Compressed Columns Research Articles

Investigations Into the Stability of Thin-Walled Composite Structures with Top-Hat Cross-Sections

Abstract This paper presents a study of compressed thin-walled composite columns with an open cross-section. The tested specimens with a top-hat cross-section were made of CFRP material. Two arrangements of composite layers [0/-45/45/90]s and [90/0/90/0]s were compared. The paper focuses on the buckling phenomenon and the determination of the critical loads of the structure. It includes both numerical analyses using the finite element method (FEM) and validation on real specimens made using the autoclave technique. A comparison is made between the results obtained by both methods. The critical forces of the real specimens were determined using the P-wc3 approximation method. Both the evaluation of the buckling shape and the values of the critical forces showed a significant correlation between the experimental and numerical tests. This paper also compares the tested lay-ups.

Prediction of the mechanical performance of compressed circular CFST columns with circumferential debonding gap

Concrete-filled steel tubular (CFST) structures have been widely used in high-rise buildings and long-span bridges for the high strength and ductility due to the confinement effect of the concrete core provided by the steel tube. This beneficial composite action could be damaged by circumferential debonding gap (CDG), which is nearly unavoidable in real CFST structures. Reliable formulations to predict the influence of CDG on the mechanical performance of compressed circular CFST columns are needed. In this paper, the experimental parameters and results of compressed circular CFST columns with CDG are summarized to discuss the deficiencies of the parameters chosen in the tests. Detailed finite element simulation procedures for compressed circular CFST columns with CDG, based on ABAQUS, are then introduced, verifying their accuracy by test results. Based on the validated finite element models, a database of compressed circular CFST columns with and without CDG, including strength, ductility and stiffness of specimens is established; it is obtained by covering suitable parameter ranges for CDG and CFST structures, in accordance with real applications. Successively, new formulations able to predict the ultimate load capacity, the reduction factor, the ductility and the stiffness of specimens are derived by the Evolutionary Polynomial Regression (EPR) methodology, demonstrating good accuracy and low complexity.

Experimental realization of a soft topological acoustic switch

Acoustic topological insulators have revolutionized our understanding of acoustic wave propagation, providing a robust way to manipulate acoustic waves. Acoustic switches offer new possibilities for logical operations, and the topological insulators further enrich the robustness of their signal execution process. To date, most studies in this field are focused on designing a static acoustic structure. However, the experimental realization of a dynamic topological phononic logic to switch acoustic waves is still a great challenge. Here, we experimentally demonstrate a topological acoustic switch based on compressible rubber columns, where the topological propagation route can be dynamically switched by external pressure. Our simulation and experiment results show that when the acoustic system is compressed, the trivial band gap can be efficiently switched to the nontrivial band gap, resulting in dynamic modulation of acoustic communication with high transmission efficiencies. Our study provides a guide to design a soft topological acoustic switch, which exhibits enormous application potential in acoustic signal sensing and topological transistors.

Axial compression of seawater sea sand concrete columns reinforced with hybrid FRP–stainless steel bars

Using fibre-reinforced polymer (FRP) bars instead of steel bars to reinforce concrete columns in harsh environments has become important for solving corrosion problems. The brittleness of FRP bars significantly reduces the column ductility. It has been proposed that columns can be reinforced with hybrid FRP and steel bars to improve ductility, but related research is very limited. In this research, the axial compression behaviour of seawater sea sand concrete (SSC) columns reinforced with hybrid FRP bars and stainless steel (SS) bars was studied. In total, 84 SSC columns were designed, including 15 SS reinforced SSC (SS-SSC) columns, 15 glass-FRP (GFRP) reinforced SSC (GFRP-SSC) columns, 45 hybrid FRP–SS reinforced SSC (FRP–SS-SSC) columns and nine plain SSC columns. The failure modes, load–axial displacement curves, bearing capacity and ductility were analysed, considering the effects of the reinforcement types, reinforcement ratios and concrete strength. The results show that ductility could be significantly improved by hybrid reinforcements; the ductility indexes of the FRP–SS-SSC columns were close to those of the SS-SSC columns. The proposed equation could accurately predict the bearing capacity of SSC columns. Furthermore, a theoretical stress–strain relationship for the studied axial compression SSC columns is proposed.

