Nonlinear Finite Element Analysis Research Articles

Development and Performance Evaluation of an Auxetic Yield Metal Damper for Enhanced Seismic Energy Dissipation

In this study, a new auxetic yield metal (AYM) damper is introduced for the first time based on the application of the auxetic structure. The performance of the proposed system is investigated via nonlinear finite element analysis by using ABAQUS commercial code. These types of steel dampers are fabricated from mild steel plate with elliptical holes and dissipate energy through the inelastic deformation of the constitutive material. To assess the capability of the proposed AYM damper, a set of nonlinear quasi-static finite element analyzes has been conducted on the damper with various geometric parameters. To ensure that the numerical models accurately predict the responses of AYM dampers, experimental validation techniques were employed. This validation confirms the models' sufficient accuracy in representing the dampers' behavior. According to the results, the proposed AYM damper exhibits a low yield displacement, stable hysteretic loops, a good range of ductility, and a high energy dissipating capacity. The specific energy absorption and ductility of the proposed auxetic damper are 32.5J/kg and 59, respectively. With its ductile behavior, this damper can dissipate a large amount of earthquake input energy. Furthermore, it is found that the use of proposed auxetic dampers in the steel frame, increases the hardness, strength and ductility of the frame and the energy absorption increased by 210%.

Punching failure and analytical model for rectangular flat slabs with equal flexural capacities in orthogonal directions

Despite the practical use of rectangular flat slabs with equal flexural capacities in orthogonal directions, their punching behavior has not been addressed. In this paper, the mechanical behavior of such slabs under varying tensile reinforcement ratios and plan dimensions has been investigated, using nonlinear finite element analysis in ABAQUS. Initially, the numerical model of the interior slab-column connection under static vertical loads was developed and thoroughly verified using 20 symmetrical and 9 asymmetrical specimens, covering wide variations in various parameters. Subsequently, parametric studies were conducted on rectangular slabs with equal flexural capacities in both directions, utilizing 54 simulations. The results indicated that the slab aspect ratio strongly affected the load-rotation curves, tensile reinforcement stress, cracking patterns, and shear forces in both directions, as well as their symmetry, despite being designed with equal flexural capacities in orthogonal directions. A novel approach, derived from the critical shear crack theory (CSCT), was developed for this slab type and then compared with existing models. It is noted that the ACI code cannot accurately predict the punching capacity. Although the EN1992–1-1 (2023), MC2010, and CSCT models accurately predict punching capacity, especially when the MC2010 and CSCT models account for two directional rotations, they lack in predicting deformation capacity. However, the proposed model offers accurate predictions for punching and deformation capacities. Its innovations include refining the load-rotation equation, validating the CSCT failure criterion, and quantifying the non-uniform shear force between orthogonal directions.

Structural Performance of Reinforced Concrete Beams with Steel Fibres as Secondary Reinforcement: Experimental and Pre-peak Numerical Modelling

This research consists of an experimental and a numerical investigation into improving the structural performance of reinforced concrete (RC) beams by incorporating hooked-end steel fibres. Experimentally, steel fibres were added to the concrete matrix of 80 mm × 180 mm × 1500 mm RC beams with fibre contents of 0%, 0.5%, and 1%, without replacing traditional reinforcement bars. Each beam underwent a four-point flexural test using a hydraulic press under static loading to evaluate the influence of fibres on flexural behaviour. The numerical analysis aimed to model the macro-scale flexural behaviour of RC beams using a 3D finite element approach in ABAQUS. Challenges in modelling steel fibres include their discrete nature and computational demands due to intricate meshing and convergence issues. The Simplified Concrete Damaged Plasticity Model was used to characterize the compressive and tensile behaviours of plain and steel fibre reinforced concretes. Nonlinear finite element analysis was performed to predict pre-peak load versus mid-span deflection and crack propagation. The model, which does not explicitly simulate steel fibres, was validated against experimental data, showing strong agreement and confirming its effectiveness in capturing the flexural behaviour of steel fibre reinforced concrete beams. Experiments Results showed that steel fibres enhance the flexural performance. Beams with steel fibres exhibited higher first crack loads, ultimate loads, flexural strengths, and toughness. Additionally, the fibres increased crack numbers, reduced crack spacing and length, and improved post-cracking behaviour. The simulation results were subsequently validated against experimental data. The results of the numerical finite element analysis were in good agreement with those of the experiments.

