ABSTRACT Two alternative approaches for densifying the Multi‐Stripe Analysis (MSA) results are presented, aiming to obtain synthetic MSA data at intensity measure (IM) levels not originally captured by the analysis. Motivation comes from the computational cost of using complex structural models to assess the seismic response, often leading to running MSA at few IM levels with a limited number of ground motions. Still, a continuous representation of multiple engineering demand parameters (EDPs) given the IM level is sometimes required, for example, for rapid damage assessment when sensor information is available after a seismic event that corresponds to an “intermediate” IM value not matching the ones available from MSA. The first proposal is for a non‐parametric method that employs a correlation‐preserving record‐wise linear interpolation scheme. The second is a parametric method that employs a correlation‐preserving moment‐wise linear interpolation scheme based on a joint lognormal distribution assumption. The validity of the proposed methods is examined against actual MSA data calculated for a nine‐story steel moment resisting frame building and a reinforced/prestressed concrete bridge. Both approaches show merit, subject to sensitivity to sample size: As expected, interpolation fidelity degrades when the spacing between the IM levels increases and/or fewer ground motions are available.
ABSTRACT All previous studies on the recommendation, quantification, and assessment of accidental torsion due to torsional ground motion were based on a set of single‐storey buildings and were extrapolated to multistorey buildings either under the assumption of a special class of torsionally coupled buildings (SCTB) or without any scientific rationale. This paper presents a procedure that enables computation of the required accidental eccentricity for a given (general‐class) multistorey building, rather than attempting a generalised recommendation on normalised accidental eccentricity that is independent of the building. Two different frameworks are proposed: one for the equivalent static procedure (ESP) and another for the response history analysis (RHA). The ESP framework considers each storey separately and recommends computing the required accidental eccentricity at the respective storey level, using the recommendations reported by the authors elsewhere for single‐storey buildings. The RHA framework extends that reported by the authors elsewhere for single‐storey buildings by relaxing the SCTB assumptions and instead accounting for the contributions of multiple triplets of torsionally coupled modes. The results from these frameworks are numerically assessed against five buildings (ten‐storied) with various plan layouts and horizontal setbacks, subjected to a suite of recorded events comprising horizontal pairs and the torsional component of ground motion. In a nutshell, this paper presents the first‐ever framework that can address accidental torsion in a given multistorey building without assuming it is an SCTB.
ABSTRACT Retaining walls with multiple anchor levels are widely used as permanent excavation support systems for the construction of linear infrastructures. Yet, their seismic behaviour remains largely unexplored, and current design approaches rely on conventional procedures that do not adequately reflect the actual dynamic response of these systems. This paper addresses this gap by introducing a rational framework for the seismic design of multi‐anchored retaining walls based on a reliable prediction of their dynamic performance. A high‐fidelity numerical benchmark is first developed, consisting of a series of nonlinear dynamic analyses of a case study carried out using the OpenSees finite element framework. The resulting response is then reproduced using a practice‐oriented model with a clear physical basis and negligible computational cost. The comparison shows that the simplified method is able to capture the seismic response of the retaining structure with reasonable accuracy, while providing useful insight into the governing dynamic mechanisms. The robustness of the approach is further supported by its successful application to a second, independent case study. Overall, the results indicate that the proposed simplified method represents a promising tool for the seismic design of multi‐anchored retaining structures.
ABSTRACT Aging and environmental exposure progressively deteriorate the physical and mechanical properties of construction materials, thereby affecting the safety and functionality of existing infrastructure. Corrosion of steel rebars in reinforced concrete structures is widely acknowledged as the most common and detrimental degradation phenomenon, as it affects both the local and global structural performance. This issue is particularly relevant for the European bridge stock, which mainly consists of reinforced concrete bridges built in the last century, according to outdated design standards and using materials often not compliant with current requirements. As several infrastructural assets are approaching the end of their lifespan and require urgent retrofitting interventions, reliable tools for assessing their long‐term safety and seismic performance are urgently needed to support resilience‐informed infrastructure management. In this work, a probabilistic framework was proposed to assess the time‐variant seismic performance of archetype reinforced concrete bridge piers with different geometrical configurations, namely short and slender piers. The effects of degradation phenomena, including reinforcement corrosion, corrosion‐induced concrete cracking and creep were modeled through consolidated analytical formulations and implemented in a numerical model. Multiple Stripe Analysis was carried out to derive time‐variant fragility curves, aiming to assess the influence of degradation phenomena and their inherent uncertainties on the seismic performance of the pier. Seismic fragility evolution curves were also developed and presented herein, to provide useful tools in management frameworks. The results show that long‐term seismic performance is significantly affected by pier geometry and by the uncertainties associated with deterioration‐related input parameters, highlighting the importance of explicitly accounting for aging effects in seismic risk assessment of existing reinforced concrete bridges.
