The steel tube confined concrete (STCC) column piers of marine structures have been proposed in recent years. The main advantages of STCC piers include the convenient construction process and ...improved core concrete strength. This research presents an experimental investigation on stainless steel tube confined concrete (SSTCC) column piers subjected to axial loading. Thirty two specimens were prepared and tested. Test variables included section shape, steel tube thickness, and concrete strength. Failure modes, axial ultimate compressive strength, strain characteristics, rigidity, confinement effect, and ductility were comprehensively investigated. Test results demonstrated that the main failure modes for circular and square specimens were concrete shear failure and steel tube fracture caused by concrete deformation, respectively. The axial compressive ultimate strength was affected by the tube thickness and concrete strength. The ultimate strength increased with the increase in the confinement factor, and the increasing ratio of the circular specimens was five times to that of square specimens. The differences in axial ultimate compressive strength of SSTCC column piers, carbon steel tube confined concrete column piers, and concrete filled steel tube column piers were also analyzed. Increasing tube thickness could increase the ductility and rigidity of the specimens. Moreover, axial ultimate compressive strengths were calculated and discussed based on different calculation models.
•Axial compression behaviors of stainless steel tube confined concrete (SSTCC) column piers were experimentally studied.•The differences in failure modes, ultimate strength, strain, rigidity, confinement effect, and ductility were discussed.•The differences in axial strength of SSTCC column piers, CSTCC column piers, and CFST column piers were analyzed.•Axial ultimate compressive strengths were calculated and compared using different calculation models.
•Application of the system-based direct design method to stainless steel frames subjected to combined gravity and wind loads is presented.•Six baseline cold-formed stainless steel frames are ...investigated, including the three main stainless steel families.•System reliability calibrations are presented for the Eurocode, US and Australian design frameworks, covering different wind-to-dead load ratios.•System safety factors γM,s and system resistance factors ϕs are proposed for the target reliability indices typically adopted in national design frameworks.
In the process of developing the next generation of design standards for steel structures, most relevant international structural codes including AISC360, AISC370, AS/NZS4100 and Eurocode3 already incorporate preliminary versions of system-based design-by-analysis approaches that allow a direct evaluation of the strength of steel and stainless steel structures from advanced numerical simulations. As a result, recent research works have focused on building rigorous structural reliability frameworks to investigate acceptable target reliability indices for structural systems and to develop new design methods in conjunction with adequate system safety factors and system resistance factors. Although design recommendations exist for the direct design of hot-rolled and cold-formed steel structures based on advanced finite element analysis, the extension of the method to other materials such as stainless steel is under development. This paper is part of a research effort to build a reliability framework for stainless steel structures subject to different load combinations and presents the results of system reliability calibrations carried out on six stainless steel portal frames subjected to combined gravity and wind loads. The study covers the most common stainless steel families and three international design frameworks (i.e., Eurocode, US and Australian frameworks). From the reliability calibrations derived, suitable system safety factors γM,s and system resistance factors ϕs are proposed for the direct design of stainless steel frames under combined gravity and wind loads using advanced numerical simulations.
•Cyclic behavior of HSS-FTS-RSLs was experimentally investigated.•The replaceability of three types of spandrel beam-to-link connections was evaluated.•The detailed FE models were developed.•The ...spandrel beam-to-link connection behaviors were analyzed.
