Built-up Box Research Articles

Parametric study of 3D steel moment connections with built-up box column subjected to biaxial cyclic loads

In this numerical research, the variation of cyclic behavior of beam-to-box column connection was studied. Dimensional and load conditions were parametrically evaluated with the goal of assessing the applicability and use of this biaxial moment connection according to the Seismic Provisions, such as bending strength and rotation capacity, secant and tangent stiffness, dissipated energy and strong column-weak beam relationship. A total of 83 different models of 3D connections were developed using in ANSYS software with the load at the top of the column. Results show a cyclic behavior not controlled by axial load. However, the variations of clear span to depth beam ratio caused degradation of the strength, secant and tangent stiffness as well as in dissipated energy. The 80% of plastic moment of beam and rotation at 4% interstory drift were reached for all models analyzed according to criteria established in AISC 341. Finally, the configurations designed with low levels of axial load are controlled by the design of the web panel zone shear, while configurations designed for high levels of axial load are controlled by the strong column-weak beam criterion. • The hysteretic response curves of the joints with end-plate connections and built-up box column subjected to cyclic loading were plumped. • The beam can concentrate the inelasticity effectively in a wide deformation range. • The behavior exhibited is acceptable for 7 < L/d < 20 ratio. • A numerical prequalification was possible.

Investigation of built-up box columns composed of four cold-formed steel channels

A three part study was conducted to investigate the compression behavior of a built-up box column made from four cold-formed steel (CFS) channels, including an experimental program, finite element study, and evaluation of building code prediction approaches. The experimental study included fifteen box column specimens with various effective lengths and varied eccentricity. Twist and warping of the ends of the specimen were restrained. The test results indicated that the dominant failure modes were global flexural buckling, local buckling, and concentrated localized deformation caused by local buckling. A finite element (FE) study was then conducted to broaden the investigation beyond the tested configurations and it was found that varying the screw spacing from 150 mm to 450 mm has little influence on the axial compressive behavior (less than 4%) and that web height-to-thickness ratio was a key parameter affecting axial compression strength. Finally, the accuracy and applicability of the available design methods for predicting the strength of the box columns were evaluated including the ”effective width method” in which the modified slenderness ratio was not considered in AISI S100-16, the ”direct strength method” in AISI S100-16, the method in the Chinese building code, and the method in EN 1993-1-3. For the box columns considered in this study, the four design methods produced predictions of the concentric axial compression strength that were between −33% to ＋6% of the expected actual strength. The selected design methods produced the average results of eccentric axial compression strengths that were between 8% to 25% conservative as compared to the test and FEA results.

Design of locally buckling cold-formed steel built-up columns formed by unlipped channel sections

This study proposes a design procedure for the local buckling strength prediction of cold-formed steel (CFS) built-up I and box section columns based on the Effective Width Method (EWM) and the Direct Strength Method (DSM). For this, the ultimate strength of the built-up sections made of two plain unlipped channels is obtained using the finite element (FE) analysis. First, some compression tests on built-up sections are performed to validate the FE models. Then, a detailed parametric study using the validated FE models is conducted for sections with a wide range of slenderness (1≤λl≤3) where λl is the square root ratio of yield stress to the local buckling stress of the cross-section. The results show that the local buckling strength of built-up I sections is equal to the sum of its section’ strength, whereas for box sections, the strength can be 20%–25% higher as the nesting of sections will alter the local buckling characteristics. The EWM (with k factor approach) and authors’ DSM based design procedure can predict the strengths of the built-up I sections well but predict conservative strengths for the built-up box sections. This issue is resolved in this paper by proposing a simple cross-sectional model based on the constrained local buckling deformations of the built-up box section. When the buckling stress results of the proposed model were used with the EWM and authors’ DSM design procedures, the predicted local buckling strength results matched well with those of the present numerical study. In addition, the proposed design procedure provided more accurate strength predictions than the existing DSM and those presented in the literature for the built-up section columns.

