Multiple Performance Objectives Research Articles

Multi-objective design of parametric equivalent-input-disturbance approaches with application to vehicle suspension systems

A multi-objective parametric design method is developed for an equivalent-input-disturbance-based control system with mismatched disturbances. Different from the existing design methods that calculated control parameters by stability conditions, multiple performance objectives including unmeasurable output estimation, disturbance rejection, noise suppression, input refinement, and robustness, are simultaneously optimized in the developed design. First, for the sake of low computation complexity, the closed-loop system is represented. Then, the parameterization of the design conditions for multiple performance objectives is given. Further, a nonlinear optimization method is used to perform the performance-oriented system design. Lastly, the efficacy and benefits of the developed methods are demonstrated through simulations of a quarter-vehicle suspension system and comparisons with other alternative methods.

Multiple performance objective design for a sliding isolator with variable curvature

Thanks to its variable mechanical properties, the sliding isolator with variable curvature (SIVC) has recently attracted significant attention in seismic isolation research. Nevertheless, designing an SIVC is a challenging task, as it usually involves more design parameters than a conventional sliding isolator. To expedite the application of SIVCs, this study proposes a systematic design method that enables SIVCs to achieve multiple performance objectives corresponding to dual earthquake levels. The method comprises linear and nonlinear design stages. During the linear design stage, the linearized isolator parameters that comply with the design-basis-earthquake (DBE) and maximum-considered-earthquake (MCE) seismic demands specified in a design code are determined. Subsequently, in the nonlinear design stage, the isolator geometric parameters are determined based on the linearized parameters. While the linear design procedure is generic and applicable to all types of SIVCs, the derived formulas for determining the isolator geometric parameters in the nonlinear design stage are tailored for the polynomial friction pendulum isolator (PFPI). Finally, the proposed method is demonstrated by implementing a PFPI design for a 5-story reinforced-concrete (RC) building. The effectiveness of the proposed design method is validated through dynamic analysis of a hysteretic structural model representing the RC building with two different types of PFPIs subjected to 23 spectrum-compatible ground motions. The results demonstrate that, despite their different mechanical features, both types of PFPIs can accomplish the “preset” DBE and MCE design objectives. Additionally, the simulated results highlight the advantages of using different types of PFPIs.

Simulation and optimization of prefabricated building construction considering multiple objectives and uncertain factors

The construction of prefabricated buildings involves complex processes, which have high uncertainties and objective conflicts, hindering the improvement of construction performance. This study aims to simultaneously optimize the activity logic and multiple construction performance objectives (concerning time, cost, quality, and CO2 emissions) of prefabricated building construction under the influence of uncertain factors. The eliminate, combine, rearrange, and simplify (ECRS) technique is combined with intelligent simulation technology to develop a simulation-based optimization method for prefabricated building construction considering multiple objectives and various uncertain factors. This method is characterized by enabling activity-logic improvements, revealing mathematical relationships between uncertain factors, activity parameters and construction performance, and achieving the trade-off optimization of construction performance objectives in various uncertain environments. A typical prefabricated building project is used for demonstrating and validating the method. The results show that the proposed method reduces the construction time by 5.73% through the ECRS technique, and further achieves a 10.53% reduction in construction cost, a 10.10% improvement in construction quality, and 60.32% CO2 emission mitigation through multiobjective optimization when only resource allocation is considered. Considering the interaction between resource allocation conditions and other three uncertain factors, the construction time is mainly affected by the supply of materials and weather conditions, while the familiarity level of work affects the construction time, cost, and CO2 emissions. The proposed method and findings of this study can facilitate robust decision-making by project managers when addressing the trade-offs between cost reduction, schedule shortening, quality improvement, and CO2 reduction under various uncertain scenarios.

