Strength Of Columns Research Articles

Strength and Deformation of Concrete-Encased Grouting-Filled Steel Tubes Columns Exposed to Monotonic Quasi-Static Loading Conditions

This study aimed to evaluate the effectiveness of a novel concrete-encased column (CE) using small circular steel tubes filled with cementitious grouting material (GFST) as the primary reinforcement instead of traditional steel bars. The research involved three different types of reinforcement: conventional steel bars, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars, and concrete-filled steel tubes with the same reinforcement ratio as steel bars. Twenty-four circular concrete columns were tested and categorized into six groups based on the type of reinforcement employed. Each group comprised four columns, with one subjected to concentric axial load, two subjected to eccentric axial load (with eccentricities of 25 mm and 50 mm, respectively), and one tested under lateral flexural loads. To validate the experimental results, finite element (FE) analysis was conducted using ABAQUS software version 6.14. The experimental findings for concentric load reveal that columns with the second type of reinforcement, concrete-filled steel tubes with 30% of the reinforcement ratio of steel bars exhibited a failure load 19% lower than those with steel bars, while columns with the third type of reinforcement, concrete-filled steel tubes with the same reinforcement ratio as steel bars achieved a failure load 17% greater than the traditional steel bars. The FE analysis demonstrates good agreement with the experimental outcomes in terms of ultimate strength, deformation, and failure modes.

Effect of imperfection on behaviour of axial loaded square and rectangular concrete-filled steel tubular columns

Axial compressive strength of Concrete Filled Steel Tubular (CFST) columns is significantly improved owing to lateral confinement and the interaction between steel tube and concrete core. Occasionally there exists an initial gap between the concrete core and steel tube which may occur due to improper compaction, shrinkage in concrete, lack of curing of concrete core, etc., consequently, the compressive strength of the column is reduced. Present study shows that the presence of a gap between the concrete core and steel tube reduces the axial strength of CFST column to some extent; however, it results in an enormous fall in the ductility of column. A total of 22 specimens, including 2 hollow steel tube subjected to axial compressive loading, were tested. The main parameters of these tests were the circumferential gap. The influence of gap on the failure mode and ultimate strength of the CFST specimens were investigated. The results show close agreement between calculated and experimental results in terms of load-deformation response and ultimate strength. The behavior of CFST columns with a gap is analyzed, to investigate the impact of different parameters on ultimate strength. A maximum limit of 1.4 to 5.9 gap ratio is proposed, and a simplified formula is suggested to estimate the effect of a gap on ultimate strength.

Comparison and Enhancement of Design Procedures for Guideline Expressions to Predict the Compressive Capacity of FRP-Wrapped Concrete Members

The FRP wrapping of reinforced concrete columns is a simple way to increase the axial load capacity of such members with substandard concrete quality. A total of 2197 specimens were collected as a database to discuss the efficiency of predicting axial compressive strength of FRP-wrapped concrete columns according to several national and international guidelines. Various aspects of the database, including fiber type, unconfined strength and specimen geometry used to investigate the guidelines, and results are presented in terms of averages, standard deviations, and ratio of overestimated specimens. The performance of these expressions was compared with one another based on these statistical results and graphs, and those that captured the behavior best were identified for specific subsets. Recognizing the expressions’ inadequacy in capturing efficiency improvements related to radius to area and confinement ratios, some improvements in the form of coefficients for lateral confinement stress in the Turkish Building Earthquake Code were introduced, specifically for certain subsets.

Optimization of Structural Steel Used in Concrete-Encased Steel Composite Columns via Topology Optimization