Research on the Seismic Performance of Prefabricated Bridge Piers Using UHPC Grout under an Eccentric Load

At present, research on prefabricated piers is limited to the axial compression state. However, many piers are under small eccentric compression in practical engineering. In this article, the seismic performance of ultrahigh performance concrete (UHPC)-grouted corrugated pipe-connected piers under small eccentric compression was studied. A pseudostatic test was carried out by using a prefabricated pier column model connected with UHPC-grouted corrugated pipes. The failure mechanism of the plastic hinge area of the column base was studied, and the failure mode, energy dissipation capacity, displacement ductility, and ultimate bearing capacity were compared with those of an ordinary axially compressed pier column structure. The result shows that compared to the conventional cast-in-place(CIP) pier, the overall energy dissipation capacity and the ductility factor of assembled pier with UHPC-grouted corrugated pipe-connection were decreased approximately by 5.0% and by 10%, respectively. The pinching phenomenon of the hysteresis curve of the precast pier was more obvious. When the assembled piers were under small eccentric compression, the overall energy dissipation capacity was close to that of conventional CIP piers and the ductility factor was improved by 20%. Comparison of two precast piers using the same UHPC grout connections shows that the stiffness degradation process of precast pier under small eccentric compression was similar to that under axial compression. But the ductility coefficient of precast pier under small eccentric compression increased by about 20%. The small eccentric compression caused different damage degrees in the plastic hinge zone at the bottom of the precast column. The ultimate load in the same direction as the additional bending moment was 55% lower than that of the opposite direction.

Eccentric compression behavior of Steel-FRP composite bars RC columns under coupling action of chloride corrosion and load

In order to investigate the eccentric compression behaviors of steel-FRP composite bar (SFCB) reinforced concrete (RC) columns subjected to chloride corrosion, the mechanical experiments of chloride corroded SFCBs and SFCBs RC eccentric compression columns were conducted. The effect of reinforcement type and ratio, eccentricity, slenderness, stress level and corrosion duration on bearing capacity, deformation, crack and failure pattern were investigated. The results showed that the strength retention ratio of reinforcement decreases with the increase of corrosion duration, the ultimate strengths of steel rebar, SFCB and FRP rebar decreased by 12.2%, 9.9% and 3.6%, respectively, when compared with those of uncorroded counterparts. With the increase of steel content of reinforcement, the load bearing capacity of eccentric compression RC column increases while the deformation decreases gradually. The load bearing capacity of corroded steel, SFCB and FRP RC columns maximally decreased by 16.6%, 12.4% and 7.2%, respectively, when compared with those of uncorroded counterparts. Based on the simplified materials constitutive relations and reasonable basic assumptions, formulae for discriminate failure mode, moment magnification factor and bearing capacity were developed. The predicted failure pattern, moment magnification factor and bearing capacity are in good agreement with the test results, confirming the validity of the proposed formulae, the results can be used as a reference for engineering application.

Asymmetric Cantilever Construction Control of a U-Shaped Box Concrete Continuous Bridge in Complex Environment

The bridge of Shanghai Metro Line 10 over Metro Line 6 is a U-shaped concrete single-box double-cell concrete box beam continuous bridge. A novel method is applied to construct the asymmetric cantilever prefabricated and assembled continuous bridge due to the limited construction space and the complex environment. Four mechanical state control methods are applied during the T-shape structure construction process: tensioning pre-stressed steel strand, jacking by the axial force servo system, adjusting the leg reaction force, and setting the auxiliary leg. Auxiliary measures such as the compressive column, side-span counterweight, and temporary pre-stressing are also taken into consideration. The finite element method simulations are performed to measure effects of the four control methods during the construction process. The front leg force of the bridge erection machine and the deflection of the bridge are then monitored. It was deduced that the simulated and measured values of the cantilever T-shape structure are controlled within the limit range during the construction process.

Hindered thermal warping triggers tensile cracking in the cores of compressed columns of a fire-loaded tunnel segment structure: Efficiency and accuracy of beam theory prediction, compared to FEM

