Increase In Slenderness Ratio Research Articles

Nonlinear Analysis of Hollow Slender Reinforced Concrete Columns Subjected to Concentric and Eccentric Loads

Abstract This paper investigates the load capacity and failure modes of slender hollow RC column under axial and eccentric loads. For the slender hollow columns, different load eccentricities and hole shapes are used. The finite element software ABAQUS is used to model and analyze the columns. The experimental test result is used to conduct a verification investigation of the nonlinear finite element modeling. All specifications of the experimentally tested columns are taken into consideration in the modeling to establish the verification of the model. When the modeling and test results are compared, it is noticeable that they are in good agreement. As a result, the modeling’s accuracy is proved. Then, a parametric study included different slenderness ratio, section shape, concrete strength and SFR strengthened has been done with the same modeling method. The effects of these variables on the column load capacity are investigated. It is found that increasing slenderness ratio led to smaller peak load. Increasing of moment of inertia of square and circular section decreased the peak load capacity. The maximum bearing capacity increased with higher concrete strength. Also, SFR distribution through the length of columns effected on load bearing capacity.

Mechanical performances of high‐strength concrete‐filled steel tubular medium–long columns with square cross section

AbstractIn order to investigate the influence of concrete strength, slenderness ratio, and eccentricity on the ultimate bearing capacity, initial stiffness, and other mechanical properties of square high‐strength steel tubular medium–long column, a total of 11 square column specimens were designed and made. The compression tests were carried out, and the load–longitudinal deformation curve, load–deflection curve, longitudinal strain distribution curve of mid‐span section, and several failure modes of the composite column were obtained. Numerical simulations were conducted, and the results are in good agreement with the experimental results. It is found that the concrete strength has little effect on the initial stiffness of the square high‐strength concrete‐filled steel tubular medium–long column, and the ultimate bearing capacity and initial stiffness decrease with the increase of slenderness ratio and eccentricity, and the eccentricity has a particularly significant influence on the bearing capacity.

Airbag loading test and numerical simulation on out-of-plane mechanical behavior of a cast-in-situ composite wall with MTPC

Although infilled walls are designed to serve as nonstructural components in frame buildings, their out-of-plane (OP) collapse during earthquake events may trigger additional damage to other structural components and inflict heavy casualties. Taking advantages of the metal tailing porous concrete (MTPC) and light-gauge steel studs, a new cast-in-situ composite wall with MTPC (CCWM) can be developed and regarded as a potential substitute for traditional masonry infilled walls. This paper experimentally investigates the OP mechanical behavior of a full-scaled CCWM via airbag loading test. A CCWM specimen with dimension of 2.4 m × 1.2 m × 0.2 m is fabricated by pouring MTPC into the cavity formed by panels and light-gauge steel stud system. The specimen is placed vertically in an elaborate loading system composed of steel frame, reaction brace, horizontal beams and a polyethylene airbag. Under the uniform OP force provided by the slowly inflated airbag, the failure pattern, load-displacement curves and strains of light gauge steel studs of the CCWM are observed and recorded during the test. Moreover, the finite element model of the specimen is developed in ABAQUS platform and the effects of slenderness ratio and aspect ratio on the OP mechanical behavior of the CCWM are numerically investigated. The results indicate that the specimen cracked vertically along the central line of the upper half part of the wall, and the connections between the support plates and vertical lattice studs are vulnerable locations for the CCWM. Owing to the special constitution of the CCWM, the arching action is short-term, and the crack strength can be adopted as the OP bearing capacity of the CCWM since it is quite close to the ultimate strength. Moreover, numerical results reveal that the OP strength and stiffness of the CCWM decrease when the slenderness ratio increases, but enhance with increasing aspect ratio.

