Behavior Of Concrete Structures Research Articles

Experimental analysis of the tensile behavior of concrete reinforced with Brazilian glass textile

In this study, the mechanical behavior of concrete structures reinforced with one and two layers of the Brazilian glass textile “AR-360” was verified through direct tensile tests. The analysis of the mechanical behavior of the structures was performed with stress-strain curves, evaluating the transition points of the formed stages, rupture mode, rupture stress and strain, as well as an analysis comparing experimental results with analytics. Regarding the results, there was a structural inability of the pieces reinforced with a layer of glass textile. In the samples in which reinforcement with two layers of the aforementioned material was evaluated, the three stages present in the stress-strain curves were correctly identified, as predicted in the literature for the structures evaluated.

Numerical model for time-dependent cracking and deflection of large-span concrete bridge structures

A new computational framework is proposed to analyse the simultaneous occurrence of multiple physical processes affecting the long-term behavior of large-scale concrete structures. Relying on the additivity of small strain, the framework comprehensively takes the nonlinearity of concrete creep, cyclic creep induced by traffic load, concrete shrinkage, concrete cracking, normal-strength steel rebars and prestressing strands relaxation into account, and other physical processes are further imagined. The algorithm is implemented with Abaqus/Standard with the aid of several user-supplied subroutines. The implicit time integration scheme is deemed appropriate for large-scale structures. The framework is systematically validated by several classical experimental results. Finally, a three-dimensional study of a three-span continuous rigid frame bridge with 270 m main span is performed. Comparison between the experimental and numerical results further reveals the contributions of various potential influencing factors. The proposed model shows promise for predicting the time-dependent performance of large-scale reinforcement concrete (RC) structures.

Data-driven shear strength predictions of prestressed concrete hollow-core slabs

Although providing sufficient shear strength is crucial in the design of hollow-core slabs (HCS) to prevent shear failure, conventional shear equations for HCS could not always represent the non-linear relationship between the shear strength and influencing parameters, especially for deep HCS. Back-propagation-neural-network- (BPNN)-based models could be a possible solution since they have been widely used in predicting structural behaviour of other concrete structures. However, the feasibility of such an application has not been examined previously. Therefore, a set of BPNN-based models with and without optimisation algorithms were proposed for predicting the shear strength of prestressed HCS. The proposed BPNN-based models were trained and verified against a database of 227 HCS tested in shear. Comparisons between BPNN-based and mechanics-based models were also performed. The corresponding performances of different models were evaluated by the mean Vut/Vpre, R2, RMSE, MAE and MAPE criteria. To the author's best knowledge, this is the first study to apply hybrid-BPNN-based models for shear strength prediction of HCS. The study found that all proposed BPNN models were effective in predicting the shear strength, while the ACO-BPNN model yielded the best predictions among all the BPNNs. It was also shown that the ACO-BPNN model provided better predictions than the ACI 318 code provisions with/without the size effect factor. Besides, the well-trained ACO-BPNN model could present the size effect of slab thickness on shear strength, which was not explicitly considered in ACI 318. In summary, the ACO-BPNN-based model could a rational tool for predicting shear strength for HCS.

Behavior of Concrete Structures of 5-storey Shopping and Residence Buildings due to Earthquakes using Spectrum Response Analysis

Behavior of Concrete Structures of 5-storey Shopping and Residence Buildings due to Earthquakes using Spectrum Response Analysis

Introducing advanced nanocomposites to improve the efficiency and stability of the concrete systems as the main part of bridge construction