Although the use of steel framed-tube structures (SFTSs) under intense earthquakes loads helps to prevent fatalities, the plastic hinges at the ends of spandrel beams cannot properly developed due to low clear span-to-depth ratios, resulting in poor ductility and recoverability. To address this problem, high-strength steel framed-tube structures with replaceable shear links (HSS-FTS-RSLs) were proposed, which combine the advantages of replaceable shear links and high-strength steel (HSS). This paper presents an experimental research program including three 2/3-scale single-story single-span sub-structure specimens with three types of spandrel beam-to-link connections: bolted end-plate connection, bolted web connection, and bolted splice-plate connection. The global seismic response and replaceability of the specimens were evaluated. Nonlinear finite element models of the specimens were established and validated with the experimental results. Test results demonstrated that the three specimens developed the expected ductile failure of the shear links while the spandrel beams and columns were damage-free, showing excellent energy dissipation and deformation abilities. The usage of HSS effectively maintained the structural components in essentially linear elastic range. The specimen with bolted end-plate connection exhibited a stable hysteretic response and high resistance. This connection type possesses reliable force transmission, convenient construction, no-slippage property, and the shortest replacement time. The connection rotation as a result of bolt slipping and bolt bearing significantly contributed to the total shear link rotation for the specimens with bolted web connection and bolted splice-plate connection. This led to the increased deformation ability and ductility as well as the pinching of hysteretic loops. Post-earthquake recoverability can be achieved as expected. The acceptable residual story drifts θre that allow for easy replacement of the shear links were 0.41%, 0.31%, and 0.42% corresponding to the specimen with bolted end-plate connection, bolted web connection and bolted splice-plate connection, respectively. The detailed finite element models of the test specimens accurately predicted the experimental behavior.
Medium manganese steels are promising alloys for highly demanding sheet steel applications. However, cold-rolled intercritically annealed ultrafine-grained dual-phase medium manganese steels exhibit ...Lüders banding, which is detrimental for the mechanical properties and for the surface finish after forming. Therefore, it is essential to prevent the formation of Lüders bands. To achieve this, it is crucial to understand the underlying micromechanisms of their formation and propagation. While the nucleation of Lüders bands was studied before in these alloys, understanding of their propagation is lacking. Here, we use electron channelling contrast imaging, with a resolution of ~8 nm to examine the defect populations within and across the Lüders front. While macroscopic digital image correlation shows a uniform strain gradient across the Lüders front, quasi in-situ tensile tests in combination with microscopic electron channelling contrast imaging investigations reveal strain localized regions (termed plastic zones) within the Lüders front. These plastic zones are aligned with the macroscopic Lüders front and parallel in nature, with less deformed regions sandwiched between them. Additionally, it is observed that the size and distribution of the plastic zones are affected by the mechanical stability of austenite. We further demonstrate the role of strain partitioning between the austenite and ferrite (austenite being the softer phase) in the formation of the plastic zones.
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•The seismic behavior of two reinforced concrete (RC) walls with openings on scale of 1/3 accompanied by steel reinforced concrete (SRC) was investigated.•The walls behavior was assessed to determine ...their patterns of cracking failure mode, loading capacity, strength, and stiffness and dissipated energy with respect to the generated deformations.•After performing the loading test in the forms of lateral cyclic load as well as constant axial gravity load, the results of walls’ cyclic behavior, walls’ strength and stiffness degradation indexes, walls’ cumulative energy, and walls’ ductility were extracted based on displacement controlled and compared. Then, by means of FEM, the numerical analyses of both walls were performed.•The backbone curves for the FE models were then compared with the experimental diagrams and a desirable agreement between the results was observed.•This study can be useful in applied structural engineering because of applying eccentric braces at openings of a reinforced composite shear wall.
Reinforced concrete shear walls with the steel reinforced concrete frames is a common lateral force resisting structural system that is applied high-rise steel buildings in various forms. In this study, seismic behavior of two reinforced concrete (RC) shear walls with openings accompanied by steel reinforced concrete (SRC) on scale of 1/3 were investigated. One of the shear walls consisted of a steel truss reinforced concrete (STRC) with a specified eccentricity in each story level and its end was connected to the bracing’s steel beam. Both of the shear walls were coincidentally subjected to specific constant gravity load and cyclic load. Behavior assessment of shear walls included determination of the failure mode cracking pattern, loading capacity, strength, stiffness and dissipated energy with respect to generated deformations. Results revealed that the shear wall with encased steel brace (ESB) was more effective in terms of all the mentioned parameters compared to SRC wall. In the following, pushover curves for shear walls were investigated using finite element (FE) models and confidentiality of analytical models and prediction of behavior of these walls were verified based on real prototypes. Finally, effects of axial gravity load variations on FE models of both shear walls were evaluated. This study can be useful in applied structural engineering because of applying eccentric braces in openings of a reinforced composite shear wall.
