Fiber Beam Model Research Articles

An efficient nonlinear hybrid model of energy dissipation piers utilizing fiber beam and self-developed hysteretic spring elements

Energy dissipation piers comprised of concrete filled steel tubular (CFST) columns and steel shear links can exhibit good seismic performance by reasonable collaborative optimization design of columns and links. Considering the time and economic costs of experiments and fine element analysis (FEA), an efficient and accurate numerical model is critical to investigate the hysteretic behavior of energy dissipation piers under earthquake action. Therefore, a hysteretic constitutive law for steel shear links is first proposed including the theoretical shear force-deformation skeleton curve and the unloading and reloading rules during hysteretic loading. Next, a hysteretic spring model is developed for efficiently simulating the hysteretic mechanical behavior of steel shear links, which is validated to have good accuracy with comparison to fine FEA and experimental results. Then, a simplified hybrid model consisting of the self-developed spring model and fiber beam model and two multi-scale FEA models with different levels of refinement are established for nonlinear analysis of energy dissipation piers, respectively. The comparison of numerical and test results confirms that the innovative fiber beam-spring hybrid model can accurately describe the hysteretic performance of energy dissipation piers, especially the detailed mechanical behavior of steel shear links and column feet, which provides an efficient numerical tool for analysing the collaborative working mechanism of energy dissipation piers and similar energy dissipation structures.

Advanced Fiber Beam Finite Element Model for Neural Network Training in Vibration-Based Bridge Monitoring

Recent advancements in civil infrastructure monitoring have witnessed the increasingly high-performance sensor technologies and data-driven algorithms, opening up new possibilities for assessing structural conditions. In recent years, there has been a growing interest in leveraging the potential of Artificial Intelligence for civil infrastructure monitoring. One promising approach is the use of computational models to train and test data-driven algorithms aiming to tackle damage detection problems. To enhance the effectiveness of such procedures based on simulated data, this study proposes a high-performance beam finite element model for training a neural network model able to predict the dynamic response of the structure and for generating various damage scenarios. Compared to 2D and 3D finite element models, the advanced fiber beam model offers superior computational efficiency while accurately capturing the nonlinear behavior of structural elements. Specifically, a force-based beam finite element based on a damage-plasticity model is implemented to describe damage and degradation of materials in reinforced concrete girders. Through the simulation of the dynamic structural response under withe noise excitation, a neural network model representing the structure in the undamaged conditions is obtained. The prediction error of such network model is investigated as a suitable measure for the definition of a damage indicator able to detect the presence of damage (concrete cracks and reinforcement yielding). The integration of an advanced fiber beam model, accurate constitutive law and neural network models shows promising potential in the monitoring of existing bridges.

Performance and damage states assessment of thin-walled steel bridge piers with end-corrosion under earthquake loading

End-corrosion is typical damage to steel bridge piers, which will reduce the seismic performance. Unlike overall uniform corrosion, end-corrosion results in more complex stresses on bridge piers, however, there are few related studies. This study aims to analyze the mechanical performance of corroded bridge piers and to establish a method for evaluating the seismic damage status of steel piers considering circumferential uniform end-corrosion. Firstly, the effect of corrosion parameters on key performance points of bridge piers is quantitatively analyzed using the validated finite element model. The calculation method of critical displacement value corresponding to different damage states of the end-corroded bridge pier is proposed. A high-precision fiber beam element analysis model is developed to simultaneously consider the effects of end-corrosion and shear stiffness variation. The results show that the degradation degree of yield displacement of the end-corroded bridge pier is relatively small. In contrast, the ultimate displacement, capacity point displacement and bearing capacity are significantly affected by corrosion parameters, and the degradation degree after corrosion can reach more than 30%. The pier damage ratio formula proposed in this study can accurately describe the degradation of the ultimate value, and the calculation error is almost controlled within 15%. The multi-node variable section (MNVS) fiber beam model proposed in this study has higher analysis accuracy, which can be improved by more than 16% compared with the traditional fiber beam model. In addition, the accuracy of the MNVS model in the dynamic analysis is verified by inputting the seismic records under three site conditions. Finally, considering the characteristics of end-corrosion, an evaluation method and procedure for seismic damage status of the steel pier with end-corrosion is established.

