Seismic behavior of damaged buildings: a comparison of static and dynamic nonlinear approach (original) (raw)
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Mechanism based assessment of damaged building’s residual capacity
. The residual capacity REC Sa is defined as the minimum spectral acceleration (at the period T eq of the equivalent SDOF) corresponding to building collapse. When referring to peak ground acceleration a g as damaging intensity parameter, REC ag is defined as the minimum anchoring peak ground acceleration such as to determine building collapse. For a given spectral shape, REC ag corresponds to REC Sa scaled by the spectral amplification factor for T eq . REC Sa and REC ag , generally indicated as REC, lower with increasing damage level in buildings; hence REC may be very useful in estimating the post-seismic building safety. In a recent work it has been shown how it is possible to derive REC (REC Sa and REC ag ) through Pushover Analyses (PA), where a suitable modification of plastic hinges for damaged elements is applied. The applicability of PA for damaged structures is verified in [2] by comparison of the PA results with those on nonlinear time-history analyses. On the other hand, it is unrealistic that in the aftermath of an earthquake, when the assessment of building safety has to be performed in an emergency situation, there would be time for the execution of detailed nonlinear analyses. Acknowledging the need for easier and faster evaluation tools, in [3] a simplified MEChanism based method (MEC) for evaluating the building REC was preliminary tested. The present work extends the comparison of the results (in terms of REC), that could be obtained by PA and MEC analyses, considering a number of Reinforced Concrete (RC) frames building typologies. Moreover, by adopting the MEC approach, the possible variation of REC as a function of seismic demand is investigated. The simplified method can be used to explore the possible ranges of REC variation for RC building classes considering the anticipated mechanism formation after an earthquake; in addition, it could be used in the post-seismic phase for estimating the REC of damaged buildings having undergone identifiable plastic mechanisms and for fast assessment of damage-dependent collapse fragility curves.
Damage-dependent vulnerability curves for existing buildings
Earthquake Engineering & Structural Dynamics, 2013
Seismic behavior of damaged buildings may be expressed as a function of their REsidual Capacity (REC), which is a measure of seismic capacity, reduced by damage. REC can be interpreted as the median value of collapse vulnerability curves. Its variation owing to damage is a useful indication of increased building vulnerability. REC reduction, indicating the lowering of seismic safety after an earthquake (performance loss, PL), represents an effective index for assessing the need of seismic repair/strengthening after earthquakes. The study investigates the applicability of a pushover-based method in the analysis of damaged structures for the case of existing under-designed RC buildings. The paper presents a systematization of the procedure in an assessment framework that applies the capacity spectrum method based on inelastic demand spectra; furthermore, the vulnerability variation of a real building is investigated with a detailed case study. The behavior of damaged buildings is simulated with pushover analysis through suitable modification of plastic hinges (in terms of stiffness, strength and residual drift) for damaged elements. The modification of plastic hinges has been calibrated in tests on nonconforming columns. The case study analysis evidenced that, for minor or moderate damages, the original structural displacement capacity was only slightly influenced, but the ductility capacity was significantly reduced (up to 40%) because of the increased structure deformability. This implied performance loss in the range 10%-20%. For severe damages the PL ranged between 41% and 56%. Local mechanism types exhibit PL nearly double with respect to global mechanism types. realistic estimate of evolving seismic risk during a seismic sequence, suitable modeling of building vulnerability variation should be considered. The variation in building safety owing to seismic damage is implicitly recognized by building tagging procedures, which are applied after major seismic events . In such procedures, post-earthquake safety is generally evaluated by visual inspection, with an expert assessment of damage level, extent and the related building usability by a team of experienced practitioners. However, if varied vulnerability is to be considered within a consistent quantitative assessment framework, analytical modeling of building performance loss (PL) is preferable.
Correlation study between seismic acceleration parameters and damage indices of structures
Engineering Structures, 2001
This study describes numerically, the interdependency between several seismic acceleration parameters and diverse structural damage indices. Peak ground motion, spectral and energy parameters are used for characterising the seismic excitation. On the other hand both, structural and nonstructural damage is considered, expressed by the modified Park/Ang overall structural damage index (OSDI), the maximum interstory drift (ISD) and the maximum floor acceleration. After the numerical evaluation of several seismic parameters, nonlinear dynamic analyses are conducted to furnish the structural damage status. The degree of the interrelationship between the seismic parameters and the damage indices is provided by correlation coefficients. The investigation is carried out for a reinforced concrete plane frame system designed after Eurocodes 2 and 8 (EC2, EC8) and the aim is to determine the characteristics of the accelerograms that exhibit the strongest influence on structural and nonstructural damages. The numerical results have shown, that peak ground motion seismic parameters provide poor or fair correlation with the OSDI, whereas the spectral and energy parameters provide good correlation. Furthermore, the central period and the strong motion duration after Trifunac/Brady exhibit poor correlation with the OSDI. All these results give reason to recommend the spectra and energy related seismic intensity parameters as reliable descriptors of the seismic damage potential.
