Column Curves Research Articles

Cyclic axial stress-strain model for circular CFST columns under compression loading

This study presents an experimental investigation of twenty-seven numbers of concrete-filled steel tubular (CFST) columns under cyclic axial compression loading to investigate the influence of grade of concrete, length-to-depth (L/D) ratio, and age of concrete on the cyclic axial performance of CFST columns. The L/D ratios were varied in the range of 3–10, while diameter-to-thickness (D/t) ratios of the tube were selected as 13 and 26. The main parameters studied were the peak axial strengths, displacement ductility, post-peak stiffness, and post-peak strengths of CFST columns. The backbone curves of CFST columns obtained from the cyclic tests were found to be similar to the monotonic load-deformation behavior. Test results were also compared with various confinement models available in the literature. A modified cyclic confinement model has been proposed in this study to accurately predict the cyclic behavior of CFST columns. The predicted stress-strain response using the developed confinement model matched well with the test results.

Developing a Sensitive Platform to Measure 5-Methyltetrahydrofolate in Subjects with MTHFR and PON1 Gene Polymorphisms.

Inadequate levels of 5-methyltetrahydrofolate (5-MTHF) and the T variant of MTHFR C677T have been suggested to be associated with an increased risk of developing mental illness, whereas the PON1 SNP variant provides a protective role. However, reports validating the methodology for plasma 5-MTHF levels in schizophrenia patients are limited. A sensitive LC–MS/MS system using an amide column and calibration curve was determined by dialyzed human plasma, and applied to schizophrenia patients and healthy controls in Taiwan, and the differences between the subgroups were discussed. This analysis system meets regulation criteria, and the lower limit of quantification for 5-MTHF levels was 4 nM from 200 μL plasma, within 7 min. The mean plasma 5-MTHF levels in schizophrenia patients (n = 34; 11.70 ± 10.37 nM) were lower than those in the healthy controls (n = 42; 22.67 ± 11.12 nM) significantly (p < 0.01). 5-MTHF concentrations were significantly lower in male carriers than in female carriers (18.30 ± 10.37 nM vs. 24.83 ± 11.01 nM, p < 0.05), especially in subjects who were MTHFR CT/PON1 Q allele carriers. In conclusion, this quantitative system, which employed sensitive and simple processing methods, was successfully applied, and identified that schizophrenic patients had significantly lower levels of 5-MTHF. Lower plasma 5-MTHF concentrations were observed in male subjects.

Testing, modelling and design of 7A04-T6 high-strength aluminium alloy RHS columns under axial compression

The buckling behaviour and resistances of extruded 7A04-T6 high-strength aluminium alloy rectangular hollow section (RHS) columns under axial compression are reported in this paper. Nineteen RHS columns with member relative slenderness of 0.44–2.70 and cross-sections of Class 2–4 were conducted. Finite element (FE) models were developed and verified against the test failure modes, axial load-end shortening or mid-height lateral displacement curves and buckling resistances, and parametric analyses with a wide range of member and cross-section slenderness were performed. The generated test and FE results of 7A04-T6 high-strength aluminium alloy RHS columns were compared with current design methods specified in Chinese, European, American and Australian/New Zealand codes. The results indicated that the former three standards yielded conservative flexural buckling resistance predictions by about 9%, while slightly unsafe results were found for Australian/New Zealand standard, with all satisfactory reliability level. However, Chinese code resulted in the most conservative local-flexural buckling resistance predictions by about 35%, while conservative results under smaller member slenderness and overestimated ones under larger member slenderness were observed for other three standards, leading to scattered data and failing to reach target reliability indices. A series of improved design approaches shown to be safe and efficient for 7A04-T6 high-strength aluminium alloy RHS columns were suggested and validated by reliability analyses, including modified design curves for RHS columns to flexural buckling on Chinese and American standards, and three ways of proposals to imperfection terms with new coefficients as well as the direct strength method (DSM) in the framework of Chinese standard for RHS columns to local-flexural buckling.

