Slender Concrete Columns Research Articles

Axial Load-Bending Moment (P-M) Interaction of Geopolymer Fiber-Reinforced Concrete Slender Columns Reinforced with Steel, Glass Fiber-Reinforced Polymer, or Hybrid Double Layer

Axial Load-Bending Moment (P-M) Interaction of Geopolymer Fiber-Reinforced Concrete Slender Columns Reinforced with Steel, Glass Fiber-Reinforced Polymer, or Hybrid Double Layer

Behavior and design approach of ultra-high-performance concrete slender columns

The existing literature concerning the behavior of slender columns made of reinforced ultra-high-performance concrete (UHPC) is severely limited. Furthermore, current design standards lack specific guidelines for reinforced UHPC (R–UHPC) slender columns. Based on this, a comprehensive experimental investigation was conducted on four columns with 2 % steel fiber content subjected to compression to explore the influence of eccentricity ratios (e/h0 = 0, 0.15, 0.3, and 0.6) on the compression behavior of the R–UHPC slender columns. The results revealed that all R–UHPC slender columns experienced failure due to compressive zone UHPC crushing, with no observed concrete spalling. Moreover, a detailed parametric study was conducted on 3000 R–UHPC slender columns using a validated finite element model. By analyzing the parameters and employing the moment magnification method, a statistically derived design equation for effective flexural stiffness (EI) was formulated. The results indicated that EI decreased with increasing eccentricity ratio and increased with rising slenderness ratio. Additionally, calculation formulas for determining cross-section strength were proposed for R–UHPC slender columns, accounting for the contribution of tensile zone UHPC to the overall section strength. Finally, the proposed design approach was validated by comparing predicted results with available experimental data.

Experimental behaviour of square high-performance concrete slender columns under biaxial eccentric loading

Experimental behaviour of square high-performance concrete slender columns under biaxial eccentric loading

Finite Element of Composite Reinforced Concrete Slender Columns Subjected to Eccentric Loads

The relationship between reinforced concrete column tests and finite element behavior is crucial for understanding and optimizing the structural performance of these elements. Concrete columns are integral components in buildings and infrastructure, and testing them under various conditions provides valuable data on their strength, stiffness, and failure mechanisms. Finite element analysis, on the other hand, is a powerful numerical method used to simulate the complex behavior of structures under different loads. By correlating experimental results from concrete column tests with finite element models, engineers can validate and refine their simulations, ensuring that the computational models accurately represent the physical reality. This iterative process of testing and analysis allows for the development of more reliable and efficient design methodologies, leading to improved structural performance and safety in construction projects. The synergy between experimental testing and finite element behavior not only enhances our understanding of structural dynamics but also contributes to the advancement of innovative and resilient construction practices. The results shows a good coincidence between the experimental and theoretical results.

Experimental and numerical investigations of precast circular reinforced concrete slender columns with intermediate connection

This paper carries out experimental and numerical investigations on the axial performance of circular Reinforced Concrete (RC) precast slender columns with an intermediate connection. A series of tests are carried out to study the effects of longitudinal reinforcement ratio (ρ), and embedded length of steel bars (Lb) of precast columns on their axial performance under concentric loading. Test results show that increasing the reinforcement ratio and the embedded length of the precast columns significantly improves the axial performance of the precast slender columns. Nonlinear finite element models (FEM) are developed to simulate the performance of the columns experimentally observed. The accuracy of the FEM is validated against the test results and found to reasonably predict the axial performance of tested columns.

