Box Columns Research Articles

Effect of weld specifications on seismic performance of built-up box columns

Application of built-up box sections as columns of steel moment frames is very favorable due to their bi-directional flexural resistance. According to seismic provisions, for built up box columns, within a zone adjacent to the beam flange, flange and web plates of box columns shall be joined by complete joint penetration (CJP) groove welds. In spite of the fact that fillet welds are much easier to execute and are economically more efficient, they are prohibited within the panel zone of columns. In this paper the effect of weld specifications on seismic performance of panel zone in built-up box columns with corner welded joints is experimentally investigated, mainly focusing on the comparison of performance of fillet and groove welds used for fabrication of this type of columns. Based on the results of the experimental program on 1:2 scale specimens, representing beam to column connections of steel special and intermediate moment frames built using fillet and groove welds in panel zones, it is concluded that the performance of fillet welds could be as good as CJP groove welds in panel zones of built-up box columns for the qualifying drift angle of steel moment frames.

Numerical Study of Panel Zone in a Moment Connection without Continuity Plates

ABSTRACT Built-up box columns are more frequently used in earthquake-prone regions such as Japan and Iran. As the installation process of continuity plates and welding inspection are difficult, expensive, and time-consuming, this study was aimed at experimentally and numerically investigating continuity plate elimination from built-up box columns with regard to the seismic design specifications of special and intermediate moment resisting frames. Results of an experimental study of three full-scale rigid connections between I-beam and box-column subjected to cyclic loading were used for comparison and verification of numerical results. Experimental study showed that samples reached story drift angle of 0.06 radians before experiencing the permissible strength degradation. Therefore, the tested connections satisfied the criterion for special moment resisting frame (SMRF) in AISC. Based on observations of crack initiation and propagation in the experimental study, a rupture index (RI) was employed to investigate the effects of different complete joint penetration (CJP) groove welding methods used in the experimental study on connection ductility as well as to identify the regions prone to crack initiation and propagation. Both the numerical and experimental results showed the superiority of using back plate in CJP welding.

Seismic Performance Evaluation of Steel Box-Column Connections with ESW Stiffeners

The purpose of this study is to evaluate the seismic performance of steel box-column connections with electro-slag welding (ESW) stiffeners. Steel box columns have been widely adopted in seismically active areas, such as Japan and Taiwan. It is a common practice to weld diaphragm plates to the inner walls of steel box columns using the ESW process. However, there is still a lack of study evaluating the seismic performance of these steel box-column connections. In the first part of this paper, a literature review examines ESW stiffeners and their impacts on steel box-column connections. In the second part, finite element analysis is conducted on ESW misalignment and eccentricity. The result shows a correlation between connection failures and ESW stiffeners. In addition, ESW fusion diameters can affect the connections more significantly than ESW eccentricities and the thickness of diaphragm plates.

Presenting a New Detail for the Rigid Connection Between I-Shaped Beam and Concrete-Filled Steel Tube Column with Stiffened Channel Link

Connections play an important role in the response of steel moment resisting frames to seismic loading. Prequalified rigid connections are applicable to I-shaped or box columns. In I-shape beam to concrete-filled tube (CFT) column connections, continuity and doubler plates cannot be added to the column. Various details have been proposed to address this issue, many of which are not constructionally convenient to implement. The aim of this study is to present a simple and suitable detailing for I-shape beam to concrete-filled tube column connections. To that end, six full-scale experimental samples were built and subjected to cyclic quasi-static loading. In the samples, stiffened and un-stiffened channel links were used to connect the beam to the column. In each sample, the stiffeners were installed on a different position on the channel link. The results showed that compared to the connection in which the beam is directly connected to the column, using the stiffened channel link with stiffeners along the beam’s flange increases the strength and ductility of the connection by 12% and 72%, respectively. Considering their desirable performance and easy implementation, these connections can be considered as a suitable detailing for I-shape beam to CFT column connections in seismic regions.