The nonlinear Finite Element Method (FEM) is the current gold standard for the thermo-mechanical analysis of reinforced concrete structures. As an alternative, this paper is devoted to a model reduction strategy which reduces the CPU time by a factor of 500. This strategy combines Fourier series-based solutions for the thermal conduction problem, and thermo-elastic Timoshenko beam theory. Temperature histories known to be relevant for fire accidents enter series solutions quantifying the conduction of heat into a closed cell frame consisting of slabs, walls, and columns. Corresponding temperature profiles are translated into thermal eigenstrains. The latter are represented as the sum of three portions: (i) their cross-sectional averages (called thermal eigenstretches); (ii) their cross-sectional moments (called thermal eigencurvatures); and (iii) the remaining eigenstrain distributions (called eigenwarping). The latter portion is hindered at the cross-sectional scale, giving rise to non-linearly distributed self-equilibrated thermal stresses. The eigenstretches and eigencurvatures, in turn, are constrained at the scale of the frame structure. Together with external mechanical loads, they enter the exact solutions of thermo-elastic Timoshenko beam theory with equivalent cross-sections accounting for the different material properties of concrete and steel. Axial normal stresses, quantified from beam-theory-related normal forces and bending moments, are superimposed with the hindered-warping-induced stresses. These stresses agree well with corresponding results obtained by the nonlinear FEM. As regards the load carrying behavior of the columns, excessive thermal tensile strains at the periphery of the columns trigger, in the core of the columns, large tensile stresses which even exceed the strength of concrete. Respective cracking events are considered through reduced effective columnar cross-sections. Right after initiation of cracking, around 12min after the start of the heating process, the cracks propagate for some 30sec quite rapidly, and very much slower thereafter. If the initial cross-sections of the columns are increased, more pronounced hindered thermal warping, together with less quickly evolving compressive forces, results in earlier cracking. Overall, it is concluded that tensile cracking is the key material non-linearity, at least during the first 30min of the fire test, with maximum temperatures up to 300°C.

Foreword to the special issue on new developments in structural stability.

Foreword to the special issue on new developments in structural stability.

Hysteretic performance of Q690 high-strength steel box-section columns with slender webs

High-strength steel (HSS) has a higher yield-tensile strength ratio and a lower fracture elongation than conventional mild steel, resulting in poor ductility in comparison to the latter. This paper aims to investigate the hysteretic performance of Grade Q690 steel welded box-section columns with slender webs. Four full-scale specimens were subjected to low-cycle horizontal reciprocating loading tests, and the failure mode, evolution of plasticity in the cross-section, energy dissipation capacity and ductility were studied. A finite element modeling procedure verified from the test results was used for a more extensive parametric analysis, and the influence of the width-to-thickness ratio, the axial compression ratio and the column slenderness ratio on the evolution of plasticity in the cross-section as well as the ductility were studied. The results show that plastic local buckling dominates the failure mechanism of welded box-section columns with slender webs. With an increase of the width-to-thickness ratio, axial compression ratio and column slenderness ratio, the evolution of plasticity in the cross-section and the ductility performance of the column gradually deteriorate, and the ductility coefficient within the selected parameter range is small, but it still has the capacity for energy dissipation. Limiting the axial compression ratio and width-to-thickness ratio to meet the requirements of elastic–plastic inter-story drift, HSS box-sections with slender webs can be incorporated in seismic design with low ductility requirements based on the concept of seismic performance design. In addition, a prediction formula for the ductility coefficient is proposed, which can provide a reference for the application of high-strength steel box-section beam–columns with slender webs in seismic design.

On the propagation of acoustic–gravity waves due to a slender rupture in an elastic seabed

The propagation of waves from a vertical uplift of a slender rectangular fault in a sea of constant depth is discussed, accounting for water compressibility, gravity and seabed elasticity. The compressed water column results in the generation of acoustic–gravity waves that travel at the speed of sound in water. Acoustic–gravity waves are found to terminate after a finite time, with the decay time most influenced by seabed rigidity, which is in contrast to the rigid stationary-phase model where signals persist indefinitely. At certain frequencies acoustic–gravity waves couple with the elastic seabed and travel at the shear velocity (speed of sound in an elastic solid). Improved estimates of the critical frequencies are derived. Moreover, besides the usual tsunami, a second – very small amplitude – surface wave mode travelling at the speed of sound arises under certain frequencies. We derive the cut-off frequency for this mode. The acoustic modes possess a frequency spectrum which depends on the time evolution and spatial properties of the rupture. We find that appropriate filtering of the acoustic–gravity wave signal can reveal characteristic peaks that encode information on the fault's geometry and dynamics.

