Slenderness Ratio Research Articles

Assessing the impact of inertial load on the buckling behavior of piles with large slenderness ratios in liquefiable deposits

Pile foundations used in liquefiable deposits often have large slenderness ratios, and these piles are particularly vulnerable to earthquake-induced soil liquefaction and occur buckling instability under axial load alone as soils around the pile liquefy. However, insight into the precise impact of inertial load on the buckling behavior of piles in liquefiable deposits is still lacking, and the current methods used to calculate the critical buckling load of the pile in liquefiable ground usually ignore inertial load. In light of the above, two shaking table tests were carried out to clarify the impact of inertial load on the buckling behavior of piles partly embedded in saturated sands. Moreover, a novel calculation method considering inertial load was presented to accurately estimate the critical buckling load of the pile in liquefiable deposits. The feasibility of the presented method had been verified using the results from a centrifuge experiment and an analytical method along with a finite element method. Furthermore, parametric analysis was conducted to study the effect of soil type, peak ground acceleration (PGA), pile diameter, and unsupported length ratio on the critical buckling load of the pile in liquefiable soils. Finally, comparing the calculated results of critical buckling load between the method presented in this paper and the method in the design code confirmed the limitation of the current design code. These combined analyses demonstrate that the critical buckling load of the pile decreases due to the action of inertial load, resulting in the pile being more susceptible to buckling failure. Therefore, designers have to consider the impact of inertial load during the seismic design of pile foundations in liquefiable soils.

Beam-column behavior and design equations for high-strength composite filled tube (CFT) members: Investigating the interaction between section and member slenderness ratio

This paper investigates the influence of the section and member slenderness ratio on the axial-moment interaction behavior for high-strength concrete-filled tube (CFT) members. An extensive parametric study is conducted with the aim of extending the material strength limitations in the AISC 360-22 for composite members and investigating the reduction of strength as the member slenderness increases. A 2D fiber-based model using OpenSees software was developed and calibrated based on experimental studies to conduct an extensive parametric study, which includes; (1) member (global) slenderness; (2) section slenderness; (3) section's aspect ratio; (4) material strength; (5) level of axial loading. The study demonstrates that the unconservative error in the current design equations can be as high as 25 % for high member slenderness, while the conservatism in the high section slenderness can be more than 200 %. The proposed interaction curve and the design equations demonstrate high accuracy in predicting the maximum strength of the CFT members under combined loading conditions for a wide range of parameters, including the conventional strength CFT members. A fundamental insight into behavior is presented along with the results. This paper discusses the potential simplification of these findings into design equations that can be used in everyday practice.

Follow effect of low cost glass fibre reinforced polymer (GFRP) on the performance of concentrically loaded concrete column

(FRP) plays a major role in the strengthening of existing structures due to the age of the structure or natural calamities like earthquakes, floods, cyclones, etc. For reducing the size of structural members, the FRP wrapping assists to achieve the performance of the structure. Concrete is widely used due to its advantages and FRP is added to improve its quality in terms of strength. A study has been conducted on 21 cylinders based on their slenderness ratio. The slenderness ratios in the columns were 8, 16, and 24. At thicknesses of 5 mm and 7 mm, two types of wrap materials (UDCGFRP) and (WRGFRP)] were employed. Up to the point of failure, the columns were subjected to monotonic axial compressive force. The column’s yield loads, and ultimate load, were deduced from the load-deflection curves. The overall, uni-directional cloth provided the most effective confinement and led to a highly desirable failure mechanism, which was a gradual process.

Elliptical Orbit Design Based on Air-Breathing Electric Propulsion Technology in Very-Low Earth Orbit Space

Very-low Earth orbit (VLEO) space below 200 km is essential for high-quality communications and near-Earth space environment detection. Due to the significant atmospheric drag, orbital maintenance is required for spacecraft staying here. Based on air-breathing electric propulsion (ABEP) technology, this paper analyzed the orbital boundary conditions of the spacecraft under the constraints of parameters including slenderness ratio, thrust-to-power ratio, drag coefficient, and effective specific impulse. The energy balance is the key constraint for low VLEO orbits, which is determined by the drag coefficient, slenderness ratio, and thrust-to-power ratio. Under the existing technical conditions, the lowest circular orbit (along the terminator) is about 170 km. An elliptical orbital flight scheme is also analyzed to reach a 150 km perigee. A half-period control method was proposed based on the on–off control method for the elliptical orbit, which could enable the spacecraft to maintain a stable 150–250 km elliptical orbit.