Experimental and numerical studies on the axial compression performance of hexagonal stiffened CFDST stub columns

In this paper, the authors conducted sixteen axial compressive tests on the hexagonal ultra-high performance concrete-filled steel tubular stub columns. The parameters studied in this research program included the cross-sections, section width, the steel tube thickness, and the hollow ratio. Based on the experimental results, the failure modes, axial load-shortening curves, composite strength, and ductility coefficient of the column were illustrated and discussed. The results indicated that stiffeners can significant delay the local bucking of steel tube and improve the interaction between the ultra-high performance concrete (UHPC) and the steel tubes. To simulate the mechanical response of these new types of columns, the authors developed a fiber-beam model (FBM) including the local buckling of steel tubes and the confinement effect. Then, the authors conducted a parametric study to discuss the influence of the hollow ratio, the steel tube thickness, and the strength of steel and concrete. Finally, the authors proposed a new method for predicting capacity and verified it against the test/numerical results. With the comparison of the design rules recommended by the current design codes, the new method proposed in this paper showed a good agreement with the test/numerical results. It can provide a reference for related engineering design.

Experimental and two-scale numerical studies on the behavior of prestressed concrete-steel hybrid wind turbine tower models

Prestressed concrete-steel hybrid (PCSH) wind turbine tower has been recognized as an efficient alternative to traditional steel tube supporting towers for wind farms in harsh sites such as mountain regions. To investigate the global and local mechanical behavior including failure patterns of a full scale PCSH wind turbine towers, an experimental study on a substructure of a scaled PCSH tower is carried out firstly. Then, a material subroutine for three-dimensional (3D) fiber beam elements suitable for implicit analysis on the mechanical behavior of the substructure of the scaled PCSH tower is developed. A two-scale numerical model of the substructure of the scaled PCSH wind turbine tower employing the developed 3D fiber beam elements and solid elements is developed. The accuracy and efficiency of the developed two-scale numerical model for the behavior simulation of the substructure of the scaled PCSH wind turbine tower is illustrated by comparing the numerical results with the experimental measurements. Additional comparison of the simulation results using the developed two-scale numerical model is made with them of a model using sole 3D fiber beam elements and a model using sole solid elements, respectively. Results show that the force–displacement curve determined with the developed two-scale model is close to the test result and coincident well with that of the two models using 3D fiber beam elements and the solid elements. The developed two-scale model can describe the global behavior, the local failure patterns and the stress distribution of the tested specimen accurately with improved simulation efficiency. Finally, the validated two-scale modelling approach is employed to analyze the static behavior, modal parameter, and fatigue of the optimized full-scale PCSH wind turbine tower previously developed by the authors. The simulation results show that the two-scale model can reflect the stress of the PCSH wind turbine tower at the critical position as well as the global mechanical behavior with higher computational efficiency. The fiber beam model can be used for predicting only global, but not local, behavior.

A coupled hygro-thermo-mechanical fiber beam model for reinforced concrete structures

The mechanical behavior of reinforced concrete is affected by the environmental fluctuations of temperature and humidity. In traditional structural analysis of the using beam element, the influence of coupled hygro-thermo-mechanical effect was considered by correction coefficient terms based on data fitting of specimens, which was not very suitable for the analysis of large or complex structures. In order to catch complex behavior of reinforced concrete using beam element, a coupled hygro-thermo-mechanical fiber beam model is developed for the analysis. The model uses a sequential coupled analysis approach based on the framework of original microprestress solidification (MPS) theory and fiber beam element method, which contains important features of reinforced concrete beam such as non-uniform ageing, creep, shrinkage, thermal dilation. Several concrete beam and reinforcement concrete beam experiment data, contrasting examples between the fiber beam element model and conventional 3D solid element model and a typical example of reinforced concrete box beam on structural scale were used to verify the presented model. Overall, good results were obtained in all the tests. The results show that the MPS intrinsic creep property could predict the behavior of concrete beams well. Area weighted average temperature and average relative humidity is an efficient simplified method to catch the MPS intrinsic creep property. Fiber beam element model coupled with MPS intrinsic creep property and a finer subdivision scheme can predict the behavior of beam well under complicated conditions as well as 3D solid element model. The model developed in this study can be used for large structures efficiently.

