•Eighteen CFSST specimens made of rolled austenitic or duplex stainless steel tubes were tested under compression.•Finite element models were validated against the experimental results.•Calculation ...methods for the compressive strength of CFSST stub columns were proposed.
Concrete-filled stainless steel tube (CFSST) members combine the advantages of the outstanding corrosion resistance of stainless steel and the composite action in concrete-filled steel tube (CFST) system. However, accurate calculation methods for this type of structures are currently limited and research into CFSST members with hot-rolled stainless steel tubes are not available. In this paper, the compressive behavior of CFSST stub columns has been investigated through a comprehensive experimental and numerical program. A total of 18 specimens, including 9 concrete-filled austenitic stainless steel tube (austenitic CFSST) and 9 concrete-filled duplex stainless steel tube (duplex CFSST) stub columns, were tested under compression. The varying parameters in the experimental study included the thickness of the stainless steel tube and the strength of the concrete. Finite element (FE) models duplicating the tests were developed, which were subsequently used in parametric study to generate a wider range of data and to investigate the influence of the tube thickness and concrete strength on the ultimate capacities of CFSST stub columns. Based on the generated data, it was found that the current European and Chinese standards for concrete-filled carbon steel tubes underestimate the resistances of CFSST members significantly. To this end, new calculation methods developed based on these European and Chinese design rules have been proposed, which were shown to provide improved strength predictions for both the austenitic and duplex CFSST members.
Hydrogen interaction with structural materials, especially stainless steels, is of great importance due to the acute effect that it can have on them. Stainless steels have become very common in many ...applications, and in water and high pressure environments in particular, due to their high levels of corrosion resistance and broad range of strength. Steel's durability is very much dependent on its microstructure and interaction with hydrogen. The action of hydrogen can lead to changes in mechanical properties, phase transformation and eventually to environmentally-assisted failure, which is known as hydrogen embrittlement (fracture). The susceptibility of steels to this hydrogen fracture mechanism is directly related to the interaction between traps (defects) and hydrogen. In this research, we study hydrogen fracture mechanisms through hydrogen interaction with trapping sites by thermal desorption spectrometry (TDS), and the calculation of hydrogen trapping energies states. Microstructure effects on hydrogen were investigated by exploring different stainless steels, including: austenitic stainless steel (AUSS), ferritic-austenitic (duplex) stainless steel (DSS), and super martensitic stainless steel (SMSS). The objective of this study is to determine the influences of thermal desorption analysis on the crystal structure of different stainless steels in order to better understand the trapping mechanisms of hydrogen in a variety of structure materials. It was found that the AUSS has the greatest stability of austenitic (γ) phase– ∼22% higher than DSS and ∼45% higher than SMSS. Moreover, the AUSS presented the lowest hydrogen trapping values of ∼31% compared with DSS and ∼25% compared with SMSS.
Hydrogen fracture mechanism was found to be highly dependent on the hydrogen trapping states and even more on the γ-phase stability. The hydrogen trapping mechanisms are discussed in detail.
•Hydrogen trapping mechanisms in structure materials were investigated using TDS.•The relation between γ stability, trapping states and fracture mechanism is studied.•Low trapping levels were identified with severe surface damage by hydrogen.•High γ-phase stability was identified with severe surface damage by hydrogen.•The γ → α′ phase transition was related to irreversible trapping site for hydrogen.
The elimination of inclusions in steelmaking processes has been widely studied. The removal of inclusions by slags containing the rare earth oxide Cesub.2Osub.3 are studied using an integrated ...numerical model. The integrated model involves the inclusion motion model, interfacial tension calculation model, surface tension calculation model of slag, and the mass action concentration model, based on ion and molecule coexistence theory. The motion behaviors of both solid Alsub.2Osub.3 inclusions and 50%wtAlsub.2Osub.3–50%wtCaO liquid inclusions of varied sizes at CaO-Cesub.2Osub.3-SiOsub.2-Alsub.2Osub.3(-MgO) slag systems are evaluated. The results show that it is more difficult to remove the inclusions with smaller sizes and in slag with a higher viscosity. Liquid inclusions are more difficult to remove than solid inclusions. It is found that the CaO-Cesub.2Osub.3-SiOsub.2-Alsub.2Osub.3-MgO refining slag shows a better ability to remove Alsub.2Osub.3 inclusions than that of the CaO-SiOsub.2-Alsub.2Osub.3-MgO slag. The reason for this is that the addition of the rare earth oxide Cesub.2Osub.3 can decrease the viscosity of slags, as well as improving the wetting effects of slags on Alsub.2Osub.3 inclusions. For two slags systems, the CaO-Cesub.2Osub.3-SiOsub.2-Alsub.2Osub.3-MgO slag system shows a better ability to remove Alsub.2Osub.3 inclusions than the CaO-Cesub.2Osub.3-SiOsub.2-Alsub.2Osub.3 slag system. The addition of 5% to 8% Cesub.2Osub.3 in a CaO-SiOsub.2-Alsub.2Osub.3-MgO slag is an optimized case for industrial applications.