Out of-plane failure analysis of masonry walls subjected to hydrostatic and hydrodynamic loads induced by flash floods

Damage surveys from past flash flood events show that the combined hydrodynamic impulsive loading and the subsequent hydrostatic loading due to rising water levels caused the failure of masonry walls/buildings. However, limited studies have been conducted to understand the responses of masonry walls to these loading states. To bridge this knowledge gap, an explicit 3D shell element based finite element modelling method that incorporates a homogenised anisotropic masonry material model was developed and applied to analyse the out-of-plane collapse behaviour of masonry walls under flash flooding conditions. The developed modelling method was validated with an available experimental study of masonry wall subjected to hydrostatic loading conditions. It was then extended to comprehend the behaviour of masonry walls under hydrodynamic impulsive water pressures. Results reveal that the effect of hydrodynamic impulsive loading generated by the first hit of the flash flood water is significant in reducing the stiffness of the masonry. This reduction in stiffness can result in an early collapse of the wall, even with a gradual rise of hydrostatic water level. This study has also evaluated the behaviour and damage patterns of masonry walls with two different slenderness ratios (single brick/24.5 and double brick/11.7) under flash flooding and prescribed the maximum percentage of surface area of inundation that the walls can resist. The importance of considering hydrodynamic impulsive loading in designing masonry buildings vulnerable to flash flooding and the capability of the modelling technique developed in this research for evaluating their vulnerability under these flooding scenarios are highlighted.

Embodied Energy Optimization of Prestressed Concrete Road Flyovers by a Two-Phase Kriging Surrogate Model.

This study aims to establish a methodology for optimizing embodied energy while constructing lightened road flyovers. A cross-sectional analysis is conducted to determine design parameters through an exhaustive literature review. Based on this analysis, key design variables that can enhance the energy efficiency of the slab are identified. The methodology is divided into two phases: a statistical technique known as Latin Hypercube Sampling is initially employed to sample deck variables and create a response surface; subsequently, the response surface is fine-tuned through a Kriging-based optimization model. Consequently, a methodology has been developed that reduces the energy cost of constructing lightened slab bridge decks. Recommendations to improve energy efficiency include employing high slenderness ratios (approximately 1/28), minimizing concrete and active reinforcement usage, and increasing the amount of passive reinforcement.

Behaviour of axially-restrained slender steel tubes exposed to fire

The behaviour of axially-restrained slender steel tubes exposed to fire was studied. Fire tests and corresponding finite element (FE) simulations were conducted on four specimens with varying slenderness ratios and axial restraint stiffness. The accuracy of FE simulation was validated against the test results. Both the test and numerical results showed that the axially-restrained slender steel tubes buckled at much lower temperatures than steel columns. Continuous temperature elevation was then required to complete their buckling, because the steel maintains considerable stiffness at the buckling temperature. Parametric analysis was conducted based on FE simulations to investigate the effect of the slenderness ratio, axial restraint stiffness, and peak temperature on the behaviour of axially-restrained slender steel tubes exposed to fire. Empirical equations were established for the buckling temperature and post-fire residual lateral displacement using response surface methodology. These equations demonstrated a strong ability to fit the experimental data and predict the responses for new scenarios.

An improved analytical model of a thick defective phononic crystal for bending wave excitation

This research aims to advance the existing analytical model, which was based on the Euler–Bernoulli beam theory, for predicting the velocity amplitude of bending waves excited while amplified by defective phononic crystals (PnCs) with piezoelectric elements. The previous analytical model falls short for thick defective PnCs and is limited to low frequencies. Hence, the Timoshenko beam theory is newly incorporated to address these issues, considering shear deformations and rotational inertia. Its performance is validated against a finite element model. It confirms that the proposed analytical model outperforms its predecessor, which was suitable for thin defective PnCs with a slenderness ratio above 10 and frequencies around 2 kHz. Remarkably, the improved analytical model demonstrates excellent predictive capabilities up to 40 kHz for thick defective PnCs with a slenderness ratio of around 2.5. With a relative error of less than 1% compared to the finite element model, this advanced approach also demonstrates time-efficient and stable computational performance. This work introduces three contributions. First, it pioneers the proposal of an electromechanically coupled analytical model for predicting the performance of defect-mode-enabled bending wave excitation. Second, this enhanced analytical model surpasses existing counterparts in terms of both accuracy and computational stability, particularly for thick defective PnCs, even at high frequencies. Last, the analytical model dramatically reduces the computation time.