Assessment of the influence of nonlinear soil effects on seismic response of RC structures with floating columns considering soil–structure interaction

Nonlinear dynamic properties of soil crucially influence structural responses during seismic events, highlighting the interdependence between soil and structural behavior. Incorporating soil–structure interaction (SSI) significantly increases structural vulnerability, especially in irregular conditions, compared to traditional fixed-base structures. Despite the emerging construction of reinforced concrete structures with floating columns in urban areas, their seismic performance, particularly when considering soil-structure interaction, remains largely unexplored. Therefore, this study aims to investigate the structural seismic response of mid-rise reinforcement concrete structures with and without floating columns situated on multilayered soil deposits, incorporating the effects of SSI. The nonlinearity of the soil materials was modeled using an isotropic hardening elastoplastic hysteretic constitutive model. A three-dimensional numerical investigation, employing finite element nonlinear time history analysis, was conducted to study seismic responses of structures under different configurations and base conditions. The results were presented as the ratio of structural responses with soil-structure interaction to fixed-base responses subjected to earthquake events. Structures with floating columns exhibited 1.43 times higher peak lateral storey displacement and 55% higher inter-storey drift ratio compared to those without, considering soil-structure interaction. The analysis results demonstrated a decrease in base shear values of up to 35% when accounting for SSI effects.

A Unified Deflection Theory Model for Multi-Tower Self-Anchored Suspension Bridges with Different Tower–Girder and Cable–Girder Connections

This study presents a unified analytical model for multi-tower self-anchored suspension bridges integrating tower–girder connections (TGCs) and cable–girder connections (CGCs) within the framework of deflection theory. The connections are modeled as horizontal springs, and governing equations are derived based on force equilibrium and compatibility conditions. A comparison with a nonlinear finite element analysis under various live load scenarios confirms the accuracy of the proposed model. A parametric analysis reveals that increasing the CGC stiffness reduces girder deflection, decreasing the maximum vertical deflection by nearly 42.3% when the stiffness is increased from 0 to infinity and moving the maximum displacement from the mid-span section to the mid-tower section. Additionally, CGCs modify the load distribution between the main cable and the girder, limiting the longitudinal displacement of the tower in which the mid-tower displacement is reduced by 45.50%. Tower–girder connections improve the anchoring of the side cable to the tower. When connection stiffness is low, side- and middle-tower stiffness significantly reduce girder deflection, though this effect decreases with increasing stiffness. Enhancing mid-tower stiffness similarly reduces its longitudinal displacement regardless of the tower–girder connection. In longitudinal floating systems, mid-tower displacement rises with increasing side-tower stiffness. Establishing a unified analysis model reveals the key parameters in the structural analysis of suspension bridges, enabling an easier and faster analysis of multi-tower self-anchored suspension bridges.

Numerical investigation of existing RC exterior beam-column joints under cyclic loading: case study of 1971 algerian building

Many reinforced concrete (RC) buildings constructed in Algeria before the 1980s may have serious structural deficiencies and are considered substandard according to the Algerian seismic code. Specifically, the failure of the beam-column joints has been the cause of building collapse in many earthquakes in the past: Alasnam October 10, 1980 and Boumerdes May 21, 2003. In this work, the behavior of RC exterior beam-column joints under quasi-static cyclic loading is studied by 3D nonlinear finite element analysis using ANSYS software. To perform the non-linear analysis, the load was applied step by step and the modified Newton-Raphson method was used for the solution. In order to prove that the program successfully captures the necessary response parameters without any modifications to the structure details, some available experimental works were modeled and non-linearly analyzed using ANSYS. Moment-rotation and load-displacement relationships were compared with the experimental data. It was observed that the results are quite similar to each other. Thereafter, a typical RC exterior beam-column joint belonging to a building constructed for residential use in Algeria in 1971 was modeled using ANSYS. The joint was subjected to quasi-static cyclic loading, and its performance was examined in terms of load resistance and failure. The moment-rotation hysteresis curve has been established. The hysteretic loops of the joint, representing the existing structure, showed stiffness degradation and strength deterioration.

