Acceleration-sensitive Nonstructural Components Research Articles

Seismic resilient performance of code-designed, base-isolated slender steel buildings in firm soils

The seismic response of slender base-isolated structures can be significantly compromised during strong earthquakes, as significant tensional forces or uplifts can be demanded to exterior and corner base isolators. Nevertheless, there are few studies published in the literature where the expected seismic response of fully-designed base-isolated buildings according to a given base-isolation code or standard is shown and discussed when subjected to ground motions records related to the design earthquake scenario. In this paper, the authors present the results obtained from the cases of study of four code-designed base-isolated buildings, from 8 to 24 stories in height, with different global slenderness ratios H/L: 2.0, 2.5, 4.0 and 6.0. Subject buildings were assumed to be located at the city of Puebla, Mexico, in firm soil sites. Buildings were designed according to current base-isolation guidelines for the Manual of Civil Works (MOC) using the modal response spectrum analysis method while neglecting the vertical component in the design process. The base isolation system was composed of high-damping rubber bearings (HDRB). The considered structural system above the isolation system was a dual system composed of special concentrically steel braced frames (SCBFs) and special moment steel frames (SMFs). The resulting base-isolated (TI) to fixed-base (Tfb) natural periods ratio for the designed buildings was within the range 2.55 ≤ TI/Tfb ≤ 3.02. Nonlinear dynamic analyses were conducted for the designed buildings when subjected to five strongest pairs of orthogonal ground motions recorded during the September 19, 2017 Puebla-Morelos earthquake, which correspond to the design earthquake scenarios considered in MOC. In addition, the impact of the vertical ground motion component was evaluated for the most critical station. From the obtained results, it can be concluded that for the studied buildings, the modal response spectrum design method was safe enough to achieve resilient seismic designs. Nevertheless, net tensile forces and uplifts were triggered in corner base isolators, particularly for ground motion records which corresponding displacement spectra was close to the code displacement spectra for the target design base-isolated period TI. Tensile forces and uplifts in base isolators were slightly increased when considering the action of the vertical ground motion component of the critical station. In addition, peak accelerations at the floor levels were moderately increased when considering the vertical component, which may have detrimental effects in acceleration-sensitive non-structural components and the shear capacity of floor systems.

Probabilistic floor spectra for fully self-centering structures with flag-shaped hysteretic behavior

Self-centering structures are emerging structural systems developed for enhancing the seismic resilience of building structures by minimizing residual displacements. Various investigations were conducted to study the design methods and seismic performance of self-centering structural systems, but the research on nonstructural performance in self-centering structures is limited. This paper aims to develop the probabilistic floor spectra that can be used for designing the acceleration-sensitive nonstructural components in self-centering building structures under near-fault ground motions. To this end, comprehensive dynamic analyses were conducted to obtain the floor spectra. 320 near-fault ground motions were selected for considering the seismic excitation's uncertainty. The Anderson-Darling test was adopted to estimate the probabilistic distribution of the floor spectra. The test results indicate that the floor spectra follow the logarithmic normal distribution under earthquakes. The effects of the nonlinear properties of primary self-centering structures (including the initial period, hysteretic features, and structural damping) and the damping of the nonstructural components on the median and dispersion of floor spectra were discussed based on the parametric dynamic analysis results. The prediction model of the probability density function of the probabilistic floor spectra for self-centering structures was developed based on the artificial neural network algorithm. The software FloorSpectraNet was developed to facilitate practical applications.

