Nonlinear Finite Element Program ABAQUS Research Articles

Parametric study on the flexural behavior of steel fiber reinforced concrete beams utilizing nonlinear finite element analysis

Reinforced concrete beams undergo significant internal forces and deformations under extensive loading and have flexural or shear failure based on the reinforcement detailing and geometric properties. The addition of steel fibers increases the deformation and load carrying capacities that leads to ductile behavior. The main contribution of fibers is the improvement of the composite tensile capacity, which results in improved flexural and shear responses. This study numerically investigates the effect of fiber properties on the flexural behavior of steel fiber reinforced concrete (SFRC) beams for both compression and tension failure. First, three specimens from prior experimental studies are modeled using the nonlinear finite element program ABAQUS and the analytical results are verified by comparison with the test results. Contrary to prior nonlinear models, the developed model accurately predicts the damage pattern, descending portion of the load-displacement relationship, and ultimate displacement, which lead to a reliable estimation of energy dissipation capacity and ductility. A comprehensive parametric study is then conducted to examine the effect of tension reinforcement ratio, fiber volume fraction, and fiber aspect ratio on the flexural behavior of both reinforced concrete and SFRC beams. The influence of these key parameters is investigated by comparing the peak load, displacement ductility, peak stiffness, service stiffness, energy dissipation capacity, and damage pattern for both reinforced concrete and SFRC beams. The analytical results indicate that the addition of steel fibers up to 2.0 % leads to a slight increase in the load carrying capacity, while the displacement ductility and energy dissipation capacity are significantly improved. Furthermore, the utilization of 1.0 % steel fibers is observed to be sufficient to modify the failure mode of over reinforced concrete beams from brittle compression failure to tension failure.

Finite Element Analysis of Weak-Axis Composite Connections Under Cyclic Loading

This paper describes a numerical study on weak-axis composite connection through the nonlinear finite element program ABAQUS. After the simulation and validation of experimental results, a total of 16 models were created to investigate the influence of the different parameters on the structural performance, and their hysteresis responses, rupture index distribution of beam flange welds were discussed in detail. The RBS connection scheme could develop extensive inelastic deformation in RBS region, thus reducing the weld rupture possibility. The thicker the concrete slab, the larger the bending moment under positive bending, and the higher the RI values at the beam bottom flange weld and also the neutral axis. The structural behavior was insensitive to the variation of the parameter reinforcement ratio as the reinforcements did not work well, and it is recommended to arrange reinforcements according to the construction requirements. Changing the weld access hole form has a little influence on the bearing capacity and rotation capacity, but the PEEQ and RI distributions are sensitive to this parameter. The design option of long access holes could provide a further means to reduce the fracture possibility of beam flange groove weld to a reasonable level, thus achieving a favorable performance of weak-axis column bending connections in a composite moment-resisting frame.

NUMERICAL MODELING OF CONCRETE COMPOSITE STEEL TUBES

In modern days, building design emphasizes on enhancing flexibility of the floor space by reducing the cross section of column size. Enhancing compressive strength of concrete on a smaller column gives more strength and more usable floor space. The use of high strength concrete in smaller column, endeavor to brittle failure. This would be prevented by reducing space of stirrup for higher ductility. However, this causes the stirrup to form a natural plane of separation between the confined concrete core and the unconfined concrete cover, the risk of a premature spalling of the concrete cover increases. This is one important reason why it is advantageous to use Composite Columns consisting of Concrete-Filled Steel Tubes (CFST) instead of traditional Reinforced Concrete Columns. This study aims at developing a suitable constitutive model addressing the behavior of Concrete Filled Steel Tubular column on the compressive response under axial loads. Ultimate load carrying capacities obtained by the Authors using experiments have been compared with the Numerical model values. Three-dimensional nonlinear finite element models developed to study the force transfer between steel tube and concrete core. The nonlinear finite element program ABAQUS 6.12-1 is used. The interaction between steel tube and concrete core is the discussing issue for understanding the behavior of Concrete-Filled Steel Tube Columns (CFST). The numerical results validated with experimental data extracted from previous researchers (International & National) in the field including few experiments by the Authors in terms of Ultimate loads and deformation modes. Modeling related problems such as the definition of boundary conditions, imperfections, concrete-steel interaction, material representation and others are investigated using a comprehensive parametric study. The numerical results are validated through comparison with experimental data in terms of ultimate loading and deformation modes. A comparison of ultimate failure loads from nonlinear finite element program ABAQUS 6.12-1 with the predicted failure load from Eurocode Part-4 (EC4) (British Standards Institutions), ACI-318 (2005) (American Concrete Institute), for axially loaded columns will be carried out in this research study From the study it is concluded that, developed Numerical model fits nearer to perfection and depicts the behavior well with 5-10% error. Also, behavior when only Steel tube is loaded has been depicted with loading only Concrete-infill and loading on both infill and Steel tube simultaneously and the combination gave higher ultimate loads. The numerical results validated well with the previous researchers too.