Analytical model for concrete-filled double skin tube columns with different cross-sectional shapes under axial compression

The existing theoretical analysis models of concrete-filled double skin tube (CFDST) columns are limited to the analysis of CFDST columns with circular outer and inner tubes (CC-CFDST). The purpose of this paper is to propose a unified model for CFDST columns with different cross-sectional shapes, including CFDST columns with rectangular outer and inner tubes (RR-CFDST), CFDST columns with square outer and inner tubes (SS-CFDST), CFDST columns with square outer and circular inner tubes (SC-CFDST), CFDST columns with circular outer and square inner tubes (CS-CFDST), CC-CFDST columns. The CFDST columns with different shapes (original columns) are replaced with equivalent CC-CFDST columns by assuming that they have the same cross-sectional areas of the inner and outer steel tubes and concrete. The difference in mechanical properties between the original column and the equivalent column is attributed to the difference in the confining effect of the steel tube on the core concrete caused by the different shape, which is considered by the shape effect coefficient ke. The proposed model is verified by collected experimental data of CFDST columns with different cross-sectional shapes. The mean value and coefficient of variation of the ratio of the calculated bearing capacity to the experimental bearing capacity are 1.006 and 0.119, respectively. The results show that the proposed model can predict the axial compression bearing capacity and load–deflection curves of CFDST columns accurately.

A REVIEW PAPER ON THE AXIAL BEHAVIOUR OF CONCRETE FILLED STEEL TUBES CONTAINING HIGH VOLUME WASTE TYRE RUBBER CONCRETE.

One of the solution to reduce tire waste is by incorporating rubber as ne aggregate replacement, producing a rubberized concrete. This type of concrete generally has lower compressive strength, however, could potentially be used as structural application due to its inherent ductility. Crumb rubber concrete, in which a portion of the mineral aggregates in concrete is replaced by the waste tire rubber, has attracted great research attention as a sustainable building material. It is a promising solution to the over-exploitation of river sand and the recycling of waste tire rubber. However, the concrete strength decreases signicantly when crumb rubbers were used to replace the ne mineral aggregates. A reliable strength reduction model for the crumb rubber concrete with ordinary strength is essential for its practical use in engineering structures. With different volume replacement ratios of rubber ne aggregate and thicknesses of steel tube, 12 rubberized concrete- lled steel tube (RuCFST) columns were fabricated. Then axial compressive tests were completed. The test results show that RuCFST columns exhibit lower axial compressive capacity and higher ductility than normal CFST columns. The steel tube of the RuCFST with a high rubber replacement ratio is more prone to local buckling and the axial load-displacement curves of RuCFST columns tends to exhibit hardening post- peak response. Based on the experimental results, the relationship between the critical value of the connement coefcient and the rubber replacement ratio of RuCFST columns was obtained.

Sectional Analysis of Reinforced Engineered Cementitious Composite Columns Subjected to Combined Lateral Load and Axial Compression

The ultra-high tensile ductility of ECC provides an alternative way to enhance the ductility of structural members by using high-ductile matrix material instead of simply increasing reinforcements. However, the application of ECC members is still limited due to the relatively short research time and the lack of design specifications. Being equivalent to eccentric compressive members, a sectional analysis of RECC columns subjected to combined lateral load and axial compression are proposed in this paper. Based on the design theory of load capacity of eccentric compression columns and the unique constitutive model of ECC, the calculation equations for the sectional load capacity of RECC columns are derived. The analytical prediction of the load capacity of RECC column is evaluated in comparison with that of experiments that confirm the capacity of the proposed calculation method to capture the behavior of the RECC column accurately. The strength-interaction diagrams showing the axial force-moment (N-M) interaction curves are then constructed for analysis using the proposed calculation equations. A parametric study is also carried out by using the proposed calculation equations, demonstrating the effects of ultimate tensile strain of ECC, compressive and tensile strength of ECC, yield strength of steel bar, and reinforcement ratio on the N-M interaction curves of RECC columns. The investigations exhibited in this paper are expected to provide insight into the design principles of RECC columns.