Wind-structure interaction analysis of empty cylindrical silos for various slenderness ratio

Wind is the flow of air within the earth’s atmosphere, which affects any structure greatly. Studies on the effect of wind loading on shell structures is an important field of structural research. Many shell structures, such as, chimneys, silos, tanks etc. are an integral part of the advancement of the industry and agriculture. Such shell structures are vulnerable against aerodynamic excitation and can be subjected to structural failure due to vortex-induced vibration, ovalling, buckling, rupture, over-turning etc. The present study focuses on the static fluid–structure interaction analysis to assess the wind pressure and wind-induced deformation of cylindrical silo shells. Cylindrical silos are a type of shell structure for storing granular materials, such as grains, wheat, cement, coal, fly-ash etc. Cylindrical silos very much susceptible to radial deformation and buckling failure under wind loading in empty state. In the present study the authors have conducted the wind-structure interaction studies on intermediate to tall (slenderness ratio range: 1.5 to 4.0) cylindrical silo shells for terrain category 2, as per IS-875: part 3, 2015. The silos are flat topped with uniform thickness and fixed at the base, free at the top. The logarithmic law is used to simulate wind velocity profile. The circumferential mean wind pressure coefficient distribution for each silo, is calculated and compared with Indian standard. This study is conducted for smooth flow with very low turbulence intensity for simplicity. This study exhibits that, with the increase in slenderness ratio from 1.5 to 4.0, the magnitude of negative pressure coefficients decreases, however no significant increase can be seen for positive pressure coefficients. The sway of the silos increases with the increment in slenderness ratio. The radial deformation is dominant in the intermediate portion and the nature of deformation is typical for each silo. Based on the nature of radial deformation the critical locations can be identified, which need to be strengthened to resist wind-induced deformation. It is also seen that the presence of flat roof provides significant strengthening at the top of the silos against wind-induced radial deformation.

Construction of Uniaxial Interaction Diagram for Slender Reinforced Concrete Column Based on Nonlinear Finite Element Analysis

Slender reinforced concrete column may fail in material failure or instability failure. Instability failure is a common problem which cannot be analyzed with first-order analysis. So, second-order analysis is required to analyze instability failure of slender RC column. The main objective of this study was to construct uniaxial interaction diagram for slender reinforced concrete column based on nonlinear finite element analysis (FEA) software. The key parameters which were studied in this study were eccentricity, slenderness ratio, steel ratio, and shape of the column. Concrete damage plasticity (CDP) was utilized in modeling the concrete. Material nonlinearity, geometric nonlinearity, effect of cracking, and tension stiffening effect were included in the modeling. The results reveal that, as slenderness ratio increases, the balanced moment also increases, but the corresponding axial load was decreased. However, increasing the amount of steel reinforcement to the column increases the stability of the column and reduces the effect of slenderness ratio. Also, the capacity of square slender RC column is larger than rectangular slender RC column with equivalent cross section. However, the result is close to each other as slenderness ratio increased. Finally, validation was conducted by taking a benchmark experiment, and it shows that FEA result agrees with the experimental by 85.581%.

Buckling Knockdown Factors of Composite Cylinders under Both Compression and Internal Pressure

The internal pressure of a thin-walled cylindrical structure under axial compression may improve the buckling stability by relieving loads and reducing initial imperfections. In this study, the effect of internal pressure on the buckling knockdown factor is investigated for axially compressed thin-walled composite cylinders with different shell thickness ratios and slenderness ratios. Various shell thickness ratios and slenderness ratios are considered when the buckling knockdown factor is derived for the thin-walled composite cylinders under both axial compression and internal pressure. Nonlinear post-buckling analyses are conducted using the nonlinear finite element analysis program, ABAQUS. The single perturbation load approach is used to represent the geometric initial imperfection of thin-walled composite cylinders. For cases with the axial compressive force only, the buckling knockdown factor decreases as the shell thickness ratio increases or as the slenderness ratio increases. When the internal pressure is considered simultaneously with the axial compressive force, the buckling knockdown factor decreases as the slenderness ratio increases but increases as the shell thickness ratio increases. The buckling knockdown factors considering the internal pressure and axial compressions are higher by 2.67% to 38.98% compared with the knockdown factors considering the axial compressive force only. The results show the significant effect of the internal pressure, particularly for thinner composite cylinders, and that the buckling knockdown factors may be enhanced for all the shell thickness ratios and slenderness ratios considered in this study when the internal pressure is applied to the cylinder.

