Behavior and design of fastenings with headed anchors at the edge under tension and shear load

ABSTRACT: In the present paper the theoretical aspects and the application of the non-linear finite element program MASA for analysis of anchorages placed at an edge of a concrete block are discussed. After an introduction the structure of the finite element (FE) code is briefly described. The results of the simulations are shown and compared with experimental data. They confirm that the FE code is able to simulate realistically the behavior of anchorages. Subsequently a parametric study is caITied out and the results are discussed

Microbial Monitoring of Common Opportunistic Pathogens by Comparing Multiple Real-Time PCR Platforms for Potential Space Applications

Because the International Space Station is a closed environment with rotations of astronauts and equipment that each introduce their own microbial flora, it is necessary to monitor the air, surfaces, and water for microbial contamination. Current microbial monitoring includes labor- and time-intensive methods to enumerate total bacterial and fungal cells, with limited characterization, during in-flight testing. Although this culture-based method is sufficient for monitoring the International Space Station, on future long-duration missions more detailed characterization will need to be performed during flight, as sample return and ground characterization may not be available. At a workshop held in 2011 at NASA's Johnson Space Center to discuss alternative methodologies and technologies suitable for microbial monitoring for these long-term exploration missions, molecular-based methodologies such as polymerase chain reaction (PCR) were recommended. In response, a multi-center (Marshall Space Flight Center, Johnson Space Center, Jet Propulsion Laboratory, and Kennedy Space Center) collaborative research effort was initiated to explore novel commercial-off-the-shelf hardware options for space flight environmental monitoring. The goal was to evaluate quantitative or semi-quantitative PCR approaches for low-cost in-flight rapid identification of microorganisms that could affect crew safety. The initial phase of this project identified commercially available platforms that could be minimally modified to perform nominally in microgravity. This phase was followed by proof-of-concept testing of the highest qualifying candidates with a universally available challenge organism, Salmonella enterica. The analysis identified two technologies that were able to perform sample-to-answer testing with initial cell sample concentrations between 50 and 400 cells. In addition, the commercial systems were evaluated for initial flight safety and readiness

Psychophysiological processes of stress in chronic physical illness: a theoretical perspective

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75576/1/j.1365-2648.1990.tb01843.x.pd

Three-dimensional Modelling of Poorly Detailed RC Frame Joints

This paper presents preliminary work on three-dimensional numerical modelling of seismic strengthening measures for poorly detailed reinforced concrete frames, primarily designed for gravity loads, as was typical in seismic-prone countries before the introduction of more advanced seismic codes in the early 1970s. These buildings are at risk due to inadequate structural detailing, deficiencies in reinforcement anchorage and the absence of measures to prevent brittle failure modes. Representative beam-column joints tested experimentally at the University of Pavia are analyzed using a continuum finite element program specially developed for detailed modelling of fracture in quasi-brittle materials. The microplane material model with relaxed kinematic constraint is used for the concrete. In the first stage of this work, which is presented in this paper, the proper modelling of the behaviour of smooth reinforcement with hooked ends, as well as the accurate representation of brittle shear failure modes in joints, are of particular interest. In the second stage of the project, strengthening measures that incorporate post-installed anchors for connection to the existing structure will be assessed

Numerical analysis of compressed concrete columns confined with CFRP: Microplane-based approach

This paper presents the results of numerical studies carried out on concrete columns confined by Carbon Fiber Reinforced Polymer (CFRP) and loaded in uni-axial compression. A numerical simulation of confined columns experimentally tested by [1] is performed for relatively small concrete specimens of constant size but with different cross-section corner radius. The experimental results, reported in terms of axial stress–strain relationships and failure modes, constitute a useful database for the calibration of numerical models. These results clearly demonstrate that CFRP confinement is much less effective in square than in circular cross-sections. Therefore, the influence of the corner radius on the non-uniform stress distribution due to confinement, is numerically investigated using the proposed microplane-based model that takes into account the effect of multi-axial stress states in concrete. The experimental results are used to calibrate and verify the prediction capability of a three-dimensional finite element code (3D FE) that is based on the microplane constitutive law for concrete [2]. In the finite element model carbon fibers are modelled using nonlinear truss elements, while epoxy resin as well as concrete are modelled using microplane-based constitutive law and 3D finite elements. Given that experimental results for unconfined and confined configuration are available for each specimen, the 3D FE concrete model has been preliminarily calibrated on unconfined concrete specimens and then used in the analysis of a confined specimen. It is demonstrated that numerical models can predict behavior of confined concrete columns from the experimental investigations, confirming the predictability of the numerical microplane-based approach used

MESOSCALE MODELING OF CONCRETE: MICROPLANE-BASED APPROACH

In the paper mesoscale model for plain concrete, based on the microplane theory [1] is presented. In the model concrete is treated as a bi-phase composite material, consisting of coarse aggregate and mortar matrix. The presence of interfacial transition zone (ITZ) between the two phases is neglected. The numerical study is based on the experimental tests performed by Wang and Wu [2] on small square concrete columns confined with CFRP and subjected to uniaxial compressive loads. The tests results, reported in terms of axial stress-strain relationships and failure modes, represent useful data base for the calibration of numerical models. In the first step of the study, only the unconfined concrete cylinder (R75) has been modeled at mesoscale. An important aspect of the proposed model is the generation of a random aggregate structure in concrete, which is based on a generation procedure implemented in Matlab R2013b. The mesoscale analysis of the unconfined cylinder is performed by using the finite element code MASA [3]. The constitutive law for mortar is based on the microplane model, while aggregates have been considered linear elastic. It is demonstrated that the numerical model is capable to correctly reproduce the mechanical behavior of the unconfined cylinder, confirming the predictability of the used approach