Supplemental Energy Dissipation Research Articles

Investigation of scalable chiral metamaterial beams for combined stiffness and supplemental energy dissipation

Abstract Metamaterials have gained important interest in the research community attributable to advances in additive manufacturing enabling their fabrication at reasonable costs. The vast majority of their applications and demonstrations are at micro- and nano-scales, and challenges remained regarding the larger scale applications. In this paper, we are interested by the scalability of metamaterials, targeting structural engineering applications. To do so, we explore mechanisms capable of providing both bending stiffness and high-performance energy dissipation. Our study includes beams constructed with chiral topologies of different structural hierarchy orders, and we also explore three new topologies that we termed chiral friction, chiral-rectangular and chiral-hexagonal design to engineer the beams and the use of friction rods with tunable post-stress that inserted longitudinally through the beams to provide enhanced friction. The mechanical performance of the metamaterial beams is characterized through a series three-point bending tests. Of interest is to evaluate the bending stiffness, shape recoverability, and energy dissipation capabilities. We find that the chiral-hexagonal topology equipped with a non-stressed friction rod exhibit excellent energy dissipation capabilities, showing an improved loss factor by 11.9 times compared to the control beam using 68% of its materials density. Moreover, the use of the post-stress mechanism shows that it is possible to augment both its shape recovery and bending stiffness up to 99.3% and 47.1%, respectively. Overall, our investigation shows that it is possible to engineer scalable metamaterial beams targeting structural engineering applications, and that the use of topology optimization and strategically designed post-tensioning mechanism can allow tuning of mechanical performance.

An Innovative Retrofitting Technique of an Industrial Prefabricated Building Without Evacuation

This paper presents a seismic retrofit of an industrial-type precast reinforced concrete building structure using friction dampers. The project consisted of retrofitting two precast reinforced concrete buildings, one of which will be presented in this paper. Precast concrete is one of the industrial structures' most preferred construction methods due to its low cost, fast construction, and availability in rural areas. Unfortunately, most structures constructed before “Specification for Buildings to be Built in Seismic Zones(TBDY 2018)[5]” are not sufficiently engineered and are expected to perform poorly when exposed to a significant seismic event. The general characteristic of precast reinforced concrete buildings built before TBDY 2018 is their relatively high concrete quality (compared to cast-in-place reinforced concrete buildings) and better reinforcement workmanship. But they have some characteristic weaknesses as well. Weak beam-column connections, high drift ratios due to heavy beams, instability problems, and lack of frame behavior can be considered primary weaknesses. General classical retrofitting techniques include increasing beam/column sections or adding new reinforced concrete or steel members to the system or FRP(fiber-reinforced polymer) wrapping. Mostly classical retrofitting needs additional foundations. All these techniques require a long construction period, causing evacuation and stopping building usage. Because stopping the production cost can be tolerated by the owners, a retrofitting approach that can be assembled during the normal function of the industrial structures is required. As a result of this requirement, friction dampers are selected as the supplemental energy dissipation device. ASCE 41-17 [10] is employed for the building's damper design and performance evaluation. Before the damper study, some instability and weak connection problems are solved by traditional strengthening measures. The most effective damper configuration and capacities are selected after an iterative trial-and-error linear study using the simplified methods developed by PROMER. Nonlinear push-over analyses are conducted after linear prestudies. Finally, a nonlinear time-history analysis is performed for confirmation of the results. , It is shown that the proposed retrofit scheme satisfies the desired performance goals for both DBE and MCE events. Overall, it is considered that the proposed retrofit scheme with dampers provides the optimal solution for the Project stakeholders from a performance, design, constructability, and economic point of view. Some application photos will be presented, and methods will be explained in detail in the paper. The friction damper behavior is based on the rotational friction hinge concept. The dampers increase building damping, causing a decrease in earthquake demand. As a result, dampers provide passive energy dissipation and protect buildings from structural and nonstructural damage during moderate and severe earthquakes.

