Seismic Response Of Nonstructural Components Research Articles

Seismic response of non-structural components in multi-storey steel frames

This paper investigates the elastic and inelastic seismic response of non-structural components in multi-storey steel moment framed structures and derives predictive relationships for their displacements and spectral accelerations. Within 38 primary structural steel frames, non-structural components characterised by various periods and strength reduction factors, are modelled as single-degree-of-freedom systems which are fixed to individual floors. The primary structures are three, five, and seven-storey steel moment-resisting frames, designed according to the provisions of Eurocode 8. Detailed nonlinear time history analyses are conducted, employing a large set of 100 ground motion records from both far-field and near-field sources. These records are scaled to two distinct levels to simulate the response of primary structures in both elastic and inelastic states. The influence of the ground motion type and the inelasticity level in the non-structural components is examined in detail. The sensitivity to strain hardening and viscous damping considerations is also assessed and discussed. Based on the results, representative relationships for predicting the inelastic displacement ratios are proposed. In addition, various provisions stipulated in European design guidance for determining the spectral accelerations are critically evaluated and improvements are suggested with due consideration for the inelasticity of both the non-structural components and the primary structures.

Influence of the anchorage shear hysteresis on the seismic response of nonstructural components in RC buildings

This article presents a numerical study on the influence of the anchorage shear hysteresis on the seismic response of nonstructural components (NSC) connected to multi-storey reinforced concrete (RC) buildings, and of the anchorage itself. To cover a variety of different types of shear hysteresis shapes, this contribution considered the experimental results obtained for five types of post-installed anchors. The results were used for calibrating the hysteresis model of the anchorage connecting an ideal NSC with rigid fixture and a 12-storey RC building host-structure. Using a suit of 40 earthquake records and assuming a single NSC at each storey level anchored by a single fastener, a series of non-linear dynamic analyses of the structure-fastener-nonstructural system was carried out. The results showed significant differences in terms of maximum acceleration and force of the NSC and anchorage, respectively, depending on the type of anchor. These seismic demands were sometimes larger than those required by the reviewed code provisions for rigid NSC, but also for the most restrictive code-case for flexible NSC. The results presented different amounts of scatter, mostly related to the size of the annular gap and of the loading stiffness of the anchorage. It is shown that the maximum force achieved by the anchorage is directly related to the peak relative velocity of the NSC within the gap region. It was concluded that the shape of the shear hysteresis of the anchorage highly influences the response of the NSC and the anchor itself and should not be neglected in practice.

Influence of a Soft Story on the Seismic Response of Non-Structural Components

Multi-story, reinforced-concrete (RC) building structures with soft stories are highly vulnerable to damage due to earthquake loads. The soft story causes a significant stiffness irregularity, which has led to numerous buildings collapsing in previous seismic events. In addition to the structural collapse, the failure of non-structural components (NSCs) has also been observed during past earthquakes. In light of this, this study investigates the effect of a soft story and its location on the seismic behavior of a supporting building and NSCs. The soft story is assumed to be located on the bottom (ground), middle, and top-story levels of the considered building models. Story displacements and inter-story drift ratios are evaluated to assess structural behavior. The floor response spectra and the amplification effects of NSC on the floor acceleration responses are studied to understand the behavior of NSCs. The analysis results revealed that the bottom soft story exhibits a considerable vertical stiffness irregularity, and its position substantially affects the floor response spectra. The amplification in the floor acceleration response was found to be greater at the soft-story level. This study reported that middle soft-story buildings exhibit the most remarkable amplification in the component’s acceleration. Finally, peak floor response demands are compared with the code-based formulation, and it is found that the code-based formulation’s linear assumption may lead peak floor response demands to be underestimated or overestimated.

