Simple Design Procedure Research Articles

Graphic Procedure for the Optimum Design of Elastomeric Isolators

A simple graphic procedure for the optimum design of elastomeric seismic isolation devices is proposed. Starting from the design requirements concerning a base-isolated building, such as the device’s stiffness, maximum displacement, and vertical load, as well as the code checks on the device, the procedure allows defining the optimum values of the mechanical and geometrical parameters, such as rubber shear modulus, diameter, and thickness, and the number of rubber and steel layers. In more detail, the procedure allows for first identifying the ranges of the geometrical characteristics through a graphic representation of code checks in terms of the rubber’s diameter and volume, and then their specific values that allow one to obtain the optimum solution according to the design requirements for any fixed values of the mechanical characteristics of the materials. The graphic representation represents a suitable tool to better understand the role and influence of the different checks. The procedure can be easily automated by means of a computer code.

Experimental testing and analysis of the axial behaviour of intermeshed steel connections

This paper presents the work carried out on a collaborative tripartite project between the USA, Republic of Ireland and Northern Ireland to create and investigate the design, development and testing of a new class of intermeshed steel connections (ISCs) that do not rely on field welding and minimise bolting, thus targeting the facilitation of fast disassembly of steel structures and material reuse. This research took advantage of fully automated, precise, advanced manufacturing cutting technologies (e.g. laser, waterjet and high-definition plasma cutting) to achieve a connection method in steel that previously was only possible in materials such as timber, with the potential to revolutionise the steel construction industry. The paper outlines the ongoing research work by the collaborative team, focusing on the design, fabrication, finite-element analysis (FEA) and scaled experimental testing of side ISCs for the flanges of open sections, which included the use of state-of-the-art digital image correlation technology for non-contact measurements. A simplified connection design procedure is presented based on yielding of the side plates. This design procedure is refined based on the results of experimental testing and FEA of the local axial behaviour of the flange connection, addressing stress concentrations in the flange, fabrication tolerances and material overstrength.

An integrated performance‐based design framework for building‐foundation systems

AbstractThis paper presents a framework for the inclusion of transient and residual foundation deformations within performance‐based seismic design of buildings. A refinement of existing displacement‐based design procedures is proposed that reduces iteration when obtaining the expected peak foundation rotation. Empirical equations are developed based on numerical time‐history analyses that provide an estimation of foundation residual deformations based on the foundation peak rotation. Additional complexities due to deformation within the foundation are discussed regarding how they influence the design and building performance. The design framework is complemented by a simplified analytical design procedure (i.e., hand calculations) to design building‐foundation systems. A design example is given for a six‐storey concrete wall building, which is analyzed by time‐history analysis to demonstrate the application and accuracy of the design procedure.

Ultra-thin and high-efficiency full-space Pancharatnam-Berry metasurface.

Full-space metasurfaces (MSs) attract significant attention in the field of electromagnetic (EM) wave manipulation due to their advantages of functionality integration, spatial integration and wide applications in modern communication systems. However, almost all reported full-space metasurfaces are realized by multilayer dielectric cascaded structures, which not only has the disadvantages of high cost and complex fabrication but also is inconvenient to device integration. Thus, it is of great interest to achieve high-efficiency full-space metasurfaces through simple design and easy fabrication procedures. Here, we propose a full-space MS that can efficiently manipulate the circularly polarized (CP) waves in dual frequency bands by only using a single substrate layer, the reflection and transmission properties can be independently controlled by rotating the optimized meta-structures on the metasurface. Our full-space metasurface has the potential to design multifunctional devices. To prove the concept, we fabricate the device and measured it in microwave chamber. For the reflection mode, our metasurface can behave as a CP beam splitter at the frequency of f1 = 8.3 GHz and exhibit high efficiencies in the range of 84.1%-84.9%. For the transmission mode, our metasurface acts as a meta-lens at the frequency of f2 = 12.8 GHz for the LCP incidence, and the measured relative efficiency of the meta-lens reaches about 82.7%. Our findings provide an alternative way to design full-space metasurfaces and yield many applications in EM integration systems.

