Compressive Strength Of Columns Research Articles

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.

The Efficiency of Using Machine Learning Techniques in Fiber-Reinforced-Polymer Applications in Structural Engineering

Sustainable solutions in the building construction industry have emerged as a new method for retrofitting applications in the last two decades. Fiber-reinforced polymers (FRPs) have garnered much attention among researchers for improving reinforced concrete (RC) structures. The existing design guidelines for FRP-strengthened RC members were developed using empirical methods that are based on specific databases, limiting the accuracy of the predicted results. Therefore, the use of innovative and efficient prediction tools to predict the behavior of FRP-strengthened RC members has become essential. During the last few years, efforts have been progressively focused on the use of machine learning (ML) as a feasible and effective technique for solving various structural engineering problems. Its capability to predict the behavior of complex nonlinear structural systems while considering a wide range of parameters offers a distinctive opportunity to make the behavior of RC members more predictable and accurate. This paper aims to evaluate the current state of using various ML algorithms in RC members strengthened with FRP to enable researchers to determine the capabilities of current solutions as well as to find research gaps to carry out more research to bridge revealed knowledge and practice gaps. Scopus databases were searched using predefined standards. The search revealed ninety-six articles published between 2016 and 2023. Consequently, these articles were analyzed for ML applications in the field of FRP retrofitting, including flexural and shear strengthening of RC beams, flexural strengthening of slabs, confinement and compressive strength of columns, and FRP bond strength. The results reveal that 32% of the reviewed studies focused on the application of ML techniques to the flexural and shear strengthening of RC beams, 32% on the confinement and compressive strength of columns, 6.5% on the flexural strengthening of slabs, 22% on FRP bond strength, 6.5% on materials, and 1% on beam–column joints. This research also revealed that the application of various ML algorithms has shown a significant improvement in resistance prediction accuracy as compared with the existing empirical solutions. Supervised learning techniques were the most favorable learning method due to their good generalization, interpretability, adaptability, and predictive efficiency. In addition, the selection of suitable ML algorithms and optimization techniques is found to be mainly dictated by the nature of the problem and the characteristics of the dataset. Nonetheless, selecting the most appropriate ML model and optimization algorithm for each specific application remains a challenge, given that each algorithm is developed with different principles and methodologies.

Analysis of compressive strength of AAC masonry columns strengthened circumferentially

AbstractThe compressive strength of the columns was tested on six models made of AAC (autoclaved aerated concrete) masonry elements. Three models were built without strengthening, while the others were made circumferentially strengthened with the FRCM system. The columns were made with cross‐sectional dimensions of 0.18 × 0.18 m and a height of 1.90 m. During the test, strains and the manner of model cracking were also observed. The reinforcement increased the compressive strength by 20%. The test results were compared with the results of analytical calculations.

Axial compressive behavior of steel-tube-confined concrete-filled-steel-tubes

Concrete-filled steel tubes (CFST) are widely used in civil engineering practice, and a significant shortcoming of such members is the insufficient and delayed concrete confinement by the steel tube. The configuration of steel-tube-confined CFST (T-CFST), employing an outer steel tube as additional external confinement to the internal CFST, was recently proposed by the authors. The preliminary study has validated the great potential of T-CFST in new construction and strengthening. Against this background, this paper aims to investigate the influence of critical parameters in the axial compressive behavior of T-CFST stub columns through a rigorous systematic experimental study. Test results showed that not only the shear failure was prevented, but also the compressive strength was significantly improved for T-CFST due to the effective concrete confinement by the outer steel tube. Apart from the increasing steel ratio of the outer tube and the inner tube, the concrete confinement also can be enhanced as the ratio of the outer tube and the inner tube steel ratio increases. To fully develop the mechanical properties of T-CFST, sufficient confinement should be employed at the column ends to prevent premature failure there. The development of the longitudinal stress and hoop stress were analyzed and compared for the outer tube and the inner tube, and the calculating method was proposed to determine the longitudinal and hoop stress components at the column compressive strength. Based on the superposition method, a suitable prediction method was proposed to determine the compressive strength of T-CFST, and the prediction results were well close to the experimental results in this study.

