Numerical Nonlinear Buckling Analysis of Tapered Slender Reinforced Concrete Columns (original) (raw)
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Behavior of Slender Reinforced High Performance Concrete Columns under Biaxial Loading
Columns are structural elements used primarily to support compressive loads. The short column is one in which the ultimate load at a given eccentricity is governed only by the strength of the materials and the dimensions of cross section. Slender concrete columns are economically appealing in tall buildings design; the rentable space over the many floors can be increased by a substantial margin through reduction of the column sections. The slenderness of a column may result in the ultimate load being reduced by lateral deflections of the column caused by bending. Reinforced concrete columns are generally subjected to eccentric compression as a result of their location in the structure, their cross section or the type of forces they bear. Many columns are subjected to this kind of loads, for example the corner columns of a building. The analysis of slender reinforced concrete columns is complicated because the buckling analysis must take account of the non-linear properties of the materials and also construction imperfections. Exact analysis methods are generally complicated and unsuitable for everyday design. Over the last few decades, the development in material technology, especially with the availability of super plasticizers, led to the production of High Performance Concrete. With the robust growth of construction with HPC, the design of slender concrete columns is now a subject of considerable relevance. One application of HPC has been in the columns of high-rise buildings. Buckling has become more of a problem in recent years since the use of high-strength materials requires less material for load support-structures and components have become generally more slender and buckle-prone. Key words Reinforced concrete column, slenderness ratio, high performance concrete column, bi-axial loading and P-M Interaction diagram. Introduction Columns are structural elements used primarily to support compressive loads. The short column is one in which the ultimate load at a given eccentricity is governed only by the strength of the materials and the dimensions of cross section. A slender column is one in which the ultimate load is governed not only by the strength of the materials and the dimensions of the cross section but also by the slenderness, which produces additional bending moment due to lateral deformations. For eccentrically loaded short columns, the column behavior will follow the linear path until intersect the interaction diagram. For eccentrically loaded slender columns, the column will follow a non-linear path until intersects the interaction diagram. This means that, due to non-linear effects the actual moment on the column is greater than the linear moment. [1] Slender concrete columns are economically appealing in tall buildings design; the rentable space over the many floors can be increased by a substantial margin through reduction of the column sections. The slenderness of a column may result in the ultimate load being reduced by lateral deflections of the column caused by bending. Reinforced concrete columns are generally subjected to eccentric compression as a result of their location in the structure, their cross section or the type of forces they bear. Many columns are subjected to this kind of loads, for example the corner columns of a building. The analysis of slender reinforced concrete columns is complicated because the buckling analysis must take account of the non-linear properties of the materials and also construction imperfections. Exact analysis methods are generally complicated and unsuitable for everyday design. [2] Over the last few decades, the development in material technology, especially with the availability of super plasticizers, led to the production of High Performance Concrete [3]. With the robust growth of construction with HPC, the design of slender concrete columns is now a subject of considerable relevance. One application of HPC has been in the columns of high-rise buildings. Buckling has become more of a problem in recent years since the use of high-strength materials requires less material for load support-structures and components have become generally more slender and buckle-prone. As a result, the slenderness limits based on normal strength concrete (NSC) have to be reassessed to make use of the merits of HPC. Attempts have been made to modify the theory of analysis of slender columns by introducing effects of inelastic behavior and large deformations. There are two important limits for the slenderness ratio, which are the upper limit for the short column and maximum slenderness limit. The upper slenderness limit is the limit that when the column exceeded is considered a long column. On the other hand, the maximum slenderness limit is stipulated to avoid carrying out second order analysis of the column, which is burdensome and more complicated [1].