Advance High-Strength Steel for External Diaphragm Box Column Production by Using Robotic GMAW

Advance High-Strength Steel for External Diaphragm Box Column Production by Using Robotic GMAW

Residual stresses of box and I-shaped columns fabricated from S960 ultra-high-strength steel

Ultra-high-strength steel (UHSS) with a nominal yield stress of 960 MPa is of significant interest for the design of heavily loaded compressive members, such as high-rise buildings, long-span bridges and large-scale infrastructure. However, the residual stresses induced by the fabrication process can be detrimental to the structural members. In particular, compressive residual stresses can result in premature buckling and the ultimate strength of fabricated columns will be reduced. To date, research pertaining to the distribution of the residual stresses for UHSS column is limited. An experimental program about the measurements of residual stress distributions for UHSS box and I-shaped columns is therefore presented herein. Measurements of residual stress were undertaken on two box and two I-shaped columns having various width-to-thickness ratios by using the non-destructive neutron diffraction method. The distributions of residual stress in three orthogonal directions for each specimen was measured. The influences of column width-to-thickness ratio on residual stress distributions were investigated and discussed. In addition, simplified analytical models for the box and I-shaped column were established to facilitate the buckling analysis for such UHSS columns. Comparisons of the residual stress distributions between the experimental results and analytical model demonstrated a good agreement and this model can be safely used for the fabricated high-strength-steel (HSS) and UHSS column.

Experimental study on fire resistance of cold-formed steel built-up box columns

Abstract Cold-formed steel built-up box columns are commonly used in mid-rise cold-formed steel buildings to resist applied loads. Numerous studies have been conducted to evaluate the load-bearing capacity of the columns at ambient temperature but there is very limited research on the fire resistance of the built-up columns. In this paper, a full-scale experimental investigation on fire responses of sixteen axially loaded cold-formed steel built-up box columns was conducted. As a benchmark, the load-bearing capacity of the columns at ambient temperature was tested first. The effects of heating rate, load ratio, and temperature distribution pattern on the fire responses of the columns were investigated in the fire tests. The test results indicated that increasing the load ratio led to a significant decrease in the member critical temperatures, which consequently reduced the fire resistance of the columns considerably. For those columns with an applied load ratio lower than 0.6, they were expected to have member critical temperatures higher than 500 °C. Moreover, with thin-walled steel and no fire protection the column temperatures increased quickly, leading to failure in no more than 12 min in a fast fire even with a low load ratio. It was also found that creep deformation associated with the low heating rate was one of the important factors that could be detrimental to the fire resistance and member critical temperature. As for the effect of temperature distribution patterns in the columns on the member critical temperature, it was found that the member critical temperatures for specimens with non-uniform temperature distribution were slightly higher than those with uniform temperature distribution.

Influence of single hat crash box flange triggering and impactor top plate welding strategy on axial crash foldability of AHSS & UHSS sheets

Axial crash tests are usually performed in order to assess the crash foldability of AHSS & UHSS sheets in the framework of a material homologation process. With a real component like single hat column geometry with RSW flange welded and MAG welded top/down head plates crash box design, it is getting more and more difficult to assess properly the crash performance of AHSS & UHSS steel grades with tensile strength Rm ⩾ 1000 MPa (RSW: resistance spot welded, MAG: metal active gas welded). The crash box flange is namely excessively stiff and prevents the initiation of a proper crash-folding pattern, resulting in a high amount of material failure, which makes some judgement about material crash ability difficult. Therefore the present experimental investigation focuses on the one hand on the triggering strategy in the top flange area to break the excessive stiffness of the spot-welded flange. On the other hand some effort has been put in the improved joining strategy of the top impactor head plate to the crash box itself. The top head plate is usually necessary in real components for load transfer to the crash box and fixation to the surrounding body in white structure. Some excessive welding of the top impactor plate, especially in the already largely stiffened spot-welded flange region, has however a strong detrimental effect on crash fold initiation. The welding of the top head plate in the flange and back crash box areas is avoided, thus increasing the degrees of freedom between top impactor plate and crash box column along with an effective reduction of the initial crash box bending stiffness. Some minimized welding of impactor plate to the crash box column, especially avoiding flange areas, allows a successful initiation of the crash folding process but only in combination with pressed round triggers in the flange area near the first spot weld. With these modifications it is first possible to assess and rank the intrinsic axial crash foldability of the material with Rm ⩾ 1000 MPa by means of a crack length based crash index.