Investigation of seismic fragility curves of unbonded FREIs: Adaptive characteristics and modeling sensitivity

AbstractFiber‐reinforced elastomeric isolators (FREIs) are composed of layers of elastomer reinforced with either steel or fibers, and can be placed in a bonded or unbonded configuration between the upper and lower supports. The use of fiber reinforcement in FREIs was intended to reduce the production and installation costs compared to common steel‐reinforced elastomeric isolators (SREIs) and to develop an isolator suitable for widespread application, particularly in developing countries. The unique rollover deformation exhibited by unbonded FREIs (UFREIs), due to their flexible fiber reinforcement, enables them to adapt to multiple performance objectives at different hazard levels. In this study, the impact of different numerical models of UFREIs on the seismic response and failure probability of structures is investigated. The research employs incremental dynamic analysis and the development of fragility curves for different limit states, considering three sets of ground motions (including far‐field and pulse‐like). Moreover, the effect of full rollover was investigated by comparing the fragility curves of UFREIs when supported on modified support geometries, which involved three types of support: unmodified, accelerated, and delayed full rollover. The effectiveness of the adaptive characteristics to behave as a displacement restrain is demonstrated. The results emphasize the importance of employing an accurate model to simulate the behavior of UFREIs as an adaptive device for effectively utilizing their potential capacity, particularly at larger displacements where there is more dissipated energy due to full rollover.

Comfort, carbon emissions, and cost of building envelope and photovoltaic arrangement optimization through a two-stage model

The design of a high-performance building necessitates tradeoffs among multiple performance objectives, and many simulation-based optimization tools have been developed for this purpose. In practice, these tools are often constrained by excessive computational load and tight project deadlines. This study aimed to develop a holistic approach to rapidly identify optimal building design schemes. A novel two-stage model was developed as a surrogate to conventional physics-based models, which were then linked to multi-objective optimization algorithms, namely, NSGA-II, NSGA-III, and C-TAEA, in search of the Pareto optimal and best design schemes. The performance of the two-stage model was further enhanced by applying the least absolute shrinkage and selection operator (LASSO) and Neural Architecture Search methods and learning from the statistical layer. The above approach was tested in the design of an apartment building for seniors in Northern China such as thermal comfort, carbon, and cost. The optimal design achieved through the compromise optimum can significantly reduce thermal discomfort, life-cycle carbon emissions, and high levels of daylighting conditions. The design scheme was visualized using a geometrical remodel module. This study contributes methodologically to complex multi-objective building optimization problems with practical implications for design.

Response surface methodology based synchronous multi-performance optimization of CMOS low-dropout regulator

An easy-to-use efficient auto-design approach to achieve a synchronous optimization and solution for multiple performance objectives of a CMOS low-dropout regulator (LDO) circuit is proposed. As a core algorithm, response surface methodology (RSM) is adopted to automatically implement the design parameter modeling and solving of the LDO. The precision response surface models for the temperature coefficient (TC) and power supply rejection ratio (PSRR) are established efficiently based on only 27 sets of Cadence sampling datasets, by which the optimal performance solution with a superior tradeoff on TC and PSRR can be obtained. Along with a complete auto-design flow, the pre/post-layout simulations of the LDO circuit by SMIC 180 nm/3.3 V CMOS technology are performed, it can be observed that the auto-improved LDO has a significant better 35.20 ppm/°C TC feature compared with 48.46 ppm/°C that recorded by the manual design. Synchronously, the PSRR is improved from −59.497 Hz@DC to −92.89 Hz@DC with a great increase ratio by 56 % up.

Multi-objective optimizations of solar receiver based on deep learning strategy in different application scenarios

Efficient and secure operation of solar receivers is key to the development of concentrated solar power (CSP). Its precise and quick optimization is essential for receiver to achieve optimum thermal performance and safety across diverse application scenarios. In this study, we propose a hybrid model based on numerical simulation and deep learning to achieve this target. The hybrid model accounting for conduction, convection and radiation shows a small relative error (<2%) in over 96 % cases. We apply the model to two different application scenarios considering multiple performance objectives simultaneously and demonstrate that it can identify optimal structure parameters and heliostat scale for each inlet flow rate of the receiver. In combination with gas turbines, maximum efficiencies of 48.9 %, 53.2 %, and 56.8 % are achieved for flow rates of 0.5, 0.75, and 1 kg/s, respectively. When integrated into heating systems, the receiver achieves a maximum thermal efficiency of 89.8 % with a heliostat field scale of 5.76 MW. Furthermore, for the operation optimization, the proposed aiming strategy results in a 76 ℃ reduction in maximum tube wall temperature compared to the conventional aiming strategy. Our approach not only provides an advanced solution for rapid cavity receiver design and operation optimization but also has the potential for extension to other structures.

