• Earthquakes and Structures
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• v.19 no.3
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• pp.189-196
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• 2020

The near-collapse performance limit is defined as the deformation at the 20% drop of maximum base shear in the decreasing region of the pushover curve for ductile framed buildings. Although monotonic pushover analysis is preferred due to the simple application procedure, this analysis gives rise to overestimated results by neglecting the cumulative damage effects. In the present study, the acceptabilities of monotonic and cyclic pushover analysis results for the near-collapse performance limit state are determined by comparing with Incremental Dynamic Analysis (IDA) results for a 5-story Reinforced Concrete framed building. IDA is performed to obtain the collapse point, and the near-collapse drift ratios for monotonic and cyclic pushover analysis methods are obtained separately. These two alternative drift ratios are compared with the collapse drift ratio. The correlations of the maximum tensile and compression strain at the base columns and beam plastic rotations with interstory drift ratios are acquired using the nonlinear time history analysis results by the simple linear regression analyses. It is seen that these parameters are highly correlated with the interstory drift ratios, and the results reveal that the near-collapse point acquired by monotonic pushover analysis causes unacceptably high tensile and compression strains at the base columns, as well as large plastic rotations at the beams. However, it is shown that the results of cyclic pushover analysis are acceptable for the near-collapse performance limit state.

• Structural Engineering and Mechanics
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• v.67 no.6
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• pp.587-601
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• 2018

Elevated water tanks are inverted pendulum type structures where drift limit is an important criterion for seismic design and performance evaluation. Explicit drift criteria for elevated water tanks are not available in the literature. In this study, probabilistic approach is used to determine maximum drift limit for damage state of yielding and damage state of collapse for the elevated water tanks supported on RC frame staging. The two damage states are defined using results of incremental dynamic analysis wherein a total of 2160 nonlinear time history analyses are performed using twelve artificial spectrum compatible ground motions. Analytical fragility curves are developed using two-parameter lognormal distribution. The maximum allowable drifts corresponding to yield and collapse level requirements are estimated for different tank capacities. Finally, a single fragility curve is developed which provides maximum drift values for the different probability of damage. Further, for rational consideration of the uncertainties in design, three confidence levels are selected and corresponding drift limits for damage states of yielding and collapse are proposed. These values of maximum drift can be used in performance-based seismic design for a particular damage state depending on the level of confidence.

• International Journal of High-Rise Buildings
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• v.1 no.1
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• pp.1-13
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• 2012

The importance of appropriate use of damping evaluation techniques and points to note for accurate evaluation of damping are first discussed. Then, the variation of damping ratio with amplitude is discussed, especially in the amplitude range relevant to wind-resistant design of buildings, i.e. within the elastic limit. The general belief is that damping increases with amplitude, but it is emphasized that there is no evidence of increasing damping ratio in the very high amplitude range within the elastic limit of main frames, unless there is damage to secondary members or architectural finishings. The damping ratio rather decreases with amplitude from a certain tip drift ratio defined as "critical tip drift ratio," after all friction surfaces between primary/structural and secondary/non-structural members have been mobilized.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.6
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• pp.11-20
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• 2013

In this paper, the quantitative damage index for reinforced concrete (RC) columns with non-seismic details were presented. They are necessary to carry out the postearthquake safety evaluation of RC buildings under 5 stories without seismic details. The static cyclic test of the RC frame sub-assemblage that was an one span and actual-sized was first conducted. The specimen collapsed by the shear failure after flexural yielding of a column, lots of cracks on the surfaces of columns and beam-column joints and the cover concrete splitting at the bottom of columns occurred. The damage levels of these kinds of columns with non-seismic details were classified to five based on the load-displacement relationship by the test result. The residual story drift ratios and crack widths were then adapted as the quantitative index to evaluate the damage limit states because those values were comparatively easy to measure right after earthquakes. The highest one among the residual story drift ratios under the similar maximum story drift ratio decided on the residual story drift ratio of each damage limit state. On the other hand, the lowest and average ones among the respective residual shear and flexural widths under the similar maximum story drift ratio decided on the residual shear and flexural widths of each damage limit state, respectively. These values for each damage limit state resulted in being smaller than those by the international damage evaluation guidelines that are for seismically designed members under the same deformations.

• Steel and Composite Structures
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• v.9 no.5
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• pp.457-471
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• 2009

This study investigates the role of accidental torsion in seismic reliability assessment. The analyzed structures are regular 6-story and 20-story steel office buildings. The eccentricity in a floor plan was simulated by shifting the mass from the centroid by 5% of the dimension normal to earthquake shaking. The eccentricity along building heights was replicated by Latin hypercube sampling. The fragilities for immediate occupancy and life safety were evaluated using 0.7% and 2.5% inter-story drift limits. Two limit-state probabilities and the corresponding earthquake intensities were compared. The effect of ignoring accidental torsion and the use of code accidental eccentricity were also assessed. The results show that accidental torsion may influence differently the structural reliability and limit-state PGAs. In terms of structural reliability, significant differences in the probability of failure are obtained depending on whether accidental torsion is considered or not. In terms of limit-state PGAs, accidental torsion does not have a significant effect. In detail, ignoring accidental torsion leads to underestimates in low-rise buildings and at small drift limits. On the other hand, the use of code accidental eccentricity gives conservative estimates, especially in high-rise buildings at small drift limits.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.2
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• pp.119-127
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• 2023

In this paper, seismic performance evaluation was carried out for eight circular reinforced concrete columns designed seismically by KRTA[1]and KCI[8]. Primary design parameters for such columns included many longitudinal reinforcements, yield strength of reinforcements, the vertical spacing of spirals, aspect ratio, and axial force ratio. The test results showed that all the columns exhibited stable hysteretic and inelastic responses. Based on the test results, drift ratios corresponding to each damage state, such as initial yielding, initial cover spalling, initial core concrete crushing, buckling, and fracture of longitudinal reinforcement and final spalled region, were evaluated. Then, those ratios were compared with widely accepted damage limit states. The comparison revealed that the existing damage states were considerably conservative. This implies that additional research is required for the damage limit states of such columns designed seismically by current Korean design codes.