Displacement-based design procedure for the seismic retrofit of existing buildings with self-centering dissipative braces

Existing framed buildings, especially those designed according to outdated seismic codes, often offer inadequate seismic protection levels due to material degradation, low amount of reinforcement and poor construction details. Among the possible retrofit strategies, elasto-plastic dissipative braces (EPDBs) can be installed to provide supplemental stiffness and energy dissipation in the main resisting frame. Since they are based on the plastic deformation of sacrificial steel components, EPDBs are inherently affected by scarce recentering capability, i.e., presence of residual deformation at the end of the mainshock that could impair their effectiveness for aftershock events. As demonstrated in recent seismic sequences, there might be not enough time to restore (e.g., though hydraulic actuators and a reaction frame) the undeformed configuration of the structure before a subsequent shock. This issue can be overcome through self-centering dissipative braces (SCDBs), i.e., braces equipped with dampers characterized by a “flag-shaped” hysteretic behavior, which inherently facilitates the immediate re-centering of the frame. Despite this evident benefit, there is still lack of practical design procedures for the seismic retrofit of buildings through SCDBs. To fill this gap, a direct displacement-based design procedure for SCDBs tailored to building frames is here conceived and illustrated. The proposed method aims at achieving simultaneously two performance requirements: (i) a target maximum roof displacement under the ultimate-limit-state seismic event; (ii) the absence of significant residual inter-storey drifts at the end of the shaking. The implementation of the procedure is described by two applications to a steel and to a reinforced concrete case-study building. Nonlinear time-history analyses are carried out to prove the effectiveness of the proposed method, along with a comparison of the seismic performance offered by SCDBs versus traditional EPDBs implemented in the same case-study buildings.

3D response simulation of a bridge with a posttensioned base rocking steel pier under sequential loading of traffic loads, braking force, and earthquake excitations

AbstractThis paper presents finite element (FE) investigations of the seismic response of a bridge incorporating a base rocking steel pier. The pier consists of a circular steel tube, circular end plates, posttensioned (PT) tendon(s), and supplemental energy dissipation devices, and is configured to rock at its interface with the foundation. The main characteristic of such a pier is its ability to ensure small residual drifts after undergoing inelastic deformations during cyclic loading. The system has a tendency to close the gap due to the presence of superstructure dead load (DL) and tendon posttensioning force. Using experimental data, the calibration of the FE procedure is done at the material, component, and global system levels. The FE model of a prototype bridge is developed with the rocking pier modelled by continuum elements while superstructure, bearing units, abutment walls and backfill material modelled by discrete elements. The analysis procedure includes the application of one or two earthquake excitations, traffic loads, and braking force. The varied parameters are the diameter‐to‐thickness ratio of the column, presence of a PT tendon, addition of supplemental energy dissipaters (EDs), base plate dimensions, height of ED chairs, and ED strength. The results of dynamic FE studies demonstrate that a bridge utilizing such a pier has the potential to undergo consecutive earthquakes without sustaining significant damage and return to its original position without requiring abutment component stiffness and strength.

Seismic Upgrade of Steel Frame Buildings by Using Damped Braces

Supplementary energy dissipation has proved to be an effective way of protecting structures from the disastrous effects of earthquakes and has been used in the last decades both in new and in existing constructions. In this regard, various procedures for the design of the damping system for the seismic retrofit of buildings have been formulated over the years, mainly focused on reinforced concrete (RC) constructions, which represent the largest part of the existing stock in many seismic-prone countries. The study deals with the assessment of a displacement-based design procedure for proportioning the damping system recently proposed in the literature for RC framed buildings, with the goal of establishing a good practice for the application of the procedure to steel buildings as well. The method was applied to three case-study frames, regular in plan and in elevation, which were assumed as being representative of old structures designed without consideration of seismic requirements. The retrofit was performed by using chevron braces equipped with dampers with an elastic-perfectly plastic behavior. The method aimed at defining the properties of the dampers to achieve a target performance in terms of the maximum lateral deflection for a specific level of seismic intensity. The effectiveness and reliability of the proposed procedure was eventually assessed by evaluating the seismic performance of the upgraded steel structures in static and dynamic non-linear analyses.