Examining mechanical behavior of steel-bamboo composite I-section column under long-term loading

The steel-bamboo composite structure is a novel composite structure, which is characterized by light weight and high bearing capacity of structural components, as well as excellent seismic performance and good thermal performance of fabricated buildings. To facilitate its engineering application and better understanding the deformation law of composite column during design reference period, mechanical properties of steel-bamboo composite column under long-term loads are investigated in this paper. 27 composite I-section columns were designed and fabricated, among which 18 specimens were first investigated in static loading test with steel ratio and slenderness ratio as main parameters, failure modes and effect of each parameter on the axial compression performance was observed and analyzed. Then, a self-balanced loading device was designed to perform long-term loading test on 6 specimens with loading level and steel ratio as main parameters, and the other 3 specimens were adopted to monitor the temperature effect on creep. The creep process of specimens was observed and the nonlinear fitting analysis of creep data was carried out using Burger model. Once the predetermined long-term loading duration was reached, the secondary static loading test were carried out to study the influencing factors of bearing capacity and deformation, as well as their variation laws. Further, calculation formula of yield bearing capacity was derived by analyzing yield conditions of composite column, as two calculation methods of ultimate bearing capacity were proposed based on superposition principle and limit equilibrium theory. Results show that the composite columns have good integrity, high deformation capacity and bearing capacity, which improves significantly with the increase of steel ratio and decreases with the increase of slenderness ratio. Creep deformation become basically stable after 90 days of loading, which can be accurately described by Burger model. After the long-term loading, ductility and ultimate strain of the specimens were obviously increased, while the bearing capacity was not significantly affected. The average error between the theoretical and experimental results of yield and ultimate bearing capacity is smaller than 7%, which indicates that the established calculation methods have high accuracy and are suitable for predicting the bearing capacity of steel-bamboo composite I-section columns. It is proved that scientifically designed steel-bamboo composite columns have reliable bearing capacities and controllable deformations, and can be safely applied to practical projects.

High-Strength Reinforcing Steel Bars: Low Cycle Fatigue Behavior Using RGB Methodology

Low cycle fatigue life of high-strength reinforcing steel bars (ASTM A706 Grade 80), using photogrammetry by RGB methodology is evaluated. Fatigue tests are performed on specimens under constant axial displacement with total strain amplitudes ranging from 0.01 to 0.05. The experimental observations indicate that buckling of high-strength reinforcing bars results in a damaging degradation of their fatigue life performance as the slenderness ratio increases, including an early rebar failure as the total strain amplitude increases since it achieves the plastic range faster. In addition to this, the results show that the ratio of the ultimate tensile strength to yield strength satisfies the minimum of 1.25 specified in ASTM A706 for reinforcement. On the other hand, the RGB methodology indicates that the axial strains measured by photogrammetry provide more accurate data since the registered results by the traditional experimental setup do not detect second-order effects, such as slippage or lengthening of the specimens within the clamps. Moreover, the RGB filter is faster than digital image correlation (DIC) because the RGB methodology requires a fewer computational cost than DIC algorithms. The RGB methodology allows to reduce the total strain amplitude up to 45% compared to the results obtained by the traditional setup. Finally, models relating total strain amplitude with half-cycles to failure and total strain amplitude with total energy dissipated for multiple slenderness ratios (L/d of 5, 10, and 15) are obtained.

Experimental evaluation of lime column as a ground improvement method in soft soils

Lime column (LC) is an effective method for ground improvement which causes reduction in settlement and enhancement in bearing capacity of soft soils, subsequently resulting in economical foundations. This study investigates the effects of LC on soft soil with the help of laboratory tests. Firstly, basic laboratory tests are performed on natural soil followed by load deformation tests on untreated and LC treated soils. LC effects on natural soil are studied by changing various parameters like shear strength of soil (54 kPa, 32 kPa, 14 kPa), slenderness ratio (4, 5.5, and 7) and spacing to diameter ratio (2, 3). Experimental results show that LC significantly increases load carrying capacity and stiffness for soils having higher shear strength. For soil samples of 54 kPa and 32 kPa, the load carrying capacity increases by 48 and 21% respectively whereas 75% increase in average stiffness (β = 1.75) is observed. However, LC are found to be ineffective at very low shear strength of 14 kPa. In case of group LC, increasing column spacing from 2 to 3D (D: diameter of LC) significantly decreases load carrying capacity of treated soil. It is also observed that increase in LC slenderness ratio causes a decrease in ultimate load carrying capacity.