Guidelines for Nonlinear Finite Element Analysis of Reinforced Concrete Columns with Various Types of Degradation Subjected to Seismic Loading

Concrete columns are considered critical elements with respect to the stability of buildings during earthquakes. To improve the accuracy of column damage and collapse risk estimates using numerical simulations, it is important to develop a methodology to quantify the effect of displacement history on column force–deformation modeling parameters. Addressing this knowledge gap systematically and comprehensively through experimentation is difficult due to the prohibitive cost. The primary objective of this study was to develop guidelines to simulate the lateral cyclic behavior and axial collapse of concrete columns with different modes of failure using continuum finite element (FE) models, such that wider parametric studies can be conducted numerically to improve the accuracy of assessment methodologies for critical columns. This study expands on existing FEM research by addressing the complex behavior of columns that experience multiple failure modes, including axial collapse following flexure–shear, shear, and flexure degradation, a topic which has been underexplored in previous works. Nonlinear FE models were constructed and calibrated to experimental tests for 21 columns that sustained flexure, flexure–shear, and shear failures, followed by axial failure, when subjected to cyclic and monotonic lateral displacement protocols. The selected columns represented a range of axial loads, shear stresses, transverse reinforcement ratios, longitudinal reinforcement ratios, and shear span-to-depth ratios. Recommendations on optimal material model parameters obtained from a parametric study are presented. Metrics used for optimization include crack widths, damage in concrete and reinforcement, drift at initiation of axial and lateral strength degradation, and peak lateral strength. The capacities of shear–critical columns calculated with the optimized numerical models are compared with experimental results and standard equations from ASCE 41-17 and ACI 318-19. The optimized finite element models were found to reliably predict peak strength and deformation at the onset of both lateral and axial strength failure, independent of the mode of lateral strength degradation. Also, current standard shear capacity provisions were found to be conservative in most cases, while the FE models estimated shear strength with greater accuracy.

A co-rotational finite element for nonlinear analysis of hollow section steel frames accounting for local buckling via lumped damage mechanics

To reduce engineering costs, the search for more efficient materials and design concepts leads to slender structures. Consequently, the need for geometrically nonlinear analysis is becoming increasingly important. Besides, the phenomenon of local instability becomes more evident when dealing with structural components with hollow cross-sections composed of slender plates and shells. It is usual to employ elastoplastic shell finite element models for dealing with such problems, which leads to analyses with high computational costs. Therefore, this paper proposes a geometrical nonlinear beam finite element, developed for the nonlinear analysis of hollow section steel frames, accounting for local buckling. The finite element is locally formulated as the traditional linear Euler-Bernoulli beam element. A co-rotational description of motion is then employed to account for large displacements and rotations. The local buckling phenomenon is taken into account by a lumped damage model, which concentrates the effects at inelastic hinges. The inelastic hinge´s yield functions are defined in terms of the co-rotational nodal axial forces and bending moments, as well as in terms of damage variables. The local buckling of the hollow sections is accounted by the adopted damage evolution law. The inelastic rotations are governed by the normality rule and the evolution laws of the internal variables. A predictor-corrector algorithm is employed at element level, whereas the Newton-Raphson method solves the global nonlinear equilibrium equations. To assess the accuracy of the proposed model, the numerical results obtained in this study are compared against available numerical and experimental responses. The numerical results show good accuracy, which corroborates that the proposed model might be used in practical applications.