Guidelines for seismic assessment of damaged buildings
Structural post-earthquake functionality is conventionally evaluated by trained engineers via visual inspection of the damage. A building is tagged "Green" (unrestricted access), "Yellow" (restricted access), or "Red" (no access) according to the severity of the observed damage. Whether the damage implies an actual decay in safety level of the building occupants during aftershocks is essentially left to judgment. We propose to use engineering analyses performed prior to an earthquake to determine the level of degradation in building safety implied by several different damage states. We use the loss of capacity (in ground motion terms) associated with each damage state as the quantitative measure of degradation. The likelihood that an aftershock will exceed a specific (reduced) capacity provides an objective criterion for assigning the appropriate tagging condition to that damage state. This knowledge can help engineers decide on the appropriate occupanc...
IJERT-Damage Assessment of Multistoried Structures under Seismic Loading using Pushover Analysis
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/damage-assessment-of-multistoried-structures-under-seismic-loading-using-pushover-analysis https://www.ijert.org/research/damage-assessment-of-multistoried-structures-under-seismic-loading-using-pushover-analysis-IJERTV3IS100082.pdf The buildings which do not fulfill the requirements of seismic design may be affected by either damage or collapse if shaken by a severe ground motion which results in huge economic and loss of life. A building has the potential to wave back and forth during an earthquake and severe wind storm. This is called fundamental mode, and is the lowest frequency of building response. Most buildings, however, have higher modes of response, which are uniquely activated depending up on the intensity of earthquakes. The purpose of this paper is to assess the damage and to evaluate the performance of the structures which are already designed and analyzed using linear static analysis for seismic loads as per the Indian codes IS-456, IS-1893 and IS-13920. It is proposed to study the performance of the structure before and after the linear state. To make such assessment, simplified linear-elastic methods are not adequate. Thus, the structural engineering community has developed a new generation of design and seismic procedures (ATC-40, FEMA-356 and FEMA-440) that incorporate performance based structures and is moving away from simplified linear elastic methods and towards a more non-linear technique i.e., Pushover analysis which is a series of incremental static analysis. It is carried out on the 12-storied building modal which was designed and analyzed for the earthquake analysis using STAAD for two seismic load cases (Zone-3 and Zone-5) considering both are Special Moment Resisting Frames. Pushover analysis is propounded to perform by SAP to get the extent of damage experienced by the structure at target displacement by the sequence of yielding of components, plastic hinge formation and failure of various structural components. Finally both the frames which were designed to linear static analysis for earthquake loading performed well and the damage is within the limits. Initially, yielding of the beams taken place then yielding of columns. This shows that the analysis theory is based on the strong column and weak beam i.e., both the frames behaving as ductile frames.
Evaluation Of A Framed Structure Damaged ByThe 1997 Umbria-Marche Earthquake
WIT Transactions on the Built Environment, 1970
The post-earthquake evaluation analysis of a reinforced concrete structure, which experienced inelastic behaviour during the Italian seismic event that damaged the Umbria and Marche regions in 1997, is presented. Since only the bare frame of the building had been completed when the two main shocks occurred, this case study offers the infrequent chance of developing field observation of structural response under strong ground motions without any form of interaction with infills as well as other non-structural elements. Damage is assessed by applying a general procedure, previously proposed within the same research which yields an automatic calibration of the free coefficients contained in the analytical damage model utilised. The results obtained by assuming a modified version of the Park and Ang functional as the reference model for this inquiry, show a substantial correlation between the index values and the classification of the degraded state of the structure formulated on the basis of expert guidelines. At the same time, a mean value of the user-defined constant included in the functional expression notably differing from average literature suggestions emerges from the supporting statistical calibration analysis carried out. Survivability of the building under aftershocks and future events is also predicted, as the final step of the procedure applied.
