Simplified inelastic seismic analysis of base‐isolated structures using the N2 method

Kilar, Vojko; Koren, David

doi:10.1002/eqe.978

Cited by 34 publications

(21 citation statements)

References 35 publications

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“…In the extended N2 method the results of the pushover analysis are further multiplied by correction factors, which can be obtained by means of elastic modal analysis for a given distance from the CM. Recently the N2 method has been applied, though with some modifications, to baseisolated symmetric (27) and asymmetric structures (11). In pushover analyses the lateral loads were always applied in the vertical plane through the centre of mass (CM) of the superstructure.…”

Section: Seismic Analysesmentioning

confidence: 99%

Aspectos económicos de un sistema de aislamiento sísmico de base para bastidores de acero en altura

Kilar¹,

Petrovčič²,

Šilih³

et al. 2013

Inf. constr.

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SUMMARYThe paper deals with the effects and costs of implementing a base isolation system for the mitigation of the seismic risk of an existing steel rack structure. Different realistic distributions of the payload mass and occupancy levels, which form different plan asymmetric variants, have been analysed. The results obtained by the pushover analysis (N2 method) are presented as top floor envelopes and as plastic hinge damage patterns. In the presented cost study, the cost of the implementation of the proposed base isolation system is compared with the estimated costs of structural repairs to the damaged structural members of the superstructure, as well as with estimated expenses of the downtime period. The results have shown that base isolation is, in general, not economically feasible for lower ground motion intensities, whereas it could be of great benefit in the case of moderate and high intensities, especially if the downtime period is taken into account. 409-15 RESUMEN

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Section: Seismic Analysesmentioning

confidence: 99%

Aspectos económicos de un sistema de aislamiento sísmico de base para bastidores de acero en altura

Kilar¹,

Petrovčič²,

Šilih³

et al. 2013

Inf. constr.

View full text Add to dashboard Cite

show abstract

“…In the authors' recent paper [14], several modifications of the original N2 method were proposed, to account better for the behavior of base-isolated structures. The major modifications are a threelinear idealization of the pushover (capacity) curve, based on the first yield of the superstructure, and the introduction of an additional damping reduction factor, which should, in general, be obtained by an iterative procedure, and represents the reduction in demand due to the damping of the isolators.…”

Section: Symmetric Building Structuresmentioning

confidence: 99%

“…It was found that, even under such complex irregularity conditions, the results obtained by using this approach correlated well with the results obtained from NLDA. In order to merge the proposed N2 method for base-isolated structures [14] with the extended N2 method for fixed-base structures, several issues have to be first addressed:…”

Section: Plan-asymmetric Building Structuresmentioning

confidence: 99%

“…The symmetric variant of the same structure was already used in [14], where all data about the geometry, masses, and periods can be found, as well as some design details (a g = 0.35g) for the fixed-base variant of the building.…”

Section: Basic Geometrymentioning

confidence: 99%

“…It has been shown that the correct usage of base isolation systems can, if certain structural rules, 868 D. KOREN AND V. KILAR limitations and rational technological limits are taken into account, substantially reduce the negative torsional effects produced by structural asymmetry, and thus justify the higher cost of such a protective system. This paper attempts to contribute to the assessment of the behavior of baseisolated plan-asymmetric building structures by means of the N2 method [13], which has already been successfully applied to the analysis of (frame-type) symmetric base-isolated structures [14].…”

Section: Introductionmentioning

confidence: 99%

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The applicability of the N2 method to the estimation of torsional effects in asymmetric base‐isolated buildings

