Search results for "Creep"

How does shear zone nucleate? An example from the Suretta nappe (Swiss Eastern Alps)

2016

In order to address the question of the processes involved during shear zone nucleation, we present a petro-structural analysis of millimetre-scale shear zones within the Roffna rhyolite (Suretta nappe, Eastern central Alps). Field and microscopic evidences show that ductile deformation is localized along discrete fractures that represent the initial stage of shear zone nucleation. During incipient brittle deformation, a syn-kinematic metamorphic assemblage of white mica + biotite + epidote + quartz precipitated at ca. 8.5 ± 1 kbar and 480 ± 50 °C that represent the metamorphic peak conditions of the nappe stacking in the continental accretionary wedge during Tertiary Alpine subduction. The…

Creep Behavior of Poly(lactic acid) Based Biocomposites

2017

Polymer composites containing natural fibers are receiving growing attention as possible alternatives for composites containing synthetic fibers. The use of biodegradable matrices obtained from renewable sources in replacement for synthetic ones is also increasing. However, only limited information is available about the creep behavior of the obtained composites. In this work, the tensile creep behavior of PLA based composites, containing flax and jute twill weave woven fabrics, produced through compression molding, was investigated. Tensile creep tests were performed at different temperatures (i.e., 40 and 60 °C). The results showed that the creep behavior of the composites is strongly inf…

Certhia tianquanensis Li, a treecreeper with relict distribution in Sichuan, China

2002

Certhia tianquanensis Li, 1995, is characterised as a distinct species and is combined withC. discolor in the superspeciesC. [discolor]. This probably relict species occupies an extremely small range, and has so far been found at only four sites in western Sichuan, China. It is characterised by a long tail (likeC. discolor), an extremely short bill (similar toC. nipalensis), the patterning on the underside, with white chin and throat and beige chest and abdomen (likeC. himalayana), a striking voice (clearly different fromC. discolor and all otherCerthia species), and a large genetic distance fromC. d. discolor in the cytochrome-b gene. Unlike its closest relativeC. discolor, C. tianquanensi…

Behavioural responses of Eurasian treecreepers, Certhia familiaris, to competition with ants

1997

Competition for a specific resource that is essential for the survival of both the competitors may be intense even between very dissimilar taxa. However, the importance of the effects caused by such interspecific competition has seldom been emphasized. These effects can appear as differences in individual foraging behaviour during the breeding season, which can result in critical variation in fitness. In this study we examined the effects of wood ants (Formica rufa group) on the abundance of other invertebrates on tree trunks and on the foraging site selection of breeding Eurasian treecreepers, which use the same habitat as wood ants. Arthropods were scarcer on the trunks with ants present;…

Food availability and the male's role in parental care in double-brooded TreecreepersCerthia familiaris

1996

The aim of this work was to examine differences in paternal and maternal care in a double-brooded, monogamous species, the Treecreeper Certhia familiaris, in relation to food availability. As a measure of parental care, we recorded the hourly feeding activity of parents when the nestlings from their first and second breeding attempts were 7 and 12 days old. Feeding frequency of the first brood increased with the age of the nestlings and also with the brood size when 12 days old. While the feeding activities of the females were similar with respect to the first and second broods, the males were less active and failed to provide any food to their nestlings in 15 cases out of 28 second broods.…

Thresholds in selection of breeding habitat by the Eurasian treecreeper (Certhia familiaris)

2005

Abstract Assessment of habitat thresholds is a topical issue in ecology, both from theoretical and applied perspectives. We examined how forest structure influences selection of breeding habitat in the Eurasian treecreeper (Certhia familiaris). It is an old-growth forest passerine, which can be considered an umbrella species. Habitat selection data, covering five breeding seasons, were collected from a study area across three spatial scales: (a) territory core scale (a radius of 30 m), (b) territory scale (a radius of 200 m) and (c) large scale (a radius of 500 m). Logistic regression analyses revealed that the radii of 30 and 200 m from the nest were the most important spatial scales for t…

Fenomeni lenti nelle fasi di costruzione ed esercizio degli impalcati da ponte precompressi

2010

Creep effects and stress adjustments in cable-stayed bridges with concrete deck

2010

In construction stages of cable-stayed bridges with prestressed concrete deck, the influence of creep on stresses and strains is very important in order to foresee the final patterns of internal forces and displacements. In cantilever construction, the concrete deck can be considered, in each stage, as a continuous beam resting on elastic restraints, which modify with successive additions of new segments, until the last one has been assembled. In these stages stress relaxation in concrete occurs as well as vertical displacements increase. Ehen structure has been closed by inserting midspan segment, stress redistribution begins, due to creep. Deformation and internal force development in con…

A Viscoelastic Model for the Long-Term Deflection of Segmental Prestressed Box Girders

2017

Most of segmental prestressed concrete box girders exhibit excessive multidecade deflections unforeseeable by past and current design codes. To investigate such a behavior, mainly caused by creep and shrinkage phenomena, an effective finite element (FE) formulation is presented in this article. This formulation is developed by invoking the stationarity of an energetic principle for linear viscoelastic problems and relies on the Bazant creep constitutive law. A case study representative of segmental prestressed concrete box girders susceptible to creep is also analyzed in the article, that is, the Colle Isarco viaduct. Its FE model, based on the aforementioned energetic formulation, was succ…

Computer vision and thermal monitoring of HMPE fibre rope condition during CBOS testing

2020

Abstract Fibre rope usage in deep sea lifting operations is gaining more prominence in recent times. With rope minimum break loads (MBL) comparable to that of their steel wire counterparts, the use of high modulus polyethylene (HMPE) ropes is seen as a viable option for use in subsea construction cranes. The ropes are worn out during use and visual inspection remains one of the main methods of determining whether a fibre rope is to be retired from use, therefore a natural extension is condition monitoring through computer vision. Creep and temperature are constraining with HMPE ropes and should be monitored continuously, particularly when the rope is cyclically bent over sheaves. Additional…