Non-Linear Finite Element Analysis of Flexural Reinforced Concrete Beam using Embedded Reinforcement Modeling

Reinforced concrete is one of the most widely used building materials in Indonesia due to its workability, easiness, and reasonable price. Meanwhile, it is very important to understand the response of these elements during the loading process to ensure the development of an effective structure and one of the most effective numerical methods for reinforced concrete elements is the Finite Element Analysis (FEA). This study was, therefore, conducted to investigate the flexural behavior of reinforced concrete beam using a nonlinear finite element analysis through the application of the MSC MARC/MENTAT software program. This involved the use of a solid element to represent concrete while the truss bar was applied for reinforcing steel after which multi-linear and bilinear models were considered for the two elements respectively while embedded reinforcement model was applied to model the rebar. Moreover, the beam model was also studied and compared with experimental data from previous literature. The result showed the load-deflection to have significantly increased due to an increment in the steel reinforcement yield strength. The same was also observed for the concrete compressive strength while a decrease was recorded in deflection due to the reduction in the compressive strength because the strain was reaching the crushing value. Furthermore, the concrete tension model was found to be the same with the experimental results with the tensile strength observed to have lost its strength after reaching the tensile stress while the contact behavior of the modeled reinforced concrete beam showed the existence of a slip at the support and loading points

Numerical Investigation of Reinforced Concrete Beam Due to Shear Failure

This paper investigates the possibility of using a multi-surface plasticity model to predict shear failure in reinforced concrete beams. The analysis is carried out using the in-house software called 3D-NLFEA. The constitutive model for the concrete material is based on the plasticity-fracture model, which had previously developed to simulate the behavior of concrete cover spalling in reinforced concrete columns. To obtain the asymmetric shear failure pattern, random material properties imperfection for each meshed element is used. Two beams available in the literature are investigated and compared with the analysis results using 3D-NLFEA. From the comparisons, excellent agreement between the analysis and the test result was obtained. 3D-NLFEA can predict the peak load accurately. The peak load prediction only varies 2.19% for beam OA1 and 3.28 % for beam OA2, and it was lower than the test results. The failure crack patterns also show a typical diagonal crack extension from the support to the loading steel plate

Τριδιάστατα μη-γραμμικά υβριδικά προσομοιώματα για την ανάλυση μεγάλη κλίμακας κατασκευών από οπλισμένο σκυρόδεμα