Numerical study of a novel SMA-based self-centering beam-to-column connection

As an alternative option for conventional rigid beam-to-column welded connections, self-centering steel beam-to-column connections were developed to reduce or eliminate the residual deformation of the structure and mitigate or avoid structural damages. This paper presents a finite element analysis of a novel self-centering beam-to-column connection with shape memory alloy (SMA) tendons as recentering and energy dissipation elements and comb-teeth dampers (CTDs) as supplementary energy dissipation devices. Firstly, the configuration and structural behavior of the proposed connection is depicted and explained; then, with the aid of previous experimental models, the validation of finite element modeling methods is examined. In the following, detailed numerical models are established and analyzed to assess the effects of key design parameters on the cyclic behavior of the proposed connection. Finally, an analytical model is formulated to predict the whole cyclic behavior of the proposed system. The results indicate a great recentering and energy dissipation capacity for the proposed connection. It is shown that incorporating CTDs in the proposed connection can significantly enhance the cyclic response of the connection with roughly no adverse impact on self-centering ability. It is also concluded that there must be an adequate initial prestress in SMA tendons to exploit the maximum recentering ability of the proposed connection. Furthermore, comparing the structural performance metrics of the proposed connection reveals that the connections with higher damper geometric shape coefficients own higher ultimate strength and better energy dissipation capacity with almost unchanged recentering capability. Conversely, the longer the damper teeth height is, the lower performance parameters in the connections could be observed. Results also show reasonable concordances between the analytical model predictions and finite element analysis results. The results of this study can serve as tools to facilitate the practical design of SMA-based self-centering connections.

Damage-control design and hybrid tests of a full-scale two-story buckling-restrained braced steel moment frame with sliding gusset connections

Buckling-restrained braces (BRBs) are widely adopted as supplementary energy dissipation devices in steel moment frames (MFs) in Asia to improve the energy dissipation capacity of the whole system. Such systems are referred to as buckling-restrained braced moment frames (BRB-MFs). Nevertheless, adopting BRBs does not guarantee desirable seismic performance of the whole system, as frame action may cause premature fracture or buckling of BRB corner gusset connections, and such frame-to-gusset interaction may limit the ductility of such system. In our previous studies, a sliding corner gusset connection was proposed and proved to be able to substantially reduce the detrimental frame action at the connection level. In this paper, study was extended to (1) damage-control design of BRB-MFs with such connections in pursuit of enhanced system ductility, and (2) experimental evaluation on seismic behavior of BRB-MFs with such connections at the system level. The damage-control design method was first presented and a full-scale two-story BRB-MF designed by such procedure was experimentally studied under four levels of earthquake loading through hybrid tests, followed by a pseudo-static test to examine its failure mode. Test results showed that the sliding gusset connections effectively released the frame action at the system level. By adopting the damage-control design procedure, the test BRB-MF exhibited excellent seismic performance up to an inter-story drift ratio of ± 3 %, and plastic hinges of the MFs developed in the controlled positions without fracture or buckling under four levels of earthquake loading. With the improved ductility of MFs, BRBs achieved their full potential as energy dissipation devices.

Retrofitting of a Precast Reinforced Concrete Industrial Building Using Friction Dampers Without Stopping Functionality

