Nonlinear Behavior Of Concrete Research Articles

Investigation on mechanical performance of prestressed concrete box‐girder bridge strengthened using composite trusses with different shapes

AbstractIn this study, a finite element (FE) model of an existing prestressed concrete box‐girder (PCB) bridge is developed using Abaqus/Explicit (2022), and a series of FE simulations are conducted to examine the results of composite trusses (CTs) in strengthening PCB bridges with different shapes. A concrete damage plastic model of concrete is used to predict the nonlinear behavior of concrete. Field tests and theoretical calculations are performed to verify the rationality of the model. Three CTs of different shapes, that is, a K‐shaped composite truss (KCT), an X‐shaped composite truss (XCT), and a triangle‐shaped composite truss (TCT), are used to strengthen the PCB bridge models. The deflection, load distribution, distortion, and surface connection forces under two types of lane loads (European code [EU] and Chinese code [CC]) are discussed. The results show that the CT can reduce the deflection and distortion of the PCB bridge and improve the load distribution. However, the different CT shapes offer other strengthening effects. Among them, the XCT reduces deflection the most significantly, that is, by 8.9% and 17.1% under the two load modes, separately. In addition, the XCT improves the load distribution of the PCB bridge the most significantly. The KCT reduces the distortion of the PCB bridge the most significantly and decreases the stress ratio by 75.36%. Moreover, the deflection of the PCB bridge under the EC is more significant, indicating that the lane load defined by the EC is larger than that by the CC. The maximum surface connection forces are different under the same load mode for the different CTs. However, in all the models, the bending moment at surface‐2 is insignificant. Based on the analysis results, five assumptions are introduced. Using the KCT as an example, the plane model of the reinforced section is simplified, and a canonical equation is established to calculate the load distribution factor. The 324 coefficients and 18 free terms in this canonical equation are deduced, which provides a theoretical basis for strengthening PCB bridges using CTs.

NONLINEAR FINITE ELEMENT ANALYSIS OF REINFORCED CONCRETE SHEAR WALLS

Advanced computational modeling for the nonlinear analysis of reinforced concrete shear walls is presented. To this end, thirteen shear walls, with height-to-width ratios of 1.0 and 2.0, were analyzed and compared with the experimental data reported by Lefas and co-workers in 1990. These ratios were carefully chosen to enable the structural assessment of shear walls with realistic geometry under monotonic horizontal loading via computer simulations. In the analysis, the nonlinear behavior of concrete was represented by fracture-plastic constitutive models, implemented in the context of smeared crack approach and crush band method. From the results presented, it is shown that the modeling approach presented in this paper is capable of predicting the full response of the walls with good accuracy. This includes the post-cracking response, failure loads and crack patterns at various stages of loading, which are useful to characterize failure process. The influence of key parameters (height-to-width ratio, axial load ratio, web reinforcement ratio) on overall response is discussed.

Ultimate torsional resistance and failure modes of FRP-strengthened reinforced concrete members: A nonlinear design model

Reinforced concrete (RC) structural members, especially flanged and spandrel beams, bridge girders, curved beams, and eccentrically loaded beams may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, far too little attention has been paid to the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, a limited number of guidelines specified the design of externally bonded FRP systems in torsion. This study provides an important opportunity to advance the understanding of the torsional behavior of FRP-strengthened members by developing a nonlinear design model predicting the failure mode and ultimate torsional resistance of FRP-strengthened RC members subjected to torsion. Serious discussions and analyses of desired failure modes emerge by defining two balanced conditions between the components, and eight failure regions. The first balanced condition defined between FRP and concrete specifies the failure mode of the member, and the second balanced condition defined between steel and concrete is used for the analysis of steel reinforcement stresses. A clear design approach is proposed in this study to access the desired percentage of the externally applied FRP sheets based on the required torsional strength. Moreover, the ultimate stresses and strains of concrete struts, steel reinforcements, and FRP sheets are derived by incorporating the nonlinear behavior of concrete. To evaluate the validity of the design method, 70 FRP-strengthened specimens are collected from 11 previous studies; then, a comparative analysis is conducted among the experimental results, the estimations of the presented model, and the predictions of the commonly available guidelines for torsional strengthening. The excellent agreement between the test results and the presented model estimations confirms the validity and accuracy of the presented model.

