Built-up Box Sections Research Articles

The effect of multi-pass welding on residual stresses in fillet welded built-up steel box sections

The effect of multi-pass welding on residual stresses in fillet welded built-up steel box sections

Numerical investigation and design of lightweight aggregate concrete-filled cold-formed built-up box section (CFBBS) stub columns under axial compression

Cold-formed built-up box sections (CFBBS) have emerged as a promising solution for applications in light gauge steel framing systems and modular construction. However, they suffer from the inherent local buckling effect. Concrete infill has proven effective in mitigating this issue, yet existing codified provisions lack specific guidelines for the design of concrete-filled CFBBS stub columns. This paper proposed a design methodology that aims to predict the ultimate compressive strength of lightweight concrete-filled CFBBS stub columns. Leveraging finite element (FE) modelling techniques, this study augmented the existing test database and shed light on parametric influences, considering practical considerations, on the structural performances and axial compressive behaviour. The proposed design approach demonstrated superior prediction accuracy and consistency compared to other evaluated design approaches in this study.

Web crippling resistance of cold-formed steel built-up box sections through experimental testing, numerical simulation and deep learning

This study proposes a deep-learning framework, namely a deep belief network (DBN), for investigating the web crippling resistance of cold-formed steel (CFS) built-up stiffened box sections. A total of 12 new web crippling tests are presented initially, which were carried out under interior-two-flange (ITF) and end-two-flange (ETF) loading conditions. In the experimental tests, two cross-section dimensions were considered, and the overall web depth varied from 290 mm to 550 mm. The yield strength of the specimens varied from 371.7 MPa to 643.6 MPa. The specimens were characterised by different screw spacing, varying between 50 mm and 300 mm. An elasto-plastic finite element (FE) model was developed and validated against the test results. Subsequently, a total of 1,356 data points for training the DBN were generated based on the validated FE model. When a comparison was made against the test results, the absolute percentage error of the DBN predictions was found to be around 10%. Using the DBN predictions which were based on the validated FE model, a comprehensive parametric study was undertaken to investigate the effects of section thickness, yield strength, bearing length and screw spacing on the web crippling resistance of CFS built-up stiffened box sections. New design equations for predicting the ITF and ETF web crippling resistances of CFS built-up stiffened box sections were then proposed, and a reliability analysis was undertaken to assess the feasibility of the proposed equations.

An investigation on stiffened cold-formed steel unequal angle box section columns

Built-up box sections are gaining popularity as column members in cold-formed steel (CFS) construction. Applications include CFS trusses, space frames, and portal frames. Two identical CFS unequal angles are used in this article to form built-up rectangular angle box columns (BUABC). These BUABC, which can be plain or with stiffeners (longer and shorter legs), are grooved on the faces of the columns in the major and minor axis directions and connected with self-drilling screws (fasteners) through their lips. There are no reports in the literature on the advantages of stiffeners (longer and shorter legs) provided in BUABC. This paper presents 78 new results for the BUABC as plain and with stiffeners (longer and shorter legs), including 14 test results and 64 finite element (FE) results. The axial strengths of BUABC with two stiffeners in the longer leg and one stiffener in the shorter leg showed an increase of about 28% on average when compared to the axial strength of plain BUABC, according to the experimental results. The FEA-derived ultimate loads and failure modes are in good agreement with the experimental results. The verified FE model was then used in the parametric study to investigate the effect of stiffeners (longer and shorter legs) on the axial strength of BUABC. The parametric study considered two distinct geometries with two distinct lengths (300 mm and 600 mm). The axial strengths of the stub BUABC tested against the Direct Strength Method (DSM) prediction were conservative, up to 3% on average, while they were 13% conservative for the short BUABC. This shows that the DSM prediction was more conservative, with an increase in slenderness that was governed by the modified slenderness ratio. The DSM strength predictions were less conservative for the stub BUABC that failed due to local buckling, whereas the DSM strength predictions were more conservative for the short BUABC that failed due to a combination of local and flexural buckling.