Design optimization of hybrid isolation bearing for base-isolated buildings catering to multi-level performance fortification criteria

The adaptive seismic isolation system has attracted significant attention from researchers due to its multi-stage behavior and which can be used for multi-staged performance-based design. This paper introduces the configuration and mechanical behavior of a novel hybrid isolation bearing (HIB) combined with sliding bearings and rubber springs. The proposed isolator has three levels of stiffness and can achieve decoupling of horizontal and vertical performance. From the static test conducted on HIB500_R200, it is evident that the HIB displays a three-stage stiffness characteristic. The experimental stiffness values match well with the theoretical values, with a maximal error of 7.18%. Subsequently, an optimal design function for HIB-based isolation structures aiming to satisfy multiple performance objectives is established based on isolation effectiveness and displacement, utilizing the mode-superposition response spectrum and equivalent linear method. The optimization function can effectively and swiftly provide the optimal friction coefficient and the diameter of the rubber spring. A Performing elastoplastic analysis of HIB-based structures adopted for optimization function and traditional design method is performed using Seismostruct software. The numerical analysis reveals that the maximum error between the seismic isolation coefficient and the ratio of shear displacement amplitude values, as well as their theoretical predictions, is only 3.4%. And it also has higher safety redundancy than the traditionally designed isolation structures under mega earthquakes.

A multi-objective design tool for decarbonising buildings at the concept stage

To enable the move to carbon-neutral building structures with net-zero operation requires a step change in how buildings are designed. Modern buildings are designed by multidisciplinary design teams each of which has competing performance objectives. Daisy is a flexible performance-based parametric design tool which harnesses computational design workflows to enable designer-led multi-objective optimisation, allowing for the design of buildings which simultaneously achieve high performance across multiple performance objectives. A case study of designs for a 63-storey commercial building is presented that demonstrates how early design space analysis facilitates better-performing buildings across architectural and engineering performance metrics and the potential of multi-objective optimisation for enabling the move towards carbon-neutral building structures. Beyond building structures, the design methodology established for Daisy can be applied to a broad range of civil engineering optimisation problems using a flexible and accessible design space formulation that can be adapted for project-specific design requirements. Designs generated using the Daisy methodology demonstrated that by increasing the spatial daylight autonomy of the benchmark building by 14.7%, the building can be moved from the 10% of designs with the highest energy use intensity to lower than 97% of other simulated designs. However, this design change significantly increases the building embodied carbon, with the new design having a building embodied carbon which is higher than 90% of other buildings simulated. Alternatively, by reducing the spatial daylight autonomy by 32.8%, the design can have an energy use intensity which is lower than 75% of other simulated designs, with a 4.4% reduction in energy use intensity, and a building embodied carbon which is lower than 60% of other simulated designs, enabling a 1.3% reduction in building embodied carbon.

DESIGN OF POLYNOMIAL FRICTION PENDULUM ISOLATOR CONSIDERING MULTIPLE PERFORMANCE OBJECTIVES

Previous studies have revealed that sliding isolators with variable curvature (SIVCs) possess better isolation performance than that of conventional isolators, because of their variable mechanical property. However, their applications are hindered by the lack of a systematic design method. To accelerate the implementation of the advanced SIVC technology, this paper proposes a performance-based design method for one type of SIVCs called the polynomial friction pendulum isolator (PFPI). The proposed method that consists of a linear and a nonlinear design stages is able to satisfy multiple performance objectives under dual earthquake levels. In the linear stage, the linearized isolator parameters that comply with design code in the DBE and MCE levels are determined, while in nonlinear stage, the PFPI parameters are determined based on the linearized parameters. Finally, the feasibility of the proposed design method is verified by the dynamic responses of a hysteretic building model with the designed PFPIs

A multi-objective optimization framework for designing urban block forms considering daylight, energy consumption, and photovoltaic energy potential

