Built-up Columns Research Articles

Structural Characteristics of Welded Built-up Square Concrete Filled Tubular Stub Columns Associated with Concrete Strength

Thin Walled Cold-Formed Concrete Filled Tubular Square Column are manufactured by flare welding at center of column width for cold formed L shape plates of 4 piece and improved composite effect of concrete and steel by vertical inner anchor. Also, Axial resistance of concrete is increased by confine effect of steel tube and steel prevent local buckling of steel column. In this study, we introduced manufacture method of thin walled cold-formed square column steel square concrete filled tubular column and structural performance of the welded built-up square stub column was verified by structural test for ten specimens with parameters of concrete strength, type of steel tube, width to thickness ratio of steel tube.

Retrofitting of Moment Connection of Double-I Built-Up Columns using Trapezoidal Stiffeners

Double-I built-up columns are used extensively in low and medium rise steel structures. When I beam is connected to double-I built-up columns, through the column cover plate, the load transfer at the joint becomes a disturbing problem. To retrofit the connection, a new geometry is considered. In this method the each flange of the beam is connected to the column by a trapezoidal stiffeners plate. A series of five non-linear three-dimensional finite element models were developed using ABAQUS program to study the behavior of the retrofitted connection under cyclic loadings. The outcomes of numerical investigations indicate that the proposed retrofitting method is a proper choice for “special moment frames (SMF)” and the retrofitted models have sufficient strength and ductility. It reduces also the risk of brittle fracture of the full penetration groove weld.

Modification of Moment Connection of I-Beam to Double-I Built-Up Column by Reinforcing Column Cover Plate

Traditional moment connections of I-beam to double-I built-up column have some problems. They are the stress concentration, brittle fracture of the welds and semi-rigid behavior of the connection. To upgrade the connection behavior, it is proposed to replace parts of the column cover plate, situated in critical areas where the beam flanges (or flange plates) connect to the column cover plate, by thicker and larger plates. To investigate the cyclic behavior of the proposed connection, a series of nonlinear finite element analysis were carried out on different models. Results indicate that the modified connection has such a strength and ductility that can be used in special moment frames. Its stiffness is also in the range of a fully restrained connection.

Application of Full Depth Side Plate to Moment Connection of I-Beam to Double-I Column

Double-I built-up columns are used extensively in low and medium rise steel structures. These sections have inherent compression, torsion and bending strength in all directions. The open sides of this type of column are covered with plates. When I beams are connected to double-I built-up columns through the column cover plate, the load transfer at the joint becomes a disturbing problem. To modify the connection, the authors propose a special type of connection using side plates. In this method the end of a beam is connected to the column by full depth side plates instead of direct welding of the beam ends to the column. The new geometry eliminates the traditional welded connection between the end of the beam and the face of the column. A series of eight non-linear, three dimensional finite elements models were developed to study the behaviour of the connection under cyclic loadings. The results obtained from the numerical analyses indicate that the proposed connection geometry has sufficient strength and ductility to be applied in “special moment frames (SMF)” as a “full strength” connection.

Numerical and analytical investigation of collapse loads of laced built-up columns

Built-up columns are often used in steel buildings and bridges providing economical solutions in cases of large spans and/or heavy loads. Two main effects should be taken into account in their design that differentiate them from other structural members. One is the significant influence of shear deformations due to their reduced shear rigidity. The second is the interaction between global and local buckling. These effects are addressed here from both a numerical and an analytical point of view for laced built-up columns. It is concluded that the largest loss of capacity occurs when the local and global Euler critical stresses and the yield stress all coincide. This reduction in capacity becomes more prominent in the presence of imperfections, reaching magnitudes in the order of 50%. Despite the detrimental effects of mode interaction many major design codes do not provide sufficient pertinent guidance. In order to address this issue, a simple analytical method is proposed for calculating the collapse load of laced built-up members taking into account the above effects as well as global imperfections, local out-of straightness and plasticity, which is then verified by means of nonlinear finite element analysis, using either beam or shell elements. The proposed method is found to provide improved accuracy in comparison to EC3 specifications in cases of global elastic failure.

Stability of Built-Up Timber Beams and Columns: Accounting for Modulus of Elasticity Variability

Built-up beams and columns comprised of dimension lumber fastened with nails, bolts or lag screws, are common in construction. Current design practice for stability checks is to use the lower-tail modulus of elasticity ( Emin ) value tabulated for dimension lumber; however, this ignores the averaging effect on Emin that occurs when the mechanically fastened laminations are constrained to deflect in unison. In this paper, we propose a method for checking stability of these assemblies that is based on established statistical theory. A factor ( Cs ) is proposed to adjust Emin value used in column and beam stability calculations to account for the reduced variability of E when the laminations are constrained to deflect together. Using Cs to account for the reduction of Emin variability produces more efficient designs with respect to stability. Two examples are provided and each results in larger design capacities compared to current design methods for built-up beams and columns.