Axial compressive behavior of cold-formed steel built-up box-shape columns with longitudinal stiffeners

This paper presents a study on the behavior of cold-formed steel built-up box-shape columns with longitudinal stiffeners (CFS-BCL) under axial compression. The specimens are fabricated using a pair of channel sections and lipped channel sections with longitudinal stiffeners, which are expected to enhance the local buckling resistance of the web. Sixteen specimens were prepared for compression tests, with varying lengths and screw arrangements. Prior to the tests, initial geometric imperfections of the specimens, material properties, and shearing-resistance behavior of the screw fasteners were measured. The results indicate that screw arrangements have a significant effect on simply supported specimens; reducing the screw spacing from 300 mm to 100 mm can increase load-bearing capacity by up to 11%. Finite element models were developed using ABAQUS and validated against test results. The parametric analysis revealed that screw arrangements had minimal impact on the local buckling capacity of specimens, with an increase in capacity of <8%. However, global buckling behavior was significantly affected by screw arrangements, resulting in an increase in capacity of up to 20% for slender columns. The test and analytical results were compared with the Direct Strength Method (DSM), and indicate that the DSM is conservative when the non-dimensional slenderness ratio λg and λl is higher than 1.2 and 1.4, respectively. The coefficients of the DSM were modified based on the test and simulation results, and its predictive accuracy was found to be highly increased.

Analysis of the Effect of Slenderness Ratio on Nominal Moment in T Section

T-section is similar to the single-symmetry plane. Mostly used in railway engineering, temporary work stands and machinery equipment. In the AISC1999 specification, due to the unfamiliarity with the T-section. Therefore, a conservative definition of a tee fracture is a noncompact section. With the evolution of the times, there are more and more researches on T-section. The T-section is defined as the flange slenderness and the web slenderness. The calculation formula of the nominal moment (Mn) is mainly limited by the slenderness ratio. In recent years, the AISC2017 has added limiting laterally unbraced length for the limit state of yielding (Lp) and limiting laterally unbraced length for the limit state of inelastic lateral-torsional buckling (Lr) to the calculation formula of the nominal flexural strength (Mn) of the T-section. The nominal flexural strength (Mn) shall be the lowest value obtained according to the limit states of yielding moment (Mp), lateral-torsional buckling (LTB). Therefore, this study will analyze and compare the changes in the AISC2017 with the previous norm. Largest laterally unbraced length along either flange at the point of load has 3% difference between AISC2017 and other specifications in plastic moment.

Axial compression stability of corroded circular steel tubes in simulated seawater environments

To investigate the influence of seawater corrosion damage on the axial compression stability of circular steel tubes, this study proposes a novel method (hereinafter referred to as the ‘thickness equivalent method’) for calculating the equivalent wall thickness based on the yield load determined through material property tests. To this end, a formula for calculating the equivalent regularised slenderness ratio of corroded circular steel tubes is derived. Subsequently, corrosion, material property and axial compression tests are conducted using circular steel tubes with different sectional dimensions, and numerical models are developed. The numerically obtained load–lateral displacement and load–strain curves are in good agreement with the test curves, validating the accuracy of the numerical models. Finally, a parameter study is conducted using the validated numerical models. To facilitate the examination of corroded circular steel tubes, a novel formula, representing a continuous function of the regularised slenderness ratio as opposed to the previous piecewise function, for computing the stability coefficient is derived. The test results demonstrate that the proposed method accurately predicts the ultimate axial compression bearing capacity of corroded circular steel tubes. Furthermore, based on the theoretical derivation, the relationship between the axial compression ultimate bearing capacity and the corrosion ratio for ϕ48 × 3 and ϕ57 × 3.5 steel tubes, considering various equivalent regularised slenderness ratios, is established.