Koren

Kilar

2010

Earthq Engng Struct Dyn

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The paper deals with the applicability of the extended N2 method to base-isolated plan-asymmetric building structures. The results obtained by the usual pushover analysis of a 3D structural model are further combined with the aid of linear dynamic (spectral) analysis to account for the dynamic effects caused by structural asymmetry. In the paper, the method has been applied to the seismic analysis of a mass-eccentric four-storeyed RC frame building isolated with lead rubber bearings. Three different positions of the center of isolation system (CI) with respect to the center of mass (CM) and the center of stiffness of the superstructure (CS) were considered. The response was analyzed for three different eccentricities, three different torsional to lateral frequency ratios of the superstructure, and two ground motion intensities. The stiffness of the isolators was selected for three different protection levels, which resulted in elastic as well as moderately to excessively damaged superstructure performance levels. The results are presented in terms of the top, base and relative displacements, as well as the stiff/flexible side amplification factors. A more detailed insight into the nonlinear behavior of the superstructure is given in a form of ductility factors for the flexible and stiff side frames. The results of the extended N2 method for selected lateral load distributions are compared with the average results of nonlinear dynamic analyses. It was concluded that the extended N2 method could, with certain limitations, provide a reasonable prediction of the torsional influences in minor to moderately asymmetric base-isolated structures. Figure 6. Maximum ductility factors for the (a) flexible and (b) stiff side, for A10 and the CI = CM distribution. and relative displacements are presented in Figures 3-5, whereas the damage patterns are presented in Figures 6-8.Observing the displacements at the CM, it is evident that the softer isolators-as expected-result in larger top and base displacements and smaller relative displacements than the harder ones. It can be seen that the agreement with the results of NLDA is fairly good, and within the standard deviation boundaries until the eccentricities of the superstructure exceed approximately 15-20%, in extreme cases. For larger eccentricities, all the displacements obtained by the extended N2 method tend to be underestimated, especially in the case of the harder isolators, where much more damage occurs in the superstructure. The best results were obtained in the case of the 1st and PSC distributions, which give similar results, whereas the TRI distribution underestimates Figure 7. Maximum ductility factors for the flexible side, for A20 and the CI = CM distribution.Figure 8. Maximum ductility factors for the flexible side, for A30 and the CI = CM distribution. THE APPLICABILITY OF THE N2 METHOD 881 Figure 10. Maximum ductility factors for the models A10-A30 and the CI = CS distribution.to provide a better estimation of the NLDA results; however, the results obtained in ...

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Inelastic response of RC frame buildings with seismic isolation

Cardone

Flora

Gesualdi

2012

Earthq Engng Struct Dyn

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A comprehensive parametric study on the inelastic seismic response of seismically isolated RC frame buildings, designed for gravity loads only, is presented. Four building prototypes, with 23 m by 10 m floor plan dimensions and number of storeys ranging from 2 to 8, are considered. All the buildings present internal resistant frames in one direction only, identified as the strong direction of the building. In the orthogonal weak direction, the buildings present outer resistant frames only, with infilled masonry panels. This structural configuration is typical of many existing RC buildings, realized in Italy and other European countries in the 60s and 70s. The parametric study is based on the results of extensive nonlinear response-time history analyses of 2-DOF systems, using a set of seven artificial and natural seismic ground motions. In the parametric study, buildings with strength ratio (Fy/W) ranging from 0.03 to 0.15 and post-yield stiffness ratio ranging from 0% to 6% are examined. Three different types of isolation systems are considered, that is, high damping rubber bearings, lead rubber bearings and friction pendulum bearings. The isolation systems have been designed accepting the occurrence of plastic hinges in the superstructure during the design earthquake. The nonlinear response-time history analyses results show that structures with seismic isolation experience fewer inelastic cycles compared with fixed-base structures. As a consequence, although limited plastic deformations can be accepted, the collapse limit state of seismically isolated structures should be based on the lateral capacity of the superstructure without significant reliance on its inherent hysteretic damping or ductility capacity

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Simplified inelastic seismic analysis of base‐isolated structures using the N2 method

Cited by 34 publications

References 35 publications

Aspectos económicos de un sistema de aislamiento sísmico de base para bastidores de acero en altura

Aspectos económicos de un sistema de aislamiento sísmico de base para bastidores de acero en altura

The applicability of the N2 method to the estimation of torsional effects in asymmetric base‐isolated buildings

Inelastic response of RC frame buildings with seismic isolation

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Simplified inelastic seismic analysis of base‐isolated structures using the N2 method

Cited by 34 publications

References 35 publications

Aspectos econ&#243;micos de un sistema de aislamiento s&#237;smico de base para bastidores de acero en altura

Aspectos econ&#243;micos de un sistema de aislamiento s&#237;smico de base para bastidores de acero en altura

The applicability of the N2 method to the estimation of torsional effects in asymmetric base‐isolated buildings

Inelastic response of RC frame buildings with seismic isolation

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Aspectos económicos de un sistema de aislamiento sísmico de base para bastidores de acero en altura

Aspectos económicos de un sistema de aislamiento sísmico de base para bastidores de acero en altura