Desired Performance Objectives Research Articles

Practical performance-based design of friction pendulum bearings for a seismically isolated steel top story spanning two RC towers

A case study of performance-based design is presented for a seismically isolated steel structure that rests on top of two adjacent high-rise reinforced concrete towers, the latter separated by means of an expansion joint. The isolation system comprises Friction Pendulum Bearings (FPBs) that are designed to accommodate two salient characteristics of the system. First, the isolated top floor is subjected to narrow-band floor acceleration histories as the ground motion excitation is filtered by the dynamic response of the supporting towers. Second, the displacement demands imposed to the FPBs are affected by the in-phase or out-of-phase movement of the supporting structures, with the latter case potentially giving rise to higher displacement capacity requirements for the bearings. In a search for a solution beyond conventional design norms, the probability of bearing failure associated with a wide range of FPB displacement capacities was determined via an explicitly risk-consistent performance-based seismic design. Overall, the case-specific design approach is shown to be able to meet any desired performance objective, consistently determining the final compromise between safety, cost-efficiency and practicability.

Self-centering energy-absorbing rocking core system with friction spring damper: Experiments, modeling and design

The Self-Centering Energy-Absorbing Rocking Core with friction spring damper (denoted as the SCENARIO system) is a novel steel structural system that can achieve excellent self-centering performance in low-rise buildings. This research presents the physical tests and design procedure of the SCENARIO system, which consists of a rocking core (RC) and two friction spring dampers (FSDs). The basic mechanical response of the friction ring spring group included in the FSD is first described through a preliminary experimental study. Three repeated rounds of reverse cyclic load tests of the SCENARIO system are conducted. The test results show reliable and stable self-centering hysteretic behavior. After removing the applied force at the maximum loading roof drift ratio of 5%, the SCENARIO specimen achieved near-zero residual drift. During the entire loading process, the RC can remain elastic. The two FSDs included in the SCENARIO specimen show yield force reduction and stiffness increase under three repeated rounds of cyclic loading. However, there was no damage to any components in the FSD after the tests. Following the experimental study, the finite element model of the SCENARIO system is introduced and verified. Then, nonlinear dynamic analyses (NDA) are performed to determine the influences of the yield force reduction and stiffness increase of the FSD on the seismic performance of the proposed system. Finally, a performance-based design procedure is proposed using the direct displacement design method for the SCENARIO system. The results from the NDA indicate that the SCENARIO system designed via the proposed design procedure can achieve the desired performance objective and excellent self-centering behavior under the maximum considered earthquakes.

Performance of a novel slider device in multi-storey cold-formed steel modular buildings under seismic loading

A 0.25-scale three-storey stacked modular steel structure, with a novel slider device used at each floor level, was built, and subjected to seismic biaxial base excitation in a series of shake table tests. The test results were reported in the literature by the first author of this paper, which showed that the proposed slider device and the modular steel structure performed well under seismic loading. This paper extends the work of previously reported shake table tests by developing a numerical model. The numerical model has been validated against the test results of the three-storey modular structure. The validated numerical model has then been extended to a six-storey structure consisting of six modules in total (one unit at each floor) with the same material, link, member and constraint properties as used in the three-storey building. The applied gravity loads for each module were also the same as that in the three-storey test structure. The six-storey structure has been subjected to a range of earthquake records from the El Centro, Delta, Kalamata, Chihuahua, Corinthos, Westmorland and Chi-Chi earthquakes that occurred in the past; all these records were scaled according to the loading standard (AS/NZS 1170) for a design site located in Wellington City, New Zealand. These further analysis results on six storey modular structure provide better indication of how a full-scale perfectly built multi-storey modular steel structure with the slider units behaves in practice. As revealed by the analysis results, the proposed sliding system in the six-storey modular steel structure can achieve all the desired performance objectives. When subjected to the scaled earthquake records applied in both the longitudinal and transverse directions, the modules slide in alternate directions at different floor levels within a maximum displacement defined by the 2.5% drift requirement and subsequently self-centered within a tolerance of 5 mm at the conclusion of the severe shaking. While sliding, all modules remain stable and were not prone to any collapse and soft-storey failure at lower levels. During the severe shaking, more than 80% of the seismic input energy is dissipated through friction and rubber hysteresis in the proposed system.