REALISTIC APPROACH AND DESIGN OF SLENDER REINFORCED CONCRETE COLUMNS - A CASE STUDY
IAEME PUBLICATION, 2020
Slender Reinforced concrete columns are subjected to significant lateral deformation, fails mainly by buckling, due to development of secondary moment. Reinforced Concrete columns with larger height with respect to lateral dimension are subjected to significant lateral deformation on application of external load (either axial or eccentrical) and subsequently develop secondary moment. This moment induces additional deflection and hence there is an increase in secondary moment. As a result the load-moment curve becomes non-linear. It is obvious that due to this secondary moment the load carrying capacity of the column is reduced. Prediction of ultimate load for reinforced concrete slender columns involves study of buckling through material non-linearity and cracking behaviour of cross section, since the failure occurs in inelastic range. The present design methods of reinforced concrete slender columns suggested by American, British and Indian code provisions are either empirical or involve cumbersome procedure. To circumvent the above, a simple, realistic and rational theory is proposed, incorporating the behaviour of reinforced concrete slender columns rectangular in cross section, bent in single curvature. The theory also incorporates the material non-linearity and effect of cracking at the time of failure. An experimental investigation is undertaken to validate the theory developed. In addition, design charts are prepared based on the theory and a realistic design procedure is proposed for practical applications.
Analysis of Prismatic and Linearly Tapered Reinforced Concrete Columns
Journal of Structural Engineering, 1987
A rational analysis describing the ultimate strength and behavior of reinforced concrete columns of linearly tapering cross section under axial load and end moments is presented. The conjugate beam method is used to calculate the second-order effects (i.e., the additional moment caused by the applied axial load). An interactive computer program for use with microcomputers is presented. The program uses iterative procedures for calculating moment-thrust-curvature relationships along the member, including the secondorder effects. It determines the failure load as well as the failure mode of a slender, linearly tapered, reinforced concrete column. The results obtained from the computer model are compared with available experimental results.
International Journal of GEOMATE, 2021
Tapered columns are a type of column that is used for different purposes, including architectural purposes or structural needs to take into account the changes that occur to moments along with the height of the column. For example, in highway bridges, tapered columns are used to reduce the number of moments transmitted to the base of the columns and from there to the foundation. This research studied the analysis of short reinforced concrete columns with variable cross-sections along the column in a linear manner by using the ANSYS V.15 software package. The variables that were studied included the type of section, solid or hollow, the ratio of longitudinal and transverse reinforcement, the ratio of the hollowness, and the comparison of numerical results with those obtained from the previous study. The results we obtained from the simulation of the numerical analysis of the models showed a very good agreement with the results of the experimental studies for them. This agreement can also be observed through statistical analysis using the arithmetic mean and standard deviation when compared. Thus, the proposed model by numerical analysis and hypotheses is suitable for formulating the behavior of these reinforced concrete tapered column models under the effect of axially applied load and other variables. The behavior of column models is based on applied loads, load-displacement curves, crack patterns, and failure modes. The results showed that increasing the ratio of longitudinal and transverse reinforcement increases the resistance of the R.C. column models and the ductility index with a decrease in the corresponding lateral displacement. This behavior is observed when changing the section from hollow to solid. Finally cracks pattern is represented in the concrete crushing and concrete spalling out of some parts at the end of the tapered and diagonal cracks in different places, especially at the end of the tapered.
A New Design Methodology for the Ultimate Capacity of Slender Prestressed Concrete Columns
This paper presents a new method for computing the flexural rigidity, EI, of prestressed concrete columns at their ultimate capacity. Flexural rigidity is needed to evaluate the critical buckling load which is used in the magnification formula. The proposed methodology for computing EI is based on two fundamental relationships: (1) the moment versus curvature relationship at a given load eccentricity, and buckling under the assumption of pure concentric load. The proposed EI model was used with the moment magnification formula to obtain moment versus axial load interaction diagrams for a number of slender prestressed concrete columns. The diagrams were compared with those obtained from a finite element analysis and very good agreement was observed. Also good agreement was observed with available experimental test results. Comparisons with current code formulations and PCI recommendations are made, and a new procedure is proposed. Several numerical design examples, illustrating the new method, are provided.