Urban form significantly influences building energy consumption. However, most research has primarily focused on quantifying the relationship between the two factors, with limited exploration of optimizing urban form to enhance building energy performance. Moreover, studies often fail to consider multiple performance objectives simultaneously. This study proposes a multi-objective optimization framework for early urban design stage to improve energy and environmental performance in residential block layouts. The performance objectives include energy consumption, photovoltaic energy potential, and sunlight hours. The framework is implemented using the parametric platform Rhino & Grasshopper, where a parametric model controls the layout of blocks. Ladybug Tools plugin is employed for performance simulation, and Wallacei is used for optimization. An ideal residential block in Jianhu City, China, is taken as a case study. The study generates a total of 1896 valid solutions, including 58 Pareto solutions. The performance of the Pareto solutions demonstrates considerable improvements, indicating the effectiveness of optimizing urban form for enhancing energy and environmental performance. Compared to the initial solution, a typical Pareto solution showcases a 1.5% reduction in energy consumption, a 52.7% increase in photovoltaic energy potential, and a 50% increase in sunlight hours. These findings underscore the pivotal role of urban block morphology in influencing energy consumption, photovoltaic potential, and daylighting. The proposed multi-objective framework in this study enhances and facilitates sustainable block form design, which is expected to provide technical support for energy-efficient or low-carbon urban design.

A Distributed Scheme for Voltage and Frequency Control and Power Sharing in Inverter-Based Microgrids

Grid-forming inverter-based autonomous microgrids present new operational challenges as the stabilizing rotational inertia of synchronous machines is absent. The design of efficient control policies for grid-forming inverters is, however, a nontrivial problem where multiple performance objectives need to be satisfied, including voltage/frequency regulation, current limiting capabilities, and active power sharing and a scalable operation. We propose, in this article, a novel control architecture for frequency and voltage control, which allows current limitation via an inner loop, active power sharing via a distributed secondary control policy, and scalability by satisfying a passivity property. In particular, the frequency controller employs the inverter output current and angle to provide an angle droop-like policy, which improves its stability properties. This also allows us to incorporate a secondary control policy for which we provide an analytical stability result, which takes line conductances into account (in contrast to the lossless line assumptions in the literature). The distinctive feature of the voltage control scheme is that it has a double-loop structure that uses the dc voltage in the feedback control policy to implement a power-balancing strategy to improve performance. The performance of the control policy is illustrated via simulations with detailed nonlinear models in a realistic setting.

Multi-objective optimization and evaluation of PEMFC performance based on orthogonal experiment and entropy weight method

The operating condition parameters of temperature (T), anode relative humidity (RH_a), cathode relative humidity (RH_c), anode stoichiometry ratio (St_a), and cathode stoichiometry ratio (St_c) have a coupling influence on the multiple performance objectives of current density (I), pressure drop (ΔP), temperature difference (ΔT), and non-uniformity of oxygen (N) in the actual operation process of proton exchange membrane fuel cell (PEMFC). Based on the orthogonal experiment method (OEM) and entropy weight method (EWM), a new multi-objective optimization method and mathematical expression for evaluation of a PEMFC performance were proposed to clarify the influence ability of T, RH_a, RH_c, St_a, and St_c on I, ΔP, ΔT, and N and comprehensively evaluate the performance of a PEMFC in multiple performance objectives situations. The L18(37) orthogonal array was first designed by the OEM to form eighteen groups of schemes for multi-objective optimization. By analyzing the range and variance, the significance order and optimal parameter combination were individually obtained under four performance objectives. The comprehensive performance objective of output performance (OP) was then proposed, and the EWM was used to calculate the respective weight value of four performance objectives in OP. The mathematical expression of OP was calculated as OP = 0.51 I + 0.08 ΔP + 0.19 ΔT + 0.22 N, indicating that current density was the most important parameter. Eighteen groups of schemes were scored and ranked and the OP score of Scheme 6 was the highest with a value of 0.788. Finally, the analysis of range was performed again for OP scores, and the optimal combination of T = 343.15 K, St_a = 3, St_c = 3, RH_a = 20%, and RH_c = 20% was achieved, which was better than Scheme 6. This study redresses the limitation of single-performance objective optimization and maximizes the comprehensive performance of PEMFC considering multi-objectives.

Sustainability-Oriented Optimization and Decision Making of Community Buildings under Seismic Hazard

Optimization and decision-making tools are often utilized to enhance the performance of community buildings under extreme events, but this may compromise the ability of future generations to enhance performance. Hence, a sustainability-oriented approach is required to enhance the performance of community buildings under extreme events. In this context, this paper proposes an optimization and decision-making framework considering multiple performance indicators, including socioeconomic and environmental consequences as well as retrofit costs. These performance indicators are assessed by utilizing performance-based assessment methodologies in terms of sustainability dimensions. The performance indicators are then exploited as multiple performance objectives in a genetic optimization to determine the Pareto optimal solutions. Finally, the Pareto optimal solutions are utilized for decision making to extract ideal solutions for the given retrofit costs. The ideal solutions provide trade-offs between the consequences of extreme events and the retrofit costs required to reduce the consequences of extreme events.

