Steel Structural Members Research Articles

Impact of Firefighting Sprays on the Fire Performance of Structural Steel Members

The feasibility of coupled computational fluid dynamics (CFD) and finite element (FE) simulations to aid the planning of fire intervention tactics and the effectiveness of structural cooling during firefighting were investigated. Water sprays, generated using fire monitors, were characterized using bucket tests and the results were used for calibrating the CFD spray model. The cooling ability of the sprays was measured experimentally by applying them onto a fire exposed steel beam. The experimental results showed that water application produces a sudden drop in steel temperatures and after 10–15 s, no significant further reduction in temperature was observed. The CFD-FE coupling was performed using the adiabatic surface temperature method, extended here to include the cooling by water droplets. The coupled CFD-FE model was validated using the experimental data and applied to simulate the intervention to a developing warehouse fire, showing how an attempt to cool the structure reduces the temperatures but does not stall the fire-spread. In fact, the intervention -induced vapor generation was found to enhance the flow of hot gases and accelerate the fire-spread if the water resources are inadequate. Thermal and stress analyses of the cooled and uncooled truss beams were performed, showing how the spray cooling halted the truss mid-span deformation.

Numerical investigation of the strength and design of cold-formed steel built-up columns

The paper concerns built-up cold-formed steel (CFS) structural members composed of three or four component lipped channel sections. Finite element (FE) models are calibrated against recently conducted experimental results and used to perform a parametric study of the strength and behaviour of CFS built-up section columns, considering column the length, section thickness and screw spacing as independent variables. The strengths thus obtained combined with experimental ultimate strengths are compared with strength predictions obtained using the North American Specification for the Design of Cold-formed Steel Structural Members, which specifies the use of a modified slenderness ratio for built-up members composed of two sections connected back-to-back. The same data is used to assess a recently proposed design method for predicting the strengths of the studied 3C and 4C built-up sections, and potentially multi-cell built-up sections more generally, based on effective rigidities coupled with the Direct Strength Method. The proposal includes a design procedure for built-up sections experiencing flexural-torsional buckling, which is neither explicitly stipulated in current design standards nor discussed in-depth in previous studies, and generally provides accurate strength predictions. A reliability analysis is included in the paper to calculate resistance factors to accompany the proposed design provisions.

Seismic Retrofitting Method Using CFRP Sheets for H-Section Steel Beam with Variable Cross Section

Severe damage to steel bridge piers and steel rigid-frame piers starting from regions of abrupt change in cross section has been widely reported. Therefore, finding a simple and effective seismic retrofitting method for steel structural members with variable cross sections to improve their plastic deformation performance is currently an urgent concern. The objective of this study was to establish an effective seismic retrofitting method for H-section steel beams with abruptly variable cross sections using a carbon fiber–reinforced plastic (CFRP) sheet because of its outstanding properties such as light weight, high strength, and superior durability. Bending and bending-shear cyclic loading tests were conducted with two parameters, including the type of CFRP sheets, and whether or not polyurea putty was inserted between the CFRP sheet and steel beam. The test results indicate that the proposed retrofitting method using intermediate-modulus CFRP and polyurea putty increases the load-carrying capacity, ductility, energy dissipation capacity, and bending stiffness of H-section steel beams significantly without any failure. Further, by implementing finite-element (FE) analyses considering the actual cyclic plasticity properties of steel, anisotropic performance of the CFRP sheets, and nonlinear bond-slip properties of the polyurea putty layer, the cyclic loading test results were reproduced accurately. Moreover, in the cases in which the polyurea putty was applied, parametric FE analysis of the CFRP bonding method with and without creating a stepped length at the top of each CFRP sheet showed that the retrofitting method without the stepped length was similar in effectiveness to the method with the stepped length.

Experimental study on seismic behavior of welded H-section stainless steel beam-columns

Previous studies have shown that structural stainless steel material has significant cyclic hardening characterized by strain amplitude dependence and unsaturation under cyclic loadings, which could have a remarkable impact on the seismic performance of stainless steel structures. Whether the current stainless steel structure design codes based on their static performance can accurately predict the seismic capacities of stainless steel structural members is worth studying. This paper investigates the hysteretic behavior of welded H-section stainless steel members under combined constant compression and uniaxial cyclic bending. A total of 24 specimens were tested, which covered a variety of test variables including stainless steel grade, section slenderness, axial compression ratio and loading history. Residual stresses of the welded H-sections considered in this study were measured. Then, the failure mode, hysteretic response, ductility coefficient and energy dissipation of welded H-section stainless steel beam-columns were fully obtained from the tests. Cyclic hardening was observed at the structural member level in the tests. The effect of loading history on seismic behavior was thoroughly discussed. It was found that various loading histories can obviously influence the strengths and deformation capacities of welded H-section stainless steel beam-columns resulting in their discrete seismic behavior, mainly due to the unsaturated cyclic hardening feature of stainless steels. Moreover, the current design codes including European Code, American Specification, Australia/New Zealand Standard and Chinese Specification underestimate the seismic capacities of welded H-section stainless steel beam-columns.

