Increase In Slenderness Ratio Research Articles

Numerical Study on the Lateral Load Response of Offshore Monopile Foundations in Clay: Effect of Slenderness Ratio

To meet growing energy demands, offshore wind turbines (OWTs) with higher energy outputs are being developed, presenting increased challenges for their foundation design. Over the past decade, extensive research on the design optimization of OWT support structures has significantly reduced the anticipated costs of offshore wind farm development. Various design methods have been developed and applied in practice, each with its own advantages and limitations. In this study, 3D finite element (FE) modeling, validated against the measured response of a large-scale test monopile, is used to investigate the lateral load response of monopiles with different geometries and slenderness ratios in smaall and large displacements. The results are compared to the standard p–y method, and specific behavioral and design aspects of large-diameter monopiles, such as the moment contribution ratio from different resisting components and the minimum embedment length criteria, are evaluated and discussed. The results showed that the maximum and minimum differences between the 3D FE modeling and one-dimensional (1D) DNV p–y method are 41% and 11% for large displacements, and 32.5% and 13.3% for small displacements, respectively. As the slenderness ratio increases, the discrepancy between the finite element (FE) modeling results and the 1D DNV p–y method decreases, with an average difference of about 13% across all monopile diameters at an L/D ratio of 10, in both small and large displacements, indicating the reasonable accuracy of the 1D method for slenderness ratios of 10 and above. Among the three minimum embedment length criteria examined, the DNV recommended and vertical-tangent criteria offered shorter embedment lengths. The primary resisting moment across all slenderness ratios comes from the distributed lateral load along the monopile shaft (MCRp−y), which increases as the L/D ratio increases.

Effect of slenderness ratio on axial compression behavior of circular wood columns strengthened with high-performance bamboo-based composites

Developing sustainable high-performance bamboo-based composites (HPBBC) with carbon sequestration benefits as reinforcement material is of great significance in promoting the application of HPBBC and securing ancient wooden buildings. Available column reinforcement methods have damage characteristics, which are unsuitable to be applied in ancient wooden columns because the ancient building needs to be preserved in the current conditions. The wooden column was bound with HPBBC and spaced steel strips to achieve damage-free strengthening. The slenderness ratio is an essential factor affecting the mechanical properties of wood poles, which is significant to be studied. The effect of the slenderness ratio on the axial compression behavior of circular wood columns strengthened with HPBBC was investigated in this study. The test results showed that the slenderness ratio significantly influences the failure mode, load-bearing capacity, and deformability of strengthened circular wood columns. The typical failure mode of short columns was a crushing failure, while the long columns were buckling failures. The load-carrying capacity and longitudinal strain of strengthened circular timber columns decrease significantly with increasing slenderness ratio. The lateral displacements or buckling appearance increases significantly with the increasing slenderness ratios of the strengthened timber column. A load-bearing capacity formula was proposed to predict the load capacity of strengthened circular wood columns based on their axial compression damage characteristics. The error between the calculated and tested results is less than 8.2 %.

Analysis of Elastic Buckling and Static Bending Properties of Smart Functionally Graded Porous Beam