High-strength steel deep H-shaped and box columns under proposed near-fault and post-earthquake loadings

This paper presents the seismic evaluation of high-strength steel first-story columns in a seven-story dual system, composed of a special moment-resisting frame (SMRF) and buckling-restrained braced frame (BRBF), in near-fault and post near-fault earthquakes. Nonlinear time history analyses were conducted on the frame to develop loading protocols that represent seismic demands on the first-story columns in the dual system. The proposed near-fault displacement protocol has a large displacement pulse from -2 to +4% drift, followed by small displacement cycles oscillated at a residual drift of 2.5%. The proposed far-field displacement protocol is an increasingly cyclic displacement protocol with one cycle after a drift of 2%. Two built-up H-shaped column specimens (HC-20-B and HC-20-C) and two built-up box column specimens (HBC-40-B and HBC-40-C), representing the first-story columns in the dual system, are tested under constant axial force (0.2Py or 0.4Py) and lateral drifts based on the proposed loading protocols. These specimens that satisfy the compactness requirement of highly ductile members in AISC 341-16 (2016) show acceptable seismic performance under the near-fault earthquake loading. However, the flexural strength of HC specimens decreases with increasing drift, and that of HBC specimens increases without strength degradation. The HBC specimens can perform well in the subsequent near-fault or far-fielding earthquake loading, which is not the case for the HC specimens due to significant local buckling. The NIST (2017) backbone curve reasonably predicts the test envelope of the HC specimens, but significantly underestimates the test envelope of the HBC specimens.

Web crippling of cold-formed steel built-up box sections

This research focused on the experiments, numerical simulations and design of cold-formed steel (CFS) built-up box sections failed by web crippling. The built-up box sections were formed by fastening two equal-sized unlipped channel sections face-to-face by self-tapping screws. Thirty-five web crippling tests are firstly described, which were conducted under Interior-Two-Flange (ITF), End-Two-Flange (ETF), Interior-One-Flange (IOF) and End-One-Flange (EOF) loading cases. The number and location of screws were varied along the channel flange width to study the influences of screw arrangements. The specimens were loaded along the major axis and the minor axis. Numerical simulations were also conducted. The experimental results were used in the development and validation of nonlinear finite element (FE) models. After validation, the validated numerical models were used for a comprehensive parametric investigation accounting for various cross-section dimensions, bearing lengths and screw arrangements. The experimental and numerical data were used to evaluate the design methods provided in the current design codes. Finally, two different design methods were proposed and assessed through the reliability analysis.

Seismic performance of stainless-steel built-up box columns subjected to constant axial loads and cyclic lateral deformations

The seismic behavior of stainless-steel built-up box columns subjected to constant axial loads and cyclic lateral deformation that are used in special moment frames (SMFs) has been investigated through finite element (FE) analysis. A total of 208 numerical models were conducted to cover a range of parameters affecting the seismic behavior of the columns. These include the web slenderness ratio, flange slenderness ratio, global slenderness ratio, axial load level, and lateral loading protocol. The performance indices of overstrength factor, axial shortening, out-of-plane deformation, plastic hinge length, and rotation capacity were calculated and compared. Local buckling of the columns also was investigated and was shown to be responsible for a sharp rise in plastic strain and premature fracture. Predictive empirical formulas are proposed for calculating the plastic hinge length and axial shortening. All previous experimental data on built-up box columns composed of different types of steel materials were collected and added to the FE analysis results to form a reliable database. It was found that ASCE 41-17 conservatively calculated the plastic rotation angles of the built-up box columns. Furthermore, it was indicated that the highly ductile limits of AISC 341-16 for stainless-steel built-up box columns are satisfactory.

Experimental and numerical studies on stress concentration factors of high strength steel fabricated box X-joints

High strength steel (HSS) is commonly available in the form of steel plates. The built-up box tube with sharp corners which is welded from four steel plates is usually fabricated for construction. The stress concentration factor (SCF) is crucial for the determination of the hot spot stress range which governs the high-cycle fatigue resistance of tubular joints. This paper presents experimental and finite element (FE) investigations on the SCF of HSS fabricated box X-joints. Four X-joints which are fabricated from built-up box tubes with a nominal yield stress of 890 MPa are tested under brace axial compression. The SCFs at typical hot spot locations are obtained using strip strain gauges. A FE model which has been validated against the test results is employed to conduct the parametric study on totally 112 fabricated box X-joints. The loading cases of brace and chord axial loading are covered. The effects of brace to chord width ratio, chord width to wall thickness ratio and brace to chord wall thickness ratio on the SCFs at the hot spot locations are revealed. The CIDECT SCF formulae are shown to be not suitable for the fabricated box X-joints under brace and chord axial loading. More accurate SCF equations are proposed to calculate the SCFs at the hot spot locations of the box X-joints.