Comparison on seismic resilience of hybrid, isolation, and damping control reinforced concrete frame-shear wall buildings

To investigate the effectiveness of different vibration control methods in realizing seismic resilience of reinforced concrete (RC) frame-shear wall structures, four cases with different control methods were designed, including the damping control building using energy dissipation cladding panels (EDCPs) (RCFSW7-D), isolated building (RCFSW7-I), isolated building with enhanced stiffness of superstructure (RCFSW7.5-I), and hybrid control building using both EDCPs and isolation (RCFSW7-H). The critical seismic responses and resilient performance of four cases were analyzed based on the Chinese code. Maximum inter-story drift ratios (MIDRs) of RCFSW7-I, RCFSW7.5-I, and RCFSW7-H under maximum considered earthquake were 36%, 51%, and 72% lower than that of RCFSW7-D, respectively. Although the stiffness of superstructure of RCFSW7.5-I and RCFSW7-H were approximately identical, the MIDR of RCFSW7-H was 44% smaller than that of RCFSW7.5-I. Meanwhile, the maximum absolute floor accelerations (MAFAs) of three isolated structure under MCE were approximately 70% lower than that of RCFSW7-D. The seismic resilience level of RCFSW7-D was Level 1, which is dominated by the damage of structural components (SCs) controlled by MIDR and acceleration-sensitive non-structural components (ASNSCs) controlled by MAFA. The seismic resilience levels of RCFSW7-I and RCFSW7.5-I successfully increased to Level 2, leading by the effectively control of MAFA and damage of ASNSCs. However, the MIDR was not sufficiently controlled even the stiffness of superstructure was increased. In contrast, hybrid control building significantly reduced both the MIDR and MAFA through the currently utilization of seismic isolation and EDCPs, especially the MIDR and damage of SCs, leading to a seismic resilience level of Level 3.

Seismic resilience analysis of self-centering prestressed concrete frames with generalized flag-shaped hysteretic behavior

To increase the stiffness and energy dissipation of conventional self-centering concrete joints, this paper proposes a self-centering prestressed concrete frame with a generalized flag-shaped hysteretic behavior (GFS-SCPC). First, the working mechanism of the GFS-SCPC joint is clarified, and the key parameters affecting the generalized flag-shaped hysteresis are proposed: the second stiffness ksθ and the energy dissipation ratio βE. Subsequently, the three-dimensional self-centering prestressed concrete frame with flag-shaped hysteretic behavior (FS-SCPC) and GFS-SCPC frames are established, and the time history analysis and incremental dynamic analysis (IDA) method are carried out to compare their seismic performances. Finally, according to the FEMA P-58 specification, the resilience indexes of the frames with different hysteretic parameters are evaluated to clarify the influence of ksθ and βE. The results show that the energy dissipation capacity of the GFS-SCPC frame increases with larger second stiffness ksθ and the energy dissipation ratio βE. The increase of ksθ effectively controls the maximum drift angle and acceleration response of the GFS-SCPC frame, which would reduce the vulnerability of the structure. The main structure of the GFS-SCPC frame remains undamaged after the earthquake, and the loss mainly comes from the damage of the acceleration-sensitive non-structural components of the upper floors. The increase of ksθ can effectively reduce the damage degree of non-structural components and further reduce the resilience indexes, including casualties, repair time and repair cost, while the increase of βE alone does not significantly improve the resilience indexes. Therefore, the proposed GFS-SCPC frame with larger second stiffness has better seismic resilience performance.

Assessing the feasibility of achieving functional recovery goals through seismic retrofit of existing reinforced concrete buildings

Damage from past earthquakes has significantly hampered post-earthquake building function, threatening community resilience, and motivating consideration of functional recovery in building design and assessment. This study examines whether it is feasible to achieve functional recovery in retrofit of existing reinforced concrete buildings, focusing on seven buildings retrofit with various motivations and strategies. The seismic response of these buildings was nonlinearly simulated, and functional recovery was probabilistically assessed. The results show that retrofits targeting life safety may or may not achieve functional recovery goals. Achieving functional recovery depends especially on the reduction of drift demands and collapse probability. However, the acceleration increase associated with many retrofits can increase function loss due to the criticality of acceleration-sensitive nonstructural components if such components are not retrofitted. We also examine other performance metrics, that is, economic losses and immediate occupancy limits of ASCE/SEI 41, showing that these provide imprecise, and in the case of the immediate occupancy conservative, proxies for functional recovery.