Background: A Smart Functionally Graded (SFG) porous beam is a Functionally Graded (FG) Porous beam consisting of a piezo-electric layer integrated on the top layer. Aim: This research work addresses the lack of information by examining the bending as well as elastic buckling performance of SFG beams having two distinct Porosity Distributions (PDs). The main purpose of this research work is to study and analyze the bending deflections as well as CBLs of SFG beams with two different PDs, considering various boundary conditions, voltage levels (20V and 100V), and changes in slenderness ratio. Objective: The objectives of this work are as follows: to analyze the impact of variations in voltage levels and slenderness ratios on the critical buckling and bending properties of the SFG beam and to showcase the effect of variation in the slenderness ratio on the dimensionless normal stress through the thickness of the Hinge-Hinge beam. Method: The research work analyzes the elastic buckling as well as static bending of Smart Functionally Graded (SFG) porous beams, considering the equations derived from the Timoshenko beam theory. To simulate the results and analyze the various effects, the ANSYS software has been utilized in this paper. Results: This research work examines how the slenderness ratio impacts the maximum deflection, CBL, along with stress distribution. Experimental data demonstrates that as the slenderness ratio increases, CBL reduces, and maximum deflections in SFG porous beams increase. Also, it has been observed that normal stress distribution shifts from linear to non-linear and changes significantly. Further, the PDs significantly affect the static bending as well as the buckling performance of the beam. The symmetric distribution pattern provides superior buckling capability and enhanced bending resistance compared to the unsymmetric distribution pattern. Additionally, it has been found that as the voltage across the SFG increases, the buckling load increases and the deflection of the beam decreases. Conclusion: This research work has analyzed the effects of slenderness ratio and voltage level on the Critical Buckling Load (CBL) and bending properties of SFG porous beams, considering four different boundary conditions and a fixed set of parameters. The key findings of this paper are that as the slenderness ratio increases, the CBL decreases, and distribution shifts from linear to nonlinear region. Changes are significant, whereas maximum deflection increases. A significant effect is observed in the performance of static bending and buckling of SFG beams. It has been investigated that with an increase in voltage across the SFG beam, the buckling load increases, whereas the maximum deflection of the beam decreases.

Compressive bearing capacity of steel dual-angle with cruciform welding filler plates based on failure modes

The bearing capacity of steel dual-angle with cruciform welding filler plates (i.e., DACWP) under axial compression is the primary purpose of this paper. Six DACWP specimens were prepared with different width-thickness ratios (i.e., 15.63, 12.50, 10.42) and slenderness ratios (i.e., 45, 75). Axial compression tests were carried out to analyze the failure mode, load-displacement curve, and load-strain history of the specimens. Subsequently, a finite element model was established and calibrated by test results, providing further insights into the influence of the slenderness ratio and width-thickness ratio on the bearing capacity of DACWP. Finally, a calculation method of bearing capacity based on different failure modes was proposed. The results show that, with a constant width-thickness ratio, the DACWP transits from torsion failure to bending failure with the increase of slenderness ratio. Particularly, the transition slenderness ratio of failure is found to be proportional to the slenderness ratio and the width-thickness ratio. In the case of torsion instability, the slenderness ratio has little effect on the bearing capacity, while the width-thickness ratio exhibits an opposite effect. Specifically, the bearing capacity of DACWP decreases with the increase of slenderness ratio and width-thickness ratio. The calculation formula proposed in this paper can be used to calculate the bearing capacity of DACWP.

Eccentric compressive behavior of T-shaped welded multi-partition composite members

Six T-shaped welded multi-partition composite members were tested under eccentric compression loading by considering the influence of eccentricity and eccentric angle. The test results showed that no weld tearing occurred when the specimen was damaged, indicating that the two vertical welds could ensure the overall working performance of the specimen. The specimens exhibited the smallest bearing capacity when failing along the asymmetric axis, which was the most dangerous situation. The parametric analysis is conducted by a verified finite element model considering the influence of the slenderness ratio, section height-to-width ratio, section depth-to-width ratio, concrete and steel grade, steel ratio, and eccentric angle. If concrete contributes a larger proportion to the bearing capacity, the interaction curve of axial force and bending moment tends to protrude. Conversely, the interaction curve of axial force and bending moment gradually shrinks as the slenderness ratio increases. Based on this observation, a calculation method of T-shaped welded multi-partition composite members under eccentric compressive loading along the asymmetric axis is proposed by considering the effect of the slenderness ratio. Formulas for bearing capacity under biaxial eccentric compression are proposed based on the results of the parametric analysis.

