Ultimate Strength Of Columns Research Articles

Failure mechanisms and curvature radius effect in fixed ended flat oval LDSS slender column under axial compression

This paper presents the different failure mechanism of fixed ended flat oval LDSS (Lean Duplex Stainless Steel) slender column under axial compression by using the finite element software Abaqus. The load capacity is presented in terms of yield load and the deformation modes at ultimate load (?u) and post ultimate load at 1.5 ?u. Based on the deformation at ultimate deformation (?u) and post ultimate load at 1.5?u, failure mechanisms are identified as viz., 1) Local to local yielded buckling , 2) Local to local yielded flexural, 3) Flexural to flexural yielding , which ultimately depend on the slenderness of the column. The low slenderness column was found to have higher load capacity of column as compared to the higher slenderness column. The parametric effect of changes of curvature radius of cross-section on ultimate strength of column has also been presented showing the semi-circle section to have the highest strength.

Development of analytical model for predicting compressive behavior of engineered cementitious composites‐concrete encased steel composite columns

AbstractAnalytical models which can reliably predict the load–deformation behaviors and the ultimate strength of columns are indispensable tools for the practical design. In this paper, an analytical model is developed to predict the compressive load–deformation behavior and the ultimate capacity of engineered cementitious composite confined concrete encased steel (ECC‐CES) composite columns. The proposed analytical model employs the effective material stress and strain compatibility approaches for the predictions of compressive load–deformation response of ECC‐CES columns. The material constitutive models for ECC, concrete, and steel are first established, and then used in the analytical model. The effect of ECC and steel confinement on the concrete core and the softening behavior of steel column due to compression buckling are also considered. Based on the experimental results, appropriate strength reduction factors are proposed so that the effective material stresses can be calculated. The strength predictions from the proposed analytical methods and different design codes are compared with the experimental and numerical results. It was found that the proposed analytical models using effective material stresses gave better predictions than many commonly used design codes.

Experimental and numerical studies of circular sandwiched concrete axially loaded CFDST short columns

This paper aims to experimentally and numerically investigate the compressive behavior of circular concrete-filled double-skin steel tubular (CFDST) short columns, in which only the sandwiched concrete is under axial compression. In total, 28 CFDST columns were loaded axially, and their axial load-shortening curves, ultimate strength and failure modes were briefly discussed. Results suggest that the wall thickness and yield stress of outer steel tube have a significant effect on the failure modes, while the concrete strength shows an insignificant effect. The tested columns exhibited good ductility concerned by seismic resistant design. The ultimate strength of the columns using STK490 outer steel tubes was about 20–26% than that of ones with STK400 outer steel tubes. With an increase in the concrete strength and wall thickness of outer steel tube, the ultimate strength of the columns was improved by 32% and 43%, respectively. Moreover, finite element (FE) models were established and verified by comparing with the test results, and then an extensive parametric analysis was carried out to ascertain the effects of key variables on the compressive behaviour of the studied CFDST short columns. Finally, based on the numerical and test results, a novel formula was proposed to estimate the ultimate strength of CFDST columns, and high prediction performance was found in the proposed formula. The proposed formula is not only applicable for the strength prediction of CFDST columns, but also for that of steel tube confined concrete (STCC) columns.

Experimental study on square concrete-filled double skin steel tubular short columns

Concrete-filled double skin steel tubular (CFDST) columns have been increasingly applied in the fields of bridge and building construction due to their superior structural performance. This paper experimentally studied the compressive behavior of square CFDST short columns with double internal steel tubes (2 × SHS or 2 × CHS). The influence of concrete strength, eccentricity ratio, and section hollow ratio on the strength, deformation, and ductility of specimens was systematically investigated. Experimental research showed that the concrete strength had the most remarkable impacts on the ultimate strength of the column, followed by the section hollow ratio. However, the effect of eccentricity ratio on the ultimate strength of the column could be nearly neglected. The ductility of the column was positively correlated with the section hollow ratio, which was completely contrary to the effect of concrete strength. Nevertheless, the eccentricity ratio negligibly affected the ductility of the column. Furthermore, comparisons of the experimental ultimate strength of CFDST columns were made with three different design methods (AISC-360, Eurocode 4, and Han's formulae). The design formulae suggested by Han et al. (2009) could better predict the ultimate strength of CFDST short columns with double internal square steel tubes, but the prediction result was unconservative to some extent. Finally, the simplified formulae were proposed to estimate the ultimate strength of CFDST short columns, which could authentically reflect the combined impacts of the eccentricity ratio and section hollow ratio.

