A Modified Three-parameter Lognormal Distribution For Seismic Demand Assessment Considering Collapse Data

Azad Yazdani,Hessan Salehi,Mohammad Sadegh Shahidzadeh 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.1

Consideration of parameter uncertainty in structural seismic performance has become an important issue in the last decade. A common means of including such uncertainties is through the reliability theory. Seismic reliability assessment is concerned with calculation of probability of exceeding a certain structural limit state against a ground motion intensity measure. However, an important factor which affects the reliability index is the selection of probability distributions for structural demand. Usually a lognormal distribution is assumed by researchers but recent studies show that such simple assumption may result in misleading reliability measures. In this study, a three parameter lognormal distribution is proposed to be used to describe seismic behavior at relatively high intensity measures. This distribution is unique as it considers the missing or collapse data and at the same time incorporates a location parameter to disregard the less likely displacements at high spectral accelerations in Incremental Dynamic Analysis (IDA). It was shown by means of the Shannon’s entropy that uncertainty of calculating the reliability index using the proposed distribution is minimum compared to other available methods and therefore it is recommended to be used for reliability assessment of collapse prevention limit state.

Probabilistic study of the influence of ground motion variables on response spectra

Yazdani, Azad,Takada, Tsuyoshi Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.39 No.6

Response spectra of earthquake ground motions are important in the earthquake-resistant design and reliability analysis of structures. The formulation of the response spectrum in the frequency domain efficiently computes and evaluates the stochastic response spectrum. The frequency information of the excitation can be described using different functional forms. The shapes of the calculated response spectra of the excitation show strong magnitude and site dependency, but weak distance dependency. In this paper, to compare the effect of the earthquake ground motion variables, the contribution of these sources of variability to the response spectrum's uncertainty is calculated by using a stochastic analysis. The analytical results show that earthquake source factors and soil condition variables are the main sources of uncertainty in the response spectra, while path variables, such as distance, anelastic attenuation and upper crust attenuation, have relatively little effect. The presented formulation of dynamic structural response in frequency domain based only on the frequency information of the excitation can provide an important basis for the structural analysis in some location that lacks strong motion records.

Probabilistic study of the influence of ground motion variables on response spectra

Azad Yazdani,Tsuyoshi Takada 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.39 No.6

Response spectra of earthquake ground motions are important in the earthquake-resistant design and reliability analysis of structures. The formulation of the response spectrum in the frequency domain efficiently computes and evaluates the stochastic response spectrum. The frequency information of the excitation can be described using different functional forms. The shapes of the calculated response spectra of the excitation show strong magnitude and site dependency, but weak distance dependency. In this paper, to compare the effect of the earthquake ground motion variables, the contribution of these sources of variability to the response spectrum’s uncertainty is calculated by using a stochastic analysis. The analytical results show that earthquake source factors and soil condition variables are the main sources of uncertainty in the response spectra, while path variables, such as distance, anelastic attenuation and upper crust attenuation, have relatively little effect. The presented formulation of dynamic structural response in frequency domain based only on the frequency information of the excitation can provide an important basis for the structural analysis in some location that lacks strong motion records.

A reliability-based approach to investigate the challenges of using international building design codes in developing countries

Arman Kakaie,Azad Yazdani,Mohammad-Rashid Salimi 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.80 No.6

The building design codes and standards in many countries usually are either fully or partially adopted from the international codes. However, regional conditions like the quality of construction industry and different statistical parameters of load and resistance have essential roles in the code calibration of building design codes. This paper presents a probabilistic approach to assess the reliability level of adopted national building codes by simulating design situations and considering all load combinations. The impact of the uncertainty of wind and earthquake loads, which are entirely regional condition dependent and have a high degree of uncertainty, are quantified. In this study, the design situation is modeled by generating thousands of numbers for load effect ratios, and the reliability level of steel elements for all load combinations and different load ratios is established and compared to the target reliability. This approach is applied to the Iranian structural steel code as a case study. The results indicate that the Iranian structural steel code lacks safety in some load combinations, such as gravity and earthquake load combinations, and is conservative for other load combinations. The present procedure can be applied to the assessment of the reliability level of other national codes.

Reliability-based fragility analysis of nonlinear structures under the actions of random earthquake loads

Mohammad-Rashid Salimi,Azad Yazdani 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.1

This study presents the reliability-based analysis of nonlinear structures using the analytical fragility curves excited by random earthquake loads. The stochastic method of ground motion simulation is combined with the random vibration theory to compute structural failure probability. The formulation of structural failure probability using random vibration theory, based on only the frequency information of the excitation, provides an important basis for structural analysis in places where there is a lack of sufficient recorded ground motions. The importance of frequency content of ground motions on probability of structural failure is studied for different levels of the nonlinear behavior of structures. The set of simulated ground motion for this study is based on the results of probabilistic seismic hazard analysis. It is demonstrated that the scenario events identified by the seismic risk differ from those obtained by the disaggregation of seismic hazard. The validity of the presented procedure is evaluated by Monte-Carlo simulation.

Reliability-based fragility analysis of nonlinear structures under the actions of random earthquake loads

Salimi, Mohammad-Rashid,Yazdani, Azad Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.1

This study presents the reliability-based analysis of nonlinear structures using the analytical fragility curves excited by random earthquake loads. The stochastic method of ground motion simulation is combined with the random vibration theory to compute structural failure probability. The formulation of structural failure probability using random vibration theory, based on only the frequency information of the excitation, provides an important basis for structural analysis in places where there is a lack of sufficient recorded ground motions. The importance of frequency content of ground motions on probability of structural failure is studied for different levels of the nonlinear behavior of structures. The set of simulated ground motion for this study is based on the results of probabilistic seismic hazard analysis. It is demonstrated that the scenario events identified by the seismic risk differ from those obtained by the disaggregation of seismic hazard. The validity of the presented procedure is evaluated by Monte-Carlo simulation.

Performance-based reliability assessment of RC shear walls using stochastic FE analysis

Arina Nosoudi,Hooshang Dabbagh,Azad Yazdani 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.80 No.6

Performance-based reliability analysis is a practical approach to investigate the seismic performance and stochastic nonlinear response of structures considering a random process. This is significant due to the uncertainties involved in every aspect of the analysis. Therefore, the present study aims to evaluate the performance-based reliability within a stochastic finite element (FE) framework for reinforced concrete (RC) shear walls that are considered as one of the most essential elements of structures. To accomplish this purpose, deterministic FE analyses are conducted for both squat and slender shear walls to validate numerical models through experimental results. The presented numerical analysis is performed by using the ABAQUS FE program. Afterwards, a random-effects investigation is carried out to consider the influence of different random variables on the lateral load-top displacement behavior of RC members. Using these results and through utilizing the Monte-Carlo simulation method, stochastic nonlinear analyses are also performed to generate random FE models based on input parameters and their probabilistic distributions. In order to evaluate the reliability of RC walls, failure probabilities and corresponding reliability indices are calculated at life safety and collapse prevention levels of performance as suggested by FEMA 356. Moreover, based on reliability indices, capacity reduction factors are determined subjected to shear for all specimens that are designed according to the ACI 318 Building Code. Obtained results show that the lateral load and the compressive strength of concrete have the highest effects on load-displacement responses compared to those of other random variables. It is also found that the probability of shear failure for the squat wall is slightly lower than that for slender walls. This implies that β values are higher in a nonductile mode of failure. Besides, the reliability of both squat and slender shear walls does not change significantly in the case of varying capacity reduction factors.