Seismic design and performance evaluation of controlled rocking dual-fused bridge system

It is crucial for highway bridges to remain operational after strong earthquakes as they are critical infrastructures to transport resources. In this study, an innovative seismic-resilient bridge structural system, named controlled rocking dual-fused bridge (CRDFB) system, is proposed. The CRDFB system is designed to dissipate the earthquake energy by the use of replaceable Lead-Extrusion Dampers (LEDs) at the base of the rocking piers. The state-of-the-art Equivalent Energy Design Procedure (EEDP) is adopted and modified to design the CRDFB system to achieve different performance at different levels of shaking intensities. The proposed step-by-step EEDP allows engineers to design the CRDFB system to achieve the desired performance objectives with simple hand calculations and without iterations. A 2-span and a 3-span CRDFB prototypes located in Vancouver, Canada, are designed using the proposed EEDP. To validate the performance of the proposed CRDFB system, advanced three-dimensional analytical models of prototypes are developed using OpenSees and subjected to a broad array of two-dimensional and three-dimensional nonlinear time history analyses. Simulation results show that CRDFB prototypes can successfully achieve the targeted performance, as specified by EEDP design, at different shaking intensities. Hence, the proposed CRDFB system can be designed efficiently using the EEDP design procedure outlined in this paper, and be used as an efficient, reliable, and resilient seismic force-resisting bridge system for high seismic zones.

An Improved Adjustable Modulation Strategy for Three-Level NPC Inverters Considering Dynamic Loading Applications

Three-level neutral-point-clamped (NPC) inverters are being widely adopted in low-voltage low-power applications. For an intended application, the modulation strategy and the operating conditions are the two key factors that highly influence the major performance indices of the NPC inverter, such as efficiency, harmonic distortion, and voltage oscillations at neutral point (NP). Considering dynamic loading applications where the operating point varies significantly, this paper proposes an improved adjustable pulsewidth modulation (PWM) strategy for a three-level NPC inverter that can alter its modulation pattern to meet desired performance objectives for the full operation range. It has been shown that by varying two control parameters namely discontinuity control parameter and bias control parameter, the proposed modulation strategy changes its pattern between the most efficient generalized discontinuous PWM to NP oscillations-free partial dipolar PWM strategy. Additionally, to obtain a tradeoff between the performance parameters-efficiency, NP oscillations, and waveform quality-The proposed strategy has the ability to settle at the intermediate modulation patterns by transforming into a hybrid modulation signal. Furthermore, considering NP voltage unbalance mitigation as major technical challenge in adjustable modulation strategy, a voltage unbalance compensator that exhibits satisfactory balancing performance for the entire variations of modulation patterns and operating conditions has also been presented. The performance of the proposed modulation strategy in conjunction with voltage unbalance compensator has been evaluated in simulation by widely varying the speed and load of induction motor, and verified in experimentation.

Plastic analysis and performance-based design of coupled steel plate shear walls

The coupled steel plate shear wall (C-SPSW) configuration consisting of two SPSWs linked by coupling beams at the floor levels, in addition to providing architectural flexibility, has been shown to exhibit superior seismic performance. While the shear strength of the infill panels due to tension field action is the primary source of lateral load resistance in a C-SPSW, the moment resisting actions of the boundary frames and the coupling beams connections provide substantial strength for the system. As such, in order to achieve material-efficient designs, rational procedures are needed to explicitly account for this strength, while maintaining the desirable performance for various hazard levels. Similar to planar SPSWs, the C-SPSW systems have been designed using the conventional force-based design approach, which typically requires several iterations to optimize the design for performance and efficiency. This research employs the principles of plastic analysis to quantify the contribution of the frame action to the overall strength of C-SPSWs and adopts the philosophy of the performance-based plastic design (PBPD) methodology to develop procedures for the efficient seismic design of such systems. To investigate the effectiveness of the proposed design procedure, 8- and 12-story case study C-SPSWs were designed, and their numerical models were analyzed using pushover and response history analyses. The seismic performance of the prototypes were evaluated using two suits of ground motions representing 10/50 and 2/50 hazard levels. The analysis results indicated that the C-SPSWs designed using the proposed approach successfully met the desired performance objectives for both seismic hazard levels considered.