This research presents the use of advanced nanocomposites in bridge building as a way to improve the stability and efficiency of concrete structures. By using nanocomposites, problems with performance under different loading circumstances, durability, and structural integrity have to be addressed. This study examines the structural behavior of concrete structures reinforced with cutting-edge nanocomposites using shear deformation theory, a numerical solution process, and Hamilton’s principle. The research starts out by examining the makeup and features of nanocomposite materials, emphasizing how they may enhance the structural and mechanical qualities of concrete. The dynamic response and stability of concrete structures reinforced with nanocomposite under various loading scenarios are assessed using numerical simulations and analysis grounded on Hamilton’s principle. The complex relationship between mechanical performance, structural geometry, and material composition is captured by the shear deformation theory. The behavior of nanocomposite-reinforced concrete structures, including their stiffness, strength, and weight fraction of nanocomposites, may be fully understood thanks to this theoretical framework. The study’s conclusions provide insight into how well-suited sophisticated nanocomposites are for boosting the strength and stability of concrete constructions, especially when it comes to building bridges. Engineers and researchers may enhance concrete system performance and design for robust and sustainable infrastructure development by using shear deformation theory, Hamilton’s principle, and numerical solution methodologies.

Mesoscale discrete simulation of flexural behavior of FRP-strengthened RC beams using 3D RBSM

A widely adopted method of strengthening existing reinforced concrete (RC) structures, especially for marine concrete structures, is to use external bonded fiber-reinforced polymer (FRP). However, although numerous studies in this field have been reported, accurate simulation of localized material behaviors such as crack opening and interfacial sliding remains challenging. Compared to other simulation methods, mesoscale models offer the promise of capturing these complexities. Nevertheless, there has been very little application of mesoscale simulations in analysis of FRP-strengthened RC structures due to a lack of relevant constitutive models. To fill this gap, the authors have recently developed local bond models for the FRP-concrete interface in the three-dimensional rigid body spring model (3D RBSM). The model’s parameters are defined with easily interpretable physical implications and straightforward computational methods. In this work, this mesoscale model is extended and applied to simulate the flexural behavior of FRP-strengthened RC beams. The simulation results closely align with experiments in both global and local behaviors. The parametric study conducted in this work highlights the critical role of interfacial normal bond strength between FRP and concrete in dictating flexural behavior. The capability of 3D RBSM in simulating the strain distribution along the FRP and capturing intricate localized behaviors aligned with flexural and shear forces is demonstrated. Overall, this paper reinforces the potential of 3D RBSM as a robust tool for analyzing the complex behaviors of FRP-strengthened concrete structures.

A tensorial energy-release-rate based anisotropic damage-plasticity model for concrete

This paper proposes an anisotropic damage model for concrete to capture its plasticity and damage behavior effectively. Utilizing the framework of continuum damage mechanics, the model considers the influence of plastic Helmholtz free energy on damage evolution. This approach explicitly deduces damage-related thermodynamic forces without resorting to assumptions such as strain equivalence or energy equivalence. The proposed model employs tensile and compressive damage tensors to describe the development of anisotropic damage in concrete. The solution for plastic strain utilizes the empirical plasticity model. Furthermore, a unified evolutionary criterion for isotropic and anisotropic damage is also established, incorporating damage yield functions and orthogonal flow laws. Numerical simulations are conducted to validate the model’s ability to reproduce typical nonlinear behaviors of concrete structures under various load conditions.

Concrete Structures Reinforced with FRP BAR

Abstract: Fiber reinforced polymer (FRP) bars have been widely used in civil engineering used as a substitute for steel reinforcement because it has many advantages such as high strength-to-weight ratio, electromagnetic neutrality, light weight, ease of handling and no corrosion. Moreover, the productive technology becomes more and more mature and industrialized so that FRP has become one economic and competitive structure material. Based on the recent researches, this paper mainly introduces progress in the studies on concrete structures reinforced with FRP bars. These contents in this paper includes the bond performance of FRP bars in concrete, Compression Behavior, flexural behavior, and ductility of concrete structure reinforced with FRP bars in the past few years in the world .

