11%. On the other hand, the analytical models evaluated overestimated the corbel capacity by more than 62%, on average. Therefore, the proposed modeling choices provide better predictions of ultimate capacity than the evaluated analytical models and can be used to assess the corbel design under more complex boundary conditions.

A dislocation density-based crystal plasticity damage model for rolling contact fatigue of gradient grained structures

A dislocation density-based crystal plasticity damage model is presented for a numerical study on the spalling behavior of gradient grained structures under rolling contact fatigue loading. The topology of the gradient grained structure is constructed using Voronoi tessellations. The fatigue damage is coupled into a dislocation density-based crystal plasticity model where the evolutions of the dislocation density and fatigue damage are considered. The process of spalling is characterized by the evolution of fatigue damage in the polycrystalline structures. The evolutions of contact pressure, stresses, dislocation density, plastic strain, and fatigue damage of gradient grained structures with regard to rolling cycles are investigated. Moreover, the effect of the gradient form and residual stress on the rolling contact fatigue behavior is studied. The simulation results reveal that the gradient grained structures and the residual stress influence the rolling contact fatigue resistance.

Strengthening of Reinforced Concrete Non-Circular Columns with FRP.

Fiber reinforced polymer (FRP) strengthening in circular columns is known to be more effective than in rectangular and square columns because of the uniform distribution of confining pressure. This study explores the effectiveness of using carbon-FRP anchors to improve the confinement of square reinforced concrete (RC) columns strengthened with FRP. Sharp corners in non-circular columns cause stress concentration on the corners, reducing the effectiveness of strengthening. To address this, the study examines the impact of three different anchor configurations on two sizes of FRP-strengthened square columns. The results show that the proposed anchors distribute stresses to a greater extent, resulting in a more uniform distribution of stresses and better confinement. For the best performance, it is proposed that the anchor fans surround the corners of the cross section. Experimental findings and finite element analysis results using the Concrete Damage Plasticity model in the ABAQUS material library match.

Investigation of Load–Displacement Characteristics and Crack Behavior of RC Beam Based on Nonlinear Finite Element Analysis Using Concrete Damage Plasticity

Crack patterns provide critical information about the structural integrity and safety of concrete structures. However, until now, there has been a lack of sufficient studies on using the Finite Element (FE) method to investigate the characteristics of the crack patterns of reinforced concrete (RC) beams. Therefore, this study aims to develop an FE model to analyze the load–displacement and crack characteristics of a beam under a four-point bending test using the concrete damaged plasticity (CDP) model that accounts for the influence of mesh size. The simulation results were validated against experimental results, including mesh convergence analysis, energy balance, load characteristics, and crack patterns. A parametric study was then conducted using this model to investigate the influence of the rebar’s diameter, number, and spacing on the RC beam’s load–displacement characteristics and crack behavior. The findings demonstrate that the FE model accurately simulates the working behavior of the RC beam, with a maximum deviation at a cracking load of 8.7% and crack patterns with a maximum deviation in the mean crack height of 12.1%. In addition, the results of the parametric study suggest that the rebar configuration significantly affects the RC beam’s loading carrying capacity. This study provides deeper insights into the use of FE modeling for analyzing the behavior of RC beams, which can be useful for designing and optimizing structures in civil engineering.

An improved constitutive model for steel tube-confined ultra-high-strength concrete