Experimental investigation of the effect of slenderness ratio and retention time on the separation performance of a two-phase horizontal separator

This study investigates the effect of the slenderness ratio (L/D) on the performance of a three-phase separator for constant retention times in the oil phase. The research combines experimental measurements with statistical analysis. To determine the controlling parameters of separation efficiency. The experiments varied 4 independent variables: slenderness ratios (2:1, 4:1, and 5:1); total mass flow rates (2, 3, 4, 5, and 6 GPM); oil layer thickness (9 18 27 and 36 mm) and composition. In addition, the oil flow rate, as part of the total flow, was varied to allow the oil retention time to be held constant. Taguchi and full factorial statistical analysis methods were used to analyse the results. The performance was seen to increase with increasing slenderness ratio for constant retention time. This implies that the slenderness ratio has a positive effect on separation. However, this is not a simple relationship. The main independent variables that affect separation were identified as total flow and aspect ratio, but the interaction of flow rate and slenderness ratio can cancel each other out. The interaction of the oil layer and slenderness ratio is normally insignificant but becomes controlling when the aspect ratio and flow effect cancel each other out. The performance decreases as the oil layer thickness increases and the aspect ratio decreases. This indicates that separators with shorter and wider configurations are less efficient than those with longer and slimmer designs.

Axial-compression performance and numerical-simulation analysis of steel tube coal gangue concrete column

Coal gangue is a solid waste produced in the process of coal mining, excessive accumulation will occupy land and pollute the environment. It is one of the most effective means to realize comprehensive utilization of coal gangue by replacing some aggregates in concrete and applying it to engineering structures. In this paper, based on C30 concrete, by changing the replacement rate of coal gangue, slenderness ratio, and steel pipe wall thickness, 17 Coal gangue concrete-filled steel tubular (CGC-FST) columns were designed and made, and the axial compression tests were carried out. The results show that the failure mode of the CGC-FST column is similar to that of CFST, and the annular band shear buckling occurs on the wall of the steel pipe, and the higher the slenderness ratio, the more the number of buckling in the middle. With the increase of coal gangue substitution rate, the ultimate bearing capacity of the CGC-FST column decreases gradually, and the ductility of the specimen decreases slightly. The increase in slenderness ratio reduces the ultimate bearing capacity of the member, the failure form changes from material failure to stable failure, and the material properties are not fully utilized. The most obvious way to improve the bearing capacity and ductility of gangue steel tube members is to increase the steel content. Through the finite element simulation analysis of more working conditions of the CGC-FST column, the calculation formula of the bearing capacity of the CGC-FST column is fitted, which can effectively predict the bearing capacity of the CGC-FST column in a certain range.

Numerical Analysis of the Shape Effect on the Mechanical Behaviors of Rocks in True 3D Compression Test

Rock strength parameters are usually indispensable for rock engineering design. Under the experimental testing conditions, the shape effect could significantly affect the measured results. Previous findings from uniaxial tests reveal that the measured rock strength gradually decreases with the increase in the slenderness ratio, which is mainly ascribed to the end effect. However, it is still unclear how strong the influence of the end effect on the shape effect is in true 3D tests. In the present study, rock mechanical behaviors in response to the variation in slenderness ratio are detailly examined in true 3D tests. The calculated results show that rock strength progressively decreases as the slenderness ratio increases. But the rock strength in true 3D tests still deviates far from the actual even though the slenderness ratio goes beyond 2, which is mainly caused by the interface friction along the two extra σ2-normal specimen faces. It is interesting that the slenderness ratio increases lead to an increase in the measured stiffness as well. The calculated results suggest that symmetry in the experimentally defined typical arc-shaped curves σ1(σ2) at constant σ3 are neglected most likely due to the stronger end effects in true 3D tests, and the accurate rock strength parameters are not obtained only through using slender specimens.

