Buckling of Pretwisted Steel Columns (original) (raw)
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INFLUENCE OF PRETWISTING ANGLE ON THE BUCKLING CAPACITY OF STEEL COLUMNS: A REVIEW
A column is a vertical compression member designed to transmit compressive loading. It is generally seen that when a slender member is loaded in compression, it will bow sideways or buckle, and if the load is then increased further the column will eventually fail in bending. Buckling is a mode of failure that is mainly observed in compression members due to structural instability. A pretwisted column has its strong flexural plane weakened and its weak flexural plane strengthened, leading to a favourable effect on buckling strength of the pretwisted column. A linear buckling analysis study was conducted for boxed and unboxed sections for columns with varying twist angles to study the effect of twist angle variation on improvement in buckling capacity. The studies reviewed that buckling capacity increased upto an optimum twist angle value and further reduced. It was found that pretwisting is effective to increase the buckling capacity of columns.
Journal of Constructional Steel Research, 2019
The objective of this work is to develop design guidance for existing hollow steel columns that are retrofitted by infilling concrete into the tubes. The primary challenge is the unknown effect of the existing preload on the steel columns prior to the concrete infill. Composite performance and buckling behaviour of circular hollow section (CHS) steel columns strengthened by infilling concrete under preload was experimentally and numerically investigated in this study. A total of 34 CHS steel columns were tested under pin-ended boundary conditions, and the overall buckling failure modes and corresponding ultimate buckling resistances were recorded. Prior to the member testing, material properties of the steel columns and the infilled concrete were attained. By means of the finite element (FE) software package ABAQUS, elaborate FE models for the CHS columns strengthened by infilling concrete were developed and validated against the obtained test results, which were further verified with other available test data. Using the validated FE models, systematic parametric studies were conducted to examine the influences of the major factors affecting the ultimate capacities of the CHS columns strengthened by infilling concrete, including preload ratios, steel and concrete strengths, steel ratios, initial global imperfections, eccentricity ratios and column slenderness ratios. The obtained test and numerical results were therefore utilised to develop design criteria for predicting the overall buckling resistance of CHS steel columns strengthened by infilling concrete. In view of the difficulty of determining the key parameters in practice and the uncertainty of the strengthening process, a new simplified design coefficient was proposed, taking into account the influence of the preload. It has been demonstrated that accurate and reasonable strength predictions can be provided by the proposed design method.
Buckling behaviour of prestressed steel stayed columns with imperfections and stress limitation
Engineering Structures, 2009
A steel column that is reinforced by prestressed stays, generally has an increased strength in axial compression. In the past, greater emphasis was placed on obtaining a higher critical buckling load. However, detailed knowledge of the post-buckling behaviour is important to ensure the safety and efficiency of the structure. The current work examines the buckling behaviour of a stayed column with geometrical imperfections, and stress limitation relating to possible material failure. A geometrically nonlinear model accounting for imperfect buckling behaviour of a stayed column was formulated using the Rayleigh–Ritz method, and then validated, using the finite element method. It is shown from these studies that the system tends to be most sensitive to imperfections at a prestress level that yields the highest critical load, and that the real maximum load capacity seems to increase as the prestress increases with a given configuration. The findings suggest that the optimal prestress should be greater than that found from using the previous convention that was based on linear analysis.
Strengthening of short reinforced concrete columns by using pre-tensioned steel
Engineering Research Journal - Faculty of Engineering (Shoubra)
Columns are the most important structural elements in any building. When an increase in loads is expected as a result of a change in the use of the building or as a result of errors in design or construction, strengthening becomes essential to increase column capacity. One of the available strengthening techniques is pre-tension steel jackets Therefore, the behavior of short reinforced concrete columns strengthened using this confining technique under uniaxial vertical load is investigated. Steel jacket consists of two u-shape steel parts connected by four angles back-to-back or plates using high strength bolts. External pretension load is applied using external high strength bolts of diameter 16 mm. This study focus on the behavior of columns strengthened using pre-tensioned steel jackets. The experimental program was achieved by testing ten short reinforced concrete square columns of dimensions 150x150 mm and 1500 mm in height. The columns were strengthened using pre-tensioned steel jacket. Columns were divided into five groups to accomplish the research objective. The following parameters affecting the behavior of the strengthened columns are considered; (1) thickness of steel sheets, (2) connections type of steel jacket, (3) value of pre-tension stresses, (4) surface conditions of columns, (5) value of applied vertical load during strengthening and (6) geometry of concrete columns. For the range of the studied parameters, the experimental results show that the use of this technique increases columns failure load by about 7 % to 55 % depending on the effect of each parameter.The experimental results were analyzed numerically and new design formula to predict the ultimate compressive strength of the strengthened concrete columns using this technique was proposed. The average and the standard diviation of the numerical ultimate load to the experimental failure load are 0.98 and 0.04 respectively for the range of the studied parameters.