Efficient numerical analyses of RC beams subjected to impact loading using axial-flexure-shear fiber beam model

Similar to wind and seismic loading, impact loading induced by e.g. vessel or vehicle collisions is another type of extreme loading that has become one of the major hazards for the safety of our infrastructural systems such as bridges and buildings. The development of effective strategies which can realistically quantify structural responses under impact loading becomes increasingly important. The widely-used finite-element (FE) simulations using general-purpose FE programs often require excessively high computational cost. This paper therefore aims to develop and implement a computationally efficient axial-flexure-shear fiber beam model based on Timoshenko beam theory with consideration of material non-linearity for the analyses of reinforced concrete (RC) beams under impact loading. The axial, flexural and shear deformation of RC sections during impact are effectively coupled at the fiber and material level. Numerical accuracy of the proposed fiber beam model for non-linear dynamic impact analyses is verified using experimental data from 15 sets of drop-hammer impact tests on scaled RC beams, including flexure-dominant slender beams and shear-dominant deep beams, which demonstrate the great advantage of the proposed fiber beam model over the classical Euler–Bernoulli fiber beam model for applications to impact scenarios where shear deformation of RC members becomes non-negligible.

An efficient axial-flexure-shear fiber beam model for dynamic analyses of beam–column framed structural systems under impact loading

Impact loadings induced by collisions from an external impacting object (e.g. a vessel, a vehicle) severely threaten the safety of our infrastructural systems such as bridges and buildings. It is therefore critical to develop effective strategies to quantify the impact loadings and dynamic structural responses so that the safety of structures can be pre-estimated. Although the extensively used finite-element simulations can generally provide realistic predictions of impact forces and dynamic responses of structures subjected to vessel or vehicle collisions, they are often computationally expensive. Therefore, the development of computationally efficient simplified impact models using macro-elements has drawn the attention of many researchers. This paper aims to develop a more general-purpose simplified impact model for dynamic analyses of beam–column framed structural systems under impact loading with consideration of shear effects in beam–column members. The well-known Timoshenko beam theory is adopted to develop a fiber beam model that couples the axial, flexural and shear actions in beam–column members at the fiber and material level. A parametric study is then conducted to thoroughly assess the numerical performance of the proposed simplified impact model using several sets of circular columns with different cross-section diameters and height–diameter ratios under the impact from a barge vessel, the complex finite-element model of which was developed and validated by the author previously. The study indicates that the proposed simplified impact model using the axial–flexure–shear fiber beam model enables a sufficiently accurate prediction of the time-histories of impact forces and dynamic responses of both flexure-dominant high columns and shear-dominant short columns under different impact scenarios.

Nonlinear Numerical Simulation of Finite Elements Based on Fiber Beam Elements With Shear Effects for Structures

The classical fiber beam model based on the Euler-Bernoulli beam theory ignores the influence of shear deformation on the section. To get a more accurate beam element model, based on the fiber beam element with shear effects and the Timoshenko beam theory, the stiffness matrix of the fiber beam element was deduced, and the dual effects of geometric nonlinearity and material nonlinearity were considered at the same time, combined with the elastoplastic incremental theory. Then, the nonlinear finite element analysis theory for the structure under the complex stress state of compression, bending and shear was established. Finally, a program was coded on MATLAB to conduct finite element numerical simulation of the typical compression-bending-shear members of reinforced concrete and rectangular concrete-filled steel tube, and the nonlinear full-process load-displacement curves were obtained. The analysis of the numerical examples show that, the established nonlinear finite element analysis theory is universal, feasible and correct.

