Circular Columns Research Articles

Post-blast capacity evaluation of concrete-filled steel tubular (CFST) column based on machine learning technique

In the present study, the post-blast axial load-bearing capacity of the CFST column under the close-in explosion is investigated. Dynamic response and residual axial load capacity (RALBC) of 1599 circular CFST columns are numerically studied using a validated finite element model. The effects of column dimensions, material properties, blast loading, and axial load ratio are discussed. Based on the huge database, prediction models of RALBC are developed using three commonly used machine learning techniques including Extreme Gradient Boosting (known as XGBoost), Artificial Neutral Network (ANN), and Support Vector Regression (SVR). Comparison results show that the prediction model generated by the XGBoost performs the best among the three methods followed by the ANN and SVR methods. The RALBC of the CFST columns can be estimated rapidly and accurately with the prediction model developed in the present study. Finally, the feature importance of the input variables is analyzed using the additive feature attribution method SHAP (Shapley Additive ExPlanation). The results show that geometric parameters are the main factors impacting the RALBC of the CFST columns under close-in explosion.

Behavior of CFRP confined circular CFST columns reinforced with internal latticed steel angles under seismic loading

This paper investigated the hysteretic behavior of CFRP confined concrete-filled steel tube (CFST) reinforced with internal latticed steel angles. The parameters studied were the diameter-to-thickness ratio, the CFRP wrapping layers and the axial compression ratio. The failure modes, hysteretic curves, skeleton curves, stiffness degradation, ductility and energy dissipation capacity were presented and discussed. Experimental results revealed that the ultimate load and drift capacity increased by 18.8% and 33.5% when the plastic hinge region was confined by CFRP, all specimens failed due to the compression-bending failure in the plastic hinge region. Moreover, the CFRP can significantly improve the energy dissipation capacity under higher axial compression ratios. After testing, the developed finite element model was also used to perform parameter analysis, with a total of 53 specimens analyzed, and based on the parameter analysis results, the design equation for the drift capacity was proposed.

Performance of Hollow Concrete Filled Circular Steel Tube Column Subjected Axial Loading

To improve the behavior of hollow concrete filled steel tube, a novel type of reinforced hollow concrete circular steel tubular member (RHCFST) was put forward and its axial behavior was studied. The finite element analysis model of 12 RHCFST short columns under axial compression was established by using ABAQUS. The influence of steel tube’s strength and wall thickness, diameter of steel bar with normal strength, sandwich concrete’s thickness and strength on the mechanical properties of members were investigated. The results showed that the loading process can be defined as five stages: elastic, elastoplastic, descending, strengthen and gentle stage. The new composite structure has good cooperative performance. The ultimate bearing capacity increaseswith the increase of yield strength and wall thickness of steel tube, thickness and strength of sandwich concrete and diameter of steel bar with normal strength.

Estimation of lateral stress of stirrups at peak stress and residual stress of confined concrete at stirrups fractured in confined concrete under axial compression

The lateral stress of stirrups at the peak stress of confined concrete was closely related to the load-bearing capacity and deformability of concrete columns, while the fracture of stirrups affected the axial deformability of concrete columns after the peak stress of confined concrete. In this paper, 156 circular concrete columns confined with spiral stirrups and 141 square concrete columns confined with mesh stirrups were tested under axial compression. The effects of the compressive strength of unconfined concrete, the volumetric ratio and the yield strength of stirrups on the lateral stress of stirrups at peak stress and the residual stress of confined concrete at stirrups fractured were analyzed. Furthermore, the prediction models for evaluating the lateral strain of stirrups at the peak stress of confined concrete were established by considering the effects of the volumetric ratio and type of stirrups and the compressive strength of concrete, which had high prediction performance. In addition, the method for judging whether stirrups fractured or not was developed, which was suitable for evaluating the stirrups with and without yield platform. The prediction model for evaluating the residual stress of confined concrete at stirrups fractured was proposed.