Time-varying damage evolution of concrete under cyclic disturbance loading- an experimental observation utilizing AE and DIC

Cyclic disturbance loading affects the continuous operation of concrete structures. This study aims to better understand the failure behavior of concrete structures under cyclic disturbance loading. This study combined acoustic emission (AE) and digital image correlation (DIC) technologies to study mechanical failure behavior and damage evolution of concrete materials under cyclic disturbance loading and unloading. The AE event time-frequency characteristics, surface principal strain program, and damage parameters of samples with different cyclic disturbance amplitudes were obtained by theoretical calculation. The results reveal that when minor disturbance amplitudes are applied, the elastic modulus of concrete specimens tends to increase. When the disturbance amplitude is too large, the elastic modulus of the specimens drops, leading to faster specimen failure. The AE characteristic parameters exhibit a Felicity effect after the sample is subjected to a cyclic disturbance loading. Moreover, the larger the amplitude of the disturbance load, the more frequent the low-frequency and high-amplitude events generated during the final rupture, the higher the concentration of the principal strain on the sample's surface, and the wider the crack band distribution. AE energy and Effective crack are consistent in characterizing damage, and the changing trend of these two damage parameters can better reflect the deterioration process of concrete. The research results will provide practical and theoretical insights for safely operating and maintaining concrete structures.

Transient bending analysis of the graphene nanoplatelets reinforced sandwich concrete building structure validated by machine learning algorithm

This paper demonstrates a thorough examination of the bending behavior of sandwich concrete building structures that are reinforced with graphene nanoplatelets (GPLs). The analysis is confirmed using a machine learning technique. Sandwich structures have notable benefits in terms of strength, longevity, and thermal insulation, making them well-suited for many building applications. Integrating GPLs into the concrete matrix improves the mechanical characteristics and performance of these structures, especially in terms of bending behavior. This study utilizes a machine learning technique to verify the characterization of the temporary bending behavior of a concrete building structure reinforced with graphene nanoplatelets. The approach utilizes a dataset consisting of simulated bending data to create a prediction model that can reliably estimate the temporary bending response of the reinforced structure under different loading situations. The machine learning algorithm’s effectiveness and dependability in optimizing the design and performance of graphene nanoplatelets reinforced sandwich concrete building structures are demonstrated through validation against simulated results. This provides engineers and designers with a powerful tool. This study enhances the comprehension and use of machine learning approaches in analyzing and designing sophisticated structural materials and systems.

Compressive and Bonding Performance of GFRP-Reinforced Concrete Columns

The use of glass-fiber-reinforced polymer (GFRP) bars as an alternative to steel bars for reinforcing concrete (RC) structures has gained increasing attention in recent years. GFRP bars offer several advantages over steel bars, such as corrosion resistance, lightweight, high tensile strength, and non-magnetic properties. However, there are also some challenges and uncertainties associated with the behavior and performance of GFRP-reinforced concrete (GFRP-RC) structures, especially under compression and bonding behavior. Therefore, there is a need for comprehensive experimental investigations to validate the effectiveness of GFRP bars in concrete columns. This paper presents a study that aims to address these issues by conducting experimental tests on GFRP-RC columns. The experimental tests examine the mechanical properties of GFRP bars and their bond behavior with concrete, as well as the axial compressive behavior of GFRP-RC columns with different reinforcement configurations, tie spacing, and bar sizes. The findings reveal that GFRP bars demonstrate a comparable, if not superior, compressive capacity to traditional steel bars, significantly contributing to the load-bearing capacity of concrete columns. The study concludes with a set of recommendations for further exploration, underscoring the potential of GFRP bars in revolutionizing the construction industry.

Finite element method for sustainable and resilient structures made with bar and fiber -reinforced EAFS concrete

Structural engineers have to address the climate change challenge by designing sustainable and resilient structures. At this juncture, Electric Arc Furnace Slags (EAFS), a steel-industry waste, are used in replacement of natural aggregates to enhance concrete properties. Moreover, steel and synthetic fibers are added to improve the postcracking behavior while the traditional bar reinforcement enhances the tensile performance. This makes EAFS concrete substantially ductile compared to normal concrete, which contributes to a higher structural resiliency, and hence minimizes functionality disruptions. However the use of fiber and bar -reinforced EAFS concrete in structures is still limited due to the uncertainties introduced by EAFS and fibers. This justify the development of advanced modeling techniques (ie. Finite element Analysis, FEA), which can be used to predict the behavior of EAFS concrete structures at the designing stage. This work build up from the extensive work of the coauthors in the testing of EAFS concrete and, more recently, in the developed FEA of fiber-reinforced EAFS concrete. In this paper the modeling of bar reinforcement is added to the FEA to study the behavior of structural elements made with fiber-reinforced EAFS concrete. The presented FEA is validated through full-scale experiments (four-point flexural test), which shows that the presented FEA is appropriate. The presented numerical model enables to study phenomena difficult to study from experiments or in-situ such as the cracking. It is worth noting that the addition of steel fibers reduced the crack mouth opening displacement in 29.3% and the depth of the cracks in 12.7% in the presented EAFS concrete.

