CFRP strengthening of steel columns subjected to eccentric compression loading

Amir Hamzeh Keykha 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.1

Steel structures often require strengthening due to the increasing life loads, or repair caused by corrosion or fatigue cracking. Carbon Fiber Reinforced Polymers (CFRP) is one of the materials used to strengthen steel structures. Most studies on strengthening steel structures have been carried out on steel beams and steel columns under centric compression load. No independent article, to the author's knowledge, has studied the effect of CFRP strengthening on steel columns under eccentric compression load, and it seems that there is a lack of understanding on behavior of CFRP strengthening on steel columns under eccentric compression load. However, this study explored the use of adhesively bonded CFRP flexible sheets on retrofitting square hollow section (SHS) steel columns under the eccentric compression load, using numerical investigations. Finite Element Method (FEM) was employed for modeling. To determine ultimate load of SHS steel columns, eight specimens with two types of section (Type A and B), strengthened using CFRP sheets, were analyzed under different coverage lengths, the number of layers, and the location of CFRP composites. Two specimens were analyzed without strengthening (control) to determine the increasing rate of the ultimate load in strengthened steel columns. ANSYS was used to analyze the SHS steel columns. The results showed that the CFRP composite had no similar effect on the slender and stocky SHS steel columns. The results also showed that the coverage length, the number of layers, and the location of CFRP composites were effective in increasing the ultimate load of the SHS steel columns.

Experimental Performance Evaluation of Concrete-Filled Steel Tube Columns Confined by High-Strength Steel Bolts

Salih K. Alrebeh,Ahmed D. Ahmed,Ali K. Al-Asad,Talha Ekmekyapar 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.4

Concrete-steel composite columns have been utilized prevalently as load-bearing members in structures. The present study investigates the uniaxial behavior of concrete-filled steel tube (CFST) columns, which were proposed to provide high-strength steel bolts as external confinement to enhance the structural behavior of CFST columns. A total of 18 CFST columns were designed, out of which 12 columns were confined with steel bolts and 6 columns were unconfined; all columns were tested under axial compression. A mixture of self-compacting concrete (SCC) was utilized to fill all the test specimens. This study proposed an innovative approach to increase the restriction on lateral expansion of steel wall during elastic loading stage, which is expected to enhance structural behavior of CFST column. Test parameters included the effect of steel bolt spacing, three different (L/D) ratios, and two diffrent (D/t) ratios. The test findings demonstrated that the compression strength, axial stiffness, toughness, and ductility behavior of CFST columns increase as the spacing of steel bolts decreases and the improvement becomes more pronounced as the (L/D) and (D/t) ratios decrease. In addition, the compression capacity of the improved CFT short, medium, and long columns were enhanced by 25.3, 9, and 3.5%, respectively. A design model was developed to estimate the ultimate compression behavior of the improved CFST columns using steel bolts, and a close correlation was obtained between experimental findings and the proposed model.

Mechanical behaviour of composite columns composed of RAC-filled square steel tube and profile steel under eccentric compression loads

Hui Ma,Jiacheng Xi,Yaoli Zhao,Jikun Dong 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.38 No.1

This research examines the eccentric compression performance of composite columns composed of recycled aggregate concrete (RAC)-filled square steel tube and profile steel. A total of 17 specimens on the composite columns with different recycled coarse aggregate (RCA) replacement percentage, RAC strength, width to thickness ratio of square steel tube, profile steel ratio, eccentricity and slenderness ratio were subjected to eccentric compression tests. The failure process and characteristic of specimens under eccentric compression loading were observed in detail. The load-lateral deflection curves, load-train curves and strain distribution on the cross section of the composite columns were also obtained and described on the basis of test data. Results corroborate that the failure characteristics and modes of the specimens with different design parameters were basically similar under eccentric compression loads. The compression side of square steel tube yields first, followed by the compression side of profile steel. Finally, the RAC in the columns was crushed and the apparent local bulging of square steel tube was also observed, which meant that the composite column was damaged and failed. The composite columns under eccentric compression loading suffered from typical bending failure. Moreover, the eccentric bearing capacity and deformation of the specimens decreased as the RCA replacement percentage and width to thickness ratio of square steel tube increased, respectively. Slenderness ratio and eccentricity had a significantly adverse effect on the eccentric compression performance of composite columns. But overall, the composite columns generally had high-bearing capacity and good deformation. Meanwhile, the mechanism of the composite columns under eccentric compression loads was also analysed in detail, and the calculation formulas on the eccentric compression capacity of composite columns were proposed via the limit equilibrium analysis method. The calculation results of the eccentric compression capacity of columns are consistent with the test results, which verify the validity of the formulas, and the conclusions can serve as references for the engineering application of this kind of composite columns.