Nonlinear analysis of concrete-filled thin-walled steel box columns with local buckling effects
Journal of Constructional Steel Research, 2006
Local buckling of steel plates reduces the ultimate loads of concrete-filled thin-walled steel box columns under axial compression. The effects of local buckling have not been considered in advanced analysis methods that lead to the overestimates of the ultimate loads of composite columns and frames. This paper presents a nonlinear fiber element analysis method for predicting the ultimate strengths and behavior of short concrete-filled thin-walled steel box columns with local buckling effects. The fiber element method considers nonlinear constitutive models for confined concrete and structural steel. Effective width formulas for steel plates with geometric imperfections and residual stresses are incorporated in the fiber element analysis program to account for local buckling effects. The progressive local and post-local buckling is simulated by gradually redistributing the normal stresses within the steel plates. Two performance indices are proposed for evaluating the section and ductility performance of concrete-filled steel box columns. The computational technique developed is used to investigate the effects of the width-to-thickness ratios and concrete compressive strengths on the ultimate strength and ductility of concrete-filled steel box columns. It is demonstrated that the nonlinear fiber element method developed predicts well the ultimate Liang, Q. Q., Uy, B. and Liew, J. Y. R., "Nonlinear analysis of concrete-filled thin-walled steel box columns with local buckling effects", Journal of Constructional Steel Research, 2006, 62(6), 581-591.
Slovak Journal of Civil Engineering, 2011
Reinforced and concrete-encased composite columns of arbitrarily shaped cross sections subjected to biaxial bending and axial loads are commonly used in many structures. For this purpose, an iterative numerical procedure for the strength analysis and design of short and slender reinforced concrete columns with a square cross section under biaxial bending and an axial load by using an EC2 stress-strain model is presented in this paper. The computational procedure takes into account the nonlinear behavior of the materials (i.e., concrete and reinforcing bars) and includes the second-order effects due to the additional eccentricity of the applied axial load by the Moment Magnification Method. The ability of the proposed method and its formulation has been tested by comparing its results with the experimental ones reported by some authors. This comparison has shown that a good degree of agreement and accuracy between the experimental and theoretical results have been obtained. An average ratio (proposed to test) of 1.06 with a deviation of 9% is achieved.
Engineering, Technology & Applied Science Research
The stability and strength of slender Reinforced Concrete (RC) columns depend directly on the flexural stiffness EI, which is a major parameter in strain calculations including those with bending and axial load. Due to the non-linearity of the stress-strain curve of concrete, the effective bending stiffness EI always remains variable. Numerical simulations were performed for square and L-shaped reinforced concrete sections of slender columns subjected to an eccentric axial force to estimate the variation of El resulting from the actual behavior of the column, based on the moment-curvature relationship. Seventy thousand (70000) hypothetical slender columns, each with a different combination of variables, were used to investigate the main variables that affect the EI of RC slender columns. Using linear regression analysis, a new simple and linear expression of EI was developed. Slenderness, axial load level, and concrete strength have been identified as the most important factors affe...
Fibers
Most reinforced concrete (RC) structures are constructed with square/rectangular columns. The cross-section size of these types of columns is much larger than the thickness of their partitions. Therefore, parts of these columns are protruded out of the partitions. The emergence of columns edges out of the walls has some disadvantages. This limitation is difficult to be overcome with square or rectangular columns. To solve this problem, new types of RC columns called specially shaped reinforced concrete (SSRC) columns have been used as hidden columns. Besides, the use of SSRC columns provides many structural and architectural advantages as compared with rectangular columns. Therefore, this study was conducted to explain the structural performance of slender SSRC columns experimentally and numerically via nonlinear finite element analysis. The study is based on nine RC specimens tested up to failure, as well as eighteen finite element (FE) models analyzed by Abaqus soft wear program. ...
Journal of Constructional Steel Research, 2015
This paper presents an efficient mathematical model for studying the global buckling behavior of concrete-filled steel tubular (CFST) columns with compliant interfaces. The present mathematical model is used to evaluate exact critical buckling loads and modes of CFST columns for the first time. The results prove that the presence of finite interface compliance may significantly reduce the critical buckling load of CFST columns. A good agreement between analytical and experimental buckling loads of circular CFST columns is obtained if at least one among longitudinal and radial interfacial stiffnesses is high. The design methods compared in the paper give conservative results in comparison with the experimental results and analytical results for almost perfectly bonded layers. The parametric study reveals that critical buckling loads of CFST columns are very much affected by the diameter-to-depth ratio and concrete elastic modulus. Moreover, a material nonlinearity has a pronounced effect for short CFST columns, and a negligible effect for slender ones.