Fragility analysis for performance-based blast design of FRP-strengthened RC columns using artificial neural network

In this paper, fragility analysis for performance-based blast design of FRP-strengthened RC columns is carried out. The blast intensity levels, performance levels and performance objectives of the RC columns are defined. A simplified probabilistic risk assessment framework incorporating the performance-based design concept and fragility analysis is established. Since fragility analysis is the most important but time-consuming process of probabilistic assessment risk, an artificial neural network (ANN) based fragility analysis framework is proposed to improve its computational efficiency. Based on the rapid fragility analysis method, fragility curves of several typical RC columns with or without FRP strengthening are calculated to analyze their damage probabilities. This study provides avenues for engineers to estimate the failure probabilities of RC columns with or without FRP strengthening under blast loads and make decisions quickly.

A unified stress-strain model for LRS FRP-confined concrete columns with square and circular cross-sections

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites with an ultimate elongation of greater than 5% offer superior deformation and energy dissipation abilities over traditional carbon or glass FRP when used them in lateral confinement of concrete under the same confinement level. However, a flexible model for predicting the stress-strain relationship of concrete columns confined with LRS FRP is not yet perfectly developed, especially for noncircular columns experiencing nonuniform confining stress. Accordingly, an extensive database of LRS FRP-confined square and circular concrete columns with corner radius ratios varying from 0 to 1 was employed to establish a unified stress-strain model. This model not only includes the determinations of key points, but also attempts to define the threshold confinement level to distinguish the post-peak strain-hardening and strain-softening behaviors. The mathematical expression of the model is simple; it also avoids discontinuities in the prediction of different cross-sections. The proposed model is verified to be accurate in predicting the complete stress-strain curves of LRS FRP-confined square and circular concrete columns with hardening and softening behaviors. In addition, it outperforms the existing theoretical models in predicting the ultimate strength and the ultimate axial strain.

Compressive performance of bamboo sheet twining tube-confined recycled aggregate concrete columns

This paper proposes a new structure for a recycled aggregate concrete (RAC) column confined by a bamboo composite tube (BCT), and the performance of the RAC is further improved by mixing short bamboo strips. An experimental and analytical study of the behavior of bamboo sheet twining tube-confined recycled aggregate concrete (BSTRAC) columns under axial compression is presented. A total of thirty-six axially loaded BSTRAC columns were manufactured to investigate the effects of the number of bamboo sheet layers (BCT thickness) and the volume content of short bamboo strips. The results indicated that the BCT had strong lateral confinement as well as the ability to bear axial loads, which resisted lateral expansion deformation, and the increase in BCT thickness led to an increase in compressive strength and ductility. In addition, the short bamboo strips could improve the compressive strength, ductility and residual bearing capacity of the axially loaded BSTRAC column. Based on the compressive performance of short bamboo strip-reinforced RAC, ten existing FRP-confined concrete models were considered to predict the ultimate stress, ultimate strain and axial stress–strain curves of BSTRAC columns. It can be concluded that some existing models can be used to predict the ultimate stress and ultimate strain of BSTRAC columns accurately; moreover, a few models provide reasonable predictions for the BSTRAC specimens of stress–strain curves.

Blast fragility analysis of RC columns considering chloride-induced corrosion of steel reinforcement

Chloride-induced corrosion of steel reinforcement is one of the key factors that influences the life cycle performance and load-carrying capacities of concrete structures. For concrete structures that might be subjected to explosion hazards during the service life, the fragility analysis with the consideration of chloride-induced rebar corrosion provides quantitative information on lifecycle performance of structures against blast loading. This study performs the fragility analysis of reinforced concrete (RC) columns considering chloride-induced corrosion of steel reinforcement subjected to blast loading. General corrosion and pitting corrosion are considered in this study. Monte Carlo simulations are carried out in the study to calculate the failure probabilities. The mean and standard deviation of the degraded diameter and yield stress of the reinforcement up to 90 years after the corrosion initiation is established, which is incorporated in the existing empirical formulae for constructing the P-I curves of RC columns to predict its deteriorated blast loading-resistance capacity with time. In the analysis the blasting scaled distance is used as the demand intensity measure, random fluctuations of the peak reflected pressure, positive blast loading duration, concrete compressive strength, thickness of the concrete cover, diameter and yield stress of steel reinforcement are considered in the simulations. The blast fragility curves of typical RC columns are generated with respect to different damage levels corresponding to the number of years after corrosion initiation. It is found that the damage probability of RC columns increases significantly with steel reinforcement corrosion deterioration. Parametric analyses have shown that the column size is a more dominant factor, in comparison with the reinforcement ratio, of the RC columns on the blast resistance capacity corresponding to the minor damage levels. It is also found that the longitudinal reinforcement ratio is a less dominant factor than transverse reinforcement ratio on blast fragility curves of RC columns to resist blast loading. The blast resistance capacity of RC columns deteriorates significantly with corrosion damage.