Behaviour and design of demountable steel column-column connections

Dongxu Li,Brian Uy,Vipul Patel,Farhad Aslani 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.2

This paper presents a finite element (FE) model for predicting the behaviour of steel column-column connections under axial compression and tension. A robustness approach is utilised for the design of steel columncolumn connections. The FE models take into account for the effects of initial geometric imperfections, material nonlinearities and geometric nonlinearities. The accuracy of the FE models is examined by comparing the predicted results with independent experimental results. It is demonstrated that the FE models accurately predict the ultimate axial strengths and load-deflection curves for steel column-column connections. A parametric study is carried out to investigate the effects of slenderness ratio, contact surface imperfection, thickness of cover-plates, end-plate thickness and bolt position. The buckling strengths of steel column-column connections with contact surface imperfections are compared with design strengths obtained from Australian Standards AS4100 (1998) and Eurocode 3 (2005). It is found that the column connections with maximum allowable imperfections satisfy the design requirements. Furthermore, the steel column-column connections analysed in this paper can be dismantled and reused safely under typical service loads which are usually less than 40% of ultimate axial strengths. The results indicate that steel column-column connections can be demounted at 50% of the ultimate axial load which is greater than typical service load.

Numerical investigation of SHS steel beam-columns strengthened using CFRP composite

Amir Hamzeh Keykha 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.25 No.5

Carbon Fiber Reinforced Polymer (CFRP) is one of the materials used to strengthen steel structures. Most studies on strengthening steel structures have been done on steel beams and steel columns. No independent study, to the researcher’s knowledge, has studied the effect of CFRP strengthening on steel beam-columns, and it seems that there is a lack of understanding on behavior of CFRP strengthening on steel beam-columns. However, this study explored the use of adhesively bonded CFRP flexible sheets on retrofitting square hollow section (SHS) steel beam-columns, using numerical investigations. Finite Element Method (FEM) was employed for modeling. To determine the ultimate load of SHS steel beam-columns, ten specimens, eight of which were strengthened with the different coverage length and with one and two CFRP layers, with two types of section (Type A and B) were analyzed. ANSYS was used to analyze the SHS steel beam-columns. The results showed that the CFRP composite had no similar effect on the slender and stocky SHS steel beam-columns. The results also showed that the coverage length, the number of layers, and the location of CFRP composites were effective in increasing the ultimate load of the SHS steel beam-columns.

Numerical analysis and horizontal bearing capacity of steel reinforced recycled concrete columns

Hui Ma,Jian-yang Xue,Yunhe Liu,Jing Dong 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.22 No.4

This paper simulates the hysteretic behavior of steel reinforced recycled concrete (SRRC) columns under cyclic loads using OpenSees software. The effective fiber model and displacement-based beam-column element in OpenSees is applied to each SRRC columns. The Concrete01 material model for recycled aggregate concrete (RAC) and Steel02 material model is proposed to perform the numerical simulation of columns. The constitutive models of RAC, profile steel and rebars in columns were assigned to each fiber element. Based on the modelling method, the analytical models of SRRC columns are established. It shows that the calculated hysteresis loops of most SRRC columns agree well with the test curves. In addition, the parameter studies (i.e., strength grade of RAC, stirrups strength, steel strength and steel ratio) on seismic performance of SRRC columns were also investigated in detail by OpenSees. The calculation results of parameter analysis show that SRRC columns suffered from flexural failure has good seismic performance through the reasonable design. The ductility and bearing capacity of columns increases as the increasing magnitude of steel strength, steel ratio and stirrups strength. Although the bearing capacity of columns increases as the strength grade of RAC increases, the ductility and energy dissipation capacity decreases gradually. Based on the test and numerical results, the flexural failure mechanism of SRRC columns were analysed in detail. The computing theories of the normal section of bearing capacity for the eccentrically loaded columns were adopted to calculate the nominal bending strength of SRRC columns subjected to vertical axial force under lateral cyclic loads. The calculation formulas of horizontal bearing capacity for SRRC columns were proposed based on their nominal bending strength.

Hysteretic behaviors and calculation model of steel reinforced recycled concrete filled circular steel tube columns

Hui Ma,Guoheng Zhang,A. Xin,Hengyu Bai 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.83 No.3

To realize the recycling utilization of waste concrete and alleviate the shortage of resources, 11 specimens of steel reinforced recycled concrete (SRRC) filled circular steel tube columns were designed and manufactured in this study, and the cyclic loading tests on the specimens of columns were also carried out respectively. The hysteretic curves, skeleton curves and performance indicators of columns were obtained and analysed in detail. Besides, the finite element model of columns was established through OpenSees software, which considered the adverse effect of recycled coarse aggregate (RA) replacement rates and the constraint effect of circular steel tube on internal RAC. The numerical calculation curves of columns are in good agreement with the experimental curves, which shows that the numerical model is relatively reasonable. On this basis, a series of nonlinear parameters analysis on the hysteretic behaviors of columns were also investigated. The results are as follows: When the replacement rates of RA increases from 0 to 100%, the peak loads of columns decreases by 7.78% and the ductility decreases slightly. With the increase of axial compression ratio, the bearing capacity of columns increases first and then decreases, but the ductility of columns decreases rapidly. Increasing the wall thickness of circular steel tube is very profitable to improve the bearing capacity and ductility of columns. When the section steel ratio increases from 5.54% to 9.99%, although the bearing capacity of columns is improved, it has no obvious contribution to improve the ductility of columns. With the decrease of shear span ratio, the bearing capacity of columns increases obviously, but the ductility decreases, and the failure mode of columns develops into brittle shear failure. Therefore, in the engineering design of columns, the situation of small shear span ratio (i.e., short columns) should be avoided as far as possible. Based on this, the calculation model on the skeleton curves of columns was established by the theoretical analysis and fitting method, so as to determine the main characteristic points in the model. The effectiveness of skeleton curve model is verified by comparing with the test skeleton curves.