Damage evaluation and failure mechanism analysis of axially compressed circular concrete-filled steel tubular column via AE monitoring

Concrete-filled steel tubular (CFST) columns are frequently used as the main load-bearing components in engineering structures due to their excellent load-bearing capacity. However, the presence of steel tube makes it impossible to accurately detect the damage characteristics of concrete by only relying on traditional mechanical measurement methods. This article quantitatively investigates the concrete damage of circular CFST column during axial compression based on the acoustic emission (AE) technique. Through the cumulative AE parameters including amplitude, count, and energy, the axial compression process of the CFST column can be divided into five main stages (Stage I is divided into two substages) to represent the different damage degree. The damage characteristics of concrete at each stage were explained by combining AE results and mechanical phenomena. A sensitivity analysis of the axial compression process was carried out using the Historic Index (HI) and Severity (Sr) and found that the sudden rise in HI and Sr corresponded to the changes in the different loading stages. The Improved b (Ib) value analysis calculated from the AE amplitudes reflects the evolution mechanism of the crack and can be used for the identification of the final failure moment of the specimen. Finally, a new method for processing and analyzing AE parameters was proposed, which effectively enhanced the dimensionality of real-time monitoring information on the damage of concrete filled in the steel tube.

An Application of BP Neural Network to the Prediction of Compressive Strength in Circular Concrete Columns Confined with CFRP

The neural network comprises many neurons with extensive interconnections operating parallel and performing specific functions. This paper establishes a BP neural network prediction model for the compressive strength of CFRP-confined concrete based on a large number of experimental data to study the predictive ability of the BP neural network on the compressive strength of CFRP-confined concrete and the output performance of the neural network model. The model is based on a BP neural network that has been trained using many experimental data. An investigation is being conducted on the effect of different data combinations on the accuracy of the predictions made by the neural network model. The high-precision BP network model is created into generic and simplified formulae for application convenience. These formulas are developed based on the theory of neural networks. The neural network models' findings and the empirical formulae for making predictions are compared and discussed. The BP neural network accurately predicts the compressive strength of CFRP-confined concrete, with over 90% of its data points having less than 15% error. In comparison, the regression model shows less accuracy, with less than 70% of its data points having an error within 15%. Compared to traditional regression models, the simple linear equation derived using Purelin instead of Sigmoid as the transfer function only adds a constant term. The average value of prediction/test results is 1.011. The analysis results show that BP neural network can extract the input and output parameters' data information well and obtain a high-accuracy prediction model. The coefficient of variation is 0.112, which indicates that the prediction accuracy and stability are greater than average.

RC columns strengthened with engineered cementitious composite (ECC) jacketing

This article aims to study the uniaxial compressive behavior of reinforced concrete (RC) columns strengthened with engineered cementitious composite (ECC) jackets. For this purpose, two advanced ECC mixtures containing polypropylene fibers were designed, and ECC jackets were cast to confine fourteen circular column specimens. Longitudinal and transverse grooving, sandblasting, and abrading were used as surface preparation techniques to achieve better adherence of ECC jackets to eight control (reference) column specimens, while two specimens with no surface preparation but with the same jacketing were used as a reference. The four remaining concrete column specimens lacking either internal reinforcement or an ECC jacket were used as control. All the specimens were subjected to concentric loading to determine the efficiency of ECC jacketing in enhancing load-carrying capacity and ductility. The experimental results revealed that compared to the control column, the reference specimens subjected to longitudinal grooving as surface preparation and ECC jacketing exhibited improvements of up to 1.3 and 2.5 times in their load-bearing capacity and energy absorption, respectively. Besides, ECC jacketing in specimens with the longitudinal grooving method increased the reference columns’ initial and secant stiffness values by up to 3.2 and 1.6 times, respectively. Finally, the models reported in the literature were evaluated in terms of their ability to capture the stress-strain curves of the ECC jacketed RC columns used in the present study.

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.