Damage assessment of adjacent buildings under earthquake loads
This paper deals with damage assessment of adjacent colliding buildings under strong ground motion. In previous studies, the structure input-response pair is used to examine pounding effects on adjacent buildings under seismic loads. In this paper, pounding of adjacent buildings is assessed using input energy, dissipated energy and damage indices. Damage indices (DI) are computed by comparing the structure's responses demanded by earthquakes and the associated structural capacities. Damage indices provide quantitative estimates of structural damage level, and thus, a decision on necessary repair can be taken. Adjacent buildings with fixed-base and isolated-base are considered. The nonlinear viscoelastic model is used for capturing the induced pounding forces. Influences of the separation distance between buildings, buildings properties, such as, base-condition (fixed or isolated), and yield strength on damage of adjacent buildings are investigated. The set of input ground motions includes short-, moderate-and long-duration accelerograms measured at near-fault and far-fault regions with different soil types. Earthquake records with different characteristics are considered to study damage of adjacent buildings under seismic loads. Numerical illustrations on damage of fixed-base and isolated-base adjacent buildings with elastic–plastic force–deformation relation are provided.
Incremental Dynamic Analysis (IDA) is a parametric analysis method that allows evaluating the structural performance under seismic loads more accurately than traditional static and dynamic analyses. With respect to a single non-linear analysis, the incremental dynamic analysis has the advantage to evaluate the structural performance under different levels of intensity, scaling proper ground motion records, until the structure collapses or until a fixed level of deformation is reached. In this study the potentialities of incremental dynamic analysis have been investigated in identifying the damaged elements in existing irregular r.c. buildings and a comparison with the results of static Pushover Analyses has been performed. In particular a strongly irregular building has been considered, representative of a particular manufacture and of an historical period of economic growth and speculation; it has not structural problems but suffers from abandonment and weathering effects. An interpretation of IDA procedure has been proposed, with the set of a mean IDA capacity curve, then bi-linearized in order to close the pushover procedure according to the extended N2 method. The aim is to underline in a specific case study how the choice of a methodology can affect the definition of recovery interventions, especially in the case of historical buildings, where the criterion of minimum intervention should be followed in order to preserve the original features.
Evaluation of the structural response under seismic actions using non-linear static methods
Earthquake Engineering & Structural Dynamics, 2006
The paper investigates the degree of accuracy achievable when some non-linear static procedures based on a pushover analysis are used to evaluate the seismic performance. In order to assess the significance of different sources of errors, three types of structural systems are analysed: (i) single-degree-of-freedom (SDOF) systems with different hysteretic behaviour; (ii) shear-type multi-degree-of-freedom (MDOF) systems with elastic-perfect plastic (EPP) shear force-interstorey drift relationships; (iii) a steel momentresisting frame with rigid joints and EPP moment-curvature relationship. In SDOF systems, the source of approximation comes only from the calibration of the demand spectrum, while in MDOF systems some further errors are introduced by the schematization with an equivalent SDOF system. The non-linear static procedures are compared with rigorous time-history analyses carried out by considering ten generated earthquake ground motions compatible with the Eurocode 8 elastic spectra. It was found that SDOF systems with longer periods satisfy the equal displacement approximation regardless of the hysteretic model, while hysteresis loops with smaller energy dissipated indicate lower response for shorter periods. This is the opposite of what predicted by the ATC-40 capacity spectrum method, which underestimates and overestimates, respectively, the actual response of low-and high-ductility systems. Conversely, the inelastic spectrum method proposed by Vidic, Fajfar and Fischinger leads to the most accurate results for all types of structural systems. The analyses carried out on EPP shear-type frames point out a large concentration of the ductility demand on some storeys. However, such a concentration markedly reduces when some hardening is accounted for.
Bulletin of Earthquake Engineering, 2010
Several procedures for non-linear static and dynamic analysis of structures have been developed in recent years. This paper discusses those procedures that have been implemented into the latest European and US seismic provisions: non-linear dynamic time-history analysis; N2 non-linear static method (Eurocode 8); non-linear static procedure NSP (FEMA 356) and improved capacity spectrum method CSM (FEMA 440). The presented methods differ in respect to accuracy, simplicity, transparency and clarity of theoretical background. Non-linear static procedures were developed with the aim of overcoming the insufficiency and limitations of linear methods, whilst at the same time maintaining a relatively simple application. All procedures incorporate performance-based concepts paying more attention to damage control. Application of the presented procedures is illustrated by means of an example of an eight-storey reinforced concrete frame building. The results obtained by non-linear dynamic time-history analysis and non-linear static procedures are compared. It is concluded that these non-linear static procedures are sustainable for application. Additionally, this paper discusses a recommendation in the Eurocode 8/1 that the capacity curve should be determined by pushover analysis for values of the control displacement ranging between zero and 150% of the target displacement. Maximum top displacement of the analyzed structure obtained by using dynamic method with real time-history records corresponds to 145% of the target displacement obtained using the non-linear static N2 procedure.