Axial compression behavior of steel reinforced concrete columns after chloride-induced corrosion

Corroded steel reinforced concrete (CSRC) structures in coastal environments face a serious durability issue. This paper investigated the axial compressive performance of CSRC columns experimentally. Twelve CSRC columns with different corrosion ratios and slenderness ratios were designed and subjected to electrochemical corrosion tests and axially loaded tests to reveal their failure mode and performance deterioration laws. The test results revealed that the ultimate bearing capacity and stiffness of CSRC specimens decreased significantly, while the ductility index decreased slightly, with increasing corrosion ratio and slenderness ratio. Furthermore, comparisons were made between the experimental results of the ultimate bearing capacity of CSRC columns and the calculated results from three different design methods (Eurocode 4, JGJ 138–2016, and ANSI/AISC 360–22). A modified design formula was derived theoretically for the ultimate bearing capacity of CSRC columns, based on Eurocode 4, considering the cracking and confinement effects after corrosion. Finally, a new finite element modeling method for simulating CSRC columns was proposed, and different finite element models considering different effects were compared to further verify the rationality and necessity of considering both effects simultaneously in the modified bearing capacity calculation formula.

Numerical Study on Retrofitting of Hot Rolled Steel Beams with Cold-formed Steel Encased Channels-Design Concept using Machine Learning Method

The paper presents a numerical investigation on the retrofitting of Hot-Rolled Steel (HRS) beams using Cold-Formed Steel (CFS) encasing channels. The open cross-section HRS channel is transformed into a closed cross-section by encasing the CFS channel. This transformation increases the torsional rigidity of the structural member and helps in reducing the vulnerability of Lateral-Torsional Buckling (LTB). Parametric studies were carried out using numerical analysis. The existing experimental results were used for validation of the numerical model. A total of 600 numerical simulations including design parameters such as thickness of the CFS channel, intermediate spacing between the spot welds (connecting HRS and CFS channels), slenderness ratio, and the cross-sectional dimensions of the HRS beam were considered. The analyses indicated that the effectiveness of the retrofitting increases with an increase in the slenderness ratio of the HRS channel. Machine Learning (ML) method called Symbolic Regression (SR) was used to formulate an equation predicting the increment in the moment capacity as a function of parameters investigated. Finally, a simple design concept is suggested to determine the required CFS channel thickness and intermediate spot weld spacing to achieve the required increment in the moment capacity after retrofitting.

Design recommendation of cold-formed steel built-up sections under concentric and eccentric compression

A parametric investigation and design proposal for the back-to-back built-up cold-formed steel (CFS) channel sections with V-stiffeners and Σ-stiffeners under concentric and eccentric loading are presented in this paper. A nonlinear finite element model considering the initial geometric imperfection was developed and validated against experimental results. A total of 594 simulations were conducted involving a variety of slenderness ratios, eccentric axis directions, eccentricity, screw spacing and number of longitudinal holes. Simulation results including the load-carrying capacity, failure modes, ultimate bearing capacity versus eccentricity relationships, and load versus lateral displacement relationships were discussed. The influence of several member parameters on the load-carrying capacity and buckling modes was analyzed. Additionally, the applicability of the design strengths calculated from Chinese standard GB50018–2002 and North American specifications AISI S100–16 was evaluated based on the preliminary experimental results and simulation results. It was shown that both methods are conservative. Finally, a proposed DSM-based interaction equation considering the relationship between P/Pnd and M/Mnd was proposed and evaluated.

Appraisal of masonry infill walls dynamic characteristics: An analytical study

Due to the infill masonry high vulnerability observed in recent earthquakes, the knowledge concerning the infills' out-of-plane seismic behaviour has been the focus of several research works in the last years. The in-plane/out-of-plane interaction, boundary conditions, openings, slenderness, and aspect ratio have been reported as the main parameters that affect the out-of-plane infill wall capacity. However, the study of the impact of those parameters on the wall modal properties still needs further investigation. This research aims to perform a numerical study where a detailed numerical strategy is assumed to simulate the infilled reinforced concrete frames. The numerical model is calibrated using results from modal identification tests (wall with and without openings). A parametric study is carried out to assess the effect of wall geometry, slenderness, openings ratio, openings position and boundary conditions on the walls' out-of-plane frequencies. Eventually, analytical formulations were proposed to quantify the dynamic characteristics of the infill wall based on their geometric and mechanical characteristics.

