Concrete Encased Steel Columns Research Articles

Investigation the behavior of LWAC encased steel columns after exposure to elevated temperature

AbstractThis paper presents experimental and numerical investigations on the behavior of eccentrically loaded lightweight aggregate concrete encased steel (LWACES) columns after exposing to elevated temperatures. Sixteen concrete encased steel (CES) columns were considered in the study, 12 of which were exposed to elevated temperature then eccentrically loaded up to failure at different eccentricity ratios. The effect of temperature on the load–displacement relationships, failure load, and failure modes of the concrete encased steel (CES) columns was monitored and evaluated. Experimental results have shown that as the temperature increases, the load bearing capacity of the CES columns decreased. It has also been showed that, at high temperature, the normal‐weight concrete encased steel (NWCES) columns experienced larger degradation of the load bearing capacity compared to that of LWACES columns. Also, this study presents a numerical simulation of the behavior of LWACES columns at elevated temperatures with eccentric compressive load. The numerical model was implemented in conducting parametric study to understand the effect of temperature distribution, concrete cover, eccentricity ratio, and high temperature levels on the behavior of the thermally exposed (CES) columns. Numerical results have revealed that, at temperature value of 500°C, the ultimate capacity of LWACES with eccentricity ratios of 0.75, and 1 has decreased by 17%, and 23%, respectively, compared to that of the column with eccentricity ratio of 0.5.

The Seismic Behavior of Rectangular Concrete-Encased Steel Bridge Piers: A Review

This paper proposes a review of the previous research work and the representative publications regarding the seismic behavior of the concrete-encased steel (CES) columns. Concrete-encased steel sections are composed of steel sections encased in reinforced concrete members. The research work recently showed increased attention to this type of column due to its advantages compared to conventional reinforced concrete columns. Firstly, the analytical studies of the behavior of the CES columns under axial loads, including comparative studies between different research works, are presented. Then, the behavior of the CES columns under combined axial and flexural loads is also highlighted. An overview of the analytical confinement material models is addressed. In addition, the discussion and summary of the seismic behavior of the CES columns and the important parameters affecting the seismic behavior of these types of columns are included. Although important progress has been made by the previous studies in the CES columns under the axial load and the combination of axial and seismic loads, they fundamentally focused on the building columns, and little attention was paid to the impact of lateral reinforcement and their configuration in bridge piers. Due to the lack of studies on the parameters affecting the seismic behavior of the bridges, more studies should still be made to better understand the behavior of the CES bridge piers. This paper provides a reference for the research and engineering practice of concrete-encased steel bridge piers. It also concludes with suggestions for future studies to integrate the seismic requirement of the CES bridge piers in Canada.

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%.

Study on seismic performance of prestressed composite joint with CESA columns

Several issues persist in the design and construction of conventional prestressed concrete encased steel (CES) frame structures. This includes the need to strengthen the steel flanges and webs during the passage of prestressed tendons and longitudinal reinforcements through the joint, and insufficient compaction of the concrete cast in the joint core. Therefore, a novel type of prestressed CES frame structure was developed using concrete-encased steel angle (CESA) columns to replace the conventional CES columns. To investigate the seismic shear performance of this new type of prestressed composite joints to propose a method for predicting the shear capacity of joint cores, this study performed tests and nonlinear analysis on three prestressed joints and one non-prestressed joint under low cyclic loading. The failure patterns, energy dissipation, stiffness degradation, deformation recovery performance, and ductility properties were examined for these joints. The effects of prestress level, axial compression ratio, web thickness, stirrup ratio, and steel angle ratio are also discussed. Two formulas are proposed to predict the shear capacity of joint cores based on the fitting of tests and finite element analysis. The results revealed that the oblique crushing of concrete occurred in the joint core at the peak load, resulting in shear failure. Increasing the thickness of the steel web effectively enhanced the horizontal peak load to increase the shear capacity in the joint core. However, an increase in the axial compression ratio may reduce ductility. The formulas developed to predict the shear capacity of the joint core exhibited much higher accuracy, where the simplified practical formula can facilitate convenient design implementation. Overall, these findings demonstrate excellent seismic shear behavior for prestressed composite joints while providing technical support for applications in such types of prestressed frame structures.