Optimization of reinforced concrete columns with variable circular cross-section hollowed using the criterion of instability and mechanical strength

PurposeThis study aims to optimize the structural design of reinforced concrete columns with variable hollow circular sections.Design/methodology/approachThe columns were optimized according to the criteria of instability (buckling) and mechanical strength (compression and/or tensile strength). To perform the optimizations, routines are developed in Python using the penalty and sequential linearization programming (SLP) function methods to optimize the elements satisfying the buckling and stress criteria.FindingsAt the end of the optimization process, the optimal section is obtained for the example of a circular column with a variable section, this section has an average radius of 5% smaller than that initially defined.Originality/valueThe theoretical basis for column optimization and the structuring of an algorithm in Python language for the computational resolution of these problems are presented in a didactic way, as well as the comparative efficiency of the methods.

Behavior of eccentrically loaded circular concrete-filled steel tube stub columns with localized corrosion

In this paper, 12 concrete-filled steel tube (CFST) stub columns with localized corrosion were tested under eccentric load. The effects of the depth ratio, size and location of localized corrosion, and loading eccentricity on the eccentric compression behavior of circular concrete-filled steel tube stub columns were investigated. A finite element model of circular CFST stub columns with localized corrosion under eccentric load was developed and then parameter analysis was carried out. Based on the experimental and numerical results, it was found that the load bearing capacity decreases with increasing the depth ratio and size of localized corrosion. The localized corrosion at the mid-height caused more significant capacity deterioration than that at the column ends. In addition, the localized corrosion with γ = 0° and 180° has more adverse effects on the capacity of eccentrically loaded CFST columns than that with γ = 90°. Moreover, the localized corrosion with γ = 0° (at compression side) is more harmful than that γ = 180° (at tension side) for the specimens with compression-controlled failure, and vice versa for the specimens with tension-controlled failure. Finally, a design model of eccentrically loaded CFST column with localized corrosion was proposed based on an established equivalent specimen. The results suggested that the proposed model predicted the load bearing capacities with reasonable accuracy.

A comparative study of concrete columns reinforced with steel and GFRP bars

In the world of structural and construction engineering, construction industry has been widely adapting new techniques along with advanced materials. These new techniques and advanced materials have lots of advantages over the long term of structures, serviceability, durability, ductility, strength, resistance, etc. When steel is used in marine environments, it corrodes quickly, which leads to damage of the structure. Hence Fiber Reinforced polymers can/replace steel partially or completely in RCC structures. In this study, short circular RCC columns made up of M20 grade concrete and reinforced with steel and GFRP bars are subjected to uniaxial compression is studied. In the experimental study, three short circular concrete columns reinforced completely with steel rebar and with 50% steel and 50% GFRP bar are cast and tested under concentric uniaxial compression. The behaviour of short circular concrete columns completely with steel as longitudinal reinforcement is compared with that of concrete columns reinforced with 50% steel and 50% GFRP bars. The compressive strength and ductility of short circular concrete columns reinforced 50% steel and 50% GFRP bars are found to be higher than columns with 100% steel reinforcement.

Effectiveness of Stiffeners in CFDST Columns: Comparative Study

Concrete-filled double-skin tube (CFDST) columns are considered one of most efficient forms of steel-concrete composite columns, which provide higher axial strength and better ductility compared with their counterpart concrete-filled tube (CFT) columns. This paper aims to numerically investigate and compare the performance of axially loaded circular CFDST short columns provided with stiffeners in inner tubes and outer tubes. Circular steel hollow sections have been adopted for inner as well as outer tubes, and rectangular steel stiffeners were fixed in inner and outer tubes to check the effectiveness of stiffeners in stiffened CFDST columns. These CFDST columns were investigated numerically by using a verified finite-element (FE) model from commercially available software. Behavior of 36 unstiffened, inner-tube stiffened, and outer-tube stiffened CFDST columns (12 each) was studied. The FE results were verified by comparing them with previous test results. The FE analysis study has exhibited an increase in peak load (load-carrying capacity) up to 26% and 15% in outer-tube stiffened CFDST columns compared with unstiffened and inner-tube stiffened CFDST columns, respectively. Also, enhanced ductility has been observed in case of these stiffened CFDST columns.

