Seismic fragility, loss and resilience provide a rational basis for decision making in new construction/retrofitting. The inter-storey-isolation (ISI) is a relatively recent seismic vibration control technology for taller buildings. The isolation bearings are placed at an intermediate storey to isolate the upper storey block (USB), which also acts as a non-conventional tuned mass damper (TMD) to the lower storey block (LSB) to reduce the vibration. This study presents the seismic fragility, total expected annual loss ratio (TEALR), the life cycle cost (LCC) and the resilience index (RI) for buildings with ISI. The ISI is shown to considerably reduce the seismic fragility, TEALR and LCC and enhances the RI. Alternative building frames and high damping rubber bearings (HDRBs) are considered to be subjected to a suite of near fault, pulse type ground motions. The reduction in seismic fragility by the ISI system is shown first; followed by the reduction in the TEALR/LCC and enhancement of the RI in respect to the pertinent damage scenarios. A functionality recovery approach is adopted while estimating the RI. These improvements are shown to be maximized by a sufficiently high (nearly 100%) mass ratio (ratio of mass of the upper storey block to the lower storey block) and higher level of viscous damping (e.g. 20%) in the HDRBs. Not only the structural damage(s) but the non-structural and economic damage(s) are also noted to be prominent. Best performances are observed under moderate seismic hazard level but diminishes gradually for extreme hazard, owing to the reduced efficiency of isolation and de-tuning by the incipient nonlinearity.

The optimal performance of the Adaptive Negative Stiffness Device (ANSD) assisted building system has been proposed to mitigate the seismic responses of 14-story building. In the proposed implementation, the building block above the ANSD-augmented story imparts the effect of a non-conventional Tuned Mass Damper (TMD) (with large mass ratio) on the lower block and is simultaneously imparted with the isolation effect due to ANSD induced flexibility. The ANSD composed of viscous damper in addition to their negative stiffness thereby helps in dissipating the input energy and controls the large displacement in the NSD. The optimal parameters are derived based on the optimal tuning and damping ratio obtained from a state-space analysis, considering non-classical damping. To check the efficacy, non-linear time-history analysis are performed subjected to a number of ground motions (from the SAC project) representing varying degree of hazard levels. Statistical analysis reveals that the proposed system is effective in reducing seismic responses compared to its uncontrolled counterpart.

Inter Storey Isolation (ISI) shows promise for seismic vibration control in relatively tall buildings. With proper design, an ISI system isolates the upper storey block (USB) and emulates the effect of a nonconventional Tuned Mass Damper (TMD) on the Lower Storey Block (LSB) to reduce the seismic responses considerably. The vulnerability of conventional Base Isolation (BI) under pulse type motions was reported in the past. This study demonstrates the adverse effect of pulse type motions on the performance of ISI systems. An inclusive set of building configurations and bearing typology for the ISI system are employed and are subjected to two suites of unidirectional pulse and non-pulse type ground motions pertaining to varying hazard levels. Extensive nonlinear dynamic analysis of the frame-ISI systems are carried out. Representative statistics of the pertinent responses from each suite are contrasted to demarcate the effect of pulse type motions. The pulse type motions are shown to degenerate the efficiency of an ISI system to significantly amplify the seismic demands (and associated uncertainties) by allowing transmission of low frequency components (reminiscent of pulse(s)) to the response time histories. Response-specific amplification factors for the demands are assessed. The FEMA suggested guideline is shown to severely underestimates the bearing displacements, which is potentially dangerous. This deficiency is addressed by suggesting a modification factor in the FEMA formulae. The influence of the pulse period, mass ratio, damping in the bearing and hazard levels on the amplification of demands are discussed. However, this investigation considers a limited number of framing systems and isolation bearings subjected to a limited number of ground motions, which may be expanded in future study.

An optimal Intensity Measure (IM) is key to accurate prediction of the Engineering Demand Parameters (EDPs) in structures subjected to seismic excitations. This study synthesizes a structure-specific, vector-valued IM for assessing the EDPs in Inter-Story-Isolated (ISI) buildings under near-fault (pulse and non-pulse type) ground motions. The synthesis is inspired by the comparable modal masses in the fundamental and another higher (generally second) mode in ISI buildings. The synthesis accommodates the dual mode participation by employing the respective pseudo-spectral accelerations Spa and the spectral shape (‘epsilon’ε) parameters in the proposed IM as components. A suite of pulse and non-pulse type motions are employed for the synthesis and subsequently fitting an IM vs. EDP regression model. Thereafter, the “Efficiency” and “Sufficiency” analysis are conducted for validation. The EDPs are obtained by non-linear dynamic analyses on alternative building frames with High Damping Rubber Bearing (HDRB) based ISI systems. A Principal Component Regression (PCR) is employed for accommodating the multi-collinearity in the IM. The choice of the Principal Components (PCs) adopts a leave-one-out cross-validation approach. The proposed IM is shown to offer higher Efficiency and Sufficiency compared with the existing non-structure-specific (Peak Ground Acceleration, Velocity, Displacement, Arias Intensity, Cumulative Absolute Velocity, Characteristic Intensity, Specific Energy Density etc.) and structure-specific (Acceleration/Velocity Spectrum Intensity, Housner Intensity, Pseudo-spectral acceleration at fundamental time period etc.) IMs. Higher Efficiency is also noted under the pulse type motions comparing the non-pulse ones. The IM is more efficient in predicting the Inter-Story Drift Ratios (IDRs), Total Drift Ratios (TDRs) than the Peak Floor Accelerations (PFA) and Bearing Displacements (PBD). The proposed IM is shown to be unbiased and robust.