Pengaruh Jarak Sekrup terhadap Kapasitas dan Perilaku Penampang Tersusun Boks (Closed Section) Baja Canai Dingin

The capacity and behaviour of cold-formed steel built-up sections are affected by the arrangement of the connections. This study aims to determine the effect of the screw spacing to the bending capacity and behaviour of the cold-formed steel built-up box section which made from lipped-channel (1.0 mm thick, 81 mm web height, 8.5 mm lip height, upper and lower wing width 38 mm and 40 mm). A total of 19 beams with a length of 1200 mm each are subjected to pure bending moments by applying two point loads spaced 600 mm in the midspan. The screw spacing variations in the moment span are 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 328 mm, and 350 mm. The test results show the average of bending capacity of the beam test is increasing with the reduction in screw spacing while the screw configuration also affects the beam capacity. Analysis of the bending capacity using the effective width method and the direct strength method based on AISI S100-16 gives very conservative results. The failure mode of the built-up box sections were observed in the form of local buckling, distortion, and lateral-torsional buckling.

Nonlinear behavior of cold-formed stainless steel built-up box sections under axial compression

Stainless steel is a highly versatile material, possessing a unique selection of properties that can be exploited in structural (load bearing) applications. In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of built-up cold-formed stainless steel box sections as compression members are becoming popular. The AISI/ASCE Standard, SEI/ASCE-8–02 and AS/NZS do not include the design of stainless-steel built-up channels and very few experimental tests or finite element analyses have been reported in the literature for such face to-face cold-formed stainless-steel channel box sections. Thus, this paper presents a numerical investigation on the behavior of cold-formed stainless-steel built-up channel box sections. Three different grades of stainless steel i.e., duplex EN1.4462, ferritic EN1.4003 and austenitic EN1.4404 were considered. Effect of screw spacing on the axial strength of such built-up channel box sections was investigated. As expected, most of the short and intermediate columns failed by either local–global buckling interaction or just by local buckling, whereas the long columns, failed by global buckling. A comprehensive parametric study was carried out covering a wide range of slenderness and different cross-sectional geometries to assess the performance of the design guidelines by AISI and AS/NZS. In total, 180 finite element models were analyzed. From the results of the parametric study, it was found that the AISI and AS/NZS are conservative by around 15% for duplex grade (EN1.4462) of stainless-steel built-up box columns. However, for ferritic (EN1.4003) and austenitic (EN1.4404) grades of stainless-steel built-up box columns, the AISI and AS/NZS were conservative by only 5%.

Experimental study of the influence of welding space in cold-formed built-up box flexural members

Current building codes for cold-formed steel structures specify flexural design guidelines for C open sections. Nevertheless, there are no guidelines to estimate the capacity for a cold-formed built-up box-beam composed of two C-sections in contact, considering weld seam spacing as a relevant constraint. This research compares the nominal flexural strength of a beam section, determined by theoretical formulations described in AISI S100-16, and experimental investigation on 20 beams, considering four seam-weld spacings (ranging from 0 mm -continuous- to 900 mm). The length of the specimens was 1800 mm, with a cross-section of 220 mm × 160 mm; the base material thickness was 1.5 mm. The experimental and analytical evidence suggests that a maximum separation between seam welds (amax), calculated as a mean value between the theoretical distortional buckling lengths for the single C-section (Lcrd-S) and the box-section (Lcrd-D), results in a reasonable parameter to guarantee the maximum capacity of the box section. It is imperative to continue performing tests and computational modeling for these profile configurations and, thus, suggest an improved formulation.

Simplified design method of cold-formed steel columns with built-up box sections

The built-up box section members in this paper consist of single cold-formed steel (CFS) C-section and U-section basic components, which are connected by self-drilling screws at the flanges. This study incorporates experimental and theoretical research on the buckling behavior and ultimate strength of axially loaded pin-ended CFS built-up box section columns as affected by local and local-flexural interactive buckling modes. In total, 28 specimens were prepared and tested under axial compression. The test results revealed visible local buckling or local-flexural interactive buckling for specimens. Thereafter, finite element models were established by the ABAQUS software and validated with the structural behavior of the test specimens. The effects of the slenderness ratio, web depth-to-thickness ratio and screw spacing on the ultimate strength of the built-up columns were investigated based on the numerical analysis. Finally, based on the test results of this research as well as previous works in the literature, a simplified design method was proposed to predict the ultimate strength of built-up box section columns. By comparing the predicted results against the test results, the proposed method was subsequently validated.