Determining the behaviour of jet-grouting elements using a laboratory scale

Jet grouting is a developing technology for soil improvement in most soil types. It offers advantages such as relatively short execution and a high volume of soil rehabilitation. Nonetheless, due to the complexity of this method, related scientific research is ongoing. This study presents a design and fabrication process for equipment capable of constructing soil–cement columns using a high-pressure injection mechanism at the laboratory scale. The columns are constructed using the device in Firouzkouh 161 silica sand. The effect of energy on the diameter of the columns constructed at laboratory scale is evaluated. The behaviour of such columns built using full-scale elements is evaluated using resistance testing on core-sampling specimens. The results showed that an increase in pressure injection leads to logarithmic growth in the diameter of the element. It was found that an increase in pressure had a greater effect on the diameter than an increase in injection duration. The uniaxial compressive strength of the specimens showed a 35% decrease in the horizontal core in comparison with the vertical core. The compressive strength of columns without core sampling was 2.3–2.5 times that of the columns with core sampling.

GFRP wrapped concrete column compressive strength prediction through neural network

Wrapping of fibre over the concrete columns significantly improves the compressive strength and ductility behaviour of columns. In this study the compressive strength of the Glass Fibre Reinforced Concrete (GFRP) wrapped concrete columns were studied under axial compression. The parameters varied are types of GFRP (Surface Mat, Chopped Strand Mat and Woven Roving Mat), number of plies (0, 1 ply and 3 plies) and period of curing (7, 14 and 28 days). Twenty-one standard cylindrical specimens were tested to failure under compression testing machine. The GFRP confined concrete columns increases the compressive strength by 30% for different types of fibres. The change in the number of plies from one to three improves the strength six times. The Artificial Neural Network (ANN) is an alternate tool used to accurately estimate the confined strength of the wrapped columns. The multi-layer neural network has been used with back propagation training algorithm. The predicted strength was compared with the experimental results. A good correlation was obtained between the predicted strength by ANN model and experimental values with correlation coefficient R values of 0.992, 0.999 and 0.999 for training, validation and testing data sets.

Pre- and post-heating behavior of concrete-filled steel tube stub columns containing steel fiber and tire rubber

Concrete-filled steel tube (CFST) columns are increasingly used in different structures owing to their excellent load carrying capacity provided by the interaction between the concrete core and steel tube. However, there is lack of information on the design and prediction of the behavior of CFST columns with rubberized concrete core when they are exposed to elevated temperature. This paper presents a study on the axial compressive behavior of short CFST columns containing steel fiber and tire rubber particles exposed to elevated temperatures. To this effect, steel fibers were added at two volume fractions of 1% and 1.5% and tire rubber particles were added as fine aggregate at two replacement ratios of 5% and 10% to the concrete core. CFST columns were exposed to four temperatures of 20 (as control), 250, 500 and 750 °C, and then axial compression tests were conducted on them. The experimental test results show that an increase in the exposure temperature to 500 °C does not have a significant influence on the compressive strength of CFST columns, whereas an increased temperature to 750 °C results in a significant decrease (34%) in the compressive strength of the columns. It is also found that an increase in the exposure temperature, steel fiber volume fraction and rubber replacement ratio lead to an increase in the axial and lateral strain corresponding to the compressive strength of CFST columns. It is shown that the predictions of the compressive strength and axial stress–strain relationship by the proposed model are in good agreement with the tests results of both unheated and post-heated CFSTs.

Compressive behavior of built-up double-box columns consisting of four cold-formed steel channels

Thirty specimens of built-up double-box columns consisting of four cold-formed steel channels were experimentally tested under concentric and eccentric axial compression. The test specimens had varied cross-sectional dimensions (outside dimensions equal to 89 mm × 147 mm or 86 mm × 96 mm), different effective lengths (3200 mm, 1700 mm, 210 mm, or 135 mm), and different thicknesses (1.2 mm or 1.5 mm). The load vs. displacement curves and the measured compression strength of specimens were obtained and the failure modes were analyzed. The test results showed that the failure mode of the long specimens (L/r between 103 and 108, where L is the calculated length of the column, r is the minimum radius of gyration) was flexural buckling about the weak axis. The typical failure modes of medium length specimens (L/r between 53 and 57) and short specimens (L/r between 4 and 8) subjected to concentric axial compression were deformation concentration caused by large local buckling. The failure mode of the medium length specimens under eccentric axial compression was flexural buckling, except for the specimens whose web height was 147 mm and the eccentricity direction was along the minor axis, for which the failure mode was deformation concentration. Then, finite element (FE) models considering geometric, material, and contact nonlinearity were developed, compared to experimental results, and used to explore a wider design space. The FE analysis results showed that the slenderness ratio of the column and the web height-to-thickness ratio have an important influence on the strength of these columns. Finally, the applicability and effectiveness of calculating compression strength for this type of built-up column using methods such as “Effective Ratio of Width-to-Thickness Method” in Chinese code, “Effective Width Method” in AISI and “Direct Strength Method” in AISI, were evaluated by comparison with the test and FE results. For all the columns analyzed with slenderness ratio greater than 105, it is reasonable to use these methods to calculate the concentric axial compression strength of columns. The methods in China and AISI S100-16 were found to be conservative for calculating the eccentric axial compression strengths of these built-up double box columns.