Improved design procedure for battened cold-formed steel built-up columns composed of lipped angles

The present paper reports the numerical parametric study on the structural behaviour of battened cold-formed steel built-up box columns composed of four lipped angles. The validated numerical model with the experimental results reported by the author in the comparison paper was employed to carry out parametric studies to produce numerical data over a wider range of global column slenderness by varying the sectional compactness of the lipped angle section, batten spacing, and global column slenderness. The numerically derived results were employed to check the accuracy of the current design rules. The results of the assessment revealed the limitation of the current design rules in the prediction of the capacity of the CFS built-up battened box columns, which was mainly associated with the influence of unbraced chord slenderness and interconnector stiffness on the buckling behaviour. Therefore, improved design procedure was proposed in the framework of AS/NZS specifications (AS/NZ 4600:2018) and European standards (EN1993-1-3:2006) for the safe, less scattered and reliable design strength predictions of battened CFS built-up columns composed of four lipped angles.

Cyclic Behavior of Electroslag Welded Joints in Beam-to-Built-Up Box Column Steel Moment Connections

AbstractSteel special moment frames (SMFs) with built-up box columns are often used in taller buildings when two orthogonal axes of participating moment frames intersect. Interior diaphragm (or con...

Study on the impact behaviour of concrete-encased CFST box members

This paper presents an experimental and numerical study on the lateral impact behaviour of concrete-encased concrete-filled steel tubular (CFST) box beams and columns. A total of 20 specimens with test parameters including the impact energy, the boundary conditions and the axial load level, are tested under a drop hammer impact apparatus. The experimental results, namely the failure modes, the time-history of the impact force and mid-span deflection, as well as the whole impact process, are analysed. It shows that the specimens fail in a shear-flexural pattern under the impact. The major features of the impact force and mid-span deflection curves are summarised and analysed. The influence of test parameters on the impact behaviour of the specimens, namely the peak value of the impact force, the impact duration and the residual mid-span deflection, are also discussed. A finite element analysis (FEA) model is established to investigate the composite effects between the RC and CFST components. The analysis shows that the RC component is the major impact resistance component in the structure. The CFST components, on the other hand, is well protected by the RC component and do not experience severe damage. The composite effects make the structure safer under impact loading and easier to be restored after impact.

Behaviour of cold-formed steel built-up battened columns composed of four lipped angles: Tests and numerical validation

This article mainly investigates the behaviour and strength of built-up battened box column composed of lipped angles under axial compression. Ten specimens were fabricated and tested under pinned with warping-restrained end condition including two different cross-section dimensions of columns with five different geometric lengths. Three material tensile coupon tests were conducted to obtain the material properties of the steel used for fabricating the test specimens. The overall initial geometric imperfections were measured. The plate slenderness, member slenderness, chord slenderness and slenderness of batten plates may affect the compression behaviour of cold-formed steel built-up battened box columns and were accordingly investigated. It was found that the chord slenderness significantly affects the compressive strength of the built-up columns. Test results, including the compression resistances, the load versus displacement responses and the deformed shapes were presented. The test strengths were compared with the design strengths predicted using the North American Specifications (AISI-S100:2016), EuroCode (EN1993-1-3:2006) and design equations proposed by EI Aghoury et al. The design strengths predictions by these two design standards were unconservative, with EI Aghoury et al.’s standard performing better. Finite-element models were developed and verified against the test results.

