Fiber Beam-column Model Research Articles

Efficient numerical simulation of steel-UHPC composite structures based on a fiber beam-column model

To satisfy the demands of different engineering scenarios, ultra-high performance concrete (UHPC) is usually combined with steel to form various steel-UHPC composite structures. This study proposes an efficient numerical method for simulating steel-UHPC composite structures. A finite element analysis program, SU-COMPONA, is developed, which combines the fiber beam-column model and the concept of smeared cracks. Rational material constitutive laws are proposed and integrated into the program to describe the uniaxial behavior of UHPC and steel fibers. The proposed numerical method is validated against sufficient experimental data for various steel-UHPC composite structures, including reinforced UHPC beams and slabs, steel-UHPC composite beams and slabs and steel-UHPC-steel sandwich beams. In addition, the simulation performance is evaluated quantitatively. The results show that the proposed method can predict the ultimate capacity, the load-deflection curve and the development of crack widths with satisfactory accuracy and stability. Compared with the elaborate three-dimensional finite element method, the proposed method based on the fiber beam-column model is a competitive numerical approach that can achieve higher efficiency with slightly less accuracy.

A fiber beam-column model for damage assessment of traditional Chinese timber structures

ABSTRACT This study proposes a fiber beam-column model that takes into account the anisotropy of wood and the embedment behavior of the rocking column to assess the impact of wood damage on the lateral performance of traditional Chinese timber structures. Subsequently, numerical analyses corresponding to a full-scale quasi-static test of a traditional Chinese timber framework are conducted to verify the accuracy of this fiber beam-column model. By considering factors such as residual deformation and wood decay in the column base, the degradation behavior of traditional Chinese timber structures can be evaluated. This study provides a foundation for discussing and further researching the damage assessment of traditional Chinese timber structures.

A Visual Data-Informed Fiber Beam-Column Model for the Analysis of Residual Hysteretic Behavior of Post-Earthquake Damaged RC Columns

ABSTRACT Seismic damage to components and structures may cause extensive degradation of the seismic capacities of the damaged buildings. The analysis of the residual hysteretic behavior of post-earthquake damaged components and structures is a critical step in the assessment of their residual seismic capacities. Whereas, the difficulty in quantifying the damage distribution of materials in post-earthquake damaged components leads to the challenge of quantitative analysis of their residual behavior (i.e. residual stiffness, strength, energy dissipation). In this study, a visual data-informed fiber beam-column model was developed to analyze the residual hysteretic behavior of post-earthquake damaged RC columns under cyclic loads. To begin with, the method for quantifying the damage strain fields of the columns according to their inspected visual data was proposed. Then, the stress-strain relations of the materials considering the effect of damage strain fields were constructed, and the visual data-informed fiber beam-column model was proposed for the analysis of the residual hysteretic behavior of post-earthquake damaged RC columns subjected to cyclic lateral loads. At last, the proposed model was validated by comparing model results with existing test data. The comparison shows that the proposed visual data-informed fiber beam-column model can accurately analyze the concrete crushing surfaces, the residual load-displacement responses, and the energy dissipation capacities of post-earthquake damaged RC columns, facilitating the evaluation of the residual seismic capacities of post-earthquake damaged RC columns.

One-dimensional fiber beam-column model and two-dimensional fixed crack model for numerical simulation of UHPC structures