Experimental and numerical investigation on axial behavior of circular and square slender reinforced columns

To investigate the axial performance of slender concrete-filled steel tube (CFST) columns reinforced by outer steel tube and sandwiched concrete jackets, an axial compression test was conducted on 20 circular and square slender reinforced columns. The study aimed to examine the influence of the cross-sectional shape, steel content of the outer tube, the strength of sandwiched concrete, and slenderness ratio on the failure mode, load-displacement curves, and ultimate load. A comparative test on six slender CFST columns was also conducted. The test results showed that the local buckling degree of the outer steel tube in square reinforced columns was greater than that in circular reinforced columns, while the overall bending deformation was smaller. The influence of the sandwiched concrete strength on the load-displacement curve was weaker compared to the influence of the outer tube thickness and slenderness ratio. As the slenderness ratio increased, both the longitudinal and lateral strains of the specimens tended to decrease. The difference in strain between the tension and compression sides was more pronounced in circular reinforced columns than in square reinforced columns. The average SI values of circular and square reinforced specimens were 1.05 and 1.00, respectively, but the gap in SI values between the two types of reinforced columns is reduced as the slenderness ratio increases. Then, a numerical model on the slender reinforced columns was established by the finite element software ABAQUS. A good agreement was obtained between test results and simulation results. The mechanical mechanism of typical slender reinforced columns was further analyzed, including longitudinal stress contour map of concrete, the development of longitudinal stress of steel tube, as well as distribution of transverse confinement stress. A formula was subsequently proposed based on a design code to predict the load-bearing capacity of the retrofitted columns, the prediction results agreed well with the experimental data.

Performance and evaluation theory of axial compression capacity for steel angle and tube members in wildfire

This paper deals with the performance of axial compression capacity for steel angle and tube members subjected to wildfire. An indirect thermo-mechanical coupling model of steel members, of which the accuracy was verified by the experimental results, was established to investigate the mechanical and wildfire resistance performance from different perspectives, such as bearing capacity, temperature distribution and critical temperature. Parametric analysis was conducted to further determine the key parameters including slenderness ratio, cross-sectional sizes and wildfire conditions that affect the change rule of axial compression capacity for steel angle and tube members. It reveals that the bearing capacity and critical temperature significantly decreased as the slenderness ratio increased, and the difference in wildfire resistance between steel angle and tube became enlarged with the increase of slenderness ratio. Comparatively, the critical temperature of steel angle was obviously lower than that of steel tube, since the additional bending deformation at mid-span induced by the non-uniform temperature distribution on cross-section was more evident for the angle member. Moreover, a calculation method for the ultimate capacity and critical temperature of steel members under wildfires was proposed, which turned out to be reliable to provide reference for wildfire resistance design of steel angle and tube members.

Failure behavior of steel dual-angle with cruciform welding filler plates under compression

This paper focuses on the failure behavior of steel dual-angle with cruciform welding filler plates (DA-CWP) under compression. A total of three DA-CWP specimens were fabricated and tested under axial compression, where different slenderness ratios (i.e., 45, 60, 75) were considered for comparison. The failure performance was experimentally investigated from different perspectives, such as failure mode, ultimate capacity and strain development. Subsequently, numerical simulation was performed to further reveal the effect of slenderness ratio and filler plate type on the failure behavior of DA-CWP. Finally, A theoretical method to distinguish the compressive failure mode of DA-CWP was proposed, and the bending-torsion transition slenderness ratio calculated by theoretical method was compared with the one from simulation for verification. The results demonstrate that the failure mode of DA-CWP changes from torsion to bending as the slenderness ratio increases, gradually decreasing its ultimate capacity. Due to the lower torsion stiffness of steel dual-angle with alternate plates (DA-AP), the torsion instability is more prone to occur for DA-AP, resulting in larger deformations of DA-AP compared to DA-CWP under identical compression. The theoretical method proposed in this study provides a good prediction for the bending-torsion transition slenderness ratio of DA-CWP under axial compression, which can provide reference for ultimate capacity design.