Experimental and numerical investigations on the axial capacity of cold-formed steel built-up box sections

Built-up box sections are becoming increasingly popular for column members in cold-formed steel (CFS) construction; uses of such sections include CFS trusses, space frames, and portal frames. In this article, the built-up box sections are formed through two identical lipped channels connected at their flanges with self-drilling screws. In such an arrangement, independent buckling of the individual channels is prevented by the screws. This paper presents an experimental investigation on axial capacity of built-up CFS box sections. Tests were conducted for different values of slenderness from short to slender columns. In total, the results from 16 experimental tests are reported. Of these, 8 tests were conducted on built-up CFS box sections and the remaining 8 tests were conducted on single channel sections. Load-axial shortening relationship, and failure modes are discussed for built-up columns. Nonlinear finite element (FE) models were developed for built-up CFS box sections and single channels. FE models considered material nonlinearities, initial imperfections and modeling of intermediate fasteners. FE results showed good agreement against the test results. A parametric study was conducted which comprises 148 models to investigate the effect of fastener spacing on axial capacity of built-up CFS box sections. Both FE and test results were compared against the design strengths calculated in accordance with the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS). From the comparison, it was observed that the AISI & AS/NZS are conservative by around 17% while determining the axial capacity of such built-up CFS box columns.

Load-deformation characteristics and performance of internal diaphragm connections to box columns

This paper presents numerical and theoretical studies on the performance of internal diaphragm connections to box columns. The study aims to investigate the static and cyclic performances of the connections including the behavior of diaphragms. This paper contains an assessment of the numerically and theoretically parametric studies on plate-to-box column connections considering several influence parameters, such as diaphragm, plate width, and column thickness. Subsequent sections discuss the prediction and validation of strength of the connections, followed by the performance of wide flange (WF) beam-to-box column connections. The results are presented and discussed as finding that diaphragms were the key elements to enhance the performance of the connections.

Rib-reinforced moment connection of steel beam to box column

Due to their excellent biaxial bending strength, box columns are widely employed in countries with high seismic risk such as Iran and Japan. Although extensive research into the moment connections between I-beams and wide-flange columns has been conducted, a review of the literature indicated that studies on I-beam to box column moment connections are insufficient. To fill this gap, the cyclic behaviour of a two-sided moment connection of an I-beam to built-up box column was studied in this work. Non-linear finite-element models of the connection were developed and validated using test results available in the literature. In the studied connection, the beam flanges are joined to the column flange through flange plates. To reinforce the connection, vertical top and bottom rib plates were welded to the column flange and the flange plates. A parametric study was carried out to investigate the influences of the geometry of the rib plates on the behaviour of the connection. The results indicated that rib plates decrease the stress on the groove weld between the flange plates and the column flange and have insignificant influences on the global responses of the connection.

Slenderness limits for fabricated S960 ultra-high-strength steel and composite columns

Ultra-high-strength steel (UHSS) has been gaining increasing attention globally due to its significant structural and economic benefits. Specifically, the use of UHSS in steel and composite column sections can reduce the dimensions and self-weight of the structural components. However, the utilisation of UHSS slender sections also renders the structural members more susceptible to local buckling. The reduced ductility as well as less strain hardening of UHSS can also affect the post-buckling load. In order to clarify the local buckling and post-buckling load of compressive members using UHSS plates, the authors herein present an extensive experimental program. A total of sixteen steel and composite specimens are tested with the slenderness limits (λey) and effective widths (be/b) being identified. Finite element models which account for the effects of residual stress and initial geometric imperfection are developed to capture the buckling behaviour of the box and I-section columns. The enhancement of local buckling and post-local buckling load of UHSS composite sections due to the presence of infilled concrete is demonstrated. In addition, the slenderness limits and effective widths of both bare steel sections and composite sections incorporating UHSS plates are further compared with existing codes of practice. Corresponding design recommendations are consequently provided.

Structural behaviour of concrete-encased CFST box stub columns under axial compression

The axial performance of a type of concrete-encased CFST box stub column, which consists of the outer reinforced concrete (RC) box column and six embedded CFST components, is investigated in this study. A total of eight axial compression tests on the concrete-encased CSFT box specimens under axial compression were carried out. A finite element analysis (FEA) model was developed to analyze the structural behavior of the composite columns. The effects of material nonlinearity and interaction properties between the concrete and the steel tubes on the simulation were considered. The verified FEA model was then used to conduct a full-range analysis on the load-deformation responses. The results of typical failure modes, internal load and stress distributions and the contact stresses between the concrete and the steel tubes were also discussed. Parametric studies were conducted to investigate the effects of geometric and material properties on the compressive behavior of the concrete-encased CSFT box members. Finally, a simplified model was proposed to predict the ultimate strength and the initial stiffness of the concrete-encased CFST box stub columns under axial compression.