Experimental investigation of flexural buckling behaviour of self-compacting lightweight concrete-filled cold-formed built-up box section (CFBBS) columns

This paper presents an experimental investigation of the flexural buckling behaviour and resistance of innovative self-compacting lightweight concrete (LWSCC)-filled cold-formed built-up box section (CFBBS) columns. A series of sixteen LWSCC-filled CFBBS columns and four reference hollow columns formed by two nested asymmetric lipped channel sections using breakstem rivets at flanges with various member relative slendernesses ratios, concrete strengths and section sizes were tested under pin-ended boundary conditions. Material tests and initial global geometry imperfection measurements were carried out and reported in present study. The failure modes and deformation developments, lateral deflection distribution along the column specimens, flexural buckling resistance and load-end shortening relationship of the specimens were scrutinised and discussed concerning the effect of parameters and the associated coupling effects. Furthermore, a comprehensive strain analysis was conducted and reported based on the longitudinal and lateral strain developments at both compression and tension zones under flexure; it was found that the composite action abated as the member length increased. Finally, as there is no existing design codes for LWSCC-filled CFBBS columns, the experimental results were used to evaluate the applicability of relevant international codified provisions, including Eurocode (EC4), Australia/New Zealand Standard (AS/NZS 2327) and America Specification (AISC 360-16). It was found that AS/NZS 2327 yielded the most accurate and moderately scattered predictions while the predictions from EC4 were found to be the most scattered but with reasonable accuracy and those from AISC 360-16 were overly conservative, albeit the least scattered among these design codes.

Experimental investigation of lightweight aggregate concrete-filled cold-formed built-up box section (CFBBS) stub columns under axial compression

This paper presents an experimental investigation of cold-formed built-up box section (CFBBS) stub columns infilled with lightweight aggregate concrete under concentric loading. The experimental programme included a series of twenty-four lightweight aggregate concrete-filled built-up box sections comprising by two nested cold-formed thin-walled C-sections using breakstem rivets at flange and eight reference hollow sections for comparison purposes. These built-up sections of four different cross-section sizes were infilled with three different lightweight concrete compression strengths, i.e., 20, 30 and 40 MPa. The failure modes, ultimate compressive load and load-end shortening relationship of the test specimens were compared and discussed. A set of performance indices was calculated from the test results to evaluate the structural performance from several aspects. In addition, the confinement effect of the specimens was investigated extensively based on the strain development. Finally, the experimental results are used to evaluate the applicability of the design equations specified in the existing codified provisions, including Eurocode (EC4), Australia/New Zealand Standard (AS/NZS 2327) and America Specification (AISC 360-16). It was found that EC4 with consideration of effective area of the outer CFBBS in the design provided the most accurate and less scattered predictions. Predictions from AS/NZS 2327 were generally found to be slightly unsafe while those from AISC 360-16 were conservative.

Pre-Stress Linear and Nonlinear Buckling of Cold-Formed Steel Built-up Box Studs

In construction industry, cold-formed steel sections become more pertinent in place of hot-rolled steel members. The design guides for CFS are inadequate and hence it is substantial to investigate their governing behaviours as material failure and structural instability (buckling). This study aims to analyse how the buckling behaviours of face-to-face built-up box short columns are administrated by the application of end plates with three different welded spacing. Sixgeometric models were analysed with ANSYS 2020 R1, numerical software, to evaluate the pre-stress linear and non-linear buckling loads of built-up box studs. The results distinguish the application of end plates and the most effective welded spacing for built-up geometry. It is significant that end plates are more advantageous to resist the maximum compressive loads whereas 509.6 mm is the relevant welded spacing for built-up box section. It is additionally suggested to analyse the governing of weld spacing and end conditions of various built-up geometries: box, sigma and I studs through numerical and experimental analysis.

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.

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.

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%.

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.

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.

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.