Multi-domain model-based control of an adaptive façade based on a flexible double skin system

Adaptive envelopes have the potential to significantly reduce energy use in buildings while ensuring high performance. These envelopes interact with multiple interconnected domains, such as daylight, indoor air quality, thermal comfort, and energy use, which can often conflict with one another. Identifying and developing suitable control strategies that can optimally manage the envelope’s impact on many domains and avoid sub-optimal operations is an open challenge. Conventional approaches commonly adopted in buildings and building envelope control based on schedules or relatively simple decision trees may be unable to tackle the dynamic behaviour of adaptive envelopes. Due to their complexity, more advanced control approaches based on simulation-informed decision-making are scarce in both research and practice. In this work, we propose a multi-domain model-based control (MBC) algorithm for an adaptive façade concept based on a flexible Double Skin Façade (DSF). The proposed method, which aims for a balanced performance over different comfort domains and energy use, employs a co-simulation approach where the DSF is modelled in a Building Energy Simulation (BES) tool and the control algorithm to manage the simulation and optimize the control of the façade is developed in a generic programming language. To the best of our knowledge, this is one of the first attempts to design and demonstrate the effectiveness of a simulation-informed control strategy that can handle and optimise the behaviour of a complex façade by considering multiple performance objectives. The innovation of this approach lies in the MBC algorithm that selects the optimal façade state among over seventy possible states at each timestep, the practical demonstration of the feasibility in a BES tool, and the complexity of the controlled façade system. To verify the effectiveness of the proposed control approach, we compared the innovative MBC to more traditional control strategies, such as schedule and rule-based controls, revealing how it enabled the façade to achieve a better performance in all the analysed domains. By applying the MBC to three different year periods, we showed that the energy and environmental performance was within the selected comfort criteria for all the domains for>80% of the occupied hours, and an energy reduction of up to 70% was simultaneously obtained if compared to more traditional approaches. The control approach presented in this study and the simulation method employed can be used not only to improve the performance of advanced adaptive façades by providing an effective solution to the challenge of balancing multiple conflicting performance domains but also for more conventional building envelope systems that exhibit a certain degree of dynamic behaviour.

Multi-Objective Finite-Frequency H ∞/GH 2 Static Output-Feedback Control Synthesis for Full-Vehicle Active Suspension Systems: A Metaheuristic Optimization Approach

In this paper, the problem of multi-objective control for active suspension systems with polytopic uncertainty is addressed via <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GH</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> static output feedback with a limited-frequency characteristic. For the overall analysis of the performance demanding both vehicle-ride comfort related to vertical- and transversal-directional dynamics and the time-domain constraints related to the driving maneuverability, a seven-degree-of-freedom full-vehicle model with an active suspension system is investigated. The robust static output-feedback control strategy is adopted because some state variables may not be directly measured in a realistic implementation. In designing this control, the finite-frequency H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> performance using the generalized Kalman—Yakubovich—Popov lemma is optimized to improve the passenger’s ride comfort, while the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GH</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> performance is optimized to guarantee the constraints concerning the suspension deflection limitation, road-holding ability, and actuator saturation problem. This control synthesis problem is formulated as nonconvex bilinear matrix inequalities and requires simultaneous consideration of different finite-frequency domain ranges for vertical and transversal motions for evaluating the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∞</sub> performance. These design difficulties are overcome by the proposed multi-objective quantum-behaved particle swarm optimizer, which efficiently explores the relevant trade-offs between the considered multiple performance objectives and eventually provides the desired Pareto-optimal control set. Further, the numerical simulation cases of a full-vehicle active suspension system are presented to illustrate the effectiveness of the proposed control synthesis methodology in frequency and time domains.

A Stackelberg Game-Theoretic Exploration Rendering Robustness and Optimality for Performance Improvement of Fuzzy Mechanical Systems.