Comparison of hexahedral and tetrahedral elements in finite element analysis of the foot and footwear

Finite element analysis has been widely used in the field of foot and footwear biomechanics to determine plantar pressures as well as stresses and strains within soft tissue and footwear materials. When dealing with anatomical structures such as the foot, hexahedral mesh generation accounts for most of the model development time due to geometric complexities imposed by branching and embedded structures. Tetrahedral meshing, which can be more easily automated, has been the approach of choice to date in foot and footwear biomechanics. Here we use the nonlinear finite element program Abaqus (Simulia, Providence, RI) to examine the advantages and disadvantages of tetrahedral and hexahedral elements under compression and shear loading, material incompressibility, and frictional contact conditions, which are commonly seen in foot and footwear biomechanics. This study demonstrated that for a range of simulation conditions, hybrid hexahedral elements (Abaqus C3D8H) consistently performed well while hybrid linear tetrahedral elements (Abaqus C3D4H) performed poorly. On the other hand, enhanced quadratic tetrahedral elements with improved stress visualization (Abaqus C3D10I) performed as well as the hybrid hexahedral elements in terms of contact pressure and contact shear stress predictions. Although the enhanced quadratic tetrahedral element simulations were computationally expensive compared to hexahedral element simulations in both barefoot and footwear conditions, the enhanced quadratic tetrahedral element formulation seems to be very promising for foot and footwear applications as a result of decreased labor and expedited model development, all related to facilitated mesh generation.

Nonlinear analysis of short concrete-filled double skin tube columns subjected to axial compressive forces

Proper material constitutive models for concrete-filled double skin tube (CFDST) columns with circular cross-section and subjected to axial compressive forces are proposed and verified against experiment data using the nonlinear finite element program Abaqus. It is shown that CFDST columns can provide a good confining effect for concrete core, especially when the diameter-to-thickness ratios of both the outer and the inner tubes are small. In addition, empirical equations are proposed to predict the lateral confining pressure of the concrete core for CFDST columns. Finally, the axial strengths of the CFDST columns calculated by the proposed formulations are compared with AISC formulations against the experimental data. It has been shown that the proposed formulations are better than the AISC formulations.

Effects of Strain Rate on Reinforced Concrete Beam

The strain-rate effects of reinforced concrete beams are studied in this paper. Considering the strain-rate effects of structural material, dynamic responses of reinforced concrete beams subjected to monotonic loading and cyclic loading at different loading rates that might be experienced during earthquakes are simulated using the nonlinear finite element program ABAQUS. The influences of loading rate on loading capability and failure mode of reinforced concrete beams are investigated. The results show that as the loading rate increases, the loading capability increases, the increment is associated with the shear span ratio and loading mode. The increment at cyclic loading is smaller than that at monotonic loading; as the shear span ratio changes, the failure mode changes, the increment changes; the failure mode has nothing to do with the loading rate.