Post-fire performance of circular steel tube confined steel-reinforced concrete slender columns: Testing, simulation and design

Steel tube confined steel-reinforced concrete (STCSRC) stub columns offer good residual bearing capacity, great ductility, and large stiffness after fire exposure because inner steel profiles are unaffected by exterior temperature. Nonetheless, instability issues exist in STCSRC slender columns, and study into the mechanical characteristics of post-fire slender specimens is critical. At present, no relevant study on the axial performance of STCSRC slender columns after fire exposure has been reported. In this paper, nine circular STCSRC slender columns that had been exposed to fire were tested under axial load. The failure modes, axial load–displacement relationship, and lateral deflections of STCSRC columns were discussed. Furthermore, heat transfer analysis models and mechanical analysis models were established, and the effects of crucial variables on the buckling responses of STCSRC slender columns were explored. Among the parameters studied, sectional diameters and steel profile to concrete area ratio have a significant impact on buckling capacity. To calculate the buckling capacity of the post-fire STCSRC slender column, a simplified calculation method according to JGJ/T 471–2019 was proposed.

Experimental and numerical studies of circular precast concrete slender columns with intermediate connection filled with high-performance concrete

Precast concrete (PC) slender columns with intermediate connections are often used in building construction. However, no studies have been performed on the behavior of PC slender columns with intermediate connections filled with high-performance concrete namely engineering cementitious composites (ECC) and strain hardening cementitious composites (SHCC). This paper presents the testing and computer modeling of axially loaded PC slender columns with splices filled with ECC and SHCC. Experimental program and results are presented on nineteen PC slender columns under concentric compressive load up to collapse. The test parameters include the longitudinal reinforcement (µ) ratio, and embedded length of steel bars/infilled concrete connection (Le). Three different reinforcement ratios of 0.027, 0.031, and 0.036 are considered. The embedded length of steel bars/intermediate concrete connection varies from 15D, 22.5D, and 30D where D is the bar diameter. Experimental results indicate that the use of longer steel bars/intermediate concrete connection and a higher reinforcement ratio can significantly enhance both the cracking and ultimate loads of PC slender columns with an intermediate concrete connection. The elastic stiffness of the PC slender columns with ECC and SHCC connection is found to increase by 150% and 93%, respectively when compared to the control specimen. Similarly, filling the splice of the PC columns with ECC and SHCC improves the energy absorption capacity by 107% and 138%, respectively. Nonlinear three-dimensional finite element models (FEMs) are developed accounting for the initial imperfection of the slender columns and their accuracy is validated by experimental results. It is shown that the FEM can provide an accurate simulation of the performance of PC columns with splice connection.

Minimum design bending moment for systems of equivalent stiffness

In this article, the minimum design bending moment of concrete slender columns is studied by assuming a system of equivalent stiffness. For concrete structural parts such as slender columns, their stiffness is dependent on the loading, originated from lumped and distributed masses, and the rheological behavior of the material. The latter alters the concrete’s modulus of elasticity, introducing changes over time. Basically, the desired transformation is from a one-dimensional non-prismatic system to another prismatic one which exhibits an equivalent bending stiffness. As the bending stiffness changes due to the change of the problem’s independent variables, the geometric characteristics of the transformed system reflect the same dependence as the original system. This implies changes in the minimum design moment since it is linked to the dimensions of the equivalent section. To assess the hypothesis proposed, a numerical simulation is conducted over a real structural system using a vertical loading ranging from zero up to the critical buckling force, taking into account the change in the modulus of deformation of concrete and assuming a certain level of cracking of the material. The results obtained showed that the strategy of using a system of equivalent stiffness simplifies the analysis of non-prismatic elements because the problem is reduced to a prismatic element of equivalent properties. Besides that, due to the incorporation of the concrete creep in the problem, the maximum moment obtained in the equivalent system needs to be multiplied by a factor of 2.94 in order to equal the maximum moment occurring in the original system.

Behavior and design of circular concrete columns strengthened with textile-reinforced mortar subjected to eccentric compression