Stress reduction effects of ultra-high performance fiber reinforced concrete overlaid steel bridge deck developed with a new interfacial bond method

The effects of a 25 mm of UHPFRC overlay on reducing the stress of the open ribs-stiffened orthotropic steel decks (OSDs) are assessed experimentally and analytically. To integrate the UHPFRC overlay and the OSDs, an adhesive-based bonding technique is developed and evaluated beforehand using a pull-off test and a three-point bending test, where a 3 MPa of excellent bond strength and an invisible slip demonstrate the reliability of the technique. With the developed bonding technique, an up to 80% of strain reduction and a peak clipping phenomenon are observed in the strain of the critical locations of the steel deck and structural members in the hotspot areas due to the UHPFRC. In addition, it is found that the superior high strengths and the strain-hardening of UHPFRC can postpone the initiation and propagation of cracks. As a result, an effective enhancement of stiffness of OSDs and an apparent fatigue life extension can be achieved even with a thin layer.

Underwater strengthening and repairing of tubular offshore structural members using Carbon Fibre Reinforced Polymers with different consolidation methods

Offshore structural steel members will need strengthening or repairing due to various reasons. Strengthening is often required due to work over demands or increased environmental loads. Repairing becomes essential as the steel members are usually severely corroded due to the marine conditions. Conventional hot work strengthening and repairing solutions become very expensive and retrofitting using Fibre Reinforced Polymers (FRPs) is an economical alternative. This paper investigates strengthening and repairing of offshore steel tubular members using Carbon Fibre Reinforced Polymers (CFRPs) with the help of experimental testing and an analytical study. Two different specimen sizes which were representative of members in offshore structures namely leg and brace were examined in the study. Partial length strengthening of steel tubular members subject to combined loading of axial compression and bending was carried out using different curing environments (in air and underwater curing). Strengthening and repairing of leg and brace specimens with multiple layers of CFRP retrofitted in underwater conditions were also investigated. Two different consolidation methods (underwater vacuum consolidation and underwater stricture consolidation) were compared with the help of full length strengthening of leg specimens. Although partial length strengthening proved to be less effective, partial length repairing of corroded tubular members were successful in restoring their intact capacity. Full length strengthening for underwater leg specimens were experimentally tested and it was found to improve the structural behaviour in many aspects like ultimate strength, load displacement behaviour, elastic slope, energy absorption, and ductility. A novel technique of underwater vacuum consolidation of retrofit laminates was demonstrated through a set of full length strengthened leg specimens. Underwater vacuum consolidation proved to be advantageous compared to the normal underwater stricture consolidation. An analytical check to identify whether a retrofitted tubular member would reach its target section properties was also introduced. Overall, the paper demonstrates multiple successful applications of FRP composites for underwater strengthening and repairing of offshore steel tubular members. Studies like this expanding the current knowledge on how the FRP retrofitted steel tubular behave within a real offshore structure are essential to increase the uptake of this technology in the oil and gas industry.

Integrating visual sensing and structural identification using 3D-digital image correlation and topology optimization to detect and reconstruct the 3D geometry of structural damage

This paper describes a novel technique for detecting internal or unseen damage in structural steel members by combining measurements from full-field three-dimensional digital image correlation (3D-DIC) with a topology optimization framework. Unlike the majority of conventional methods that rely on specialized forms of surface-penetrating waves or radiation imaging, this work employs optical cameras to measure surface strains and deformations using the 3D-DIC technique followed by an optimization approach to detect the existing damage. This data-rich representation of the structural component’s behavior is then used to reconstruct the underlying subsurface abnormalities via an inverse mechanical problem. The inverse problem is solved using a topology optimization formulation that iteratively adjusts a fine-tuned finite element model (FEM) of the structure to reveal irregularities within it. Having recently demonstrated the feasibility of detecting and reconstructing defects in small-scale structural components, this paper expands on the authors' previous work to demonstrate the feasibility and performance of the proposed method through an experimental program in which a set of large-scale structural steel beams with and without buried defects tested using a full-field 3D DIC sensing approach. The structure’s initial FEM is first created to discretize the member into elements whose constitutive properties are treated as unknowns in the optimization problem. The goal of the optimization is to minimize the discrepancies between the observed full-field response measured experimentally using DIC and that computed numerically using the model. To that end, an objective function is first computed as the sum of residuals by mapping both responses onto a common grid, which is then pushed to a minimum via the method of moving asymptotes (MMA) as the optimization algorithm. This study demonstrates that the proposed approach can identify unseen damage with an average accuracy (ACC) score of 96.80% on the defined configurations, with relatively minimal false identifications.