Numerical analyses of the force transfer in concrete-filled steel tube columns

The interaction between steel tube and concrete core is the key issue for understanding the behavior of concrete-filled steel tube columns (CFTs). This study investigates the force transfer by natural bond or by mechanical shear connectors and the interaction between the steel tube and the concrete core under three types of loading. Two and three-dimensional nonlinear finite element models are developed to study the force transfer between steel tube and concrete core. The nonlinear finite element program ABAQUS is used. Material and geometric nonlinearities of concrete and steel are considered in the analysis. The damage plasticity model provided by ABAQUS is used to simulate the concrete material behavior. Comparisons between the finite element analyses and own experimental results are made to verify the finite element models. A good agreement is observed between the numerical and experimental results. Parametric studies using the numerical models are performed to investigate the effects of diameterto-thickness ratio, uniaxial compressive strength of concrete, length of shear connectors, and the tensile strength of shear connectors.

Behaviour of headed stud shear connectors for composite steel–concrete beams at elevated temperatures

The behaviour of composite steel–concrete beams at elevated temperatures is an important problem. A three-dimensional push test model is developed herein with a two-dimensional temperature distribution field based on the finite element method (FEM) and which may be applied to steel–concrete composite beams. The motivation for this paper is to increase the awareness of the structural engineering community to the concepts behind composite steel–concrete structural design for fire exposure. The behaviour of reinforced concrete slabs under fire conditions strongly depends on the interaction of the slabs with the surrounding elements which include the structural steel beam, steel reinforcing and shear connectors. This study was carried out to consider the effects of elevated temperatures on the behaviour of composite steel–concrete beams for both solid and profiled steel sheeting slabs. This investigation considers the load–slip relationship and ultimate load behaviour for push tests with a three-dimensional non-linear finite element program ABAQUS. As a result of elevated temperatures, the material properties change with temperature. The studies were compared with experimental tests under both ambient and elevated temperatures. Furthermore, for the elevated temperature study, the models were loaded progressively up to the ultimate load to illustrate the capability of the structure to withstand load during a fire. It is concluded that finite element analysis showed that the shear connector strength under fire exposure was very sensitive. It is also shown that profiled steel sheeting slabs exhibit greater fire resistance when compared with that of a solid slab as a function of their ambient temperature strength.

Modeling the effect of corrosion on bond strength at the steel–concrete interface with finite-element analysis

This paper examines the basic influence of corrosion on bond strength at the steel–concrete interface and the associated slip and cracking. A nonlinear finite-element model is developed to account for the effect of corrosion on deterioration of the bond. Deterioration of the mechanical interaction between the corroding reinforcing steel and the concrete is modeled with the nonlinear finite-element program ABAQUS. The contact pressure normal to the steel–concrete interface is reduced when the concrete cracks, which occurs along with a decrease in the cross-sectional area of the steel bar and the decrease of the friction coefficient between the steel and the concrete. The loss of contact pressure and the decrease in the friction coefficient with the mass loss of steel bars are evaluated using pullout test specimens with different levels of rebar corrosion. Finally, the relationship between the loss of bond strength and the mass loss of the steel rebar is established. The model gives reasonably accurate predictions of bond strength for three independent experimental studies. Key words: bond, concrete, corrosion, mechanical interaction, reinforcing steels, slip, steel-concrete interface.

Finite element analysis of CFT columns subjected to an axial compressive force and bending moment in combination

Proper material constitutive models for concrete-filled tube (CFT) columns subjected to an axial compressive force and bending moment in combination are proposed and verified in this paper by using the nonlinear finite element program ABAQUS compared against experimental data. In the numerical analysis, the cross sections of the CFT columns are categorized into three groups, i.e., ones with circular sections, ones with square sections, and ones with square sections stiffened with reinforcing ties. It is shown that the steel tubes can provide a good confining effect on the concrete core when the axial compressive force is large. The confining effect of a square CFT stiffened by reinforcing ties is stronger than that of the same square CFT without stiffening ties but weaker than that of a circular CFT. Nevertheless, when the spacing of reinforcing ties is small, a CFT with a square section might possibly achieve the same confining effect as one with a circular section.