Investigating the influence of plate geometry and detonation variations on structural responses under explosion loading: A nonlinear finite-element analysis with sensitivity analysis

Abstract This study presents the results of a numerical analysis of the response of Domex 700 and Dormex 1100 steel plates with varying geometries, combined with several different parameters such as a thickness of up to 6 mm and a trinitrotoluene (TNT) mass. Using ABAQUS software, finite-element analysis was run to examine the structural response ability of the steel plates to explosions. In terms of deformation and energy dissipation, the results showed a large differentiation. A sensitivity analysis was used to examine each simulation result in terms of the structural response performance to explosions and identify the variables that had the greatest impact on variations in the thickness, material, geometry, and TNT mass. The best numerical simulation results were found using the multi-attribute decision-making (MADM) approach. Annotations are utilized to assist in identifying the various modifications made during testing. Annotations LXXI to LVIII achieved the lowest value of 6.176 × 10−09, signifying the best results according to calculations made using the MADM approach. This is evidenced by the structural events, demonstrating that the deformation, von Mises stress, and energy dissipation in the circular plate structure were not significantly impacted by the explosion. The variables that most significantly affect variations in deformation, von Mises stress, and dissipated energy – variables that significantly impact the structural response to explosions – are identified through the sensitivity analysis approach. The results of this research can be used to optimize the structural response performance of circular plates.

Nonlinear finite element analysis of steel-concrete composite beams with cellular I-section under hogging moment

Adopting hybrid cellular I-sections can favor optimizing steel consumption, as the higher steel grade is localized only in the compression tee. In addition, continuous steel-concrete composite cellular beams allow the construction of longer spans due to the combination of higher bending stiffness of the cellular I-section and its connection with the concrete slab, further the continuous of the beam, which provides a better distribution of the bending moment diagram. However, due to the hogging moment on the support regions, the steel-concrete composite beam can present lateral instability of the compression flange accompanied by web distortion, named Lateral-DistortionalBuckling (LDB). No investigations have evaluated the behavior of steel-concrete composite beams with hybrid cellular I-section under hogging moment. This way, the present study aims to assess the behavior of the structure in question using a nonlinear finite element model via ABAQUS software. The investigation consists of verifying the beams' failure mode, considering plastic behavior or LDB, and the effectsof different combinations of steel grades for the hybrid I-section, and further comparing the use of hybrid and homogeneous steel profiles on the composite beams.

Parametric assessment of new O-ring bracing performance under progressive collapse using nonlinear analysis

Progressive collapse poses a significant threat to the structural integrity of buildings under extreme loading conditions, necessitating robust design strategies to mitigate its effects. This paper extends prior research by the same authors on the performance of O-ring bracing during progressive collapse in comparison with other bracing systems. The primary objective is to investigate various design parameters and configurations that optimize the performance of O-ring bracing systems under progressive collapse scenarios through a comprehensive parametric assessment. Nonlinear finite element analysis is employed to evaluate different design parameters, including the size, shape, orientation, and strength of O-ring braced sections, and connection detailing. These factors are assessed for their influence on structural strength, stiffness, and ductility. The parametric study identifies configurations that significantly enhance structural resilience, providing recommendations for future designs aimed at preventing progressive collapse in O-ring braced frames. Data AvailabilityAll data is available from the Authors upon reasonable request.

Numerical Validation of Long-Term Behaviour of Reinforced Recycled Aggregate Concrete Beam

Abstract This research presents an advanced computational framework for predicting long-term deflection, crack width, and creep recovery in reinforced concrete beams incorporating recycled aggregate. The study employs a sophisticated nonlinear finite element analysis using Diana FEA software to construct three distinct models based on widely adopted design codes, i.e., Eurocode 2 EN 1992-1-1, fib Model Code (2010), and ACI 209R-92. The numerical models were rigorously validated through comparative analysis with extant experimental data, with a specific focus on examining the effects of creep, shrinkage, and loss of tension stiffening on long-term deflection, crack width, and creep recovery. This investigation specifically addresses the calculation of long-term deflection, crack width, and creep recovery in recycled aggregate concrete beams subjected to sustained loading over a 3000-day period. The study findings indicate that the fib Model Code (2010) is the most reliable for predicting long-term deflection, crack width, and recovery phenomena, consistently aligning closely with experimental results. In contrast, Eurocode 2 EN 1992-1-1 tends to overestimate deflections during early loading. While ACI 209R-92 shows lower error percentages initially, it significantly underestimates deflections by the end of the loading period.