A Study on the Behaviour of Cold Formed Built - Up Steel Compression Member

The use of cold-formed thin-walled steel structural members has increased in recent years. Especially, Cold-formed steel columns are widely used in the construction industry due to their lightweight, easy installation, erection and economy. The strength and efficiency of cold-formed steel profiles depends on the cross-sectional shape, which controls the three fundamental buckling modes: local, distortional and global. As most of their sections are open with only one symmetrical axis, they would likely fail by twisting and interacted with the other buckling modes such as local and distortional buckling. In order to improve the ultimate strength of columns, a built-up column section with distinct shape was selected from the detailed study of Literatures and three specimens of thickness 1.6mm were fabricated with different lengths 500mm, 600mm and 700mm. Consequently, buckling behaviour of built up steel members was investigated theoretically with Direct Strength Method (with the help of CuFSM) as well as experimentally and the results were compared with the buckling modes obtained numerically using ANSYS software and it is found that the ultimate load carrying capacity of the column increases with the decrease of slenderness ratio and finally a new innovative and economical column element was presented.

Flexural buckling behaviour of 690 MPa high strength steel H-section columns

The paper describes a numerical study on columns fabricated from high strength steel (HSS) plates with nominal yield stress of 690 MPa. The study comprised 4 benchmark models validated by testing data and 144H-section parametric study models. The benchmark models were firstly created and validated against testing data for the accuracy. A full-scale parametric study was carried out to investigate effect of flange width/thickness ratio (α), web height/thickness ratio (β), geometrical imperfection (D) and residual stress (R) on overall buckling behaviour of the columns. The purpose of the study was to understand the relationship between section geometry, imperfections and column strength fabricated by welding from 690 MPa high strength steel plates. The H-section HSS columns were studied in this paper for the buckling behaviour along the minor axis in which direction those columns have smaller stiffnesses.It is shown that all those factors can be classified into three groups according to their impact on column strength (expressed with strength reduction factor χ): favourable factor (α), adverse factor (β and D) and uncertain factor (R). α and χ are positively correlated: χ increases at different rates as α increases. It is an effective way to increase α to improve column strength when α is a small value. χ decreases with the increase of β at very low rate and the effect of β on χ is not very obvious. D could produce more pronounced deterioration effect on ultimate strength of columns with higher α. The effect of residual stress (R) on H-section column strength is related with α: for the columns with higher α value, higher residual stress could produce more serious strength reduction effect. Residual stress does not always have negative effect on χ. It could produce beneficial effect on the ultimate strength of high strength steel H-section columns as long as α is reasonably small.The paper also shows a comparison of analysis results with existing standards including Eurocode 3 and GB50017-2017. For Eurocode 3, curve a0 can accurately predict χ with λ¯ when D = 0.03%. When D = 0.20%, curve b gives the best-fit prediction.

Mechanical properties of wood columns with rectangular hollow cross section

Abstract A rectangular hollow wood column made of Spruce-Pine-Fir (SPF) lumbers was developed, for the purpose of improving the utilization efficiency of timber. The present work conducted experimental investigations of the columns under centrically and eccentrically compression. A wide range of slenderness ratios of columns and eccentricities of loads was considered to carefully examine the failure modes in columns. The results indicated that combined material failures and buckling failures were observed for the intermediately slender columns under axial compression, while buckling failures were observed for the long columns. The ultimate strength of columns under axial compression significantly decreased with the increase of slenderness ratios. The predicted results by the tangent modulus theory closed to those of experiments. The bending failure, which underwent a pronounced nonlinear process, was the major characteristic of the intermediately slender column with an eccentric compressive load. Typically, the load carrying capacity of columns showed a decreasing trend with an increasing in eccentric ratios. Both the secondary bending and material nonlinearity were important factors that impacted the nonlinear response of the column. An analytical model was proposed for evaluating the load carrying capacity of the rectangular hollow columns under the interaction between compression and bending. There was good agreement between the results of the experiments and calculations.