Performance-Based Characterization and Quantification of Uncertainty in Damage Plasticity Model for Seismic Fragility Assessment of Concrete Structures

Seismic probabilistic risk assessment requires explicit consideration and quantification of all sources of uncertainty. Although uncertainties in earthquakes and basic material properties, such as nominal concrete compressive strength, strain at maximum stress, and modulus of elasticity of concrete, have been considered in some studies, uncertainties in parameters used to model the nonlinear behavior of concrete are often not considered. Recent recommendations in design standards have incorporated performance-based limit states in the design and risk assessment of nuclear power plants. These recommendations have implicitly mandated that the uncertainty in the nonlinear behavior of concrete needs to be characterized and quantified in accordance with different performance limit states. This study focused on nonlinear model parameters in the concrete damage plasticity model (CDPM) and their characterization in terms of material strength parameters. Furthermore, a performance-based characterization and quantification of uncertainties in nonlinear model parameters was also conducted. Data from existing experimental studies were used to study the uncertainties in CDPM and were used as a basis for the proposed quantification.

Assessment on the structural impact of the slabs with joists used in the reinforced concrete structures in Burundi

Introduction. This paper addresses the effect of reinforced concrete slabs with joists on the behavior of reinforced concrete buildings.
 
 Materials and methods. Firstly, models of 3-storey, 6-storey, 9-storey and 12-storey buildings were used to determine internal longitudinal forces in the most heavily loaded column on the ground floor and to identify the unloading action of slabs with joists. Secondly, natural periods of the structures were identified by solving the modal equation of vibration in reinforced concrete building models to identify the effect of the unloading action on the flexibility of a reinforced concrete building. Tables and diagrams were used to analyze and interpret the results.
 
 Results. For the ratio of 4.72 between the weight of one square meter of a reinforced concrete slab and the weight of joists used in one square meter of the slab, the unloading effect varies from 15.18 to 16.78 % and from 15.74 to 16.10 % in the columns, respectively, for the ultimate limit state and the serviceability limit state of a reinforced concrete building. The unloading action, induced by the slabs with joists, reduces the flexibility of a reinforced concrete building. Flexibility reductions are illustrated by reductions of the values of the natural periods from 6.74 to 6.98 % for the 3-storey building, from 5.77 to 6.74 % for the 6-storey building, from 5.36 to 6.56 % for the 9-storey building and from 4.26 to 7.84 % for the 12-storey building.
 
 Conclusions. The use of slabs with joists reduces the mass by 15 % and has an unloading effect on a reinforced concrete structure; it also boosts the building flexibility by 6 % and deteriorates the deformability due to the non-linear behaviour of concrete.

PROGRESSIVE DAMAGE ANALYSIS OF STEEL-REINFORCED CONCRETE BEAMS USING HIGHER-ORDER 1D FINITE ELEMENTS

The present work investigates progressive damage in steel-reinforced concrete structures. An elastic-perfectly plastic material response is considered for the reinforcing steel constituent, while the smeared-crack approach is applied to model the nonlinear behavior of concrete. The analysis employs one-dimensional numerical models based on higher-order finite elements derived using the Carrera unified formulation (CUF). A set of numerical assessments is presented to study the mechanical response of a steel-reinforced notched concrete beam loaded in tension. The predictions are found to be in very good agreement with reference experimental observations, thereby validating the numerical approach. It is shown that CUF allows for the explicit representation of the constituents within the composite beam, resulting in accurate solutions in a computationally efficient manner.

Prediction of Immediate Deflections for RC Beams Using Stress-varying Modulus of Elasticity

This paper discusses the immediate deflection calculation of reinforced concrete beams and their consistency with the experimental results. For this purpose, a total of six T-beams with low, medium, and high reinforcement ratios were tested and then, deflection behavior was compared with the well-known Branson (1965) and Bischoff (2005) approaches. Although both approaches could yield close results for the low reinforcement at service loads by using a constant modulus of elasticity, they underestimated the deflections of medium and highly reinforced beams. Thus, the nonlinear behavior of concrete that changes with stress was also considered in the subsequent analyzes. As a result, the developed new approach could predict the experimental deformations very accurately, especially at the level of service loads.

