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This study evaluated the effect of traditional and conservative endodontic access cavity designs in combination with WaveOne Gold and TruNatomy instrumentation systems on the fracture resistance of mandibular first molars by means of nonlinear finite element analysis (FEA). Micro-CT images of 4 human mandibular first molars were used to generate representative FEA models. The mandibular first molars samples were scanned before and after endodontic access cavity preparation and instrumentation of all 3 canals. Five nonlinear static loads were applied vertically and horizontally to specific contact points on the occlusal surface of the teeth. Maximum von Mises stress before failure and distribution of von Mises strains were recorded and compared between groups. Molars with conservative endodontic access cavities required similar levels of loads to reach failure compared with their control samples, whereas molars with traditional endodontic access cavities required significantly reduced loads in order to fail. According to the numerical investigation, the type of instrumentation system was found to have an insignificant effect on the fracture resistance of the teeth under study. Von Mises stress was concentrated around the cervical region and in the larger distal roots for all numerical models. The fracture resistance of mandibular first molars is influenced significantly by a reduction in dental hard tissue, which was found to control the level of the ultimate failure load for each tooth. [ABSTRACT FROM AUTHOR]

Modelling of concrete through 3 D constitutive material models is a challenging subject due to the numerous nonlinearities that occur during the monotonic and cyclic analysis of reinforced concrete structures. Additionally, the ultimate limit state modelling of plain concrete can lead to numerical instabilities given the lack of steel rebars that usually provide with the required tensile strength inducing numerical stability that is required during the nonlinear solution procedure. One of the commonly used 3 D concrete material models is that of the Kotsovos and Pavlovic, which until recently it was believed that when integrated with the smeared crack approach, it can only be used in combination with relatively larger in size finite elements. The objective of this study is to investigate into this misconception by developing different numerical models that foresee the use of fine meshes to simulate plain concrete and reinforced concrete specimens. For the needs of this research work, additional experiments were performed on cylindrical high strength concrete specimens that were used for additional validation purposes, whereas results on a reinforced concrete beam found in the international literature were used as well. A discussion on the numerical findings will be presented herein by comparing the different experimental data with the numerically predicted mechanical response of the under study concrete material model. [ABSTRACT FROM AUTHOR]

A computationally efficient and robust simulation method is presented in this work, for the cyclic modeling of reinforced concrete (RC) structures. The proposed hybrid modeling (HYMOD) approach alleviates numerical limitations regarding the excessive computational cost during the cyclic analysis and provides a tool for the detailed simulation of the 3D cyclic nonlinear behavior of full-scale RC structures. The simplified HYMOD approach is integrated in this work with a computationally efficient cyclic concrete material model so as to investigate its numerical performance under extreme cyclic loading conditions. The proposed approach adopts a hybrid modeling concept that combines hexahedral and beam-column finite elements (FEs), in which the coupling between them is achieved through the implementation of kinematic constraints. A parametric investigation is performed through the use of the Del Toro Rivera frame joint and two RC frames with a shear wall. The proposed modeling method managed to decrease the computational cost in all numerical tests performed in this work, while it induced additional numerical stability during the cyclic analysis, in which the required number of internal iterations per displacement increment was found to be always smaller compared with the unreduced (hexahedral) model. The HYMOD provides for the first time with the required 3D detailed FE solution tools in order to simulate the nonlinear cyclic response of full-scale RC structures without hindering the numerical accuracy of the derived model nor the need of developing computationally expensive models that practically cannot be solved through the use of standard computer systems. [ABSTRACT FROM AUTHOR]

Highlights • 3D detailed modelling of reinforced concrete structures. • Introduction of damage factors accounting the crack opening/closure effect. • New material algorithm for concrete under cyclic and dynamic loading conditions. • Validation is performed by comparing the numerical results with experimental data. • Computational efficiency and robustness of the proposed algorithm are presented. Abstract Accurate nonlinear dynamic analysis of reinforced concrete structures is necessary for estimating the behavior of concrete structures during an earthquake. A realistic modeling approach to assess their strength and their ability to carry the expected seismic forces is of great importance. Although a number of constitutive models and modeling approaches have been proposed in order to capture the behavior of reinforced concrete structures under static loading conditions, only a few of these numerical models have been extended to dynamic problems. The objective of this paper is to integrate a computationally efficient 3D detailed modelling of concrete structures with damage factors that take into account the opening and closing of cracks, as well as, damage factors for steel reinforcement considering the surrounding concrete damage level, in order to capture the level of damage and stiffness degradation of structures undergoing many loading cycles. In the adopted numerical model, the concrete domain is discretized with 8-noded isoparametric hexahedral finite elements, which treat cracking with the smeared crack approach, while the steel reinforcement is modeled as embedded beam elements inside the hexahedral mesh. The validity of the proposed method is demonstrated by comparing the numerical response with the corresponding experimental results of various reinforced concrete structural members and structures. Based on the numerical investigation, it was found that the proposed integration of the damage factors with computationally efficient concrete and steel material models can efficiently predict both static and dynamic nonlinear behavior of concrete structures, with the ability to capture the complicated phenomenon of the pinching effect. [ABSTRACT FROM AUTHOR]