Structural characteristics of welded built-up square CFT column-to-beam connections with external diaphragms

Generally, a box tube, which is used for an existing square CFT structure, is made by welding four plates. The manufacturing efficiency of this steel tube is poor, and it also needs special welding technology to weld its internal diaphragm and the through diaphragm. Therefore, an interior-anchor-type square steel tube was developed using the method of cold-forming thin plates to prevent welding of the stress concentration position, and to maximize the section efficiency. And, considering of the flow of beam flange load, the efficiency of erection and the weldability of the diaphragm to thin walled steel column, the external diaphragm connection was selected as the suitable type for the welded built-up square CFT column to beam connection. And, an analytical study and tests were conducted to evaluate the structural performance of the suggested connection details and to verify the suggested equations for the connection details. Through this study, the composite effect of the internal anchor to concrete, the resistance and stress distribution of the connections before and after the existing column is welded to the beam, the effective location of welding in connection were analyzed.

Seismic Response Evaluation of Moment Resistant Frame with Built-Up Column Section

Problem statement: Moment Resisting Frame (MRF) is widely used as lateral resisting systems when sufficient ductility and deformability are to be met. Response of these structures is strictly dependent upon behavior of their joints, w hereas the analysis of steel moment resisting frame s generally has been performed without considering th e accurate connection behavior. Approach: In this study Finite Element (FE) models had been deve loped to obtain the moment-rotation relations of theoretically fixed connection types which were wid ely utilized in Iran. Using moment-rotation relation obtained from FE analysis, 2D global struc tural model of MR buildings were developed afterwards to evaluate the behavior of the structur es globally. Nonlinear static and dynamic analyses were carried out subsequently to investigate the st ructural behavior of MRFs having built-up column sections. Results: The results proved considerable effects of beam co lumn connection behavior on nonlinear response of structures. Conclusion/Recommendations: It was recommended to consider the effects of connection properties in analysis and de sign of the MRF.

Shear stiffness of pallet rack upright frames

Pallet rack uprights are braced in the cross-aisle direction forming a frame, which behaves like a built-up column. Currently two approaches prevail in the racking industry to determine the shear stiffness of these frames. The Rack Manufacturers’ Institute (RMI) code uses a theoretical formula whereas the Federation Europeenne de la Manutention (FEM) code requires testing. There is a considerable difference in the stiffness values determined by the two approaches. A literature review showed that the stiffness predicted by the RMI code could be up to 20 times higher than the experimental stiffness. The shear stiffness of the frames is influenced by the bracing pattern and the connections between the elements. Local distortion of the thin walled open section upright, joint eccentricity and slip due to bolt clearances all affect the behaviour of the frames. The present paper describes experimental and numerical studies conducted at Oxford Brookes University to evaluate shear stiffness.

Strength buckling predictions of cold-formed steel built-up columns

The aim of this paper is to propose a design procedure for predicting the buckling strength of built-up, cold-formed steel columns based on the two well known methods; the effective width method and the Direct Strength Method. Several design approaches, based on different elastic buckling solutions, were considered in this investigation. Traditional hand methods, without interaction effects between the different modes, and a new numerical spline finite strip method were used to predict the buckling stresses. All of the proposed methods were compared with experimental data on plain and lipped, built-up columns. Results have shown that the effective width approaches are more accurate than the Direct Strength Method. However, both methods can be investigated using more experimental data to assess a practical design method for built-up columns.

A numerical method for buckling analysis of built-up columns with stay plates

A new numerical model based on the spline finite strip method is presented here for the analysis of buckling of built-up columns with and without end stay plates. The channels are modelled with spline finite strips while the connecting elements are represented by a 3D beam finite element, for which the stiffness matrix is modified in order to ensure complete compatibility with the strips. This numerical model has the advantage to give all possible failure modes of built-up columns for different boundary conditions. The end stay plates are also taken into account in this method. To validate the model a comparative study was carried out. First, a general procedure was chosen and adopted. For each numerical analysis, the lowest buckling loads and modes were calculated. The basic or "pure" buckling modes were identified and their critical loads were compared with solutions obtained using analytical methods and/or other numerical methods. The results showed that the proposed numerical model can be used in practice to study the elastic buckling of built-up columns. This model is considered accurate and efficient for the local buckling of short columns and global buckling for slender columns.