Seismic design of non-structural components mounted on irregular reinforced concrete buildings

The seismic response of non-structural components (NSCs) attached to irregular reinforced concrete (RC) multi-storey buildings is underestimated by current European design provisions. This paper presents a new design model for NSCs, accounting for the effect of torsion and seismic capacity of an irregular RC primary structure (P-structure). The proposed model is a modification of the current Eurocode 8 (EC8) model for the acceleration amplification factor of NSCs. It is based on the results of some 5000 nonlinear dynamic finite element analyses conducted on thirty-three building cases. The finite element analyses covered a wide range of parameters including plan layout, seismic capacity, fundamental vibration period, total height, floor rotation, ground type and eccentricity ratio. The proposed model has been demonstrated to be an improvement over EC8 model, especially for NSCs mounted on the flexible side and in tune with the fundamental vibration period of a P-structure.

Evaluation of the Floor Acceleration Response Spectra of Numerical Building Models Based on Recorded Building Response Data

ABSTRACT The recorded floor acceleration responses of a wide variety of instrumented buildings are used to evaluate the findings of previous numerical studies regarding the effect of different parameters on the seismic response of nonstructural components (NSCs). These relevant parameters include, but are not limited to, the lateral force resisting system, modal periods, and inelastic behavior of supporting building; the intensity and frequency content of ground excitation; damping ratio, tuning condition, and location of NSCs. The data from instrumented buildings are also used to validate relationships proposed by the first two authors for the estimation of NSC damping modification factor.

Methodology for seismic risk screening of existing buildings in Canada: Non-structural component scoring system

The National Research Council of Canada (NRC) has recently developed a Semi-Quantitative Seismic Risk Screening Tool (SQST) to supersede the 1993 NRC Manual for Screening of Buildings for Seismic Investigation. The proposed screening tool incorporates a methodology for estimating global seismic risk of existing buildings associated with failure of their non-structural components. The methodology assesses global seismic risk using a qualitative yet comprehensive scoring system. The scoring system consists of a global non-structural component score and acceptable threshold scores. The global score is based on the most critical components. It combines a basic score with score modifiers for key parameters affecting the seismic response of non-structural components. The acceptable threshold score is based on the building’s consequence of failure, the building’s importance category, and the component factor. The scoring system is calibrated to be consistent with the seismic risk acceptance criteria previously developed for preliminary seismic risk screening of existing buildings, based on Canadian seismicity, building age, remaining occupancy time, and consequences of failure.

Seismic demands on nonstructural components anchored to concrete accounting for structure‐fastener‐nonstructural interaction (SFNI)

SummaryThis paper investigates the influence of the hysteretic shear behavior of postinstalled anchors in concrete on the seismic response of nonstructural components (NSCs) using numerical methods. The purpose of the investigation is to evaluate current design requirements for NSC and their anchorage. Current design guidelines and simplified methods, such as floor response spectra (FRS), typically approach the dynamics of the structure‐fastener‐NSC (SFN) system using simplified empirical formulae. These formulations decouple the structure from the NSC and neglect the behavior of the anchor connection, with the assumption of full rigidity. There is a lack of knowledge on the complex interaction between a host structure, the fastening system, and the NSC, herein referred to as structure‐fastener‐nonstructural interaction (SFNI). More specifically, it is important to investigate whether and how the actual hysteresis shear behavior that takes place in the anchorage could alter the seismic response of the SFN system and its components. Herein, the results of extensive nonlinear dynamic analyses (NLDA) with different models for the anchorage force‐displacement relationship are presented and compared with those obtained with FRS procedures and current code provisions. The anchor models include (a) linear‐elastic, (b) bilinear, and (c) a recently developed hysteresis rule. The results of the NLDA showed that the first two approaches are not able to reflect the behavior of an anchor loaded in dynamic shear. Moreover, when using the more refined hysteresis model, it appears that current code provisions might underestimate the component and anchor shear amplification factors for rigid NSC fixed to the host structure through anchors.