ABSTRACT The seismic response of lightly damped structures is strongly affected by the level of damping in their modes of vibration. This investigation assesses the influence of the damping model on the estimated seismic response and damage of a portfolio of 97 tall pre‐Northridge steel moment resisting frame buildings located in the Financial District of the city of San Francisco, California, during the 1989 Loma Prieta earthquake, using an advanced probabilistic regional seismic risk framework previously developed by the authors. Building responses and damages were computed using three different damping models, namely the one used in ASCE 7–22 (ASCE), the one recommended in the 2023 Los Angeles Tall Buildings Structural Design Council (LATBSDC), which is also adopted in the Tall Building Initiative (TBi), and the one recently developed by Cruz and Miranda (CM). Results indicate that the CM damping model predicts seismic responses and damages that, on average, fall between those estimated by the ASCE and TBi models. In particular, peak building responses and damages to gypsum partition walls can change by as much as 30% and 75%, respectively, when using the ASCE or TBi damping models with respect to those computed with the CM damping model. However, responses and damages at different building heights, not just where responses and damages are maximum, can change by much more than 30% and 75%, respectively. Moreover, peak responses and damages to gypsum partition walls can change by nearly 50% and more than 400%, respectively, if the ASCE damping model is used instead of the LATBSDC or TBi damping model. Additionally, changes in peak damages to other building components may be significantly larger than those observed for gypsum partition walls due to a change in the building damping model. Large changes in building responses and damages may also lead to significant changes in expected monetary losses. These findings illustrate the significance of the building damping model on regional seismic risk assessment results. They also highlight some of the limitations of the damping models currently used in ASCE and LATBSDC/TBi.
ABSTRACT The rocking motion resembles the dynamic behaviour of various structures, and therefore, it is fundamental for many earthquake engineering applications. Despite its importance, modelling the rocking motion remains an open and challenging topic owing to its highly non‐linear and sensitive dynamic behaviour. Several rocking models have been proposed in the scientific literature, yet, in most cases, with limited or partial validation against experimental results. To this end, this study proposes a novel compliant contact model for simulating the response of block‐type rocking structures. The model is calibrated using data from an experimental campaign on dry‐joint interfaces and features a hysteretic, rate‐independent term that captures the joint‐closure tests. Moreover, the model includes a non‐linear viscous damping term calibrated to match energy dissipation for any angular coefficient of restitution value. Subsequently, the proposed model is validated against an extensive experimental campaign of more than 400 free‐rocking and forced‐rocking shaking‐table tests of limestone blocks with various geometries.
ABSTRACT The growing demand for rapid post‐earthquake functional recovery and minimal structural damage has promoted the development of low‐damage seismic design strategies. Controlled rocking systems have emerged as an effective seismic structural solution for enhancing seismic resilience. To provide experimental evidence for the development of resilient steel structures, this study presents a full‐scale Controlled Multiple‐Rocking‐Column System (CMRCS) developed as part of the RObust BUilding SysTem (ROBUST) project. The system comprises two exterior controlled multiple‐rocking‐column frames and a central low‐damage secondary frame. The secondary frame carries the gravity loads assigned to Grid 2 and provides supplemental lateral resistance. Low‐damage rocking joints are installed at both ends of the rocking columns at each storey. Under frequently occurring earthquakes (FOEs), the CMRCS is designed to behave similarly to a conventional moment‐resisting steel frame, while the multiple‐rocking mechanism is intended to be activated at higher seismic intensities. Full‐scale shaking‐table tests were conducted on a 3‐storey steel frame specimen subjected to ground motions with peak ground accelerations (PGAs) ranging from 0.055 g to 0.62 g. The test results demonstrated that the structure exhibited satisfactory seismic performance, characterized by negligible residual drifts and no visible damage throughout the test sequence. Moreover, the proposed system also satisfied the immediate occupancy performance objective even under very rare earthquake‐level excitation (PGA of 0.62 g), thereby confirming the effectiveness, robustness and seismic resilience of the proposed system.