Ultra-high performance concrete (UHPC), with much higher compressive strength, tensile strength and ultimate tensile strain than normal concrete, has been experimentally investigated and applied in engineering structures more and more widely. However, there are few numerical models appropriate for the accurate and efficient simulation of UHPC or reinforced UHPC (R/UHPC) flexural members including beams and columns as well as shear-critical members such as shear walls till now, which brings obstacles to the analysis and design of UHPC structures. In this study, the uniaxial skeleton and hysteretic rules for UHPC under tensile and compressive loads are first proposed and verified by material tests. The formulas to calculate all the basic parameters in the model are put forward for convenient use. Then the fiber beam-column model for flexure-dominated UHPC members is established in ABAQUS 2017 software and six R/UHPC column specimens subjected to cyclic load are simulated. Based on simulation results, the equations of transition curves in the uniaxial rules are determined, which have significant influence on the predicted hysteresis curves. On the other hand, a new two-dimensional fixed crack based constitutive model for shear-critical UHPC members is further proposed and implemented in ABAQUS 2017 software by considering the compressive softening due to principal tensile strain and shear stress–strain relationship along cracks of UHPC. Finally, ten R/UHPC shear wall specimens under cyclic loads as well as four R/UHPC deep beams under monotonic loads are simulated and the accuracy of the proposed 2D model for UHPC is validated.

Component-based model of semi-rigid connections for nonlinear analysis of composite structures

In order to achieve better mechanical performance and construction efficiency, the outrigger bracket with a “through type” interior diaphragm (OBTID) connection is proposed for application in semi-rigidly connected composite structures. The mechanical behaviour of OBTID connections in two frame tests under lateral cyclic loads is investigated to reveal the failure mechanism. Based on the test observations, a component-based model is proposed to analyse the nonlinear behaviour of semi-rigid connections by decomposing the connection components and putting forward the constitutive law of each component. Furthermore, the proposed model is implemented in a general commercial finite element package and a program for nonlinear analysis of semi-rigidly connected composite structures is developed by combining the component-based model with the previous fiber beam-column model. Then, a comparison between the numerical results and experimental results in both connection level and frame level indicates that the proposed component-based model can predict the complex nonlinear behaviour of semi-rigid connections with good accuracy. Additionally, the contribution of bolt slip to connection rotation is analysed to clarify the pinching effect, and the semi-rigidity of OBTID connections are compared with provisions of Eurocode 3 and that of other similar semi-rigid connections.

Seismic Response Analysis of Isolated and Nonisolated Continuous Girder Bridges under Multidimensional Near-Field Ground Motions

In this study, the responses of isolated bridges and nonisolated bridges are studied under multidimensional seismic motions. First, damage constitutive models of steel bars and concrete materials were combined with the fiber beam-column element model, and the isolated bearing model considering bearing failure was selected. The bridge numerical analysis model was then established. The seismic responses of isolated and nonisolated bridges were analyzed under near-field ground motions (fling-step and forward-directivity ground motions) and far-field ground motions. It was found that the seismic responses of nonisolated bridges, such as deck acceleration, pier displacement, pier damage, and bearing displacement under near-field ground motions, were higher than those under far-field ground motions. Under far-field ground motions, isolation bearings effectively reduced various seismic responses of structures and had isolation effects. Under forward-directivity TCU102 ground motions, the minimum isolation ratios of isolation bearings for peak acceleration of the girder in the Z direction, pier displacement, and pier shear force were −0.14, −2.65, and −0.05, respectively. The low-isolation ratio and significant damage to the isolation bearings indicate that the isolation bearings cannot be directly used under near-field conditions.

Simple rebar anchorage slip macromodel considering corrosion

Reinforcement slip in the footing of a reinforced concrete (RC) column can significantly influence the lateral displacement of the column, a critical structural response under lateral loads such as seismic loading. Many past researchers studied and developed models to capture the anchorage slip of rebar; however, there is still a need for a model that can reflect the actual bond-slip relationship (especially in the presence of corrosion) and yet is simple-to-use for structural analysis. In this study, a simple bar stress-slip macromodel is developed to predict reinforcement anchorage slip given a rebar stress. The proposed rebar anchorage slip model is derived by implementing a macromodel solution based on a simple bond stress distribution function that captures the bond stress distribution numerically obtained from a real bond-slip relationship. Available experimental bond stress-slip data collected from literature are used to optimize the model parameter in the proposed bond stress distribution function, which reflects the impact of the structural parameters on the rebar slippage such as concrete strength and corrosion level. The proposed rebar slip model is then incorporated into a fiber beam-column model for numerical analysis, and is further validated by comparing flexural behavior of several RC columns (with and without corrosion) based on the numerical model with the experimental data. The results demonstrate the importance of incorporating rebar slippage and corrosion effect on bond. Using this fiber beam-column model, seismic performance of an example RC bridge column is evaluated, and one can conclude the rebar slip plays a critical role in the seismic evaluation. As the proposed rebar slip macromodel provides simple formulation and it is explicitly expressed with a model parameter that can be updated easily to incorporate new information, it is practical for structural analysis applications.