Assessment of seismic acceleration demands on nonstructural components in moderately ductile RC frame buildings designed according to NBC 2015

This paper presents an extensive investigation of the seismic demands on acceleration-sensitive nonstructural components (NSCs) attached to reinforced concrete moment-resisting frame buildings with limited ductility and designed according to the National Building Code of Canada. A total of four benchmark structures with varying heights are considered in this study. Linear and nonlinear time-history analyses were performed using artificial ground motions compatible with Montreal site Class C uniform hazard spectra having 2% and 10% probabilities of being exceeded in 50 years. Seismic acceleration demands on NSCs were evaluated by assessing the horizontal height factor Ax, the component dynamic amplification factor Ar, and the component force factor Sp compared with various building code provisions. The overall acceleration demands of NSCs are discussed, and a corresponding optimized Sp profile is proposed to improve the estimation of the seismic force demands on NSCs at the rooftops of buildings located in moderate seismic zones.

Assessment of the effects of non-structural components on the seismic reliability of structures via a block diagram method

Under a specific ground motion excitation, even if structural components all satisfy a target performance level, the serviceability of the structure might get affected by the performance of non-structural components. Although the overall performance of a structure is affected by the performance of both structural and non-structural components, seismic reliability and fragility analyses usually only focus on the structural elements and their load-carrying capacity. The present study aims to assess the influence of the acceleration-sensitive non-structural components on the seismic reliability of the entire structure. The distinguishing feature of the proposed approach is the adoption of reliability block diagrams for the analysis of each structure, allowing for different combinations of damage for structural and non-structural components. Results are shown for 5-, 10- and 15-story buildings, to demonstrate the significant effects of non-structural components on their overall seismic reliability. Such effects prove to be more evident for the lower damage levels, and the higher seismic intensities. It is shown that non-structural components can lead to a reduction of the overall seismic reliability ranging from 22% to 100%, for situations related to the life safety and collapse prevention performance levels, under the effects of the design basis and maximum considered earthquakes, respectively.

Seismic resilience assessment of self-centering prestressed concrete frame with different energy dissipation ratio and second stiffness

This paper presents the effects of two key parameters, energy dissipation ratio and second stiffness, on the seismic performance and resilience of self-centering prestressed concrete (SCPC) frames. The dynamic parametrical analyses under different earthquake intensities and fragility analyses under different performance level have been carried out, the maximum drift (MD) - residual drift (RD) joint probability density method suitable for SCPC structure was proposed, and the damage distribution law of structural members and typical non-structural members was analyzed. The influence of different parameters on the resilience indicators of SCPC framework was studied based on the FEMA P-58 resilience assessment framework. The results indicate that the main structure of the SCPC frame remained intact, while the acceleration-sensitive non-structural components accounted for more than 80% of the total repair cost and repair time. Increasing the second stiffness could reduce the high-order modal effect of the SCPC structure response and the loss in the upper part of the SCPC frame. Increasing energy dissipation ratio could reduce the maximum response of the structure and improve the building resilience. When the energy dissipation ratio was increased from 0.2 to 0.8, the repair cost and repair time were decreased by 13.1% and 17.2%, respectively, under maximum considered earthquake (MCE), and the residual displacement of the structure was still within the re-centering limit of 0.2%.

Feasibility of a nonlinear spectral approach for peak floor acceleration of multi-story bilinear hysteretic buildings