A key challenge in seismic performance assessment is selecting ground motions that accurately represent site-specific hazard characteristics. Although matching conditional distributions of spectral shape and duration ensures hazard consistency, it becomes computationally prohibitive for code-based evaluations of large building inventories. Current codified approaches, such as FEMA P695 and Canada's performance-based unified procedure, rely on incremental dynamic analysis (IDA) with generic records followed by site-specific adjustment. However, existing adjustment equations are calibrated only for collapse and are based on regular ductile structures, limiting their applicability across noncollapse performance levels and diverse building archetypes where structural sensitivity to spectral shape and duration may differ. This study develops new predictive equations for spectral shape and duration adjustment factors across multiple performance levels, considering both component-level and global performance criteria. A database of 45 code-compliant reinforced concrete moment frames was analyzed using systematically selected ground motions. Regression analyses demonstrated that fundamental period and a normalized backbone area index are robust predictors of spectral shape and duration sensitivity, outperforming the period-based ductility factor employed in current guidelines. Validation at two Canadian sites revealed that unadjusted IDA produced substantial bias, with the mean annual frequency of exceeding various performance levels overestimated by 50%-80%. Raw IDA underestimated median performance intensities by up to 22%, and FEMA P695 produced inconsistent adjustments, overestimating intensities in Vancouver by over 50% and underestimating them in Montreal by up to 16%. The proposed equations reduced these errors to below 11% across all performance levels and closely reproduced multiple stripe analysis results.
Estimation of the time required for damaged building components to return to their pre-earthquake conditions through repair is a critical element in assessing the seismic resilience of buildings, and it requires consideration of uncertainty. This study investigated such time distributions using actual time-to-restoration data obtained from earthquake-affected buildings through a questionnaire survey. As a starting point, data for 131 buildings that did not incur severe structural damage and disruptions to lifeline infrastructure from the 2022 Fukushima-ken Oki earthquake in Japan were analyzed. Hierarchical Bayesian Weibull/mixed-Weibull regression yielded an empirical model describing the probability of restoration as a function of time for seven building component types, including columns and beams, exterior walls, partition walls, interior doors, ceilings, lighting fixtures, and plumbing. The following conclusions were drawn from the developed model. (1) Building components are clearly divided into those with high and low restoration priorities. (2) High-priority building components, including plumbing, lighting fixtures, partition walls (in cases of falling), and ceilings (in cases of falling), are restored approximately 75-132 days after an earthquake, with 99% probability. (3) The restoration of low-priority building components occurs approximately randomly over time. The synthesized time-to-restoration distribution, incorporating probabilistic estimates of lifeline infrastructure downtime as initial delays, highlights that both the lifeline infrastructure downtime and subsequent phase duration substantially affect the overall distribution given a ground motion level defined by the Japanese building code. These results provide useful information that supports the resilience-based seismic design of buildings.
ABSTRACT Floating floor structures (FFSs) represent a powerful seismic protection technique that can substantially decrease the responses of both the main building and the attached nonstructural components. Nonetheless, the high flexibility of the isolation layer results in significant relative motion between the floated floor slabs and the primary structure, a major drawback of this system. To overcome this limitation, this paper introduces a variant tuned mass damper inerter (V‐TMDI) aimed at further improving the seismic performance of FFSs. First, an analytical model of a multistory FFS equipped with a V‐TMDI is formulated, and the governing equations are derived. The effects of the V‐TMDI frequency ratio and damping ratio on the stochastic responses of the FFS are examined. Next, a numerical optimization framework is developed to identify the optimal V‐TMDI parameters. A parametric investigation is subsequently conducted to examine how the configuration of the combined FFS–V‐TMDI system affects these optimal parameters. The robustness of the V‐TMDI is further evaluated by comparison with a traditional V‐TMD. Finally, time‐history analyses of a multistory building subjected to earthquake excitations are performed to confirm the efficiency of the proposed approach. The results indicate that, compared with the fixed‐floor structure (FS), the maximum roof displacement of the main structure, the first‐story interstory drift, and the absolute acceleration of the top floating floor slab in the FFS with V‐TMDI are reduced by approximately 53%, 50%, and 67%, respectively. Moreover, compared with a conventional FFS, the V‐TMDI reduces the peak relative displacement of the top‐floated floor slab with respect to the main structure by approximately 50%.