Analytical plasticity‐based model for soil–structure interaction of lumped system on heterogeneous soil media

AbstractIn the present study, an analytical approach is developed for the soil–structure interaction for the linear, eq. linear and elastic‐perfectly plastic layered soil strata. The amplification factor is calculated at the top of a lumped structure incorporating layered soil, foundation, and super‐structure deformation. The equation of motion of the system under the normalized earthquake excitation is solved using the direct integration method. MATLAB script is developed to carry out the parametric study, and nonlinear time history analysis is performed. The present methodology is compared with the finite element model (FEM), which shows good agreement. The computational time is much less than the FEM method. A parametric study is carried out in terms of soil heterogeneity, mass ratio, slenderness ratio, excitation frequency, and material model. The results indicate that due to the heterogeneity of the soil, the response of the structure is increased significantly; with the increase in the mass ratio, the amplification factor decreases with excitation frequency up to resonance, and the effect of mass ratio is negligible at the higher frequency range; with the increase in slenderness ratio, the amplification factor increases up to resonance, however, at higher frequency ranges there is no effect of slenderness ratio.

Experimental study on eccentric compressive behaviors of 6061-T6 aluminum tubular long columns filled with concrete

In this paper, eccentric compressive experiments of 12 circular and 6 square concrete-filled 6061-T6 aluminum tubular (CFAT) long columns were carried out. The influence of the section form, thickness of aluminum tube, slenderness ratio, and eccentricity on the flexural performance of CFAT long columns was investigated. The results showed that all the specimens exhibited flexural-dominated failure. The variation of eccentricity had little impact on the overall failure mode of the aluminum tube, while it dramatically influenced the failure mode of the internal concrete. The internal concrete failed in concrete crushing for all the square columns, while it remained intact for the circular columns. This indicates that circular tubes provide a better constraint effect on the internal concrete, there by increasing the ultimate strain of concrete under compression. It was also found that the increase of eccentricity leads to the weakening of the confinement afforded to the internal concrete, while the increase of slenderness ratio has no obvious effect on the restraining effect. Finally, the applicability of current design provisions for concrete-filled steel tubular (CFST) long columns to CFAT long columns was evaluated, and design suggestions were proposed.

Effect of Dynamic Wind Load on Tall Structure Using Gust Factor Method

With advancements in construction materials and design technologies, as well as the context of substantial urban growth, tall structures are increasing day by day, and the cost of land is also rising. Hence, constructing tall structures is the best way to expand vertically. In this study, shear force and bending moment multipliers were calculated using MATLAB for 155,040 data samples. The main objective of the paper was to investigate the effect of the gust factor on a 100m tall structure, while keeping the B/H ratio between 0.2 and 1.2 and the L/B ratio of the building varying from 0 to 50. The height of the structure was varied from 50m to 450m to analyze the shear force and bending moment multipliers. Furthermore, the study aimed to examine the effect of the fundamental frequency of the building structure on the gust factor and to prepare elastic spectra accordingly.
 As the slenderness ratio increases, the gust factor also increases. The gust factor for flexible structures was higher than that for stiff buildings. The elastic spectra revealed that with an increase in frequency, the gust factor decreases, and at a certain frequency value, it becomes constant. The current study utilized shear force and bending moment multipliers, as well as the elastic spectra of gust, to calculate shear force and bending moment. This method proved to be quicker than manual calculations. The shear force and bending moment obtained from the present study were compared to those from IS 875:2015, and the error was found to be smaller than 10%.

Influence of slenderness ratio on the lateral force of a slender body at high angle of attack

