http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
- 中文 을 입력하시려면 zhongwen을 입력하시고 space를누르시면됩니다.
- 北京 을 입력하시려면 beijing을 입력하시고 space를 누르시면 됩니다.
RISS 인기검색어
- 검색키워드
- 저자 : Jerome F. Hajjar (검색결과 3 건)
- 무료
- 기관 내 무료
- 유료
-
Energy-based sidesway collapse fragilities for ductile structural frames under earthquake loadings
Deniz, Derya,Song, Junho,Hajjar, Jerome F. Elsevier 2018 ENGINEERING STRUCTURES Vol.174 No.-
<P><B>Abstract</B></P> <P>In assessing the likelihood of structural collapse under strong earthquake motions, uncertainties in structural properties and ground motions can be incorporated by use of a probabilistic analysis framework in conjunction with analysis methods such as incremental dynamic analysis (IDA). Maximum inter-story drift ratio (<I>IDR</I>) is typically selected as the key descriptor to characterize the global behavior of structural system in such a probabilistic assessment. The structural collapse capacity is often defined in terms of a threshold value of <I>IDR</I> or a reduced slope of the IDA curve between a selected seismic intensity measure and the corresponding <I>IDR</I>. However, collapse assessment approaches based on <I>IDR</I> may not accurately represent the overall structural collapse behavior due to redistribution and variation of local damage within the structure. Moreover, results of collapse predictions are found to be sensitive to variability in such drift measures, and assumed threshold values used in the collapse criterion. Recently, an energy-based seismic collapse criterion has been developed to describe collapse in terms of dynamic instability of the whole structural system caused by gravity loads. Using the energy-based collapse criterion, this paper proposes a more effective sidesway collapse risk assessment approach of ductile planar frames subjected to horizontal seismic loadings based on a new key descriptor of structural performance. The key descriptor, designated as the equivalent-velocity ratio, is related to the ratio of the energy dissipated through structural degradation to the seismic input energy. Using the equivalent-velocity ratio, a probabilistic collapse assessment method is developed for systematic treatment of uncertainties in the ground motions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new descriptor’s been proposed for seismic performance of ductile moment frames. </LI> <LI> New seismic demand models and collapse fragility relations are obtained for frames. </LI> <LI> The new collapse fragility relations are compared with the traditional approaches. </LI> <LI> The developed techniques help achieve reliable prediction of structural collapse. </LI> </UL> </P>
-
Saykin, Vitaliy V.,Nguyen, Tam H.,Hajjar, Jerome F.,Deniz, Derya,Song, Junho Elsevier 2017 ENGINEERING STRUCTURES Vol.147 No.-
<P><B>Abstract</B></P> <P>The prediction of collapse of structures has gained growing attention recently, as it is important to be able to predict and model structural collapse due to extreme loads. A lack of accurate, pragmatic, and validated structural collapse models currently limits the capabilities for predicting collapse due to possible extreme loads. This research compares three finite element deletion strategies that account implicitly for fracture under monotonic loading to be used as predictive tools for collapse modeling of steel structures. The first strategy employs a Void Growth Model (VGM) to simulate the initiation of softening and the Hillerborg model for modeling of material softening, followed by an element deletion strategy that is developed in this framework. The second strategy adds a Bao-Wierzbicki model to the VGM strategy (VGM-BW) in order to account more directly for fracture initiation in lower and negative triaxiality regions. The third strategy is a constant critical strain (CS) approach that does not include softening but instead deletes an element when it achieves a peak equivalent plastic strain. The parameters of the VGM strategy were calibrated to a comprehensive set of experimental test results of circumferentially notched tensile (CNT) coupon specimens, the Bao-Wierzbicki parameters in VGM-BW strategy were determined analytically through tensile coupon (TC) specimens, and the CS approach used a constant value for equivalent plastic strain at softening initiation. These strategies were then validated through comparison with experimental test results of specimens commonly used for material characterization of steel. The results establish the accuracy and effectiveness of the VGM strategy for high-fidelity parametric simulation capabilities for collapse of steel structures and provide recommendations for where additional experimental research is needed to validate regions of low and negative triaxiality.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 3 finite element deletion fracture strategies compared for collapse modeling of steel structures. </LI> <LI> Strategies calibrated analytically and by particle swarm optimization to a set of test results. </LI> <LI> Strategies validated by comparison with experimental test results from variety of specimens. </LI> </UL> </P>
-
Vitaliy V. Degtyarev,Stephen J. Hicks,Jerome F. Hajjar 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.43 No.3
Accurate design models for predicting the shear resistance of headed studs in solid concrete slabs are essential for obtaining economical and safe steel-concrete composite structures. In this study, symbolic regression with genetic programming (GPSR) was applied to experimental data to formulate new descriptive equations for predicting the shear resistance of studs in solid slabs using both normal and lightweight concrete. The obtained GPSR-based nominal resistance equations demonstrated good agreement with the test results. The equations indicate that the stud shear resistance is insensitive to the secant modulus of elasticity of concrete, which has been included in many international standards following the pioneering work of Ollgaard et al. In contrast, it increases when the stud height-to-diameter ratio increases, which is not reflected by the design models in the current international standards. The nominal resistance equations were subsequently refined for use in design from reliability analyses to ensure that the target reliability index required by the Eurocodes was achieved. Resistance factors for the developed equations were also determined following US design practice. The stud shear resistance predicted by the proposed models was compared with the predictions from 13 existing models. The accuracy of the developed models exceeds the accuracy of the existing equations. The proposed models produce predictions that can be used with confidence in design, while providing significantly higher stud resistances for certain combinations of variables than those computed with the existing equations given by many standards
연관 검색어 추천
이 검색어로 많이 본 자료
활용도 높은 자료