The influence of anchored CFRP on the torsional and bending behavior of sulfate damaged RC beams

Reinforced Concrete (RC) structural elements are subjected to continuous capacity deterioration due to different overloading situations or environmental conditions, such as sulfate attack, steel corrosion, and alkali-activated binders. Therefore, ensuring the system's integrity is a challenging issue faced by municipal and governmental agencies. This raises the need to upgrade the structural capacity by the utilization of strengthening materials of different material types, such as the externally bonded Carbon Fiber Reinforced Polymer (CFRP) that proves efficiency in increasing the flexural and shear capacities of the strengthened system along with maintaining their ductile type of failure. In contrast, a major deficiency exists in the externally bonded technique, the debonding failure, limiting the benefits from the FRP material's high tensile strength and could be solved using a proper and efficient anchoring method. A new and novel use for the CFRP anchored strengthening system was proposed in this study to upgrade the beam's capacity against the effect of sulfate attack damage. The behavior of simply supported strengthened beams was examined in this study under the effect of combined torsional and bending stresses using the Nonlinear Finite Element Analysis (NLFEA) technique using twenty-two models that are divided into six main groups. The investigated parameters were the depth of the anchored CFRP (wfa) (0.00 hf, 0.25 hf, 0.50 hf, 0.75 hf, and 1.00 hf) and sulfate damage cycles (0 (without), 60, 90, and 150 cycles). The structural efficiency of the modeled beams was examined using the torsion-twist curves, the torsion and twist capacities at the ultimate stage, failure mode, stiffness (pre and post-cracking), steel, stirrups, and CFRP strains, and finally, the energy absorption. It has been found that the resulting improvement percentage has a directly proportional relationship with the depth of the anchored CFRP. In contrast, an inversely proportional relationship exists between the improvement percentage and the number of exposed sulfate damage cycles. In conclusion, applying externally boned anchored CFRP has a superior contribution to the RC beams structural performance.

Topology optimization for metastructures with quasi-zero stiffness and snap-through features

Quasi-zero stiffness (QZS) is highly demanded in passive vibration isolators. Most of the existing design methods of QZS vibration isolators are typically based on mechanism designs, where pre-defined structural configurations, components, or mechanisms with certain features, such as negative stiffness, are required to synthesize the designs. This work introduces topology optimization for QZS structure designs, enabling the design of structures without pre-definitions and resulting in single-part designs rather than structural assemblies. We propose novel mathematical formulations of the objective function based on the QZS force-displacement curve and generic mathematical formulations of the optimization problem. An extended moving isosurface threshold method is used to solve the formulated optimization problem. In addition, topology optimization of metastructures with snap-through features and an alternative design method that synthesizes QZS metastructures by combining snap-through structures with positive stiffness elements are also presented. The optimized snap-through metastructures are numerically validated by nonlinear finite element analysis (NFEA) and experiment, which shows negative stiffness and snap-through characteristics. Numerical examples and investigations are presented for the QZS structures designed by both optimization and synthesis methods. The NFEA results reveal the QZS designs obtained from the two methods can achieve approximately constant stiffness of 0.502 N/mm over a 17 mm displacement range and 0.402 N/mm over a 12 mm displacement range, respectively.