Thermo-mechanical compression tests on steel-reinforced concrete-filled steel tubular stub columns with high performance materials

David Medall,Carmen Ibáñez,Ana Espinós,Manuel L. Romero 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.49 No.5

Cost-effective solutions provided by composite construction are gaining popularity which, in turn, promotes the appearance on the market of new types of composite sections that allow not only to take advantage of the synergy of steel and concrete working together at room temperature, but also to improve their behaviour at high temperatures. When combined with high performance materials, significant load-bearing capacities can be achieved even with reduced cross-sectional dimensions. Steel-reinforced concrete-filled steel tubular (SR-CFST) columns are one of these innovative composite sections, where an open steel profile is embedded into a CFST section. Besides the renowned benefits of these typologies at room temperature, the fire protection offered by the surrounding concrete to the inner steel profile, gives them an enhanced fire performance which delays its loss of mechanical capacity in a fire scenario. The experimental evidence on the fire behaviour of SR-CFST columns is still scarce, particularly when combined with high performance materials. However, it is being much needed for the development of specific design provisions that consider the use of the inner steel profile in CFST columns. In this work, a new experimental program on the thermo-mechanical behaviour of SR-CFST columns is presented to extend the available experimental database. Ten SR-CFST stub columns, with circular and square geometries, combining high strength steel and concrete were tested. It was seen that the circular specimens reached higher failure times than the square columns, with the failure time increasing both when high strength steel was used at the embedded steel profile and high strength concrete was used as infill. Finally, different proposals for the reduction coefficients of high performance materials were assessed in the prediction of the cross-sectional fire resistance of the SR-CFST columns.

Experimental and numerical study on fire resistance of tubed steel-reinforced concrete stub columns under eccentric compression

Jie-Peng Liu,Yonghui Xing,Keyan Song,Wei-Yong Wang 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.4

This paper presents a series of eight fire tests conducted on circular tubed steel-reinforced concrete columns subjected to eccentric loads. The cross-sectional temperature, axial displacements, fire resistance, and failure modes were recorded and discussed. The influence of key parameters-load ratio, load eccentricity, and wall thickness of the steel tube—on the deformation and fire resistance of the circular tubed steel-reinforced concrete columns were also investigated. Subsequently, the coupled thermal–stress model was developed using the ABAQUS program to investigate the effects of key parameters on both thermal distribution and fire resistance. For the thermal analysis, the considered parameters comprised the cross-section dimensions, the thickness of the steel tube, and types of concrete, and for the fire resistance analysis, they were the load ratio, load eccentricity, thickness of the steel tube, and concrete and H steel strengths. The results showed that the cross-section dimensions have a relatively larger influence than the thickness of the steel tube and the types of concrete on the temperature distribution of the columns. Regarding the fire resistance of the columns, the effects of the load ratio and thickness of the steel tube are remarkable, whereas the concrete and H steel strengths and the load eccentricity have a minor influence. The calculation methods were simplified to determine the steel temperature of a column in a fire, and the N–M curves of the eccentric members subjected to ISO 834 standard temperature are presented. Using the simplified methods, the steel temperature, and the N–M curves of the eccentric circular tubed steel-reinforced concrete columns can be evaluated for any value of the significant parameters, such as the thickness of the steel tube, load ratio, and concrete strength.

The Composite Steel Reinforced Concrete Column Under Axial and Seismic Loads: A Review

Mostafa M. A. Mostafa,Tao Wu,Xi Liu,Bo Fu 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.6

The composite steel reinforced concrete (SRC) columns with the form of partial or full encasement of the steel section in the reinforced concrete (RC) have attracted pervasive attention due to their advantages compared to the conventional RC columns. This paper aims to summarize the representative publications regarding the SRC columns. Firstly, the analytical studies of the SRC columns, including comparative studies between available codes to address the philosophy of design and the limits in the available codes of design, bond slip behavior, analytical confi nement material models, and fi nite element analysis, are addressed. In addition, the discussion and summary of the axial behavior of the SRC columns and the important parameters aff ecting the axial behavior of these types of columns were included. It also attempts to cover the parameters aff ecting the seismic behavior of the SRC columns. Important progress has been made by the previous studies in the SRC columns under the axial load and the combination of axial and seismic loads, but they fundamentally focused on the columns with the simple arrangement of steel section, and a few attention was paid to the new type of SRC columns with rotated cross-shaped steel section whose webs coincide with the diagonal lines of the columns’ section. Due to the lack of study and the brittle failure of the columns with lightweight and high strength concrete, more studies should still be made to know the behavior of the SRC columns. The paper concludes with suggestions for the future studies to enhance the eff ectiveness of the SRC columns.