Fiber element modeling of circular double-skin concrete-filled stainless-carbon steel tubular columns under axial load and bending

Circular concrete-filled double-skin steel tubular (CFDST) columns with external stainless-steel are high-performance composite columns that have potential applications in civil construction including the construction of offshore structures, bridge piers, and transmission towers. Reflecting the limited research performed on investigating their mechanical performance, this study develops a computationally efficient fiber model to simulate the responses of short and slender beam-columns accounting for the influences of material and geometric nonlinearities. Accurate material laws of stainless steel, carbon steel, and confined concrete are implemented in the mathematical modeling scheme developed. A new solution algorithm based on the Regula-Falsi method is developed to maintain the equilibrium condition. The independent test results of short and slender CFDST beam-column are utilized to validate the accuracy of the theoretical solutions. The influences of various column parameters are studied on the load-axial strain [Formula: see text] curves, load-lateral deflection [Formula: see text] curves, column strength curves, and interaction curves of CFDST columns. Design formulas are suggested for designing short and beam-columns and validated against the numerical results. The computational model is found to be capable of simulating the responses of CFDST short and slender columns reasonably well. Parametric studies show that the consideration of the concrete confinement is important for the accuracy of the prediction of their mechanical responses. Furthermore, high-strength concrete can be utilized to enhance their load-carrying capacity particularly for short and intermediate slender beam-columns. The strengths of CFDST columns computed by the suggested design model are in good agreement with the test and numerical results.

M-N interaction curves for rectangular concrete-filled steel tube columns subjected to uniaxial bending moments

abstract: In this paper, a computational code was developed to obtain M-N interaction curves for rectangular concrete-filled steel tube columns considering the strain compatibility in the cross-section. Considering the composite section subjected to uniaxial bending moments, expressions were developed to determine normal force, moment resistance, neutral axis depth and components resistance of cross-section. Such expressions were implemented in a computational tool developed to the authors and that allows to obtain the M-N pairs of strength. The steel and concrete ultimate strains were defined with the aid of the Brazilian standard for reinforced concrete structures ABNT NBR 6118. The obtained results were compared to simplified curves defined according to the theoretical models of ABNT NBR 8800, ABNT NBR 16239, EN 1994-1-1 and literature data. The proposed model showed good agreement with literature results and had good precision to estimate the ultimate moment values. To further understand the resistance of composite columns under uniaxial bending moments, parametric study was performed to evaluate the influence of the compressive strength of concrete, yielding strength of steel and steel area ratio on M-N interaction curves. The results indicate that the yielding strength of steel and the steel area ratio were the variables that most influenced the values of composite columns resistance (normal force and bending moment).

Cadmium Removal from Giant Squid (Dosidicus gigas) Hydrolysate in Fixed-Bed Columns Packed with Iminodiacetic Resin: Tools for Scaling up the Process.

Giant squid hydrolysate (GSH) elaborated from different batches from a fishing company was evaluated for cadmium removal. Fixed-bed column packed with iminodiacetic resin as adsorbent was used. GSH solution at different cadmium concentrations were fed in the fixed-bed column and breakthrough curves were evaluated. A high degree of metal removal from the solution was achieved and the saturation point (Ce/C0 ≤ 0.8) was achieved more quickly at higher concentrations of cadmium. The maximum capacity of adsorption (q0) was obtained using the Thomas model, where 1137.4, 860.4, 557.4, and 203.1 mg g−1 were achieved using GSH with concentrations of 48.37, 20.97, 12.13, and 3.26 mg L−1, respectively. Five cycles of desorption of the resin with HCl (1 M) backflow and regeneration with NaOH (0.5 M) were also evaluated, where no significant differences (p-value > 0.05) were observed between each cycle, with an average of 935.9 mg g−1 of qmax. The in-series columns evaluated reached a total efficiency of 90% on average after the third column in GSH with a cadmium concentration of 20.97 mg L−1. This kind of configuration should be considered the best alternative for cadmium removal from GSH. Additionally, the chemical composition of GSH, which was considered a quality parameter, was not affected by cadmium adsorption.