Efficient cross-sectional profiling of built up CFS beams for improved flexural performance

In the past, many efficient profiles have been developed for cold-formed steel (CFS) members by judicious intermediate stiffening of the cross-sections, and they have shown improved structural performance over conventional CFS sections. Most of this research work was based on numerical modelling, thus lacking any experimental evidence of the efficiency of these sections. To fulfill this requirement, experimental studies were conducted in this study, on efficient intermediately stiffened CFS sections in flexure, which will result in easy and simple fabrication. Two series of built-up sections, open sections (OS) and box sections (BS), were fabricated and tested under four-point loading with same cross-sectional area. Test strengths, modes of failure, deformed shapes, load vs. mid-span displacements and geometric imperfections were measured and reported. The design strengths were quantified using North American Standards and Indian Standards for cold-formed steel structures. This study confirmed that efficient profiling of CFS sections can improve both the strength and stiffness performance by up to 90%. Closed sections showed better strength performance whereas open sections showed better stiffness performance.

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.

Optimum design of tied-arch bridges under code requirements using enhanced artificial bee colony algorithm

In this study, optimum design algorithm is presented for tied-arch bridges under AASHTO-LRFD Bridge Design Specifications provisions. It is decided that in tied-arch bridges ties, arch ribs, and bottom and top bracings are made of built-up box sections, whereas built-up I sections are utilized for floor beams and stringers. Bars are adopted for hangers. In the formulation of the optimization problem, design variables are selected as the cross sectional dimensions of steel plates not that of I and box sections. Design pools are prepared for steel plate sections in addition to the hanger bars so that the optimization algorithm can select appropriate steel plates, construct I and box built-up sections for members of 3-D tied-arch such that the weight of the bridge is minimized. In addition to design code requirements, geometrical constraints among its elements that are required for manufacturability of the bridge are also considered. The design process of tied-arch bridges differs from that of steel framed structures. It necessitates consideration of moving vehicle loads. Design optimization algorithms require the response of bridges under several design load arrangements and in the construction of influence lines. This is achieved by using open application programming interface (OAPI) facility of SAP2000. The solution of discrete nonlinear programming problem is obtained by using the proposed Enhanced Artificial Bee Colony algorithm (eABC). The proposed algorithm is compared with Standard Artificial Bee Colony (ABC) and Exponential Big Bang-Big Crunch (eBB-BC) algorithms to evaluate its performance.

An experimental study on fire damage of structural steel members in an industrial building

Abstract In this paper an experimental study on the fire damage of the unprotected structural steel members is presented after exposure to fire in an industrial fabric established for embellishment of glass wares in 1997. Following the ignited fire flashover occurred, explosions happened, and finally 50,000 m 2 areas were heavily damaged. The structural bearing system of compartments was designed as moment-resistant frames having 11.80 m height. In some halls a space truss roof construction with tubular steel bars which were joining in Mero type assemblies was pin-supported on the columns which were fix on their bottom. Steel columns were made from hot rolled I sections or built-up box sections. Tensile tests were performed on specimens taken from various columns and a tubular space truss member in order to determine post fire mechanical properties. Also, residual factors defined as the ratio of post fire mechanical properties to those at room temperature, and exposed temperatures of the samples were estimated by referring the results of a previous work in the literature. In this approximation, yield strength to ultimate tensile strength ratio of the samples subjected to controlled heating to and cooling from elevated temperatures in the previous work were taken as the reference, and the present results were evaluated based on those results. All the findings obtained from this experimental study were used as a tool in order to get an information about the hazard level which helped for final decision whether removal, reusage or strengthening of the structural steel bearing members might be needed for the compartments of the steel industrial plant exposed to fire hazard.

NUMERICAL ANALYSIS OF AXIALLY LOADED COLD-FORMED STEEL BUILT-UP BOX SECTION

Built up box section is a doubly symmetrical section in which two C-channel connected at the flange using self-drilling screw. They are generally used in the construction industry to obtain higher rigidity, when a single section is not sufficient. Despite being widely used in the construction industry, there are limited studies on built-up box section. Moreover, the current design code does not provide clear design guideline for the calculation of built-up box section. Therefore, research on the built-up box section is important. This paper presents a finite element model to predict the compressive strength and simulate the behavior of cold-formed steel built-up box section. The finite element model was developed using ABAQUS CAE/6.14. Comparison of the finite element and experimental results showed good correlation. The model well predicted the behavior of the built-up box column.