• Steel and Composite Structures
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• v.19 no.1
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• pp.173-190
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• 2015

This study presents an analytical investigation on the seismic response of a medium-rise buckling-restrained braced frame (BRBF) under the near-fault ground motions. A seven-story BRBF is designed as per the current code provisions for five different combinations of brace configurations and beam-column connections. Two types of brace configurations (i.e., Chevron and Double-X) are considered along with a combination of the moment-resisting and the non-moment-resisting beam-to-column connections for the study frame. Nonlinear dynamic analyses are carried out for all study frames for an ensemble of forty SAC near-fault ground motions. The main parameters evaluated are the interstory and residual drift response, brace displacement ductility, and plastic hinge mechanisms. Fragility curves are developed using log-normal probability density functions for all study frames considering the interstory drift ratio and residual drift ratio as the damage parameters. The average interstory drift response of BRBFs with Double-X brace configurations significantly exceeded the allowable drift limit of 2%. The maximum displacement ductility characteristics of BRBs is efficiently utilized under the seismic loading if these braces are arranged in the Double-X configurations instead of Chevron configurations in BRBFs located in the near-fault regions. However, BRBFs with the Double-X brace configurations exhibit the higher interstory drift and residual drift response under near-fault ground motions due to the formation of plastic hinges in the columns and beams at the intermediate story levels.

• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.2747-2756
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• 2023

Reinforced Concrete (RC) shear walls are one of the civil structures in nuclear power plants to resist lateral loads such as earthquakes and wind loads effectively. Risk-informed and performance-based regulation in the nuclear industry requires considering possible accidents and determining desirable performance on structures. As a result, rather than predicting only the ultimate capacity of structures, the prediction of performances on structures depending on different damage states or various accident scenarios have increasingly needed. This study aims to develop machine-learning models predicting drifts of the RC shear walls according to the damage limit states. The damage limit states are divided into four categories: the onset of cracking, yielding of rebars, crushing of concrete, and structural failure. The data on the drift of shear walls at each damage state are collected from the existing studies, and four regression machine-learning models are used to train the datasets. In addition, the bagging ensemble method is applied to improve the accuracy of the individual machine-learning models. The developed models are to predict the drifts of shear walls consisting of various cross-sections based on designated damage limit states in advance and help to determine the repairing methods according to damage levels to shear walls.

• Steel and Composite Structures
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• v.3 no.3
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• pp.185-198
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• 2003

The concept of performance based seismic design has been gradually accepted by the earthquake engineering profession recently, in which the cost-effectiveness criterion is one of the most important principles and more attention is paid to the structural performance at the inelastic stage. Since there are many uncertainties in seismic design, reliability analysis is a major task in performance based seismic design. However, structural reliability analysis may be very costly and time consuming because the limit state function is usually a highly nonlinear implicit function with respect to the basic design variables, especially for the complex large-scale structures for dynamic and nonlinear analysis. Understanding statistical properties of the structural inelastic deformation, which is the aim of the present paper, is helpful to develop an efficient approximate approach of reliability analysis. The present paper studies the statistical properties of the maximum elastoplastic story drift of steel frames subjected to earthquake load. The randomness of earthquake load, dead load, live load, steel elastic modulus, yield strength and structural member dimensions are considered. Possible probability distributions for the maximum story are evaluated using K-S test. The results show that the choice of the probability distribution for the maximum elastoplastic story drift of steel frames is related to the mean value of the maximum elastoplastic story drift. When the mean drift is small (less than 0.3%), an extreme value type I distribution is the best choice. However, for large drifts (more than 0.35%), an extreme value type II distribution is best.

• Steel and Composite Structures
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• v.32 no.1
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• pp.91-110
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• 2019

In the present study, the effects of six different ground motion scaling methods on inelastic response of nonlinear steel moment frames (SMFs) are studied. The frames were designed using energy-based PBPD approach with the design concept using pre-selected target drift and yield mechanism as performance limit state. Two target spectrums are considered: maximum credible earthquake spectrum (MCE) and design response spectrum (DRS). In order to investigate the effects of ground motion scaling methods on the response of the structures, totally 3216 nonlinear models including three frames with 4, 8 and 16 stories are designed using PBPD approach and then they are subjected to ensembles of ground motions including 42 far-fault and 90 near-fault pulse-type records which were scaled using the six different scaling methods in accordance to the two aforementioned target spectrums. The distributions of maximum inter-story drift over the height of the structures are computed and compared. Finally, the efficiency and reliability of each ground motion scaling method to estimate the maximum nonlinear inter-story drift of special steel moment frames designed by energy-based PBPD approach are statistically investigated, and the most suitable scaling methods with the lowest dispersion for two groups of earthquake ground motions are introduced.