The slenderness ratio is an important feature of the slender body, but the effect of slenderness ratio on the lateral force of the slender body at high Angle of attack have not clearly. In this paper, the Detached eddy simulation (DES) method is verified and adopted to simulate the flow of five models with slenderness ratio SR=10, 12.5, 15, 17.5 and 20. The simulation is carried out under the conditions of 15.3m/s incoming flow and 55° Angle of attack. Based on the simulation results, the vorticity magnitude and surface pressure coefficient of the five models are compared. It is concluded that the increase of slenderness ratio will increase the fluctuation cycle of pressure along the axial direction. To further analysed the relationship between pressure distribution and lateral force in different models, the pressure values of multiple sections were extracted and integrated to draw the change curve of unit lateral force coefficient along the X direction. From the analysis of unit lateral force coefficient, the difference of pressure between the two sides induced by asymmetric vortex at the head is the main source of lateral force. The unit lateral force coefficient (Cfzpm ) of the model with small slenderness ratio oscillated more dramatically and attenuated more slowly than that of the model with large slenderness ratio, due to the interaction between the head vortex and the high-pressure region at the bottom of body with a small slenderness ratio at a large Angle of attack. The interaction between the head vortex and the bottom high-pressure region makes the lateral force coefficient of the model with small slenderness ratio not necessarily significantly smaller than that of the model with large slenderness ratio. With the increase of slenderness ratio, the influence of head vortex on the pressure distribution of rear surface decreases, and the asymmetry of rear surface pressure distribution decreases. The conclusion of this paper can help to solve the problem of lateral force coefficient variation that may occur in multistage rocket engineering.

Hysteresis performance of section steel reinforced concrete-filled rectangular stainless steel tubular columns

Due to high bearing capacity and excellent seismic performance, the section steel reinforced concrete-filled rectangular steel tube has been widely applied in engineering. The application of stainless steel for outer steel tube can improve the durability performance of members. In this study, ABAQUS software was used to perform nonlinear seismic analysis on section steel reinforced concrete-filled rectangular stainless steel tubular columns, and the numerical model was validated against experimental data. The mechanism and parametric study of the hysteresis performance were conducted. These parameters mainly include: concrete strength, strength of stainless steel, strength of section steel, steel ratio of stainless steel tube, steel ratio of section steel, axial compression ratio, and slenderness ratio. The analysis results showed that: increasing the strength of stainless steel tube and concrete can significantly improve the bearing capacity of members, but the strength of section steel has little effect; the bearing capacity decreases with the increasing slenderness ratio; when the axial compression ratio is smaller than 0.4, increasing axial compression can improve the bearing capacity. The strength of each material shows little influence on the shape of load–displacement skeleton; the axial compression ratio presents high effect on the shape of descending stage of curve, and the larger the axial compression ratio, the steeper the descending stage; the slenderness shows high influence on curve shape, and the larger the slenderness, the less the elastic stiffness, and the more gentle the descending stage of curve. Finally, a simplified load–displacement hysteretic model was proposed, which exhibits good agreement with finite element numerical analysis.

A Study on Effective Compressive and Shear Properties of Tetrahedral Lattice Materials

Tetrahedral lattice materials can be used as the core of a sandwich structure. The properties of tetrahedral lattice materials can be controlled by modifying their geometrical parameters and relative density. In this paper, a tetrahedral lattice structure deformation mechanism-based theoretical analysis model is established to predict the effective mechanical properties of the structure under compressive and shear loadings. The analytical solutions are subsequently verified by finite element analysis of a large-scale lattice material model. Based on the obtained results, the effects of the geometrical parameters, relative density, and shear deformation are discussed. At a specific relative density, as strut inclination angle increases: (1) the effective compressive modulus in the z-direction increases; (2) the effective compressive modulus in x- and y-directions, and the effective shear modulus in xy-, xz-, and yz-directions firstly increases but then decreases; (3) the effective Poisson’s ratios [Formula: see text] and [Formula: see text] increase, whereas, [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] decrease. With an increase in relative density, the effective compressive and shearing modulus increase, the effective Poisson’s ratios remain constant, [Formula: see text] and [Formula: see text] are always equal to 0 when the strut inclination angle is [Formula: see text]. The effect of shear deformation on the effective mechanical properties increases as the slenderness ratio increases. The predicted effective properties enable the tetrahedral lattice unit cells to be treated as “material” in the design and analysis process.