Compression-bending behaviour of steel-reinforced concrete-filled circular steel tubular columns with preload

Due to different construction processes, for steel-reinforced concrete-filled steel tubular (SRCFST) columns, its outer steel tube and inner reinforcing steel can often be used as the vertical support of concrete pouring formwork and floor in the construction process. Therefore, before the whole member is stressed together, steel components may alone or together generate an initial stress, and then affect the mechanical performance of the entire column. In this study, the structural behaviour of circular SRCFST columns with preload effects under coupled compression and bending is analyzed via the verified finite element (FE) model. The influence of different preload ways, namely only preload on the steel tube, and preload on both the steel tube and reinforcing steel, are investigated. Moreover, the relevant factors influencing the performance of SRCFST columns are also studied. The results show that the load versus deflection curves of SRCFST columns with different preload ways are basically identical. In addition, the main parameters affecting the ultimate strength influence coefficient (kp) are the preload ratio, the load eccentricity and slenderness ratio. Finally, the compression-bending calculation method considering the influence of the preload effects is proposed to calculate the ultimate strength of circular SRCFST columns with preload effects.

Axial compressive behavior of rubberized concrete-filled steel tube short columns

With different volume replacement ratios of rubber fine aggregate and thicknesses of steel tube, 12 rubberized concrete-filled steel tube (RuCFST) columns were fabricated. Then axial compressive tests were completed. The test results show that RuCFST columns exhibit lower axial compressive capacity and higher ductility than normal CFST columns. The steel tube of the RuCFST with a high rubber replacement ratio is more prone to local buckling and the axial load-displacement curves of RuCFST columns tends to exhibit hardening post-peak response. Based on the experimental results, the relationship between the critical value of the confinement coefficient and the rubber replacement ratio of RuCFST columns was obtained. Then, the axial compressive strength of RuCFST columns was investigated by Eurocode4, AISC360-16 and GB 50936-2014 codes. The results show that the predictions by those codes are conservative. Finally, by considering the higher ductility of RuCFST columns and full use of material properties, a modified formula to calculate the compressive strength of RuCFST columns was proposed and then validated by the experimental results.

Behavior of GFRP-RC columns under axial compression: Assessment of existing models and a new axial load-strain model

Concrete structures reinforced with fiber-reinforced polymer (FRP) bars (referred to as FRP-RC structures) are becoming increasingly popular, whereas there is a lack of a robust full-range axial load-strain model for FRP-RC columns, which is fundamental for the design and advanced analysis of FRP-RC structures. To this end, a review and assessment of existing confined compressive concrete ultimate axial stress (or strain) models (including models for glass FRP (GFRP) spiral-confined concrete (GFSCC) and models for FRP partially confined concrete (FPCC)) against a newly established database are reported in this paper. The comparisons show that the models of FPCC are applicable to GFSCC. A new design-oriented full-range axial load-strain model is then proposed for GFRP-RC columns of circular cross-section by explicitly considering the behavior of three key components in FRP-RC columns, namely, confined concrete core, FRP longitudinal reinforcement and concrete cover. The novelty of the proposed model is that the constitutive models of the three components in FRP-RC columns can be considered in separation. The proposed model, which is able to capture the strain softening behavior properly, provides satisfactory predictions of the axial load-strain test curves of FRP-RC columns.

