The Experts below are selected from a list of 136530 Experts worldwide ranked by ideXlab platform
Francesca Da Porto - One of the best experts on this subject based on the ideXlab platform.
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seismic fragility curves of as built single span masonry arch bridges
Bulletin of Earthquake Engineering, 2016Co-Authors: Giovanni Tecchio, Marco Dona, Francesca Da PortoAbstract:Masonry arch bridges are crucial elements in the railway transportation network throughout Europe. Although significant advances in seismic risk assessment of various bridge types have been made by developing fragility curves of generalized classes of structures, there are no comparable tools for masonry arch structures. In this context, this paper presents the construction of seismic fragility curves of single-span masonry bridges according to the Limit Analysis Method. An iterative procedure is implemented to define the capacity curve of the equivalent single degree of freedom system through non-linear kinematic Analysis. The process involves determination of the collapse mechanism, calculation of the Limit load multiplier, and definition of the thrust line. The intrinsic variability of the seismic action is incorporated with the use of different sets of elastic spectra compatible with EC 8 Type-1 spectrum for various types of soil, with peak ground acceleration varying over the range 0.05–1.5 g. The fragility curves of the generalized classes of single-span masonry bridges are finally obtained from the effective ranges of the main geometric and material parameters affecting arch bridge capacity.
Hoon Huh - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Limit Analysis formulation for impact simulation of structural members
International Journal of Solids and Structures, 2006Co-Authors: Kee Poong Kim, Hoon HuhAbstract:Abstract This paper introduces an extended concept of Limit Analysis to deal with the dynamic equilibrium condition considering the inertia and strain-rate effect for dynamic behavior of structures. The conventional Limit Analysis Method has been applied to only static collapse Analysis of structures without consideration of dynamic effects in the structural behavior. A dynamic formulation for the Limit Analysis has been derived for incremental Analysis dealing with time integration, strain and stress evaluation, strain hardening, strain-rate hardening and thermal softening. The time dependent term in the governing equation is integrated with the WBZ-α Method. The dynamic material behavior is described by the Johnson–Cook model in order to consider strain-rate hardening and thermal softening as well as strain hardening. Simulations have been carried out for impact Analysis of a Taylor bar and an S-rail and their numerical results are compared with elasto-plastic explicit Analysis results by LS-DYNA3D. Comparison demonstrates that the dynamic finite element Limit Analysis can predict the crashworthiness of structural members effectively with less effort and computing time than the commercial code compared. The crashworthiness of a structure with the rate-dependent constitutive model is also compared to that with the quasi-static constitutive relation in order to investigate the dynamic effect on deformation of structures.
Athanasios Pappas - One of the best experts on this subject based on the ideXlab platform.
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rocking of offshore lighthouses under extreme wave impacts Limit Analysis analytic formulations and distinct element Method
Engineering Structures, 2021Co-Authors: Athanasios Pappas, Alessandro Antonini, Dina Dayala, Darshana T Dassanayake, Alison RabyAbstract:Abstract This study describes the structural response of historic lighthouses to extreme wave impacts. Located offshore on exposed rocks, 19th Century lighthouses were built with large interlocked granite blocks and have survived weathering for nearly two centuries. Under extreme wave impacts, lighthouses of this structural typology may uplift and rock, whereas sliding is prevented by the vertical interlocking. The uplift and sliding thresholds calculated with the Limit Analysis Method reveal why this structural system is capable of bearing extreme wave impacts without failure. The ingenious vertical keying is proven to be a major characteristic that contributes to the resilience of these lighthouses. The structural response is explained with the use of analytic formulations of the rocking motion. Detailed Analysis of the response to wave impact is conducted with reference to Wolf Rock lighthouse. The impact wave corresponding to a 250-year effective return period is identified using non-stationary Bayesian extreme Analysis. Moreover, wave flume tests on a scaled cylindrical structure were performed to identify the wave impact force time-history shapes. Based on two waves: a theoretical time-history based on existing models in the literature and the measured time-histories from small-scale experiments, a series of synthetic force time-history sequences are generated for the purposes of a parametric Analysis. This parametric Analysis, with the Distinct Element Method, using the commercial software 3DEC, reveals the influence of the duration and shape of the force time-history function. For impacts with the same impulse values, shorter time impacts produce the most intense opening of joints, despite causing smaller horizontal displacements. Furthermore, variability in the structural response is revealed even for impacts of the same impulse, duration and maximum force but different shape of the force time-history.
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invited rock mounted iconic lighthouses under extreme wave impacts Limit Analysis and discrete element Method
THE 9TH INTERNATIONAL CONFERENCE ON COMPUTATIONAL METHODS (ICCM2018), 2018Co-Authors: Athanasios Pappas, Alessandro Antonini, Dina Dayala, Aliso RabyAbstract:This paper deals with the resilience of rock mounted lighthouses impacted by extreme waves. The investigated lighthouse of Wolf Rock is built with large and meticulously dovetailed granite blocks. For this structural typology, uplift of blocks and separation of joints is possible under intense wave impacts. Sliding between subsequent courses of stones is Limited by the existence of vertical keys between the blocks. The lateral forces that can trigger uplift and rocking, a highly non-linear behaviour, are calculated with the use of Limit Analysis Method through an iterative procedure written in Python programming language. Three different overturning mechanisms, which correspond to different hypotheses about the working section of the lighthouse, are considered for the uplift. The most conservative Limits, i.e. with only a portion of the circular section taking the load, are representative for small and medium waves which can cause a small uplift and very local opening of a joint. The mechanism that considers the whole section, i.e. less conservative, is more representative for very strong wave impacts. The sliding failure mechanism is also considered. The Limit Analysis thresholds are validated with Discrete Element (DE) time-history analyses using the commercial software 3DEC. Intense uplift and rocking, especially present when the less conservative Limit Analysis thresholds are exceeded. The study also revealed the beneficial role of the vertical keys, without which the lighthouse would fail due to intense sliding before the overturning mechanisms are activated.
