•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.
•Investigating seismic performance of RC exterior joints made with high-strength materials.•Studying the effect of reducing bar congestion on hysteresis behavior of beam-column joints.•Studying ...various design parameters using non-linear finite element method.•Comparing the experimental and analytical results of RC joints containing different steel rebar grades.
This paper reports an experimental investigation of the seismic performance of exterior beam-column joints reinforced with Grade 600 longitudinal reinforcing bars in beams and columns made with high strength concrete of 70 MPa. For this purpose, six half-scale reinforced concrete (RC) exterior connections were designed in accordance with the ACI 318-14 Code requirements for a special moment frame. The variables yield strength of longitudinal bars, concrete compressive strength, flexural reinforcement ratio, ratio of the column to beam flexural capacity, and longitudinal bar size were investigated by subjecting all the specimens to quasi-static reversed cyclic loading at drift ratios of up to 5.3%. In specimens with identical flexural strengths, the amounts of longitudinal reinforcing bars were reduced in beam and column by approximately 27% due to enhancement in their yield strength. Up to a drift ratio of 4.5%, all the specimens reinforced with high-strength steel (HSS) reinforcing bars exhibited an overall seismic behavior comparable to that observed for joints containing Grade 420 MPa bars regarding load-carrying capacity, failure mode, energy dissipation capacity, pinching width ratio, and secant stiffness. It was while all the specimens reached their theoretical load-carrying capacities. In the case of specimens with identical reinforcing bar ratio of Grade 600, the experimental evidence revealed that utilizing high-strength concrete (HSC) was able to improve the cumulative energy dissipation and pinching width ratio by a maximum of 30% and 26%, respectively, at a drift ratio of 4.5%; while HSC did not considerably affect secant stiffness and average peak load. A parametric study was also performed through finite-element analysis (FEA) to investigate the influence of different design parameters such as the grade and spacing of joint hoops, the ratio of the column-to-beam flexural capacity, and column depth-to-bar diameter, on the strength, stiffness, energy dissipation capacity and equivalent damping of the specimens.
It is common in the composites literature to find usage of terminology that is a legacy of monolithic materials such as metals, ceramics and polymers. With the aim of alleviating ambiguity and ...misinterpretations that can result from such usage, this article attempts to clarify concepts and definitions related to the mechanical behavior of fiber reinforced composites. Focus is placed on failure mechanisms and modes in composite materials, and their comparison with metals. Of special interest is the limit to a material's load-carrying capacity, commonly described as “strength”, which is a subject of major confusion in the literature. The various versions of strength, e.g., residual strength, open-hole tensile strength, in-situ strength and compression after impact strength are scrutinized from the point of view of their being material properties. It is recommended that the practice of loose and ill-defined usage of the strength terminology should be abandoned in favor of resorting to proper use of critical stress states for relating those to the load-carrying capacity under consideration.
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•A database is collected for concrete encased steel composite columns under various loading types.•The applicability of EN 1994-1-1 for concrete encased steel composite columns is ...evaluated.•Sensitivity study is performed to assess the accuracy of EC4 method.•An analytical procedure is developed to construct the axial force-bending moment diagrams.•A unified design method is proposed to construct the interaction diagrams.
This paper presents a unified approach to evaluate the axial force and moment interaction strength curve of Concrete Encased Steel (CES) composite columns made of different steel and concrete grades. A database was established by collecting the test results of CES composite columns in the literature covering concrete compressive strength ranging from 20 to 104 MPa and steel yield strength from 280 to 913 MPa. A sensitivity study was then carried out to investigate the effect of different design parameters on the accuracy of the current design method EN 1994-1-1 in predicting the ultimate strength of CES composite columns. These design parameters include characteristic strength of materials, steel contribution ratio, concrete cover thickness ratio, longitudinal reinforcement ratio, and volumetric ratio of transverse reinforcement. Analytical study was performed through a self-compiled computer program which was developed based on materials strain compatibility principle. The comparison between the analytical results and test results confirms the validity of the proposed method to provide reasonable prediction of cross-sectional axial-moment interaction curves for CES columns for a wide range of steel and concrete grades. The existing EC4 method, which is based on plastic design principle, was found to be un-conservative in predicting the cross section resistance of CES composite columns with high strength concrete and high strength steel. Further enhancement was made to the proposed method to include both the strain gradient effect and concrete confinement effect to achieve a better agreement with the test results reported in literature. Finally, a simplified method was proposed to construct the axial-moment interaction curves of CES columns, which can be used as a unified approach to design such columns with normal and high strength steel and concrete materials.