The bottom story of modern buildings is often left as an open space to accommodate architectural functionality. However, this configuration tends to concentrate large deformations and severe damage in the bottom story under earthquakes, unintentionally forming a soft-story mechanism. To this end, this paper proposes a shape memory alloy (SMA)-based rocking podium structure, which employs a group of rocking columns at the bottom story to isolate the superstructure from experiencing significant damage while preserving the functional open space. The rocking columns are anchored to the foundation and podium using SMA bolts, which are adopted to enhance lateral resistance and dissipate seismic energy without impeding the recentering process. Gap openings are allowed to occur at column ends, forming rocking interfaces that can be closed with the aid of gravity and restoring force provided by SMA bolts. This study investigates the working mechanism of the proposed system and validates the concept through a 1/4-scaled proof-of-concept test on an SMA-based rocking column. A refined three-dimensional solid-element model is developed in ABAQUS to enable detailed local response observation. In addition, a multi-spring model representing a three-story SMA-based rocking podium structure is established in OpenSees to evaluate its seismic performance at the structural level. Incremental dynamic analysis (IDA) is conducted under varying seismic intensity levels. For comparison, a three-story moment-resisting frame (MRF) is also developed in OpenSees.
ABSTRACT Seismic fragility assessment of reinforced concrete (RC) bridges exposed to corrosive environments must reliably capture time‐dependent deterioration impacts. Climate change compounds this challenge through nonstationary temperature and humidity variations that accelerate bridge corrosion. Due to the embedded significant computational cost, prior studies typically develop corrosion‐based seismic fragility models at coarse, discrete time intervals (e.g., every 10 years). In contrast, this study proposes a surrogate‐based, two‐stage analysis framework that enables high‐resolution, time‐continuous seismic fragility assessment of columns and bearings in RC bridges under corrosion deterioration and climate change. In Stage I, normalized deterioration factors are treated as explicit stochastic inputs that modify bridge attributes (e.g., material properties and cross‐sectional dimensions), which are fed into numerical simulations to obtain corresponding bridge seismic demands and capacities. These bridge demand/capacity data are then used to train Gaussian‐process surrogates conditioned directly on the deterioration factors. In Stage II, climate‐change and corrosion scenarios are separately modeled to generate nonstationary, time‐dependent trajectories of deterioration factors, which are propagated through the surrogates to produce continuous, time‐PGA fragility surfaces over the bridge lifetime. Monte Carlo simulations are also integrated to quantify and propagate uncertainties across different modeling steps. The proposed methodology is demonstrated through three‐span continuous RC bridges in Eastern Canada, a region characterized by moderate seismicity and pervasive chloride‐induced corrosion due to heavy use of de‐icing salts. Results show that the framework captures how ground motion intensity, climate change, bridge service life, construction year, and geometric attributes jointly influence high‐resolution evolutions of fragility estimates. The methodology provides an extensible platform for time‐dependent, multi‐hazard fragility and risk assessment and offers valuable insights to support bridge design, inspection, maintenance, and retrofit decision‐making.
ABSTRACT Seismic isolation effectively protects structures by decoupling them from ground motion. However, large isolation displacements may induce pounding against adjacent retaining walls, amplifying displacement and shear demands on the superstructure. Although moat‐wall pounding has been extensively addressed numerically and experimentally, the tangential frictional component at the impact interface has received comparatively less attention, particularly regarding its isolated contribution to floor rotations and perimeter engineering demand parameters in base‐isolated buildings. This study numerically evaluates the effect of friction during moat‐wall pounding on the response of a symmetric base‐isolated prototype building with a 2:1 plan aspect ratio, uniformly distributed identical lead rubber bearings, and no intentional mass or stiffness eccentricity to isolate the rotational effects induced by frictional impact from other sources of torsional response. For the considered prototype, results indicate that including friction has a negligible effect on normal impact forces but significantly increases floor rotations and perimeter demands relative to the center of mass. Frictional impact increases perimeter interstory drifts to approximately twice the value observed at the center of mass, while perimeter accelerations increase by approximately 15% relative to the center. Results show that the frictional component of moat‐wall pounding alone can induce non‐negligible rotational response, highlighting the importance of including friction in simulations of potential impact in seismically isolated buildings.