A Meso-scale study to predict high-temperature behavior of concrete structures in a hygral-thermal-chemical-mechanical framework

Fire has become one of the common hazards that a concrete structure faces in today’s world. Considering the heterogeneity of concrete and the contrasting nature of the constituents at high temperatures (cement paste dehydrates and shrinks while aggregate expands in volume), the use of a homogeneous macroscopic model to predict concrete's thermo-mechanical performance is questionable. Therefore, a more realistic description of concrete (in terms of explicit consideration of coarse aggregate and cement mortar rather than homogenized concrete medium) is needed to characterize the behavior of a concrete structure under such severe loading conditions (e.g., fire). In fact, the performance of a macro-scale (meter size or higher) concrete structure is the coupled effect of the various physico-chemical processes that occur within its constituents at meso-scale, a scale (mm-cm scale size) where coarse aggregates are randomly distributed in a mortar paste medium. Therefore, it is required to develop a model that explicitly considers the constituents' contrasting nature and the different thermo-hygral-mechanical processes at the scale of occurrence of these processes. Hence, in this contribution, a meso-scale based model is developed in a coupled hygro-thermo-chemo-mechanical (HTCM) framework to investigate the effect of high temperature on the thermo-mechanical performance numerically (e.g., in terms of spalling, deformation, residual capacity, etc.) of fire-exposed plain and reinforced concrete structural elements (e.g., slab, beam, etc.). Simulated results and validation with experimental data (taken from the literature) highlight several crucial aspects related to obtaining a more precise residual capacity of a concrete structure, which is impossible to reproduce with a homogenized macroscopic model. The study highlights that the failing of random concrete parts at different times during high-temperature exposure can not be simulated with a homogenized assumption. Further, a mesoscopic model does not require transient creep strain to be specified explicitly. The primary influencing factors behind this transient creep strain, such as the different thermo-chemical and thermo-mechanical damage of the concrete constituents (cement paste, aggregate), thermal-incompatibility of the components and associated damages, etc., are implicitly taken into account in a meso-scale model.

A review of fracture propagation in concrete: fundamentals, experimental techniques, modelling and applications

A comprehensive overview of fracture propagation in concrete, covering various aspects ranging from fundamentals to applications and future directions, is presented. The introduction presents an overview of fracture propagation in concrete, emphasising its importance in understanding the behaviour of concrete structures. The fundamentals of fracture propagation are then explored, including concrete as a composite material, crack initiation and propagation mechanisms, types of fractures and the factors that influence fracture propagation. Next, experimental techniques for studying fracture propagation are discussed, encompassing both destructive and non-destructive testing methods, such as acoustic emission, ultrasonic testing, digital image correlation and advanced imaging techniques like X-ray computed tomography and scanning electron microscopy. Modelling approaches, including continuum damage mechanics, the finite-element method, the discrete-element method, the lattice discrete particle model and hybrid models, for simulating and predicting fracture propagation behaviour are then reviewed. The applications of fracture propagation in concrete are highlighted, including structural health monitoring, design optimisation, failure analysis and repair and rehabilitation strategies. Research opportunities for further improvement are addressed. This article should serve as a valuable resource for researchers, engineers and professionals in the field, providing a comprehensive understanding of fracture propagation in concrete and guiding future research endeavours.