Concrete-encased steel composite columns are preferred for their exceptional ductility and strength, particularly in high-rise buildings. This research aims to enhance both the strength and ductility of these composite columns by increasing the height of the steel profile. Typically, hexagonal or circular openings, referred to as castellated elements, are incorporated into the steel profile to achieve this height increase. This study employed a topology optimization method to identify the ideal opening shape for the steel profile in concrete-encased steel composite columns. The analysis revealed a sinusoidal-like opening shape, which was then refined for manufacturing. The optimal opening shape was used to increase the height of the existing steel profile, and nonlinear analyses were conducted to evaluate the effectiveness of this new optimized steel profile in concrete-encased steel composite columns. Two concrete-encased steel composite columns were designed: one with the optimal steel profile and the other with a standard steel I profile. ANSYS APDL 19.0 software was used to simulate an experiment based on an existing concrete-encased steel column to validate the nonlinear analysis. The verification analysis demonstrated a remarkable similarity between the experimental and numerical load–displacement graphs, indicating that the numerical analysis was reliable. In the analysis of the composite columns, both axial and lateral forces were applied in the nonlinear analyses. The axial force was applied at 15% of the column’s capacity, while the lateral force was applied until the composite column reached a state of failure. The results of the nonlinear analyses allowed for a comparison of load–displacement curves and the performance of the composite columns. In comparison to the standard steel I profile, the steel profile with the optimal opening shape increased load-carrying capacity by approximately 19% and energy absorption capacity by approximately 24%.

Behavior of large SCFST column with different confinement effects under pseudo-static loading

In this study, tests of twenty-four square concrete filled steel tubular (SCFST) columns with different structural sizes by the pseudo-static method were conducted to investigate the influence of the confinement effects. In addition, the structural size and the confinement effect are respectively represented by column width and width-to-thickness ratio. The experimental results, including the failure mode, the lateral load-displacement curves and the indices of the seismic performance were recorded and analyzed. The mode of failure is typical compressive flexure pattern. As the structural size increases or the confinement effect decreases, the nominal flexure strength of SCFST column decreases. Compared of the nominal flexural strength of small column, the influence of confinement effect is more significant on that of large column. The displacement ductility coefficient, the mean energy dissipation factor and the relative stiffness decrease with the increasing column width. Then enhanced confinement effect has no obvious influence on the displacement ductility coefficient of the SCFST column. When the confinement effect increases, the energy dissipation capacity of the SCFST column increases. Finally, the modified calculated method considering size effect is established, and this method is applicable to predict the bending moment of the SCFST column with different confinement effects and structural sizes.

Numerical investigation and design of lightweight aggregate concrete-filled cold-formed built-up box section (CFBBS) stub columns under axial compression

Cold-formed built-up box sections (CFBBS) have emerged as a promising solution for applications in light gauge steel framing systems and modular construction. However, they suffer from the inherent local buckling effect. Concrete infill has proven effective in mitigating this issue, yet existing codified provisions lack specific guidelines for the design of concrete-filled CFBBS stub columns. This paper proposed a design methodology that aims to predict the ultimate compressive strength of lightweight concrete-filled CFBBS stub columns. Leveraging finite element (FE) modelling techniques, this study augmented the existing test database and shed light on parametric influences, considering practical considerations, on the structural performances and axial compressive behaviour. The proposed design approach demonstrated superior prediction accuracy and consistency compared to other evaluated design approaches in this study.

Axial compressive behavior and model analysis of BFRP-jacketed corroded and pre-damaged circular reinforced concrete columns

Corrosion of steel reinforcements degrades the structural performance of reinforced concrete (RC) columns under static and seismic loads. Such corroded RC columns are usually retrofitted with fiber-reinforced polymer (FRP). However, existing studies on the retrofitting of RC columns with corrosion and load-induced damage are limited. To confirm the effectiveness of basalt FRP (BFRP) jacketing on the compressive behavior of corroded and pre-damaged RC columns, this study performed axial compression tests on eleven circular RC columns. The columns were fabricated, corroded, pre-damaged, and then jacketed with BFRP composites and reloaded to investigate the effects of BFRP layer number, corrosion ratio, and pre-damage degree. When jacketed by BFRP, the ultimate strength and ultimate strain of RC columns increased with BFRP layer numbers, ranging from 5% to 98% and 448% to 926%, respectively. Further, the ultimate strength and elastic modulus of the jacketed RC columns decreased with the increase in pre-damage degrees and corrosion ratios, while the ultimate strain was little affected. Buckling and corrosion of longitudinal bars significantly reduced the bar stresses at the ultimate state of BFRP-jacketed RC columns and resulted in local rupture of BFRP. This adverse effect became more pronounced as the corrosion ratio increased, but was alleviated by BFRP jacketing. On the other hand, a refined rebar stress-strain model was developed by addressing the effects of buckling, corrosion, and lateral confinement. Further, a feasible constitutive model for corroded hoop-confined columns was determined by validating the existing test results. Finally, models for the ultimate strength, ultimate strain, and stress-strain response of BFRP-jacketed corroded and pre-damaged RC columns were developed.