308 σ.Αντικείμενο της παρούσας Διατριβής αποτέλεσε η διερεύνηση της μη-γραμμικής συμπεριφοράς κατασκευών οπλισμένου σκυροδέματος με τριδιάστατα υβριδικά προσομοιώματα πεπερασμένων στοιχείων. Η έρευνα αυτή έχει ως σκοπό την ανάπτυξη νέων ή βελτίωση υπαρχουσών μεθόδων προσομοίωσης κατασκευών από οπλισμένο σκυρόδεμα, με σκοπό τον ορθότερο και ασφαλέστερο σχεδιασμό των κατασκευών αυτών. Στα πλαίσια της παρούσας Διατριβής, αναπτύχθηκε ένας κώδικας βασισμένος στις αρχές του εγγενούς αντικειμενοστραφούς προγραμματισμού (ReConAn: Reinforced Concrete Analysis) ο οποίος περιέχει στις βιβλιοθήκες του όλα τα πεπερασμένα στοιχεία και καταστατικούς νόμους υλικών με τους οποίους πραγματεύεται η ερευνητική αυτή εργασία. Τα αποτελέσματα έδειξαν ότι ο νέος κώδικας είναι αρκετά γρήγορος σε σχέση με τα εμπορικά λογισμικά (Femap with NXNastran, Opensees). Επιπρόσθετα, αναπτύχθηκε ένα λογισμικό μετεπεξεργασίας (ReConAn Eye) το οποίο επιτρέπει την αναπαράσταση της ρηγμάτωσης. Ο κώδικας ReConAn, ενσωματώνει προσομοιώματα τριδιάστατων εξαεδρικών πεπερασμένων στοιχείων για τη λεπτομερή προσομοίωση κατασκευών οπλισμένου σκυροδέματος. Παράλληλα, έχει τη δυνατότητα προσομοίωσης του φαινομένου της ρηγμάτωσης μέσω της θεώρησης της μεθόδου της διανεμημένης ρωγμής (smeared crack approach) η οποία συνδυάζεται με τον αλγοριθμικά βελτιωμένο καταστατικό νόμο υλικού σκυροδέματος των Kotsovos & Pavlovic ο οποίος ενσωματώνεται για πρώτη φορά σε τριδιάστατα εξαεδρικά πεπερασμένα στοιχεία 8 κόμβων, γεγονός το οποίο καθιστούν την προτεινόμενη μεθοδολογία προσομοίωσης ταχύτατη. Οι οπλισμοί προσομοιώνονται ως εγκιβωτισμένα στοιχεία δοκού (στοιχείο δυνάμεων ΝΒCFB) τα οποία λαμβάνουν υπόψη την διατμητική και καμπτική στιβαρότητα των ράβδων οπλισμού. Η ακρίβεια των αποτελεσμάτων και η υπολογιστική συμπεριφορά του προτεινόμενου προσομοιώματος συγκρίθηκαν με άλλες μεθοδολογίες προσομοίωσης οι οποίες ενσωματώνονται σε εμπορικά λογισμικά πακέτα που υπάρχουν διεθνώς (ΑΤΕΝΑ, ABAQUS, LS-DYNA, ANSYS). Αναπτύχθηκε μία νέα μεθοδολογία αναγνώρισης εγκιβωτισμένων ραβδωτών στοιχείων οπλισμού εντός εξαεδρικών στοιχείων. Η μέθοδος αυτή επιτρέπει την ελεύθερη τοποθέτηση των οπλισμών εντός των εξαεδρικών στοιχείων και απαιτεί ελάχιστο υπολογιστικό χρόνο για την αναγνώριση και δημιουργία του δικτύου των εγκιβωτισμένων πεπερασμένων στοιχείων οπλισμού. Αναγνωρίστηκε η αδυναμία των λεπτομερών τριδιάστατων προσομοιωμάτων να μοντελοποιήσουν μεγάλης κλίμακας κατασκευές από οπλισμένο σκυρόδεμα λόγω του μεγάλου υπολογιστικού κόστους και αναπτύχθηκε ένα νέο τριδιάστατο μη-γραμμικό υβριδικό προσομοίωμα πεπερασμένων στοιχείων για την ανάλυση κατασκευών από οπλισμένο σκυρόδεμα. Για τον σκοπό αυτό, έγινε η σύνδεση του φυσικού στοιχείου δυνάμεων ΝΒCFB οπλισμένου σκυροδέματος με το εξαεδρικό στοιχείο σκυροδέματος με εγκιβωτισμένες ράβδους. Η λογική διακριτοποίησης μίας κατασκευής με υβριδικό προσομοίωμα, προβλέπει την προσομοίωση των κατασκευαστικών μελών τα οποία αναμένεται να αναπτύξουν σημαντικές μη-γραμμικότητες μέσω τριδιάστατων λεπτομερών προσομοιωμάτων και τα υπόλοιπα κατασκευαστικά μέλη μέσω στοιχείων δοκού-υποστυλώματος.Modeling of RC structures with beam-column type finite elements was proven to be insufficient and inaccurate, especially when dealing with shear dominated structural members and structures with complex geometries. Nevertheless, this type of finite element is used widely for the analysis and design of RC structures due to its computational efficiency which is attributed to the resulting reduced-size numerical finite element models. Based on these limitations, an extensive literature survey was conducted, with the intention to allocate the most promising beam-column FE formulation for modeling RC structures. It was concluded that one of the most numerically advanced beam FE type was the Natural Beam-Column Flexibility-Based (NBCFB) element, which was incorporated in ReConAn software code following an extensive parametric investigation regarding its nonlinear numerical behavior. The second objective of this Dissertation was the literature investigation of 2D and 3D nonlinear modeling methods for RC structures with the purpose of acquiring a general idea about the trends on more sophisticated FE models. Furthermore, the selection of the numerically most promising 3D modeling method was a primary objective, in order to develop a sophisticated software tool capable of predicting the nonlinear response of full-scale RC structures in an acceptable computational time. After this literature review, it was concluded that the existing three-dimensional modeling techniques exhibit a number of limitations for capturing the nonlinear behavior of RC structures and that the corresponding software with sophisticated models for the simulation of nonlinear phenomena, such as cracking and detailed rebar modeling, are very sparse. This is attributed to the numerical restrictions and difficulties described above, whereas the required CPU resources become excessive when dealing with such numerical models even for the case of small-scale FE models. It is well known that the analysis of multistory RC buildings is performed through the use of beam-column elements which allow fast simulation times without serious numerical instabilities. In order to be able to analyze this type of structures with three-dimensional constitutive material models incorporated into 3D finite elements and the use of standard CPU systems, the availability of a powerful software tool is not enough. This constraint derives from the fact that CPU processors are bounded from an upper limit which is determined from the hardware itself. Processing power was not and will never be enough since the demand for the solution of larger numerical models constantly increases. In general, this is attributed to the necessity of large-scale simulations with detailed models for the purpose of capturing, as realistically as possible, the nonlinear behavior of structural systems. Therefore, the third objective of this Dissertation was to determine numerical techniques which will overcome these limitations when dealing with full-scale RC structures. A well-known approach that is used widely in computational mechanics is the use of parallel solvers which in this case will become a subject of future work. A second approach for overcoming this numerical restriction is to use models which combine different types of FE models and which will be called “hybrid models”. This type of modeling assumes that shear dominated structural members with an expected highly nonlinear behavior are modeled with 3D detailed finite elements and the rest of the structure is modeled with simpler beam-column finite elements. This technique leads to a reduction in the complexity of the model and of the required computational demand for the solution of the discretized model, retaining at the same time an acceptable accuracy during the analysis procedure. Finally, the last objective of this research work, was the development of an object-oriented FEA code, capable of easily incorporating advanced numerical techniques and modeling methods for the analysis of RC structures. In addition, it will have the ability to incorporate easily future work and simulation enhancements, which will result into a more general FEA code that will provide the ability of realistic and reliable predictions of the nonlinear response of any type of structure. For the purpose of developing an extendable and sustainable program code, modern programming techniques are used and new numerical methods are developed to create the necessary program structure which will incorporate these state of-the-art features. It is the author’s personal opinion that this task is of great importance, especially when dealing with the solution of computationally complex numerical problems.Γεώργιος Α. Μάρκο

