Kinematics of shear bands   总被引：2，自引：2，他引：0  

Dimitrios Kolymbas 《Acta Geotechnica》2009,4(4):315-318

Shear bands appear at limit states of soil bodies. They are analysed as thin zones of localised deformation that takes place as simple (i.e. dilatant) shear. It can be observed, however, that shear bands are discontinuous and also may be “reflected” at rigid boundaries. These phenomena appear as incompatible with the assumed shear deformation. The analysis in this paper reveals the kinematics of such “incompatibilities” in terms of continuous deformation fields.  相似文献   

Modelling of R/C members accounting for shear failure localisation: Hysteretic shear model          下载免费PDF全文

Dimitrios K. Zimos  Panagiotis E. Mergos  Andreas J. Kappos 《地震工程与结构动力学》2018,47(8):1722-1741

Reinforced concrete (R/C) frame buildings designed according to older seismic codes represent a large part of the existing building stock worldwide. Their structural elements are often vulnerable to shear or flexure‐shear failure, which can eventually lead to loss of axial load resistance of vertical elements and initiate vertical progressive collapse of a building. In this study, a hysteretic model capturing the local shear response of shear‐deficient R/C elements is described in detail, with emphasis on post‐peak behaviour; it differs from existing models in that it considers the localisation of shear strains after the onset of shear failure in a critical length defined by the diagonal failure planes. Additionally, an effort is made to improve the state of the art in post‐peak shear response modelling, by compiling the largest database of experimental results for shear and flexure‐shear critical R/C columns cycled well beyond the onset of shear failure and/or up to the onset of axial failure, and developing empirical relationships for the key parameters defining the local backbone post‐peak shear response of such elements. The implementation of the derived local hysteretic shear model in a computationally efficient beam‐column finite element model with distributed shear flexibility, which accounts for all deformation types, will be presented in a companion paper.  相似文献   

Conditional spectrum based ground motion record selection using average spectral acceleration          下载免费PDF全文

Mohsen Kohrangi  Paolo Bazzurro  Dimitrios Vamvatsikos  Andrea Spillatura 《地震工程与结构动力学》2018,47(1):265-265

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Modelling of R/C members accounting for shear failure localisation: Finite element model and verification          下载免费PDF全文

Dimitrios K. Zimos  Panagiotis E. Mergos  Andreas J. Kappos 《地震工程与结构动力学》2018,47(7):1631-1650

Reinforced concrete (R/C) frame buildings designed according to older seismic codes represent a large part of the existing building stock worldwide. Their structural elements are often vulnerable to shear or flexure‐shear failure, which can eventually lead to loss of axial load resistance of vertical elements and initiate vertical progressive collapse of a building. In this study, a computationally efficient member‐type finite element model for the hysteretic response of shear critical R/C frame elements up to the onset of axial failure is presented; it accounts for shear‐flexure interaction and considers, for the first time, the localisation of shear strains, after the onset of shear failure, in a critical length defined by the diagonal failure plane. Its predictive capabilities are verified against experimental results of column and frame specimens and are shown to be accurate not only in terms of total response, but also with regard to individual deformation components. The accuracy, versatility, and simplicity of this finite element model make it a valuable tool in seismic analysis of complex R/C buildings with shear deficient structural elements.  相似文献   

Pulse-like versus non-pulse-like ground motion records: Spectral shape comparisons and record selection strategies     

Mohsen Kohrangi  Dimitrios Vamvatsikos  Paolo Bazzurro 《地震工程与结构动力学》2019,48(1):46-64

Pulse-like records are well recognized for their potential to impose higher demands on structures when compared with ordinary records. The increased severity of the structural response usually caused by pulse-like records is commonly attributed to the spectral increment around the pulse period. By comparing the building response to sets of spectrally equivalent pulse-like and ordinary records, we show that there are characteristics of pulse-like records beyond the shape of the acceleration response spectrum that affect the results of nonlinear dynamic analysis. Nevertheless, spectral shape together with the ratio of pulse period to the first-mode structural period, T_p/T₁, are confirmed as “sufficient” predictors for deformation and acceleration response metrics in a building, conditioned on the seismic intensity. Furthermore, the average spectral acceleration over a period range, AvgSA, is shown to incorporate to a good proxy for spectral shape, and together with T_p/T₁, form an efficient and sufficient intensity measure for response prediction to pulse-like ground motions. Following this latter route, we propose a record selection scheme that maintains the consistency of T_p with the hazard of the site but uses AvgSA to account for the response sensitivity to spectral shape.  相似文献   

Seismic risk assessment of liquid storage tanks via a nonlinear surrogate model          下载免费PDF全文

Konstantinos Bakalis  Dimitrios Vamvatsikos  Michalis Fragiadakis 《地震工程与结构动力学》2017,46(15):2851-2868

