Steel Hollow Structural Sections Research Articles

Seismic Local Buckling Limits for Hollow Structural Section and Built-Up Box Columns

Recently completed research on seismic local buckling limits for steel hollow structural section (HSS) and built-up box columns is featured. These National Center for Research on Earthquake Engineering (NCREE) studies are led by Dr. Chung-Che Chou and Dr. Tung-Yu Wu in the Department of Civil Engineering at National Taiwan University (NTU). Dr. Chou also serves as the NCREE Director. Dr. Chou’s research has focused on seismic testing, analysis, and design for steel and post-tensioned self-centering structures. Some recent work includes studies on hybrid simulation of a full-scale steel moment frame, a post-tensioned self-centering brace, novel prediction models for early earthquake warnings, and earthquake reconnaissance work in eastern Taiwan. Dr. Chou’s numerous accolades include the Awards for Excellent Research and Technology Transfers for his leadership on a research team developing a sandwiched buckling-restrained brace and a self-centering brace. Dr. Wu’s research interests include collapse behavior of cold-formed HSS columns under seismic loading, subwavelength seismic metamaterial structures, crack growth in railway crossings under high wheel-rail impacts, and seismic resilience of steel buildings. In addition to multiple scholarships and fellowships, Dr. Wu’s honors include the Raymond C. Reese Research Prize, awarded by the American Society of Civil Engineers (ASCE) for papers representing notable achievements in research with impact on design. The National Science and Technology Council is supporting this research on seismic local buckling limits for HSS and built-up box columns. Selected highlights from both projects are presented, along with a preview of future research tasks.

Web crippling design of cold-formed high strength steel SHS and RHS at elevated temperatures

This study investigates the web crippling capacities of cold-formed high strength steel (CFHSS) hollow structural section members at elevated temperatures. A numerical investigation on square and rectangular hollow sections (SHS and RHS) undergoing web crippling was performed at various temperatures from 21 °C to 1000 °C. Finite-element (FE) models were firstly developed to replicate the available web crippling tests on CFHSS SHS and RHS members. After validation, extensive parametric studies with 784 specimens covering all four codified web crippling load cases in the current cold-formed steel design specifications were performed. The reductions of web crippling capacities at elevated temperatures were compared against the corresponding yield strength and elastic modulus reduction factors of the materials. The suitability of available web crippling design provisions in current codes of practice and literature to CFHSS sections at elevated temperatures was evaluated. Comparison results reveal that the direct strength method (DSM) previously proposed by the authors at ambient temperature could be extended to elevated temperature conditions and would provide rather consistent and reliable predictions than other existing provisions. A modified DSM is put forward in this paper and it is found that the modified DSM is suitable for web crippling design of the CFHSS sections at both elevated and ambient temperatures, and moreover, can also be used for cold-formed stainless steel SHS and RHS of various grades. Therefore, the modified DSM is recommended to be used for web crippling design of CFHSS and stainless steel SHS and RHS at elevated and ambient temperatures.

Comparing Numerical Results for Seismic Performance of Portal Steel Frames Braced with Steel: HSS Brace, Glulam Timber Brace, and Timber‐Steel‐BRB

This study involves the application of timber‐based bracings elements. For this purpose, seismic analyses are performed on special portal steel frames without the brace and diagonally braced with Glued Laminated Timber (glulam) and Timber‐Steel Buckling Restrained Brace (TS‐BRB), and the results are compared with the same configuration using steel Hollow Structural Sections (HSS) bracing, using OpenSees structural analyzer. First, to verify the accuracy of the modeling, the numerical results are compared with experimental measurements on several types of elements: (a) diagonally braced frame with steel Hollow Structural Sections with a concentrically steel braced frame which was tested by the quasi‐static method under cyclic loading protocol by previous researchers, (b) diagonally glulam braced frame with results of shake table tests on single‐story timber braced frames, and (c) Timber‐Steel Buckling Restrained Brace (TS‐BRB) frame with experimental results of Heavy Timber Buckling‐Restrained Braced Frame (HT‐BRB). In the second step, the aforementioned timber base bracing alternatives (glulam, TS‐BRB) are applied in the special portal steel frame, then the seismic performance of the frame is investigated under pushover, cyclic, time history, and incremental dynamic analysis (IDA), and then the results are compared with the behavior of similar portal frame in two conditions without the brace and diagonally braced with the steel‐HSS brace. Results showed that steel‐HSS, glulam, and timber‐steel buckling restrained braces have significant roles in energy dissipation, increasing shear capacity, decreasing interstory drift, and decreasing weight and cost of estimation of the structure.