Accurate and computationally efficient nonlinear static and dynamic analysis of reinforced concrete structures considering damage factors

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.The European Research Council Advanced Grant “MASTER-Mastering the computational challenges in numerical modeling and optimum design of CNT reinforced composites” (ERC-2011-ADG 20110209).http://www.elsevier.com/locate/engstruct2020-01-01hj2019Civil Engineerin

State-of-the-art investigation of wind turbine structures founded on soft clay by considering the soil-foundation-structure interaction phenomenon – optimization of battered RC piles

Nonlinear dynamic modelling of full-scale wind turbine structures and soil-structure interaction considerations using the 3D detailed approach is the most accurate method of investigating the mechanical response of these structures, but not yet feasible due to numerous reasons. The two main numerical problems that do not allow for this type of analysis to be performed, are the numerical instabilities that immerse during the dynamic analysis and the excessive computational demand. This work will present the computational response of a newly developed algorithm that is used herein to perform modal analysis of wind turbine structures for the investigation of soil-foundation-structure interaction phenomenon. An extensive numerical investigation is presented that foresees the performance of modal and pushover analysis on a wind turbine structure that has an 80 m steel tower and is founded on different soil profiles. The 3D detailed models constructed herein consider the effect of soil-foundation-structure interaction by discretizing for the first time the superstructure, pile foundation and soil domains through 8-noded hexahedral elements, achieving maximum modelling accuracy. The soil material properties used in this research work derived from an onsite geotechnical investigation performed for the needs of the WindAfrica project. After validating the ability of the proposed modelling approach to capture the mechanical behaviour of reinforced concrete foundations through the use of experimental data found in the international literature, the optimum inclination of battered piles was studied through an excessive numerical parametric investigation. Based on the numerical findings, the optimum inclination of the battered piles was that of 10 degrees, where the failure of the wind turbine structure was found to be located at the base of the steel tower due to local buckling.The Research Development Programme (RDP), University of Pretoria.http://www.elsevier.com/locate/engstruct2022-03-01hj2021Civil Engineerin

Parallel adaptive fluid-structure interaction simulations of explosions impacting on building structures

We pursue a level set approach to couple an Eulerian shock-capturing fluid solver with space–time refinement to an explicit solid dynamics solver for large deformations and fracture. The coupling algorithms considering recursively finer fluid time steps as well as overlapping solver updates are discussed. Our ideas are implemented in the AMROC adaptive fluid solver framework and are used for effective fluid–structure coupling to the general purpose solid dynamics code DYNA3D. Beside simulations verifying the coupled fluid–structure solver and assessing its parallel scalability, the detailed structural analysis of a reinforced concrete column under blast loading and the simulation of a prototypical blast explosion in a realistic multistory building are presented