Built-up battened columns under lateral cyclic loading

Built-up members with battens designed for typical 2–2.5% of axial load may not behave satisfactorily in the presence of lateral seismic loads. Analytical evaluation of double-channel battened cantilever members designed as per the current practice, and subjected to constant axial compressive load and gradually increasing lateral load showed that the members failed to reach their expected flexural capacity due to lateral instability. The design of members was modified by changing the configuration of battens in the expected plastic-hinge region, i.e., reducing the spacing of battens in end panel by half, and designing battens for a shear demand due to moment capacity of section. The members with battens designed for moment capacity could able to reach the expected flexural strength. Five half-scale test specimens of battened members designed as per the current practice and improved design method were subjected to axial load and gradually increasing cyclic load. The specimens designed as per improved design method showed excellent performance in terms of lateral strength, lateral stiffness, moment rotation characteristics and energy dissipation capacity.

Experimental investigation on built-up columns

This study presents a direct experimental verification of the AISC-LRFD slenderness ratio formulas for built-up compression members. Comparisons of slenderness ratios as specified in various design codes including the AISC-ASD, the AISC-LRFD, the AS-4100 and the CSA S16-01, are also provided. Test results concluded from this study show that the 1999 LRFD formulas generally result in conservative design strengths. However, the 2005 LRFD yields slightly higher strength due to the use of a higher resistance factor of 0.9 instead of 0.85. The design strengths determined based on the slenderness ratio formulas of the Australian Code (AS-4100) are even more conservative. For back-to-back snug-tight bolted sections, the Canadian Code (CSA S16-01) gives virtually the same design outcome as the LRFD. While for back-to-back welded sections, the CSA S16-01 tends to yield a less conservative design.

진동대 실험을 통한 조립식 스틸 전단 패널의 비선형 동적 거동

본 연구의 목적은 인장으로만 저항하는 경사진 스트랩과 기둥으로 구성된 조립식 스틸 (CFS) 전단 패널의 지진하중에 대한 비선형 거동을 조사하는 것이며, 이를 위해 실제 크기의 2층 건물을 설계한 후 진동대 실험을 수행하였다. CFS 전단 패널은 연성이 큰 경사진 스트랩이 주 횡 저항 시스템으로 작용하며, 중력 저항 부재인 기둥은 'ㄷ'자 형태의 스터드를 용접한 것으로서 비콤펙트단면을 가지며 국부 좌굴로 인해 자신의 최대 모멘트 강도를 발휘하지 못한다. 진동대 실험을 통하여 스트랩이 대부분의 에너지를 인장측만으로 핀칭 형태를 가지며 소산하며, 기둥은 국부 좌굴로 인해 기둥은 자신의 최대 강도를 발휘하지 못하나 전체 에너지 소산에 공헌을 하고 있음을 보여주었다. 본 연구 결과, 비록 구조물이 단순할지라도 지진 시 실제 비선형 거동을 진동대 실험으로 조사하는 것은 매우 중요한 과정임을 확인하였다. The purpose of this study was to investigate the nonlinear behavior of a cold-formed steel (CFS) shear panel, which was composed of built-up columns and tension-only diagonal straps for bracing, when excited by earthquake motions. For the purpose, shaketable tests of a full-scale two-story cold-formed steel (CFS) shear panel were conducted. in the shear panel, the diagonal strap is a major lateral force resisting system, which is a very ductile member, and the columns, which are gravity resisting members, are fabricated by wooing studs, which can't develop their full flexural strength because they may buckle locally. The test results showed that the straps dissipate most of energy of the shear panel in a tension-only and pinched way and the columns dissipate it relatively smaller than the straps but they still contribute to overall dissipation. As a result of this study, investigating real nonlinear behavior of a structure in earthquakes is a very important process by shaketable tests even though it is simple.

Shear Buckling of Sandwich, Fiber Composite and Lattice Columns, Bearings, and Helical Springs: Paradox Resolved