Experimental study and analysis of the bond-anchorage properties of laminated flattened-bamboo lumber connections with glued-in steel rod

To improve the utilization rate of raw bamboo and reduce the amount of adhesive, this paper studied a new type of laminated bamboo lumber, that is, laminated flattened bamboo lumber. The monotonic pull-out tests were carried out on 56 specimens with glued-in steel rods of three different diameters (12 mm, 16 mm, and 20 mm, respectively; the thickness of the adhesive layer was 3 mm) of laminated flattened bamboo lumber, and the effect of anchorage length and diameter of the steel bar on the mechanical properties of bond anchorage were studied. In addition, the specimens with a diameter of 12 mm and an anchorage length of 100 mm were selected to study the effect of different thicknesses of the adhesive layer (between 2 mm and 4 mm) on the mechanical properties of bonded anchorage. The results showed that the failure modes could be divided into three types. For the specimens with the same anchorage length, the larger the diameter of the glued-in steel bar was, the larger the ultimate pullout load would be; when the diameter of the steel bar was the same, the ultimate pullout load of the specimens increased with the increase of the anchorage length. When the diameter of the glued-in steel bar was 12 mm, the average bond strength decreased with the increase in slenderness ratio. When the diameter of the glued-in steel bar was 16 mm and 20 mm, the average bond strength first increased and then decreased with the increase of the slenderness ratio, and the turning slenderness ratio points were 8.75 and 5, respectively. The ANOVA analysis with parameters revealed that the rebar’s diameter and length significantly impacted the bond-anchorage characteristics of the glued-in rod connection in laminated flattened bamboo lumber.

Compressive performance of an innovative tall pier with composite box section

To improve the seismic performance of tall-pier bridges, an innovative tall pier with a composite box section, composed of four-limb concrete-filled steel tube (CFST) columns and low-yield-strength (LYS) steel plates, was proposed based on the principle of capacity design and the replaceable fuse concept. Both axial and eccentric compression tests were conducted on a series of specimens to study the compressive performance of the composite tall pier. Parametric analysis was performed to investigate the effects of load eccentricity, slenderness ratio, thickness, and yield strength of the LYS steel plates on the compressive capacity using validated finite element (FE) models. The main results indicate that the composite tall pier fails with global bending deformation and elastoplastic instability under axial or eccentric compression. The compressive capacity and initial stiffness of the composite tall pier decrease significantly with an increase in eccentricity or slenderness ratio, and the influences of eccentricity and slenderness ratio are essentially independent. Additionally, the increase in the thickness of the steel plates enhanced the flexural stiffness and compressive capacity, and reduced the uneven loading distribution for the pier. Under axial compression, the pier can be simplified as a CFST lattice column connected by steel beams and LYS steel plates. Finally, practical formulas for the compressive capacity are proposed considering the connection and restraint effects of the LYS steel plates on the CFST columns, which can be used to predict the compressive capacity of the novel composite tall pier.

Ultimate bearing capacity of UHPC-encased CFST medium-long columns under axial compression

To study the effect of slenderness ratio on the ultimate bearing capacity of UHPC (ultra-high performance concrete)-encased concrete-filled steel tubular (UC-CFST) columns, a total of nine specimens under axial compression were tested. A finite element model, considering the effects of material nonlinearity and interaction between concrete and steel tube, was developed. A full-range analysis was carried out on the typical load–deformation response of the UC-CFST medium-long columns. The experimental and numerical analysis results showed that with the increase in slenderness ratio, the deformation capacity of the UC-CFST columns increased, the ultimate bearing capacity decreased, and the failure mode changed from exceedance of compressive strength to loss of stability. The internal forces and stress distributions at the mid-height section of the columns at different stages were also investigated. Finally, the applicability of various methods for calculating the ultimate bearing capacity of ordinary concrete-encased CFST (OC-CFST) columns to UC-CFST columns was discussed, including the methods recommended by Chinese standard T/CECS 188-2019, European standard Eurocode 4, Australian/New Zealand joint standard AS/NZS 5100.6 : 2017 and American standard ANSI/AISC 360-16. It was found that the method recommended in AS/NZS 5100.6 : 2017 was suitable for calculating the ultimate bearing capacity of UC-CFST medium-long columns.