This study aims to accurately simulate the compressive behavior of ultra-high-strength concrete (UHSC) under various confinement conditions through conventional triaxial and equi-biaxial compressive tests. The triaxial compressive tests revealed that the stress and dilation angle of the concrete varies with changes in axial plastic strain and confining pressure, which is not well-considered in existing mechanical models for UHSC material. To address this limitation, an improved constitutive model based on the concrete plastic damage (CDP) model is proposed in this paper. The improved model incorporates the confining pressure in the flow rule and the hardening/softening rule, in addition to the axial plastic strain. The tensile and compressive meridians of the yield surface are calibrated based on the triaxial and biaxial compressive test results. Furthermore, the study proposes formulas for expressing the stress–strain relation and the lateral-to-axial plastic strain relation of UHSC under different confining pressures. These formulas help generate the hardening/softening rule and the dilation angle evolution of the flow rule, respectively. To verify the proposed constitutive model, the study simulated tests on UHSC-filled steel tube (UHSCFST) stub columns under compression using the finite element method. The simulated results of the peak bearing capacity of the tested UHSCFST stub column specimens are satisfactory, and the interaction between the steel tube and the concrete is reasonably predicted. The proposed improved constitutive model has the potential to accurately simulate the compressive behavior of UHSC under different confinement conditions, which can aid in the design of composite columns made with UHSC materials.

Axial compressive behaviour of composite steel elements incorporating rubberised alkali-activated concrete

This study presents an experimental and numerical investigation into the axial compressive behaviour of steel tubes infilled with rubberised alkali-activated concrete. An experimental programme involving circular and square concrete filled steel tubes with different length-to-diameter or length-to-width ratios and concrete infill mix designs with varying rubber contents, of up to 60% crumb rubber replacement of natural aggregates, is firstly described. A detailed account of the experimental results, including the axial capacity, stiffness, toughness, ductility, stress-strain response, and failure patterns, is given. The numerical study is performed in ABAQUS/CAE and the concrete compressive behaviour is modelled using the Concrete Damaged Plasticity model with a modified function for the compressive behaviour. The numerical results are validated against the experimental results, and a parametric study involving 315 finite element models is carried out to cover a wide range of concrete and steel material properties and different steel tube dimensions. The results show that an increase in rubber content in the concrete infill leads to a reduction in the axial capacity; however, this reduction is lower than that observed for unconfined specimens. The results also illustrate an increase in ductility with higher rubber content, which is mainly noticeable for members with circular sections as compared to those with square sections. The experimental and numerical results are used to examine the axial capacity prediction approaches in Eurocode 4 and AISC 360, with particular focus on assessing the confinement effects. It is shown that codified prediction equations for square concrete filled steel tubes give reasonably accurate results. Both codes, however, result in poor predictions for circular concrete filled steel tubes, with Eurocode 4 leading to unsafe predictions while AISC 360 gives overly conservative estimates. Modifications to Eurocode 4 and AISC 360 axial capacity approaches for circular tubes are proposed and are shown to offer significant improvement in terms of safety and accuracy of design.

Damage distribution and mechanical properties analysis of CRTS III slab track under uneven subgrade settlement

Due to the complex geological conditions along the high-speed railway, the subgrade uneven settlement (USS) is inevitable, and the safety and stability of the railway are significantly affected. In this paper, a three-dimensional solid model of the CRTS III slab track is established. Based on the concrete damaged plasticity (CDP) model, the influence of USS on structural damage, deformation, stress, and gap is analyzed. Simultaneously, as a reinforced concrete structure, the structure reinforcement is an essential part of strengthening its tensile capacity. Consequently, the distribution of internal reinforcement is considered in detail, and the influence of reinforcement on the mechanical properties of the track structure is further explored. The results show that the base plate is the most vulnerable component under the USS, and its primary damage locations are the middle and edge of the USS and the middle track slab edge. The next component that is susceptible to damage is the self-compacting concrete, whose primary damage locations are the longitudinal outer side of the limit lug boss and the USS middle. The damage of each component increases monotonically with increasing settlement amplitude, first increasing and then decreasing with increasing wavelength, especially noting the cases of L = 15–20 m, which is the most unfavorable wavelength range for most amplitudes. The difference between the results under the CDP and linear elastic models increases with the increase in damage. The reinforcement significantly influences the value, range, and location of the structural concrete damage. The component of load-bearing stress shifts from concrete to reinforcement at severe damage locations.