The Behavior of Piles Installed in Medium Dense Sand Within MSE Wall System

Mechanically Stabilized Earth Walls (MSE) were widely used in several essential infrastructures, such as the abutments on a bridge. The need for a support base of a shallow or a deep bridge increased in the MSE wall system. In this research, factors affecting the performance of laterally loaded piles embedded in medium dense sand with a relative density of 50% behind an MSE wall were studied using lower-scale models in the laboratory. For instance, the effect of pile offset and the slenderness ratio on the pile's lateral capacity and pressure on the MSE wall. Three different slenderness ratios were introduced (i.e. L/D of 19.3, 21.7, and 24.1). The results showed a significant increase in pile lateral capacity occurring with the increase in pile offset or slenderness ratio (i.e., L/D). While increasing the pile offset reduced, the pressure on the wall so that the wall's effect will be insignificant when the pile offset reaches a value of 6D.

The Effects of Inlet Flow Rates and Slenderness Ratio on the Separation Performance of a Horizontal Three-Phase Separator

Summary In the first part of this work, the development of a capital cost optimization model for sizing three-phase separators was described. The developed model uses generalized reduced gradient nonlinear algorithms to determine the minimum cost associated with the construction of horizontal separators subject to four sets of constraints. In the second part, an experimental test rig was designed and used to investigate the effect of gas flow rate, liquid flow rate, and slenderness ratio (L/D) on the separation performance of horizontal three-phase separators. The results indicated an inverse relationship between an increase in gas and liquid flow rate and the separator outlet quality. It also indicated a direct relationship between an increase in slenderness ratio and separator outlet quality. The results also showed that the gradient change of the percentage of water in the oil outlet with respect to slenderness ratio decreased to ratios of 6:1. Hence, the separation rate increased. At ratios greater than 6:1, the separation still increases, but the gradient change in separation drops off, implying that the benefit in terms of separation is diminishing beyond this point. Therefore, the optimal slenderness ratio for technical reasons is 6:1.

Effect of geometry on the compression characteristics of bonded brickwork

Bonded brickwork walls of large thickness constructed with double or triple bricks are common in loadbearing historical masonry structures in many regions which require interventions and compression capacity evaluation. However, current design provisions for compression capacity prediction are primarily based on single brick prisms and wallette specimens. Due to anisotropic nature of masonry, the strength and deformation characteristics of bonded brickwork with double and triple brick thicknesses are different to the single leaf brickwork; and their design using the provisions of single leaf bonded brickwork specimens may be un-conservative. To expand the knowledge on the compressive behaviour of bonded brickwork, a detailed numerical investigation has been reported in this paper. A simplified Finite element (FE) based micro-modelling technique was implemented to simulate the compression response of bonded brickwork specimens. The developed FE modelling technique was initially verified against the experimental predictions of compressive capacities and axial stress-strain curves. The numerical modelling results iterated that there was no noticeable increase in the compressive capacity of the masonry with increase in the brickwork thicknesses due to increased number of weak head joints. The validated models were then employed to study the effect of slenderness of the bonded brickwork specimens on the axial compression response. The height to thickness (slenderness) ratios of the bonded brickwork were varied from 1.4 to 10.9 for analysing 30 different cases with two brick strengths. Results showed that with increasing slenderness ratio, the compressive strength of the bonded brickwork reduces for all bonded thicknesses. The parametric study indicates that the slenderness ratio influences the compression characteristics of bonded brickwork specimens; subsequently, correction factors for the compressive strengths determined with different slenderness ratios of brickwork specimens are proposed.

Simulation of Turbulent Flow with High Reynolds Number over an Elliptical Cylinder

A complex turbulent flow with high Reynolds number (Re= 5 × 105, 1 × 106, 2 × 106 and 3.6 × 106) over an elliptical cylinder, is investigated using 2D URANS equations with a standard k-ε turbulence model. The present study compares the effect of various upstream velocity profiles on the variations in flow characteristics along the surface of an elliptical cylinder having variable axis ratios. The comparison of results with the published data for a circular cylinder in cross flow shows the importance of axis ratio and other velocity profiles to reduce the drag force and variation in pressure distribution. Drag force over an elliptical cylinder is found to be lower than that of a circular cylinder. The drag force is seen to increase with increasing slenderness ratio. The drag coefficient of an elliptical cylinder with an axis ratio 0.6 is found to reduce by half as compared to that of a circular cylinder. The influence of slenderness ratio and velocity profile over back pressure recovery, flow separation and shear stress distribution is observed for an elliptical cylinder.