This paper presents a seismic retrofit of an industrial-type precast reinforced concrete building structure using friction dampers. This project consisted of retrofitting two precast reinforced concrete buildings, of which one of them will be presented here. Precast concrete is one of the most preferred methods of construction for industrial structures due to its low cost, fast construction and availability in rural areas. Unfortunately, most structures constructed before “Specification for Buildings to be Built in Seismic Zones(TBDY 2018)” are not sufficiently engineered and are expected to have poor performance when exposed to a major seismic event. Because stopping the production cost can be tolerated by the owners, a retrofitting technique that can be assembled during normal function of the industrial structures is required. As a result of this requirement, friction dampers are selected as the supplemental energy dissipation device. ASCE 41-17 [10] is employed for the damper design and performance evaluation of the building. Before the damper study, some instability and weak connection problems are solved by some traditional measures of strengthening. The most effective damper configuration and capacities are selected after an iterative trial-and-error linear study using the simplified methods developed by PROMER. Nonlinear push-over analysis are conducted after linear prestudies. Finally, a nonlinear time-history analyses is performed for confirmation of the results. , It is shown that the proposed retrofit scheme satisfies the desired performance goals for both DBE and MCE events. Overall, it is considered that proposed retrofit scheme with dampers provides the optimal solution for the stakeholders of the project from a performance, design, constructability, and economical point of view. Some application photos will be presented and methods are explained in detail in the paper. The friction damper behavior is based on the rotational friction hinge concept

Seismic vulnerability assessment of reinforced concrete buildings having nonlinear fluid viscous dampers

Seismic resilience is the residual capacity of a damaged system for recovering and sustaining an acceptable level of performance as a consequence of a seismic event. Firstly, this paper summarizes the current calculation framework of seismic resilience using fragility analyses. After that, a new metric based on vulnerability analyses is developed to calculate seismic resilience. Finally, a typical hospital building is adopted as a single building and then retrofitted with supplemental Energy Dissipation Systems (EDS) to show the applicability of the new metric and compare it with the current calculation model of the seismic resilience. The considered supplemental EDS is the Nonlinear Fluid Viscous Damper (NFVD) located as the diagonal damper-brace system. The seismic performance of the supplemental EDSs is to enhance structural performance by reducing induced lateral displacements and as a result the level of physical damages and losses. To this end, Incremental Dynamic Analysis (IDA) is implemented to achieve the damage fragility and vulnerability curves. A comparison of the fragility, vulnerability, and functionality curves indicates that NFVDs are potentially useful for attenuating seismic damages to structural and non-structural components.

Deformation‐based design of seismically isolated bridges

AbstractA performance‐based design procedure is proposed for seismically isolated bridges with/without supplemental energy dissipation devices. Considering multiple performance levels (PLs), the proposed method initially identifies the critical hazard level and “near‐optimal” alternatives of the isolation system. Both performance and economy are evaluated based on the inelastic response of reduced‐degree‐of‐freedom (RDOF) isolation and energy dissipation systems. Nonlinear response history analysis (NLRHA) of the multi‐degree‐of‐freedom (MDOF) system is employed in successive design steps, corresponding to different PLs, to refine the design solution through the control of a broad range of material strains and deformations. The above characteristics aim to deliver a rigorous and broadly applicable design method that reduces the high computational effort characterising complex design frameworks, while addressing identified deficiencies of alternative displacement‐based methods. The efficiency of the proposed design methodology is demonstrated by applying it to an actual bridge that was previously designed for ductile behaviour. Alternative isolation and energy dissipation schemes are investigated. Assessment of the design through NLRHA reveals in all cases enhanced seismic performance and cost reduction in the substructure design, thus rendering base‐isolation an appealing design alternative.

Design and Experimental Assessment of a Prestressed Lead Damper with Straight Shaft for Seismic Protection of Structures

This study introduces a new energy dissipation device with a high damping capacity for the seismic protection of buildings. The device exploits the friction losses between a movable shaft and a lead core to dissipate the seismic energy and takes advantage of the prestressing of the lead material to control the friction force. Numerical analyses are introduced to evaluate the influence of prestressing on the axial force of the device. Cyclic tests performed on a prototype demonstrate the high damping capability, with an equivalent damping ratio ξeff of approximately 55%, a robust and stable response over repeated cycles and a low sensitivity of the mechanical properties to the frequency, suggesting that the proposed device may be a potentially effective solution for providing supplementary energy dissipation to structures in seismic areas. Moreover, the device is able to endure multiple cycles of motion at the basic design earthquake displacement, ensuring maintenance-free operation even in presence of repeated ground shakes.