Numerical Analysis of Strength Capacity of High-Performance Reinforced Concrete Columns with Varied Parametric Study

Introduction: This study includes the analysis of the strength capacity of high performance reinforced concrete columns subjected to concentric axial loading. The main variables are based on the compressive strength of concrete and steel reinforcing ratios. All the columns are fixed, supported by two ends. Methods: This study is based on a calculation done according to ACI Code-318M-2011 equations for columns analysis to evaluate the ultimate strength then applied these load on samples to compare between them by software program Prokon V.3. The comparison is based on reinforcement ratio and moment resistance capacity. Results: The analysis results show that when increasing the main reinforcement with high-performance concrete led, there will be an increased load capacity by about (40 to 215%) and moment resistance capacity by about (35 to 50%) with the same load conditions. According to the analysis of the results, the moment resistance capacity of constant sample value with different reinforcing ratio leads to these resist depending on the load applied, and the concrete compressive strength of columns. Conclusion: Reasonable correlation of the results is demonstrated, which ensured the adequacy of the analysis by test program, both hand calculation and software Prokon.V.3.

C-FRCM Jacket Confinement for RC Columns under Impressed Current Cathodic Protection

In coastal regions, chloride penetration causes steel reinforcing bar (rebar) corrosion in reinforced concrete structures, leading to durability problems in existing structures. A new intervention method, impressed current cathodic protection and structural strengthening (ICCP-SS), was adopted to rehabilitate sea–sand concrete columns. A carbon fiber-reinforced cementitious matrix (C-FRCM) was used as a dual-functional material in the ICCP-SS system, wherein the C-FRCM served as both an anode and a strengthening material. This study aimed to consider the effects of the total charge density on the confinement effect of C-FRCM jackets and the compressive strength of columns under ICCP-SS intervention to demonstrate the long-term effectiveness of the ICCP-SS intervention method for sea–sand RC columns and to investigate the appropriateness of existing strength models for RC columns strengthened by C-FRCM jackets under impressed current cathodic protection (ICCP). The experimental program included a total of nine reinforced concrete stub columns. Prior to the compression tests, the columns were subjected to 270 days of accelerated corrosion and 250 days of cathodic protection under protective cathodic current densities of 20 and 60 mA/m2. This paper presented an experimental program, a comparison between short-term and long-term test results of ICCP-SS, a comparison of existing strength models, and a discussion on the appropriateness of the existing models for C-FRCM jackets subjected to an applied current.

Effects of uniformly distributed side corrosion on thin-walled open cross-section steel columns

Compressive capacity of the thin-walled steel columns, corroded uniformly over their entire side surface length is analysed in this paper. The thin-walled profile steel columns are often used for bridges, rail and road building constructions. Loss of the profile mass that appears due to corrosion growth reduces the cross-sectional area and influences column compressive capacity. Computational models of the structure are assumed based on the observation of existing corroded columns. The theory of thin-walled profiles is taken for the analysis. Models simulating the walls weakening due to corrosion growth are considered on the example of three thin-walled steel profiles: semi-closed channel section, two semi-closed channel section connected by webs and HKS profiles. Different patterns and degrees of corrosion growth were considered and, as a result, changes of the profile cross-sectional geometry were observed. Theoretical considerations of thin-walled compressed corroded steel columns stability are illustrated by bearing capacity calculations. Geometric cross-sectional characteristics are determined and the system of stability equations is solved. The calculation results are presented in the form of graphs illustrating the effects caused by the geometry change due to corrosion defects. The reduction of column compressive strength in each of the considered case is observed. Moreover a variation of the buckling mode from flexural one into warping is noticed in one of the analysed items. It has been found that more dangerous corrosion growth pattern appears when asymmetric loss of the profile wall thickness arises. That may change the form of buckling from flexural one into warping.