Non-intrusive parametric hyper-reduction for nonlinear structural finite element formulations

Model Order Reduction (MOR) is a core technology for the creation of comprehensive executable Digital Twins, since it efficiently reduces the computational burden of high-fidelity models. When dealing with nonlinear structural Finite Element analyses, several Hyper-Reduction (HR) approaches have been developed to reduce the computational cost. Nonetheless, HR approaches are typically intrusive in nature, posing challenges when it comes to integration into existing (commercial) software. Recently, data driven Non-Intrusive MOR methodologies have been proposed. However, these techniques often suffer from overfitting and violate key physics properties, leading to unstable behavior. This work proposes to use Scientific Machine Learning to reintegrate critical stability-preserving physics properties. It introduces a data-driven, physics-augmented, parametric approach that combines Proper Orthogonal Decomposition (POD) with a Partially Input Convex Neural Network (PICNN) architecture. The proposed method effectively reduces the computational burden associated with parametric static nonlinear elastic structural problems while retaining material consistency, hyper-elasticity, and material stability properties in the Reduced Order Model. Numerical validation on several structural models subjected to geometrical and material nonlinearities under static loading conditions demonstrates the effectiveness of the POD-PICNN approach. Additionally, three different sampling strategies have been compared to assess their impact on the method performance. The results emphasize that physics-augmentation is required, as it inherently embeds essential physical constraints into the neural network architecture, ensuring stable and consistent behavior, while highlighting its potential for dynamic and multiphysics applications.

Isothermal aging effect on SAC interconnects of various Ag contents: Nonlinear simulations

Abstract The mechanical behavior of the tin (Sn)–silver (Ag)–copper (Cu) (SAC) lead-free solders is strongly influenced by the isothermal aging due to the evolution of the microstructure and mechanical properties. This study aims to examine the influence of pre-isothermal aging at 100°C on the mechanical behavior of different SACN05 alloys with different silver content including N = 1 , 2 , 3 N=1,\hspace{.25em}2,\hspace{.25em}3 and 4% by applying nonlinear finite element analysis. The mechanical properties, including elastic and inelastic properties, of the SAC systems with various Ag percentages are gathered from the literature and incorporated in thorough thermomechanical simulations. In addition to the unaged solders condition, two aging periods, 6 and 12 months, are studied. The computational results showed that the mechanical response of pre-aged SACN05 solders is significantly influenced by the aging duration and silver content. Specifically, interconnects with higher Ag percentage are shown to be more resistive to aging and expected to have lower thermally induced inelastic deformations, strains, and strain energies. Therefore, better thermal fatigue performance and improved failure resistance is potentially expected. However, the pre-isothermally aged SACN05 solders generally exhibit lower resistance to the accumulations of inelastic strains and strain energies. Thus, it is probable that pre-aged SACN05 solders will demonstrate deterioration in thermal fatigue performance compared to unaged interconnects. Nonetheless, the aged SAC solder systems could be an innovative solution for designing electronic devices regularly exposed to shock and impact loading as the aging process significantly reduces the brittleness of the SnAgCu alloys.

Experimental and numerical investigation of failure modes in RC frame structures designed using the equivalent linearization method

The codes of many countries currently employ the column-to-beam flexural strength ratio (CBFSR) based on frequent earthquake internal forces to achieve the expected strong-column-weak-beam (SCWB) ductile failure mode. However, real earthquake damage indicates a general failure to achieve SCWB. The design method based on frequent earthquake internal forces struggles to consider factors such as internal force redistribution and variable axial forces under rare earthquakes. Therefore, developing a seismic design method directly based on rare earthquake internal forces is crucial. The equivalent linearization method is a practical approach for obtaining the internal forces of RC frame structures under strong earthquakes without extensive nonlinear computations. In this paper, nonlinear finite element analyses of RC frame structures with expected SCWB failure modes under various structural parameters were conducted to obtain ductility coefficients under rare earthquakes. Using the equivalent linearization method based on secant stiffness, the equivalent stiffness and damping of beams and columns were calculated. Simplified parameters were determined for engineering applications to facilitate seismic design based on rare earthquake internal forces. Two RC frame structures were designed using both the equivalent linearization method and the CBFSR code method, and then subjected to pseudo-static low-cycle reciprocating loading tests. The study investigated failure modes and hysteretic energy dissipation, as well as overall stiffness and bearing capacity under earthquake conditions. Results showed that the equivalent linearization method can effectively direct RC frame structures to achieve the expected strong earthquake failure mode.The dynamic time history analysis was performed on finite element models of different heights, and the results indicated that the equivalent linearization method significantly reduced plastic hinge occurrences and ductility coefficients of column ends, resulting in improved seismic performance compared to the CBFSR code method.