Simulation of four-point bending tests for the viscoelastic fracture properties of concrete

Understanding the fracture properties of concrete, such as crack propagation behavior and fracture energy, is crucial for designing and evaluating concrete structures. Experimental results are insufficient and cannot be directly employed for a comprehensive analysis of the fracture behavior of concrete structures under load, particularly when considering concrete as viscoelastic with the presence of cracks. Recognizing the time and cost constraints of traditional experimental testing, this research leverages numerical simulations as a cost-effective alternative to determine viscoelastic material parameters. Thus, the critical evaluation of concrete fracture properties, fundamental for the design and assessment of concrete structures, is addressed. Employing a finite element method for four-point bending tests, the study systematically investigates parameters such as initial crack depth, displacement acceleration, and time step. The material properties of concrete are described using viscoelastic models. The findings provide valuable insights into crack propagation behavior and deformation characteristics, emphasizing the significant influence of the modulus of elasticity on both maximum load values and displacement. These findings contribute to a deeper understanding of the structure's response and underscore the importance of considering these parameters in similar simulations. The study highlights the importance of considering these parameters in simulations to enhance the understanding of concrete fracture behavior. The paper's contributions can extend to optimizing concrete mixtures, formulating repair strategies, and improving structural assessments. Further research is suggested to improve the accuracy of simulations and investigate material properties under various conditions.

Nonlinear semi-numeric analysis and simplified analysis of polymer fiber-reinforced concrete prisms under three-point bending test conditions

This paper presents a semi-numeric nonlinear analysis and a simplified analysis for evaluating the load-displacement behavior of polymer fiber-reinforced concrete elements under three-point bending test conditions. The considered elements were notched and unnotched prisms. The nonlinear semi-numeric analysis was based on the moment-curvature relation, plastic hinge approach, and virtual work method. The simplified analysis assumed multilinear load-displacement behavior of the prisms under three-point bending test conditions. It included four variants for the input tensile strength properties and crack widths considered for the serviceability and ultimate limit state. The notched polymer fiber-reinforced concrete prism three-point bending test results from a prior study were the basis for evaluating the simplified analysis, which was subsequently compared with the nonlinear semi-numeric analysis outcomes from the same investigation. Additionally, the simplified analysis and the nonlinear semi- numeric analysis were used to determine the load-displacement behavior of unnotched polymer fiber-reinforced concrete prisms with heights ranging from 25 mm to 250 mm. The results indicate that the simplified analysis provides a practical and efficient method for estimating the behavior of polymer fiber-reinforced concrete structures under three-point bending test conditions, yielding relatively accurate results with minimal computational effort compared to the more exact nonlinear semi-numeric analysis.

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.

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Temperature evolution and activation energy sensitivity analysis for early-age concrete elements using a 3-D finite difference model

Concrete structures are prone to cracking due to non-uniform temperature distribution caused by the heat released during cement hydration. Accurate prediction of temperature evolution is crucial for the design and control of concrete temperature in construction. This paper presents the development of a 3-dimensional (3-D) finite difference (FD) model for predicting the thermal behavior of early-age concrete structures during the hardening stage. The proposed model was verified against temperature measurements from two concrete elements, showing good accuracy in predicting temperature evolution. The sensitivity analysis on activation energy revealed its significant influence on the peak temperature in the concrete core and the temperature difference between the center and surface. The proposed model can assist in control of concrete temperature thus preventing early-age thermal issues, ensuring the expected life span and durability of concrete structures.

Analyzing cyclic loading behavior of concrete structures: A peridynamic approach with softening models and validation

This study introduces a bond-based peridynamic (BB-PD) approach for analyzing concrete structures under cyclic loading, with the aim of comprehensively addressing crack propagation and concrete crushing phenomena. The model’s generality is enhanced by eliminating the need for calibration. Additionally, a practical method is proposed to incorporate the hardening effect of steel bars, making it applicable to reinforced concrete structures. The accuracy of the approach is evaluated through numerical examples under various loading conditions, and the results are validated by comparing them with standard experiments using an implicit arc-length method. By eliminating the use of constant or adaptive parameters typically found in explicit methods, the arc-length method, combined with the proposed material model, effectively captures the behavior of both ordinary and reinforced concretes subjected to cyclic loading.