Compressive performance of SWSSC-filled CFRP-stainless steel composite tube columns

The structure of concrete confined by carbon fiber-reinforced polymer (CFRP) and stainless steel tubes was investigated. The columns, which take advantage of the ductility and corrosion resistance of stainless steel, are composed of stainless steel tube, core seawater and sea sand concrete (SWSSC) and outer FRP. Forty circular SWSSC-filled FRP-stainless steel composite tube columns (SCFSSCTs) were manufactured and subjected to axial compression tests. After fracturing of the FRP, the failure modes of the specimens mainly showed extrusion expansion, with a small amount of shear failure. The increase in the thickness of the stainless steel and the number of FRP layers resulted in a significant improvement in the load capacity and deformation capacity of the structure, which was more evident in the specimens with higher steel contents. With the increase in the number of FRP layers, the increases in ultimate stress and ultimate strain were 40.4% − 130.0% and 118.6% − 282.4%, respectively, compared with the column with single stainless steel confinement. The stress–strain curves for the SCFSSCTs were similar to those of structures reinforced by FRP and carbon steel and were divided into four stages. Models were proposed to predict the full axial stress–strain curves of SCFSSCTs, including the ultimate point and the peak point.

Experimental study on the mechanical properties of concrete canvas and CFRP jointly confined circular concrete columns under axial compression

Concrete canvas (CC) has good corrosion resistance and fire resistance, but it is rarely used in civil engineering. In this study, CC and carbon fiber-reinforced polymer (CFRP) are jointly used to reinforce concrete columns (i.e., jointly confined specimens) to expand their engineering application. To explore the axial compressive performance of combined CC-CFRP confinement concrete columns, 13 sets of specimens were designed in this study based on the number of CFRP layers, number of CC layers and volumetric stirrup ratio. The conclusions are as follows: 1) based on acoustic emission (AE) technology, the presence of CC can improve the uneven deformation of the concrete, and the jointly confined specimen has better energy dissipation capacity; 2) based on the experimental data, the peak stress of the jointly confined specimen is reduced by up to 10% compared with the CFRP-confined specimen (i.e., the single confined specimen), and the ultimate strain is increased by at least 56.2%, which shows that the jointly confined method is reasonable and feasible; and 3) the peak stress and ultimate strain models of the jointly confined specimen are obtained by numerical fitting, and a stiffness-based design-oriented compressive stress–strain model for the jointly confined specimen is proposed. Compared to existing models, the proposed model has higher accuracy, which can provide a theoretical basis for further research.

Prediction of Axial Compressive Load-Strain Curves of Circular Concrete-Filled Steel Tube Columns Using Long Short-Term Memory Network.

No study has been reported to use machine learning methods to predict the full-range test curves of circular CFST columns. In this paper, the long short-term memory (LSTM) network was introduced to calculate the axially compressive load-strain curves of the circular CFST columns according to an experiment database of limited scale. To improve the feasibility of input data for the recurrent neural network algorithm, data preprocessing methods and data configurations were discussed. The prediction results indicate that the LSTM network provides more accurate estimations compared with the artificial neural networks, random forest and support vector regression. Meanwhile, this method can be used to calculate the mechanical properties including the elastic modulus, ultimate bearing capacity, and the ductility of the columns with acceptable accuracy for engineering practice (the prediction error within 20%). For future research, it is expected that the machine learning method will be applied to predict the structural response of different members under various loading conditions.

Investigation of Circular Hollow Concrete Columns Reinforced with GFRP Bars and Spirals

Glass fiber-reinforced polymer (GFRP) reinforcements are useful alternatives to traditional steel bars in concrete structures, particularly in vertical structural elements such as columns, as they are less prone to corrosion, and impart increasing strength and endurance of buildings. There is limited research on the finite element analysis (FEA) of the structural behavior of hollow glass fiber-reinforced polymer reinforced concrete (GFRPRC) columns. The hollow portion can be used for the service duct and for reducing the self-weight of the members. Numerical analysis of the compressive response of circular hollow concrete columns reinforced with GFRP bars and spirals is performed in this study. This article aims to investigate the axial behavior of hollow GFRP concrete columns and compare it with that of solid steel reinforced concrete (RC) columns as well as hollow steel RC columns. The Abaqus software is used to construct finite element models. After calibration of modeling using an experimental test result as a control model, a parametric study is conducted. The columns with the same geometry, loading, and boundary conditions are analyzed in the parametric study. It is resulted that the hollow GFRP concrete columns provide a greater confinement effect than the solid steel RC columns. The average variation in the ultimate axial load-carrying capacities of the experimental results, from that of the FEA values, is noted to be only 3.87%, while the average difference in the corresponding deformations is 7.08%. Moreover, the hollow GFRP concrete columns possess greater axial load and deformation capacities compared with the solid steel RC columns.