Seismic Response and Damage Analysis of an Isolated Bridge Subjected to Near-Fault Ground Motion

In this study, the seismic response and damage behavior of an isolated bridge under near-fault ground motion are studied and compared with the non-isolated bridge. To consider the local damage of the bridge pier and its evolution process, the nonlinear behavior of the bridge pier in the analysis is simulated by the fiber beam-column element model combined with the damage constitutive model of steel and concrete materials. The mechanical behavior of the isolation bearing is simulated by the three-dimensional isolation bearing model that can consider the instability and failure of the bearing. It is found that the isolation bearings do not work, and even amplify the seismic response of the bridge (pier displacement and pier shear) under the near-fault ground motion. This amplification also leads to more severe damage to the piers of the isolated bridge. In the case of the analyzed concrete bridge type and near-fault earthquake data, it can be concluded that the used isolating lead rubber bearings should not be recommended. In general, it can be stated that the selection of the types of bridge bearings in near-fault areas should always be analyzed in detail by designers in order to avoid unintentional amplifying of the bridge’s seismic response.

A fast and accurate method for the seismic response analysis of reinforced concrete frame structures considering Beam-Column joint deformation

Many previous investigations of reinforced concrete (RC) frame structures have demonstrated that beam-column joints may experience significant nonlinearities under earthquake excitations. However, most available analysis methods assume that the joint region remains rigid. Because joint failure may result in strength and stiffness losses and even induce structural collapse, it is difficult for an analytical model with a rigid joint assumption to obtain an accurate prediction of the structural nonlinear response. The behavior of a joint is mainly affected by the shear deformation of the joint core and bond-slip of beam longitudinal reinforcements in the joint. Although many different types of modeling approaches have been presented to effectively represent the behavior mechanism of beam-column joints, the introduction of joint models inevitably increases the complexity of the analytical model of the global structure and the effort of the solution process. Therefore, achieving highly efficient analysis on the premise of accurately predicting the seismic response of RC frame structures is still a topic that deserves investigation. This study presents an efficient analysis method for the accurate evaluation of the nonlinear response of RC frames considering the effect of beam-column joint deformation based on the concept of local inelasticity separation. The proposed method captures the bond-slip behavior at beam ends by adding inelastic rotation hinge mechanisms to the ends of the existing inelasticity-separated fiber beam-column model and uses a sliding hinge mechanism to simulate the inelastic shear response of the joint core. A small number of additional inelastic degrees of freedom that are separated from the global displacement degrees of freedom of the structure is introduced to describe both the inelastic rotation behavior and the inelastic deformation of the proposed bond-slip hinge mechanism and the sliding hinge mechanism. Consequently, the Woodbury formula can be utilized for nonlinear iterative solutions to avoid updating the global stiffness matrix, thus significantly improving the computational efficiency. The exactness of the proposed method is verified against experimental data, and its application is illustrated through a seismic response analysis example.