Textile-reinforced mortar (TRM) is a cheaper and eco-friendlier material for the concrete confinement than steel and fiber-reinforced polymer (FRP). The behaviors of plain concrete slender columns with circular cross-section strengthened with TRM under eccentric compression were analyzed both experimentally and analytically in this paper. The test results showed that TRM could effectively inhibit the extension of cracks in columns, and increasing the number of textile layers from one to three led to a 44% increase in ultimate load. Meanwhile, the secondary moment of columns relative to the total moment varied from 20% to 35%, which was positively related to the confinement effectiveness of TRM. Then, a comparison of the behaviors of confined concrete columns under axial load-flexural moment (P-M) loading demonstrated that the confinement provided by TRM was relatively insufficient when compared to steel and FRP, behaving a post-peak softening phase of compressive constitutive curves. However, the textile with high tensile strength improved the stress distribution of cross-section of eccentrically loaded columns, thereby observing a much slower reduction in ultimate load with the increase of the eccentric ratio. Finally, according to a cross-section bearing capacity analysis, the procedure of analytical calculations was proposed to predict the ultimate load of TRM-confined concrete columns at a given eccentric ratio. Furthermore, the proposed analytical calculations provided a parametric study to reveal the correlation between the eccentric ratio and the number of textile layers, and then a simplified regression formula for design purpose was developed. This research highlights the behavior and design of concrete strengthened with TRM under P-M loading, which would give researchers and engineers an insight.

Evaluation of Stability Resistance Factor for Slender Concrete Columns Internally Reinforced with Fiber-Reinforced Polymer Bars

The validity of the stability resistance factor in the moment magnification procedure for the analysis of slender columns reinforced with fiber-reinforced polymer (FRP) bars (FRP-RC columns) has not yet been considered in the literature. The development of such a factor, compatible with current building codes, is discussed in this paper. In the development process, first, the variability of the ultimate strength of slender FRP-RC columns was investigated, and the effect of variations in geometric and material properties on this variability was determined. The results of the variability study were later used in the first-order reliability analysis to estimate the appropriate stability resistance factor. The results of the analysis show that a stability resistance factor of 0.75 or 0.7, depending on the flexural stiffness expression, is representative of typical slender FRP-RC columns. Thus, we propose the use of this value, in combination with the recommended load factors.

Stiffness Reduction Factor for Slender Concrete Column Reinforced with Fiber-Reinforced Polymer Bars

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Calculation Model for Estimation of Residual Bearing Capacity of Damaged Reinforced Concrete Slender Columns

This work is devoted to the study of the influences of various parameters on the bearing capacities of compressed reinforced concrete columns of varying flexibilities damaged during operation. Experimental tests of pilot samples were carried out, and results were analyzed on the basis of which it was established that significant longitudinal bending was observed in the direction of the x-axis. By analyzing the influences of the angle and depth of damage on the behavior and nature of the destruction in the experimental samples, three main destruction patterns were identified. An analysis of the experimental and statistical models showed that the greatest influences on the bearing capacity of the samples were the depth of the damage and the angle of the cut, and the effect of the height of the samples was virtually negligible. A model of calculation for the residual bearing capacities of compressed damaged reinforced concrete elements of different flexibilities was developed. The results of the comparison testify to the good coincidence of the theoretical values with the values obtained from the actual experiment (the difference of an average of no more than 29.8%), indicating that the proposed method can be applied in building practice.

Reliability of slender concrete columns designed according to the Eurocodes

For compressed structural elements that are likely to lose stability, the second-order theory has to be incorporated into the design process. In Eurocode 2 (EN 1992-1-1, 2004), there are three methods for calculating the effects of the second-order theory, and there are some doubts as to whether the General nonlinear method has a sufficient degree of reliability. For this reason, six specimens of slender columns were designed, fabricated, and tested. All of the column specimens failed due to the loss of stability inside their design interaction diagram, which allows for an analysis of the reliability of the design method in Eurocode 2. As a part of an experimental campaign, prediction of the experimental behaviour of the specimens was carried out. Based on a numerical model, the safety factor for the tested columns was observed, and the likelihood of a possibly unsafe design is explained and presented.