A generic method for remote sensing satellites conceptual design and rapid sizing based on "design for performance" strategy

Some fundamental and unique characteristics of space are (1) global perspective, (2) above the atmosphere, (3) gravity-free environment, (4) abundant resources, and (5) exploration of space itself. If the mission doesn't rely on some fundamental and unique characteristics of space, it will likely cost more to do in space than in air or on Earth [1]. On the other hand, design of complex systems like satellites involves selecting design parameters (DPs) to satisfy the required constraints while meeting desired performance objectives. These parameters are often coupled, and their relationships not easily understood, and it makes the design an iterative process with high complexity [2]. But in spite of high costs and complexities, demands for space missions are increasing, so space missions inevitably must be engineered in such a way that the users' needs be met better, cheaper, faster, and with less risk than before. That is the reason why more research is required to improve the space missions engineering process.

Task and Motion Planning for Manipulator Arms With Metric Temporal Logic Specifications

The aim is to synthesize control inputs for robotic manipulator arms that ensure a desired task specification is executed while optimizing a desired performance objective. We use metric temporal logic (MTL) to express the task specifications defined in terms of manipulating objects and implemented a hierarchical method combining mixed integer-linear programming (at high-level) to obtain a candidate MTL task specification defined in terms of the location of the arm end-effector and gradient descent based optimization (at low-level) for automatic synthesis of the motion plans to execute such candidate task specifications. The gradient descent algorithm is performed over the feasible input space to optimize the manipulator arm trajectory from a given arbitrary initial condition to perform the task at hand. We demonstrate the efficacy of our method by simulating a task specification on a Baxter robot.

SUSTAINABLE SEISMIC RETROFITTING OF A RC BUILDING USING PERFORMANCE BASED DESIGN APPROACH

In the past twenty years, sustainable development has become a challenging subject across many scientific fields. With the built environment as the major component of societies, sustainable construction has been the main player in the whole sustainability mentality. To emphasize on the importance of incorporating sustainability in to seismic retrofitting, three different retrofitting methods (base isolation, concrete jacketing, and steel jacketing) are evaluated for a typical 4-story RC school building under the 1994 Northridge earthquake’s ground motion. Using Performance Based Design approach, the objective of retrofitting is to make the building perform in the Immediate Occupancy performance level according to FEMA guidelines so that it can be used as a shelter after disasters. Results show that although retrofitting by concrete or steel jacketing can control story drifts to satisfy maximum allowable values, the performance of the building and consequent damages do not meet the desired performance objective. In addition, accounting for economic and human losses, these retrofitting options will not provide a sustainable structure if a strong earthquake happens in the future. On the other hand, not only base isolation meets the desired performance objective, but also it will provide a sustainable retrofitted structure by drastically reducing economic and human losses.

11.17: Seismic retrofitting of concentrically braced frames by rocking walls and viscous dampers

ABSTRACTIn this paper, a design procedure for seismic retrofitting of concentrically braced frames is proposed and validated. The reasons leading to the need of an enhancement of the seismic performance of these frames may be multiple. As an example, the expected response of concentrically braced buildings may not match the desired performance objectives because (1) the initial design of the structures was deficient or (2) the design performance objectives have changed in time due to an update of the seismic hazard map or to more demanding requirements of the owners of the building. In this paper, rocking walls are proposed to ensure an almost uniform distribution of the storey drifts along the height of the building. To achieve a direct and efficient control of the ultimate peak ground acceleration, the design procedure is founded on the displacement‐based approach. The equivalent viscous damping ratio capacity of the concentrically braced structure with rocking walls is calculated based on semi‐empirical relationships specifically calibrated for concentrically braced frames. Viscous dampers are added and arranged between the existing structure and the rocking walls. The design internal forces of the rocking walls are evaluated considering also the contributions of the higher modes of vibration. The proposed design procedure is applied to an eight‐storey chevron braced frame and its effectiveness verified by incremental dynamic analysis.