Experimental and numerical analyses on aluminium alloy H-section members under eccentric cyclic loading

This paper considered the combination of cyclic load and eccentric load to study the hysteretic performance of H-section 6061-T6 aluminium alloy members For this reason, this study designs and conducts the eccentric cyclic loading test of three H-section 6061-T6 aluminium alloy members with different slenderness ratios based on a reliable test system. The failure form, failure process, and bearing capacity of each member are analysed. The results show that for eccentrically loaded members, no overall buckling is observed during loading. Moreover, the members along the longitudinal direction do not fully develop plasticity, whereby such plasticity in the full sections is avoided. Plastic local buckling controls the failure mechanism of all specimens, leading to degradation in the stiffness of the specimens and generation of subsequent cracks at the local buckling sites of the webs, which in turn leads to fracture failure. Simultaneously, on the basis of the Chaboche hybrid strengthening model, the member model was established using the ABAQUS finite element (FE) software. Furthermore, the material parameters were calibrated using material test data and fitted the cyclic constitutive relationship of aluminium alloy. The effectiveness of the FE simulation method and the rationality of the constitutive model was accurately verified by experimental results. Additionally, the parameter analysis of eighteen members with different cross-sections, slenderness ratios, and eccentricities was carried out. It is shown that the increase of slenderness ratio and eccentricity result in weakening of the energy consumption capacity and bearing capacity obviously, which thereby provides a reference for the seismic design of aluminium alloy structures.

Equivalent Viscous Damping of Cross-Laminated Timber Structural Archetypes

This paper attempts to formulate an expression for the estimation of equivalent viscous damping (EVD) for cross-laminated timber (CLT) structural archetypes as a function of ductility. The paper aims at contributing toward the direct displacement-based design procedure (DDBD) of CLT structures, which makes use of equivalent viscous damping and secant stiffness estimations as proxies for the estimation of the nonlinear behavior of structures. The available hysteretic models of CLT structures are very elaborate, and the inelastic time-domain simulations using hysteretic models are not easily manageable. Hence, the adoption of equivalent viscous damping is a crucial feature of any DDBD method. In this paper, the authors estimate the EVD of a set of 16 typologies of CLT buildings with an increasing slenderness ratio. The minimum of the squared error between the maximum drift of the elastic time-history and the hysteretic response gives the EVD. The extended energy-dependent generalized Bouc Wen (EEGBW) model, calibrated on experimental data, is used to predict the inelastic seismic response of the single CLT shear wall. The correlation between EVD and ductility is compared to existing EVD formulations referring to concrete and steel structures.

Optimization of slender reinforced concrete columns subjected to biaxial bending using genetic algorithms

abstract: In this paper, a computational tool was developed to optimize the design of slender reinforced concrete columns subjected to biaxial bending considering the material and geometric nonlinearities rigorously. The optimization process utilizes the technique of genetic algorithms to find the best cross-sectional dimension and the best distribution and amount of reinforcement, to minimize the cost of the column subject to certain constraints of strength, stability, feasibility and regulatory. The analysis applies to rectangular cross-section of columns, and constant and symmetrical distribution of reinforcement. The results obtained by the developed software converge properly to an optimal solution or to a solution around the optimum in a significantly shorter time interval in relation to the results obtained when considering all solutions within the previously established domain. The effect of slenderness on the optimal design of reinforced concrete columns was also analyzed. The results showed that the column cost increases as the slenderness ratio increases, and steel becomes the predominant material to establish the equilibrium of the structural element.

