1,721,121 research outputs found
Structure-function relationships in Escherichia coli translational elongation factor G: modification of lysine residues by the site-specific reagent pyridoxal phosphate
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Nonlinear micromechanical modeling of tuff stone masonry for dynamic response analysis
No full textMasonry is a composite material made of prismatic elements (i.e. stones, bricks or blocks) and mortar or dry joints. Masonry assemblages are typically used to form load-bearing or partition walls, as well as vaults, domes and retaining walls. Different computational strategies are currently available to simulate mechanical behavior of masonry structures, but experimental data are needed to assess the accuracy of numerical and analytical models.
In this study, a micromechanical finite element (FE) model is proposed for tuff stone masonry, which has been used from ancient times to the present for construction of buildings and infrastructures (e.g. arch bridges and water distribution networks). The arrangement of stones was set up according to the running masonry bond scheme. The micromechanical modeling approach allowed the authors to distinctly simulate the behavior of stone units and mortar joints, as well as their interaction. The FE model was developed within LS-DYNA computer program to predict masonry response to quasistatic, dynamic and even impulsive loads such as blast and impact. Material properties and volumetric stress‒strain behavior of constituents (i.e. stones and mortar) were properly defined by means of laboratory test results. The nonlinear micromechanical FE model was then calibrated to get an effective reproduction of the experimental behavior of masonry specimens under different load patterns, hence assessing its numerical robustness. A satisfactory experimental-numerical comparison in terms of force‒displacement diagrams and crack patterns was found. Local limit states associated with different failure modes of masonry constituents were statistically characterized for each load pattern. Finally, the influence of material properties was assessed. This investigation was first based on a sensitivity analysis where material properties were changed according to statistical variability from experimental evidence. Then, a stochastic FE analysis was carried out by simulating material properties in compliance with discrete and continuous probability models. That procedure accounted for the actual inhomogeneity of masonry constituents. Key masonry properties such as peak resistance and ultimate displacement were statistically characterized, evaluating the propagation of material uncertainties to the macroscopic level. The micromechanical model presented in this paper will be used for dynamic response analysis of masonry walls subjected to blast loading
Stochastic finite element analysis of Portuguese adobe masonry
Full text linkEarth is a construction material which has been used since ancient times in many parts of the world according to its local
availability, low manufacturing cost, and its need for simple construction techniques. Even though earthen constructions
have good thermo-acoustic properties, they typically show a very poor performance under earthquake ground motion.
Rammed earth and adobe masonry are the main types of earthen construction. Nowadays, it is estimated that approximately
30% of the world population lives in earthen buildings and this percentage increases up to around 50% in developing
countries. Such an information highlights the need for a seismic assessment and strengthening of existing earthen structures.
The present study is focused on the mechanical behavior of the traditional adobe masonry (AM) of the Aveiro district,
Portugal, where approximately 40% of existing buildings are made of adobe and many of them have a socio-cultural value.
Extensive surveys have shown a poor state of conservation of AM buildings, the strengthening of which should be based on
a comprehensive knowledge of mechanical properties and behavior. To that aim, a nonlinear finite element (FE) modelling
approach is used to simulate the experimental behavior of AM in different boundary and loading conditions associated with
axial and diagonal compression tests. The latter are amongst the most common experimental tests used for mechanical
characterization of masonry assemblages, particularly to define their macroscopic response to uniaxial compression and
shear. Based on statistics for mechanical properties of adobe bricks and mud mortar provided by past experimental tests, a
macromechanical model of AM was developed within LS-DYNA software and validated against experimental data. The FE
models of two types of specimens subjected to axial compression and diagonal compression, separately, were generated. A
comparative analysis between numerical and experimental results, both in terms of force–displacement curves and crack
patterns, showed that the FE model was able to reproduce the real behavior of AM in different boundary and loading
conditions. Afterwards, a single-parameter sensitivity analysis was performed on each AM model to assess whether and
how the AM behavior changes under varying material properties. That analysis was the basis for a probabilistic assessment
in which a stochastic FE analysis was carried out. Each material property was assumed to be a spatially-distributed random
variable in order to reproduce the high level of inhomogeneity provided by material tests on AM constituents, that is adobe
bricks and mortar. A small number of model realizations subjected to axial compression was randomly generated through
Monte Carlo simulation technique. Two alternative types of stochastic representation were adopted. The former was a
simplified stochastic FE modeling (SFEM) in which the spatial variability of material properties was lumped into single
brick units, each of them fictitiously extended to the middle of mortar joints. In the second case, an advanced stochastic FE
modeling (ASFEM) strategy was used and consisted in a random generation of material properties for all finite elements. It
was found that even a limited number of ASFEM simulations allowed the experimental force–displacement response to be
captured
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