We consider mechanical systems with uncertainty. The uncertainty may be time varying. The bound of the uncertainty is described by its fuzzy characteristics. To design a feasible control, we start with a robust phase, which renders a control scheme that guarantees the system performance regardless of the actual value of the uncertainty. This robust phase is then followed by an optimal phase. There are design parameters in the control, which can be fine-tuned. We proposed multiple performance objectives. The goal of the choice of the control design parameters is to minimize the performance objectives. However, since these objectives are nonconciliating (meaning one's minimum is not the other one's minimum), we invoke the Stackelberg strategy for the optimal parameters. The game strategy mimics two players: one is the leader and one is the follower. Through the interplay between the two players, we show how to select the design parameters. The design procedure in both robust and optimal phases is demonstrated by a coupled inverted pendulum system.

Optimization of distribution patterns of link beams in a double‐column tall pier bent subjected to earthquake excitations

AbstractSeismic performance of double‐column tall pier bents has to date scarcely been investigated. The deployment of link beams between columns, including numbers and locations, is generally designed according to the experience of engineers, without any sophisticated procedure. This paper proposes a response surface‐based optimization procedure that searches for optimal configurations of link beams of double‐column tall pier bents, considering multiple performance objectives. The response surface model is well‐developed by considering training samples from uniform design methods, boundary conditions, and iteration procedures. With a typical double‐column tall pier bent in southwest China as an example, the correctness of the proposed procedure is validated by comparing seismic responses with those from conventional optimization methods. Furthermore, this response surface‐based procedure possesses a substantially higher time efficiency than is the case with conventional methods, due to less nonlinear time history analyses as required. The Pareto optimal front is employed to trade off competing objectives in this example and to provide potential optimal design options for engineers.

Quasi-static cyclic tests on a half-scaled two-storey steel frame equipped with Crescent Shaped Braces at both storeys: Experimental vs. numerical response

This paper discusses the results of quasi-static cyclic tests performed on a half-scaled two-storey one-bay steel pendular frame equipped with Crescent Shaped Braces (CSBs) at both storeys. The same steel pendular frame was previously tested with only one CSB device located at the first storey to validate the structural response of a single device when inserted into a realistic frame. The CSB seismic design procedure and the experimental results of this first configuration were presented and discussed in a companion paper which proved that the experimental behaviour of the single CSB matched the theoretical predictions and that the effect of connection plates was not negligible. Here the attention is focused, for the first time, on a structure fully braced along the height by CSBs as in a realistic building configuration. During the tests, the global and local responses of the structure were monitored by means of inductive displacement transducers, strain gauges and Digital Image Correlation technique. Non-linear Finite Element models were also developed to provide an in-depth interpretation of the experimental results. The objective is twofold: (i) the experimental assessment of the global performances of the braced structure in terms of stiffness, strength, ductility and energy dissipation, and (ii) the comparison between the experimental and the numerically-simulated response of the structure, with specific focus on the response of the two CSBs and on the effects of realistic connections (parasitic bending moments and bolt slippage). In conclusion, the results of the experimental test carried out on a two-storey building structure fully braced with CSBs proved that the CSB seismic design procedure is effective and the use of CSBs as diagonal braces could represent a feasible solution for buildings to achieve multiple seismic performance objectives.

A multi-performance seismic design procedure to incorporate Crescent Shaped Braces in mid-rise frame structures

This paper introduces a novel procedure for the seismic design of a new class of seismic-resisting systems for mid-rise buildings obtained by incorporating special yielding steel braces known as Crescent Shaped Braces (CSBs) into Not Moment-Resisting Frames (NMRFs). The proposed design procedure is grounded on the Performance-Based Seismic Design (PBSD) framework through the imposition of multiple seismic performance objectives with the aim of obtaining an almost uniform along-the-height seismic behavior. The desired uniform seismic behavior is ensured by imposing: (i) uniform inter-storey drifts under frequent earthquakes; (ii) widespread yielding of the braces along the building height under occasional earthquakes; (iii) minimum ductility capacity at all storeys to be exploited under rare earthquakes; (iv) minimum hardening stiffness for the mitigation of the second order (P-Δ) effects under very rare earthquakes. The desired performances are made possible by the specific features of the CSBs in terms of initial lateral stiffness, yielding strength, ductility capacity and final hardening response. The procedure is articulated in four conceptual phases and several steps to guide the professional engineer through all the main design phases, from the selection of the seismic performance objectives to the preliminary sizing of the CSB devices, up to the final design/verification through non-linear time-history analyses. The effectiveness of the proposed design procedure is finally demonstrated through an applicative example.