A performance‐based earthquake engineering approach is developed for the seismic risk assessment of fixed‐roof atmospheric steel liquid storage tanks. The proposed method is based on a surrogate single‐mass model that consists of elastic beam‐column elements and nonlinear springs. Appropriate component and system‐level damage states are defined, following the identification of commonly observed modes of failure that may occur during an earthquake. Incremental dynamic analysis and simplified cloud are offered as potential approaches to derive the distribution of response parameters given the seismic intensity. A parametric investigation that engages the aforementioned analysis methods is conducted on 3 tanks of varying geometry, considering both anchored and unanchored support conditions. Special attention is paid to the elephant's foot buckling formation, by offering extensive information on its capacity and demand representation within the seismic risk assessment process. Seismic fragility curves are initially extracted for the component‐level damage states, to compare the effect of each analysis approach on the estimated performance. The subsequent generation of system‐level fragility curves reveals the issue of nonsequential damage states, whereby significant damage may abruptly appear without precursory lighter damage states.  相似文献   

Development of collapse-consistent loading protocols for experimental testing of steel columns     

Yusuke Suzuki  Dimitrios G. Lignos 《地震工程与结构动力学》2020,49(2):114-131

In order to effectively utilize results from quasi-static cyclic testing on structural components for the earthquake-induced collapse risk quantification of structures, the need exists to establish collapse-consistent loading protocols representing the asymmetric lateral drift demands of structures under low-probability of occurrence earthquakes. This paper summarizes the development of such protocols for experimental testing of steel columns prone to inelastic local buckling. The protocols are fully defined with a deformation- and a force-controlled parameter. They are generally applicable to quantify the capacity and demands of steel columns experiencing constant and variable axial load coupled with lateral drift demands. Through rigorous nonlinear earthquake collapse simulations, it is found that the building height, the column's local slenderness ratio, and ground motion type have the largest influence on the dual-parameter loading protocol indexes. Comprehensive comparisons with measured data from full-scale shake table collapse tests suggest that unlike routinely used symmetric cyclic loading histories, the proposed loading protocol provides sufficient information for modeling strength and stiffness deterioration in steel columns at large inelastic deformations.  相似文献   

Strength-reduction factors for the design of light nonstructural elements in buildings     

Athanasia K. Kazantzi  Eduardo Miranda  Dimitrios Vamvatsikos 《地震工程与结构动力学》2020,49(13):1329-1343

Strength-reduction factors that reduce ordinates of floor spectra acceleration due to nonlinearity in the secondary system are investigated. In exchange for permitting some inelastic deformation to occur in the secondary system or its supports, these strength reduction factors allow to design the nonstructural elements or their supports for lateral forces that are smaller than those that would be required to maintain them elastically during earthquakes. This paper presents the results of a statistical analysis on component strength-reduction factors that were computed considering floor motions recorded on instrumented buildings in California during various earthquakes. The effect of yielding in the component or its anchorage/bracing in offering protection against excessive component acceleration demands is investigated. It is shown that strength-reduction factors computed from floor motions are significantly different from those computed from ground motions recorded on rock or on firm soils. In particular, they exhibit much larger reductions for periods tuned or nearly tuned to the dominant modal periods of the building response. This is due to the large differences in frequency content of ground motions and floor motions, with the former typically characterized by wide-band spectra whereas the latter are characterized by narrow-band spectra near periods of dominant modes in the response of the building. Finally, the study provides approximate equations to estimate component strength-reduction factors computed through nonlinear regression analyses.  相似文献   

Extraction and predictability of coherent intraseasonal signals in infrared brightness temperature data     

Eniko Székely  Dimitrios Giannakis  Andrew J. Majda 《Climate Dynamics》2016,46(5-6):1473-1502

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Catchment-wide estimate of single storm interrill soil erosion using an aggregate instability index: a model based on geographic information systems     

Christina Tsimi  Athanassios Ganas  Dimitrios Dimoyiannis  Spyros Valmis  Efthimios Lekkas 《Natural Hazards》2012,62(3):863-875

The main objective of this paper is to estimate interrill erosion after rainfall in the basin of Mourganis river (442?km²; Kalabaka province, Trikala prefecture, Thessaly, Greece). For the estimation of the interrill erosion, the method of Valmis et al. (1988) was used, in combination with Nearing et al. (1989). Input data of the algorithm include the slope angle of the ground surface, the rainfall, the ground cover type, the height of canopy, and the instability of ground of the study area. The spatial data were processed by standard GIS software. Soil samples were collected in the field to calibrate the model. The results comprise soil erosion maps for two specific rainfall scenarios. The first rainfall scenario refers to the most extreme rainfall in this catchment that happened on the 7/21/1959 with 48?mm/h. The second scenario is closer to average as the intensity rainfall is 3.54?mm/h. The total mass of eroded material ranges from 0.048?t/ha (assuming mean rainfall intensity) up to 3.5?t/ha (for the extreme scenario). We note that the western part of the Mourgani basin exhibits higher erosion than the eastern part.  相似文献