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

Fusion of imprecise qualitative information

In this paper, we present a new 2-tuple linguistic representation model, i.e. Distribution Function Model (DFM), for combining imprecise qualitative information using fusion rules drawn from Dezert-Smarandache Theory (DSmT) framework. Such new approach allows to preserve the precision and efficiency of the combination of linguistic information in the case of either equidistant or unbalanced label model. Some basic operators on imprecise 2-tuple labels are presented together with their extensions for imprecise 2-tuple labels. We also give simple examples to show how precise and imprecise qualitative information can be combined for reasoning under uncertainty. It is concluded that DSmT can deal efficiently with both precise and imprecise quantitative and qualitative beliefs, which extends the scope of this theory

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

Recent developments on the Component Method

The Component Method is well established and incorporated in Part 1.8 of Eurocode3 for the design of connections of steel frameworks. It is primarily intended to provide the elastic joint stiffness, although Part 1.8 includes provisions for also determining the inelastic moment-rotation response from the elastic limit to the ultimate moment. The latter provisions are empirical and use an established experimentally-based nonlinear equation to define the inelastic response. The Component Method has been further developed in recent years to determine the inelastic response using bi-linear springs with elastic and inelastic ranges. Procedures have also been developed at the University of Sydney to extend the Method into the post-ultimate range by defining tri-linear springs with elastic, inelastic and softening ranges. As well, recent research at the University of Sydney has produced a simple way to predict the moment-rotation response under fracture of components, thus enabling the Method to capture the full moment-rotation behaviour. The ability of the Method to predict full-range moment-rotation behaviour is especially useful for design by advanced analysis and progressive collapse analysis, as it allows both members and connections to be checked for stiffness and strength as part of the analysis. In parallel, an ongoing joint project between Sydney University and Tongji University on the strength of beam-to-upright connections in rack structures has extended to Component Method to cold-formed steel connections which include tang-connectors and bolts. The paper provides an overview of these recent developments of the Component Method, including the opportunity to incorporate the Method in a fully nonlinear procedure for the direct design of steel frameworks including connections by advanced analysis, also referred to as the Direct Design Method.The Australian Research Counci

Invertibility of Nonlinear Differential-Algebraic-Equation Subsystems with Application to Power Systems

For nonlinear differential-algebraic-equation subsystems, whose index is one and interconnection input is locally measurable, the problem of invertibility is discussed and the results are applied to the power systems component decentralized control. The inverse systems’ definitions for such a class of differential-algebraic-equation subsystems are put forward. A recursive algorithm is proposed to judge whether the controlled systems are invertible. Then physically feasible α-order integral right inverse systems are constructed, with which the composite systems are linearizaed and decoupled. Finally, decentralized excitation and valve coordinative control for one synchronous generator within multimachine power systems are studied and the simulation results based on MATLAB demonstrate the effectiveness of the control scheme proposed in this paper

Sciences for The 2.5-meter Wide Field Survey Telescope (WFST)

The Wide Field Survey Telescope (WFST) is a dedicated photometric survey facility under construction jointly by the University of Science and Technology of China and Purple Mountain Observatory. It is equipped with a primary mirror of 2.5m in diameter, an active optical system, and a mosaic CCD camera of 0.73 Gpix on the main focus plane to achieve high-quality imaging over a field of view of 6.5 square degrees. The installation of WFST in the Lenghu observing site is planned to happen in the summer of 2023, and the operation is scheduled to commence within three months afterward. WFST will scan the northern sky in four optical bands (u, g, r, and i) at cadences from hourly/daily to semi-weekly in the deep high-cadence survey (DHS) and the wide field survey (WFS) programs, respectively. WFS reaches a depth of 22.27, 23.32, 22.84, and 22.31 in AB magnitudes in a nominal 30-second exposure in the four bands during a photometric night, respectively, enabling us to search tremendous amount of transients in the low-z universe and systematically investigate the variability of Galactic and extragalactic objects. Intranight 90s exposures as deep as 23 and 24 mag in u and g bands via DHS provide a unique opportunity to facilitate explorations of energetic transients in demand for high sensitivity, including the electromagnetic counterparts of gravitational-wave events detected by the second/third-generation GW detectors, supernovae within a few hours of their explosions, tidal disruption events and luminous fast optical transients even beyond a redshift of 1. Meanwhile, the final 6-year co-added images, anticipated to reach g about 25.5 mag in WFS or even deeper by 1.5 mag in DHS, will be of significant value to general Galactic and extragalactic sciences. The highly uniform legacy surveys of WFST will also serve as an indispensable complement to those of LSST which monitors the southern sky.Comment: 46 pages, submitted to SCMP

Cooperative Path Planning and Constraints Analysis for Master-Slave Industrial Robots

A strategy of cooperative path planning for a master-slave multiple robot system is presented in this paper. The path planning method is based on motion constraints between the end-effectors of cooperative robots. Cooperation motions have been classified into three types by relative motions between end-effectors of master and slave robots, which is concurrent cooperation, coupled synchronous cooperation and combined synchronous cooperation. Based on this classification, position /orientation constraints and joint velocity constraints are explored in-depth here. In order to validate the path planning method and the theoretical developments in motion constraints analysis, representative experiments based on two industrial robots, Motoman VA1400 and HP20, are provided at the end of the paper. The experimental results have proved both the effectiveness of the path planning method and the correctness of the constraints analysis

Finite-Time Disturbance Observer for Robotic Manipulators

Robotic manipulators may be subject to different types of disturbances such as unknown payloads, unmodeled dynamics, and environment interaction forces. Observing these unknown disturbances in robotic manipulators is fundamental in many robotic applications such as disturbance rejection and sensorless force control. In this paper, a novel disturbance observer (DOB) is introduced based on the insights from the finite-time observer (FTO) and robot dynamics. Different from the traditional DOBs, this new observer can provide the capability to track the disturbance within a finite time. The performance of the presented observer is verified by two kinds of typical disturbances for a two-link manipulator with a comparison with several existing DOBs. The simulation results show the rapidity and accuracy of the proposed FTO