Buckling and free vibration analysis of non-prismatic columns using optimized shape functions and Rayleigh method

In this paper, optimized shape functions have been used in Rayleigh method to determine the critical buckling load and the fundamental natural frequency of non-prismatic steel-reinforced slender concrete columns. A range of admissible shape functions describing the mode shape in buckling as well as for the fundamental natural frequency of the column are considered and then an optimization strategy is developed to arrive at the optimum shape function. The results obtained from the present method based on the implementation of Rayleigh method through the concept of generalized coordinates are verified and validated by the finite element method. The application of the theory is demonstrated by two illustrative examples, both of which are steel-reinforced concrete towers that are representative of practical structures. Of particular significance is the duality between the free vibration and buckling problems which is captured and fruitfully exploited in the analysis. The effect of an additional mass located at the top of the tower is included in the investigation. Additionally, the impact of the creep behavior of the towers on results due to continuing lapse of time is critically examined and assessed. Finally, significant conclusions are drawn following the discussion of results.

Effect of the connecting beam stiffness on the bracing limit for reinforced concrete slender columns in single and multi-story frames

Abstract The main purpose of this paper is to study analytically the behavior of slender reinforced concrete columns existing in sway and non-sway structures. The studied variables were the stiffness of the beam connected to the slender columns, the stiffness of the bracing columns, and the number of bays and stories in the structure model. The stability of slender columns was studied and the required limits for the lateral bracing were determined using a finite element program to perform buckling analysis, linear analysis, and geometric nonlinear analysis for the different frame structural models. All the results obtained in this study were compared to the available methods included in the different building codes and the methods suggested by other researchers. The results indicated that the minimum value of the bracing limit, required to restrain the slender column against the side-sway, depends on the stiffness of the connecting beams, number of stories, and number of bays. The required bracing limit decreases with increasing the beam stiffness and with increasing the number of bays. However, the required bracing limit increases with the increase of the number of stories in the structure.

Behavior of Eccentrically Loaded Slender Concrete Columns Reinforced with GFRP Bars

This paper presents an experimental investigation on the behaviour of concrete columns reinforced with glass fibre reinforced polymers GFRP bars under concentric and eccentric loads. Six RC column specimens have been considered in the experimental tests with a cross section dimension of (135 mm × 135mm) at the middle portion of columns and (250 mm × 135 mm) (width ×depth) at the corbel with a total length of 1150 mm with the length between corbels (middle part) was 710 mm. Three specimens have been represented the reference specimens which are reinforced with steel bars and the other three were reinforced with GFRP bars. Tow variables have been considered in the experimental tests: the type of reinforcement (GFRP and steel) and the eccentricity ratio (e/h). All columns have been subjected to different values of eccentricity ratio (e/h): 0, 0.5, and 1. It has been concluded that the ultimate load capacity of columns reinforced with GFRP bars decreases by about 27.13% and 94.67% compared to columns reinforced with steel bars under eccentricity ratios (e/h=0) and (e/h =0.5), respectively. Whereas, ultimate load increases by about (4.79%) for the columns reinforced with GFRP bars compared to columns reinforced with steel bars at eccentricity ratios (e/h=1). The result have also shown that all specimens that have been subjected to eccentricity ratio (e/h > 0) failed by compression failure.

Effect of Hollow Shape on the Behavior of Reinforced Self-Compacting Concrete Slender Column Under Eccentric Loading

Results of testing reinforced self-compacted concrete slender columns having longitudinal holes concealing PVC pipe in their cross sections under axial compression load and uniaxial bending are presented in this paper. The effect of hollow shape on the performance of slender columns having 200x200mm quadratic cross section and 1300mm long under concentric and eccentric loads was investigated. Three different shapes of central hole: circular, square, and lozenge pattern in addition to the different load eccentricity values were considered to investigate the axial loading resistance and cracking load, lateral and longitudinal deflections of the columns. Test results have showed that altering the hollow shape inside the area of column cross section does not show a great influence on the column behavior unless the hollow ratio changed. The effect of hole shape or the hollow ratio on loading capacity is insignificant but the existence of a hole embedded longitudinally in the column significantly decreases its ultimate capacity. The effect of hollow shape or hollow ratio on a slender columns behavior subjected to eccentric loading with small ratio of load eccentricity to total column thickness (e/h=.33) was more than that of large eccentricity (e/h=1.0). Accordingly, the decrease in loading column capacity of columns was (5.0%, 2.5%, and 6.6%) compared to (3.2%, 2.2%, and 4.7%) for the same hole shapes respectively.