Performance of Shear Connector in Composite Slab and Steel Beam with Reentrant and Open Trough Profiled Steel Sheeting

The composite construction strategies realize an increasing number of sizeable applications in regions like bridges, ramps, homes, and different exceptional places. The component of composite structure considered in the study contains composite slab, profiled steel sheeting, steel beam, shear connector, and reinforcement cages. The investigation mainly focused on the structural performance of demountable shear connectors in composite slabs and steel beams with profiled steel sheeting. An extensive nonlinear finite element model was used to carry out in FE software Abaqus 6.14. Nonlinear behavior of concrete, stud connector, profiled steel sheeting, reinforcement cage, and steel beam are included in the finite element model. In this study, 24 specimens were taken into consideration to investigate the capacity of the shear connection, the load-slip curve of stud, failures modes of demountable shear connectors, and concrete crushing in the composite floor with profiled steel sheeting. The analysis confirmed that as the diameter of the shear connector increased from 19 to 22 mm, the capacity of the shear connector also increased by 54.313% and 28.903% in both open through and reentrant profiled steel sheeting, respectively. In addition, as the height of the profiled steel sheeting increased from 50 to 64 mm, the capacity of the shear connector is increased by 11.601% and 32.564% in open through and reentrant profiled steel sheeting, respectively. Similarly, when the concrete grade increased from C-40 to C-60, the capacity of the shear connector also increased by 70.128% and 48.301% with open and reentrant profiled steel sheeting, respectively. Furthermore, sensitivity analysis is done to see how much each input parameters affect the output parameter.

Earthquake damage estimation of the Koyna concrete gravity dam using explicit GFVM model considering fluid–structure interaction

In this paper, an Explicit Galerkin Finite Volume Method (E-GFVM) is employed to estimate damage paths in concrete structures through the definition of nonlinear behavior of concrete. Furthermore, to verify the accuracy and efficiency of the present method, the E-GFVM outcomes are compared with the Explicit Finite Element Method (E-FEM) which is a well-known numerical method for investigating numerous solid mechanics problems. Due to the essence of explicit methods, the method in question uses a few matrix operations in nonlinear analysis, so it diminishes computation workloads for time-dependent cases with small time-step. The reason for using E-GFVM was its simplicity and high accuracy in estimating stresses and displacements for the analysis of Computational Solid Mechanics (CSM) problems. Furthermore, one important feature of FVM is its local conservation properties which guarantee the global conservation of variables that provides more stability, particularly in dealing with complex problems. To model the nonlinear behavior of concrete, the two equivalent uniaxial stress–strain relations, taking into consideration the softening and hardening behavior in both compression and tension, are implemented in the proposed numerical method. In other words, the bi-axial concrete behavior is defined by applying the idea of current strength in principal stress space. Therefore, this study aims to introduce a new numerical method that in addition to reducing time consumption, can maintain the accuracy of the results. For reaching this purpose, first, the nonlinear behavior of concrete is modeled and two different specimens are placed under pure pressure and tension loads. The results calculated by the E-GFVM are compared with other literature. After verification of the nonlinear behavior of concrete using E-GFVM, the ability of the proposed method for analysis of a real-world case under time-dependent conditions, namely Koyna concrete gravity dam which experienced a destructive earthquake in 1967, is tested, considering the impacts of dam–reservoir interaction. Then, this problem with the same conditions is modeled and analyzed using the E-FEM. The results show that, in spite of good harmony between two utilized methods for estimating the damage on the body of Koyna dam, the CPU time of the E-GFVM became about 3 times less than the E-FEM.

A nonlinear concrete damaged plasticity model for simulation reinforced concrete structures using ABAQUS

The reinforced concrete structure is typical and widely used in many fields. The behavior of concrete is nonlinear and complex. Especially, when cracks/crushings occurred in softening phase. Thus, It is important to find a damaged model of concrete with high reliability in the numerical simulation. The nonlinear behavior of concrete is the most feature used in the simulation. This characteristic is expressed through the parameters defining the yield surface, the flow potential, and the nonlinear relationship of stress-strain in the cases of tension and compression. This paper introduces a damaged concrete model that applies to the simulation of reinforced concrete structures. The reinforced concrete beam and flat slab are selected as examples to evaluate the reliability of the model presented. Through the results achieved, the model used in this paper shows high reliability and can be used to simulate more complex reinforced concrete structures.