On the improvement of buckling of pretwisted universal steel columns
Structures, 2016
This paper investigates the improvement in elastic buckling capacity of pretwisted columns using Linear Perturbation Approach. Three different Universal Column (UC) sections of various lengths were considered in the proposed study assuming fixed-fixed and pinned-pinned end conditions. Linear perturbation analysis was first verified by comparing the critical loads of the simulated straight columns with analytical results. Numerical analysis was then extended to simulate the buckling improvement of pretwisted columns considering four different lengths of 4 m, 5 m, 6 m and 7 m, and a range of twisting angles between 0°and 180°. The results showed that the initial twisting has positively impacted the axial capacity of the pretwisted columns. This noticeable improvement is supported by the significant increase in the buckling capacity for the three UC sections, particularly at angles of twists between 120°and 150°.
Post-buckling behaviour of prestressed steel stayed columns
Engineering Structures, 2008
A steel column that is reinforced by prestressed stays generally has an increased strength in axial compression. A geometrically nonlinear model accounting for the post-buckling behaviour of the stayed column is formulated using the Rayleigh–Ritz method and then validated using the finite element method. It is found that the post-buckling behaviour is strongly linked to the level of the initial prestress. As the prestress is increased, the following different levels of the responses can be observed in sequence: initial Euler buckling that subsequently restabilizes strongly, the critical load increasing with a post-buckling path that is either stable or unstable, an upper limit for the critical load where the post-buckling is unstable after an initially rather flat response. These findings are important for designers aiming to achieve safer and more efficient designs for this structural component.
General buckling analysis of steel built-up columns using finite element modelling
Engineering Structures and Technologies, 2012
The paper investigates the general buckling of an axially loaded column using the finite element method with different slenderness ratios of axes x-x and z-z. The paper deals with three different modes of buckling. The conducted numerical experiments have suggested correction factors and appropriate buckling modes of the built-up columns. The obtained modelling results were compared with data on analytical calculations made according to Lithuanian national codes STR and Eurocode 3. The FEM analysis of the builtup column has showed that both codes (STR and EC3) are giving safe enough results for a considered type of conditions for column support. Santrauka Straipsnyje nagrinėjami plieninių spragotųjų kolonų elgsenos ypatumai, atsižvelgiant į skirtingas STR 2.05.08:2005 ir EC3-1-1 metodikas. Didžiausią susidomėjimą kelia faktas, kad, taikant EC3 metodiką, nėra nagrinėjama spragotosios kolonos kluptis apie didesnio standumo x-x ašį (1 pav.). Naudojantis turima ir kitų autorių patirtimi...
IJERT-Effect of Sectional Modulus on Universal and Hollow Steel Columns Subjected To Flexure
International Journal of Engineering Research and Technology (IJERT), 2013
https://www.ijert.org/effect-of-sectional-modulus-on-universal-and-hollow-steel-columns-subjected-to-flexure https://www.ijert.org/research/effect-of-sectional-modulus-on-universal-and-hollow-steel-columns-subjected-to-flexure-IJERTV2IS90661.pdf The sectional modulus of rolled universal and circular hollow steel section columns in BS 5950(2000) was investigated in order to determine the safety of the available section modulus when subjected to flexure. The BS 5950 (2000) was evaluated in the light of Load Resistance Factor Design (LRFD) (1999) of the American Institute of Steel Constructions (AISC) due to their similarities. Results indicate that the safety levels of UC and CHS steel columns varies with the amount of sectional modulus available in flexure while the safety values to be used which depend extensively on column sections are predicted in each column type.