Comparison of the predictability of the ultimate axial strength of elliptical CFST columns using existing square and circular section-based code formulae

The elliptical hollow section has been recently included in the family of the structural steel hollow sections. This type of steel section is also used in the production of concrete-filled steel tubular (CFST) members. For the elliptical CFST compression members, there is no specific design formulation in the current provisions, except the code called “Technical code for concrete-filled tubular structures” prepared by the Ministry of Housing and Urban-Rural Development of the People’s Republic of China. However, the formula proposed by this code for estimating the ultimate strength of the elliptical CFST columns was achieved by modifying the formula for predicting the ultimate strength of the square CFST members. In this context, the objective of this study is to evaluate the applicability of the existing code formulae that were proposed for the axially loaded CFST columns with rectangular or circular sections to that of columns with an elliptical section. To this, a data repository consisting of 97 experimentally tested elliptical CFST columns was compiled. Herein, the main criterion in the selection of the data was the axial loading condition. Thereafter, the prediction performance of these code formulae was assessed in terms of statistical parameters. The results indicated that the code formulae proposed for the circular-sectioned CFST columns have better prediction capability than that suggested for the rectangular sections. Among these design formulae proposed for the CFST columns with a circular section, the formulae recommended by the American Institute of Steel Construction, British Standard Institute, Canadian Standards Association, and Eurocode 4 performed the best prediction capability. These code formulae had the lowest mean absolute percent error values and R-squared values of higher than 0.8.

Fiber‐based hysteretic model for simulating strength and stiffness deterioration of steel hollow structural section columns under cyclic loading

SummaryAn efficient component model has been developed that captures strength and stiffness deterioration of steel hollow structural section (HSS) columns. The proposed model consists of two fiber‐based segments at a member's ends along with an elastic segment in between. The fibers exhibit nonlinear uniaxial stress–strain behavior, which is explicitly defined by uniaxial monotonic tensile and cyclic round coupon tests. The postbuckling behavior of an HSS column is traced through a proposed uniaxial effective stress–strain constitutive formulation, which includes a softening branch in compression and an energy‐based deterioration rule to trace the influence of cyclic deterioration in the inelastic cyclic straining. These may be inferred by uniaxial stub‐column tests. The component model captures the coupling between the column axial force and flexural demands. Consistent model parameters for a number of steel materials used in the steel construction in North America and Japan are proposed along with the associated model calibration process. The efficiency of the proposed model in predicting the hysteretic behavior of HSS columns is demonstrated by comparisons with physical steel column tests subjected to various loading histories, including representative ones of ratcheting prior to earthquake‐induced collapse. The proposed model is implemented in an open‐source finite element software for nonlinear response history analysis of frame structures. The effectiveness of the proposed model in simulating dynamic instability of steel frame buildings is demonstrated through nonlinear response simulations of a four‐story steel frame building, which was tested at full‐scale through collapse. Limitations as well as suggestions for future work are discussed.

Design of shear pocket connection in full-depth precast concrete deck systems

Current bridge design codes do not provide adequate criteria/procedures for designing full-depth precast concrete deck systems, especially those with shear pocket connections. Instead, these systems and their connections are designed on a case-by-case basis by either conducting necessary testing or adopting the design criteria/procedures developed primarily for cast-in-place concrete deck systems. Shear pocket connections formed using steel hollow structural sections (HSS) provide a promising solution to connecting precast concrete deck panels to the supporting girders due to their superior structural performance and simplicity of panel fabrication. The main objective of this paper is to develop criteria/procedures for designing HSS formed shear pocket connections in full-depth precast concrete deck systems. These procedures will assist bridge designers in selecting pocket dimensions, HSS thickness, pocket anchorage and reinforcement necessary to maximize the connection capacity while allowing adequate construction tolerance. Experimental investigation (push-off testing) and finite element analysis (FEA) were performed to validate the developed design criteria/procedures. Analysis and testing results indicated that the developed design criteria/procedures for HSS formed shear pocket connections are satisfactory.