Single and multiple TMD optimization to control seismic response of nonlinear structures

Tuned mass dampers (TMDs) are control devices used for supplemental energy dissipation in civil structures. In the case of structures that exhibit a nonlinear dynamic response under seismic action, their performance is affected by both the duration of the dynamic excitation and the detuning effect. In order to improve the TMD effectiveness in this scenario, the parameters of three different TMD configurations are optimized in the present work using the particle swarm algorithm. In the optimization process, two different objective functions are considered. The performance of the three optimal TMD configurations is evaluated on three single-degree-of-freedom structures with different fundamental periods subjected to a set of far-field records and a set of near-fault ground motions with strong velocity pulses. From the results of this analysis, it is found that in general, the configuration with two TMDs in series tuned to a frequency of 50% of the fundamental frequency of the healthy structure obtained the highest effectiveness when the ductility demand is greater than 5. In the case of medium-period structures with the highest ductility demand imposed by far-field ground motions, a reduction in the median ductility demand of 26% is achieved with a mass ratio of 25%. A lower effectiveness is observed against near-fault records, especially in short-period structures. Finally, the effect of the optimized TMD on multi-degree-of-freedom structures is analyzed.

Advanced Modeling of SMA Flag-Shaped Hysteresis for Nonlinear Time-History Analysis in SAP2000

AbstractSuperelastic shape memory alloys (SMAs) introduce supplementary energy dissipation with minimal residual deformation, which is desired in earthquake engineering–related applications (e.g., ...

Vibration reduction on a cantilever Timoshenko beam control subjected to combined effects of wind and earthquake loads using damped outriggers

This paper deals with the combined effects of wind and earthquake on the dynamic response of a cantilever structure. It is mainly composed of the core-structure, multi-outriggers with magneto-rheological (MR) dampers localized at different levels along of the structure and perimeter columns. These control devices are semi-active in nature and exhibit a nonlinear behaviour. One of their interesting characteristics is their ability to add supplementary energy dissipation to the structural system. Exposed to combined wind and earthquake loads, the core-structure is modelled using a Timoshenko cantilever beam. The stochastic approach based on the statistic properties is employed to estimate the degree excitations of the two natural hazards. The peak Root-Mean-Square (RMS) are evaluated to quantify the optimal location of damped outriggers. Defined as the control algorithm based on human reasoning, the Fuzzy logic is used to select the appropriate current that feeds the control devices. The obtained results indicate that the application of the fuzzy logic further minimizes the effects of bending-moment and shear force. All of these enhance the performance of the whole structural response and lead to a significantly reduction of excessive vibration to an acceptable level.

Damage protection of earthquake resistant structures by means of damped braces

Supplementary energy dissipation is an efficient technique for the retrofitting of as built framed buildings as long as the loss of capacity due to previous seismic degradation is evaluated properly. Most of the displacement-based design procedure of damped braces only considers the capacity curve of an initially undamaged structure, while the hysteretic energy is accounted for by an equivalent viscous damping. However, structures may be initially damaged by previous earthquakes, so the proportioning of the damped braces should include the effects of the cumulative damage caused by previous loading cycles. A displacement-damage-based design procedure is proposed and implemented by means of a computer-aided tool named DAMPERS (DAMage Protection of Earthquake Resistant Structures). The residual capacity that a building might experience when subjected to more than one earthquake during its nominal life is taken into account. The loss of capacity of the original structure is evaluated by a combined plastic-damage model, obtained as an in-parallel combination of elastic-perfectly plastic and elastic-softening damage mechanisms, and a damage index, accounting for the cyclic damage of each pair of mechanisms. An archetype six-storey reinforced concrete framed building, representative of the Italian residential housing stock constructed during the 1990s, is retrofitted with hysteretic damped braces designed assuming different damage evolution laws during previous earthquakes. Three configurations of masonry infills (MIs) are considered: bare frame, with nonstructural MIs; infilled frame, with a uniform in-elevation distribution of structural MIs; pilotis frame, with no MIs at the ground floor and structural MIs at the other floors. OpenSees is the computational platform for the nonlinear seismic analysis of the unbraced and damped braced structures, with reference to records scaled in line with the hypotheses adopted and considering failure modes of structural and nonstructural elements.