Increasing the use of steel scrap and enhancing its recycling utilization are important strategies for fostering the low-carbon and environmental-friendly growth of the iron and steel industry in ...China. However, the current steelmaking processes cannot efficiently remove the residual elements in the scrap, such as Cu, Sn, As, and Sb. As a result, the above elements are recycled and accumulate in the scrap, which will eventually have a negative impact on the properties of steel. Currently, there are few studies on Sb removal from molten steel. To remove the residual element Sb in molten steel, the CaO-SiOsub.2-Alsub.2Osub.3 refining slag system containing CaCsub.2 was used, and the effect of the CaCsub.2 content in the molten slag, slag quantity, smelting temperature, and initial Sb and C contents in molten steel on the Sb removal ratio in the steel was investigated, and the mechanism of Sb removal by the aforementioned refining slag system was discussed in order to provide some experimental and theoretical basis for industrialization practice. When the smelting time is 5~10 min, the removal ratio of Sb from molten steel is at its peak and can reach 45.8%. The "Sb-reversion" phenomenon will appear in the molten steel when the smelting period is progressively extended. In molten steel, CaCsub.2 will preferentially react with O and S, and as the smelting temperature decreases, the distribution ratio of Sb, Lsub.Sb, improves. An increased initial Sb content in molten steel and slag quantity are beneficial to improving the removal ratio of Sb, but an increased initial C content in molten steel is detrimental to the progress of the Sb removal reaction. The removal reaction of Sb from molten steel by CaCsub.2 is a reversible reaction, and the diffusion of the products from the interface is the limiting factor of the overall reaction.
Steel fibre reinforced concrete (SFRC) is increasingly being used in the construction of civil infrastructure. However, there are inconsistencies among international standards and guidelines ...regarding the consideration of carbon-steel fibres for the structural verification of SFRC exposed to corrosive environments. This paper presents a review of the published research regarding carbonation- and chloride-induced corrosion of SFRC, and proposes a deterioration theory for cracked SFRC exposed to chlorides and carbonation, based on the damage at the fibre-matrix interface. The review confirms an overall agreement among academics and regulators regarding the durability of uncracked SFRC exposed to chlorides and carbonation. Contrariwise, the durability of cracked SFRC is under discussion at the technical and scientific level, as there is a large dispersion on the experimental results and some of the mechanisms governing the corrosion of carbon-steel fibres in cracks and its effects on the fracture behaviour of SFRC are not fully understood.
•The cyclic behavior of high-strength STRC composite columns was investigated.•The addition of steel fibers reduced damage degree and improved ductility.•A reasonable strength matching way can make ...full use of materials’ advantages.•An evaluation method for predicting the maximum carrying capacity was proposed.
To study the cyclic behavior of steel tube-reinforced, high-strength concrete columns with high-strength steel bars, a cyclic loading test of six full-sized square columns was carried out, including one traditional reinforced concrete (RC) column and five steel tube-reinforced concrete (STRC) composite columns. The cross-sectional shape of the inner steel tube, the strength matching of the outer concrete and the core concrete, and the presence of steel fiber in outer concrete were the major parameters of the test. The research shows that steel fiber-reinforced high-strength STRC composite columns had better seismic behavior compared to RC columns. The strength matching method, where the C90 core concrete was combined with the C70 outer concrete, resulted in a better composite effect in comparison to the method of using C80 concrete in both core concrete and outer concrete. Moreover, the addition of steel fibers in outer concrete effectively reduced the damage degree and improved the ductility, resilient capacity, and energy dissipation capacity of the specimens. Finally, based on the test research and theoretical analysis, a calculation model for predicting the maximum load-carrying capacity was proposed. The model was then verified by comparing its predictions with test results.