Concept design of jacket foundations for offshore wind turbines in 10 steps

Simplified design procedures for offshore wind turbine (OWT) support structures are necessary in the concept and tender design stages for assessing the financial viability. Building upon the previous research on simplified monopile design, this paper presents a similar method to design jacket supported OWTs founded on piles or suction caissons. The method is based on the minimum and necessary data, namely the site characteristics (wind speed at reference height, wind turbulence intensity, water depth, wave height and wave period), turbine characteristics (rated power, rated wind speed, rotor diameter, cut-in and cut-out speed, mass of the rotor-nacelle-assembly) and ground profile (soil stiffness variation with depth and soil strength). A flowchart of the design process is also presented for visualisation of the rather complex multi-disciplinary analysis. Insights are given for 3 and 4 legged jackets. The calculation procedures that are required can be easily carried out either through a series of spreadsheets or simple hand calculations. An example problem emulating the design of a jacket on piles is taken from literature to demonstrate the proposed calculation procedure. The data used for the calculations are obtained from publicly available sources and the example shows that the simplified method arrives at a similar foundation to the one reported.

Magnetic damped links to reduce internal seismic pounding in base-isolated buildings

A limited gap between closely spaced structural parts may induce internal pounding in seismically isolated structures, because of notable displacement at the level of the isolation system under severe earthquakes. A gap between a fixed-base elevator shaft and the surrounding building is presented here with reference to a reinforced concrete building located in the Sicilian town of Augusta. The building, comprising a basement and three storeys above the ground level, is seismically isolated at the top of rigid columns in the basement with a hybrid isolation system including elastomeric and sliding bearings, while a steel framed elevator shaft crosses the isolation level. Despite the gap, internal pounding may occur at all levels of the superstructure when the elevator with maximum load stops at the upper floors. To reduce structural pounding effects, a magnetic damped link (MDL) between adjacent corners of the elevator and the surrounding building is proposed. This is obtained as an in parallel combination of an eddy current damped link (ECDL) and an elastic helicoidal spring, and occupies less space than traditional passive dampers and transmits considerably less forces compared to a rigid link configuration. Specifically, an ECDL consists of an outer cylindrical copper tube, as conductor, and an inner tube, equipped with an array of axially magnetized and ring-shaped permanent magnets separated by iron pole pieces, as mover. The relative motion between conductor and magnets, during seismic loading, induces an eddy current producing electromagnetic damping. Given that viscoelastic linear behaviour can be hypothesized for the MDL, a simplified iterative design procedure of the ECDL is proposed, with optimization of the thickness and radius of the magnets, thereby enhancing magnetic flux and energy dissipation. The directionality of the near-fault ground motions is investigated through nonlinear seismic analysis, comparing no connection with four configurations of the interconnection: i.e., flexible and rigid elastic links, viscous and magnetic damped links.