New modeling strategies for analyzing lateral-torsional buckling in class-4 steel structural members at elevated temperatures using beam-type elements

Fire is one of the main hazards that can affect steel buildings and bridges and was responsible, e.g., for the collapse of the Plasco building in Tehran, Iran, and the I-65 bridge in Birmingham, Alabama, USA. This vulnerability has motivated the development of advanced computational models to predict the response of steel structures to fire accurately. The mechanical response of slender steel members to fire is especially important because they fail prematurely by buckling at load values below their elastic strength. However, the structural analysis of these members typically requires advanced and complex FE models with shell elements, including initial geometric and material imperfections. These shell models are computationally expensive, complicating the carrying out of parametric and probabilistic studies. Therefore, there is a need to develop simple, accurate, and low-cost computational models as reliable as shell-type models. To overcome this knowledge gap, this paper presents two new modeling strategies that simulate the mechanical response of class-4 steel members subjected to lateral-torsional buckling in fire using Timoshenko beam-type finite elements, which significantly simplify the structural modeling. These strategies are called Fiber Beam Model (FBM) and Cruciform Frame Model (CFM) and include initial geometric and material imperfections and thermal strains. In the FBM, the steel member is represented by a single fiber of I-section beam elements, whereas in the CFM, a cruciform arrangement of rectangular beam finite element fibers idealizes it, making the CFM more complex to build than FBM. Both strategies were satisfactorily validated with experimental and numerical results of Test-1 and Test-3 carried out in the “Fire design of steel members with welded or hot-rolled class-4 cross-section” (FIDESC4) research project on a slender beam of class-4 section. Although both FBM and CFM correctly captured the LTB resistance of the tested beam, CFM can, in addition, adequately reproduce the local buckling failure and significantly reduced the computational time. That means complex fire engineering problems such as probabilistic and optimization analyses of thin-walled beams can be addressed more easily and accurately, representing an important step towards applying performance-based approaches in slender steel structures under fire.

A FIBER BEAM ELEMENT FOR THE FINITE PARTICLE METHOD CONSIDERING SHEAR AND TORSION DEFORMATON

To improve the accuracy of the finite particle method (FPM) for solving structural elastoplastic problems, the fiber beam model is combined with the solution framework of FPM. The formulas for solving the particle internal forces of the FPM fiber beam element considering shear and torsion deformation are deduced. The element uses the Timoshenko beam theory to describe the deformation state of the beam section. The displacements of an arbitrary point on the section are determined by the element pure deformation components in the element. The three-dimensional constitutive relationships of fiber materials are used in the element to consider the coupling effects between bending, shear and torsion deformation. Several numerical tests are conducted. The results show that the proposed fiber beam element can effectively simulate the elastoplastic behavior of the structure and shows higher accuracy than the plastic hinge method.

10.21: Post‐fire response of slender concrete‐filled steel tubular columns

ABSTRACTIn this paper, a fiber beam model for the simulation of the post‐fire response of slender concrete‐filled steel tubular (CFST) columns is presented. First, the model is validated against experimental results and subsequently it is employed to analyse the post‐fire response of circular CFST columns. Actually, when a fire takes place in a building, the columns are supporting load even while the fire is being extinguished. For that reason, it is important to take into account this loading condition when trying to predict their post‐fire behaviour. Therefore, in this research, the analysis is initiated when a constant load is applied to the column and, simultaneously, the specimen starts to be heated following an established heating regime (ISO 834). Maintaining the applied load constant, the cooling stage prolongs until the column reaches the room temperature. The post‐fire response of the CFST columns is studied by means of a mechanical analysis where the applied load increases progressively up to the column failure. The model considers realistic features typical from the fire response of CFST columns, such as the existence of a gap conductance at the steel‐concrete interface or the sliding and separation between the steel tube and the concrete. Finally, the post‐fire response of CFST columns is studied in depth taking as reference experimental results used in validation. The variation of the residual strength with load level for realistic fire resistance times is calculated and analysed.