Numerical simulation of size effect in concrete-encased high-strength steel columns under axial compression

Concrete-encased steel (CES) columns are extensively utilized in practical engineering due to their outstanding performance. However, there have been limited studies on the size effect of CES columns. To investigate the influences of stirrup ratio, steel ratio, and steel strength grade on the axial capacity and the mechanism of the size effect of members under axial compression, a finite element (FE) analysis model that considers the interaction between the size effect and the confinement effect is established and verified. The study results demonstrate that the nominal stress of CES columns can be remarkably increased by employing high-strength steel and enhancing the steel ratio. However, the nominal stress decreases as the cross-sectional size of specimen increases, indicating the presence of the size effect. Moreover, increasing the steel strength grade, stirrup ratio, and steel ratio can decrease the degree of reduction of the nominal stress. Furthermore, comparison of the FE analysis findings and the calculation results of EN1994–1–1:2010(Europe), AISC360–16 (U.S.), and JGJ138–2016(China) revealed that the three codes fail to accurately assess the axial capacity of CES columns. The accuracy and safety reserve of the codes calculation results are even more inadequate for the larger cross-sectional specimens. Finally, a theoretical formula that considers the size effect and confinement effect is developed to calculate the bearing capacity of CES columns, and its applicability and reliability are verified.

Negative stiffness-enhanced seismic damping technology for an over-track complex with concrete-encased steel columns

The resilient transit-oriented model stimulates the necessity of seismic performance enhancement or retrofitting of over-track complexes with concrete-encased steel slender supporting columns. This study proposes a novel low-damping-ratio-based vibration control approach and easy-to-use design for over-track complexes by flexibly installing the negative stiffness amplification system (NSAS) at the multistory of the over-track building and lower podium. Moreover, a multilocation-oriented design strategy and fitted formulae are developed for the NSAS-damped complex with enhanced energy-dissipation efficiency and an adjustable structural modal shape. By utilizing the negative stiffness device, dashpot, and tuning spring, the NSAS is theoretically constructed, and a simplified model of the NSAS-damped over-track complex is established. Stochastic response analysis and parametric investigation are performed to quantify the benefit of the NSAS-damped story over the conventional control method. Then, easy-to-use design formulae are provided in the initial design and parameter modification stages to realize the simultaneous control of the upper and lower structures. Based on a typical over-track complex with concrete-encased steel slender supporting columns, design cases are analyzed for the NSAS and conventional viscous dampers to verify the applicability of the proposed NSAS and design. The results indicate that the target-story located NSASs contribute a higher-efficiency approach to realize the significant performance improvement or retrofit of the over-track complexes without perturbing the daily function. Particularly, NSASs tailored for distinct stories in the over-track complex effectively satisfy the modification demand for structural modal shape and enhanced energy dissipation efficiency, which cannot be realized by conventional viscous dampers or the existing design of NSASs in normal buildings. In addition, the NSAS-damped story demonstrates a released stiffness abruptness and robust seismic performances against various earthquakes.

Lateral load-displacement response of flexure-dominant concrete-encased steel columns based on ASCE/SEI 41

Concrete-encased steel (CES) column, in which structural steel is encased in an RC section, is widely used in high-rise or heavily-loaded structures due to its great load-carrying capacity, rigidity, and durability. Nevertheless, the development of performance-based seismic design is still insufficient for CES structures, especially for evaluating the lateral load-displacement relationship. As a commonly-used performance-based seismic design (PBSD) guidance, current ASCE/SEI 41 guides global engineers to conduct the seismic evaluation of RC, steel, masonry, and timber structures. Nevertheless, ASCE/SEI 41 fails to give the modeling parameters for CES members owing to insufficient research concerning the steel-concrete interaction. In this paper, a lateral load-displacement curve for flexure-dominant CES columns under a nonlinear static procedure is proposed based on the provisions of RC members in the current ASCE/SEI 41. In the proposed curve, different constitutive laws are applied to consider different confinement of concrete; the slip between the structural steel and surrounding concrete is considered by reduced lateral stiffness; meanwhile, the end rotation caused by the bar-slip in RC is also taken into account to simulate the lateral behavior better. With a detailed calculation procedure, a comparison with experimental results of 42 CES columns in different references is reported to verify the applicability of the proposed curve. It can be concluded that the proposed curve can produce reasonable predictions of cracking load, cracking displacement, yield load, yield displacement, peak displacement, and strength degradation of flexure-dominant CES columns, leading to a feasible way to evaluate the lateral response of CES columns in practical design.

