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Collapse Mechanism (collapse + mechanism)

Distribution by Scientific Domains
Engineering50%

Selected Abstracts

Karst Collapse Mechanism and Criterion for Its Stability

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2001
HE Keqiang
Abstract Karst collapse, caused by natural or artificial abstraction of groundwater, has been a focus of environmental geological problems for its ever-increasing hazardousness. The potential erosion theory and vacuum suction erosion theory, which reveal the origin of karst collapse macroscopically, are popularly accepted. However, a mathematic prediction criterion for karst collapse cannot be established only by these two theories. From a new perspective, this paper attempts to explain the microcosmic mechanism of karst collapse on the basis of these two theories. When the shear stress surpasses the shear strength of soil, a certain point or a certain plane in the unconsolidated soil covering karst caves will fail under the mechanical effects of water and air as well as its load-pressure, and with the increase of damaged points, a breaking plane appears and the soil on karst caves is completely damaged; as a result, the karst ground collapses. On the basis of the Mohr-Coulomb failure theory and previous studies, the paper presents a prediction criterion of karst collapse. Finally, by taking, for example, nine typical cases of collapse caused by pumping tests in Guizhou, the paper gives the calculation process of the model and proves its reliability. [source]

Dynamic Collapse Mechanisms in Metal Foam Expansion

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Dirk Lehmhus
Abstract The study provides insight into decomposition of titanium hydride as foaming agent for powder metallurgically produced aluminum foams. Decomposition is characterized using thermal and kinetic analysis, allowing prediction of decomposition reactions. Such predictions are made for various time,temperature cycles, which are experimentally evaluated in parallel foaming experiments. A new explanation of foam collapse is derived from the results, which interprets hints at a maximum gas release rate, limiting maximum expansion, in terms of the existence of a maximum cell wall stretching rate and expanding foam can sustain. Thus a dynamic collapse criterion is added to existing static ones. [source]

Seismic behavior of single-story asymmetric-plan buildings under uniaxial excitation

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 9 2009
Andrea Lucchini
Abstract The critical parameters that influence the nonlinear seismic response of asymmetric-plan buildings are identified by evaluating the effects of different asymmetries that may characterize the structure of a building as well as exploring the influence of the ground motion features. First, the main findings reported in the literature on both the linear and nonlinear dynamic response of asymmetric-plan buildings are presented. The common findings and the conflicting conclusions reached in different investigations are pointed out. Then, the results of comprehensive nonlinear dynamic analyses performed for evaluating the seismic response of systems characterized by different strength and stiffness configurations, representative of a large class of asymmetric-plan buildings, are reported. Findings from the study indicate that the building response changes when moving from the linear to the nonlinear range, so that the seismic behavior of asymmetric-plan buildings, apart from the source of asymmetry, can be always classified as irregular. Additionally, it was observed that as the seismic demands cause amplification of system nonlinearity with increasing earthquake intensity, the maximum displacement demand in the different resisting elements tends to be reached with the same deformed configuration of the system. The resultant of the seismic forces producing such a maximum demand is located at the center of resistance and corresponds to the collapse mechanism of the system that provides the maximum lateral strength in the exciting direction of the seismic action. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Aluminum "Egg-Box" Panel as an Energy Absorber for Pedestrian Protection

ADVANCED ENGINEERING MATERIALS, Issue 7 2010
Sravanthi Nowpada
Abstract This paper evaluates the quasi-static performance of lightweight aluminum "egg-box" panels which have an improved architecture specifically designed to increase the energy absorption capability. In its entirety, the egg-box panel structure investigated herein is made up of arrays of positive and negative frusta. To understand the collapse mechanism and the factors influencing the energy absorption thereof, compressive tests were conducted under similar test conditions on two single frusta, one constrained in situ and the other separated from the egg-box panel exposing the free,free edges. Their load-displacement histories show characteristics that are similar, with a rise in load to a point where they plateau at a steady state load for the entire collapse time. But the energy absorbed by the in situ constrained frustum is 80% greater than that separated from the egg-box panel with free,free edges. [source]

Application of micropolar plasticity to post failure analysis in geomechanics

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2004
Majid T. Manzari
Abstract A micropolar elastoplastic model for soils is formulated and a series of finite element analyses are employed to demonstrate the use of a micropolar continuum in overcoming the numerical difficulties encountered in application of finite element method in standard Cauchy,Boltzmann continuum. Three examples of failure analysis involving a deep excavation, shallow foundation, and a retaining wall are presented. In all these cases, it is observed that the length scale introduced in the polar continuum regularizes the incremental boundary value problem and allows the numerical simulation to be continued until a clear collapse mechanism is achieved. The issue of grain size effect is also discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Critical buckling load of paper honeycomb under out-of-plane pressure,

PACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2005
Li-Xin Lu
Abstract Two out-of-plane buckling criteria for paper honeycomb are proposed by analysing the structure properties and the collapse mechanism of paper honeycomb: these are based on the peeling strength and ring crush strength of the chipboard wall. Taking into account the orthotropic, initial deflection and large deflection properties of the chipboard wall, the two new mechanical models and the calculation methods are developed to represent the out-of-plane critical load of paper honeycomb. Theoretical calculations and test results show that the models are suitable for describing the collapse mechanism of paper honeycomb. The peeling strength and ring crush strength determine the critical buckling load of paper honeycomb in different stretch phases. The out-of-plane critical buckling load can be predicted when the two models are integrated. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Collapse load factor of planar frames using a modified genetic algorithm

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2004
A. Kaveh
Abstract In this article an analytical method is developed for identifying basic collapse mechanisms of rigid-jointed two-dimensional frames. In this approach, the deformation of each member is completely defined by four translations and one rotation. The behaviour of such an element lies in between that of a truss element and a flexural one. Once the basic collapse mechanisms are identified, the genetic algorithm is used to identify the mechanism corresponding to the least possible load factor. Examples are included to illustrate the efficiency of the present method compared to the use of a simple genetic algorithm. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Mechanisms of ultrasound foam interactions

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009
J. B. Winterburn
Abstract An experimental investigation into the effects of two frequencies of low-power ultrasound on detergent (Teepol) stabilised air-water foams is presented. Foam was subjected to ultrasound at 28 and 40 kHz with a power-to-foam volume ratio of approximately 3 W l,1 with particular consideration being given to the acoustic impedance discontinuity between air and water. The foam height, liquid drainage and collapse behaviour were compared to experiments conducted without ultrasound. In the case of 40 kHz ultrasound, an increased liquid drainage rate was observed and a pronounced increase and subsequent peak in mean liquid hold-up, which occurred at 4 min, was observed. These results appear to be independent of the initial liquid hold-up of the foam. Liquid drainage and mean liquid hold-up results were related to foam collapse mechanisms of homogeneous rupture (HR) and rupture front breakage (FR), concluding that rupture front breakage dominates the collapse of foam under the influence of 40 kHz ultrasound. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]