Seismic Risks Mitigation of Façadism Constructions with Supplemental Energy Dissipation

Urban renewal projects typically involve redevelopments of under-utilized old buildings and revitalizing precious land resources. Due to architectural and social-economic reasons, historical facades are sometimes retained, and new constructions are built behind them. This allows the historical facade, typically the street elevation, to remain while new real estate can be redeveloped. In the profession of architecture, this is called facadism. In many cases, these historical facades are constructed with unreinforced masonry (URM). When these facades are retained and the remaining of the building is demolished, they become free-standing walls. Temporary supports are required throughout construction works and the retained facades must be designed to prevent excessive movements, allowed for differential movements and to resist wind forces. These historical facades were made of brittle materials and were constructed many decades ago before modern design standards and materials are available. They possess very little ductility and become vulnerable when subjected to ground shaking. The present study suggests a structural system that attempts to mitigate seismic risk of facadism constructions effectively. The structural system divides the new construction, which can be a reinforced concrete structure or a steel frame structure, into two separate frames. A seismic gap is introduced between them and produces two systems of different vibrational characteristics. Supplemental energy dissipating devices such as viscous fluid or friction dampers are placed in-between adjacent floors. The proposed structural system utilizes the different vibrational responses of two frames to facilitate energy dissipation in dampers. In this article, governing equations are presented, followed by numerical simulations using historical earthquake acceleration histories. Results demonstrate that the suggested structural system is an effective methodology to suppress seismic responses of the facade and the new construction. It is concluded that damage on the retained facades can be prevented, and at the same time seismic responses to the newly constructed structure can be controlled.

In-plane and out-of-plane nonlinear seismic response of masonry infills for hospitals retrofitted with hysteretic damped braces

The present work studies the combined in-plane (IP) and out-of-plane (OOP) collapse of unreinforced masonry infills (MIs) of strategic infrastructures such as hospitals retrofitted by hysteretic damped braces (HYDBs), where immediate occupancy (IO) and structural safety (SS, e.g. life-safety or collapse prevention) are the performance levels required after low-to-high amplitude earthquakes. Despite many advances in the development of new supplementary energy dissipation systems, few investigations have evaluated their effectiveness in improving the IP-OOP response of MIs. Because of the complex articulation of medical centres, reference is made to a five-storey pavilion of the hospital campus of Avellino in Campania (Italy). Bare and infilled structural models of this reinforced concrete pavilion are designed in a medium-risk seismic zone, in order to fulfill the corresponding IP drift ratio thresholds provided by a former Italian code for limiting nonstructural damage of MIs at the serviceability limit state. The IO and SS performance levels are checked in a displacement-based design procedure of the HYDBs at the Serviceability (SDE) and Basic (BDE) Design Earthquakes. An optimization procedure is considered, taking into account that an anticipated (delayed) activation of the yielding devices may give rise to concerns about their suitability with respect to high (low) intensity seismic loads. The demolition and reconstruction of MIs, which generally goes hand in hand with the introduction of damped braces in existing frames, is avoided. To this end, exterior, with diagonal damped braces in the window bays, and interior, with less-intrusive chrevron damped braces, retrofitting systems are adopted. Two aspect ratios of MIs are analysed assuming corner arrangements along the perimeter. Nonlinear time-history analyses for the four reference seismic levels assumed in the current Italian code highlight that IP and OOP failures of MIs can be avoided when the activation of the HYDBs at the SDE can be attained without jeopardising structural safety at the Maximum Considered Earthquake (MCE).