Macro-modeling on cyclic behavior of concrete-encased steel short columns under shear failure

Concrete-encased steel (CES) structural members, in which a steel shape is encased in a reinforced concrete (RC) section, are widely applied in high-rise buildings as the primary lateral resistance systems. Because the brittle shear failure is usually observed in CES short columns under seismic excitation, it is essential to accurately evaluate the cyclic behavior of these CES short columns to ensure structural safety. In order to account for the contribution of shear action to the entire cyclic response of CES short columns, a new macro-modeling strategy implemented in OpenSees is proposed in this paper. In the proposed numerical model, the cyclic behavior of CES short columns is simulated by traditional fiber sections and a novel nonlinear shear spring in series. Therefore, the applied fiber sections can evaluate the flexural action and the effect of bar slip, and the shear action, including shear deformation and shear capacity, can be formulated by the nonlinear shear spring. After the detailed parameters (shear strength, shear stiffness, post-peak behavior, hysteretic laws, and failure criteria) of the nonlinear shear spring are defined, available pseudo-static test results are employed to validate the proposed model. The comparison between the numerical and test results indicated that the proposed model could reasonably capture the peak load, ultimate load, peak displacement, and energy dissipation of the tested CES short columns, and the existing elements in Opensees (fiber element and flexure-shear interaction element) are inappropriate to apply for modeling the cyclic behavior of CES short columns.

Temperature Field and Thermal Deformation of Steel Structural Members in Construction Engineering

The steel structure is increasingly applied in various building structures. It is of theoretical and practical significance to study the non-coordinated temperature field effects between the steel structure and external structure, and the strongly uneven temperature stress and marked deformation that ensue. However, the thermal boundary conditions are complex in the existing studies. Thus, this paper analyzes the temperature field and thermal deformation of steel structural members in construction engineering. Firstly, the relevant parameters were enumerated for the basic heat transfer modes, the temperature field of the steel members was calculated simply, and the convective heat transfer coefficients (CHTCs) of the members were discussed under different cross-sections and wind directions, presenting the accurate solution to thermal convection. Next, the thermal deformation of steel structural members was investigated to construct the thermal deformation equation of conventional steel structural members. Finally, experiments were carried out to compare the effects of different heat transfer parameters on the temperature stress of the components, and to summarize the entire process of building a thermal deformation equation for steel structure components.

A stiffness reduction method for the in-plane design of stainless steel members and frames according with EN 1993-1-4

Current design standards for stainless steel such as ASCE 8-02 and EN 1993-1-4 prescribe provisions for the design of cross-sections and members that account for material nonlinearities and strain hardening, although these features are not considered in the global design of structures. Recent studies have highlighted the need of accounting for material nonlinearities in order to design efficient and safe stainless steel structures, and it is expected that the forthcoming versions of the standards will incorporate updated rules for the global design of these structures. To contribute to this field, this paper presents a Stiffness Reduction Method (SRM) for the in-plane design of stainless steel members and frames with stocky sections based on the prescriptions given in the next version of EN 1993-1-4. The proposed approach predicts the ultimate capacity and internal forces in stainless steel structures by performing a second-order elastic analysis in which the stiffnesses of the members are reduced by a set of factors defined in this paper to account for the effect of the spread of plasticity, residual stresses and member imperfections. The accuracy of the presented method is assessed for individual stainless steel structural members (columns, beams, and beam-columns) with different cross-sections and material properties, and for austenitic stainless steel portal frames, against numerical results obtained from nonlinear analyses conducted on finite element models. A comparison between the proposed approach and the Direct Analysis Method prescribed in the upcoming AISC 370 Specification is also provided, showing that the results are comparable in the two approaches.

Project Spotlight: Waterfront apartments constructed with ease using precast concrete

The Beach, a new, three-tower complex of residential apart¬ments in Jersey City, N.J., was constructed with an architectural precast concrete exterior from Architectural Precast Innovations Inc. and hollow-core slab from Nitterhouse Concrete Products on the floors along with structural steel members.