Математическая модель равновесия столба сжимаемой атмосферы. Часть 2: Стационарные решения для давления и плотности

With the one-dimensional aerodynamic model, the problem of equilibrium of a compressible atmosphere column unlimited from above is considered. Numerical and analytical solutions of the model equations are written taking into account two equilibrium conditions: the hydrostatic condition and the equilibrium condition when the density of the column changes with time. The boundary conditions for the solution are the value of pressure or density and the corresponding gradient near the surface. The solution for pressure extends the well-known hydrostatic formula, in addition to which there is a more complex solution. The physical interpretation of the solutions based on the data of experimental measurements in the Earth's atmosphere is discussed. The analytical solution can be used to describe adiabatic atmospheric column, which is important for some applications. The research results improve understanding of processes in atmosphere and can be used for scientific and educational purposes.

Study on Eccentric Compressive Behavior of Concrete Columns Reinforced with NPR735 High-Strength Steel Bars

In this paper, eccentric compressive tests and theoretical studies of grade 735 MPa reinforced concrete columns were conducted. The eccentric distance and strength of the longitudinal reinforcement were used as experimental parameters to investigate the bearing capacity, failure mode, and strength of eccentric compressive behavior of NPR735 high-strength steel bars. When the load eccentricity of the reinforced concrete columns was small or longitudinal, the reinforcement ratio was large, and small eccentricity failure occurred. The results were similar to the failure mode of ordinary concrete columns with traditional steel bars. When the load eccentricity decreased, the bearing capacity increased, but the deflection and ductility of the specimen decreased. When the strength of the longitudinal reinforcement increased, the bearing capacity of the specimen increased slightly. Finally, according to current design methods in the concrete structure design code, the bearing capacity of the eccentric compressive column was obtained, and the calculated results were compared with the experimental results to verify the applicability of the concrete structure design code GB50010-2010 to concrete columns with grade 735 MPa reinforcement.

Calculation model of concrete-filled steel tube arch bridges based on the “arch effect”

In view of the limitations of the current code based on the equivalent beam-column method with the “rod mode” instead of the “arch mode” for the calculation of concrete-filled steel tube arch bridges, this paper takes the real bearing mechanism of the arch as the starting point and analyzes the different bearing mechanisms of the arch and eccentric pressurized column. The concrete-filled steel tube arch model test was carried out to analyze the deformation state and damage mode, and the geometric non-linear bending moment of the measured arch was compared with the bending moment value calculated by the eccentricity increase coefficient of the “rod mode.” The results showed that the transfer of internal force is from the axial force to the arch axis, causing the vertical reaction force and horizontal thrust. However, the eccentric compression column only produced the vertical force at the bottom and combines with the lateral deformation indirectly generated by the eccentric distance. In addition, the deformation stage of the arch is basically the same as that of the eccentric compression column. The final failure mode of the arch is 4-hinge damage, and the final failure mode of the eccentric compression column is single-hinge damage. The preliminary geometric non-linear bending moment value obtained by the two modes accords well. Therefore, the main factors for the difference in the bearing mechanism between the two modes are different force structures, force transmission routes, and sources of deformation. Due to the difference in the bearing mechanism, the final failure mode is different, and the deformation ability of the arch is weakened by using the “rod mode” instead of the “arch mode.” The geometric non-linear bending moment of the control section calculated by the eccentricity increase coefficient is conservative, but the influence of the geometric non-linearity of other sections is not considered enough.

Deformation of concrete under long-term influences of different types

Introduction: Creep deformation of concrete depends at the character of stress state (compression, tension, bending, etc.). At this moment in our country as well abroad the chief parameter which determine by results of long tests concrete sample is the creep of concrete. These tests are done in the mode of uniaxial compression in spring units for one or several specimens, which simulates the compression of walls and columns. But in addition to centrally compressed elements, bending is present in an important part of structures (extracentral compressed columns, slabs, beams, etc.). In unique and difficult constructions massive reinforced concrete elements (foundations, elements of supports for equipment, columns of the lower floors of high-rise buildings, etc.) are often used. In this case the real work of structures under longterm effect of loading differs at the experimental one. Objective: Design and approbation of these methods to concrete testing samples under conditions other than standard tests - in the bending and three-axial compression modes. Materials and methods: In this scientific article describe the methodology of experimental setup for investigation of creep concrete specimens in the bending mode and in the mode imitating three-axial compression, describes the parameters of testing devices, specimens under test and principles transmission of load. Results: In this scientific article results of the experimental studies are presented in the graphical form in the article; their analysis is fulfilled. Conclusions: The perspectivity of the suggested approaches to the testing of concrete specimens for long-term loads has been shown, and recommendations for changes in GOST 24544 have been prepared.