Experimental Study of the Ductility of a Submerged Arc Welded Corner Joint in a High-Performance Steel Built-Up Box Column

Submerged arc welding, which is generally used for the corner joint of box-section columns, is a welding process with a high heat input. The influence on the strength and toughness of the heat-affected zone is an important concern, especially when used with a high-performance steel that may be more susceptible to heat input. The ductility of the welded corner joint is one of the important factors to ensure safety against external forces, such as during severe earthquakes. In this study, a series of material and cyclic loading tests of the corner joint comprising SA440C high-performance steel fabricated by submerged arc welding were conducted. The experimental results indicated that the welded corner joint comprising SA440C steel is ductile enough to dissipate input energy caused by the strong ground motion from an earthquake.

Lateral cyclic testing and backbone curve development of high-strength steel built-up box columns under axial compression

The AISC 341 (2016) has a more stringent width-to-thickness (b/t) limit for highly ductile hollow box columns (HBCs) than the AIJ (2010) or Taiwan Code (2010), resulting in significant thickness difference in design. Moreover, the cyclic backbone curves based on ASCE 41 (2013) and NIST (2017) underestimate the post-buckling flexural strength of HBCs, particularly in high axial compression force. This paper presents test results of six full-scale, built-up HBCs using SM 570 M steel with the actual yield strength of 460–530 MPa. The lateral cyclic behavior of built-up columns was studied in terms of different b/t ratios, magnitudes of axial compression forces, and lateral drift histories (i.e., cyclically symmetric versus near-fault displacement histories). The built-up box columns were 290–400 mm wide with b/t ratios from 11 to 21, 4000 mm high, and tested laterally with both ends fixed after under a constant axial compression force, 2591–7935 kN. The HBC specimens which were designed based on the highly ductile member requirement in AISC 341 (2016), even under an axial compression force (=40%Py), performed satisfactorily at 4% drift and experienced flange and web fracture at 5% drift. However, the HBC specimens that satisfied the most compact b/t requirement in AIJ (2010) or Taiwan code (2010) did not perform well at 4% drift, losing the axial capacity after significant column local buckling and shortening. The gathered test data, supported by more test data in this work, were analyzed by a multiple regression method to obtain empirical formulations for predicting the maximum column moment, plastic rotation and post-yield hardening parameters. The proposed formulation reasonably predicts the first-cycle envelope curves of built-up HBCs, improving prediction results based on ASCE 41 (2013) and NIST (2017).

Compressive behavior of built-up double-box columns consisting of four cold-formed steel channels

Thirty specimens of built-up double-box columns consisting of four cold-formed steel channels were experimentally tested under concentric and eccentric axial compression. The test specimens had varied cross-sectional dimensions (outside dimensions equal to 89 mm × 147 mm or 86 mm × 96 mm), different effective lengths (3200 mm, 1700 mm, 210 mm, or 135 mm), and different thicknesses (1.2 mm or 1.5 mm). The load vs. displacement curves and the measured compression strength of specimens were obtained and the failure modes were analyzed. The test results showed that the failure mode of the long specimens (L/r between 103 and 108, where L is the calculated length of the column, r is the minimum radius of gyration) was flexural buckling about the weak axis. The typical failure modes of medium length specimens (L/r between 53 and 57) and short specimens (L/r between 4 and 8) subjected to concentric axial compression were deformation concentration caused by large local buckling. The failure mode of the medium length specimens under eccentric axial compression was flexural buckling, except for the specimens whose web height was 147 mm and the eccentricity direction was along the minor axis, for which the failure mode was deformation concentration. Then, finite element (FE) models considering geometric, material, and contact nonlinearity were developed, compared to experimental results, and used to explore a wider design space. The FE analysis results showed that the slenderness ratio of the column and the web height-to-thickness ratio have an important influence on the strength of these columns. Finally, the applicability and effectiveness of calculating compression strength for this type of built-up column using methods such as “Effective Ratio of Width-to-Thickness Method” in Chinese code, “Effective Width Method” in AISI and “Direct Strength Method” in AISI, were evaluated by comparison with the test and FE results. For all the columns analyzed with slenderness ratio greater than 105, it is reasonable to use these methods to calculate the concentric axial compression strength of columns. The methods in China and AISI S100-16 were found to be conservative for calculating the eccentric axial compression strengths of these built-up double box columns.