Passive stress-strain model and ultimate strength prediction for short steel tube confined concrete (STCC) columns allowing for size effect

Steel tubes can significantly enhance the strength and ductility of concrete-filled steel tube (CFST) and steel tube confined concrete (STCC) columns. Existing research work have mainly focused on the former type while the later type of members not only avoid longitudinal steel bulking but also provide better ductility performance to resist seismic loads which is further investigated in this paper. Based on partial-interaction shear-friction mechanics, a passive stress-strain model for short steel tube confined concrete columns is proposed. The main benefit of the proposed model is that it is based on mechanics for rectangular and circular cross-sections which could allow for the size effect. Besides, this model also gives the ultimate strength of steel tube confined concrete columns and is further simplified as a design-oriented approach. The proposed passive stress-strain model and the simplified model for the ultimate strength of concrete columns show good correlation with experimental data. Compared with three other existing approaches, the simplified model could enhance the computing efficiency to a new level. Then a parametric study is conducted to investigate the effect of specimen size on the behaviour of steel tube confined concrete columns.

Performance of seawater sea sand concrete-filled bimetallic tube (SSCFBT) stub columns under axial partial compression

This study presents the experimental findings on the mechanical performance of circular seawater sea sand concrete (SSC)-filled bimetallic tube (SSCFBT) stub columns under axial partial compression. The proposed cross-sectional configuration of the bimetallic tube consists of an external layer fabricated with carbon steel and an inside layer fabricated with stainless steel, by doing so to prevent the chloride ions in SSC from corroding the external carbon steel tube-layer. Axial partial compression tests are conducted on twelve SSCFBT specimens with steel endplates and six counterparts without endplates, and the corresponding parameters include the partial compression area ratio, endplate thickness, and specimen dimensions. The test findings suggest that the two layers of the bimetallic tube exhibit effective composite actions and the SSCFBT stub columns show favorable load-carrying capacity and ductility. The effects of various parameters on the failure mechanism, load-deformation relationship, load-carrying capacity, and strain development of SSCFBT stub columns are analyzed. Finally, the suitability of using different available design codes for conventional concrete-filled steel tubes (CFST) to predict the axial partial compressive strength of SSCFBT stub columns is evaluated.

Behavior of steel tubed rubberized geopolymer concrete columns under axial compression: Experimental study and analytical modeling

Rubberized geopolymer concrete (RuG) has become increasingly popular due to its capability of sustainable utilization of resources, but the mechanical properties of RuG could deteriorate significantly with the increase of rubber content. To mitigate the adverse effects of rubber and further promote the engineering applications of eco-friendly building materials, a new type of composite column, i.e., steel tubed rubberized geopolymer concrete (ST-RuG) columns, was proposed and tested in this paper. The influence of concrete types, rubber replacement ratios, the configurations of steel tubes, and diameter-to-thickness ratios on the compressive behavior of specimens was analyzed. The test results show that the incorporation of rubber has a deterioration effect on the strength of ST-RuG columns with a maximum degradation of 37.6%, but it can improve the ductility of specimens to a certain extent, which is slightly superior to steel tubed rubberized ordinary concrete (ST-RuO) columns. Due to the inherent brittleness of geopolymer concrete (GPC), more obvious residual behavior is detected for ST-RuG compared with ST-RuO under the same rubber replacement ratio Rf. Moreover, with the increase of Rf, the confining pressure of ST-RuG specimens gradually decreases, and a significant decreasing trend is observed for both the peak stress ratio and residual strength ratio of confined RuG. Finally, a new stress-strain model considering the effect of rubber replacement ratio is developed, and comparisons with test results reveal that the proposed model possesses satisfactory accuracy in predicting the axial stress-strain curves of steel-confined GPC and RuG.

