Influence of Diagonal Bracing Restraint on Cold-Formed Steel Perforated Columns under Axial Compression

This paper presents a numerical investigation on the influence of diagonal bracing restraint on cold-formed steel perforated columns subjected to axial compression. Finite element method (FEM) is employed to analyse the structural behaviour of perforated columns. The results obtained from the present study highlight the influence of diagonal bracing restraint on post-buckling of columns, and the distortional-flexural mode interaction is also discussed. Furthermore, the accuracy of the present model is validated by comparing the results against the available experimental data

Experimental Investigation into Steel Storage Rack Beam-to-Upright Bolted Connections

For unbraced steel storage racks, the down-aisle stability depends largely on the performance of beam-to-upright connections and column bases. Boltless connections are generally used in order to make rack structures easy to assemble and feasible to adjust the storey height. Recently, storage racks are designed to carry large amounts of goods and they are therefore raise a considerable height, which makes the improvement of the structural stability to be sufficiently important. Under the circumstances, tab-connected beam-to-upright connections with bolts are gradually used in steel storage racks. Compared with boltless connections, the stiffness, strength and ductility of the bolted connections are improved to some extent. This paper presents an experimental investigation into the moment-rotation characteristic of steel storage rack beam-to-upright bolted connections under monotonic loads. Seven groups of specimens were tested with different constructional details and three identical specimens were repeated for each group. Moreover, the single cantilever test method was employed to study the rotational behaviour of connections. Effects of various parameters, such as upright thickness, beam height and tab numbers on connection behaviour are discussed and presented in this paper. The experiments show that the failure modes of bolted beam-to-upright connections depend on the relative thickness between the upright and beam-end-connector, as well as the relative height between the beam and beam-end-connector. Furthermore, the results obtained from the present study highlight that the behaviour of connections, such as stiffness and ultimate moment capacity, are considerably influenced by the specific constructional details

Fracture simulation of constructional steels in two fracture modes

The paper presents a comprehensive study, aiming to provide useful tools for numerically predicting the fracture phenomenon in steel structures. A micro-mechanically-based fracture model is proposed, which comprises two competing and correlated fracture criteria corresponding to the shear and tension fracture modes. Yield-to-fracture strain hardening behaviour of constructional steel is also investigated, and numerical modelling technique for fracture simulation in implicit time integration analysis is addressed. Having setting out all necessary components, coupon tests covering a wide range of stress states are carried out and numerically simulated to calibrate and validate the fracture model. Numerical results agree well with the experimental results, and conclusions are drawn about the suitability of the proposed fracture model and methods for predicting fracture in both shear and tension modes.the National Natural Science Foundation of China; the Australian Research Counci

Experimental Analysis of Beam-to-upright Connections in Cold-formed Steel Storage Pallet Racks

A research program is currently in progress at Department of Building Engineering of Tongji University with the aim of investigating the behavior of cold-formed steel storage pallet racks under static and dynamic loading. This paper presents preliminary experimental analysis on the monotonic behavior of beam-to-upright connections. In the experimentation, the set-up was specially designed to accommodate precise requirement of boundary conditions and the measurement method was refined from the general ones used in rack design codes. It is shown that deformation modes of the connections were similar before failure while the failure modes were different depending on the specific constructional details. Moment-rotation characteristic curves are obtained and compared. On the base of these curves, the main parameters controlling the stiffness and moment capacity of connections, such as thickness of upright section, depth of pallet beam section, construction of beam end connector (mainly the number of tabs) and the loading direction are discussed

Calculation for Moment Capacity of Beam-to-Upright Connections of Steel Storage Pallet Racks

Steel storage pallet rack structures are three-dimensional framed structures, which are widely used to store different kinds of goods. For the easy accessibility to stored products, pallet racks are not usually braced in the down-aisle direction. The down-aisle stability is mostly provided by the characteristics of beam-to-upright connections, and the characteristics of upright base connections. In this paper, calculation for moment capacity of beam-to-upright connections is carried out. A mechanical model is presented firstly. Based on the model, moment capacity is related to the failure capacity, directly determined by the failure mode, of the topmost tab of the beam-end-connector and the corresponding upright wall. Different methods to predict the failure capacity are derived for two types of failure modes, i.e. crack of tab and crack of upright wall. The new method has shown a satisfactory agreement with experimental results demonstrating the reliability of the model in predicting the moment capacity of beam-to-upright connections