Experimental and numerical study of double-through plate connections to CFST column

This paper proposes an innovative connection known as double-through plate connection, in which two plates pass through a slotted square column with the concrete infill. The type of connection can be used to connect the steel hollow structural section (HSS) beam to the concrete-filled steel tube (CFST) column. Three specimens were tested under cyclic loading. The failure modes, hysteretic performance, stiffness, strength, ductility and classification of the joints were evaluated. The results revealed that the type of connection exhibited similar behaviors with single plate connection. The characteristics of the connection effectively reduced the stress level on the column flange and improved stress distribution. Then a nonlinear finite element (FE) model was developed and verified by the experimental results in terms of moment-rotation relationship and failure mode. The parametric analyses were utilized to explore the effect of hole shape and bolt pretension force on the connection performance. In addition, bolt slippage and load transfer mechanism in the joint region were also discussed.

Determination of geometrical imperfection models in finite element analysis of structural steel hollow sections under cyclic axial loading

Global and local imperfections are required to capture accurate buckling loads and overall structural behaviour of axially loaded structural steel hollow sections in finite element (FE) models. In this paper, three methods of geometrical imperfections are considered for square and rectangular structural steel hollow sections: (i) creating the profile of the brace using a half sine wave, (ii) applying an equivalent notional lateral load at mid-length, and (iii) combining sinusoidal local imperfections with an equivalent notional lateral load for global imperfections. When modelling the initial shape of brace members with global imperfection at mid-length of the magnitude used to establish the European buckling curves (L/1000, where L is the length of the brace member), it was found that the equivalent notional lateral load methodology could best predict the buckling capacity of brace members when compared to physical test data and European buckling curves. However, both methodologies neglect the effect of local imperfection on the initial buckling loads. When it was included by generating a continuous sinusoidal wave along the member length, it did not affect the initial buckling loads, but gave a more overall representative behaviour of the brace members.The FE model is then validated using sixteen cyclic tests for brace members. The FE results are found to match the physical tests values relatively well. In other words, when comparing the ratio of yield force, buckling resistance, and total energy dissipated estimated from the FE model to the measured values in physical tests, the mean values are found to be 1.04, 0.99 and 1.24, respectively, with a coefficient of variation of 0.07, 0.07 and 0.17, respectively.

Influence of elevated strain rate on the mechanical properties of hollow structural sections

As protective design engineering becomes more prevalent, cold-formed steel hollow structural sections are often desired design components. As such, it is necessary to understand the behavior of hollow structural sections subject to air-blast loading, including the material response under elevated strain rates. Dynamic tensile tests have hence been performed on subsize tensile coupons taken from the flats and corners of cold-formed rectangular hollow section members. Dynamic yield stresses were obtained at strain rates from 0.1 to 18 s−1, which encompasses and exceeds the range recorded during far-field blast arena testing. The dynamic increase factor was calculated for each data point and synthesized with previous cold-formed rectangular hollow section tests at even higher strain rates (100–1000 s−1). The data set was used to determine Cowper–Symonds and Johnson–Cook parameters. The resulting material models can now be used to determine the strength increase of cold-formed rectangular hollow sections subject to a wide range of impulsive, elevated strain rate loads.

Residual capacity of fire-exposed concrete-filled steel hollow section columns

Concrete filled steel hollow structural (CFS) sections are an increasingly popular means to support large compressive loads in buildings. Whilst the response of unprotected CFS sections during a fire is reasonably well researched, their post-fire residual structural performance is less well established. A better understanding of the response of fire-damaged CFS columns is needed to enable better performance-based structural fire engineering of buildings incorporating CFS sections. This paper presents post-fire residual compression tests on unprotected and protected CFS columns along with control tests on six unheated sections. The tests confirm that as the maximum exposed temperature within the cross-section increases, the residual strength capacity, ductility and axial–flexural stiffness decrease. The data are subsequently used to assess the ability to predict the residual capacity of CFS columns after fires, using available post-fire material models and in-fire and ambient structural models.

Evaluation of Rectangular Concrete-Filled Steel-Hollow Section Beam-Columns

Despite the excellent engineering properties of concrete filled tubs (CFT), they are not as widely used as traditional structural steel and reinforced concrete members. The aim of this study was to predict the buckling behavior of concrete-filled steel hollow structural section beam columns with advanced finite element methods and compare the predictions with experimental results and optimize findings and represent a finite element model for further studies. A total of 2 different specimens from the experimental study were investigated with eccentric loading and ABAQUS software is used for modeling and non-linear analysis. The specimens have square section with overall depth of 120 mm and 140 mm respectively and the thickness for all sections was 3.84 mm. The tests were performed on pin-ended Beam-columns. It is found that load could carried by concrete filled steel tube with size of 120 mm, increased about %44 in compression of steel tube section also, it increased about %108 in compression of reinforced concrete section with %3 of longitudinal rebar.