This paper presents the numerical investigation of nine Glass Fiber-Reinforced Polymer (GFRP) concrete deep beams through the use of numerically-efficient 20-noded hexahedral elements. Cracking is taken into account by means of the smeared crack approach and the bars are simulated as embedded rod elements. The developed numerical models are validated against published experimental results. The validation beams spanned a practical range of varying design parameters; namely, shear span-to-depth ratio, concrete specified compressive strength and flexural reinforcement ratio. The motivation for this research is to accurately yet efficiently capture the mechanical behavior of the GFRP-reinforced concrete deep beams. The presented numerical investigation demonstrated close correlations of the force-deformation relationships that are numerically predicted and their experimental counterparts. Moreover, the numerically predicted modes of failure are also found to be conformal to those observed experimentally. The proposed modeling approach that overcame previous computational limitations has further demonstrated its capability to accurately model larger and deeper beams in a computationally efficient manner. The validated modeling technique can then be efficiently used to perform extensive parametric investigations related to behavior of this type of structural members. The modeling method presented in this work paves the way for further parametric investigations of the mechanical behavior of GFRP-reinforced deep beams without shear reinforcement that will serve as the base for proposing new design guidelines. As a deeper understanding of the behavior and the effect of the design parameters is attained, more economical and safer designs will emerge. [ABSTRACT FROM AUTHOR]

Many constitutive models have been proposed in order to capture the realistic behavior of reinforced concrete structures under static loading conditions. Few of these numerical models manage to extend to dynamic problems. This is due to the fact that these models present increased computational demand and inability to simulate realistically the different types of mechanical behavior of reinforced concrete members. The purpose of this paper is to propose a computationally efficient constitutive method in order to simulate accurately the behavior of a wide range of reinforced concrete structural members under dynamic loading conditions. The proposed material model is based on the Markou and Papadrakakis [1] model which was an extension of the Kotsovos and Pavlovic [2] work. A solution strategy which describes the behavior of concrete during the dynamic loading is presented. The proposed algorithm describes the cyclic behavior of concrete which is dominated by the development of microcracking, macrocracking and brittle failure. It uses the implicit integration method of Newmark in order to solve the equation of motion. The concrete domain is simulated by 8- and 20-noded hexahedral elements, which treat cracking with the smeared crack approach. The steel reinforcement is embedded inside the hexahedral meshing and modeled by truss and beam elements. Accurate nonlinear dynamic analysis of reinforced concrete structures is very helpful in estimating the behavior of a concrete structures during an earthquake. Many concrete buildings have been designed according to the old seismic codes. Thus, an accurate and realistic modeling to assess their strength and their ability to carry the expected seismic forces is very important. The validity of the proposed method is demonstrated by comparing the numerical response with the corresponding experimental results of reinforced concrete members. [ABSTRACT FROM AUTHOR]

• A Nonlinear Finite Element Analysis (NLFEA) modeling approach is developed for simulating FRP-reinforced deep beams without shear reinforcement. • Extensive database of experimental and NLFEA data is established for developing AI-algorithm. • AI-model is benchmarked against several design standards [EC, ACI 440.1R-15 and the modified ACI 440.1R-15 (for size effect)] for blind predictions. • The AI-model demonstrated superior generalization on the blind prediction dataset, in comparison to the design codes. The presented work utilizes Artificial Intelligence (AI) algorithms, to model and interpret the behavior of the fiber reinforced polymer (FRP)-reinforced concrete deep beams without stirrups. This is done by first running an extensive nonlinear finite element analysis (NLFEA) investigation, spanning across the practical ranges of the different input parameters. The FEA modeling is meticulously validated against published experimental results. A total of 93 different models representing a multitude of possible FRP-reinforced deep beam designs are rigorously analyzed. The results are then utilized in building an AI-model that describes the shear capacity for FRP-reinforced deep beams. The study investigates the effect of several factors on the shear capacity and identifies the vital parameters to be used for further model development. Additionally, the developed AI-model is benchmarked against several design standards for blind predictions on new unseen data and design codes, namely: the EC, ACI 440.1R-15, and the modified ACI 440.1R-15 (for size effect). The AI-model demonstrated superior generalization on the blind prediction dataset in comparison to the design codes. [ABSTRACT FROM AUTHOR]