The Burnside ai-semiring variety defined by xn≈xx^n\approx x

Let ${\bf Sr}(n, 1)$ denote the ai-semiring variety defined by the identity $x^n\approx x$, where $n>1$. We characterize all subdirectly irreducible members of a semisimple subvariety of ${\bf Sr}(n, 1)$. Based on this result, we prove that ${\bf Sr}(n, 1)$ is hereditarily finitely based (resp., hereditarily finitely generated) if and only if $n<4$ and that the lattice of subvarieties of ${\bf Sr}(n, 1)$ is countable if and only if $n<4$. Also, we show that the class of all locally finite members of ${\bf Sr}(n, 1)$ forms a variety and so affirmatively answer the restricted Burnside problem for ${\bf Sr}(n, 1)$. In addition, we provide a simplified proof of the main result obtained by Gajdo\v{s} and Ku\v{r}il (Semigroup Forum 80: 92--104, 2010)

Behaviour of H-section purlin connections in resisting progressive collapse of roofs

When a truss roof is subjected to sudden local damage, purlins are capable of bridging the damaged truss unit, thereby increasing the robustness of the integrated roof system. To investigate the bridging capacity purlins can provide, experiments were carried out on bolted fin plate connections that join thin-walled H-section purlins to the main truss, investigating their behaviour under a main truss-removal scenario. Eight specimens with varied connection details were tested. Results of all experiments are provided in detail, including the full-range vertical resistance versus displacement curves, the collapse-resisting mechanisms, and the failure modes, being either bolt shear failure or combined bolt bearing and net-section tensile failure. Experimental results showed that better bridging capacity can be achieved by adopting relatively larger diameter bolts, reducing the bolt group height, applying higher preloading force when installing bolts, and increasing the end distance for the bolt holes. Meanwhile, a theoretical model is proposed to predict the vertical resistance versus displacement response of the purlin-to-connection assembly. This model is capable of capturing the slip of bolts, and the gradual yielding and failure of the connection components, and thus gives predictions that are in reasonably good agreement with the experimental results.The National Natural Science Foundation of China; The Australian Research Counci

THE VARIETY GENERATED BY AN AI-SEMIRING OF ORDER THREE

Up to isomorphism, there are 61 ai-semirings of order three. The finite basis problem for these semirings is investigated. This problem for 45 semirings of them is answered by some results in the literature. The remaining semirings are studied using equational logic. It is shown that with the possible exception of the semiring $S_7$, all ai-semirings of order three are finitely based

Deep Imaging of the HCG 95 Field.I.Ultra-diffuse Galaxies

We present a detection of 89 candidates of ultra-diffuse galaxies (UDGs) in a 4.9 degree$^2$ field centered on the Hickson Compact Group 95 (HCG 95) using deep $g$- and $r$-band images taken with the Chinese Near Object Survey Telescope. This field contains one rich galaxy cluster (Abell 2588 at $z$=0.199) and two poor clusters (Pegasus I at $z$=0.013 and Pegasus II at $z$=0.040). The 89 candidates are likely associated with the two poor clusters, giving about 50 $-$ 60 true UDGs with a half-light radius $r_{\rm e} > 1.5$ kpc and a central surface brightness $\mu(g,0) > 24.0$ mag arcsec$^{-2}$. Deep $z$'-band images are available for 84 of the 89 galaxies from the Dark Energy Camera Legacy Survey (DECaLS), confirming that these galaxies have an extremely low central surface brightness. Moreover, our UDG candidates are spread over a wide range in $g-r$ color, and $\sim$26% are as blue as normal star-forming galaxies, which is suggestive of young UDGs that are still in formation. Interestingly, we find that one UDG linked with HCG 95 is a gas-rich galaxy with H I mass $1.1 \times 10^{9} M_{\odot}$ detected by the Very Large Array, and has a stellar mass of $M_\star \sim 1.8 \times 10^{8}$ $M_{\odot}$. This indicates that UDGs at least partially overlap with the population of nearly dark galaxies found in deep H I surveys. Our results show that the high abundance of blue UDGs in the HCG 95 field is favored by the environment of poor galaxy clusters residing in H I-rich large-scale structures.Comment: Published in Ap