Structural fire safety design of square and rectangular tubed-reinforced-concrete columns

The tubed-reinforced-concrete (TRC) columns have gained increasing use in the high-rise buildings and large-span stadiums in China, whereas the structural fire design method for square and rectangular TRC columns is still missing. Finite element analysis of the fire performance of square and rectangular TRC columns was conducted using a sequentially-coupled thermo-stress model. This model yielded good predictions against the experimental results of square TRC columns. Fire tests on two rectangular TRC columns were also conducted and presented in this paper, to further calibrate the model. Parametric studies were then conducted, through which it was found that the fire resistance of square and rectangular TRC columns decreases with the increase of load ratio or slenderness ratio and increases as the sectional dimension enlarges. Sectional aspect ratio has a minor influence on the fire resistance of rectangular TRC columns. A practical design method was proposed, for the first time, to determine the fire resistance of square and rectangular TRC columns with or without fire protection. The buckling reduction coefficient could be determined by the EC3 buckling curve (c) or the JGJ/T471 buckling curve. The heat transfer equations given in the Japanese AIJ recommendation were modified to determine the temperatures of the steel tube and rebars and equations were proposed to determine the equivalent temperatures of the concrete core.

Mechanical Behavior and Energy Evolution of Sandstone considering Slenderness Ratio Effect

To study the influence of slenderness ratio effect on the mechanical behavior, acoustic emission properties, and energy evolution of sandstone, the uniaxial compression tests coupled with acoustic emission technology are carried out at different slenderness ratios D (0.5, 1.0, 1.5, 2.0, 3.0). The results show that a logarithmic function relationship is observed between the peak strength, the peak strain, and the elastic modulus with slenderness ratio. The failure patterns of the tested sandstone varied significantly with the increasing slenderness ratio. When the slenderness ratio, D, is lower than 1.5, complex failures and multiple shear planes are formed, while simple failures and single shear planes are generated at D larger than 1.5. Besides, the AE ringing counts are more obvious with a higher slenderness ratio, D, at the initial compression stage due to the greater body volume and more defects in the sandstone. The energy evolution curves and energy ratio distribution curves can be divided into four stages, corresponding to the stress-strain curves.

Behavior of three-chord concrete-filled steel tube built-up columns subjected to eccentric compression

An experimental investigation of a series of three-chord concrete-filled steel tube (CFST) built-up columns was conducted under eccentric compression. The influences of slenderness ratio, eccentricity ratio, eccentricity direction, and brace pattern (battened or laced) on the load bearing process, failure modes, and ultimate load-carrying capacities of the specimens were analyzed. The test results indicate that a CFST built-up column exhibits better performance than a corresponding plain steel built-up column. The ultimate strengths and stiffnesses of the three-chord CFST built-up specimens decreased with increasing slenderness ratio or eccentricity ratio. Battened specimens exhibited lower load-carrying capacities than laced specimens, and different load-bearing capacities were obtained for specimens under different directions of compression eccentricity. Using the proposed equivalent slenderness ratio, three existing design codes were evaluated to predict the stability coefficient, and a new correlation equation considering two failure modes is suggested for calculating the ultimate strength of three-chord CFST built-up columns subject to combined compression and flexure.

Presentation of Critical Buckling Load Correction Factor of AISC Code on L-Shaped Composite Columns by Numerical and Experimental Analysis

Concrete-filled steel tubular (CFT) columns have been widely used as structural members in buildings and bridges in recent years, because of their properties, such as high strength and stiffness, good ductility, and convenience for construction. In CFT columns, the bearing capacity of columns is inversely related to buckling, therefore, buckling is of particular importance at these sections, the AISC Code uses effective bending rigidity (EIeffective) to calculate the critical buckling load in concrete filled steel columns, to apply the effect of reducing concrete confinement, the AISC code provides a maximum value of 0.9 of the reduced concrete confinement coefficient for the equation. Effective bending rigidity (EIeffective), this relationship is provided in AISC code for circular and square sections, therefore, the effect of the column shape geometry on the core concrete confinement is very influential and changes the effective bending rigidity (EIeffective) of the section. The AISC code does not provide a coefficient to consider the type of cross-sectional geometry in CFT columns, therefore, in this study, three groups experimental, numerical (FEM) and theoretical were used to provide critical buckling load correction, finally, it was concluded that the critical buckling load for the cross-section (L) shape due to the lower confinement of the concrete core is 20.07% lower than the AISC code equation, also with a 67% increase in slenderness ratio, the critical buckling load decreased by 14.52%.