The behaviour of Bolders Bank glacial till under undrained cyclic loading

Analysis of foundation behaviour under repeated loading can be important to the design of offshore facilities, towers, bridges, wind turbines and other structures. Although detailed guidance is available on how some geomaterials behave under cycling, few such studies have been reported on the glacial formations that are widespread across parts of northern Europe and under the North and Baltic Seas. This paper presents a cyclic laboratory investigation involving block samples of Bolders Bank till, which is one of the most extensive North Sea glacial formations. Static and cyclic triaxial tests are reported on nominally identical, low-plasticity, high-overconsolidation-ratio specimens from Cowden, near Hull in the UK. Twenty-three cyclic tests are reported on specimens that were re-consolidated to K0 stresses before experiencing up to 3500 undrained cycles involving a range of mean and cyclic shear stress combinations. The impacts of cycling on effective stress paths and strain development, cyclic stiffness and damping ratios are reported and interpreted with respect to parallel index, oedometer and monotonic triaxial compression and extension tests. Stable, metastable and unstable patterns of behaviour are identified, along with different cyclic failure modes. The styles of cyclic response are related to the till's static yielding behaviour. While the till can only manifest quasi-elastic behaviour within a very small (Y1) kinematic yield surface (KYS), a larger second (Y2) KYS is identified within which repeated loading leads to a non-linear yet stable response, with negligible mean effective stress drifts or stiffness degradation with low and stabilising strain accumulation rates. Cyclic paths that engage and relocate the Y2 surface lead to greater permanent strains, mean effective stress drifts and stiffness decays that become progressively more marked as the magnitudes of the cyclic stress perturbation and the number of cycles increase. While cycling under stable or metastable conditions increased the ultimate undrained strength of specimens that did not develop excessive strains, most cyclic paths that exceeded and climbed the till's Hvorslev surface were unstable and eventually failed. The experiments identified the key factors that affect the till's response to repeated loading and provide a basis for developing, testing and calibrating cyclic constitutive models and establishing simplified design procedures for comparable tills.

Enhancing the performance of defected ground structure type near‐field radiofrequency WPT system by coupled‐line impedance matching

This study reports, for the first time, the use of coupled-line-based impedance matching in wireless power transfer (WPT) system. The transmitter and receiver of the WPT system are realised by microstrip feed line and symmetric coupled line at the top plane. The ground plane is realised with triangular-shaped defect along with the excitation slot mounted by an external capacitor. The defect in the ground plane and the external capacitor regulate the resonant frequency and also enable miniaturisation of the WPT system. The design is augmented with a systematic analytical approach for impedance matching and a simplified design procedure for the WPT system. A novel equivalent circuit model consisting of parallel LC network and coupled lines is also developed for the evaluation of the proposed WPT system design technique. A prototype of the system operating at 300 MHz developed on Rogers RO4350B substrate achieves a peak efficiency of 80% at a transmission distance of 17 mm. An excellent agreement between the measured and the electromagnetic simulated results is a testament of the robustness of the proposed design technique. Furthermore, evaluation of the commonly used WPT-related figure of merit shows significant enhancement when compared to the existing state of the art.

Lateral-Torsional Buckling of Singly Symmetric I-Girders with Stepped Flanges

Guidance for the lateral-torsional buckling behavior of singly-symmetric, nonprismatic (stepped flanges) sections are often absent from design specifications or are overly simplified. This paper presents simplified design procedures that estimate the buckling capacity of these complex systems that commonly face designers. The results of a robust parametric finite-element study that included 14,040 unique prismatic and nonprismatic beam sections are detailed. The study specifically examines the effects of common span-to-depth ratios, intermediate bracing schemes, degrees of monosymmetry, variable flange transitions, and moment gradients on the buckling response. A proposed weighted-average section approach as well as traditional moment gradient expressions are evaluated based on their ability to accurately approximate the finite-element solutions of these singly-symmetric and/or nonprismatic beams. The computational study and proposed design expressions focus on elastic buckling behavior, midheight loads, and stiffened web elements, such that distortional effects that may limit the beam capacity are precluded. This approach matches the assumptions used to derive the classic analytical solutions adopted in most design specifications. For a broad range of conditions, the proposed methods are shown to produce reasonable and reliable estimates of the buckling capacity obtained from the finite-element models.

Design Method for Tunable Planar Bandpass Filters With Single-Bias Control and Wide Tunable Frequency Range

A design method for a frequency-tunable planar bandpass filter is demonstrated. With the method, all reasonators can be designed with identical capacitances, allowing the filter to be tuned with identical varactors using a single bias control. This allows not only low-cost fabrication, but also a simple structure and design procedure. Moreover, the filter is based on miniaturized transmission lines. Therefore, a wide tuning range is achieved with a small size and outstanding out-of-band response. Most importantly, the method facilitates the design of a filter to vary the fractional bandwidth in a predetermined way as the center frequency is tuned. Thus, a tunable filter can be designed not only to maintain the fractional bandwidth, but also to expand or to reduce the bandwidth as the frequency is tuned. The experimental results of a compact third-order bandpass filter based on CPW lines with a 0.11λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ×0.8λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> size show a very wide frequency tuning range of 62.8% with a 3-dB fraction bandwidth that remains within 28.65±1.55% and an outstanding spurious suppression of under -40 dB up to as high as 3f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> .