An Overview of the Current Code Provisions on the Seismic Response of Acceleration-Sensitive Non-Structural Components in Buildings

The seismic response of non-structural components in civil and industrial buildings, often neglected or disregarded in the common design/assessment practice, revealed its dramatic relevance in recent seismic events that resulted in significant damage observed in the wide class of “objects” referred to as “non-structural components” (e.g., partitions, masonry infill, suspended ceilings, finishing, specific equipment and so on. The observed damage, sometimes leading to collapse of these components and even loss of human lives, highlighted the lack of knowledge that still affects both analysis procedures and design/assessment methods currently adopted for analysing their seismic response. This paper is mainly intended at providing readers with an overview of both the historical development and the current state of the formulations adopted by codes and standards for evaluating the maximum accelerations induced by seismic shakings on non-structural components. The difference among these formulations is firstly outlined and the predictions based on the most up-to-date codes are compared with the results of a wide parametric analysis based on a 2DOF system, intended at simulating the coupled response of both main structure and non-structural component. This parametric comparison shows that the current formulations are not fully capable of reproducing the effect of the interaction between main structure and non-structural components

Seismic response of nonstructural components considering the near-fault pulse-like ground motions

This paper investigates the response of nonstructural components in the presence of nonlinear behavior of the primary structure considering the near-fault pulse-like ground motions. A database of 81 near-fault pulse-like ground motions is used to examine the effect of these ground motions on the response of nonstructural components. For comparison, a database of 573 non-pulse-like ground motions selected from the PEER database is also employed. The effects of peak ground velocity (PGV), maximum incremental velocity (MIV), primary structural degrading behavior and damping of nonstructural components are evaluated and discussed statistically. Results are presented in terms of amplification factor which quantifies the effect of inelastic deformations of the primary structure on subsystem responses. The results indicate that the near-fault pulse-like ground motions can significantly increase the amplification factors of nonstructural components with primary structural period and the magnitude of increase can reach 17%. The effect of PGV and MIV on amplification factors tends to increase with the increase of primary structural ductility. The near-fault pulse-like ground motions are more dangerous to components supported by structures with strength and stiffness degrading behavior than ordinary ground motions. A new simplified formulation is proposed for the application of amplification factors for design of nonstructural components for near-fault pulse-like ground motions.

Seismic response of non-structural components attached to reinforced concrete structures with different eccentricity ratios

This paper presents average numerical results of 2128 nonlinear dynamic finite element (FE) analyses of lightweight acceleration-sensitive non-structural components (NSCs) attached to the floors of one-bay three-storey reinforced concrete (RC) primary structures (P-structures) with different eccentricity ratios. The investigated parameters include the NSC to P-structure vibration period ratio, peak ground acceleration, P-structure eccentricity ratio, and NSC damping ratio. Appropriate constitutive relationships were used to model the behaviour of the RC P-structures. The NSCs were modelled as vertical cantilevers fixed at their bases with masses on the free ends and varying lengths so as to match the vibration periods of the P-structures. Full dynamic interaction was considered between the NSCs and P-structures. A set of seven natural bi-directional ground motions were used to evaluate the seismic response of the NSCs. The numerical results show that the acceleration response of the NSCs depends on the investigated parameters. The accelerations of the NSCs attached to the flexible sides of the P-structures increased with the increase in peak ground acceleration and P-structure eccentricity ratio but decreased with the increase in NSC damping ratio. Comparison between the FE results and Eurocode 8 (EC8) predictions suggests that, under tuned conditions, EC8 provisions underestimate the seismic response of the NSCs mounted on the flexible sides of the plan-irregular RC P-structures.