Adaptive Negative Stiffness Device (ANSD) has been developed recently for passive vibration control of structures. ANSD emulates negative stiffness behavior (by exerting force toward the direction of motion) to a structure, so that, the combined structure-ANSD system shows smooth elasto-plastic force-deformation behavior with virtual yielding at target (“engaging”) displacement. The device has been studied analytically and its behavior has been demonstrated experimentally in simply supported bridge model and in Single Degree of Freedom (SDOF) structure considering limited input excitations. However, efficient and cost-effective exploitation of true potential of ANSD deserves further studies. With this being the eventual goal, in this study, we explore the performances of ANSD in seismic vibration control of a tall building by implementing a nonconventional Tuned Mass Damper (TMD) with drift control. In absence of a methodology for choice of ANSD parameters in literature, reported till date, we employ a tuning criteria for nonconventional TMD, on which the drift control is imposed as a constraint, given the special significance of drifts in tall buildings. The criteria of tuning and drift control are shown to be mutually conflicting and an algorithm is presented to address the same. Simplifying assumptions are made to develop the tuning criteria in presence of nonlinearity in ANSD and P−δ nonlinearity in tall building. A Reduced Order Modeling (ROM) approach for the building-ANSD system is developed to facilitate the algorithmic computations. Robustness of our design approach is shown under an acceptable level of detuning of TMD and near fault pulse type motions. Comparative assessment with a conventional design approach is presented to show the improvements. A step by step illustration of the developed methodology is briefly touched on in context of modern performance based approach. The study is a first step toward the possible utility of ANSD in controlling seismic vulnerability of tall buildings.

The present paper deals with the optimum performance of the passive hybrid control system for the benchmark highway bridge under the six earthquakes ground motion. The investigation is carried out on a simplified finite element model of the 91/5 highway overcrossing located in Southern California. A viscous fluid damper (known as VFD) or non-linear fluid viscous spring damper has been used as a passive supplement device associated with polynomial friction pendulum isolator (known as PFPI) to form a passive hybrid control system. A parametric study is considered to find out the optimum parameters of the PFPI system for the optimal response of the bridge. The effect of the velocity exponent of the VFD and non-linear FV spring damper on the response of the bridge is carried out by considering different values of velocity exponent. Further, the influences of damping coefficient and vibration period of the dampers are also examined on the response of the bridge. To study the effectiveness of the passive hybrid system on the response of the isolated bridge, it is compared with the corresponding PFPI isolated bridges. The investigation showed that passive supplement damper such as VFD or non-linear FV spring damper associated with PFPI system is significantly reducing the seismic response of the benchmark highway bridge. Further, it is also observed that non-linear FV spring damper hybrid system is a more promising strategy in reducing the response of the bridge compared to the VFD associated hybrid system.

The seismic response of a benchmark highway bridge isolated with passive polynomial friction pendulum isolators (PFPIs) is investigated and subjected to six bidirectional ground motion records. The benchmark study is based on a lumped mass finite-element model of the 91/5 highway overcrossing located in Southern California. The PFPI system possesses two important parameters; one is horizontal flexibility and the other is energy absorbing capacity through friction. The evaluation criteria of the benchmark bridge are analyzed considering two parameters, time period of the isolator and coefficient of friction of the isolation surface. The results of the numerical study are compared with those obtained from the traditional friction pendulum system (FPS). Dual design performance of the PFPI system suppressed the displacement and acceleration response of the benchmark highway bridge. The dual design hysteresis loop of the PFPI system is the main advantage over the linear hysteresis loop of the FPS. The numerical result indicates that the seismic performance of the PFPI system is better than that of the traditional FPS isolated system. Further, it is observed that variations of the isolation time period and coefficient of friction of the FPS and PFPI systems have a significant effect on the peak responses of the benchmark highway bridge.

The benchmark structure used in this study is the lumped mass finite-element model of 91/5 highway overcrossing located at Southern California. The effectiveness of the non-linear fluid viscous (FV) spring damper on the benchmark highway bridge subjected to six bi-directional ground motion is investigated. A parametric study is carried out to find the optimum vibration period, the damping coefficient and the velocity exponent of the FV spring damper. The methodology of the technique is to achieve adequate energy dissipation by combining the stiffness and viscous damping effect in one system. Combination of a horizontal elliptical hysteresis loops of the non-linear viscous damper plus elastic stiffness of the spring produce a dynamic inclined hysteresis loop, which has no permanent displacement at the end of the excitation. Due to inclined hysteresis loop, non-linear FV spring damper has significantly reduced the responses, such as, base shear, mid-span displacement and especially abutment displacement of the benchmark highway bridge, in comparison with the other control device.