To protect the acceleration-sensitive non-structural components in a multi-story building, a proper seismic design of them against the peak floor acceleration (PFA) is needed. The PFA, therefore, should be estimated in advance. To efficiently estimate the PFA of multi-story buildings at the inelastic stage, a nonlinear modal combination approach is provided in this study. First, for the single-story building (single-degree-of-freedom system), a PFA spectral ratio δ, defined as the ratio between the inelastic PFA and the elastic spectral amplitude, is proposed to measure the nonlinear reductions in PFA. A series of time history analysis (THA) revealed that there is a dependable relationship between the PFA spectral ratio δ, the strength reduction factor R, the post-yield stiffness ratio α, and the period T of the structure. The scatter of δ is notably smaller than the ductility demand, showing the good feasibility of a δ-R-T-α relationship for predicting δ. Second, for the multi-story building (multi-degree-of-freedom system), the floor acceleration is decoupled in the modal space, the contribution of each mode to the elastic PFA is multiplied by δ to account for the nonlinear reduction in PFA at the inelastic stage. Here δ can be determined by an appropriate δ-R-T-α relationship, while R and α are determined via a modal pushover analysis. The modified modal contributions are combined via the complete-quadratic combination (CQC) rule, forming the inelastic CQC approach. The PFAs of some 2-, 5-, and 8-story building structures with different degrees of nonlinearity are computed via the THA and the inelastic CQC approach. Results demonstrate the satisfactory accuracy of the latter. Notably, the effects of nonlinearities associated with the higher-order modes on the nonlinear PFA are well considered in the inelastic CQC, thus the un-acceptable over-estimations of the inelastic PFA, which occurs in conventional methods, are avoided.

Seismic response of acceleration-sensitive nonstructural components in a Thin Lightly-Reinforced Concrete Wall (TLRCW) mid-rise building

Experience in recent earthquakes has shown that Non-Structural Components (NSCs) in multi-story buildings exert a significant influence on economic losses. Different topics about the seismic behavior of NSCs have been investigated; however more research is needed in several areas such as the type of building structural system and the type of seismic hazard. Motivated by this observation, floor accelerations in a novel structural system, namely the Thin and Lightly-Reinforced Concrete Wall (TLRCW) building, are examined in this paper. The TLRCW system comprises thin and slender walls with deficient or nonexistent confinement at the wall edges, and web reinforcements made of welded-wire mesh with limited ductility. In this study, seismic demands on NSCs in a TLRCW building are analytically calculated and compared with current characterizations included in earthquake-resistant building codes and presented in the literature. Comparisons are performed in terms of peak floor accelerations, floor spectra, inelastic displacement ratios, and the still not completely characterized inelastic absolute acceleration ratios. Influence of elastic and inelastic behavior of NSCs as well as of the structure is also evaluated. Since the TLRCW system is becoming common in some South American countries prone (in part or wholly) to subduction earthquakes, possible influence of the type of seismic hazard (i.e., crustal earthquakes or subduction earthquakes) is accounted for. It was found that, under design-level seismic demands, floor accelerations can be very large even though the structure undergoes a significant level of inelastic excursion. It was also found that floor accelerations are, for the most part, reasonably approximated by current characterizations. Finally, the type of seismic hazard has a negligible qualitative influence on floor accelerations (only minor quantitative differences were found).

Inelastic acceleration ratio of structures under pulse-like earthquake ground motions

The Inelastic Acceleration Ratio (IAR) is a useful index for the direct computation of the maximum inelastic acceleration from the corresponding elastic one. This parameter can be used for evaluating nonlinear response of structures, as well as acceleration-sensitive non-structural components. In this paper, constant strength spectra based on IAR are proposed under pulse-like earthquake ground motions. Moreover, the effects of structural parameters, including elastic vibration period normalized by the pulse period, the strength modification factor, viscous damping ratio and the hysteretic rule are examined on this index. The results reveal that the impacts of these parameters are significant for low values of the normalized period, when T/Tp < 1, and ξ = 0.05. Furthermore, analytical equations are introduced to estimate IAR as a function of the normalized elastic vibration period and the main structural characteristics, which can be used for the seismic evaluation of the acceleration-sensitive structures and of the non-structural components.