Two dry surfaces can instantly adhere upon contact with each other through intermolecular forces such as hydrogen bonds, electrostatic interactions and van der Waals interactions
. However, such ...instant adhesion is challenging when wet surfaces such as body tissues are involved, because water separates the molecules of the two surfaces, preventing interactions
. Although tissue adhesives have potential advantages over suturing or stapling
, existing liquid or hydrogel tissue adhesives suffer from several limitations: weak bonding, low biological compatibility, poor mechanical match with tissues, and slow adhesion formation
. Here we propose an alternative tissue adhesive in the form of a dry double-sided tape (DST) made from a combination of a biopolymer (gelatin or chitosan) and crosslinked poly(acrylic acid) grafted with N-hydrosuccinimide ester. The adhesion mechanism of this DST relies on the removal of interfacial water from the tissue surface, resulting in fast temporary crosslinking to the surface. Subsequent covalent crosslinking with amine groups on the tissue surface further improves the adhesion stability and strength of the DST. In vitro mouse, in vivo rat and ex vivo porcine models show that the DST can achieve strong adhesion between diverse wet dynamic tissues and engineering solids within five seconds. The DST may be useful as a tissue adhesive and sealant, and in adhering wearable and implantable devices to wet tissues.
The behavior of reinforced concrete (RC) squat walls constructed with conventional- and high-strength materials was evaluated through tests of 10 wall specimens subjected to reversed cyclic loading. ...Primary variables included specimen height-to-length aspect ratio, steel grade, concrete compressive strength, and normalized shear stress demand. Specimens were generally in compliance with ACI 318-14. Test results showed that specimens containing conventional- and high-strength steel had similar strength and deformation capacities when designed to have equivalent steel force, defined as total steel area times steel yield stress. The lateral strength of walls with aspect ratios of 1.0 and 1.5 can be estimated using their nominal flexural strength when the nominal shear strength exceeds V.sub.mn. For specimens with an aspect ratio of 0.5, the lateral strength was close to the force required to cause flexural reinforcement yielding and less than the nominal shear strength calculated per ACI 318-14. Specimen deformation capacity decreased as the normalized shear stress increased. The use of high-strength concrete, which led to a reduced normalized shear stress demand, resulted in larger specimen deformation capacity. Keywords: deformation; drift; high strength; low-rise wall; shear; squat wall; strength.
The interest for a wider range of usable materials for the technology of selective laser melting (SLM) is growing. In this work, the manufacturing of wrought Al–Cu–Mg parts using SLM technology was ...systematically investigated. The effect of processing parameters on the density of the deposited Al–Cu–Mg samples was studied. It shows that the laser energy density plays a significant role in the densification behavior of the Al–Cu–Mg powder during the SLM process. The laser energy density value of 340J/mm3 is found to be the threshold, above which high density samples (99.8%) without imperfections and microcracks can be obtained. The SLMed Al–Cu–Mg part presents a unique layer-wise feature which consisted of an extremely fine supersaturated cellular-dendrites structure. The ultimate tensile strength of 402MPa and the yield strength of 276MPa are achieved for the SLMed Al–Cu–Mg part. The combination of grain refinement and solid solution strengthening mechanisms during SLM process are proposed to explain the high mechanical strength.