Mechanical Performance of Hybrid Graphene Nanoplates, Fly-Ash, Cement, Silica, and Sand Particles Filled Cross-Ply Carbon Fibre Woven Fabric Reinforced Epoxy Polymer Composites Beam and Column

The main goal of this study is to reduce the brittleness of a fibre-reinforced cement base structure when exposed to the effects of graphene nanoplates, fly ash, silica, sand, and cement fillers to better understand the effect of hybrid nano/micro particle fillers on the mechanical performance of cross-ply carbon fibre reinforced epoxy resin composites. A three-point bending test through the width was used to measure flexural strength. The impact tests Izod at low impact velocity and Charpy through the thickness were used to determine the dynamic fracture strengths of pre-cracked and non-cracked composite samples. Also, the compressive test method was used to measure the compressive strength of hybrid particles and short glass fibre-reinforced epoxy resin composite square and circular columns. The results show compressive strength and flexural strength. Izod impact energy, Charpy impact energy, and dynamic fracture toughness of hybrid nano/microparticle-filled fibre composites have higher values than virgin fibre composites due to the influence of graphene nanoparticles and perfect interface bonding between two dissimilar molecules of nano and microparticles, which improve the fracture toughness and absorb impact energy. Overall, the results indicate that molecules of nano/microparticle-filled carbon fibre and glass fibre-reinforced epoxy resin composites can be used in aggressive environments because of the improved mechanical properties in comparison to the virgin fibre composites. In addition, SEM micrographs clearly indicate that nano- and microparticles are resistant crack propagation and deboned of matrix fibres.

Simplified deep-learning approach for estimating the ultimate axial load of circular composite columns

Simplified deep-learning approach for estimating the ultimate axial load of circular composite columns

Experimental behavior of circular concrete-filled steel tabular columns under near-fault cyclic loadings

This study investigated the behavior of concrete-filled steel tabular (CFST) columns under near-fault cyclic loading experimentally. Ten CFST columns were tested: one under monotonic loading, one under conventional cyclic loading, and other eight under near-fault cyclic loadings. The results indicated that slow local buckling occurred at plastic hinges after 4%-drift cycles, resulted in slow strength degradation and pinching. These became more pronounced as the cycle amplitude increased. Load-carrying and deformation capacities marginally decreased by the effect of cyclic loading. Secant stiffness sharply dropped by the pulses of 4%-drift amplitude. The earlier arrival of the pulses caused higher drops of secant stiffness. Near-fault pulses imposed a considerable large amount of energy to columns, which resulted in slow local buckling, slow strength degradation, but significant stiffness degradation. Shifting the pulse cycles to the cycle five of a conventional cyclic loading history was proposed for testing structural components under near-fault earthquakes.

Experimental and numerical studies of the eccentric compressive behavior of circular RC columns strengthened with grouting-filled steel tubes

The reinforcement of concrete columns with steel tubes is a convenient and economical technique in civil engineering. To investigate the mechanical behavior of short circular concrete columns strengthened with grouting-filled steel tubes under eccentric compressive loads, five specimens with different eccentricities were tested in the present work. Finite element simulations were carried out in ABAQUS software to analyze the mechanical behavior of the reinforced columns. A parametric study was performed to evaluate the influences on the SRF, RCR, P-M, and P/Pu-M/Mu curves of the reinforced columns. The results showed that increasing the yield strength and thickness of the steel tube improved the performance of the reinforced columns. The ultimate load-carrying capacities of the specimens determined by the codes were compared with those determined by the proposed formulas. The results also showed that the ultimate load-carrying capacities of the specimens determined by the proposed formulas were more accurate.