Nonlinear Analysis of Axially Loaded Concrete-Filled Tube Columns with Confinement Effect

Proper material constitutive models for concrete-filled tube (CFT) columns are proposed and verified by the nonlinear finite element program ABAQUS against experimental data. The cross sections of the CFT columns in the numerical analysis are categorized into three groups, i.e., circular section, square section, and square section stiffened by reinforcing ties. Via the numerical analyses, it is shown that for circular CFT columns, the tubes can provide a good confining effect to the concrete especially when the width-to-thickness ratio D/t is small (say D/t 30). The confining effect of square CFT columns with reinforcing ties is enhanced by the use of reinforcing ties especially when the tie spacing is small and the tie number (or tie diameter) is large.

Ductile details for welded unreinforced moment connections subject to inelastic cyclic loading

The results of a 3-D finite element study of welded unreinforced flange beam-to-column moment connections in steel special moment resisting frames are presented. Computer models of connection subassemblies were developed using the general-purpose nonlinear finite element program abaqus. Several issues were addressed in the study: (1) geometry and size of the weld access hole; (2) benefit of a welded beam web; (3) control of inelastic panel zone deformations; and (4) effectiveness of continuity plates in reducing local demand on the connection. The analytical results provided information related to basic performance and the effects that these connection parameters have on inelastic cyclic performance, thereby furthering the current understanding of welded moment connection behavior under seismic loading conditions and leading to improved design criteria. Based on the results of the analytical study, recommendations for the seismic design of connections are given. The incorporation of the recommendations into an experimental test program showed good connection ductility in the test specimens.

A parametric study of the post-buckling behaviour of steel plates

This paper investigates the sensitivity of the buckling and post-buckling behaviour of imperfect steel plates used in ship and related marine structures when subject to variations in their initial conditions. The different aspects analysed comprise of variation in aspect ratio, boundary conditions, initial out-of-plane imperfection and material elastic and plastic properties such as strain hardening. The analyses were carried out using the non-linear finite element program ABAQUS. The results obtained for the several plate models show that the three most relevant parameters affecting the buckling and post-buckling of uniaxially loaded plates are aspect ratio, unloaded edges boundary conditions and initial out-of-plane imperfection amplitude.

Nonlinear finite element simulation of thermoviscoplastic deformation of C4 solder joints in high density packaging under thermal cycling

A nonlinear finite element model has been used to simulate the thermally induced viscoplastic deformation of the controlled collapse chip connection (C4) solder joints in a high density single chip module (SCM). The dependence of solder joint deformation on the tin content was demonstrated for various lead-rich Pb-Sn alloys with the tin content varying from 2 wt% to 10 wt%. A thermoviscoplasticity theory was introduced for modeling inelastic stress-strain response of the Pb-Sn alloys. In the theory, the creep and plasticity were separately considered and formulated. The Garafalo hyperbolic sine law was used to model the creep behavior, while the Prandtl-Reuss equation was used for the rate independent plastic deformation. The modeled SCM consists of a 5 mm silicon chip attached to 50 mm alumina substrate by an array of C4 with diameter of O.1 mm on a 0.2 mm I/O pitch. A cyclic temperature load of 0 to 100/spl deg/C at frequency of 3 cycles per hour was applied to the SCM, and a nonlinear finite element program ABAQUS was used to numerically study the effect of the tin content on the stress-strain response of the C4. It is concluded that the decrease of the tin content induces a decrease of the equivalent creep strain and Mises stress, but an increase of the equivalent plastic strain for the edge C4 in the SCM. >

A Finite Element Study of Factors Affecting Fatigue Life of Solder Joints

The elastic-plastic-creep characteristics of solder joints are implemented in a nonlinear finite element program ABAQUS by developing user defined material subroutines. An eutectic Pb-Sn solder joint of a resistor carrier under thermal cycling between 125°C and −55°C is modeled, and the effect of various parameters on the solder joint cycle life is evaluated. The strain range of the solder joint under thermal cycling loads is calculated, which is then converted into solder joint cycle life through a fatigue-life relationship proposed by Engelmaier (1983). The parameters studied include: ramp time, hold time, grain size, initial temperature, constitutive equations, material properties for solder alloys, and mesh refinement. The effects of these variations on the fatigue life of solder joints are illustrated. The described method can serve as a tool in the design and manufacturing of surface-mount (SMT) assemblies.