A detailed finite element modeling is presented for the simulation of the nonlinear behavior of reinforced concrete structures which manages to predict the nonlinear behavior of four different experimental setups with computational efficiency, robustness and accuracy. The proposed modeling method uses 8-node hexahedral isoparametric elements for the discretization of concrete. Steel rebars may have any orientation inside the solid concrete elements allowing the simulation of longitudinal as well as transverse reinforcement. Concrete cracking is treated with the smeared crack approach, while steel reinforcement is modeled with the natural beam-column flexibility-based element that takes into consideration shear and bending stiffness. The performance of the proposed modeling is demonstrated by comparing the numerical predictions with existing experimental and numerical results in the literature as well as with those of a commercial code. The results show that the proposed refined simulation predicts accurately the nonlinear inelastic behavior of reinforced concrete structures achieving numerical robustness and computational efficiency. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an automatic procedure for the generation of embedded steel reinforcement inside hexahedral finite elements is presented. The automatic mapping of the entire reinforcement network inside the concrete hexahedral finite elements is performed using the end-point coordinates of the rebar reinforcement macro-elements. By introducing a geometrical constraint, this procedure decreases significantly the computational effort for generating the input data of the embedded rebar elements in three-dimensional finite-element analysis, particularly when dealing with relatively large-scale reinforced concrete models. The computational robustness and efficiency of the proposed mesh generation method are demonstrated through numerical experiments. [Copyright &y& Elsevier]

During the last decades, many researchers have proposed a number of constitutive models for simulating the behavior of reinforced concrete structures under cyclic loading. The finite element analysis, has been used in the past, to produce solutions for specific structural members that undergo different loading conditions. The purpose of this paper is to propose a computationally efficient finite element based numerical method in order to simulate accurately and efficiently the mechanical behavior of a wide range of reinforced concrete structural members under cyclic loading. The proposed method is based on the experimental results and the concrete modeling of Kotsovos and Pavlovic (1995) as modified by Markou and Papadrakakis (2013). A new algorithmic formulation that describes the development of microcracking, macrocracking and the brittle behavior of the concrete under cyclic behavior, is presented. The concrete domain is simulated by 8- and 20-noded hexahedral elements, which treat cracking with the smeared crack approach. Steel reinforcement is modeled with truss and beam elements which are considered embedded inside the hexahedral concrete mesh. The numerical accuracy of the proposed method is demonstrated by comparing the numerically force-deflection curves with the corresponding experimental results found in the literature. [ABSTRACT FROM AUTHOR]

The importance of designing safe and economic structures in seismically active areas is of great importance. Thus, developing tools that would help in accurately predicting the dynamic properties of buildings is undoubtable a crucial objective. One of the parameters that significantly affects the seismic design of any structure is the fundamental period that is used to compute the seismic forces. It is well documented that the current design formulae for the prediction of the fundamental period of reinforced concrete buildings are simplistic and often fail to capture accurately their expected natural frequency. In addition, the design formulae do not have the ability to account for the soil-structure interaction (SSI) effect that, in some cases, significantly affects the natural frequency of buildings due to the additional flexibility induced by the soft soil. In this research work, a computationally efficient and robust 3D modeling approach is used for the modal analysis in order to investigate the accuracy of different design formulae in predicting the fundamental period of reinforced concrete buildings with and without SSI effects. In this context, 3D detailed modeling is used to generate a dataset that consists of 475 modal analyses, which is subsequently used to train and produce three predictive formulae using a higher-order, nonlinear regression modeling framework. The developed fundamental period formulae were validated through the use of 60 out-of-sample modal results and they are also compared to other existing formulae in the international literature and design codes. According to the numerical findings, the proposed fundamental period formulae are found to have superior predictive capabilities for the under-study types of buildings. • A parametric investigation on different fundamental period design code formulae is performed. • Soil-structure interaction is also accounted for in this study. • 3D detailed modeling is used to generate a dataset that consists of 475 modal analyses. Page 6 of 9. • Train different models using a higher-order, nonlinear regression modeling and the ANN method. • The proposed fundamental period formulae are found to have superior predictive capabilities. [ABSTRACT FROM AUTHOR]