Triaxial compression test of MICP sand column and simulation of failure process

Microbially induced calcium carbonate precipitation (MICP) technology can induce calcium carbonate crystals with cementation and stable performance in the process of microbial metabolism or enzymization through the regulation of environmental factors MICP can be used as a cementing agent to cement cohesionless sand particles to form the materials with the characteristics of higher strength, better durability and environmental friendliness, as well as a good engineering application prospect. In this paper, the shear strength of sand column was tested by triaxial compression tests, and the strength index was obtained. In order to further study the micro-strength mechanism and the failure process, based on the discrete element method, a numerical model of MICP cemented sand column was established considering the factors of matrix soil particle gradation, particle morphology, content ratio of induced calcium carbonate, pore distribution characteristics, inter-particle cementation and so on. The failure process of MICP cemented sand column under load was analysed by numerical simulation, and the reliability of the numerical model was tested by combining with the stress intensity curve of samples under test conditions. The results indicate that compared with the actual triaxial tests of MICP cemented sand column, although there are deviations in stress and strain, cohesion and internal friction angle, the numerical simulation shows similar development law and intensity amplitude, and the same failure trend. The work in this paper verifies the reliability of the numerical model and provides a theoretical basis for the subsequent analysis of the factors influencing the geotechnical mechanical properties of biomineralized materials.

The influence of reinforcement’s congestion to the strength of centrally compressed concrete members with GFRP reinforcement

The article presents the results of the computational analysis of compressed concrete columns of a water tank with GFRP reinforcement. It is analytically proved that with an increase in the confinement reinforcement ratio and the magnitude of the relative lateral pressure coefficient due to an increase in the congestion of the longitudinal and transverse reinforcement, the strength of the effectively compressed core increases linearly. The strength of the effectively confined concrete core in GFRP reinforced specimens is somewhat less compared to similar specimens reinforced with steel reinforcement. The coefficient of strengthening of columns (in relation to a pure concrete specimen without reinforcement) increases with increasing frequency of transverse reinforcement. At the same time, the calculated strength of columns with GFRP reinforcement is only 10% less than that of similar columns with steel reinforcement.

Revitalizing Infrastructure: Assessing Concrete Jacketing for Reinforced Concrete Column Rehabilitation

The rehabilitation of deteriorating civil engineering infrastructure, encompassing bridges, buildings, columns, beams, supporting beams, marine structures, and roads, presents a formidable challenge in contemporary engineering practice. As society's demand for upgraded infrastructure escalates, the imperative to address deteriorating structures becomes increasingly urgent. Consequently, the rehabilitation of existing infrastructure has been identified as a paramount concern warranting immediate attention. Among the myriad techniques employed, retrofitting columns with concrete jacketing stands out as one of the most prevalent methods for enhancing column strength. This investigation delves into the efficacy of concrete jacketing as a means of revitalizing reinforced concrete columns. The results evince a substantial augmentation in column capacity following retrofitting, underscoring the potential of such methods to bolster the load-bearing capabilities of reinforced concrete columns. Furthermore, the analysis reveals a more uniform stress distribution in retrofitted columns compared to their unmodified counterparts, thereby mitigating issues related to uneven stress distribution. In summation, the findings underscore the considerable promise of concrete jacketing in fortifying the strength, structural integrity, and longevity of deteriorated infrastructure.

Behaviour of Cold Formed Steel Column with Complex Edge Stiffened Web Openings

Cold-Formed Steel (CFS) sections have gained in popularity due to numerous favourable properties, and with continued research into the various restrictions of such members, their utility in the construction industry has increased dramatically. CFS sections were widely utilised in structural and non-structural applications as they offer lightweight constructions, high strength-to-weight ratios, greater stiffness due to improved sectional profiles, simplicity of installation and assembly, and so on. Optimising these CFS aspects will enable the building of structures at extremely cheap costs. Buckling occurs when the column strength exceeds the cross-section yield. Owing to CFS material characteristics, edge or double stiffeners are used as a best strategy for strengthening the CFS. The primary objective of this research is to examine the strengthening method for CFS G-section columns with edge stiffened hole sections using CATIA software. The results suggest that adding edge reinforced holes to the column enhances its rigidity. The test findings revealed that CFS channel sections with edge-stiffened web apertures had a greater compression resistance than plain channel sections. The G section column with three edge reinforced holes has a low stiffness and utilised as a support element in seismically active structures.