Multi-objective optimal design and seismic performance of negative stiffness damped outrigger structures considering damping cost

In this paper, the seismic performance of conventional damped outrigger (CDO) is improved by incorporating negative stiffness (NS) in parallel with the viscous damper. The applied negative stiffness spring upgrades the classical Maxwell damping element, which is used to describe the assembly of outrigger viscous damper and perimeter columns, to negative stiffness amplifying damper with higher damping effect. Tall buildings with such negative stiffness damped outrigger (NSDO) is described in the state space expression of the structure-outrigger-excitation augmented assembly, and the root-mean-square (RMS) responses of NSDO structures are parametrically studied to develop a direct connection between outrigger parameters and structural seismic responses. Based on these results, a multi-objective optimization method with both performance and economic objectives—reducing harmful inter-story drift and structural acceleration simultaneously with less outrigger damping cost—is proposed. Finally, this optimally designed NSDO is used to retrofit existing conventional outrigger (CO) structures as a supplemental energy dissipation outrigger. The performance of this retrofitted structure is studied and compared with that retrofitted by optimal CDO under numerous real earthquake records. Result indicates the CO structure retrofitted by NSDO substantially saves the outrigger damping cost of CDO by 85.9%, and further decreases the harmful drift and structural acceleration responses over 51% and 29%, respectively. Although optimal design of NSDO for strong earthquakes alone is the focus of this study, it is shown that NSDO is able to reduce wind-induced maximum acceleration by 33% without amplifying wind-induced maximum harmful drift.

Validation of hysteretic behavior and prediction of energy dissipation potential of aluminium shear yielding devices

Metallic dampers are used to control the seismic vibration of civil structures through supplemental energy dissipation and damping thereby minimizing damages to the primary load-resisting elements. Shear yielding devices are one type of metallic dampers in which the hysteretic energy dissipation is achieved through the inelastic deformation of metallic plates under cyclic loading. This paper presents a numerical study to evaluate the hysteretic behavior of aluminum shear yielding devices (Al-SYDs) under cyclic loading. Finite element models of eighteen numbers of Al-SYDs have been developed in a computer software ABAQUS and are validated by comparing the predicted behavior with the past test results. A parametric study is conducted to investigate the influence of web aspect ratios, web slenderness ratios, grades of aluminum alloy, and position of vertical stiffeners on the hysteretic behavior, energy dissipation potential, and displacement ductility of Al-SYDs. The energy dissipation potential of these devices is found to be strongly dependent on the aspect ratio and slenderness ratio of web plates. A simplified expression has been proposed to estimate the hysteretic energy dissipation potential of Al-SYDs. Limiting values of panel aspect ratio and web slenderness ratio have been recommended for the design of Al-SYDs.

Demands on nonstructural components in buildings with controlled rocking braced frames

AbstractControlled Rocking Braced Frames (CRBFs) have been developed as a high‐performance seismic force resisting system that can self‐center after an earthquake and avoid structural damage. A CRBF is designed to uplift and rock on its foundation, and this response is controlled using prestressing and energy dissipation devices that are engaged by uplift. Although CRBFs have been shown to have desirable structural performance, a comprehensive assessment of this system must also consider the performance of nonstructural components, which have a significant impact on the safety and economic viability of the system. The purpose of this paper is to evaluate the demands on nonstructural components in buildings with CRBFs in comparison to demands in a reference codified system, taken here as a buckling restrained braced frame (BRBF), as well as to identify which design parameters influence these demands. The responses of various types of nonstructural components, including anchored components, stocky unanchored components that slide, and slender unanchored components that rock, are determined using a cascading analysis approach, where absolute floor accelerations generated from nonlinear response history analyses of each system are used as input for computing the responses of nonstructural components. The results show that the downside of maintaining elastic behavior of the CRBF members is, in general, larger demands on nonstructural components compared to the BRBF system. These demands are not highly influenced by impact during rocking or by the supplemental energy dissipation provided, as the vibration of the CRBF in its higher modes is primarily responsible for the higher demands.