Demands on acceleration-sensitive nonstructural components in special concentrically braced frame and special moment frame buildings

This study investigates demands on acceleration-sensitive nonstructural components (NSCs) in code-compliant Special Concentrically Braced Frame (SCBF) and Special Moment Frame (SMF) structures. Previous studies have highlighted that the assumption of ASCE 7-16 for the ratio of Peak Floor Acceleration (PFA) to Peak Ground Acceleration (PGA) is overly conservative. In most previous studies, the results were based on generic analytical models with non-deteriorating structural behavior or recorded data from instrumented buildings subjected to ground motions that were significantly weaker than the design-level earthquakes. This study evaluates the acceleration demands on NSCs in 11 archetype buildings modeled using advanced techniques. The ground motions used elicit inelastic response in the frames at the level expected by ASCE 7-16 compliant designs. The study examines the effect of the ratio of NSC period to structural period, NSC damping ratio, and NSC vertical location on these demands. Results of this investigation are compared with the provisions of ASCE 7-16 and the recommendations of the recently completed effort by the Applied Technology Council 120 project (ATC-120), which are the basis for the seismic design requirements for nonstructural components in the forthcoming ASCE 7-22 standard. Equations for the PFA/PGA ratio and NSC amplification factor, which account for the dynamic characteristics of the buildings, are developed based on regression analysis of the generated data. Results of the analyses indicate that the formula recommended by ATC-120 for estimating PFA/PGA along the height of the structure, which includes building nonlinearity effects through a constant building ductility reduction factor, overestimates floor accelerations at the top floors but underestimates them in the lower floors of the archetypes considered. At the same time, results show that the NSC seismic design force equation recommended by ATC-120 is conservative for the SCBF archetypes, while it underestimates the NSC force demands in the SMFs.

Evaluation of damping modification factors for floor response spectra via machine learning model

In the last few decades, the seismic performance of Non-structural components (NSCs) has been a subject of extensive research. The dynamic behavior of NSCs, can cause damage to buildings, resulting in severe financial losses, injuries, and death. The necessity of assessing the seismic demand on NSCs in seismic design cannot be overstated. Current building regulations include overly simple relationships for defining design inertia forces on non-structural acceleration-sensitive components. Building code formulations are frequently unable to forecast realistic accelerations of NSCs. Floor Response Spectra (FRS) approach determines the seismic demands on acceleration-sensitive NSCs better. In this study, elastic FRS at a floor level of a linear single-degree-of-freedom system is investigated under near-field earthquakes. Damping modification factors (DMFs) for the elastic FRS are calculated for the various damping ratios of the NSCs ranging from 0.1% to 30%, the tuning ratio (i.e., the ratio between the NSC vibration period, Ts, to the building structural period, Tp) ranging from 0.1 to 3, and the building structural period ranging from 0.5 s to 4 s with 0.5 s interval. Also, artificial neural networks (ANNs) were employed to generate an empirical expression to determine the DMFs for elastic FRS. The DMFs were observed to be highly dependent on the building structural period, damping ratio and the tuning ratio of the NSC. The proposed expression is then compared with the existing relations in the literature. The expression is further validated by comparing the predicted DMFs to those obtained from time-history analysis with different ground motion records used to build the model.

Estimation of Floor Response Spectra for Self-Centering Structural Systems with Flag-Shaped Hysteretic Behavior

Spectral floor-acceleration demands are necessary for the seismic design of acceleration-sensitive non-structural components (NSCs). Existing studies to estimate floor response spectra (FRS) using empirical equations are based on elasto-plastic and stiffness degrading hysteretic behavior of the primary structure. In the present study, the FRS for self-centering (SC) structural systems with flag-shaped hysteretic behavior under far-fault ground motions are investigated. The FRS and dynamic amplification factor (DAF) are obtained from nonlinear response history analysis (NLRHA) of SC structural systems with flag-shaped hysteretic behavior. An equation to estimate the FRS is proposed and verified by carrying out NLRHA using a different set of far-fault ground motions. The equation to estimate FRS is shown to predict floor acceleration demands with very good accuracy.