Numerical simulations of response of tubular steel beams to close-range explosions

A numerical study of hollow and concrete-filled square tubular steel columns subjected to near-field detonations has been undertaken and validated through the experimental results. The experiments used concrete-filled and hollow square tubular columns (100×5mm SHS Grade C350) made out of cold-formed structural steel hollow sections (SHS) that were simply supported at both ends. High explosives TNT charges were placed above the top surface of the column at two different scaled standoff distances of 0.12m/kg1/3 and 0.15m/kg1/3. Failure patterns and permanent mid-span deformations were recorded and compared with the numerical analysis results. Arbitrary Lagrangian–Eulerian (ALE) formulations coupled with fluid–structure interaction (FSI) algorithms that are available in the advanced finite element code LS-DYNA were used in the numerical study. A detailed description of the numerical technique adopted in the study is presented. The models were validated with the experimental results and were used to obtain the failure pattern, permanent plastic deformation, pressure and impulse time histories, stress distribution, and energy absorption of the different configurations of the columns. The performance of hollow and concrete-filled SHS tubes for blast load mitigation was assessed and discussed.

Behavior of Concrete/Cold Formed Steel Composite Beams: Experimental Development of a Novel Structural System

The use of light-gauge steel framing in low-rise commercial and industrial building construction has experienced a significant increase in recent years. In such construction, the wall framing is an assembly of cold-formed steel (CFS) studs held between top and bottom CFS tracks. Current construction methods utilize heavy hot-rolled steel sections, such as steel angles or hollow structural section tubes, to transfer the load from the end seats of the floor joist and/or from the load-bearing wall studs of the stories above to the supporting load-bearing wall below. The use of hot rolled steel elements results in significant increase in construction cost and time. Such heavy steel elements would be unnecessary if the concrete slab thickening on top of the CFS wall can be made to act compositely with the CFS track. Composite action can be achieved by attaching stand-off screws to the track and encapsulating the screw shank in the deck concrete. A series of experimental studies were performed on full-scale test specimens representing concrete/CFS flexural elements under gravity loads. The studies were designed to investigate the structural performance of concrete/CFS simple beams and concrete/CFS continuous headers. The results indicate that concrete/CFS composite flexural elements are feasible and their structural behavior can be modeled with reasonable accuracy.

Seismic Behavior of Steel Buildings with Hybrid Braced Frames

This paper presents the seismic performance of buildings with a hybrid bracing system in which buckling-restrained braces (BRBs) are used at the lower stories with the higher level of ductility demands, and conventional buckling-type braces consisting of steel hollow structural sections (HSS) are used in the upper stories with relatively smaller ductility demands to minimize the probability of their fracture under reversed cyclic displacements. This type of hybrid braced frame (HBF) could prove economical, especially for retrofitted buildings in seismically active regions. A series of nonlinear time-history analyses was conducted to investigate the seismic performance of 3- and 6-story buildings with the hybrid bracing system. The main parameters studied are the seismic design parameters, maximum interstory drift ratios, fracture response of the HSS, and the optimal deployment of the BRBs. The seismic performance of the HBFs was compared with conventional concentrically braced frames and buckling-restrained braced frames (BRBFs) designed according to the current code provisions. Results showed that using BRBs at only a few lower levels of the HBFs gives similar performance to that of BRBFs. The incident of brace fractures in conventional HSS can be delayed or completely eliminated by using the proposed hybrid bracing systems.

Structural performance of unprotected concrete-filled steel hollow sections in fire: A review and meta-analysis of available test data

Concrete filled steel hollow structural sections (CFSs) are an efficient, sustainable, and attractive option for both ambient temperature and fire resistance design of columns in multi-storey buildings and are becoming increasingly common in modern construction practice around the world. Whilst the design of these sections at ambient temperatures is reasonably well understood, and models to predict the strength and failure modes of these elements at ambient temperatures correlate well with observations from tests, this appears not to be true in the case of fire resistant design. This paper reviews available data from furnace tests on CFS columns and assesses the statistical confidence in available fire resistance design models/approaches used in North America and Europe. This is done using a meta-analysis comparing the available experimental data from large-scale standard fire tests performed around the world against fire resistance predictions from design codes. It is shown that available design approaches carry a very large uncertainty of prediction, suggesting that they fail to properly account for fundamental aspects of the underlying thermal response and/or structural mechanics during fire. Current North American fire resistance design approaches for CFS columns are shown to be considerably less conservative, on average, than those used in Europe.