Simplified calculation method for flexural moment capacity of cold-formed steel built-up section beams

Cold-formed steel built-up section beams are commonly employed in cold-formed steel framing owing to their excellent mechanical performance. In order to develop a simplified approach for obtaining the flexural moment capacity of built-up section beams, both experimental study and numerical analysis on the flexural behavior of cold-formed steel built-up I-section and box section beams under flexural load were carried out in this study. The I-section beams are assembled from two back-to-back cold-formed steel lipped channels, and the box section beams consist of a cold-formed steel plain channel overlapping a lipped channel. First, four-point bending tests were performed on 30 simply supported specimens having 10 different configurations, and the moment capacities and failure modes of built-up section beams at ultimate loads were investigated. The failure characteristics observed were the interaction of local and distortional buckling of the web and top flange for I-section beams and local buckling of the web and top flange in pure bending for box section beams. Then, finite element models were developed to simulate the tested specimens and validated against the experimental results in terms of the moment capacities and failure characteristics. Moreover, extensive parametric studies, including section height-to-width ratio and flange width-to-thickness ratio, were conducted with the validated numerical models to identify the key factors influencing built-up section beams. Finally, a simplified calculation method considering the reduction factor of the gross section modulus of the built-up section to predict the flexural moment capacities of cold-formed steel built-up I-section and box section beams was proposed.

Parametric study of Stub-Beam Bolted Extended End-Plate connection to box-columns

This paper aims to investigate different combinations of Bolted Extended End-Plate (BEEP) beam-to-column connections where the column sections are of the built-up box type. Therefore, some allowable combinations of beam-to-column subassemblages were chosen according to the AISC provisions, such as Strong Column-Weak Beam. Since the prequalified BEEP connections are generally attached to wide-flange column sections, there will be some complexities in the erection and bolts fastening processes involved where built-up box columns are used. One of these complexities is the closed inner space of such columns. Thus, a novel connection configuration is proposed to overcome these complexities. Hence, a number of 28 different connection subassemblages were modeled in ABAQUS finite element analysis software and tested under the connection qualification cyclic loading conditions. Hence, after verifying the numerical modeling's acceptable accuracy with two experimental models, the main proposed models were investigated, and their responses were evaluated. The results of this study indicate that this new proposed connection can satisfy the connection qualification criteria. However, further experimental studies are needed to be conducted to approve the practical use of this proposed connection.

Experimental and numerical studies on axially restrained cold-formed steel built-up box columns at elevated temperatures

Experimental and numerical studies on the fire resistance of cold-formed steel (CFS) columns with built-up box-shape sections were conducted in this paper. A series of coupon tensile tests were also performed before the fire resistance tests of the columns to obtain the stress–strain relationship of the steel plate from 20 °C to 800 °C. As a benchmark, the load-bearing capacity tests of the columns at ambient temperature were conducted first, and then the fire resistance tests were performed for eight specimens considering different load ratios and axial restraining stiffness. Afterward, numerical models, including heat transfer and structural analyses, were developed to reproduce the fire-resistance behavior of the columns and verified via test results. Finally, parametric analyses were performed to investigate the influence of load ratio, axial restraint, and rotational restraint on the fire-resistance behavior of the columns. Results indicated that the primary failure mode of the specimens was a combination of local and global flexural buckling, which was sensitive to the longitudinally non-uniform temperature field. Moreover, the increase in load ratio and axial restraining stiffness led to a significant decrease in the critical temperature and failure time. Moreover, even a low level of rotational restraint could enhance the fire-resistance behavior of the column.

Numerical Study on Cyclic Response of End-Plate Biaxial Moment Connection in Box Columns

The 2008 Wenchuan-China earthquake showed the importance of considering the bidirectional seismic action as a cause of failure in column hinge mechanisms. Subsequently, the large 2011 Tohoku-Japan earthquake revealed that Special Moment Frames buildings, made of tubular columns (Hollow Structural Section or Built-up Box Section) and rigid connections with I-beams, did not suffer serious damage. However, only the ConXtech® ConXL™ moment connection has been prequalified according to the (American Institute of Construction) AISC Seismic Provisions for use with tubular columns and the rest of connections do not consider biaxial resistance. The research reported herein investigated the cyclic response of box-columns joints, connected to I beams using the four-bolt extended endplate connection, subjected to bidirectional bending and axial load on the column. To conduct the study, complex nonlinear finite element models (FEMs) of several I beam to box column joint configurations were constructed and analyzed under cyclic loading using the ANSYS software. The results reveal that the failure is concentrated in the beams of all joint configurations except for the columns with axial load equal to 75% of the column capacity, where a combined failure mechanism is achieved. The energy dissipation capacity of joints with a greater number of beams is lower than joints with fewer beams. The bidirectional effect of the seismic action and the level of axial load must be considered to avoid the formation of a column-hinge fragile failure mechanism also the behavior exhibited by 3D joints is more realistic than 2D joints according to real structures.

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.