Cyclic lateral load test and finite element analysis of high-strength concrete-filled steel box columns under high axial compression

This paper presents an experimental study of the seismic performance of high-strength concrete-filled box columns (CFBCs) under combined axial and cyclic lateral loads. Specimens were made of high-strength SM 570 M steel (with yield strengths between 520 and 580 MPa), and concrete with compressive strength (fc') greater than 80 MPa. Three parameters that affect the seismic performance of CFBCs were investigated: the width-to-thickness (b/t) ratio of the steel column, magnitude of the axial load, and the addition of concrete infill. The specimens, which were 280–420 mm in width and 2000 mm in height, were tested under combined axial (4058–10,090 kN) and cyclic lateral loads. Experimental results indicated that the lateral displacement ductility decreases significantly with an increase in either the axial load or b/t ratio. The addition of concrete infill inside a hollow steel box column does not improve the lateral displacement ductility of CFBCs under high axial load. Although the CFBC specimens satisfied the b/t requirement of a highly ductile member, as per AISC Seismic Provisions (2016), specimens under high axial load (40%Pn) failed at 4% drift, indicating that the requirement does not guarantee that CFBCs will sustain high axial load under significant drift (i.e., >3%). The Eurocode 4 (2009), AISC Specification (2010), and Architectural Institute of Japan (2014) reasonably estimate the flexural strength of high-strength CFBCs under axial load; however, ACI 318 (2011) does not. The finite element analysis program ABAQUS can be used to estimate the hysteretic behavior of specimens before significant strength degradation.

Buckling strength and ductility evaluation of thin-walled steel stiffened square box columns with uniform and graded thickness under cyclic loading

Thin-walled steel stiffened square box columns are becoming an increasingly attractive choice as cantilever bridge piers due to their architectural, structural and constructional advantages. This paper investigates the behavior of thin-walled steel columns with uniform square box sections (B) and newly proposed graded-thickness square box sections (GB) under constant axial and cyclic lateral loading. The analysis is carried out using a finite-element model (FEM) which takes into account the effect of both material and geometric nonlinearities. First, the accuracy of the employed FEM is verified based on the experimental results. Then, a GB column with size and volume of material equivalent to a B column is introduced. The proposed GB column is proved to have significant improvements in strength, ductility, and post-buckling behavior as compared to its counterpart B column. As a part of this research, a comprehensive parametric study is carried out to investigate the effects of main key parameters including: the width-to-thickness ratio parameter (Rf), the column slenderness ratio parameter (λ), the magnitude of axial load (P/Py), and the number of loading cycles (N) on the strength and ductility of the B and GB columns. Finally, a series of proposed formulae for strength and ductility evaluation of the B and GB columns is given.

A New Simple Method for the Strength of High‐Strength Steel Thin‐Walled Box Columns Subjected to Axial Force and Biaxial End Moments

The strength of Q460 steel welded thin‐walled box columns under biaxial bending is investigated by an FE model. The numerical results, together with available experimental data, are compared with the American Specification ANSI/AISC 360‐10. It shows that ANSI/AISC 360‐10 provides a good estimate over a wide range of column slenderness ratios; but it severely underestimates the strengths of beam‐columns with large slenderness ratios and slightly underestimates those of beam‐columns made from HSS with fy = 741 MPa, and the calculation is more complicated because of using an effective width concept. Therefore, a simple and effective calculation method is proposed. Also, a comparison is made between the proposed formulas and the available experimental results. It shows that the proposed formulas can precisely evaluate the local‐overall interactive buckling strength of HSS beam‐columns and, in most cases, are also suitable for beam‐columns fabricated from mild steels. The proposed formulas are simple and, meanwhile, achieve the same level of accuracy as ANSI/AISC 360‐10.