Circular steel tube-confined ultra-high performance concrete beam-column: Database, modeling, and design

The fiber beam element (FBE) model is widely used to simulate and predict the nonlinear behavior of structures owing to its simplicity and high computational efficiency. The accuracy of the FBE simulation of ultra-high-performance concrete (UHPC) filled steel tubular (UHPCFST) members is mainly dependent on the input materials and interactions between the steel tubes and concrete, such as second-order effect, yielding of steel tubes and passive confinement effect to the UHPC. This work proposes uniaxial effective stress-strain models of UHPC confined by circular steel tubes based on existing experimental data that are integrated into the FBE model to predict the nonlinear behavior of UHPCFST members. The robustness and reliability of the proposed material models are comprehensively verified against a database encompassing a wide range of materials and geometric parameters under different loading conditions (monotonic and cyclic loading). Furthermore, the application of existing design codes for computing ultimate bending strengths is assessed using an established experimental database. Finally, the ultimate bending strengths of circular UHPCFSTs are calculated using a novel and simplified N–M interaction equation. It is demonstrated that the developed material models could predict the nonlinear behaviors of circular UHPCFST members with good satisfaction, and that current design codes, to some extent, underestimate the ultimate bending strengths of circular UHPCFST columns, the proposed practical method in this study is highly accurate, with a mean value of 1.00.

Numerical Study on the Axial Compressive Behavior of Steel-Tube-Confined Concrete-Filled Steel Tubes.

To improve the concrete confinement and mechanical properties of concrete-filled steel tube (CFST) columns, a new configuration of steel-tube-confined concrete-filled steel tube (T-CFST) columns has recently been developed, in which an outer steel tube is employed externally, and the additional tube does not sustain the axial load directly. This preliminary experimental study revealed that, due to the effective concrete confinement by the outer steel tube, the T-CFST column achieves higher compressive strength and more ductile deformation compared to the CFST columns of the same steel ratio. In this study, two finite element (FE) models were developed for the T-CFST cross-section and stub column, respectively. The numerical study results revealed that the concrete can be constrained by the outer steel tube at the beginning of loading and the outer steel tube hoop stress can reach its yield strength at the column's compressive strength, showing its effective confinement to the concrete. Numerous data were generated by the developed FE model to cover a wide range of parameters. Based on that, the calculation methods for the stress components of the inner and outer steel tubes are proposed. Finally, a suitable prediction method is proposed, utilizing the superposition method to determine the compressive strength of the T-CFST stub column, and the results of the calculation method and FE model agree well with each other. This research is the basis for promoting further research of T-CFST columns.

Exploring the shear performance and predictive shear capacity of corroded RC columns utilizing the modified compression-field theory: An investigative study

Corrosion damage substantially weakens the shear strength of reinforced concrete (RC) structures, severely compromising their seismic resistance. Therefore, developing an accurate constitutive model is imperative to investigate the impact of corrosion damage on the shear resistance of RC structures. This study presents a corroded RC shear constitutive model based on the modified compression-field theory (MCFT). To capture the flexural, shear, and slip responses of corroded RC columns accurately, a nonlinear analysis model based on OpenSees is proposed. Comparing the results from four sets of quasi-static tests reveals that the proposed constitutive model and analysis framework can well simulate the seismic performance of corroded RC columns. Based on the comparative analysis, the influence of corrosion-induced damage, reinforcement ratio, and axial load on the shear performance of RC columns is discussed. The investigation findings reveal that high corrosion levels and low reinforcement ratios remarkably weaken the shear strength of RC columns. Additionally, high axial load levels accelerate the rate of post peak shear stress degradation. Moreover, this study proposes a method for estimating the shear strength of corroded RC columns based on the MCFT. The presented approach provides a solid foundation for evaluating the shear and seismic performance of existing RC structures.

