The Breathing of Webs Under Repeated Partial Edge Loading

AbstractSlender webs subjected to many times repeated partial edge loading repeatedly buckle (breathe) under this loading, which brings about the initiation and propagation of fatigue cracks in the neighbourhood of the loaded flange. This phenomenon leads to a significant “erosion” of the post-buckled behaviour of the web, which would very beneficially affect the limit state of the web if its loading were not repeated. Based on their experimental results, the authors establish user-friendly formulae such as to make it possible entirely to disregard the detrimental effect of web breathing even in the case of repeated loads, but on the condition that the maximum value of the cyclic loading is kept under a certain limi

Coordinated ultrastructural and phylogenomic analyses shed light on the hidden phycobiont diversity of Trebouxia microalgae in Ramalina fraxinea

[EN] The precise boundary delineations between taxa in symbiotic associations are very important for evolutionary and ecophysiological studies. Growing evidence indicates that in many cases, the use of either morphological characters or molecular markers results in diversity underestimation. In lichen symbioses. Trebouxia is the most common genus of lichen phycobionts, however, the diversity within this genus has been poorly studied and as such there is no clear species concept. This study constitutes a multifaceted approach incorporating aspects of ultrastructural characterization by TEM and phylogenomics to evaluate the morphological and genetic diversity of phycobionts within the sexually reproducing lichen Ramalina fraxinea in the context of Mediterranean and temperate populations. Results reveal an association with at least seven different Trebouxia lineages belonging to at least two species. T. decolorans and T. jamesii, and diverse combinations of such lineages coexisting within the same thallus depending on the analysed sample. Some of these lineages are shared by several other non-related lichen taxa. Our findings indicate the existence of a highly diverse assemblage of Trebouxia algae associating with R. fraxinea and suggest a possible incipient speciation within T. decolorans rendering a number of lineages or even actual species. This study stresses the importance of coordinated ultrastructural and molecular analyses to improve estimates of diversity and reveal the coexistence of more than one Trebouxia species within the same thallus. lt is also necessary to have clearer species delimitation criteria within the genus Trebouxia and microalgae in general.This study was funded by the Ministerio de Economia y Competitividad (MINECO CGL2012-40058-0O2-01/02), FEDER, the Generalitat Valenciana (PROMETEOII2013/021, GVA) and the Direccion General de Universidades e Investigacion de la Consejeria de Educacion de la Comunidad de Madrid - Universidad de Alcala (CCG10-UAH/GEN-5904). Drs. Arantxa Matins and Patricia Moya (Universitat de Valencia) made helpful comments on the manuscript.Català, S.; Campo, ED.; Barreno, E.; García-Breijo, F.; Reig Armiñana, J.; Casano, L. (2016). Coordinated ultrastructural and phylogenomic analyses shed light on the hidden phycobiont diversity of Trebouxia microalgae in Ramalina fraxinea. Molecular Phylogenetics and Evolution. 94:765-777. https://doi.org/10.1016/j.ympev.2015.10.021S7657779

The Influence of Shear Effects on the Deflections of Steel Box Girder Bridges

It is already well known that the shear lag phenomenon, generated by shear deformations in the flanges of box girders, can result in a very non-uniform distribution, across the flange width, of longitudinal normal stresses, and consequently can then influence girder deflections. The shear lag effects become even more pronounced in cases where flange width increases in relation to girder span. However, in box girders, where the cross-sectional area of webs usually represents a fraction of the total cross sectional area, also shear deformations of webs can significantly affect the magnitudes of girder deflections. Both these phenomena – the shear lag in the flanges and the shear deformations in the webs – become particularly manifest in box girders subjected to considerable shear forces. Such a situation occurs when a box girder bridge is under the action of usual deal and live loads