Confinement detailing of concrete encased steel concrete composite columns

Steel concrete composite construction is now gaining popularity in our country. Concrete-encased steel columns have several advantages, but like RC columns, there is a need to ensure adequate concrete confinement so that it has sufficient ductility under seismic loads. This study investigates the confinement of the concrete based on the detailing of the transverse reinforcement. The ductilities of a typical encased section that satisfies the minimum reinforcement criteria and a highly confined section with special detailing are compared. A nonlinear 3D finite element model is developed in ABAQUS for this purpose. The confined stress-strain curve for M30 grade of concrete is carefully incorporated in the special confined section. The interaction between structural steel and concrete is modelled with an 'embedded region' interaction tool available in the ABAQUS library. Based on the eigen mode of the section, the initial geometric imperfection was given. The significant increment in displacement ductility factor, plastic hinge rotation and drift ratio are observed for a special confined encased column. A parametric study has been carried out by varying the parameters; the axial load ratio, steel contribution ratio, steel width to depth ratio and transverse reinforcement spacing. It was observed that structural section aspect ratio (steel width to depth) and transverse reinforcement spacing significantly affect the ductility of the section. The plastic hinge rotation and drift ratios were also calculated for different sections.

Behavior and model evaluation of large-rupture-strain (LRS) FRP-confined concrete-encased high-strength steel columns under axial compression

Fiber reinforced polymers (FRP)-confined concrete-encased steel columns (FCSCs) have become increasingly popular. However, few studies have been conducted on the FCSCs with a large-rupture-strain (LRS) FRP tube. To this end, the axial compressive behavior of FCSCs with a polyethylene terephthalate (PET) FRP tube (PFCSCs) is investigated in this study. A total of eighteen circular stub columns (i.e., two unconfined specimens, four PET FRP-confined concrete columns (PFCCs), and twelve PFCSCs) were tested under axial compression, in which the PET FRP tube thickness, the shape and nominal yield strength of the encased steel sections were the focal points. The results indicate that the steel strength can be fully utilized because local instability of the encased steel sections can be well suppressed by the surrounding concrete. The specimens with a circular steel tube had better performance than those with a cruciform steel due to the additional confinement provided by the circular steel tube. Moreover, a model assessment suggested that the models of Lin et al. and Zeng et al. could provide relatively satisfactory predictions for the ultimate stress and strain of confined concrete in PFCSCs.

Seismic behavior of 3-D beam to L-shaped concrete encased steel composite column joint: An experimental study

Experimental investigations were conducted on the behavior of three-dimensional (3-D) beam to L-shaped concrete encased steel (CES) composite column joint under seismic loading. A total of nine corner joints, including eight joint specimens with steel beam and one joint specimens with CES beam, were designed and tested. Test variables included the configuration of encased steel, axial compression ratio, loading angle and beam type. Failure patterns, hysteretic relations, deformation and strain distribution of these joints were recorded and analyzed. The seismic behavior was evaluated from peak load, stiffness and strength degradation, ductility and energy dissipation for these specimens. Test results indicated that the mixed failure mode acted on 3-D L-shaped CES column joint, including compression-shear failure in the joint core and bending failure at the beam-column connection. Seismic behavior of specimen with solid-web steel and T-shaped steel truss was much better than that of specimen with U-shaped steel truss. As the loading angle decreased from 45° to 0°, the peak load of joint specimen decreased continuously. Although reasonably increasing the axial compression ratio improved the bearing capacity and energy dissipation capacity of joint specimen, it also degraded the ductility and collapse resistance. Moreover, the joint with CES beam had better seismic behavior compared with joint with a steel beam. In this study, the ultimate drift ratio of all joint specimens exceeded the minimum limit of 1/50 in Chinese and American codes, indicating that 3-D L-shaped CES column joint had excellent collapse resistance.