Testing, numerical modelling and design of G550 high strength cold-formed steel built-up section columns

This paper investigates the buckling behaviour and load-carrying capacity of G550 high strength cold-formed steel built-up section columns under axial compression through experiments and numerical simulations. Two types of built-up sectional profiles were formed, which were defined as built-up OI-section and built-up CB-section. Each built-up OI-section member is formed by connecting two cold-formed steel C-section members in a back-to-back manner using self-drilling screws, while each built-up CB-section member consists of a cold-formed steel C-section member and a cold-formed steel U-section member, which are connected in a face-to-face manner by self-drilling screws. The experimental programme included tensile coupon tests, initial geometric imperfection measurements and 20 pin-ended column compression tests. In the numerical modelling programme, finite element models were developed and validated against the experimental results, and then used for parametric analyses to generate a total of 250 numerical data with different cross-section dimensions and member lengths. Based on the experimental and numerical data, the accuracy of both the effective width method and the direct strength method for predicting the strengths of G550 high strength cold-formed steel built-up section columns, as set out in the American Specification, was evaluated. The evaluation results indicated that both the effective width method and direct strength method provided accurate and consistent failure load predictions for G550 high strength cold-formed steel built-up OI-section columns on average, but with some unsafe failure load predictions, while the predicted failure loads were inaccurate, scattered and conservative for G550 high strength cold-formed steel built-up CB-section columns. Moreover, the effective width method and direct strength method yielded a similar level of design consistency for G550 cold-formed steel built-up section columns, but the direct strength method resulted in more accurate and less conservative failure load predictions than the effective width method. The modifications to the codified DSM equations were proposed for G550 high strength cold-formed steel built-up section columns and shown to provide improved predictions of failure load over the design codes.

Estimation of compressive strength for spiral stirrup-confined circular concrete column using optimized machine learning with interpretable techniques

The compressive strength (CS) of a concrete column confined with spiral stirrups is an important indicator for assessing the safety and stability of concrete structures. However, achieving accurate CS estimation for confined concrete remains challenging due to the complex confinement mechanism provided by spiral stirrups. In this study, three robust machine learning (ML) algorithms—support vector regression (SVR), random forest (RF) and extreme gradient boosting (XGBoost)—are employed to predict the CS value of the spiral stirrup-confined circular concrete columns. The hyperparameters of the ML models undergo fine-tuning via Bayesian optimization with 10-fold cross-validation, and the optimized ML models are evaluated for their predictive capabilities. Results show that compared to SVR and RF, XGBoost exhibits more stable generalization performance, achieving an average coefficient of determination (R 2) of 0.944 for the 10-fold cross-validation, and demonstrates superior accuracy on the testing dataset with an R 2 value of 0.967. To provide insights into the relationship between input features and the output CS value, Individual Conditional Exception (ICE) plots, one/two-dimensional Partial Dependence Plots (PDPs), and Shapley Additive Explanation (SHAP) techniques are utilized to interpret the optimized XGBoost model. Additionally, a friendly online graphical user interface (GUI) has been specially developed based on the optimized XGBoost model to facilitate convenient CS estimation for spiral stirrup-confined circular concrete column.

Behavior of large-scale FRP-confined square RC columns with UHP-ECC section curvilinearization under eccentric compression

Implementing section curvilinearization (SC) by curving flat sides into curved sides before fiber-reinforced polymer (FRP) jacketing has been proposed to enhance the FRP confinement effectiveness of FRP-confined rectangular concrete columns. In this paper, ultra-high performance engineered cementitious composite (UHP-ECC) is proposed as the added concrete for SC, with an aim to enhance both bending and axial strengths of concrete columns given that the UHP-ECC can contribute to resisting tensile stresses for columns. Thirteen large-scale FRP-confined square reinforced concrete (RC) columns with SC using UHP-ECC were tested under eccentric compression loading to explore their eccentric compressive behavior. The test parameters included the rise-to-span ratio, the FRP thickness, the eccentricity and the surface roughness of the old concrete. The test results show that FRP confinement with SC using UHP-ECC can substantially enhance the peak axial load and the bending moment than those without SC, while the ultimate lateral displacement is marginally increased. An increase in the rise-to-span ratio leads to an increase in the peak axial load.