ABSTRACT The prestressed precast segmental bridge columns (PPSBC) have attracted increasing attention in recent years, however, there is a research gap in the mechanical behavior and seismic performance of PPSBC under combined compression‐bending‐shear‐torsion (C‐B‐S‐T) loads. To address this gap, four identical PPSBC specimens named R‐0, R‐0.16, R‐1.4 and R‐∞ were designed, and corresponding to the applied torsion‐bending moment ratio were 0, 0.16, 1.4 and ∞, respectively. Quasi‐static tests were conducted under combined C‐B‐S‐T loading to investigate the seismic performance of these specimens in terms of failure mode, stirrup strain, hysteresis response, stiffness degradation, ductility, energy dissipation capacity and joint behavior. The influence of torsion‐bending moment ratio on the seismic performance of PPSBC was also explored. The results demonstrated that the failure mode of columns R‐1.4 and R‐∞ exhibited torsional failure accompanied by joint rotation and yielding of stirrups, which was different from the bending failure of columns R‐0 and R‐0.16. The hysteresis curves of columns R‐0 and R‐0.16 were pinched, while those of columns R‐1.4 and R‐∞ displayed spindle‐like and Z‐shaped due to the large torsional load. The torsion‐bending moment ratio had a significant effect on the flexural strength, ductility and self‐recentering capacity of the PPSBC column. When the torsion‐bending moment ratio increased from 0 to 1.4, the flexural capacity of the column decreased by 27.4%, and the displacement ductility coefficient dropped from 6.3 to 3.1. The residual drift ratio of column R‐1.4 was more than 1.0%, and much larger than that of columns R‐0 and R‐0.16. Furthermore, owing to the torsional load, column R‐1.4 exhibited obvious joint rotation and enhanced energy dissipation capacity of the column. This study provides valuable insight for the improvement of the design details in related specifications and promotes the engineering application of PPSBC in accelerated bridge construction.
ABSTRACT This study develops two parallel seismic design frameworks—spectrum based iterative design (SBID) and spectrum based direct design (SBDD)—for free‐standing slender systems subjected to base excitation, founded on the principles of dimensional analysis. The formulation establishes an intrinsic relationship between the two approaches, demonstrating that they are fundamentally interlinked through consistent non‐dimensional parameters governing rocking response. Within the SBID framework, design is achieved through the combined and iterative use of stability coefficient spectra (SCS) and rocking spectra (RS), which together capture acceleration demand and rotational response. In contrast, the SBDD approach employs constant rotation spectra (CRS) to directly relate excitation intensity to a prescribed permissible rotation (implicitly ensuring stability). As such, SBDD obviates the need for iterations and enhances computational efficiency. The spectra are constructed for both idealized pulse‐type and recorded seismic excitations, illustrating their applicability across a range of loading scenarios. The methodology is further extended to bidirectional excitations, where coupled rotations about orthogonal axes are considered. It is shown that the proposed methodology can explicitly incorporate the effects of base flexibility and incidence angles of loading. Overall, the study provides a unified and efficient framework, especially for preliminary assessment and design of rocking systems.
ABSTRACT Integral abutment bridges (IABs) eliminate bearings and joints but transfer seismic demand directly into the surrounding soil, making their response highly sensitive to groundwater conditions and soil–structure interaction. This study presents a 60 g centrifuge testing programme on single‐span IABs designed to isolate the influence of water‐table elevation on seismic behaviour. Water‐table elevation was found to be a dominant control on system response. With a saturated foundation and dry backfill, spread‐footing IABs experienced the largest settlements, approaching 0.30 m, accompanied by co‐seismic ratcheting and minor global rotation. When both foundation and backfill were saturated, early backfill liquefaction shifted the response from kinematic to inertial control. Although settlements reduced to approximately 0.09 m, structural demand increased. Across all spread‐footing tests, shallow saturated backfill zones liquefied while soil beneath the footings remained partially liquefied but significantly softened, explaining large settlements without complete loss of support. Piled abutments effectively limited settlements and suppressed liquefaction near the abutments; however, under saturated foundations they developed higher peak and residual bending moments, indicating redistribution rather than reduction of seismic demand. These results demonstrate that elevated water tables can induce settlement ratcheting in spread‐footing IABs and amplify structural demand in fully saturated systems, highlighting the need for explicit groundwater load cases and SSI‐consistent design in seismic and flood‐prone regions.