A novel kinked rebar configuration for simultaneously improving the seismic performance and progressive collapse resistance of RC frame structures

Lateral collapses due to earthquakes and progressive collapses due to the sudden destruction of the columns are two of the most commonly encountered failure mechanisms for buildings. To simultaneously improve the seismic performance and the progressive collapse resistance of reinforced concrete (RC) frame structures, this paper presents a novel method using kinked rebar. Kinked rebar has a large deformability because it can be gradually straightened under a tension force, and it can be placed near the inflection points in beams under uniform vertical loads in RC frame structures. First, uniaxial tensile tests were performed to study the equivalent stress-equivalent strain relation and the deformation mode of the kinked rebar. Second, three-point and four-point bending tests were performed to investigate the load-deflection relationship and the failure modes of simply supported beams with local kinked rebar. Third, numerical simulations based on the fiber beam model were conducted to study the seismic behavior and progressive collapse resistance performance of a six-story RC frame with local kinked rebar in the beams. The mechanical behavior of the new beam section with kinked rebar was used to relocate the plastic hinges and to successfully improve the calculated progressive collapse resistance of the RC frame.

A dynamic analysis algorithm for RC frames using parallel GPU strategies

In this paper, a parallel algorithm of nonlinear dynamic analysis of three-dimensional (3D) reinforced concrete (RC) frame structures based on the platform of graphics processing unit (GPU) is proposed. Time integration is performed using Newmark method for nonlinear implicit dynamic analysis and parallelization strategies are presented. Correspondingly, a parallel Preconditioned Conjugate Gradients (PCG) solver on GPU is introduced for repeating solution of the equilibrium equations for each time step. The RC frames were simulated using fiber beam model to capture nonlinear behaviors of concrete and reinforcing bars. The parallel finite element program is developed utilizing Compute Unified Device Architecture (CUDA). The accuracy of the GPU-based parallel program including single precision and double precision was verified in comparison with ABAQUS. The numerical results demonstrated that the proposed algorithm can take full advantage of the parallel architecture of the GPU, and achieve the goal of speeding up the computation compared with CPU.

An effective model for analysis of reinforced concrete members and structures under blast loading

The traditional fiber beam model has been widely used in the seismic analysis of reinforced concrete members and structures. However, the inability to capture shear failure restricts its application to blast loadings. In this article, a numerical model that considers both rate-dependent shear behavior and damage effect is proposed based on the traditional fiber beam element. This is achieved using the modified compression-field theory with a concrete damage model and bilinear steel model in the principal directions. Meanwhile, a condensed three-dimensional stress–strain relation from the isotropic hardening plasticity model is implemented to simulate longitudinal reinforcement bars, as large shear strain would be produced under severe blast loads. The proposed model is validated by comparing the numerical and test results. The high-fidelity physics-based finite element model, validated by the same experiment, is also used in the study to prove the efficiency of the proposed model. Case studies of a reinforced concrete beam and a six-story reinforced concrete frame structure subjected to blast loads are then carried out. The results indicate that the proposed model is reliable compared with the high-fidelity physics-based model. In addition to the accuracy, comparisons of the computational time show an excellent performance with respect to the efficiency of the proposed model.

A new model for analyzing nonlinear torsion behavior of concrete filled steel tube columns with rectangular section

An experimental study on concrete filled steel tube columns with rectangular section subjected to compressionflexure-torsion combined action has been carried out. The failure modes and load-deformation hysteretic relations were obtained. Based on the principles of classical material mechanics, the relations between the torsion curvature of the section and the shear strain of the fiber on the section were established. Then the strain distribution on the rectangular section of concrete filled steel tube columns subjected to torsion was analyzed. The three-dimensional refined finite element model was also built, in order to make the precision verification. The matrix forms of the relation between the torsion curvature of the section and the shear strain of the fiber on the section were derived, and introduced into the fiber beam model considering nonlinear torsion effect on the section. The comparison between test results and calculation results showed that the fiber beam model considering nonlinear torsion effect had high modeling efficiency and solution precision for predicting the torsion behavior of concrete filled steel tube columns with rectangular sections, and was suitable for analyzing the dynamic response of various structures subjected to the combined cyclic load caused by the earthquake load.