Seismic response of nonstructural components supported by a 4-story SMRF: Effect of nonlinear soil–structure interaction

Previous studies have demonstrated that nonlinear material behavior of a building may lead to an increased seismic response of supported nonstructural components in comparison with the case when a linear material model is considered for the same building. It has also been demonstrated that this amplification of response of a nonstructural component due to nonlinear behavior of the building is more prominent when the frequency of the component is close to one of the higher modes of the building and the component is supported at a lower floor of the building. Those studies, however, did not consider the nonlinear soil–structure-interaction (SSI) that may occur during a strong earthquake. The present work investigates the effect of nonlinear SSI on seismic response of acceleration-sensitive nonstructural components attached to a four-story steel moment-resisting frame (SMRF). The results of this study show that the effect of nonlinear SSI is indeed beneficial to the response of the nonstructural components mounted on the chosen structure. In fact, if foundation–structure interface undergoes significant nonlinear deformations, the aforementioned response amplification of components due to structural nonlinearity can safely be ignored.

Seismic response of nonstructural components attached on multistorey buildings

SUMMARYThe maintenance of integrity and functionality of nonstructural components during earthquake excitations is of paramount importance since mechanical failure of those systems can have dramatic consequences in terms of property damage and life safety of the buildings' occupants. This paper explores the dynamic response of nonstructural elements attached on multistory buildings with well‐established floor diaphragm action. Depending on the type of support conditions, seismic response of nonstructural components may be controlled either by acceleration or displacement: Nonstructural components that are subjected to uniform support excitation are controlled primarily by the absolute spectral acceleration developing at their point of attachment on the supporting building. On the contrary, seismic response of multiply supported nonstructural components depends primarily on the relative displacements between successive support points that are imposed by the supporting building during lateral sway. These findings are illustrated from the analytical formulation and its solution through time history analysis of the governing dynamic equation of motion of the primary and secondary components of a system modeled using finite elements. The model encompasses the assembly of a multistory building along with a multiply supported gas pipeline network. It is shown that the dependence of the seismic response of nonstructural components may be linked to the deformed shape of the supporting building at the state of its maximum lateral roof displacement, thereby enabling the definition of design procedures for these systems. Copyright © 2014 John Wiley & Sons, Ltd.

Seismic response of nonstructural components in case of nonlinear structures based on floor response spectra method

This paper investigates the response of nonstructural components in the presence of nonlinear behavior of the primary structure using floor response spectra method (FRS). The effect of several parameters such as initial natural frequency of the primary structure, natural frequency of the nonstructural components (subsystem), strength reduction factor and hysteretic model have been studied. A database of 164 registered ground acceleration time histories from the European Strong-Motion Database is used. Results are presented in terms of amplification factor and resonance factor. Amplification factor quantifies the effect of inelastic deformations of the primary structure on subsystem response. Resonance factor quantifies the variation of the subsystem response considering the primary structure acceleration. Obtained results differed from precedent studies, particularly for higher primary structure periods. Values of amplification factor are improved. Obtained results of resonance factor highlight an underestimation of peak values according to current design codes such as Eurocode 8. Therefore a new formulation is proposed.

Effect of Building Nonlinearity on Seismic Response of Nonstructural Components: A Parametric Study

An extensive parametric study is conducted with eight code-designed steel moment-resisting frames and a series of linear and nonlinear single-degree-of-freedom nonstructural components to investigate to what degree, how often, and under what conditions the nonlinear behavior of a building may amplify the seismic response of a nonstructural component attached to it. The study comprises the time-history analysis of each of the considered frames with one of the considered nonstructural components connected to it. In each case, an ensemble of 25 recorded earthquake ground motions is used, alternatively scaling them to three different intensity levels. The study also comprises a comparison between the nonstructural component responses obtained when the supporting structure is modeled alternatively as a nonlinear and a linear system. The influence of the nonstructural component location, nonlinearity, and damping ratio and the relative values of the building and component masses and natural frequencies is investigated. It is found that, in general, the nonlinear behavior of the supporting structures reduces the seismic response of the nonstructural components in comparison with the linear counterparts. In a few cases, however, the nonstructural component response is amplified by a factor that can be as large as 5.2. These cases correspond to components located on the lower building floors, with a natural period equal to the second or third natural period of the building, and subjected to a narrow-band excitation with a dominant period close to the building’s fundamental natural period.