SUMMARY The effects of seismic pounding on the structural performance of a base‐isolated reinforced concrete (RC) building are investigated, with a view to evaluate the influence of adjacent structures and separation between structures on the pounding response. In particular, seismic pounding of a typical four‐story base‐isolated RC building with retaining walls at the base and with a four‐story fixed‐base RC building is studied. Three‐dimensional finite element analyses are carried out considering material and geometric nonlinearities. The structural performance of the base‐isolated building is evaluated considering various earthquake excitations. It is found that the performance of the base‐isolated building is substantially influenced by the pounding. The investigated base‐isolated building shows good resistance against shear failure and the predominant mode of failure due to pounding is flexural. Copyright © 2012 John Wiley & Sons, Ltd.

SUMMARY There is no consensus at the present time regarding an appropriate approach to model viscous damping in nonlinear time‐history analysis of base‐isolated buildings because of uncertainties associated with quantification of energy dissipation. Therefore, in this study, the effects of modeling viscous damping on the response of base‐isolated reinforced concrete buildings subjected to earthquake ground motions are investigated. The test results of a reduced‐scale three‐story building previously tested on a shaking table are compared with three‐dimensional finite element simulation results. The study is primarily focused on nonlinear direct‐integration time‐history analysis, where many different approaches of modeling viscous damping, developed within the framework of Rayleigh damping are considered. Nonlinear direct‐integration time‐history analysis results reveal that the damping ratio as well as the approach used to model damping has significant effects on the response, and quite importantly, a damping ratio of 1% is more appropriate in simulating the response than a damping ratio of 5%. It is shown that stiffness‐proportional damping, where the coefficient multiplying the stiffness matrix is calculated from the frequency of the base‐isolated building with the post‐elastic stiffness of the isolation system, provides reasonable estimates of the peak response indicators, in addition to being able to capture the frequency content of the response very well. Furthermore, nonlinear modal time‐history analyses using constant as well as frequency‐dependent modal damping are also performed for comparison purposes. It was found that for nonlinear modal time‐history analysis, frequency‐dependent damping, where zero damping is assigned to the frequencies below the fundamental frequency of the superstructure for a fixed‐base condition and 5% damping is assigned to all other frequencies, is more appropriate, than 5% constant damping. Copyright © 2013 John Wiley & Sons, Ltd.

SUMMARY Seismic pounding of base‐isolated buildings has been mostly studied in the past assuming unidirectional excitation. Therefore, in this study, the effects of seismic pounding on the response of base‐isolated reinforced concrete buildings under bidirectional excitation are investigated. For this purpose, a three‐dimensional finite element model of a code‐compliant four‐story building is considered, where a newly developed contact element that accounts for friction and is capable of simulating pounding with retaining walls at the base, is used. Nonlinear behavior of the superstructure as well as the isolation system is considered. The performance of the building is evaluated separately for far‐fault non‐pulse‐like ground motions and near‐fault pulse‐like ground motions, which are weighted scaled to represent two levels of shaking viz. the design earthquake (DE) level and the risk‐targeted maximum considered earthquake (MCER) level. Nonlinear time‐history analyses are carried out considering lower bound as well as upper bound properties of isolators. The influence of separation distance between the building and the retaining walls at the base is also investigated. It is found that if pounding is avoided, the performance of the building is satisfactory in terms of limiting structural and nonstructural damage, under DE‐level motions and MCER‐level far‐fault motions, whereas unacceptably large demands are imposed by MCER‐level near‐fault motions. In the case of seismic pounding, MCER‐level near‐fault motions are found to be detrimental, where the effect of pounding is mostly concentrated at the first story. In addition, it is determined that considering unidirectional excitation instead of bidirectional excitation for MCER‐level near‐fault motions provides highly unconservative estimates of superstructure demands. Copyright © 2014 John Wiley & Sons, Ltd.

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BackgroundThe genus Swertia is reported to contain potent bitter compounds like iridoids, xanthones and c-glucoflavones that are known to heal many human disorders. In contrast to high ethnomedicinally valued Swertia chirayita, its other species have not been studied extensively, in spite of their common use in traditional medicinal system in Nepalese communities. So, the present study attempts to investigate the content of total polyphenols, flavonoids, antioxidant activity and estimate the rough content of amarogentin, swertiamarin and mangiferin from different species of Swertia from Nepalese Himalayas.MethodsWhole plant parts of S. chirayita (SCH), S. angustifolia (SAN), S. paniculata (SPA), S. racemosa (SRA), S. nervosa (SNE), S. ciliata (SCI) and S. dilatata (SDI) were collected; total phenolic and flavonoid contents were quantified spectrophotometrically and in vitro DPPH free radical scavenging assay was measured. Thin layer chromatography was performed on TLC aluminium plates pre-coated with silica gel for identification of swertiamarin, amarogentin and mangiferin from those species and semi quantitative estimation was done using GelQuant.NET software using their standard compounds.ResultsThe phenolic content was highest in the methanol extract of SCH (67.49 ± 0.5 mg GAE/g) followed by SDI, SRA, SNE, SCI, SPA and SAN. The contents of flavonoids were found in the order of SCH, SPA, SRA, SNE, SDI, SCI and SAN. Promising concentration of phenolics and flavonoids produced promising DPPH free radical scavenging values. The IC50 values for the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging test was lowest in SCH (23.35 ± 0.6 μg/ml), even lower than the standard ascorbic acid among the seven studied species. A significant correlation of 0.977 was observed between the polyphenol content and antioxidant values. The TLC profile showed the presence of all three major phytochemicals; amarogentin, swertiamarin and mangiferin in all of the plant samples.ConclusionAmong the seven studied species, SCH showed anticipating results in total phenol content, flavonoid content and DPPH radical scavenging test. The less considered species of Swertia can be a potential source of bioactive amarogentin, and other useful therapeutic compounds in the alarming status of Swertia chirayita as shown by the phytochemical analysis.Electronic supplementary materialThe online version of this article (doi:10.1186/s13104-015-1753-0) contains supplementary material, which is available to authorized users.

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Performance of base-isolated buildings subjected to near-fault ground motions containing long-period pulses is of increasing concern, because these ground motions have the potential to impose large seismic demands on structures. A review of previous studies on the performance evaluation of base-isolated reinforced concrete (RC) buildings under near-fault ground motions shows that these studies lack in the consideration of seismic pounding and the use of lower bound and upper bound values of isolator properties according to the current state of practice. Accordingly, in this study the performance of a typical four-story base-isolated RC building is evaluated using a three-dimensional nonlinear finite element model, considering bounding values of isolator properties, to investigate the influences of (i) pulse-like nature of near-fault ground motions and (ii) seismic pounding with retaining walls at the base. Two sets of ground motions containing 14 far-fault non-pulse-like ground motions and 14 near-fault pulse-like ground motions, representing the risk-targeted maximum considered earthquake (MCER), are used. It is found that the response indicators of the building under near-fault motions are significantly larger than those under far-fault motions. Analysis results reveal that the building response indicators are significantly increased due to seismic pounding. Nonetheless, if a bounding analysis is conducted, consideration of seismic pounding in the analysis does not have appreciable consequences on the prediction of damage to structural elements and drift-sensitive nonstructural components, while dramatic increase in floor accelerations due to pounding is critical for acceleration-sensitive nonstructural components.

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