Data-driven seismic response prediction of structural components

Lateral stiffness of structural components, such as reinforced concrete (RC) columns, plays an important role in resisting the lateral earthquake loads. The lateral stiffness relates the lateral force to the lateral deformation, having a critical effect on the accuracy of the lateral seismic response predictions. The classical methods (e.g. fiber beam–column model) to estimate the lateral stiffness require calculations from section, element, and structural levels, which is time-consuming. Moreover, the shear deformation and bond-slip effect may also need to be included to more accurately calculate the lateral stiffness, which further increases the modeling difficulties and the computational cost. To reduce the computational time and enhance the accuracy of the predictions, this article proposes a novel data-driven method to predict the laterally seismic response based on the estimated lateral stiffness. The proposed method integrates the machine learning (ML) approach with the hysteretic model, where ML is used to compute the parameters that govern the nonlinear properties of the lateral response of target structural components directly from a training set composed of experimental data (i.e. data-driven procedure) and the hysteretic model is used to directly output the lateral stiffness based on the computed parameters and then to perform the seismic analysis. We apply the proposed method to predict the lateral seismic response of various types of RC columns subjected to cyclic loading and ground motions. We present the detailed model formulation for the application, including the developments of a modified hysteretic model, a hybrid optimization algorithm, and two data-driven seismic response solvers. The results predicted by the proposed method are compared with those obtained by classical methods with the experimental data serving as the ground truth, showing that the proposed method significantly outperforms the classical methods in both generalized prediction capabilities and computational efficiency.

Numerical Simulation of the Effect of Freeze–Thaw Cycles on the Durability of Concrete in a Salt Frost Environment

In order to improve the accuracy of the analysis of the impact of freeze–thaw cycle on concrete durability in a salt freezing environment, the numerical simulation of the impact of the freeze–thaw cycle on concrete durability in a salt freezing erosion environment is studied in this paper. Firstly, considering the influence of axial force and bending moment on the relationship between bending moment and curvature, a concrete fiber beam column model is established. Then, according to the joint influence of temperature field, stress field and seepage field on concrete in the process of freezing and thawing, the control differential equation of the freezing and thawing cycle is established. The freeze–thaw damage section is divided, the non-uniform distribution of freeze–thaw damage is determined, and the division of the freeze–thaw damage section is completed. According to the linear relationship between freeze–thaw damage degree, relative dynamic elastic modulus, freeze–thaw cycle times and position variables, the durability of concrete is numerically simulated, and the attenuation law of bond strength at different section depths after freeze–thaw is determined. The results show that the temperature curve simulated by the design method is consistent with the actually measured temperature curve, which can better reduce the temperature change of the inner core of the test block during freezing and thawing, and the relative dynamic elastic modulus is in good agreement with the actual value, which can prove that the method in this paper has certain practical application value. It is expected to provide some reference for solving the durability problem of concrete in a salt frost erosion environment and the optimal design of concrete structures.

Fully nonlinear inelastic analysis of rectangular CFST frames with semi-rigid connections

In this study, an effective numerical method is introduced for nonlinear inelastic analyses of rectangular concrete-filled steel tubular (CFST) frames for the first time. A steel-concrete composite fiber beam-column element model is developed that considers material, and geometric nonlinearities, and residual stresses. This is achieved by using stability functions combined with integration points along the element length to capture the spread of plasticity over the composite cross-section along the element length. Additionally, a multi-spring element with a zero-length is employed to model the nonlinear semi-rigid beam-to-column connections in CFST frame models. To solve the nonlinear equilibrium equations, the generalized displacement control algorithm is adopted. The accuracy of the proposed method is firstly verified by a large number of experiments of CFST members subjected to various loading conditions. Subsequently, the proposed method is applied to investigate the nonlinear inelastic behavior of rectangular CFST frames with fully rigid, semi-rigid, and hinged connections. The accuracy of the predicted results and the efficiency pertaining to the computation time of the proposed method are demonstrated in comparison with the ABAQUS software. The proposed numerical method may be efficiently utilized in practical designs for advanced analysis of the rectangular CFST structures.

An efficient approach for numerical simulation of concrete-filled round-ended steel tubes

Concrete-filled round-ended (CFRE) steel tubes are widely used in civil infrastructures. Accurate and reliable numerical models of CFRE steel tube are significantly important to mimic the actual behavior. This study presents a fiber beam-column model to simulate nonlinear behavior of CFRE steel tubes. A group of uniaxial hysteretic constitutive models was defined for the properties of the material. To verify the reliability of the presented fiber model, a large number of numerical computations have been performed by the fiber model and a traditional refined finite element model. The results confirm that the proposed fiber model can accurately predict the nonlinear behavior of CFRE steel tubes. Finally, two empirical models for the prediction of the axial bearing capacity of CFRE steel tube columns were developed.