Analysis of the Bearing Capacity of a Steel Structural Member after Reinforcement

To improve the bearing capacity of existing angle steel structures, a new and cost‐effective reinforcement method for increasing the load‐bearing capacity is proposed. This method uses steel pipes as auxiliary materials and clamps the reinforced angle steel and the auxiliary materials through fixtures to ensure that they are deformed together. The influence of the fixture spacing, the size of the reinforced angle steel member, the slenderness ratio of the members, the size of the auxiliary steel pipe, and other parameters on the reinforcement effect is studied. The results show that the smaller the fixture spacing is, the more obvious the improvement of the bearing capacity is, and the reasonable fixture spacing is related to the angle steel leg width. The larger the slenderness ratio of the member is, the more obvious the reinforcement effect of the scheme is. The steel pipe size has a significant impact on the reinforcement effect of the scheme.

Influence of Higi-frequency Induction Heating on Deformation and Residual Stress of Steel Structural Members

Influence of Higi-frequency Induction Heating on Deformation and Residual Stress of Steel Structural Members

Effect of Aluminum on Microstructure and Mechanical Properties of Weld Metal of Q960 Steel

High-strength low-alloy (HSLA) steel is used in important steel structural members because of its strength and plastic toughness. Q960 steel is HSLA steel obtained by adding an appropriate amount of alloy elements and quenching and tempering treatment on the basis of ordinary low-carbon steel. This kind of steel has strong hardenability due to the alloy elements added. Cold cracks, embrittlement and softening of the heat-affected zone easily occur after welding. In particular, the low-temperature impact toughness cannot meet the requirements and limits its use. In this paper, self-shielded welding is used to adjust the content of aluminum in flux-cored wire. The relationship between weld metal (WM) microstructure and strength and properties was studied by tensile test and impact test, and the influence mechanism of Al content on weld metal microstructure and properties was analyzed. The results show that when the content of Al is 0.21%, the impact energy at 0 °C~−60 °C is the best, the tensile strength can reach 1035 MPA and the number of pores is small. The size of inclusions in WM is mostly less than 1.0 μm Al2O3 spherical oxide. It can become the center of acicular ferrite (AF) and increase the nucleation probability. However, with the increase of Al content, large irregular AlN inclusions are produced, which reduces the tensile strength and impact energy of the welded joint.

Mechanical Behaviour of Aluminium-Timber Composite Connections with Screws and Toothed Plates.

This paper presents an investigation of the load-slip behaviour of aluminium-timber composite connections. Toothed plates with bolts are often used for connecting timber structural members with steel structural members. In this paper, toothed plates (C2-50/M10G, C2-50/M12G or C11-50/M12) have been used as reinforcement in aluminium-timber screwed connections for the first time. The push-out test specimens consisted of laminated veneer lumber slabs, aluminium alloy beams, and hexagon head wood screws (10 mm × 80 mm and 12 mm × 80 mm). Of the specimens, 12 additionally had toothed plates as reinforcement, while 8 had no reinforcement. The load carrying-capacity, the mode of failure and the load-slip response of the strengthened and non-strengthened screwed connections were investigated. The use of toothed plate connectors was found to be effective in increasing the strength of aluminium-timber composite connections and ineffective in improving their stiffness. The examined stiffness and strength of the connections can be used in the design and numerical modelling of aluminium-timber composite beams with reinforced screwed connections.

Vehicle Body and Roll Cage Assessment involving Frontal, Side and Roll-over Crash Analysis by FEA using LS-Dyna

Simulating the vehicle collision has gained importance in the automotive sector due to its accuracy, cost effectiveness and enhanced reliability. It aids in improving the safety of driver and passenger and also examine the cause of crash or collision. This numerical analysis investigates the materials capability to enhance safety. A three-dimensional vehicle model was developed along with its roll cage using solid work tool. Hypermesh work bench was employed to discretise the sensitive parts of the body and roll cage using beam 189 element having six degree of freedom at each node. The existing structural steel members were replaced with reinforced carbon fibre in all the sensitive part of the body and roll cage and its structural stability was assessed using the frontal, side and roll over crash simulation using LS Dyna. This investigation also reveals the change in internal energy, kinetic energy absorption and momentum transfer for both structural steel and carbon fiber under all the crash scenarios. The outcomes of this numerical investigation proved that the reinforced carbon fiber can be effectively replaced with the structural steel to enhance safety.