Definition of a Simplified Design Procedure of Seismic Isolation Systems for Bridges

In the recent past, numerical and experimental investigations on full-scale isolators have led to extensive improvements in seismic isolation techniques for bridge structures. Significant advances in dynamic testing techniques have been made at both software and hardware levels, and the response of an isolated bridge can be realistically simulated. In general, the response of an isolated bridge structure is strongly affected by the valley topography; therefore, high piers may not need isolation devices, since they are flexible enough to accommodate the design displacement in the elastic range. On the other hand, at those locations no hysteretic damping is provided and higher displacements can be achieved, compared to the maximum displacement allowance. In this work, a simplified procedure is proposed for the optimization of isolation systems for bridge structures. The seismic response of a designed case study structure is investigated through nonlinear time history analyses, and the effective contributions of both the nonlinear hysteretic behaviour of isolators and the elastic response of piers are considered. Regarding displacement and force responses in particular, the results show a very good agreement between mean and single-event peak responses, and the corresponding values returned by the proposed design procedure.

Seismic Response of Long-Span Domes Supported by Multi-Storey Substructures

This paper investigates the seismic response characteristics of long-span domes. The natural periods of the prominent modes are longer than medium-span domes, which leads to a greater contribution from the higher modes to the response of the long-span dome. The acceleration distributions, particularly the vertical acceleration distributions are sensitive to the dominant mode shapes of these higher modes. This leads to inaccuracies when applying the previously proposed response evaluation methods. The vibration modes of multi-storey supporting substructures also affect the excited vibration modes of the roof. In this paper, the dynamic characteristics and seismic response of 150m-span domes supported by multi-storey substructures are studied. The effects of the post- yield stiffness of multi-storey substructures are also analysed by considering two structural systems, buckling- restrained braced frames (BRBF) and damped spine frames. A simple design procedure to evaluate the equivalent static loads using amplification factors and incorporating the effects of higher modes is proposed based on response spectrum analysis and equivalent linearisation procedures. The accuracy of the proposed method is evaluated by comparing the responses with those obtained from non-linear response history analysis.

Experimental characterization of monotonic and cyclic behavior of steel-to-CLT nailed joints strengthened with composite plies

Connections play a key role in timber structures because they are the parts devoted to energy dissipation during an earthquake or, when specific hysteretic devices are introduced, their hyper-resistant design allows for a rigid fastening of those devices, thus assuring an elastic behavior of the structure under seismic loads. A promising technique to improve both the load-bearing capacity and the stiffness of joints with dowel-type fasteners, consists in increasing the embedment strength of the wood-based materials, usually by applying a superficial reinforcing layer to the timber-connection shear plane interface. In this framework, results of an experimental campaign carried out on steel-to-CLT panel nailed joints strengthened with a carbon fiber ply glued to the shear plane interface are presented and discussed in this paper. Two different load configurations (perpendicular and parallel to grain) and two different loading protocols (monotonic and cyclic) have been considered, analyzing the results in order to evaluate the effectiveness of the reinforcement technique in terms of load-bearing capacity and stiffness, with respect to the reference unreinforced configuration. Finally, the applicability of the current design method is verified together with the proposal of a simplified design procedure.