•Structural test is conducted on 14 high strength Concrete Encased Steel (CES) composite short columns.•The axial compression capacity of high strength CES columns is evaluated and compared with ...various design codes.•A concrete strength reduction factor is proposed to account for the brittleness of high strength concrete.•Parametric studies are carried out to determine the critical parameters affecting strength and ductility of CES columns.•An empirical equation is proposed to assess the ductility of high strength CES columns.
This paper presents an experimental program that studies the structural behaviour of high strength Concrete Encased Steel (CES) composite columns. The structural performance under compression, including the damage pattern, load-carrying capacity, post-peak ductility, and load-displacement response is experimentally investigated. A total of 14 specimens were tested under concentric compression. The parameters studied in this program include concrete compressive strength, steel yield strength, stirrup spacing, incorporation of steel fiber, as well as the shape of the structural steel section. To evaluate the material compatibility between high strength concrete and high strength steel, two concrete grades (C90, C130) and two steel grades (S500, S690) were used to prepare the test specimens. In addition, 0.5% volume fraction of steel fiber was added in concrete mix to minimize the inherent brittleness of high strength concrete. The comparison between test results and analytical predictions reveals the inability of existing design codes to estimate high strength CES columns, unless steel fiber and dense reinforcement are used in combination. The effect of material strength, steel fibers, volumetric ratios of hoop reinforcement, and shape of steel section on both strength and ductility of CES columns was assessed through a comprehensive parametric study. The analysis of test results demonstrates that steel contribution ratio plays a dominant role in the ductility, whereas increasing hoop reinforcement ratio and adding steel fiber has negligible effect. Finally, a simplified formula is proposed to evaluate ductility of high strength CES columns.
•The seismic behavior of concrete slender columns was investigated.•The main parameters include stirrup space, concrete strength and axial load ratio.•The yield, maximum and failure points obtained ...from ABAQUS analysis were shown.•Parameter analysis on deformation and load at different service states was conducted.
To investigate the influence of longitudinal reinforcement strength grade, stirrup spacing, concrete strength and axial load ratio (ALR) on seismic behavior of high-strength concrete (HSC) columns, seven full-scale square HSC columns reinforced with high-strength steel bars (HSSB) with nominal yield strength of 600 MPa or conventional steel bars were tested under constant axial load and cyclic lateral load. Furthermore, corresponding nonlinear finite element analysis was conducted in ABAQUS. The column top deformation and lateral load at different service states, stiffness degradation, bearing capacity degradation and strain of longitudinal and transverse reinforcement were discussed. The test result shows that using steel bars with nominal yield strength of 400 MPa as stirrup is a better choice for HSC columns and ALR is an important factor which determines whether the high-strength longitudinal reinforcement can reach its compressive or tensile yield strain before maximum point. Taking HSSB as longitudinal reinforcement (equivalent volume replacement) greatly improves the seismic behavior of HSC columns. After taking the influence of strain gradient on stress-strain relationship of compressive concrete into consideration, a confined strain gradient model (CSGM) which was suitable for finite element analysis (FEA) was established based on the model established by Razvi and Saatcioglu. Specific verification of finite element model (FEM) on deformation and lateral load at different service states were presented for further parameter analysis. The trend of displacement ductility factor were investigated in detail in numerical analysis part. With proper ALR and stirrup characteristic value, HSC columns reinforced with HSSB is able to present a displacement ductility of higher than 4, which is capable to meet the ductility demand of most codes.
This paper presents exact formulas for the reliability of linear consecutive k-out-of-n: F, and relayed consecutive k-out-of-n: F systems, having a change point at position ??, 1≤??≤??, for any ...??≤??. A change point at position ??, means that the components after this point have reliabilities that are different from those before or at position ??. The components are assumed to be independent. Practically, the change in the components reliabilities may be due to change in the stress applied. Assuming a change in stress, exact formulas of the stress-strength reliability of the systems are derived, considering two cases. The first case assumed strength and stress having the same form of distributions, while the second case assumed strength and stress having different forms of distributions. Estimation of the stress-strength reliability for both cases is discussed. Application to both cases are considered with numerical illustration.
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