Global Buckling Investigation of the Flanged Cruciform H-shapes Columns (FCHCs)

In China, increasing the application ratio of hot-rolled H-shapes has become a severe problem that the government, academia, and engineering circles must vigorously address. Research on reasonable hot-rolled H-shapes built-up columns is one of the primary methods. After reviewing the various combination columns in the existing research, the paper proposes the new flanged cruciform H-shapes columns (FCHCs) made of three hot-rolled H-shapes. Using comprehensive imperfections given by the design standard, GB50017-2017, the paper analyzes the global buckling of FCHCs subjected to the axial compression load. The global buckling factor obtained is compared with the current national design code. Comparative analysis of seventy-two specimens of Q345 and Q460 steel found that the global buckling mode of FCHCs was flexural bending buckling around the axis of symmetry, and global torsional buckling and local buckling did not occur. Furthermore, the corresponding column curves in current design codes overestimate the dimensionless buckling strength of the novel FCHCs. Therefore, designers need to drop a class to select the global buckling factor within a specific range. Finally, new column global buckling curves are proposed based on a non-linear fitting of the numerical results according to the current national design codes.

Experimental investigations of GFRP-reinforced columns with composite spiral stirrups under concentric compression

In this study, a new way to transversely reinforce square concrete columns using glass fiber reinforced polymer (GFRP) composite spiral stirrups composed of several outer rectangular GFRP stirrups and an inner spiral GFRP stirrup was proposed. The double restraints of the composite spiral stirrups overcame the shortcoming of the relatively lower elastic modulus of GFRP compared with steel and provided effective lateral restraint for the core concrete. The axial compressive performance of GFRP-reinforced square concrete columns with composite spiral stirrups was experimentally investigated. The test variables, including the stirrup spacing, stirrup diameter, longitudinal bar type and stirrup configuration, were discussed. The results indicate the following: (1) By the application of GFRP composite spiral stirrups, both a higher core concrete strength and ultimate load could be achieved compared to GFRP rectangular stirrups and GFRP composite rectangular stirrups. (2) Except for specimens 12S-150G-G and 8S-100G-G, the load versus axial concrete strain curves of GFRP-reinforced columns with composite spiral stirrups did not drop after reaching the peak but went through a stable stage, showing excellent ductility. (3) With a decrease in stirrup spacing from 100 mm to 50 mm, secondary peaks appeared on the load versus axial concrete strain curves. The decrease in the stirrup spacing effectively enhanced the core concrete strength and ductility of the columns. (4) Considering the contribution of the GFRP bars and the restraint effect of stirrups, a new method to calculate the ultimate bearing capacity of GFRP-reinforced columns with composite spiral stirrups was proposed and verified with experimental results.

Experimental investigation and design method of the flexural buckling resistance of high-strength aluminum alloy H-columns

High strength aluminum alloy members can be used if the required cross-sections are larger than those obtainable by extrusion. The application range of the current design codes for aluminum structures is limited for normal-strength material and whether high-strength members can be designed with the existed buckling curves is examined. Fourteen H-section columns made from 7075-T6 were tested under axial compression. The effects of the different material properties and imperfections on the flexural buckling behavior of normal- and high-strength columns were analyzed numerically. The column curves in European, Chinese and American specifications can predict flexural buckling resistance of such columns safely with an average underestimation of 13%, 12% and 8%, respectively. Eighty-one column buckling tests available in the literature performed on extruded sections made of aluminum alloy with the yield stress between 388 MPa and 557 MPa were collected and analyzed. Finally, a new flexural buckling curve was suggested for the estimation of flexural-buckling resistance of high-strength extruded members.

Flexural buckling of stainless steel CHS columns: Reliability analysis utilizing FEM simulations

This paper presents a numerical investigation of the ultimate limit state of imperfect columns under axial compression; the columns are made of stainless steel with a circular hollow cross-section (CHS). The subject of interest is the statistical analysis of the ultimate resistance. Statistical characteristics of input material and geometric imperfections are taken from the results of experimental research published in the literature. The first-order reliability method (FORM) along with geometrically and materially nonlinear imperfect numerical analysis (GMNIA) is conducted. The ultimate resistances of CHS columns in flexural buckling obtained from the finite element analyses are compared with the design resistances based on the corresponding European standard, considering various slenderness values. Two approaches of the initial geometrical imperfection amplitude consideration are presented. The influence of correlation between the ultimate resistance of stainless steel columns in compression and input parameters is discussed, with a focus on the geometrical imperfection influence. The results may be useful for the verification of the European standard where the flexural buckling curves of stainless steel columns are relatively new and thus are based on a relatively weaker theoretical and experimental basis compared to carbon steel.