Experimental investigation on axial compressive strength of lateral impact damaged short steel columns repaired with CFRP sheets

This paper describes an experimental study on the behavior of lateral impact-damaged short columns and then reinforced with carbon fiber reinforced polymer (CFRP). The purpose of the study was to evaluate the reinforcement effect of wrapping CFRP sheet on steel short columns with lateral impact damage. In this experimental study, thirty-three short columns were tested to study the influence of the impact energy, the loading position and the layer number of CFRP sheets on the ultimate strength of tested specimens. The ultimate strength, initial stiffness, ductility and failure modes of specimens were presented. The test results show that ultimate strength of columns has negative relation with lateral impact energy. The results also show that the closer impact position approaches to the end of specimens, the more decrease of ultimate strength shows. Wrapping CFRP sheets could improve the ultimate strength of specimens and delay local buckling. Based on the analysis of the experimental data, simplified formulas were put forward to predict the ultimate strength of the tested specimens, which show a good agreement with the experimental results.

Behaviour of hybrid concrete columns under axial compression loads

Hybrid Concrete Column (HCC) is composite column consists of two types of concrete, Normal Concrete (NC) and Self Compacted Concrete (SCC). The main objective of this work is to study the effect of outer to inner diameter ratio of hybrid concrete on the ultimate strength of column under the axial loading. Ten scaled columns (150 mm diameter and 600 mm length) were fabricated and cast with different ratio of NC to SCC and tested under axial loading. The test results were presented in term of loading and the axial and lateral strains at mid span of column length. It was found that the ultimate strength of column increased from 281 kN to 605 kN (215%). Also it was found that the strength of column increased when the SCC is in inner thickness rather than in outer thickness of the column and the strength increased with increasing the inner thickness of SCC.

A Numerical Study on the Seismic Performance of Built-Up Battened Columns

Built-up columns have been widely employed by practice engineers in the design and construction of buildings and bridges. However, failures have been observed in this type of columns in previous seismic events. This study analyses the performance of built-up columns with different configurations of battens when it is subjected to seismic loads. Four columns with different size of battens were simulated and subjected to three different intensities of axial load along with a lateral cyclic load. Results indicate that the size of battens influences significantly the seismic behavior of columns. Lower shear capacity of battens results in higher ultimate strength and ductility for built-up columns. It is observed that intensity of axial load has a significant effect on the ultimate strength of columns, but it is less influential on the yield strength. For a given drift value, the stress level in the centroid of smaller size battens is significantly more than that of larger size battens signifying damage concentration in battens rather than chords. It is concluded that design of battens for shear demand lower than code specified values only slightly reduces initial stiffness of columns; however, it improves seismic performance of battened columns.

プレストレストコンクリート骨組構造の耐震特性についての一考察

In order to improve the understanding of earthquake resistance characteristics of prestressed concrete (PC) structures designed by the current design method (route-3a), the following researches had been performed : (1) Determination of earthquake load, dead or live loads and indeterminate force in design. (2) Comparison between ultimate strength of PC beam, strength developed by PC bars in the PC beam section and required strength of beam in design. (3) Comparison between ultimate strength of columns and required strength of column in design. (4) Static elasto-plastic analyses of designed frame. The main result of this study is that equipment of PC bars in beam section is not a factor in over-strength against required strength in design and PC frame structure has the story whose shear strength is lowest of all stories in the structure essentially and this feature is caused by the large dead or live load of the structure.

Design of beam-columns in steel frames in the United States

This paper attempts to give designers an insight into the recent developments of the design criteria of steel beam-columns in the USA. The important features include (1) the ultimate strength of columns and beams that are special cases of beam-columns, (2) the secondary effects ( P-δ and P-Δ) that should be considered in the ultimate strength design of beam-columns, and (3) the simplified computer-based second-order elastic and inelastic analysis methods that are suitable for adoption in the practical design for beam-columns in rigid frames. Recommended and proposed ultimate strength design interaction equations in the USA for different categories of beam-columns are presented. Important features of these equations are summarized. Several illustrative examples are given. Directions of further research are indicated.