Multiscale modeling for compressive strength of concrete columns with circular cross-section

In order to construct a multiscale model for the compressive strength of plain concrete columns with circular cross section subjected to central longitudinal compressive load, a column failure mechanism is proposed based on the theory of internal instability. Based on an energy analysis, the multiscale model is developed to describe the failure process and predict the column's compressive strength. Comparisons of the predicted results with experimental data show that the proposed multiscale model can accurately represent both the compressive strength of the concrete columns with circular cross section, and the effect of column size on its strength.

Influence of Uniformly Distributed Corrosion on the Compressive Capacity of Selected Thin-Walled Metal Columns

Estimation of the compressive capacity of selected types of cold-formed steel columns subjected to surface corrosion is the objective of this article. Symmetric “C” section and bisymmetric “double C” section, composed of two sections connected by webs are taken into account to simulate different degrees and patterns of corrosion that appears uniformly along the inner and the outer column surfaces. Reduction of the cross-sectional area that appears due to corrosion, results in decreasing of the cross-sectional moment of inertia, variation of the principal central axes position and slope as well as in appearance of eccentricity of loading and in appearance of an additional bending moments. Reduction of the column compressive strength, changing of the buckling mode, e.g. from the flexural mode into warping, considerable increase of the column displacement are observed results of the surface corrosion growth. The theory of thin-walled bars is applied for the analysis.

Stress–strain model for fibre-reinforced polymer confined rectangular columns

Applying fibre-reinforced polymer sheets around existing columns is an innovative technique in the field of civil engineering due to their high stiffness and strength-to-weight ratio, corrosion resistance and potentially high durability. The confinement effect of high-stiffness fibre jackets simply results in an increase in the compressive strength of columns. Various constitutive models have been constructed to predict the increase in the axial strength of concrete due to the confinement effect of fibre-reinforced polymer laminates. In this paper, a new stress–strain model is proposed for square/rectangular concrete columns confined with fibre-reinforced polymer jackets. The model is an extension of previous work on circular columns, adopting a previously proposed relation to plot the stress–strain curves. The proposed model utilises a failure criterion of concrete under triaxial compression, unlike the most existing models which rely on a previously presented general formulation. A large comparative study of 163 square/rectangular concrete specimens is performed on the basis of the prediction accuracy of existing models and the proposed approach for their ultimate strengths in compression. The recommended axial stress–strain plots are used to simulate the uniaxial compressive tests. The results confirmed that the axial stress–strain relationship evaluated by the presented technique can appropriately describe the deformation under uniaxial compressive loading.

Evaluation of Ayrton–Perry formula to predict the compressive strength of batten columns

This research was performed to evaluate two analytical methods for predicting the compressive strength of batten columns. Batten columns were subjected to pure axial compression, and the compressive strength was measured. The analytical methods used included the well-known Ayrton–Perry and ultimate strength curve methods to calculate the compressive strength of imperfect solid web columns, but their validity has not yet been studied experimentally on built-up columns. The geometrical parameters considered included the batten plate spacing and dimensions and the distance between the two longitudinal chords. The results show that the analytical methods were generally valid for the prediction of the compressive strength in batten columns and solid web columns. Using the average results of the Ayrton–Perry and ultimate strength curve methods leads to the best prediction of the column compressive strength. It was also shown that the initial imperfections in the batten columns could have a more important effect than the geometrical specifications on the value of compressive strength.

Influence of Concrete Tensile Ductility on Compressive Strength of Confined Columns

A theory founded on a suitable failure criterion for concrete and on a constitutive law in uniaxial tension derived from the failure criterion is developed for axially loaded confined concrete columns. The influence of the tension‐softening behavior of the external concrete shell on the compressive strength of columns is considered, and curves are derived describing the failure axial stress as a function of the tensile strain in the cover. A critical value of the transverse reinforcement percentage is found, for which axial stress and load always increase in the total range of tensile strain. Simple expressions for axial stress and strain and for the corresponding compressive strengths are provided for three particular failure limit states. The experimental comparisons show that for static or quasi‐static and for dynamic loading, failure occurs when the tensile peak or ultimate strain values are reached in the cover, while yielding of confining steel is even reached but only in the case of low transverse ...