An experimental study was conducted to identify the shear-enhancement and failure mechanisms behind the ultimate shear strength of steel fiber-reinforced concrete (SFRC) slender beams by using the ...full field-deformation-measuring capability of digital image correlation (DIC) technology. A total of 12 large-scale simply supported SFRC and RC beams with an overall height from 12 to 48 in. (305 to 1220 mm) were tested under monotonic point load up to failure. The greater shear strength in SFRC beams originates from the ability of the fiber bridging effect that delays the propagation of the cracks into the compression zone, whose shear strength is enhanced by the compressive stresses induced by the higher load. The slow progression of the cracks keeps the compression zone depth large, thereby enabling it to contribute to a higher shear resistance. In contrast with the traditional assumption for either plain concrete or SFRC beams, where the shear contribution resulting from dowel action is completely neglected, this research clearly shows that the dowel action has an appreciable effect on the ultimate shear strength. Its contribution varies from 10 to 30% when the beam depth increases from 12 to 48 in. (305 to 1220 mm). On the other hand, the compression zone s contribution decreases from 69 to 36% with the increase in beam depth. In addition, the shear contribution from the fiber bridging effect along the critical shear crack stays approximately unchanged at 20%, irrespective of the beam depth. In this study, the minimum shear strength obtained was in the range of ?? psi (0.42?? MPa) for the beams with the greatest depth. This indicates thatthe maximum allowed shear stress limit of 1.5?? psi (0.125?? MPa) specified inACI 318-14 is on the very conservative side. Keywords: dowel action; hooked-end steel fiber; shear strength; steel fiber-reinforced concrete.
•Sudden stress reduction or stress fluctuations can be observed for the UHPFRC.•Steel fiber addition significantly influence the compressive behavior of UHPFRC.•UHPFRC in DSTCs can be more ...effectively confined than in FRP confined concrete.•The suitability of existing model for the UHPFRC in DSTCs is investigated.
This study presents the results of an experimental program on the compressive behavior of hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) with ultra-high performance fiber-reinforced concrete (UHPFRC). In total 40 specimens, including 32 hybrid DSTCs and eight FRP confined solid concrete (FCSC) specimens, were prepared and tested under axial compression. In addition to hybrid UHPFRC DSTCs, hybrid DSTCs with ultra-high performance concrete without steel fiber addition (UHPC), high-strength concrete (HSC), and normal-strength concrete (NSC) were also tested. The investigated parameters included the FRP tube thickness, steel tube thickness, void ratio, steel fiber addition, concrete type, UHPFRC-filling inside the steel tube, and the column type. The test results indicate that the hybrid UHPFRC DSTCs can exhibit highly ductile behavior when a thick FRP tube is used. However, due to the ultra-high strength and the dense microstructure of UHPFRC, the hybrid UHPFRC DSTCs are likely to exhibit more brittle behavior than the hybrid DSTCs with NSC and HSC. Even though a high confinement level is provided, sudden stress reduction or stress fluctuations can be observed for the UHPFRC in hybrid DSTCs. The influences of FRP tube thickness, void ratio, steel fiber addition, and UHPFRC-filling inside the steel tube on the compressive behavior of the hybrid UHPFRC DSTCs are significant, while the influence of steel tube thickness is insignificant. Moreover, when compared to the FCSC specimens, the presence of an inner void is beneficial for the compressive behavior of UHPFRC in the hybrid DSTCs, especially when a thick FRP tube is used. Furthermore, the performance of existing stress-strain model to predict the compressive behavior of UHPFRC in the hybrid DSTCs is investigated.