Flexural strengthening of reinforced concrete beams using external tendons

Strengthening of reinforced concrete (RC) beams is the important issue in the civil engineering practice. One of the techniques that can be applied in strengthening of such structures is prestressing using unbonded tendons. Despite the fact that many research studies have been done in the subject of external prestressing there are still some gaps in knowledge in this issue. These gaps concern especially the effect of preloading, precracking and strengthening sequence on the ultimate load and load–displacement behaviour of strengthened RC beams.The paper presents experimental and numerical research on reinforced concrete beams strengthened with external unbonded tendons. The results of experimental investigation performed on four point bending beams that were preloaded and precracked before strengthening are briefly described and discussed. On the basis of experimental observations a three-dimensional model of the beams was developed. The model considers the nonlinear behaviour of concrete, steel bars and prestressing strands. For the calibrated numerical model a parametric study was performed. The influence of the following parameters on the ultimate load, load–deflection and stress increase in tendons of beams were taken into account: concrete class, steel ratio, loading configuration, preloading level, strand shape, cross-section shape, deviator configuration.The experiments show that external prestressing is a very efficient technique for the flexural strengthening of reinforced beams. Preloading, precracking and the strengthening sequence have a minor influence on the ultimate stress increases in strands and the load-bearing capacity of beams after strengthening. It was also demonstrated that strengthening under existing external loading has a positive influence on the serviceability (deflection) limit state. The proposed numerical model confirms the good predictive capabilities for all experimentally tested beams and all considered load and structural stages. The parametric study demonstrated that the initial prestress level has a moderate influence on strengthening efficiency. It was also found that for elements that are characterised by cross-sections without wide compressive zones (i.e. rectangular cross-sections) the compressive strength is one of the key parameters that governs the ultimate load and ductility of the strengthened beam. The considered schemes of loading (two concentrated forces and uniformly distributed load) and the shapes of the tendons (in the form of broken or straight line) have a very moderate influence on the load-bearing capacity and load–displacement behaviour. The second order effects are more pronounced for beams with lower tendon eccentricities. These effects were activated after yielding of the main reinforcement. Finally, it was shown that before yielding of the main reinforcement, increases of stresses in tendons are a strong function of the stiffness of a beam and do not depend on the eccentricity of tendons or the type of supporting of tendon along the span of the beams.

Bearing Strength of Concrete with Carbon Fibre Reinforced Plastic (CFRP) Wrapping Axially Loaded through Circular Plate

Bearing strength of concrete is strongly related to contact behaviour when the loaded bearing plate penetrate over limited area of concrete surface. The model of concrete bearing was examined using the three-dimensional (3D) nonlinear explicit finite element micro-model in the ABAQUS/Explicit. The contact interaction between the concrete surface and the steel bearing plate was modelled using Surface to Surface (S-to-S) contact model. For material nonlinearity, the Concrete Damage Plasticity Material Model (CDPM) was adopted to stimulate nonlinear behaviour of concrete. The main objective of this paper is to determine the effects of external reinforcement namely Carbon Fibre Reinforced Plastic (CFRP) wrapping in strengthening the bearing capacity of concrete blocks. The concrete block models are with three different bearing ratios of unloaded-loaded area 2, 4 and 6 were investigated. The FE results have shown that the structural performance of concrete bearing with CFRP external wrapped can increase the axial load capacity up to 30% than normal concrete block without CFRP wrapped. However, the effectiveness of CFRP wrapping is decreased as the concrete bearing ratio is increased. This indicates that the CFRP wrapping is effective for concrete blocks with high contact areas.

A two-scale stochastic damage model for concrete under fatigue loading

The microscopic stochastic fracture model is extended by introducing a concept of microscale damage, whose evolution law is derived by an energy analysis on the propagation of the cracks from nano- to microscale. A material parameter termed nano-to-micro comprehensive fracture energy is found to play a key role in the random and nonlinear behavior of concrete. It is shown that the proposed model can simulate the mean and standard deviation of the complete stress–strain curve of concrete very well. Moreover, the fatigue life, stiffness degradation and their inherent randomness under various loading conditions can be well predicted by the model.