ABSTRACT The concentration of damage in the plastic hinge region of conventional reinforced concrete (RC) shear walls poses significant challenges to post‐earthquake functional recovery. To address this, the Friction Plastic‐hinge‐Supported Wall (FPSW) was proposed as a resilient alternative. This system integrates a physical hinge at the base with replaceable friction dampers, isolating inelastic deformation while protecting the upper wall. Although out‐of‐plane actions severely impair conventional RC walls, their impact on FPSWs requires investigation. This study investigates the multi‐axial seismic performance of FPSWs through subassemblage‐level quasi‐static testing under bidirectional loading. The experimental program evaluated out‐of‐plane deformation effects, damper connection details (pin‐connected vs. cross‐plate welded), and construction methods (cast‐in‐place vs. precast). Results demonstrate robust spatial stability; in‐plane strength reduction due to projection efficiency loss remained below 10% even under a significant out‐of‐plane drift of 1/50 rad. Furthermore, cross‐plate welded connections effectively eliminated mechanical slack, thereby enhancing initial stiffness and energy dissipation compared to pin connections. The tests also validated the reliability of the connection between the precast wall and the FPSW base. Finally, an analytical model accounting for out‐of‐plane interaction was developed. The proposed equations for predicting stiffness and strength agree with test results within a 15% margin, establishing a practical basis for local capacity‐design workflows.
ABSTRACT Interstory drift is a primary cause of seismic damage to building elements that span vertically between floors, such as exterior façade walls. To study this issue, a three‐story bypass‐framed cold‐formed steel exterior wall subassembly was incorporated into a recent test of a full‐scale 10‐story mass timber building at the LHPOST6 shake table facility at UC San Diego. A major objective of the test was to investigate seismically resilient details for nonstructural elements. Thus, the subassembly was designed with drift clips and a corner expansion joint to prevent interstory drift‐induced seismic damage. This paper discusses the design, detailing, and performance of the subassembly during the shake table test program. Overall, the drift clip system was found to be effective at reducing wall drifts as intended, and the expansion joint prevented corner damage entirely. However, binding of the drift clips was observed, preventing the wall from sliding freely as assumed during design. One result of this binding was that screw pullout occurred at many clip connections on the uppermost floor over the course of repeated earthquake excitations. Ultimately, damage to sheathing, windows, and exterior cladding was avoided altogether despite connection pullout. Lessons learned offer valuable insight toward improving the design and detailing practice of similar assemblies being considered for implementation.
ABSTRACT In this paper, a first‐story‐rocking system (FSRS) with gravity frame which is a seismic resilient dual lateral system was investigated. Among them, rocking frame with bilinear elastic rocking is expected to protect the upper moment resisting stories through first story rocking; Gravity frame with low‐damage joints served as a seismic resilient component that collaborates with rocking frames to optimize global stability and control the maximum displacement. As a part of the RObust BUilding SysTem (ROBUST) collaborative China‐New Zealand program, a full‐scale 3‐story FSRS with gravity frame was designed. A series of shaking table tests were conducted to evaluate the dynamic behavior and seismic performance of the FSRS with gravity frame. The test results indicated that the tested building exhibited a longer instantaneous period under stronger excitations while the fundamental period identified by the white noise remained constant. The maximum inter‐story drift ratio satisfied the limit of the current Chinese code for seismic design and the residual displacement was negligible. Horizontal vibration of the upper stories was well controlled, benefiting from the first‐story rocking motion. Moreover, the restraining effect of the composite floor and gravity frame played a crucial role in mitigating the inter‐story drift concentration in the first rocking story and the torsional response in the upper stories. The experimental results not only validated the expected excellent seismic performance of the resilient dual lateral system but also provided benchmark full‐scale data for further analyses of numerical models and design methods.
A first-generation three-dimensional (3D) viscoelastic fluid damper (VED) consists of a cylindrical piston immersed in a vessel containing a highly viscous fluid. It dissipates energy through shearing, tensile, and compressive deformations of the fluid as the piston moves in the horizontal and vertical directions. To characterize the dynamic response of the damper for vibration and seismic isolation applications, four 3D VEDs and their fluids were tested in 1989. The same four VEDs were disassembled and retested in 2025 after 36 years of storage in a basement. Rheological testing of the fluids and mechanical testing of the VEDs, conducted using the 1989 protocols, revealed no meaningful change in either the fluid properties or the force-displacement hysteretic response. These findings demonstrate the long-term stability of this VED and fluid, supporting its use for vibration and seismic isolation.