Modified seismic design of concentrically braced frames considering flexural demand on columns

SummarySpecial concentrically braced frames (SCBFs) are considered as one of the most economical and effective lateral force‐resisting systems in structures located in the regions of high seismicity. Steel braces in a braced frame undergo large axial deformations in tension and compression to dissipate the seismic energy. However, past studies have shown that SCBFs exhibit the soft‐story hinge mechanisms and unpredictable failure patterns under earthquake loading conditions. These inelastic responses along with the use of continuous structural sections as columns over consecutive floors induce flexural demand that is not considered in the current design practice. In this study, the evaluation of seismic performance of nine SCBFs designed as per the current practice has been carried out for three different story heights (i.e., three‐story, six‐story, and nine‐story) and three types of brace configurations (namely, chevron, splitX, and singleX). Three additional design techniques are also explored based on (i) the inclusion of column moments in the design; (ii) the theory of formation of plastic hinges; and (iii) the design of braces considering the forces computed at their post‐buckled stages. Nonlinear dynamic analyses of these study frames have been evaluated numerically using a computer software Perform‐3D for a suite of 40 ground motions representing the design basis earthquake and maximum considered earthquake hazard levels. Analyses results showed that the SCBFs designed as per the modified procedures achieved the desired performance objectives without the formation of soft‐story mechanism. Copyright © 2017 John Wiley & Sons, Ltd.

Achieving desired performance objectives in the energy sector through data analytics

The deployment of information technology (IT) systems in critical infrastructure (CI) sectors has gained a lot of support because of benefits such as cost savings and increased efficiencies. Unfortunately, the deployment can enable IT vulnerabilities. Senior leaders in CI sectors now find themselves in unfamiliar territory having very limited experience with IT systems and networks. Consequently, they are relying upon intuition and, in some cases, unrelated experiences to make strategic decisions that can have dire consequences. The attention to hiring highly specialised data professionals can be a challenge because of the scarcity of qualified persons available. This paper promotes the alternative of focusing on a culture change that encourages a more data-driven decision making approach. Results show that the utilities component of the Cl's energy sector can reap immediate benefits from decision making that uses a data-driven, analytical approach to assess facilities operations, security, and resilience.

Achieving desired performance objectives in the energy sector through data analytics

The deployment of information technology (IT) systems in critical infrastructure (CI) sectors has gained a lot of support because of benefits such as cost savings and increased efficiencies. Unfortunately, the deployment can enable IT vulnerabilities. Senior leaders in CI sectors now find themselves in unfamiliar territory having very limited experience with IT systems and networks. Consequently, they are relying upon intuition and, in some cases, unrelated experiences to make strategic decisions that can have dire consequences. The attention to hiring highly specialised data professionals can be a challenge because of the scarcity of qualified persons available. This paper promotes the alternative of focusing on a culture change that encourages a more data-driven decision making approach. Results show that the utilities component of the Cl's energy sector can reap immediate benefits from decision making that uses a data-driven, analytical approach to assess facilities operations, security, and resilience.

Variable recruitment in bundles of miniature pneumatic artificial muscles

The natural compliance and force generation properties of pneumatic artificial muscles (PAMs) allow them to operate like human muscles in anthropomorphic robotic manipulators. Traditionally, manipulators use a single PAM or multiple PAMs actuated in unison in place of a human muscle. However, these standard manipulators can experience significant efficiency losses when operated outside their target performance ranges at low actuation pressures. This study considers the application of a variable recruitment control strategy to a parallel bundle of miniature PAMs as an attempt to mimic the selective recruitment of motor units in a human muscle. Bundles of miniature PAMs are experimentally characterized, their actuation behavior is modeled, and the efficiency gains and losses associated with the application of a variable recruitment control strategy are assessed. This bio-inspired control strategy allows muscle bundles to operate the fewest miniature PAMs necessary to achieve a desired performance objective, improving the muscle bundle’s operating efficiency over larger ranges of force generation and displacement. The study also highlights the need for improved PAM fabrication techniques to facilitate the production of identical miniature PAMs for inclusion in muscle bundles.

Tempo

Multi-tenant database systems have a component called the Resource Manager, or RM that is responsible for allocating resources to tenants. RMs today do not provide direct support for performance objectives such as: "Average job response time of tenant A must be less than two minutes", or "No more than 5% of tenant B's jobs can miss the deadline of 1 hour." Thus, DBAs have to tinker with the RM's low-level configuration settings to meet such objectives. We propose a framework called Tempo that brings simplicity , self-tuning , and robustness to existing RMs. Tempo provides a simple interface for DBAs to specify performance objectives declaratively, and optimizes the RM configuration settings to meet these objectives. Tempo has a solid theoretical foundation which gives key robustness guarantees. We report experiments done on Tempo using production traces of data-processing workloads from companies such as Facebook and Cloudera. These experiments demonstrate significant improvements in meeting desired performance objectives over RM configuration settings specified by human experts.

