•Cold-formed stainless steel RHS undergoing combined bending and web crippling was studied.•34 tests were conducted on specimens of lean-duplex and ferritic stainless steel grades.•Parametric studies ...of 312 specimens were performed.•Current combined bending and web crippling design provisions are shown to be conservative.•Improved design rules are suggested in this study.
The behaviour and resistances of cold-formed stainless steel rectangular hollow section (RHS) members undergoing combined bending and web crippling were studied based upon experimental and numerical investigations. A test program consists of 4 pure bending tests, 7 pure web crippling tests and 23 web crippling-bending interaction tests was conducted. The RHS specimens were cold-rolled from lean-duplex and ferritic stainless steel sheets. Numerical models were built and validated against the test results. Upon validation, parametric studies comprised of 312 finite element analyses were undertaken. The obtained test and numerical results were compared with nominal resistances predicted from the American, Australian/New Zealand and European design standards for stainless steel structures. Moreover, the provisions in the North American Specification for cold-formed steel members were also evaluated. The comparison results indicate that the codified design provisions are generally safe to use for design of cold-formed stainless steel RHS members undergoing combined bending and web crippling, among which the European provision yields overly-conservative predictions. The codified web crippling-bending interaction curves can be applied for designing the stainless steel RHS members undergoing combined bending and web crippling, whilst improved predictions could be achieved by employing recently proposed bending and web crippling design rules.
•Axial performance of ultra-high strength CFST columns is presented.•Measures to improve ductility are provided.•Confinement effect should be ignored for calculating axial resistance.•Modified ...Eurocode 4 method is applicable to ultra-high strength CFST columns.
The use of high strength concrete and steel have significant advantages for composite members subject to significant compression as in the cases of high-rise buildings. Current design codes place limits on the strengths of steel and concrete due to limited test data and experience on the behaviour of composite members with the high strength materials. To extend their applications, a comprehensive experimental program has been carried out to investigate the behaviour of concrete filled steel tubes (CFSTs) with high- and ultra-high- strength materials at ambient temperature. This article presented some new findings on the axial performance of 56 short CFSTs. High tensile steel with yield strength up to 780MPa and ultra-high strength concrete with compressive cylinder strength up to 190MPa were used to prepare the CFST test specimens. The key issue is to clarify if the plastic cross-sectional resistance could be used at ultimate limit state as for CFSTs with the normal strength materials. To address this, experimental and analytical methods were adopted where the test results were compared with the predictions by various design codes world widely, and design recommendations were therefore proposed so that the prediction methods could be safely extended to the short CFSTs with the high- and ultra-high- strength materials.
The production of steel in the world is dominated by two types of technologies: BF + BOF (the blast furnace and basic oxygen furnace, also known as integrated steel plants) and EAF (the electric arc ...furnace). The BF + BOF process uses a lot of natural resources (iron ore is a feedstock for steel production) and fossil fuels. As a result, these steel mills have a significantly negative impact on the environment. In turn, EAF technology is characterised by very low direct emissions and very high indirect emissions. The raw material for steel production is steel scrap, the processing of which is highly energy-consuming. This paper analyses the energy intensity of steel production in Poland as a function of investments made in the steel industry in the years 2000–2019. Statistical data on steel production in the EAF process in Poland (which represents an approximately 50% share of the steel produced, as the rest is produced utilising the BF + BOF process) was used. Slight fluctuations are caused by the periodic switching of technology for economic or technical reasons. The hypothesis stating that there is a relationship between the volume of steel production utilising the EAF process and the energy consumption of the process, which is influenced by investments, was formulated. Econometric modelling was used as the research method and three models were constructed: (1) a two-factor power model; (2) a linear two-factor model; and (3) a linear one-factor model. Our findings show that the correlation is negative, that is, along with the increase in technological investments in electric steel plants in Poland, a decrease in the energy consumption of steel produced in electric furnaces was noted during the analysed period.
•Cyclic axial compression tests of 12 seawater and sea sand concrete-filled FRP- carbon steel composite tube (SFSCT) columns were conducted.•The thickness and type of FRPs were used as variables to ...test the failure mode, envelope and plastic strain.•The strain recoverable performance of FRPs is beneficial to the concrete shrinkage and the suppression of plastic strains.•A new stress–strain model was developed for predicting the full cyclic stress–strain response.