Floor displacement-based torsional amplification factors for seismic design of acceleration-sensitive non-structural components in torsionally irregular RC buildings

In this study, the effects of inherent building torsion on the seismic response of acceleration-sensitive non-structural components are investigated. To achieve this objective, a group of elastic torsionally irregular step-back reinforced concrete moment-resisting frame buildings are analyzed under bi-directional earthquake excitations. The floor torsional amplification factors, defined as the ratio between the floor spectral ordinate at the flexible/stiff edge to the floor spectral ordinate at the center of rigidity, are obtained as a function of the tuning ratio for varying damping ratios of non-structural components. The correlations of the peak torsional amplification factors at different floors for the rigid and flexible non-structural components are studied with their floor displacement-based torsional irregularity indices, recommended in the national building codes of the United States and India. It is observed that the torsional amplification factors are building characteristics and tuning ratio-dependent. These torsional amplification factors are further observed to be well-correlated with the corresponding floor displacement-based torsional irregularity indices for both the rigid and flexible non-structural components. Contrarily, the torsional amplification factors for the very flexible non-structural components tend to unity and are thereby observed to be independent of the characteristics of both the building and the non-structural components. Simplified and numerically validated, floor displacement-based models are proposed to compute the torsional amplification factors, which can be used in aggregation with the existing codes to design acceleration-sensitive non-structural components in torsionally irregular buildings.

Seismic demands of structural and non-structural components in self-centering precast concrete wall buildings

Self-centering (SC) precast concrete wall structures have been developed as an earthquake resilient structural system characterized by low structural damage and controllable residual drift. Despite the superior structural performance, harmonizing to seismic performance between structural and non-structural components is expected to be considered for further comprehensive performance assessment. This paper extensively evaluates the seismic demands of structural and non-structural components, especially for those sensitive to accelerations in SC precast concrete wall structures. Factors considered include building heights, earthquake ground motion types and intensities, energy dissipation, as well as base rocking, and impact against the foundation. The seismic demands of SC precast concrete walls are firstly compared with conventional reinforced concrete (RC) walls by nonlinear time history analysis (NTHA) in terms of displacement and acceleration responses. Then, attention is focused on investigating the dominant factors for the seismic demands of acceleration-sensitive non-structural components in SC precast wall structures through floor response spectrum analysis and parametric analyses. The results confirm that the SC precast walls exhibit excellent lateral response, especially with limited residual drifts. However, for the floor acceleration response, which is highly related to the demands of non-structural components, the results show that higher modes have a critical influence on SC precast wall structures. It also indicates that the floor acceleration response of SC precast wall structures is strongly influenced by the location of the story levels but not strongly influenced by the base rocking impact and energy dissipation capability.

Floor acceleration response spectra of elastic reinforced concrete frames

Nonstructural components are the members attached to building structures to realize and maintain the building functionality. Although they are not intended to bear loads, nonstructural components could be subjected to earthquake loading that may lead to failures. The floor acceleration response spectrum is used as the input for the seismic design of acceleration-sensitive nonstructural components. However, it is time-consuming to conduct time-history analyses to generate accurate floor response spectrum for a typical building, and it is therefore not convenient for seismic design. To avoid the computational cost of time history analyses, this study proposes a simplified method based on the modification of an existing methodology for the generation of floor acceleration response spectrum. The first step is to conduct a modal analysis to determine the modal properties of the supporting structure. Then, the floor response spectrum of each mode of the supporting structure is generated and combined based on modal combination rules to obtain the floor response spectrum of the supporting structure. The component dynamic amplification factors that reflect the amplification effects of the nonstructural components on the floor acceleration responses are important for the generation of floor response spectra. Three reinforced concrete moment-resisting frames are designed to evaluate the component dynamic amplification factors for which an empirical fitted formula is proposed to generate more accurate floor response spectrum for structures designed in accordance with Chinese seismic design codes. The results calculated by time history analyses are used to validate the proposed amplification factors and demonstrate the feasibility and effectiveness of the newly modified method.