Investigation of Power Losses by Various Brushless Motor Modulation Methods in Motor Mode

The paper presents a comparative analysis of different modulation techniques for BLDC motor control in terms of several types of losses in the system inverter – BLDC motor in motor mode. The experimental investigated modulation strategies are: unipolar modulation of upper (PWM-TOP or UT) transistors, a bipolar PWM-ON modulation (PWM-ON-BIP), a symmetrical modulation (PWM-PWM), a vector control and non-modulation mode. A simple equivalent circuit for the BLDC motor is used to calculate different losses and the system efficiency. On the basis of the equivalent circuit for the different modulation techniques, simple design procedures are discussed for the determination the eddy current and mechanical viscous loss, the copper loss, the hysteresis and mechanical friction loss, the voltage-drop loss of the inverter transistor and diode. Loss distribution experimental data for the brushless DT4260 motor when operating with different modulations and load torque are presented. On the basis of the obtained values for the efficiency of the studied modulations, references for use in battery powered devices such as electric vehicles, electric scooters and more are made.

Freeze-out purifier for helium refrigeration system applications

Purification systems are necessary to support commissioning and operation of helium refrigeration and associated experimental systems. These systems are typically designed for a low level of impurity (i.e., in parts per million), since a 4.5 K or 2 K helium system will solidify, or freeze out every other substance. The trace impurities can block and/or change the flow distribution in heat exchangers and potentially damage turbines or cryogenic compressors operating at high speed. Experimental systems, such as superconducting magnets, require helium purification due to inherent characteristics in their construction. These are also used for the commissioning of sub-systems, like the compressors, and cold boxes. As known from experience, molecular sieves do not remove low-level moisture impurity sufficiently. Typical commercial freeze-out purifiers using molecular sieves have very short operating times between regeneration and are inefficient requiring substantial utilities like liquid nitrogen and high-pressure operation. Based upon proven experience from a freeze-out purifier design for Brookhaven National Lab (BNL) in 1983, a liquid nitrogen assisted freeze-out purifier has been designed. This design includes a multi-pass and multi-stream heat exchanger and an activated carbon bed. The heat exchanger design is expected to minimize the liquid nitrogen usage and extend the capacity and the operating pressure range, thereby the time interval between regeneration. The goal is to provide a simple design procedure to develop and operate an efficient purifier system.

Pull-out capacity of an inclined embedded torpedo anchor subjected to combined vertical and horizontal loading

Abstract Whilst the installed torpedo anchors in offshore practice are often characterized with off-verticality, the effect of inclination on the anchor pull-out capacity has seemingly received little attention in the research literature. This paper presents a numerical study on the pullout capacities and failure envelopes of inclined embedded torpedo anchors subjected to combined vertical and horizontal loading. Using Coupled Eulerian–Lagrangian finite element method, effects of load inclination, azimuthal angle of pull-out plane and anchor inclination were sequentially evaluated. It was found the most critical pull-out plane is the one that coincides with anchor plane towards the anchor inclination direction. Its corresponding failure envelope, which can be well fitted by a closed form expression, gives the conservative estimation of anchor pull-out capacities. The comprehensive parametric investigation indicated this conservative failure envelope is mainly affected by anchor inclination and soil’s strength gradient. A series of tables with fitting constant values appropriate for different strength and inclination conditions were furnished. On these bases, a simple design procedure was developed for estimating the ultimate pull-out capacities of inclined embedded torpedo anchors. The outcomes of this work are likely of help for engineers to factor the anchor inclination into the design practice of torpedo anchors.

Performance analysis of a diffusion control method for ANC systems and the network design

Active noise control (ANC) systems have been widely used to reduce noise from indoor or outdoor sources, e.g. traffic, office/factory machines and ventilating systems. Since noise control usually needs to be executed within an extended area, the ANC network that involves a large amount of error microphones and loudspeakers is frequently employed. Distribution of the controller network saves computational burden and yields spatial diversity, which enhances the robustness of the system. This paper studies the diffusion (Diff) control for multi-channel ANC systems using filtered-x (Fx) least mean squares (LMS) algorithms. Since communication between nodes within the network makes it difficult to analyze the performance of the entire system, a comprehensive performance analysis of networked FxLMS algorithm is not available currently in literature to our best knowledge. In this paper, the convergence behavior of the Diff-FxLMS algorithm is investigated. The mean and mean squares difference equations are derived, from which the stability of the networked ANC system is analyzed and the steady-state excess mean square errors (EMSEs) for ANC controllers are obtained. Computer simulations are conducted to compare different control methods and verify the theoretical analysis. A specific 10-node network is studied in terms of the network strategy and the noise reduction performance. Moreover, using the proposed theoretical analysis, a systematic and simple design procedure for Diff-FxLMS based ANC systems is proposed. The usefulness of the theoretical analysis and design procedure is demonstrated by means of a design example.