Giovanni Tecchio - One of the best experts on this subject based on the ideXlab platform.
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seismic fragility curves of as built single span masonry arch bridges
Bulletin of Earthquake Engineering, 2016Co-Authors: Giovanni Tecchio, Marco Dona, Francesca Da PortoAbstract:Masonry arch bridges are crucial elements in the railway transportation network throughout Europe. Although significant advances in seismic risk assessment of various bridge types have been made by developing fragility curves of generalized classes of structures, there are no comparable tools for masonry arch structures. In this context, this paper presents the construction of seismic fragility curves of single-span masonry bridges according to the Limit Analysis Method. An iterative procedure is implemented to define the capacity curve of the equivalent single degree of freedom system through non-linear kinematic Analysis. The process involves determination of the collapse mechanism, calculation of the Limit load multiplier, and definition of the thrust line. The intrinsic variability of the seismic action is incorporated with the use of different sets of elastic spectra compatible with EC 8 Type-1 spectrum for various types of soil, with peak ground acceleration varying over the range 0.05–1.5 g. The fragility curves of the generalized classes of single-span masonry bridges are finally obtained from the effective ranges of the main geometric and material parameters affecting arch bridge capacity.
Lianheng Zhao - One of the best experts on this subject based on the ideXlab platform.
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variation Analysis of ultimate pullout capacity of shallow horizontal strip anchor plate with 2 layer overlying soil based on nonlinear m c failure criterion
Journal of Central South University, 2018Co-Authors: Lianheng Zhao, Yigao Tan, Zhihong Nie, Xinping YangAbstract:Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule, a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constructed. The ultimate pull-out force and its corresponding failure mechanism through the upper bound Limit Analysis according to a variation principle are deduced. When the 2-layer overlying soil is degraded into single-layer soil, the model of ultimate pullout force could also be degraded into the model of single-layer soil. And the comparison between results of single-layer soil variation Method and those calculated by rigid Limit Analysis Method proves the correctness of our Method. Based on that, the influence of changes of geotechnical parameters on ultimate pullout forces and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are analyzed. The results show that the ultimate pull-out force and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are affected by the nonlinear geotechnical parameters greatly. Thus, it is very important to obtain the accurate geotechnical parameters of 2-layer soil for the evaluation of the ultimate pullout capacity of the anchor plate.
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Stability Analysis of irregular cavities using upper bound finite element Limit Analysis Method
Computers and Geotechnics, 2018Co-Authors: Lianheng Zhao, Shan Huang, Rui Zhang, Shi ZuoAbstract:Abstract Underground cavities mainly exhibit irregular forms in nature. Due to the difficulties in describing the geometrical shape of irregular cavities and theoretically analyzing such cavities, irregular cavities are generally simplified as regular circular, elliptical or polygonal shapes in most studies. The purpose of this paper is to quantitatively describe the shape of irregular cavities using Fourier descriptors from inverse discrete Fourier transform (IDFT) theory and to translate the generation process of irregular cavity contours into a conversion between discrete frequency-domain and time-domain signals. Based on this approach, the stability Analysis of irregular underground cavities is conducted using the upper bound finite element Limit Analysis (UB-FELA) Method. The upper bound stability numbers (γcrD/c) and collapse mechanisms are presented for a series of irregular cavity depth-to-diameter ratios (H/D), internal friction angles (φ) and geometrical shape descriptors (D2, D3 and D8). The obtained results demonstrate that the stability numbers increase with increasing φ and decrease with increasing H/D and descriptor values (D2, D3 and D8). The failure mechanisms are significantly asymmetrical due to the contour fluctuations of the irregular cavity. Specifically, interlaced shear bands form between the adjacent fluctuations on the surface of the irregular cavity, which considerably differs from the failure mechanism of regular cavities. Local shear failure is the main failure form for the soil around the cavity. An obvious bottom bulge phenomenon is observed in the cavity at small internal friction angles.
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effects of shear strength reduction strategies on safety factor of homogeneous slope based on a general nonlinear failure criterion
Computers and Geotechnics, 2015Co-Authors: Lianheng Zhao, Feng Yang, Yingbin Zhang, Hancheng Dan, Weizheng LiuAbstract:Abstract Safety factor of slope is often calculated based on the conventional linear Mohr–Coulomb failure criterion. However, many experimental results show that the strength envelopes of almost all of geomaterials are characteristically nonlinear. This paper presents a Method (upper bound Limit Analysis Method) to analyze the stability of a homogeneous slope based on a general nonlinear failure criterion, in which different shear strength reduction strategies ( SSRS ) can be used. Based on the presented Method, three SSRSs (i.e. by factoring the unconfined shear strength c 0 only, by factoring the tensile strength σ t only, by factoring both the unconfined shear strength c 0 and the tensile strength σ t ) are used to calculate the safety factors of a homogeneous slope under a general nonlinear failure criterion. Compared results show different SSRSs have significant influence on the calculated safety factor.