Ultimate strength of columns laterally braced by girt–diaphragm systems

This paper deals with the stabilizing effect of girts and cladding on columns in light industrial buildings. The construction aspects of such systems are briefly reviewed and a description of their behavior is presented. Solutions available to determine column strength in column–girt–diaphragm systems are reviewed. The use of a finite-element-based software is proposed as the only practical way to analyze this type of structural system. Results of a large parametric study using a finite element model are presented and a method to evaluate the ultimate strength of actual columns is introduced. Finally, a simple hand design method is derived. Key words: diaphragm, design, finite element, girt, column, stability, statistics.

Stability design criteria for steel members and frames in the United States

Abstract This paper attempts to give designers an insight into the beam-column problem. The important parameters such as (i) the ultimate strength of columns and beams which are special cases of beam-columns and (ii) secondary effects (P-δ and P-Δ), that should be considered in the ultimate strength design of beam-columns, are identified and discussed. Ultimate strength design interaction equations recommended and proposed in the United States for different categories of beam-columns are then presented. Important features of these equations are summarized. Directions of further research are indicated.

Ultimate Strength of Biaxially Loaded H-Columns with initial deflections and eccentricities

For the purpose of finding the effect of biaxial imperfection on column strength, a series of tests on H-columns with initial deflections and eccentricities under compression combined with biaxial bending were carried out. The standard test conditions of total 28 columns are that the end sections are biaxially simply supported with warping constrained and that columns have no residual stresses before tests. Only two of them are specimens with residual stresses and the end sections of another two are simply supported with respect to weak axis bending but clamped about strong axis bending.The elastic plastic behaviors of columns tested were numerically analyzed with use of an incremental stiffeness method. The ultimate strength of columns with imperfections were also calculated from an approximate strength formula with consideration of inelastic stability. Reasonable agreement was found between the observed column strength and both calculated values.Two kinds of imperfection, eccentricity and initial deflection, have so similar effects on column strength that the difference between them seems to be negligible for designers.Such a middle-length column that its elastic buckling load equals to its fully plastic axial load is the most sensitive to imperfections. Therefore, such a column is considered as a critical one in order to determine the allowable values of imperfections.

Ultimate Strength of Columns with Biaxially Eccentric Loads

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Ultimate Strength of Columns with Residual Stresses (2 nd Report)

The author had studied this problem and reported as the I st Report few years ago. In which, A. “modified Shanley model” was studied and the concept of tangent modulus theory was accepted as a, first approximation.In this report, the author again treated the same problem more thoroughly by planning series of tests and a particular distribution of welding residual stresses i. e. “reversed” -specimens. (Here, “reversed” means that the flange ends of welded columns with I-section have tensile residual stresses, in stead of usual compressive residual stresses.) The new end-fixtures which consist of two tapered circular wedges and driving worm gears, were designed to make the perfect alignment of columns easy.The findings are follows : (a) The “reversed” -specimen (which have reversed distribution of residual stress) may reach at the highest ultimate strength of annealed-specimen, but may not exceed that value by a great amount.(b) The test results of high-tensile steel (Welten-50, YAWATA Iron & Steel Co. Ltd.) columns showed a good agreement with the theoretical calculation as well as in case of mild steel. columns in the 1st report.(c) The tangent modulus load was again verified as a good design standard for welded columns.

Ultimate Strength of Columns with Residual Stresses

Commencing about the middle of the 20 th century, considerable attention was given by researchers to the problem of obtaining the ultimate strength of metal columns with residual stresses. In this paper, the ultimate strength of a column with residual stresses is described. A “modified Shanley model” is also studied to estimate approximately the maximum load of a column and to show the influence of the initial deflection on the column behavior.The test results were referred to show the experimental verification.Conclusively the following is found, under the existence of considerable residual stresses like cooling residuals or welding residual stresses, the ultimate strength of a column may be considerably reduced, but might be much higher than the tangent modulus load calculated by means of a cross-section test (stub column test).