Concrete compressive strain behavior and magnitudes under uniaxial fatigue loading

Recent advances in concrete technology and construction have promoted an increasing utilization of concrete in fatigue-critical structures, such as wind turbine towers. While research into concrete fatigue is not a new topic and has been going on for several decades, a large majority of this research has primarily been focused on the determination of concrete fatigue capacity. However, understanding and advancing concrete fatigue behavior (e.g., fatigue stress vs. strain response) has received limited attention, even though this is also crucial, especially considering the inherently nonlinear behavior of concrete. To address this knowledge gap and further advance our understanding of concrete fatigue behavior, an experimental investigation consisting of uniaxial compressive fatigue testing of concrete cylinder specimens until failure was undertaken, and axial strains were recorded throughout the duration of fatigue loading. The behavior and evolution of concrete axial strains, including the rate of accumulation of strains, through the fatigue loading process were extensively analyzed and are reported. Additionally, the influence of key parameters, such as peak stress levels and number of cycles to failure, on peak strain evolution were investigated and are described. Magnitudes of peak axial strain at the end of the stable strain accumulation phase, as well as at failure, are also reported, and recommendations are made for estimating strain magnitudes at these critical junctures when conducting fatigue analysis and design. The results will help advance the understanding of concrete axial strain behavior under compressive fatigue loading. The results also provide guidelines for estimating the magnitudes of concrete strains under fatigue loads, which in turn will be beneficial to designers, as it allows them to also consider structural performance during the analysis and design of fatigue critical concrete structures.

Behaviour of prestressed hollow core slabs strengthened with NSM CFRP strips around openings: A finite element investigation

Prestressed Hollow Core Slabs (PHCSs) have become widely used in the construction industry owing to their economic benefits. During their service life, changes that would require openings to be situated along their spans may arise. A strengthening technique to recover or improve the original serviceability and resistances becomes indispensable. Limited research interest has been given to develop appropriate strengthening methods for the PHCSs with openings. The Near Surface Mounted (NSM) strengthening technique is among the practical and feasible solutions to rehabilitate or enhance the performance of these PHCSs. This paper demonstrates a Finite Element (FE) analysis technique to predict the responses of the PHCSs with openings, either unstrengthened or strengthened with NSM strips. The Concrete Damage Plasticity (CDP) model was successfully implemented to model the non-linear behaviour of concrete. The prestressing transmission length and the bond behaviour between the epoxy adhesive and concrete interfaces were put into practice. Acceptable agreements were found, upon validating the FE analysis results against the experimental data available in the literature. Maximum differences, compared to the experimentally attained results in the ultimate loads and the corresponding deformations of nearly 4% and −8.4%, respectively, were detected. An extensive parametric study was executed to assess the effect of various parameters on the overall behaviour of the examined slabs. The PHCS cross-sectional shape, CFRP reinforcement percentage, average precompression, opening location and size and the concrete compressive strength were taken as parameters. Above all, a gap of knowledge exits regarding the presence of design guidelines that evaluate reductions in the ultimate capacities of the PHCSs associated with the presence of openings at multiple locations along their spans and improvements experienced by employing the NSM strengthening technique. This could be bridged by utilizing the suggested modelling approach and the parametric study results in this research.

Axial performance of GFRP composite bars and spirals in circular hollow concrete columns

The fiber reinforced polymer (FRP) bars are used in hollow concrete columns (HCCs) to alleviate the steel-reinforcement corrosion problem and to make an efficient and lightweight structure. The presented study has endeavored to numerically and theoretically explore the structural behavior of hollow concrete columns (HCCs) reinforced with glass fiber reinforced polymer (GFRP) bars and spirals. Six HCCs were simulated in a commercial finite element software ABAQUS 6.14. The control finite element model (FEM) was calibrated for various variables of HCCs using the previous experimental testing results. The complex nonlinear behavior of concrete was defined using the concrete damaged plastic model (CDPM) and the behavior of GFRP bars was considered as linear elastic. The proposed FEM portrayed a close correlation with the testing results of HCCs. Moreover, the different empirical models were proposed for predicting the two-peak loading behavior of FRP-reinforced HCCs based on a large database constructed from the previous research.