Analytical study on fire resistance performance of precast concrete hollow-core slabs for electric vehicle fire in parking structures

This study evaluated the effects of fires that occur in internal combustion engine vehicles (ICEVs) and battery electric vehicles (BEVs) on the structural safety of hollow-core slabs (HCS) installed in parking structures. A fire simulation of a prototype parking structure was performed using the time–heat release rate curves of ICEVs and BEVs derived from fire experiments, and fire behavior and temperature history were derived according to the fire curve. Additionally, nonlinear finite element analysis was conducted using a general-purpose finite element analysis program, and the fire resistance performance of HCS was evaluated according to the fire curve and slab load ratio. In the case of a fire in ICEVs, the performance criteria of ISO 834–1 were met even at a slab load ratio of 0.7. However, in the case of a fire in BEVs, the standard for insulation was not met as the temperature change of the upper surface of HCS exceeded 180 K, and the load-bearing capacity was also not satisfied as the limiting deflection reached a slab load ratio of 0.7.

Numerical and analytical study on the punching shear capacity prediction for eccentrically loaded flat slabs with openings

The punching shear behavior of interior flat slab was examined in this study in the absence of shear reinforcement using numerical and analytical techniques. The effect of sensitive parameters was investigated and their influence was examined and reported including the opening existence and location, loading eccentricity, and slab height. The effect of the reinforcement ratio is neglected in most of the literature models and code provisions with the influence of loading eccentricity being addressed inappropriately. Therefore, this study adopted the nonlinear finite element analysis (NLFEA) method for the numerical part where the flat slab punching shear behavior was studied in detail. Results were compared in their behavior at both cracking and ultimate stages, absorbed energy, elastic and plastic stiffnesses, and general trend lines were provided. The effect of the reinforcement ratio was assessed indirectly with slabs of similar reinforcement area and different slab effective depths (65, 95, 125, and 155) mm where a 25 mm concrete cover was used. In addition, the NLFEA punching shear capacity results were compared with three international codes (American Concrete Institute (ACI318-119), EuroCode (EC2), and Model Code (MC2010)) to highlight their potential predictability and weakness points. It was found that the MC2010 has the most conservative prediction, followed by the EC2 and the ACI318-19 predictions. Therefore, two modification parameters were proposed for the ACI318-19 punching shear capacity calculation with R2 value of 0.98. The modified version of the ACI318-19 was validated using experimental data from the literature proving a high prediction capability.

Comparison of the Biomechanical Effect of Distal İmplants Placed at Different Angles in the All-On-Four Technique: A Nonlinear Finite Element Analysis: (Effect of Distal Implant Angles in All-on-Four)

IntroductionThe "All-on-four" technique addresses this by placing two vertical implants in the anterior region and two posterior implants angled up to 45 degrees. This study evaluates stress distribution on bone, implants, abutments, gingiva, and prostheses based on posterior implant angulation, using both standard and angled neck implants. Additionally, angled neck implants were used alongside standard implants. MethodsTo evaluate the biomechanical stress and displacement behavior of implants placed at 15°, 30°, 45°, and 30° neck-angled in the interforaminal region of using the All-on-four technique, under a 200N masticatory force on bone, implant, abutment, and prosthesis, using the FEA method with a nonlinear solver. ResultsThe stress values measured in the neck region of the angled implant and abutment placed in the distal region were highest in model IV (305 and 420 MPa), followed model III (282 and 359 MPa), model II (192 and 337 MPa) and lowest in model I (177 and 225 MPa), respectively. The mean elemental von Mises stress in the mandibular bone region where the implant was placed was highest in model I (56 MPa) and lowest in model III (40.4 MPa). ConclusionAs the angle of insertion of the implant into the bone increases, the biomechanical stress value on the implant and abutment also increases. Among the models, the lowest von Mises stress values on the implant and abutment were measured in model I and model II. Models with low stress values can be recommended for patients with clinical conditions and biomechanical risk factors.