Eccentric steel brace retrofit for seismic upgrading of deficient reinforced concrete frames

The paper presents a simplified static force-based procedure for seismic retrofit design of RC frames using internal eccentric steel braces (ESBs), connected to long beam at distance of L/8 from beam ends, to enhance seismic resistance of the frame. The technique uses the linear static procedure given in ASCE 7-16 for calculation of appropriate design base shear for frame analysis, and the AISC 360-16 seismic provisions for preliminary design of steel braces. Response modification factor R was derived based on simplified kinematics of rigid frame response and flexure hinging of link beam, to reduce the elastic base shear force for lateral load analysis of frame and design of steel braces. This shifts plastic hinges from columns, and reduces joint shear deformation, by means of capacity protected braces and beam shear. The procedure was used for the preliminary design of ESB retrofitting technique for a two-story RC frame, employing hollow box steel sections. Quasi-static cyclic tests were performed on both as-built and ESB retrofitted portal frame panels under multiple-levels of lateral displacements demands. The tests performed on frames were analysed to understand the damage mechanism and retrieve the essential seismic response properties: force–displacement capacity curves, hysteretic cyclic response and hysteretic damping, and to establish performance-based story drift limits. The experimental data was used to calibrate finite element based nonlinear numerical models in SeismoStruct. Nonlinear static pushover analysis of considered two-story ESB retrofitted frame was carried to quantify structure ductility and response modification factors. The preliminary design was verified through nonlinear time history analysis (NLTHA) for both design base earthquakes and maximum considered earthquakes. Proposed seismic design of ESB retrofit for multi-stories RC frames having three to six stories has been presented and verified through NLTHA. It indicates the promising behaviour of ESB retrofit technique as well as the efficiency of the proposed simplified design procedure.

A simple procedure for fault detectors design in SISO systems

In this work, we present a novel approach for fault detectors design and implementation in the case of actuator faults. Both the design and the implementation are focused on simplicity. The fault detector is based in an output observer that estimates the fault signal followed by a decision mechanism that detects the presence of a fault from the estimation. The observer consists of two transfer functions fed by the process manipulated variable and the sensor measurement. For the synthesis of the fault detector, we just need an input–output model of the process and two tuning parameters; one used in the observer, and the other in the decision mechanism. We present simple rules for the design considering the trade-off between the detection time, the minimum detectable fault and the false alarm rate. Our implementation method uses standard tools available in industrial control systems and we have applied it to a real two-tank system setup. The main contribution of this work is the simplicity of the design and implementation of the fault detector, making it suitable for process industry and for being managed by not experts in control systems. Another contribution is the a priori design based in intuitive engineering performance indices.

Proposition of a simplified analytical design procedure for lattice girder slabs with shuttering in cold-formed steel lipped channel section

ABSTRACT This paper presents an analytical procedure to determine the resistance of a new composite ribbed lattice slab system, composed by a lipped channel cold-formed steel (CFS) profile in minor bending fastened to a lattice girder by plastic connectors, as well as light filling elements and additional rebar. Motivated by the lack of standardized procedures for such system, this paper combines slab design prescriptions to create a computational tool that estimates load capacity and required propping during construction, serving as a basis for a design catalogue. Finally, a strong limitation of unpropped construction due to the low performance of the cold-formed profile under minor axis bending was observed, being the system able to reach spans up to 1.5 m between props in general.