Finite element analysis of impact-perforated reinforced concrete slabs

The safety of the workers and durability of structures against the impact of low-velocity falling weights is of significant importance in construction industry, especially for construction of multi-storey buildings. The empirical formulae for the estimation of the impact behavior of reinforced concrete are limited to the domain settings in which they are generated and are originally developed for high-speed velocity impacts less relevant to the construction industry. This study presents a finite element analysis procedure for the impact analysis of reinforced concrete slabs under low-velocity and high-mass impacts using the Abaqus/Explicit solver. A modified Concrete Damage Plasticity material model with strain rate effects and a physically motivated element deletion criterion has been used for modelling concrete and strain-rate-dependent elastoplastic damage model is utilized for modelling the reinforcement. A three dimensional Langrangian formulation and eight-node hexahedron elements with reduced integration are used for modelling concrete. The reinforcement is discretized with two-node beam elements. The numerical analysis is compared against three experimental impact tests carried out at Heriot-Watt University. In terms of perforation and the velocity-history of the impactor, the numerical results are found to be accurate. The validated finite element procedure is then used to estimate the minimum velocity of the impactor required to perforate, in the sense of the so-called ballistic limit, a 150 mm thick two-layer reinforced concrete slab for impactor weights 250 kg, 500 kg and 1000 kg. The obtained ballistic limits are compared to the empirical formula of UK Atomic Energy Authority: a very good correlation has been obtained, adding a second layer of validation onto the numerical procedure

Seismic assessment of small modular reactors : NuScale case study for the 8.8 Mw earthquake in Chile

Reducing greenhouse gas emissions and improving energy production sustainability is a paramount of Chile’s 2050 energy policy. This though, is difficult to achieve without some degree of nuclear power involvement, given that the geography of the country consists of many areas that are practically off-grid, whereas cannot be developed and financially exploited due to the lack of basic commodities such as water and electricity. Recently small modular reactors (SMRs) have gained lots of attention by both researchers and world policy makers for their promised capabilities of enhanced safety systems, affordable costs and competitive scalability. SMRs can be located in remote areas and at this time are being actively developed in Argentina, USA, Brazil, Russia, China, South Korea, Japan, India and South Africa. Chile’s 2010 earthquake and Fukushima’s 2011 nuclear disaster have increased significantly both the population’s fear and opposition to Nuclear Power Energy for the possible consequences of radiation on the lives of people. This paper aims to study the seismic resistance of a typical nuclear structure, being at time proposed in Small Modular Reactors, by using earthquake conditions typically seen in Chile. Since many designs are under study, a NuScale reactor from USA is analyzed under these extreme loading conditions. The major advantages of the NuScale reactor are in the power scalability (it can go from 1 to 12 reactor cores producing from 60 to 720 MWe), limited nuclear fuel concentration, modules allocated below grade and high strength steel containments fully immersed in water. The cooling effect beyond Design Basis Accident is ensured indefinitely, which induces a significant safety factor in the case of an accident. For the purpose of this study a detailed 3D detailed structural model was developed, reproducing the NuScale reactor’s reinforced concrete framing system, where nonlinear analyses was performed to assess the overall mechanical response of the structure. The framing system has been tested under high seismic excitations typically seen in Chile (Mw > 8.0), showing high resistance and capability to cope with the developed forces due to its design. Based on a Soil-Structure Interaction analysis, it was also found that the NuScale framing system manages to maintain a low-stress level at the interaction surface between the foundation and the soil, where the structural system was found to be able to withstand significant earthquake loads. Finally, further investigation is deemed necessary in order to study the potential damages of the structure in the case of other hazards such as tsunami events, blast loads, etc.https://www.elsevier.com/locate/nucengdes2020-02-01hj2019Civil Engineerin

Challenges in Modelling Reinforced Concrete Panels Subjected to Blast Load - A Critical Review

Reinforced concrete panels are widely used in modern facilities, and evaluating their blast loading capacity is vital for security-critical assets. Due to the high impulsive nature of blast loads, the response of reinforced concrete panels is characteristically different from that under static or low dynamic load conditions. The failure of individual components often initiates the blast load's destructive effects on the entire structure. The material breach can be caused by stress wave localized effects before the general structural response becomes significant. Numerical methods are one of the key methods for studying the behaviour of reinforced concrete panels under blast load. This paper aims to review the current state of practice in modelling reinforced concrete panels and predicting their blast capacity and failure mechanisms under blast load. The work addresses the research gaps associated with using advanced finite element modelling as compared to test results

A hybrid embedded cohesive element method for predicting matrix cracking in composites

The complex architecture of many fibre-reinforced composites makes the generation of finite element meshes a labour-intensive process. The embedded element method, which allows the matrix and fibre reinforcement to be meshed separately, offers a computationally efficient approach to reduce the time and cost of meshing. In this paper we present a new approach of introducing cohesive elements into the matrix domain to enable the prediction of matrix cracking using the embedded element method. To validate this approach, experiments were carried out using a modified Double Cantilever Beam with ply drops, with the results being compared with model predictions. Crack deflection was observed at the ply drop region, due to the differences in stiffness, strength and toughness at the bi-material interface. The new modelling technique yields accurate predictions of the failure process in composites, including fracture loads and crack deflection path