Overall flexural-shear buckling strength design of built-up radially battened columns

The built-up radially battened columns (RBCs) have a promising prospect in public building engineering due to their aesthetical form and good load-bearing capacity. However, their design methods are not covered in the current design specifications because of their distinctive appearance. This paper aims to present the flexural-shear buckling behavior of built-up RBCs and propose its corresponding strength design recommendations. At first, the finite element model (FEM) of the RBC is established, and a lot of examples are calculated in eigenvalue buckling analysis and elastoplastic analysis by using this FEM. Three kinds of possible first-order buckling modes are observed in the elastic buckling analysis, which are flexural-shear buckling, torsional buckling, and local buckling respectively. Only flexural-shear buckling is involved in this study, and torsional buckling will be investigated in a companion paper. Local buckling (of the chord tube wall) can be prevented by a radius-to-thickness ratio limit. It has been proven that shear deformation plays an essential role in determining the flexural-shear buckling of built-up members, thereby a unit shear angle model is established to study the shear stiffness of RBCs when they buckle overall. Then, the prediction equations for elastic flexural-shear buckling load and its corresponding normalized slenderness ratio are derived. The design curves for the ultimate load-bearing capacity of built-up RBCs are also proposed based on the numerous results from elastoplastic FEMs by changing normalized slenderness ratios. Furthermore, the compound buckling of RBCs is considered by employing a FEM that exerted the individual chord initial imperfection (FEM-c), and accordingly, a strength reduction factor caused by compound buckling is proposed. Finally, the design methods for the individual chords and radial-shaped battens are studied. The internal forces in chords and batten plates are derived and the analysis of the local buckling of batten plates is conducted. It is recommended that chords should be regarded as a member under combined compression and bending, and batten plates can be guaranteed to not lose their stability before the RBC reaches their ultimate load-bearing capacity by adopting the ‘isostable criterion’. In conclusion, these results provide a method for accurately and conservatively predicting the strength of RBCs when overall flexural or compound buckling occurs, which will expand the application of RBCs in engineering and make our public buildings more pleasing.

Performance evaluation of steel hollow box piers under bidirectional lateral cyclic loading to enhance the existing seismic verification framework

This study comprehensively evaluates the lateral performance and behaviour of stiffened steel hollow box piers under axial and lateral cyclic bidirectional loading using Finite Element (FE) analysis to develop a reliable performance-based seismic verification framework. In the first phase of the analysis, various bidirectional lateral loading patterns are examined to identify the pier's worst inelastic behaviour regarding strength, ductility, energy absorption, and failure patterns. Among these loading patterns, it was found that the circular-shaped bidirectional lateral cyclic loading (BICI) yielded the worst inelastic behaviour of the pier. Then, in phase two, an extensive comparative parametric study was conducted between the BICI and unidirectional loading pattern to evaluate the significance of important design parameters on lateral performance. Results revealed that the width-to-thickness ratio Rf, slenderness ratio λ¯ and axial load P showed significant influence under both the load patterns, whereas the modified stiffener's slenderness ratio λs′, and aspect ratio α showed more significant influence only under the BICI load pattern. Subsequently, the existing formulae proposed by authors for predicting strength and ductility under unidirectional lateral loading were reviewed and modified to incorporate the bidirectional effect. Moreover, a novel set of formulae was proposed for the BICI load pattern. Finally, an enhanced performance-based seismic verification method was developed by examining the relationship between the ductility factors of steel hollow piers under both BICI and unidirectional loading patterns. This method integrates the bidirectional effect into the existing unidirectional framework, enabling a comprehensive assessment of the piers' performance and enhancing seismic resilience.