Prediction of fire resistance of concrete encased steel composite columns using artificial neural network

Concrete encased steel (CES) columns, also known as steel reinforced concrete (SRC) composite columns, exhibit superior fire resistance due to concrete acting as a protection layer for the embedded steel section. While modern design codes have provided design guides for the fire resistance of CES columns, they are only applicable to those made of normal strength concrete. For high strength CES columns, advanced analysis is needed to capture the brittleness of high strength concrete at elevated temperature. In this paper, two methods, namely the artificial neural network (ANN) and the analytical equations, are proposed to predict the fire resistance of axially-loaded CES columns made of high strength concrete. To train the ANN, a finite difference model is developed to compute the temperature field in CES columns and it is used to establish a database containing 15,200 specimens. The cross-sectional dimensions and materials grades of the specimens are carefully selected to cover a wide range of values including those commonly adopted in real-life applications. The inputs of the ANN are identified through an extensive parametric analysis. The selected ANN consists of 7 inputs, 3 outputs and 2 hidden layers and achieves a high determination coefficient R2 value of 0.999. For practical implementation, analytical equations are also derived and achieve high R2 values above 0.953. The predictive power of the ANN and the analytical equations are examined against the observations obtained from actual fire tests, showing reasonable accuracy of prediction. Both methods are simple, of high accuracy and have implicitly accounted for temperature-dependent material degradation, and hence do not require input of temperature-dependent material properties and advanced analysis software.

Fire performance of composite columns made of high strength steel and concrete

The use of high strength steel and concrete materials for composite column construction is partly impeded by the lack of research on their fire performance. In EN1994-1-1, the highest concrete grade allowed for designing composite columns is capped at C50. This paper investigates the behaviour of concrete encased steel (CES) composite columns made of C120 concrete and S500/690 steel section under ISO834 standard fire through a series of experimental and numerical analyses. Fire tests were carried out on five high strength CES column specimens subject to varying eccentricity of loading to study their behaviours in fire. Polypropylene fibres were added into the high strength concrete mix to prevent the explosive spalling so that explicit modelling of cover spalling phenomenon can be omitted in the numerical analysis. A unified method is proposed to determine the transient strain of high strength concrete at elevated temperatures, allowing the stress-strain curves in EN1992-1-2 to be extended to high strength concrete up to C120. A numerical model, which can capture the strain reversal of concrete caused by the flexural deformation of columns at elevated temperatures, is proposed to enable a good prediction of axial displacement responses of CES columns in comparison with the test results. Finally, based on the validated numerical model and parametric studies, a new tabulated data method is proposed for the fire resistance design of CES columns with concrete class up to C90 concrete and steel section grade up to S550.

Effect of temperature on the bond-slip between I-shaped steel and concrete

This paper presents results from an experimental study on the effect of temperature on bond strength of I-shaped steel and concrete. Eleven concrete encased steel (CES) specimens were tested by home-made fire test furnace to evaluate bond strength at various constant high temperatures (20°C600°C). The test results showed that: (1) the trend of the bond-slip curves at high temperatures were much similar to that at room temperature. Compared with room temperature specimen, the ultimate bond load and the residual bond load of specimens at high temperatures were significantly decreased. The specimens with the higher temperature had the less ultimate bond load and residual bond load. (2) In the descending stage, the P-S curve of the specimens with higher temperatures had more flat slope. The P-S curve of the specimens at the temperatures higher than 250°C had invisible descending stage. The ultimate bond load of the specimen at 600°C left with only about 5% of that at room temperature. (3) The ultimate slippages (i.e. the slippage at the ultimate bond load) of specimens at high temperatures were larger than that at room temperature, and varied from 2 to 5 mm. (4) The calculation formulas of ultimate bond load, ultimate slippage, and residual bond load at different temperatures were presented, the constitutive equations of bond-slip at different temperatures were obtained, which will provide a reference for the fire-resistant design of concrete encased steel columns.