Wet multi-plate clutches have a running-in phase at the start of operation in which the friction behavior can change significantly by adjustment of the friction surfaces. This running-in behavior can ...strongly depend on the characteristics of the friction system consisting of friction material, steel plate and fluid. With the aim of good controllability and thus high reliability of the clutch from the first shift, running-in processes should be less pronounced and should be completed quickly. The article describes the influences of the steel plate on the running-in behavior. Therefore, topographical measurements of the steel plate surfaces before and after test are carried out. To characterize the steel plate surfaces, a large number of 3D surface parameters are evaluated and compared to a newly developed parameter characterizing the running-in behavior. Keywords Clutch, Steel Plate, Running-In, Surface Topography, System Assessment Nasslaufende Lamellenkupplungen weisen zu Betriebsbeginn eine Phase des Einlaufens auf, in der sich das Reibungsverhalten durch Anpassung der Reibflachen signifikant andern kann. Dieses Einlaufverhalten ist in Anhangigkeit der Charakteristika des Reibsystems bestehend aus Reibbelag, Stahllamelle und Schmierstoff stark unterschiedlich ausgepragt. Mit dem Ziel einer guten Regelbarkeit und damit hohen Zuverlassigkeit der Kupplung ab der ersten Schaltung sollen Einlaufvorgange wenig ausgepragt und schnell abgeschlossen sein. Der Beitrag behandelt Einflusse der Stahllamellenbeschaffenheit auf das Einlaufverhalten. Hierzu werden die Stahllamellenoberflachen im Neuzustand und nach Versuch umfassend topographisch vermessen. Zur Charakterisierung der Stahllamellenoberflachen wird eine Vielzahl von 3D-Oberflachenkennwerten ausgewertet und einem neu entwickelten Kennwert zum Einlaufverhalten gegenubergestellt. Schlusselworter Lamellenkupplung, Stahllamelle, Einlauf, Oberflachentopografie, Systembewertung
•Post-heating performance of CFST columns containing tire aggregate and steel fiber was studied.•A relationship for predicting the loading capacity of CFST columns under heat was proposed.•Including ...scrap-tire aggregate in concrete mixture lowered the strength of confined specimens.•Thermal treatment had no particular increasing effect on the decline of strength caused by the presence of tire.
The performance of concrete-filled steel tube (CFST) columns including scrap-tire rubber under compression and in particular changes in their behavior after thermal treatment has remained mostly understudied. This has led to the lack of the use of rubberized concrete in these columns. This study attempted to examine the post-heating performance of CFST columns subject to several temperatures (20, 250, 500, and 750 °C) with regard to the amount of scrap-tire rubber aggregate used as a volume fraction of sand (0, 5, and 10%), quantity of steel fibers in volume (0, 1, and 1.5%), and the ratio of the outer diameter to thickness of the steel tube (43 and 25.4). The specimens had high-strength concrete cores and seamless steel tubes. The total number of manufactured confined and unconfined cylindrical specimens was 114, which were then exposed to heat and axial compressive testing. Through these tests, the loading capacity, ductility, toughness, and compressive load-strain curves of different specimens were explored. Based on the results, although including the scrap-tire aggregate (by 10%) in the concrete mixture lowered the strength of the confined specimens (by 12%), thermal treatment had no particular increasing effect on this decline. Furthermore, as the quantity of steel fibers and the thickness of the steel tube in the heated and non-heated CFST specimens increased, toughness increased in all the specimens, and the ductility had an ascending trend in most specimens. In addition, the optimum quantity of steel fibers used here was 1%. In this regard, although the fibers affected the compressive strength of the CFST specimens negligibly, they demonstrated a considerable improving effect on the ductility and absorbed energy in all specimens particularly the heated ones. Up to 250 °C, the decline in strength was negligible, while above this temperature, this decline in strength was much more considerable, and also, the post-peak slope of all the curves decreased. Finally, due to the importance of predicting the strength of CFST columns after exposure to heat, a relationship for predicting the loading capacity of these columns under heat was proposed and the associated results were compared with the experimental results of this work as well as the experimental results reported by others. Good consistency was seen between the predicted and experimental results.
•UHDCC has the tensile strength from 5MPa to 20 MPa with tensile strain from 8% to 12%.•Plain UHDCC beam tests demonstrated the adequate loading capacity and ductility.•Feasibility of using plain ...UHDCC in structure without steel bar was confirmed.
To verify the feasibility of using the ultra-high ductility cementitious composites (UHDCC) for construction without steel reinforcement, the mechanical properties of UHDCC was experimentally tested at material, structural member and structure levels. The tensile strength of UHDCC was from 5 MPa to 20 MPa, the average tensile strain capacity was 8% with the maximum value up to 12%. Four-point bending tests demonstrated that the plain UHDCC beams can match the loading capacity of conventional reinforced concrete beams with the steel reinforcement ratio of 0.5–1.5%. The deflection-span ratio of all the plain UHDCC beams exceeded 1/50 at the peak load. The eccentric compressive loading tests showed that the loading capacity of plain UHDCC column was close to that of RC column with a steel ratio of 0.8%. Additionally, shaking table tests were implemented on a RC frame (steel reinforcement ratios of columns were about 2.0%) and a plain UHDCC frame. The UHDCC frame survived 3 kinds of earthquakes with the peak ground acceleration from 0.105 g to 1.178 g, and exhibited excellent inter-story drift control under extremely strong earthquakes. The performance of the UHDCC frame fulfilled the requirements of various seismic codes. The feasibility of non-steel reinforced UHDCC structure was preliminarily confirmed by this study.
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