To improve the quality of products produced from microforming, various nanolubricants have been applied in the field of micromanufacturing in recent years. In this paper, the effects of ...glycerol-based lubricant containing TiOsub.2 NPs (NPs) on micro deep drawing (MDD) of austenitic stainless steel (ASS) SUS301 were studied, and the lubrication mechanism involved was discussed. The MDD experiments were conducted with the SUS301 foils under dry, 1, 2, and 4 wt% TiOsub.2 NP lubrication conditions. The results show that the use of the TiOsub.2 nanolubricants can significantly improve the quality of the drawn cups in terms of decreased wrinkling and surface roughness. Besides, the concentration of TiOsub.2 NPs influences lubricity by reducing friction during the MDD process. The peak drawing force is the lowest when 2 wt% nanolubricant is applied, which drops to 72.54 N from 77.38 N under dry conditions. The micro cup drawn under 2 wt% TiOsub.2 nanolubricant has the best quality among those obtained under all the lubrication conditions. The lubrication mechanisms are derived from the mending effects of TiOsub.2 NPs and the formation of thin lubricant films associated with the open lubricant pockets (OLPs) and close lubricant pocket (CLPs) theory in the MDD. The CLPs function as reservoirs that retain lubricants to counteract the load pressure, whereas the OLPs lead to lubricant leakage due to the higher flow resistance. It was found that the lubricant film and NPs are insufficient at a low concentration (1 wt%), while the lubrication performance can be enhanced with increased NP concentration. However, there exist apparent agglomerations on the surface of the produced micro cup when using 4 wt% nanolubricant, which greatly deteriorates the lubricant performance in the MDD process. It is concluded that the lubricant containing 2 wt% TiOsub.2 NPs demonstrates the best lubrication performance during the MDD of ASS SUS301.
•Steel frames under pulse-like near-fault earthquakes are investigated.•Basic characteristics of forward directivity and fling step effects are discussed.•Code-compliant steel braced frames are ...carefully designed.•Steel braced frames with varying bracing parameters are studied.•Residual inter-storey drift prediction model is given for performance-based design.
This paper presents the behaviour of steel moment resisting and braced frames under pulse-like near-fault earthquakes. The key properties for characterizing near-fault ground motions with forward directivity and fling step effects are discussed, and the influence of varying brace properties on the key engineering demand parameters such as maximum inter-storey drift (MID), residual inter-storey drift (RID) and peak absolute floor acceleration (PA) is revealed. Among other findings, it is shown that the structural responses are related to spectral accelerations, PGV/PGA ratios, and the pulse period of near-fault ground motions. The moment resisting and self-centring braced frames (MRFs and SC-BRBFs) generally have comparable MID levels, while the buckling-restrained braced frames (BRBFs) tend to exhibit lower MIDs. Increasing the post-yield stiffness of the braces decreases the MID response. The SC-BRBFs generally have mean residual drifts less than 0.2% under all the considered ground motions. However, much larger RIDs are induced for the MRFs/BRBFs under the near-fault ground motions, suggesting that these structures may not be economically repairable after the earthquakes. From a non-structural performance point of view, the SC-BRBFs show much higher PA levels compared with the other structures. A good balance among the MID, RID, and PA responses can be achieved when “partial” SC-BRBs are used. To facilitate performance-based design, RID prediction models are finally proposed which enable an effective evaluation of the relationship between MID and RID.
•Validation of triethanolammonium dodecylbenzene sulfonate, a type of cationic surfactant, as a non-toxic corrosion inhibitor of Q235 carbon steel in alkaline media contaminated with chloride ...ions.•The semi-conducting property of passive film evaluated by the Mott-Schottky analysis demonstrates an decrease of Fe(Ⅱ) content of the film, which is corrborated by the XPS results.•The researched inhibitor can not only slow down the corrosion process, owing to the attack of chloride ions, but also reduce the amount of corrosion products as a consequence of gradual carbonation, which can be verifed by the Fe 2p2/3, O 1s, and C 1s spectra.
The performance of triethanolammonium dodecylbenzene sulfonate (TDS), a type of cationic surfactant, against corrosion of Q235 carbon steel in an alkaline medium simulating concrete pore solution was studied by different electrochemical test methods. Electrochemical impedance spectroscopy (EIS) results revealed an increase in the charge transfer resistance of specimens in the presence of TDS, compared with the blank system. Both donor and acceptor density with the increase in TDS concentration, evident in the Mott-Schottky plots. Furthermore, observations using an optical microscope and the analysis of X-ray photoelectron spectroscopy measurements corroborated that the pitting corrosion of the metallic surface was significantly hindered with the addition of TDS into the simulated concrete pore solution.
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