Hysteresis Behaviour of Precast Shear Wall – Slab Connection under Reverse Cyclic Loading

An experimental study focused on precast shear wall-slab joint failure is presented in this paper. For the precast specimen, the shear wall and slab are precast members and were connected with cast-in situ concrete using dowel bars. The specimen was tested under reverse cyclic loading and the structural behaviour of the connection was evaluated. The parameters considered are cracking pattern, hysteresis behaviour, energy dissipation and ductility. This study also aimed to develop 3-D finite element (FE) model of precast shear wall – slab dowel connection using ABAQUS software in order to investigate the joint failure of the specimen such as damage and hysteresis behaviour. The non-linear behaviour of concrete was defined using concrete damaged plasticity (CDP) model and the interactions between the precast members were modelled using cohesive element. FE model was then validated against the experimental results of precast dowel connection which are vulnerable to wall-slab joint shear failure. The failure pattern of the tested specimen showed the “Strong joint-Weak member” concept. The comparison between experimental and numerical results showed that the FE model developed was capable of simulating the seismic performance and the joint failure of precast shear wall-slab connection using dowel bars.

Parametric analysis on compressive strain rate effect of concrete using mesoscale modeling approach

To reveal the physical mechanism of strain rate effect of concrete subjected to compression with different loading speeds, parametric analysis on the nonlinear behavior of concrete was performed using mesoscale finite element (FE) modeling approach in this study. The effects of geometrical shape and distribution pattern of aggregates, interfacial transition zone (ITZ), loading approach, viscosity parameters, element meshing techniques and other mesoscopic influence factors on the failure pattern, compressive stress–strain relationship and dynamic increase factor (DIF) of concrete cubes were systematically investigated using explicit and implicit dynamic analysis respectively. The numerical findings indicate that the DIF is mainly induced by the inertial effect of the concrete specimen under dynamic loading and the strength enhancement should be considered in material definition. Besides, it has proved that the DIF is related to the variation of distribution pattern and geometrical shape of aggregates, and mesostructure randomness of concrete needs to be explicitly modeled in mesoscale numerical analysis. In addition, the viscosity parameter imposes significant influences on the convergence issues and the accuracy of numerical results from implicit dynamic analysis. More importantly, the variation trend of DIF is sensitive to the specific value of viscosity parameter. Key issues with regard to mesoscopic analysis of concrete specimen under dynamic loading were systematically investigated in this study and the research findings can provide valuable references for mesoscale modeling of concrete components subjected to dynamic loading with different strain rates.

Development and application of a new discrete element into simulation of nonlinear behavior of concrete

AbstractA new element based on the concept of Rigid Body Spring Model (RBSM) that inherently incorporates Poisson effect is developed and utilized to simulate the nonlinear behavior of concrete. Initially, the behavior of element in linear state is successfully verified. For the nonlinear applications in simulation of concrete, nonlinear material models are implemented based on mesoscale modeling technique that does not suffer from complexity of macroscopic models based on volumetric and deviatoric stress and strain tensors separation. Beside capability of incorporating the Poisson's ratio of the material, with the new material models implemented, the new element can represent the complex behavior of concrete. The uniaxial compressive and tensile test beside splitting tensile test on concrete specimen were simulated successfully and similar cracking patterns to the experiments were observed in the simulations.

Numerical analysis of damage and failure behavior of concrete

The paper discusses an anisotropic continuum damage model for concrete and its numerical implementation into a finite element program to provide an efficient approach suitable for boundary-value problems analyzing nonlinear concrete behavior. The phenomenological continuum approach is based on kinematic description of damage. Irreversible deformation behavior as well as volume increase of material samples even under compression loading are simulated by a damage strain rate tensor. The elastic constitutive equations are affected by damage strain tensors modeling decrease of elastic material parameters. The numerical procedure is based on the damage predictor–elastic corrector technique and the corresponding consistent tangent modulus is presented. Different experiments have been performed and deformation fields are analyzed by digital image correlation technique. Numerical simulations of the experiments show good agreement of the results and elucidate stress and damage states in the specimens. They allow prediction of failure modes of the tested specimens agreeing well with photographs of fractured cylinders and cubes. They also demonstrate the efficiency and the applicability of the proposed continuum damage model.