"Reliability Analysis of Axially Compressed Steel Columns "

"In the past, the evaluation of the strength and safety of compressed steel columns has primarily relied on deterministic concepts. However, these concepts fail to account for the significant variability observed in buckling strength test results. This study aims to address this limitation by adopting a probabilistic approach to assess the buckling strength of steel columns; following the Indian standard specification IS 800-2007. In this investigation, the statistically variable nature of the material properties is considered by treating them as random variables and assuming a normal distribution. By incorporating this variability, a more comprehensive evaluation of the buckling strength can be achieved. The buckling strength of the steel column is computed using Merchant Rankine's formula, which takes into account deductive uncertainty. This formula considers various factors such as the slenderness ratio, live load to dead load ratio, and other relevant parameters to estimate the buckling strength of the column. Furthermore, the reliability of axially loaded columns is assessed using the First Order Second Moment (FOSM) technique. The effects of the slenderness ratio and the live load-to-dead load ratio on the reliability of the columns are specifically investigated and discussed. Overall, this study contributes to a more comprehensive understanding of the buckling strength of steel columns, incorporating statistical variability and providing insights into the reliability assessment of such structural elements."

Analytical model for the compressive strength of confined concrete with textile reinforced mortar

This paper proposed an analytical model to predict the confined concrete compressive strength with textile reinforced mortar (TRM). Based on 341 compression tests, different parameters have been analyzed to clarify their influence on the compressive strength of concrete column confined with TRM. The various existing models for compressed concrete columns confined by TRM have been assessed. Then, a simplified model for concrete elements wrapped with TRM are developed and verified through a best-fit analysis of the experimental database. It found that the proposed model showed good agreement with experimental results.

Strength of Compressed Reinforced Concrete Elements Reinforced with CFRP at Different Load Application Eccentricity

Currently, many studies are devoted to the use of polymer composite materials to increase the strength and stability of concrete elements. In compressed reinforced concrete elements, the bearing capacity depends on the eccentricity of the external application of the external force and the corresponding stress-strain state, as well as the location and number of composite materials glued to the surface of the structure. The choice of a scheme for placing composite materials depending on the stress state of the structure is an urgent scientific problem. At the same time, the issue of central compression and the compression of columns with large eccentricities has been well studied. However, studies conducted in the range of average eccentricities often have conflicting results, which is the problem area of this study. The primary aim of this study was to increase the strength and stiffness of compressed reinforced concrete elements reinforced with composite materials, as well as a comparative analysis of the bearing capacity of ten different combinations of external longitudinal, transverse, and combined reinforcement. The results of testing 16 compressed columns under the action of various eccentricities of external load application (e0/h = 0; 0.16; 0.32) are presented. It is shown that the use of composite materials in strengthening structures increases the bearing capacity up to 41%, and the stiffness of the sections increases up to 30%. Based on the results of the study, recommendations are proposed for improving the calculation method for inflexible columns reinforced in the transverse direction, which take the work of concrete under the conditions of a three-dimensional stress state into consideration.

Local Instability Analysis for Axial Compressive Steel Columns

This study presents a nonlinear analysis method for steel columns considering local instability under axial compression. The stress-strain relationship of steel is developed while considering the effects of local instability utilizing the energy principles. The second-order effects are considered by stability functions, while the plasticity of steel is captured by a fiber finite element method. Nonlinear equilibrium equations are solved by the generalized displacement control method. As a result, the proposed formulations are effective, accurate, and reliable in predicting the load-carrying capacity and local instability of steel columns.

Experimental and Numerical Investigation into the Stability Behaviour of Cable-Stiffened Steel Columns.

A cable-stiffened steel column (CSSC) possesses superior stability behaviour compared to ordinary compression columns. In the past, the research emphasis has focused on the behaviours of stiffened columns under axial compression; investigations into their behaviour under eccentric loading is scant. This study aims to examine the buckling behaviour of CSSCs under eccentric loading using experimental and numerical investigations. The effects of pretension in cables and eccentricity on stability behaviours were studied. According to the current investigation, it can be demonstrated that the capacities of CSSCs are higher than those of ordinary compression columns. It has also been illustrated that both the buckling loads and modes of CSSCs can be changed by changing the load eccentricity; however, the modes of ordinary columns cannot be changed. These results could be of theoretical and engineering significance in the exploration of the behaviours of cable-stiffened columns.