Effect of Load Eccentricity on CRC Structures with Different Slenderness Ratios Subjected to Axial Compression

The use of nonmetallic reinforcement in concrete aims at the decrease in material consumption by reducing the component sizes when compared to conventional reinforced concrete structures, which inherently results in very filigree structures. Although intensive basic research has been carried out on textile-reinforced concrete for about 30 years, the subject of stability behavior has hardly been investigated so far. This study focuses the fundamental understanding of the structural behavior of slender carbon-reinforced concrete (CRC) structures subjected to axial compression. Therefore, buckling experiments have been carried out in order to quantify the influence of two parameters: the slenderness ratio of the specimens (varying between 60 and 130) and the load eccentricity (0, 2, and 4 mm). The results of the specimens that were tested with the initial load eccentricities revealed a good overall agreement with those obtained by a second-order theory approach throughout all of the investigated slenderness ratios. For the centrally pressed samples that featured high slenderness ratios, the failure stresses could successfully be predicted with Euler’s buckling formula, whereas this theory overestimated the results of the specimens with intermediate to low slenderness ratios due to the plastic buckling phenomenon. The presented study emphasizes that the consideration of the stability problem is inevitable when designing material-efficient structures made of textile-reinforced concrete.

THE MECHANICAL PERFORMANCE OF PARALLEL TDG BAMBOO LAMINATED COLUMNS (TDGLC)

A research study conducted in Thailand aimed at developing and adding value to agricultural products, specifically focusing on bamboo. The agricultural sector in Thailand plays a significant role in the economy and society, employing a large portion of the population and generating income equal to approximately 9% of the countrys GDP. The government aims to enhance the competitiveness of Thai agricultural products and increase their value for the benefit of local communities.The research focuses on utilizing bamboo for construction projects, particularly in the form of Thai Dendrocalamus Giganteus bamboo (TDG) laminated columns (TDGLC). The study involves a production process to create man-made TDGLC and investigates the mechanical properties of these columns. The research examines the performance of parallel bamboo laminated columns under axial compression tests.Specimens of TDG bamboo, aged between 3 and 4 years, were cut into strips and clamped together to form columns of various lengths and cross-sections. The cross-section sizes ranged from 100 mm to 203 mm, with lengths of 1 meter, 2 meters, and 3 meters. The compression load and classification of long and short columns were analyzed based on the proportioning of length and cross-section.The research identified specific column types that exhibited either strength failure (short columns) or buckling failure (long columns). However, two column types, C603 and C402, showed mixed results, with both strength and buckling failures. Although their slenderness ratios exceeded 60, the primary mode of failure indicated that these specimens should be classified as short columns.It was observed that defects in the specimens influenced their load capacity, with higher slenderness ratios resulting in greater lateral deflection corresponding to the peak load. The equation used to calculate the load capacities aligned well with the test results. Overall, the study contributes to the understanding of TDGLC performance in construction applications and provides insights into the mechanical behavior of bamboo columns under axial compression.

Design method of axial compression stability for cross-section corrugated plate steel special-shaped column

Obtaining a larger moment of inertia and overall stability with smaller material input, which is an effective way to improve the bearing capacity and reduce the self-weight of structural columns. This paper proposes a cross-section corrugated plate steel special-shaped column (CCSC), which is based on the optimization design idea of steel profiled-shaped column section, combined with the comprehensive consideration of the overall stability of steel structure column members, material use efficiency and building interior space utilization rate. The new CCSC is composed of three parts: core square steel pipe, corrugated plate, and flange plate. The high-out-of-plane stiffness characteristic of corrugated plate is utilized to improve the section rotation radius. The three parts above are coordinated to resist lateral load. The square steel pipe and flange plate are the main vertical bearing plates. The new special-shaped column can obtain a larger moment of inertia and overall stability with a smaller material input, thus improving the bearing capacity. Through the combination of theoretical analysis and numerical simulation, the overall stability of the axial compression of CCSC are analyzed, and the instability modes and failure modes of CCSC are revealed. The design method and suggestions for the stability of CCSC under axial compression are put forward. Then, the overall stability design and application suggestion based on conventional square steel tube is given. The results show that the stability design method of CCSC under axial compression can effectively judge the instability mode of CCSC and obtain the ultimate bearing capacity of the whole member. Compared with square steel tube columns with regularized slenderness ratio greater than 0.8 in structural design, the CCSC has obvious advantages in overall stability and steel consumption.