Design of concrete-filled high strength steel tubular X-joints subjected to compression

[EN] The structural performance and design of concrete-filled high strength steel tubular X-joints subjected to compression are investigated. A numerical investigation on the behaviour of concrete-filled high strength steel tubular chord members under concentrated bearing load has been performed. The high strength steel tubes had nominal yield stresses of 700 and 900 MPa. The infilled concrete had nominal concrete cylinder strengths of 35 and 100 MPa. In order to avoid the failure of brace members and reveal the true capacity of the X-joints, steel bearing plates were used to simulate the brace members. A finite element model was developed and validated against test results. Furthermore, a parametric study comprised 156 finite element analyses was carried out. The strengths of the concrete-filled high strength steel square and rectangular hollow section X-joints obtained from the parametric study together with available data in the literature were compared with the nominal strengths calculated from the CIDECT Design Guide. It is shown that the CIDECT design predictions exhibit significant scatter and could be unconservative for the concrete-filled tubular joints with chord sidewall slenderness ratio beyond 40 in this study. Hence, new design rules are proposed for concrete-filled high strength steel tubular X-joints subjected to compression. It is shown that the proposed design rules are able to provide reasonably good predictions.The research work described in this paper was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. 17209614).Li, H.; Young, B. (2018). Design of concrete-filled high strength steel tubular X-joints subjected to compression. Editorial Universitat Politècnica de València. 483-490. https://doi.org/10.4995/ASCCS2018.2018.7062OCS48349

Cold-Formed Ferritic Stainless Steel Tubular Sections under End-One-Flange Loading Condition

This paper presents experimental and numerical investigations of cold-formed ferritic stainless steel tubular sections under End-One-Flange (EOF) loading condition. A series of web crippling tests was conducted on cold-formed square and rectangular hollow sections of ferritic stainless steel grade EN 1.4003. The web crippling test results were used for the verification of the finite element (FE) model. Upon verification, a parametric study was performed thereafter. The codified web crippling design provisions in American, Australian/New Zealand and European standards for stainless steel structures were assessed. Improved web crippling design rules are proposed for cold-formed ferritic stainless steel tubular sections under EOF loading condition through modifying the design rules of the North American Specification and Direct Strength Method. It is shown that the modified web crippling design rules are able to provide accurate and reliable predictions

Web Crippling of Cold-Formed High Strength Steel Square and Rectangular Hollow Sections under Two-Flange Loading Conditions

The web crippling behavior of cold-formed high strength steel (HSS) square and rectangular hollow sections under End-Two-Flange and Interior-Two-Flange loading conditions is studied. The cold-formed HSS tubular sections had nominal 0.2% proof stresses of 700 and 900 MPa. Finite element (FE) models were developed and validated against test results, showing the capability of replicating the experimental web crippling strengths, failure modes and load-deformation histories. Upon validation of the FE models, an extensive parametric study comprised 112 FE analyses was performed. The web crippling strengths obtained from the experimental and numerical investigations were compared with the nominal strengths calculated from the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel structures. The comparison results show that the nominal strengths predicted by the existing codified web crippling design provisions are either unconservative or overly conservative. Hence, new design rules are proposed for cold-formed HSS square and rectangular hollow sections by means of Direct Strength Method (DSM). It is shown that the modified DSM is able to provide reasonably good predictions

Post-fire mechanical properties of high strength steels

[EN] High strength steels are becoming increasingly attractive for structural and architectural applications due to their superior strength-to-weight ratio which could lead to lighter and elegant structures. The stiffness and strength of high strength steels may reduce after exposure to fire. The post-fire mechanical properties of high strength steels have a crucial role in evaluating the residual strengths of these materials. This paper presents an experimental investigation on post-fire mechanical properties of cold-formed high strength steels. A series of tensile coupon tests has been carried out. The coupon specimens were extracted from cold-formed square hollow sections with nominal yield stresses of 700 and 900 MPa at ambient temperature. The specimens were exposed to various elevated temperatures ranged from 200 to 1000 °C and then cooled down to ambient temperature before tested to failure. Stress-strain curves were obtained and the mechanical properties, namely, Young’s modulus, yield stress (0.2% proof stress) and ultimate strength, of the cold-formed high strength steel materials after exposure to elevated temperatures were derived. The post-fire retention factors that obtained from the experimental investigation were compared with existing predictive equations in the literature. New predictive equations are proposed to determine the residual mechanical properties of high strength steels after exposure to fire. It is shown that the proposed predictive equations are suitable for both cold-formed and hot-rolled high strength steel materials with nominal yield stresses ranged from 690 to 960 MPa.Li, H.; Young, B. (2018). Post-fire mechanical properties of high strength steels. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 83-90. https://doi.org/10.4995/ASCCS2018.2018.7222OCS839

Semi-solid slurry of AZ91 magnesium alloy prepared by electromagnetic stirring near liquidus temperature

An electromagnetic stirring process near liquidus temperature was designed and demonstrated experimentally to produce semi-solid slurry of AZ91 magnesium alloy, in order to avoid not only contamination from mechanical stirring but also the inflammation of Mg alloy melt at elevated temperature. AZ91 alloy feedstock was isothermally heat treated at 600-610 for 20 min, and then stirred by electromagnetic field. Globular primary particle characteristic was observed optically in the castings. Mechanical properties were also studied

Tetra­aqua­bis­(2-{[5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl]sulfan­yl}acetato)­iron(II)

In the title compound, [Fe(C9H6N3O3S)2(H2O)4] or [Fe(POA)2(H2O)4], the FeII atom is located on an inversion center and is ligated by four O atoms of coordinated water mol­ecules in the equatorial plane while two POA ligands acting as monodentate ligands occupy the axial positions through their pyridyl N atoms, completing a slightly distorted octa­hedral coordination geometry. A three-dimensional supra­molecular network is formed by multiple O—H⋯O hydrogen-bonding inter­actions between the coordinated water donors and the uncoordinated carboxyl acceptors

catena-Poly[[(2,2′-bipyridine-κ2 N,N′)cadmium]-μ3-4-nitro­phthalato-κ4 O:O′,O′′:O′′′]

In the title polymeric compound, [Cd(C8H3NO6)(C10H8N2)]n, two O atoms from both carboxyl­ate groups of a nitro­phthalate anion coordinate to the CdII cation, forming a seven-membered chelate ring and two carboxyl­ate O atoms from another two nitro­phthalate anions and a 2,2′-bipyridine ligand coordinate to the Cd cation to complete the distorted octa­hedral coordination geometry. The carboxyl­ate groups of the nitro­phthalate anion adopt a syn–anti bridging mode, linking adjacent CdII cations and forming a polymeric chain running along the a axis. Weak intra- and inter­molecular C—H⋯O hydrogen bonding is present in the crystal structure