This paper presents an experimental investigation of a novel seawater and sea sand concrete (SSC)-filled fibre-reinforced polymer (FRP)-carbon steel composite tube column (SFSCT) subjected to cyclic axial compression loadings. The proposed structure is covered with FRP on both the inner and outer walls of a traditional carbon steel tube to solve the corrosion problem of seawater and sea sand concrete and to improve considerably the mechanical properties of the structure at the same time. Cyclic axial compression tests for 12 SFSCTs and 2 concrete-filled steel tubes were carried out. The thickness and type of FRP were used as variables to assess the mode of failure, envelope, plastic strain and stiffness at unloading. The results show that FRP can confine effectively the lateral expansion of concrete. Carbon fibre-reinforced polymer (CFRP) has a better confinement performance than basalt fibre-reinforced polymer (BFRP). According to the different confinement mechanisms of the internal and external layers of FRP on concrete, a more reasonable cyclic stress–strain model was proposed, and the superiority of the proposed model was verified by comparison with the experimental results.
Dual-phase (DP) steel is the flagship of advanced high-strength steels, which were the first among various candidate alloy systems to find application in weight-reduced automotive components. On the ...one hand, this is a metallurgical success story: Lean alloying and simple thermomechanical treatment enable use of less material to accomplish more performance while complying with demanding environmental and economic constraints. On the other hand, the enormous literature on DP steels demonstrates the immense complexity of microstructure physics in multiphase alloys: Roughly 50 years after the first reports on ferrite-martensite steels, there are still various open scientific questions. Fortunately, the last decades witnessed enormous advances in the development of enabling experimental and simulation techniques, significantly improving the understanding of DP steels. This review provides a detailed account of these improvements, focusing specifically on (
a
) microstructure evolution during processing, (
b
) experimental characterization of micromechanical behavior, and (
c
) the simulation of mechanical behavior, to highlight the critical unresolved issues and to guide future research efforts.
The tensile flow properties of austenitic (S316-L) and martensitic (S410-L) stainless steel wall structures deposited by powder-fed laser additive manufacturing (LAM) process are evaluated. The ...properties obtained by the LAM process are compared to commercial rolled sheets of these metals. Strain-rate sensitivity, work hardening, and fracture behavior are assessed by conducting uniaxial tensile testing at different strain rates (0.001, 0.01, 0.1, and 1.0 sec−1). Moreover, a correlation between the final microstructure and mechanical properties is established for the LAM products through detailed analyses of grain structures and hardness indentation measurements. The results indicate a strong dependency for the strain rate in martensitic alloys compared to austenitic alloys produced by the LAM process. Interestingly, the tensile strength of commercial rolled martensitic stainless steel sheet doubles (∼100% increase) by increasing the strain rate, while preserving its elongation to failure. Comparing the two manufacturing methods, a lower strain-rate sensitivity factor is recorded for the additive manufacturing material (m of ∼0.0336) compared to the commercial sheet (m of ∼0.0775). This lower sensitivity is attributed to coarser grain structure and greater microstructural heterogeneity of the LAM product, which stems from directional solidification and cooling phenomenon during the layer-upon-layer deposition process. In contrast, the work hardening exponent (n value) varies little (0.1834–0.2854) for the different materials and manufacturing methods. Fractographic studies reveal that the fracture mode varies from ductile rupture towards ductile-brittle with the formation of greater martensitic phases, which is in combination with the failure component changing from shear to tensile at high strain rates.
•Concrete filling significantly improves the axial load, ductility and toughness capacities of hollow CFAT, CFCST, and CFSST columns.•The effects of steel and synthetic fibers on axial load and ...pre-peak toughness capacities of CFAT, CFCST, and CFSST columns are highly limited.•The effects of steel and synthetic fibers on ductility and post-peak toughness capacities of CFCST and CFSST columns are significant.•The use of steel and synthetic fibers is much more effective to improve the post-peak behavior of the CFCST and CFSST columns than the CFAT columns.