Seismic performance of self-centering glulam frame with friction damper

The self-centering structure has good recentering capacity and seismic performance, and its application in timber structures can significantly reduce the residual displacement of the structure. In this paper, the seismic performance of the self-centering glulam (SCG) frame with friction damper (FD) is studied from three aspects: the test of beam-to-column joint, the seismic design method of frame and the dynamic time history analysis of frame. Firstly, a low-cycle reversed loading test was carried out on the glulam beam-to-column joint with the initial post-tensioned (PT) force as a variable. According to the test results, the beam-to-column joint showed both good self-centering capacity and hysteretic behavior. Then, a simplified performance-based seismic design method of the FD-SCG frame was proposed, with a 6-story self-centering frame structure as the design example. The nonlinear dynamic time history analysis and parametric analysis of the frame were conducted by the OpenSees. The dynamic time history analysis proves from both the global and local response that the frame has a good seismic response under the design basis earthquake (DBE) and the maximum considered earthquake (MCE), while the frame also has safety reserve under the MCE level. The average values of the maximum inter-story drift of the frame under the DBE and MCE levels are 0.31% and 1.92%, respectively, which are less than the design limitation. The parametric analysis results showed that the increase of the PT tendons number, that is, the increase of the second stiffness can reduce the damage of acceleration-sensitive nonstructural components.

Effect of structural characteristics on damping modification factors for floor response spectra in RC buildings

Floor response spectra (FRS) are used to compute the design floor accelerations for seismic design of acceleration-sensitive non-structural components (NSCs) in a building. In the present study, the elastic FRS at different floor levels are investigated for a set of linear and nonlinear models of both low- and mid-rise reinforced concrete (RC) frame structures. The damping modification factors (DMFs) for the elastic FRS are derived for seven different damping ratios of the NSC's (i.e. 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, and 10%), and six different levels of inelastic response in the building structure. It is observed that DMFs for the elastic FRS are influenced by both NSC and building structure characteristics. The factors affecting the DMFs for the elastic FRS include the damping ratio of the NSC, the tuning ratio (i.e. the ratio between the period of vibration of the NSC, Ts, to the fundamental period of vibration of the building structure, T1), the modal periods (T1 and T2), and the level of the building structure's inelasticity. Conversely, the vertical location of the NSC in the building structure does not affect DMFs significantly. Further, in the case of a tuned response of the NSC, the DMFs for elastic FRS are significantly higher for NSC damping ratios less than 5% and lower for NSC damping ratios greater than 5%, than those conventionally used for the elastic ground response spectra (GRS). This is true for the elastic response as well as for low levels of inelasticity in the building structure. On the other hand, at high levels of the building structure's inelasticity, the DMFs for elastic FRS approach to the conventional DMFs derived for the elastic GRS. Considering these observations, a design-oriented multilinear model is proposed to compute DMFs for the elastic FRS, accounting for the specific characteristics of the NSC (i.e. the period and the damping ratio of the NSC) and the building structure (i.e. the modal periods and the level of the inelasticity). The proposed model for computing the DMFs for elastic FRS is validated by comparing the model predictions with those obtained by time-history analyses, using a different RC frame building and an entirely different suite of ground-motion records than those that were used to develop the proposed model. The proposed model to compute DMFs for the elastic FRS can be used with both the current code-based and the performance-based seismic design of NSCs located in the inelastic building structures.

Floor response spectral analysis and fitting of museum building before and after isolation

Floor response and design spectra of a museum building before and after isolation are studied; these are used for estimating the response and seismic design of acceleration-sensitive non-structural components. First, two finite-element models of the building before and after seismic isolation are established and verified through ambient vibration tests. Second, seven earthquake motions are chosen to analyse the models; differences between floor response curves and earthquake motions are analysed based on peak acceleration and frequency spectra. Finally, taking the floor response curves as input, the floor acceleration response spectra before and after isolation are calculated, and the design spectra are fitted. Analytical results demonstrate that the dynamic characteristics of the finite-element model agree well with test values, and peak acceleration of the isolated structure is around 75% lower than that of the non-isolated structure. The predominant frequency of the floor response curves is consistent with the natural frequency of the structure. Moreover, the floor acceleration response spectra are influenced by the earthquake motions and the structures, which reflect the characteristics of both. The floor design response spectra are divided into different sections and mathematical formulas are developed. The findings could be applied to the seismic protection design of non-structural components.