The Behavior of Rectangular and Circular Reinforced Concrete Columns Under Biaxial Multiple Excitation

The aim of this study is to investigate the dynamic performance of rectangular and circular reinforced concrete (RC) columns considering biaxial multiple excitations. For this purpose, an advanced nonlinear finite element model which can simulate various features of cyclic degradation in material and structural components is used. The implemented nonlinear fiber beam-column model accounts for inelastic buckling and low-cycle fatigue degradation of longitudinal reinforcement and can simulate multiple failure modes of RC columns under dynamic loading. Hypothetical rectangular and circular columns are used to investigate the failure modes of RC columns. A detailed ground motion selection is implemented to generate real mainshock and aftershocks. It was found that multiple excitations due to aftershock has the potential of increasing the damage of the RC columns and longitudinal reinforcements are significantly affected low-cycle fatigue. Also, it was found that rectangular column is more sensitive to accumulative damage due to cyclic fatigue. This study increases the accuracy of structural analysis of RC columns and consequently improves understanding the failure modes of RC columns with different cross-sectional shapes.

Simplified fiber beam-column model for inelastic analysis of moment-resisting steel frames

Conventional fiber beam-column models require monitoring the responses of many sections along the element length to account for the speared of inelasticity. Recently, a simplified approach that utilizes predefined flexibility-distribution functions to account for the spreading of inelasticity along the element length is introduced. The new approach is much simpler than the conventional fiber models as it does not require monitoring the responses of many sections along the element length, which results in a significant reduction in computations. The main shortcoming of this simplified approach is the need to estimate empirically a cross-section-shape dependent flexibility distribution factor by calibration with exact analysis.This study proposes a simplified model with flexibility-distribution functions that does not require any calibration with exact analysis. In this proposed model, the flexibility distribution factor is automatically calculated during the analysis without any user interference. The results of the numerical analysis carried out in this study on the one-element level and on the structure level indicate the effectiveness of the proposed model.

Rational modeling for cracking behavior of RC slabs in composite beams subjected to a hogging moment

Cracking of the reinforced concrete (RC) slab is a critical problem for a composite beam subjected to a hogging moment, which hinders its application to indeterminate composite structural systems. An efficient numerical method based on the fiber beam-column model is developed for predicting the full-process nonlinear crack width development of composite beams. Several significant modeling issues involving the modeling strategies, selection of material constitutive laws, consideration of shrinkage effect, and determination of average crack spacing are discussed in detail. Rational modeling parameters are recommended and validated by several previous experiments: (i) the slight mesh-dependency can be neglected, and the midpoint integration rule with 6 and 4 uniformly distributed fibers for the slab concrete and the steel beam web, respectively, can give results with sufficient accuracy; (ii) the crack width–load curve obtained through FE analysis should be modified to rationally consider the shrinkage effect of the slab concrete with the initial shrinkage strain of about 300 με; (iii) it is rational to select the value of the average crack spacing as the transverse reinforcement spacing of the RC slab; and (iv) the constitutive laws of the tensile slab concrete and reinforcement have minor influence on the global crack width–load response, especially in the stage after the stabilization of the cracking distances. The selected smeared material constitutive laws are recommended to give a smooth and rational curve for the stage before stabilized cracking.