The main aim of this study is to compare the axial load, ductility, and toughness capacities of square concrete-filled carbon steel (CFCST), stainless steel (CFSST) and aluminum tube (CFAT) columns filled with plain concrete, single (steel) and hybrid (steel + synthetic) fiber-reinforced concrete under axial compression. To this end, the enhancement in axial load, ductility and toughness capacities of steel and hybrid fiber-reinforced CFCST, CFSST, and CFAT columns were obtained with regard to fiber volume ratio (0.5 and 1.5%), compressive strength of concrete (30 and 70 MPa) and the steel tube thickness (2, 3 and 4 mm). A total of 99 hollow, steel and hybrid fiber-reinforced CFCST, CFSST, and CFAT columns were tested under axial compression. The results showed that although the use of steel and synthetic fibers in single and hybrid form is very limited for enhancement of the axial load capacities of CFAT, CFCST and CFSST columns, the enhancement in ductility and post-peak toughness capacities are notable especially for CFCST and CFSST columns. However, the effects of steel and synthetic fibers on post-cracking behavior of the CFAT columns are not significant due to early rupture of AL tubes that cause highly brittle behavior after first peak load. In addition to this, the use of steel and synthetic fibers in hybrid form is slightly better at improving the ductility and toughness capacities of most of the CFAT, CFCST and CFSST columns than the use of steel fibers in single form.
Concrete-filled steel tubular (CFST) structure offers numerous structural benefits, and has been widely used in civil engineering structures. This paper reviews the development of the family of ...concrete-filled steel tubular structures to date and draws a research framework on CFST members. The research development on CFST structural members in most recent years, particularly in China, is summarized and discussed. The current design approaches from various countries are examined briefly. Some projects in China utilizing CFST members are also introduced. Finally, some concluding remarks are made for CFST members.
•We summarize various types of CFST members.•We advise research framework and a recent research review on CFST members.•We present various projects using CFST members in China.
•Novel steel-high performance concrete composite slab-girder for bridges.•Use of advanced ductile engineered cementitious composites.•Use of ultra-high performance concrete closure strip.•Performance ...evaluation based on cracking, strength, & energy absorbing capacities.
This paper investigates the behavior of composite girders made of high performance concrete (HPC) slab connected to steel I-beam through stud shear connectors subjected to hogging moment. Such girders are widely used in bridge construction. However, reinforcing steel bars in the negative moment region contribute significantly to the moment resistance and is found to be ineffective due to cracking of ordinary concrete. This research proposes the use HPCs containing fibers (with better crack resisting and strain hardening characteristics) in the deck slab to enhance both cracking and yield load carrying capacity of such girders at the negative moment region. Four composite girder specimens made of different types of concrete and having variable slab continuity were tested to failure under monotonic loading simulating negative moment. Three types of concrete were employed in the first three girder specimens, namely: Normal Concrete (NC), Steel Fiber-Reinforced Concrete (SFRC) and engineered cementitious composite (ECC). The fourth girder specimen was constructed using two SFRC end slabs connected together with an Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) closure strip located at the maximum negative moment mid span region. This specimen represents the case of full width -full depth deck slabs resting over steel girders with transverse joints filled with UHPFRC used to accelerate bridge construction. The SFRC and ECC composite girders showed better performance in terms of cracking characteristics (multi-cracking and smaller crack width), higher pre-cracking linear stiffness, higher cracking load, higher concrete strain development during cracking and higher strength compared to their NC counterparts.
•A new kind of composite member with an outer galvanized corrugated steel tube proposed in this paper.•Confinement mechanism of CFCSTs investigated via theoretical analysis and experimental ...research.•Steel ratio and confinement index, can characterize the behaviour of CFCSTs.•Design method for CFCSTs with the consideration of corrugation.
Concrete-filled tubular (CFT) structures are exposed to increasingly complex environments with ever-broadening applications. Anticorrosion maintenance is generally difficult and expensive for established structures exposed to the air. Due to the superior corrosion resistance and the high lateral stiffness of the corrugated steel pipe (CSP), concrete-filled corrugated steel tube (CFCST) is proposed which has the similar working mechanism with the tube confined concrete columns. Such innovative composite member has advantages such as free of maintenance, ease of construction, high load-bearing capacity, good ductility and strong interlocking effect between CSP and concrete. In order to verify the load bearing reliability of concrete-filled corrugated steel tube (CFCST), twenty-one short columns including twelve CFCSTs were tested under axial compression. It was found that the CFCST is a tube confined concrete member and behaves slightly better than tubed-concrete columns. The strain and stress of CSP are discussed in detail to clarify the confinement effect. As well, solid nonlinear finite element models (FEM) were established to investigate the influence of key factors including geometries of CSP and strength of materials, which were summarized in the confinement index. Based on early studies on steel tube confined concrete and the parameter analysis in this paper, a suitable design method to predict the ultimate axial compressive load capacity for CFCST columns is proposed in this paper.
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