Human behavior and domain knowledge in parameter design of complex systems

The design of complex systems involves selecting design parameters to satisfy the required constraints while meeting desired performance objectives. These parameters are often coupled and their relationships not easily understood. This paper presents results of an experiment to understand how designers solve parameter design problems, in the context of desalination systems. Subjects with different desalination expertise were asked to complete design tasks involving seawater reverse osmosis plants. Results confirmed that designers had difficulties understanding the sensitivity of coupled variables. More desalination knowledge was linked to better performance and designers with limited desalination knowledge tended to perform the worst due to having partial or incorrect domain knowledge. These findings have implications in design tool development and education.

Controlling the Surface of Semiconductor Nanocrystals for Efficient Light Emission from Single Excitons to Multiexcitons

Semiconductor nanostructures have shown promise for light emission across various intensity regimes. Desired performance objectives of photoluminescence efficiency, low gain threshold, large gain lifetime and bandwidth have not been met by any one nanocrystal. A physical understanding of the design principles governing these objectives is also lacking. We show that a carefully engineered CdSe/Cd,Zn,S core/shell nanocrystal uniquely meets all criteria. The key factor allowing for these improvements is the gradual core/shell boundary, which decouples the surface electronic states.

Direct Displacement-Based Seismic Design of Propped Rocking Walls

A direct displacement-based design (DDBD) methodology is described for propped rocking walls (PRWs). PRWs represent a novel seismic force-resisting system that combines passive supplemental damping devices with unbonded post-tensioned concrete rocking walls. The key aspect of the proposed design procedure is the closed-form derivation of the stabilized hysteretic response of PRWs under reverse cyclic loading. This allows the direct application of the DDBD procedure to satisfy desired displacement performance objectives under prescribed levels of seismic intensity. Nonlinear response analyses are conducted on a prototype PRW structure, designed according to the proposed DDBD procedure to evaluate its performance under strong ground shaking.

Volatility vs. Downside Risk: Optimally Protecting Against Drawdowns and Maintaining Portfolio Performance

As a consequence of recent market conditions an increasing number of investors are realizing the importance of controlling tail risk to reduce drawdowns thus increasing possibilities of achieving long-term objectives. Recently, so called volatility control strategies and volatility target approaches to investment have gained a lot of interest as strategies able to mitigate tail risk and produce better risk-adjusted returns. Essentially these are rule-based backward looking strategies in which no optimization is considered. In this contribution we focus on the role of volatility in downside risk reduction and, in particular, in tail risk reduction. The first contribution of our paper is to provide a viable way to integrate a target volatility approach, into a multiperiod portfolio optimization model, through the introduction of a local volatility control approach. Our optimized volatility control is contrasted with existing rule-based target volatility strategies, in an out-of sample simulation on real data, to assess the improvement that can be obtained from the optimization process. A second contribution of this work is to study the interaction between volatility control and downside risk control. We show that combining the two tools we can enhance the possibility of achieving the desired performance objectives and, simultaneously, we reduce the cost of hedging. The multiperiod portfolio optimization problem is formulated in a stochastic programming framework that provides the necessary flexibility for dealing with different constraints and multiple sources of risk.

ACTIVE DISTURBANCE REJECTION CONTROL TUNING EMPLOYING THE LQR APPROACH FOR DECOUPLING UNCERTAIN MULTIVARIABLE SYSTEMS

The ADRC tuning is essentially a pole-placement technique and the desired performance is indirectly achieved through the location of the closed-loop poles. However, the final choice of these poles becomes a trial-and-error strategy. In contrast with pole-placement, in the LQR method, the desired performance objectives are directly and globally addressed by minimizing a quadratic function of the state and control input. ADRC tuning employing the LQR approach is then applied for decoupling uncertain MIMO systems. This is done by considering all the coupling and interference interactions between the channels of the system as disturbances, using an ESO to estimate them in real time and then canceling its effect employing the estimate as part of the control signal.