As shown three decades ago, in situations where the initial stresses before buckling are not negligible compared to the elastic moduli, the geometrical dependence of the tangential moduli on the initial stresses must be taken into account in stability analysis, and the stability or bifurcation criteria have different forms for tangential moduli associated with different choices of the finite strain measure. So it has appeared paradoxical that, for sandwich columns, different but equally plausible assumptions yield different formulas, Engesser’s and Haringx’ formulas, even though the axial stress in the skins is negligible compared to the axial elastic modulus of the skins and the axial stress in the core is negligible compared to the shear modulus of the core. This apparent paradox is explained by variational energy analysis. It is shown that the shear stiffness of a sandwich column, provided by the core, generally depends on the axial force carried by the skins if that force is not negligible compared to the shear stiffness of the column (if the column is short). The Engesser-type, Haringx-type, and other possible formulas associated with different finite strain measures are all, in principle, equivalent, although a different shear stiffness of the core, depending linearly on the applied axial load, must be used for each. The Haringx-type formula, however, is most convenient because it represents the only case in which the shear modulus of the core can be considered to be independent of the axial force in the skins and to be equal to the shear modulus measured in simple shear tests (e.g., torsional test). Extensions of the analysis further show that Haringx’s formula is preferable for a highly orthotropic composite because a constant shear modulus of the soft matrix can be used for calculating the shear stiffness of the column, and further confirm that Haringx’s buckling formula with a constant shear stiffness is appropriate for helical springs and built-up columns (laced or battened).

Stability criteria for Timoshenko columns with intermediate and end concentrated axial loads

This paper presents exact stability criteria and buckling loads of Timoshenko columns under intermediate and end concentrated loads. The new buckling solutions show clearly the erosive effect of transverse shear deformation on the buckling capacity of the column under compressive loads, especially in stocky and built-up columns with high values of shear parameter s= EI/( κ s GAL 2) and more so when the columns ends are highly restrained such as fixed-pinned columns and fixed-fixed columns. Furthermore, for columns under an intermediate compressive load acting near the base of the column, the effect of transverse shear deformation becomes significant even when the entire column is slender. This is because the column buckling problem behaves like a stocky column problem when the load is acting over a very short portion of the column.

Structural Characterization of Built-Up Timber Columns

The use of novel built-up columns as structural members is investigated. The columns are fabricated from dimensional timber and connected with mechanically applied adhesive, using a proprietary system. An extensive test program was carried out on full-scale built-up timber columns. Axial, flexural, and squash load tests, intended to characterize the service and ultimate behaviors of the columns, are reported. The results of the test program are compared with standard calculations of allowable design capacities for non-built-up timber columns. It is concluded that the built-up columns tested may be safely designed using the same methods as are used for solid timber columns that use the material properties of the constituent timbers. This results in a significant advantage in load-carrying capacity of the built-up sections over solid sections for columns having dimensions greater than 127 × 127 mm (5 × 5 in.).

組立柱のタイロッドのねじ締結軸力解析

This paper deals with the analysis of axial loads in the tie rods to clarify the relationship between the axial loads and the ordinal number of the nuts of built-up columns which are applied the fastening torque. First of all, an experimental analysis of the change of axial loads is performed while fifteen cylindric parts of the built-up columns of spiral staircase are assembled. Next, a numerical analysis of axial loads in the first tie rod is made by the finite element method. The results are summarized as follows. (1) As the ordinal number of the nuts increases, the values of axial loads in the tie rods become higher, and as a result, the first tie rod gets the maximum load. (2) The value of axial load in the first tie rod becomes higher as the set up value of fastening torque increases and the ordinal number of the nuts increases. (3) The calculated values of axial loads in the first tie rod mostly agree with the experimental values. (4) When a set up value of the fastening torque takes 107.9, 147.1 or 186.3 N·m, the values of additional axial loads in the first tie rod decrease at a constant rate as the ordinal number of the nuts increases. (5) The proposed method used in this paper can generally analyze the actual change of axial loads in the tie rods sufficiently and accurately for the practical usage.

Buckling Loads for Built-up Columns with Stay Plates

A method to analyze the buckling load for a built-up column was introduced by Engesser in the last century. Many attempts have been made since then to derive more accurate solutions. All these continuum methods based on the Engesser approach do not consider the effect of stay plates at the end of built-up columns. Atle Gjelsvik modified Engesser's theory to eliminate this drawback. A generalized form of the governing equations provided by Gjelsvik has been presented here, and it is applicable to any built-up column with a continuous web. The buckling loads for built-up columns are obtained for different boundary conditions of practical importance. They are compared with solutions obtained using the Euler and Engesser methods. The solutions are presented in graphical form for easy use. The classical Engesser method is always conservative.

Theoretical and Experimental Study on Buckling of Built-up Columns

A generalized theory is presented here for the analysis of buckling of built-up columns with end stay plates. The theory is a modification over the method presented by Atle Gjelsvik. Buckling loads are found for columns with some typical boundary conditions. Models of built-up columns were tested under axial compressive loads for different boundary conditions. The buckling loads obtained from the experiments agree quite well with the theoretical solutions. The buckling loads obtained were higher than the classical Engesser solution, which led to the conclusion that the theory presented here is an improvement over the Engesser's theory.