Behavior of eccentrically loaded normal weight concrete encased steel columns at elevated temperature

This paper presents an experimental investigation on the behavior of normal weight concrete encased steel (CES) columns eccentrically loaded and exposed to different elevated temperature using an electrical furnace. Four CES columns were tested with cross section dimensions of 150 ×150 mm (width× depth) and 1250mm total length and encased a steel section with dimensions of 70×60× 4×4 mm (total height× flange width× flange thickness× web thickness. The top and bottom ends of the columns were designed as corbels to prevent the premature local bearing failure at the concrete due to axial load. The corbels had a cross section dimensions equal to 240mm ×150mm (width × depth) with a distance between them equal to750mm. The experimental results have revealed that all CES columns have failed by flexural buckling failure mode with concrete crushing at the middle third of the compression side column accompanied with local buckling of the steel section flange. Analysis of the test results has also indicated that when the exposed temperature increases, the failure load considerably decreases. Where, the failure load of the CES columns has decreased by 53.6%, 61.2%, and 63.6% compared to the control CES column when they exposed to temperature of 400°C, 500°C, 600°C, respectively.

Behaviour of ultra-high strength concrete encased steel columns subject to ISO-834 fire

Ultra-high strength concrete (UHSC) encased steel columns are receiving growing interest in high-rise buildings owing to their economic and architectural advantages. However, UHSC encased steel columns are not covered by the modern fire safety design code. A total of 14 fire tests are conducted on UHSC (120 MPa) encased steel columns under constant axial loads and exposed to ISO-834 standard fire. The effect of load ratio, slenderness, stirrup spacing, cross-section size and concrete cover to core steel on the fire resistance and failure mode of the specimens are investigated. The applicability of the tabulated method in EC4 (EN 1994-1-2-2005) and regression formula in Chinese code (DBJ/T 15-81-2011) to fire resistance of UHSC encased steel columns are checked. Generally, the test results reveal that the vertical displacement-heating time curves can be divided into two phases, i.e. thermal expansion and shortening to failure. It is found that the fire resistance of column specimens increases with the increase of the cross-section size and concrete cover to core steel, but decreases with the increase of the load ratio and slenderness. The EC4 method overestimates the fire resistance up to 186% (220 min), while the Chinese code underestimates it down to 49%. The Chinese code has a better agreement than EC4 with the test results since the former considers the effect of the load ratio, slenderness, cross section size directly in its empirical formula. To estimate the fire resistance precisely can improve the economy of structural fire design of ultra-high strength concrete encased steel columns.

Thermo-mechanical behaviour of ultra-high strength concrete encased steel columns in standard fires

Ultra-high strength concrete has been applied in concrete encased steel column to enhance strength and reduce usage of concrete. However, there are limited specifications in current design codes on ultra-high strength concrete encased steel columns (UHSCESC), particularly for fire effects. This paper presents numerical simulation of fire behaviour of UHSCESC exposed to standard fires. A thermo-mechanical model of UHSCESC is established by considering the effect of transient thermal strain and validated against experimental results. The effect of slenderness ratio, section size, load ratio, concrete strength, steel strength, reinforcement ratio and steel ratio on the fire behaviour of UHSCESC is investigated through parametric studies. The predicted fire resistance of UHSCESC is finally compared to EC4 results. It is found that the temperature of the steel section is lower than its critical value, and the load bearing capacity of UHSCESC is almost evenly provided by the core concrete and steel section. The slenderness, section size and load ratio have significant effects on fire resistance of UHSCESC, leading to a wide range more than 300 min. The EC4 method is not applicable to UHSCESC which may provide unconservative fire resistances up to one hour and over-conservative results of nearly four hours.