SOME ADVANCES IN CONVENTIONAL FIBER BEAM-COLUMN MODEL

The fiber beam-column model, which is an important milestone in the development of simulation technique for structural systems, has been widely used in recent years with its simplicity, efficiency and generality. However, the poor simulation results in many key issues of the structural system using the model cannot be avoided due to the limitation of the basic assumptions of the model. This paper thoroughly reviews the research group's 7-years' efforts and progress in improving the conventional fiber beam-column model to solve several critical problems in structural simulation. Firstly the conventional fiber beam-column model is developed on the platform of general finite element software MSC.Marc and further expanded to the simulation of steel-concrete composite frames. Then four new fiber beam-column models are proposed to give satisfactory prediction results to four key issues in structural simulation including the slab spatial composite effects in composite frames, the nonlinear shear and sliding effects of coupling beams, the rebar anchorage slip in the footings and the whole-process cracking behavior of RC beam and columns, respectively. These models are proved to completely keep the advantages of conventional fiber beam-column models and accurately consider the above complicated effects, according to the verifications by numerous test data and elaborate finite element analysis. Based on the proposed models, a nonlinear analysis program COMPONA-MARC is developed for commonly used structural systems such as RC, steel and steel-composite structures, which provides a powerful platform and tool for elaborate nonlinear structural simulations.

Fiber beam-column model for diagonally reinforced concrete coupling beams incorporating shear and reinforcement slip effects

Due to the improved energy-dissipation and deformation capacity compared to the conventionally reinforced concrete (RC) coupling beams, diagonally RC coupling beams are recommended by the ACI 318 code especially for a span-to-depth ratio of less than two and thus acquire more and more applications in coupled wall and core tube systems for tall buildings. This paper proposes a sufficiently accurate and efficient displacement-based fiber beam-column model for the nonlinear seismic analysis of diagonally RC coupling beams with span-to-depth ratios ranging between one and five. The model is developed on the platform of a general FEA package MSC.Marc. First, the conventional fiber beam-column element is modified to consider the flexural contribution of diagonal bars. Then the new section shear force-shear distortion and slip deformation rules are proposed and incorporated into the modified fiber element, respectively, since both the shear and reinforcement slip are critical mechanisms influencing the seismic performance of the beam. The equations for critical model parameters including the cracked shear stiffness and chord rotation limit are developed and verified based on the results of sixteen test specimens collected from previous research. The model is utilized to simulate the collected specimens together with a coupled wall system and proves to be a powerful tool for the nonlinear seismic analysis of diagonally RC coupling beams and coupled walls with satisfied accuracy, efficiency and modeling convenience.

Shear Deformation and Sliding-Based Fiber Beam-Column Model for Seismic Analysis of Reinforced Concrete Coupling Beams

AbstractConventional RC coupling beams have been widely used as key energy-dissipation components in frame-core tube structural systems for high-rise buildings. A model with sufficient efficiency, accuracy, and practicality is urgently needed for the seismic analysis of high-rise structures. According to test results, both the shear deformation and shear sliding mechanisms are critical to assessing the seismic performance of coupling beams. However, available shear models for beams and columns cannot give satisfactory results in modeling both mechanisms in finite-element analysis (FEA). To address this problem, this study takes into account the section shear force–shear strain and shear sliding laws in the traditional displacement-based fiber beam-column element, which is implemented into a general FEA package. A new section shear force–shear strain law, which can consider the pinching effect, strength and stiffness deterioration, shear capacity degradation, and arbitrary complex loading path is first pro...

RC fiber beam–column model with bond-slip in the vicinity of interior joints

This paper describes a numerically efficient approach to describe reinforcing bars bond-slip in the vicinity of interior beam–column joints, which is an effect that significantly influences frames behavior regarding stiffness and hysteretic energy dissipation capacity. The fiber-section model proposed here allows for the accurate analysis of those critical regions, taking into account the factors most relevant to the determination of its behavior, without the computational disadvantages of other more complex formulations. The methodology is defined by the fiber model based on continuous anchored bars and by its implementation into a fiber force-based finite element. The behavior of the fiber model based on anchored bars is discussed and then the fiber-section finite element is evaluated by comparison with an experimental test of a beam–column subassemblage subjected to cyclic loading. The proposed beam–column finite element is capable of predicting anchorage slip and the analytical results of the structural subassemblage agree well with the experimental results.