Behaviour of Filled Rectangular Steel HSS Composite Columns under Bi-Axial Bending

The purpose of this study was to investigate the behaviour of concrete-filled rectangular steel hollow structural section (HSS) columns formed by slender plates with large depth-to-width ratio subjected to bi-axial bending. As part of this study, four large concrete-filled thin-walled rib-stiffened rectangular HSS columns have been tested. Their steel tubes possess a depth-to-width ratio of 2.38 and a depth-to-thickness ratio of 175. Rib stiffeners were welded to the plate walls such that the stiffened plate width-to-thickness ratio (= 45) was less than that specified (= 60) in the Chinese design code. The results showed that local buckling of steel plate appeared after the specimen reached the ultimate capacity. Also, the fiber element analysis method is adapted to analyze the behaviour of specimen, in which the change of neutral axis position is considered. At last, the experimental results are compared with the values calculated from design codes, namely EC4, LRFD, CECS and DBJ. The results show that all codes provide safe ultimate capacities. Among them, the capacities calculated from DBJ yield results closest to the experimental ones and the other three design codes produce safety over 20%.

Experimental study on performance of elliptical section steel columns, under hydrocarbon fire

Elliptical structural steel hollow sections represent a recent addition to the range of steel sections available to structural engineers. However, despite the extensive interest in their use on the basis of both architectural attraction and structural efficiency, a complete absence of fire resistance design guidance is restraining applications. This paper presents the first study ever conducted to investigate the fire resistance of steel columns with Elliptical Hollow Sections (EHS). Six columns of two slenderness λ = 40.1 and λ = 50.8 were tested under three loading levels ( α L = 0.3 , 0.45 and 0.6) and subjected to a hydrocarbon fire curve. The paper provides the recorded data of axial displacements and temperature profiles of the EHS steel columns, while highlighting the unique local and overall buckling failure modes of the Elliptical Hollow Section.

Fire Resistance Design of Unprotected Concrete Filled Steel Hollow Sections: Meta-Analysis of Available Furnace Test Data

Concrete filled steel hollow structural sections are an efficient, sustainable, and attractive option for both ambient temperature and fire resistance design of columns in multi-storey buildings and are increasingly common in modern construction practice around the world. Whilst the design of these sections at ambient temperatures is reasonably well understood, and models to predict the strength and failure modes of these elements correlate well with observations from tests, this appears not to be true in the case of fire resistant design. This paper assesses the statistical confidence in available fire resistance design models/approaches that are used in North America and Europe by performing a meta-analysis which compares the available experimental data from large-scale standard fire tests performed around the world against fire resistance predictions from design codes. It is shown that available design approaches carry a large uncertainty of prediction, suggesting that they fail to properly account for fundamental aspects of the underlying mechanics during fire. Current North American design approaches for CFS columns are shown to be considerably less conservative, on average, than those used in Europe.

Response of Concrete-Filled HSS Columns in Real Fires

The use of concrete filling offers a practical alternative for achieving the required fire resistance in steel hollow structural section (HSS) columns. However, the current prescriptive-based approach has a number of constraints that in many applications restrict the utilization of concrete filling for achieving the required fire resistance. To overcome such constraints, a performance-based methodology for fire resistance design is presented in this paper. A set of numerical simulations were carried out to investigate the effect of realistic fire scenarios, loading, and stability-based failure criterion on the fire resistance of concrete-filled HSS columns with lengths ranging from 3.8 m (12.5 ft) to 10 m (32.8 ft). It is demonstrated that by adopting a performance-based approach, it is possible to achieve the required fire resistance in CFHSS columns in most practical situations.

An Approach for Evaluating the Fire Resistance of CFHSS Columns under Design Fire Scenarios

The use of concrete filling offers a practical alternative for achieving the required fire resistance in steel hollow structural section columns. However, the current prescriptive-based approach which evaluates fire resistance based on standard fire exposure does not account for realistic fire scenarios in the design of concrete-filled hollow structural section (CFHSS) columns. This article presents a methodology for evaluating the fire resistance of CFHSS columns under design fire scenarios without the need for costly computational models. The proposed approach is a derivative of the equal area concept, and evaluates the equivalent fire resistance of the column by comparing the time temperature curve of the standard fire exposure with that of the design fire exposure. The method has been validated against the results generated from finite element analysis (coupled heat transfer and strength analysis) on numerous CFHSS columns under a large number of design fires. The applicability of the approach in desi...