Global Sensitivity Analysis of Ultimate Limit States of Stainless Steel Structural Members

The article presents global Sobol sensitivity analysis of a rolled member in tension made from austenitic chromium-nickel stainless steel of type 1.4307/AISI 304 L. The statistical characteristics of yield strength and of the geometry of the rolled steel IPE cross-section are presented on the basis of published experimental research. The sensitivity analysis showed the dominant effect of the yield strength on the static resistance. The second dominant variable is the flange thickness. Higher-order sensitivity indices oriented at detecting the presence of interaction effects between input variables are very small. The characteristics of other types of sensitivity analyses oriented at quantiles or the probability of failure are discussed, especially in terms of a higher proportion of higher-order sensitivity indices. The results of Sobol sensitivity analysis of stainless steel are compared with similar results of carbon steels.

Design of confinement reinforcement for encased composite columns

Confinement reinforcement for concrete columns is designed to ensure that the columns can withstand high lateral deformations during strong earthquakes. An accurate determination of the required confinement reinforcement is vital for achieving an efficient design, especially for encased composite columns in which reinforcement congestion can be a potential problem. This paper uses the confinement requirements among three selected specifications as the basis for developing confinement equations for encased composite columns. The specification selected herein are the ACI 318, AISC Seismic Specification, and Taiwan encased composite building code. In this study, new confinement reinforcement design equations are developed and validated against experimental results. The developed confinement provision, providing a means to quantify the confinement effect of I-shaped structural steel members, significantly reduces the required confinement reinforcement for encased composite columns, and consequently alleviates the reinforcement congestion problem.

New modeling strategies for analyzing lateral-torsional buckling in class-4 steel structural members at elevated temperatures using beam-type elements

Fire is one of the main hazards that can affect steel buildings and bridges and was responsible, e.g., for the collapse of the Plasco building in Tehran, Iran, and the I-65 bridge in Birmingham, Alabama, USA. This vulnerability has motivated the development of advanced computational models to predict the response of steel structures to fire accurately. The mechanical response of slender steel members to fire is especially important because they fail prematurely by buckling at load values below their elastic strength. However, the structural analysis of these members typically requires advanced and complex FE models with shell elements, including initial geometric and material imperfections. These shell models are computationally expensive, complicating the carrying out of parametric and probabilistic studies. Therefore, there is a need to develop simple, accurate, and low-cost computational models as reliable as shell-type models. To overcome this knowledge gap, this paper presents two new modeling strategies that simulate the mechanical response of class-4 steel members subjected to lateral-torsional buckling in fire using Timoshenko beam-type finite elements, which significantly simplify the structural modeling. These strategies are called Fiber Beam Model (FBM) and Cruciform Frame Model (CFM) and include initial geometric and material imperfections and thermal strains. In the FBM, the steel member is represented by a single fiber of I-section beam elements, whereas in the CFM, a cruciform arrangement of rectangular beam finite element fibers idealizes it, making the CFM more complex to build than FBM. Both strategies were satisfactorily validated with experimental and numerical results of Test-1 and Test-3 carried out in the “Fire design of steel members with welded or hot-rolled class-4 cross-section” (FIDESC4) research project on a slender beam of class-4 section. Although both FBM and CFM correctly captured the LTB resistance of the tested beam, CFM can, in addition, adequately reproduce the local buckling failure and significantly reduced the computational time. That means complex fire engineering problems such as probabilistic and optimization analyses of thin-walled beams can be addressed more easily and accurately, representing an important step towards applying performance-based approaches in slender steel structures under fire.

A Study on the Effect of Hollow Tubular Flange Sections on the Behavior of Cold-Formed Steel Built-Up Beams

This paper deals with a study conducted on flexural behavior of cold-formed steel built-up I-beams with hollow tubular flange sections. There were two types of test sections, namely, built-up sections that were assembled with either stiffened or unstiffened channels coupling back-to-back at the web and a hollow tubular rectangular flange at the top and bottom of the web to form built-up I-beam. The flexural behavior along with the strength and failure modes of the built-up sections was examined using the four-point loading system. Nonlinear finite element (FE) models were formulated and validated with the experimental test results. It was observed that the developed FE models had precisely predicted the behavior of built-up I-beams. Further, the verified FE models were used to conduct a detailed parametric study on cold-formed steel built-up beam sections with respect to thickness, depth, and yield stress of the material. The flexural strength of the beams was designed using the direct strength method as specified in American Iron and Steel Institute (AISI) for the design of cold-formed steel structural members and was compared with the experimental results and the failure loads predicted from FE models. Since the results were not conservative, a new customized design equation had been mooted and delineated in the study for determining the flexural strength of cold-formed steel built-up beams with hollow tubular flange sections.