Experimental investigation on fire resistance of high-strength concrete encased steel composite columns

This paper presents the experimental findings on fire resistance of concrete encased steel (CES) composite columns made of C120 concrete and S500/S690 high-strength steel section. Eight full-scale CES columns were tested under concentrated load and heated under the ISO834 fire until failure. The fire performance of each CES column specimen was evaluated by analysing the fire resistance time, axial displacement-time curve, temperature-time curve, rotational angle of end support, post-fire conditions of the concrete surface and failure mode. The experimental study showed that the addition of polypropylene fibre was effective in minimizing explosive concrete spalling in high-strength CES columns to achieve comparable fire resistance time as those of normal-strength CES columns. A database containing 40 CES specimens was established to assess the accuracy of the current design methods in predicting the fire resistance of CES columns. The limitations of each design method were discussed based on whether they can provide safe and accurate predictions of the fire resistance of tested CES column specimens. Finally, recommendations were provided to modify the current methods for fire resistant design of CES columns made of high-strength concrete.

Analytical Study of Concrete-Encased Steel Column Building against Blast Load

Study of behavior of composite building with Concrete-Encased Steel (C.E.S.) columns for Blast loading is done. This is compared with the behavior of conventional building having Reinforced Concrete (R.C.) columns. In the following study, both composite and R.C. buildings are subjected to 0.1 ton, 0.3 ton and 0.5 ton TNT equivalent charge weight of blast load with a standoff distance of 20m, 30m and 40m. To study the static properties due to variation in standoff distance and blast intensity, (G+4) buildings with composite and R.C. columns are analysed using parameters like storey displacement, storey drift, bending moment are compared. The Linear Static Analysis is carried out by using ETABS 2018 software. From the results obtained, it is observed that the vulnerability of a multi-storey structure is least for a low intensity blast generated at a comfortably longer standoff distance. Keywords: Blast, TNT, loading, CES-column, composite, standoff distance, ETABS

Axial-moment interaction of high strength concrete encased steel composite columns: Experimental investigation

This paper investigates the failure mechanism and structural behavior of high strength Concrete Encased Steel (CES) composite columns subject to compression and bending. Twelve composite column specimens with C90 concrete and S500 steel section were tested under concentric compression, eccentric compression and four-point bending. All specimens had the same geometry and were reinforced with the same steel section and same amount of reinforcing bars. In some specimens, micro steel fiber was added into concrete mix with 0.5% or 1.0% dosage to delay or prevent the potential premature cover spalling. The load-carrying capacity, load-deformation response, post-peak ductility, flexural stiffness, as well as damage pattern are comprehensively analyzed. Comparison is made between the experimental results and analytical predictions using modern design codes such as EN 1994-1-1 and AISC 360–16. From the four-point bending test, the flexural stiffness obtained from the test seems to be smaller than the codes' predicted values, indicating that modification is needed to achieve better prediction of structural response of composite beams at the service load level. As for the axial force (N)-bending moment (M) strength interaction diagram, it is found AISC 360–16 gives overall more conservative prediction than EN 1994-1-1 method for high strength CES columns with C90 concrete and S500 steel. However, both methods overestimate the axial compression capacity although they can predict their flexural capacity well.

Axial compression behavior of concrete-encased cellular steel columns

This paper presents an axial compression behavior of bare and concrete-encased cellular steel (CECS) short columns. Three cellular steel configurations with different hole diameters and spacings were fabricated from the parent wide-flange hot-rolled steel shape. Eleven CECS columns using the cellular steel and four concrete-encased steel (CES) columns using the parent steel were tested to investigate the influence of the cellular steel configuration and the spacing between the closed stirrups. The test results of bare cellular steel columns showed that the failure was due to local buckling at the steel flanges and web at the hole section. The bare cellular columns exhibited the load-deformation relationship with less hardening behavior than the parent steel column. The proportional limit loads, yield loads, and maximum loads of all cellular steel columns were less than the parent column. The test results of composite columns showed that the CECS columns exhibited the failure mode, load-deformation relationship, and load-strain relationship similar to the CES parent columns. The weakening effect due to the circular openings was minimized by the concrete encasement. The compressive strength of CECS and CES columns increased as spacing of the closed stirrups decreased. A modified squash load equation is recommended for both CECS and CES composite short columns made with low-strength concrete, small amount of longitudinal rebars, and maximum stirrup spacing limit based on the ANSI/AISC360–16 specification.