Experimental Work to Study the Strengthening Effect of SFR and CFRP on a Part or Whole of the Length of Slender RC Columns

Abstract This paper is focussed on the investigation of the strengthened column by steel-fibre-reinforced (SFR) and carbon fibre-reinforced polymer (CFRP) on a part or a whole of the length of the column under axial force, and to obtain the effective length, which is responsible for the increasing of the ability of the column to resist buckling. Seven samples were designed as slender reinforced columns with dimensions of 2000 mm length and cross-sections of 120 mm x 60 mm. It was shown that the strengthening of the middle half of the column length by SFR gave an ultimate load similar to the strengthening of the whole column with same material. Also, it was found that the column strengthened by SFR increased its ultimate load by 42.6 %, 42.1 % and 33.3 % for strengthened lengths of dimensions L, L/2 and L/3, respectively, compared to the non-strengthened column. The increase in ultimate load that could be borne by the column strengthened by CFRP were 53.0 % and 33.8 % for strengthened lengths of L and L/2, respectively, only. Interaction diagram had been depended as a theoretical analysis for slender concrete columns. The interaction diagram for the column strengthened by CFRP is greater than for the column strengthened by SFR, which in turn is greater than the non-strengthened column.

Performance of circular bimetallic tube confined concrete slender columns under eccentric compression

This paper aims to investigate the performance of thin-walled circular stainless steel-carbon steel bimetallic tube confined concrete slender columns under eccentric compression. 14 slender columns including bimetallic tube confined concrete (BTCC) with and without rebar, and concrete-filled bimetallic tube (CFBT) were tested. A parametric analysis is conducted based on the validated finite-element model. The results show that the two steel tube layers worked well together and the thin-walled BTCC specimens behaved in a ductile manner. Under the same parameters, the decrease of the diameter–thickness ratio of bimetallic tube improves the bearing capacity and rigidity of the BTCC slender column, but reduces its ductility in the descending stage. The confinement effect of bimetallic tube on the concrete in BTCC columns is stronger than that in CFBT columns. When the yield strength of stainless steel and carbon steel is similar, the stainless steel–total steel ratio has little effect on the capacity of the column. Provided meeting the requirements of corrosion resistance, relatively thinner stainless steel tube is preferred to reduce the cost. The comparison between the simulation and the calculation results shows that the current design method can predict the bearing capacity of the BTCC slender column with large diameter–thickness ratio.

Hybrid system of longitudinal CFRP laminates and GFRP wraps for strengthening of existing circular concrete columns

This paper presents an investigation on the behavior of a strengthening system of longitudinal premanufactured carbon fiber-reinforced polymer (CFRP) laminates and transverse glass FRP (GFRP) wrapping for strengthening of concrete columns (here after is called a hybrid system). The idea behind using the longitudinal CFRP strips was to enhance the system by increasing the flexural stiffness of the column which is effective for the strengthening of slender columns and eccentrically loaded columns where additional flexural stiffness is required for buckling control. The study was conducted experimentally in two phases under monotonic loads. Phase I was conducted on small-scale concrete specimens to characterize the hybrid system and phase II was conducted to verify the effectiveness of the hybrid system for the strengthening of large-scale slender concrete columns. In phase I, it was observed that by applying GFRP wraps on longitudinal CFRPs, the failure mode of CFRP laminates changed from buckling/debonding to crushing to achieve the full capacity of the system. However, as expected, test results in phase I showed that the usage of wrapping without longitudinal CFRP laminates was more effective than the proposed hybrid system for the strengthening of small scale concrete columns subjected to pure axial loading. For slender columns in phase II, the hybrid system enhanced the wrapping system by adding 52%, 105%, and 94% gain for axial capacity, flexural capacity, and lateral displacement at peak load, respectively, by altering the load–deflection curve of the slender columns to achieve a higher performance level.