Analysis of FRP Shear Strengthening Solutions for Reinforced Concrete Beams Considering Debonding Failure

AbstractIn this paper, a fiber beam model previously developed by the authors for the nonlinear analysis of strengthened elements, including the effects of shear, is used to predict the response of reinforced concrete (RC) beams strengthened in shear with fiber reinforced polymers (FRP) sheets. In the previous version of the model, debonding failure of FRP was not included; hence, its application was limited to the simulation of wrapped configurations. The model is now extended to account for debonding failure in order to allow for its application to beams strengthened with U-shaped and side-bonded configurations. Existing experimental tests on RC beams strengthened in shear by FRP sheets in both wrapped and U-shaped configurations were numerically simulated. The model reproduces, with reasonable accuracy, the experimental failure loads, the load-deflection behavior, and the strains in FRP and stirrups with increasing load. The advantages of this proposal are related with the simplicity and straightforwar...

CROSS SECTIONAL SHEAR STRAIN DISTRIBUTION OF RECTANGULAR CONCRETE FILLED STEEL TUBE COLUMNS SUBJECTED TO TORSION

Tests on concrete filled steel tube columns with rectangular section subjected to pure torsion and compression-torsion were carried out, and the hysteretic curves of torsion moment versus rotational angle were obtained. Based on the principles of material mechanics, the relations between the torsion curvature of the section and the shear strain of the fiber at the section were established. Then the cross sectional strain distribution at the rectangular section of concrete filled steel tube columns was analyzed. The three-dimensional refined finite element model was also built for purpose of verification. At last, the matrix forms of the relations between the torsion curvature of the section and the shear strain of the fiber at the section were derived and introduced into the fiber beam model considering torsion effect. The comparison between the test results and calculation results shows that the fiber beam model considering torsion effect has high modeling efficiency and accuracy for predicting the torsion behavior of concrete filled steel tube columns with rectangular section, and is suitable for analyzing the dynamic response of structures subjected the combined cyclic loads due to earthquake excitations.

Damage evaluation of reinforced concrete frame based on a combined fiber beam model

In order to analyze and simulate the impact collapse or seismic response of the reinforced concrete (RC) structures, a combined fiber beam model is proposed by dividing the cross section of RC beam into concrete fiber and steel fiber. The stress-strain relationship of concrete fiber is based on a model proposed by concrete codes for concrete structures. The stress-strain behavior of steel fiber is based on a model suggested by others. These constitutive models are implemented into a general finite element program ABAQUS through the user defined subroutines to provide effective computational tools for the inelastic analysis of RC frame structures. The fiber model proposed in this paper is validated by comparing with experiment data of the RC column under cyclical lateral loading. The damage evolution of a three-dimension frame subjected to impact loading is also investigated.

Frequency characteristics of hetero-core fiber optics sensor for mechanical vibration

In this paper, we present characteristics of a hetero-core fiber optic sensor in mechanical vibration based on rigid supported beam property for vibration monitoring in fault diagnosis of the industrial equipments. A first configuration of the hetero-core fiber optic vibration sensor was rigidly supported at two fixed ends as curved setting without tension to the fiber. In order to tune the range of the detectable frequencies to be higher of the vibration sensor, a second configuration was evaluated, in which the hetero-core fiber optics was linearly-arranged with tension to the fiber. As a result, the both types of the proposed hetero-core fiber optic vibration sensors could pick up the free vibration from an impact force. Analytical natural frequencies were calculated based on an FEM fiber beam model. It was indicated that the natural frequencies from the experimental results of the 1st configuration were appropriate to the FEM results and a typical beam property, and could be tuned by the length between two fixed ends. Additionally, the 2nd configuration of the vibration sensor with tension to the fiber enabled its detectable frequencies to be dramatically higher than without tension.