Effect of Spring-Mass-Damper Pedestrian Models on the Performance of Low-Frequency or Lightweight Glazed Floors

Funding Information: This research activity has been carried out at Department of Civil Engineering and Architecture of University of Trieste, and financially supported in the framework of “ComBioDyn” Microgrants 2022 project. Publisher Copyright: © 2023 by the authors.For structural design purposes, human-induced loads on pedestrian systems can be described by several simplified (i.e., deterministic equivalent-force models) or more complex computational approaches. Among others, the Spring-Mass-Damper (SMD), Single Degree of Freedom (SDOF) model has been elaborated by several researchers to describe single pedestrians (or groups) in the form of equivalent body mass m, spring stiffness k and damping coefficient c. For all these literature SMD formulations, it is proved that the biodynamic features of walking pedestrians can be realistically reproduced, with high computational efficiency for vibration serviceability assessment of those pedestrian systems mostly sensitive to human-induced loads (i.e., with vibration frequency f1 1/130th) or low- (1/4th) mass ratio, compared to the occupant. Normal walking scenarios with frequency in the range fp = 1.5–2 Hz are taken into account for a total of 100 dynamic simulations. The quantitative comparison of typical structural performance indicators for vibration serviceability assessment (i.e., acceleration peak, RMS, CREST) shows significant sensitivity to input SMD assumptions. Most importantly, the sensitivity of structural behaviours is observed for low-frequency systems, as expected, but also for low-mass structures, which (as in the case of glazed floor solutions) can be characterized by the use of lightweight modular units with relatively high vibration frequency. As such, major attention can be required for their vibrational analysis and assessment.publishersversionpublishe

Vibration issues in timber structures: A state-of-the-art review

The increasing use of timber structures worldwide has brought attention to the challenges posed by their lightweight nature, making them more prone to vibrations than more massive structures. Consequently, significant research efforts have been dedicated to understanding and mitigating vibrations in timber structures, while scientific committees strive to establish suitable design regulations. This study aims to classify and identify the main research themes related to timber structure vibrations and highlight future research needs and directions. A bibliometricbased selection process briefly introduces each research topic, presenting the latest findings and proposals for vibration design in timber structures. The paper emphasizes the key outcomes and significant contributions to understanding and addressing vibration issues in timber structures. These findings serve as valuable guidance for researchers, designers, and regulatory bodies involved in designing and assessing timber structures subjected to vibrations

Numerical simulation of the flexural behaviour of composite glass-GFRP beams using smeared crack models

This paper presents a numerical study about the flexural behaviour of rectangular composite glass-GFRP beams, comprising annealed glass and GFRP pultruded profiles bonded with two different adhesives: (soft) polyurethane and (stiff) epoxy. The main objectives of this study were: (i) to fully characterize the non-linear behaviour of glass using the smeared crack approach; and (ii) to assess the applicability of different options to simulate adhesively bonded glass-GFRP joints. An extensive parametric study was developed to evaluate the influence of five parameters on the glass post-cracking non-linear behaviour: (i) glass fracture energy, Gf, (ii) crack band width, h, (iii) glass tensile strength, fg,t, (iv) shape of the tension-softening diagram, and (v) shear retention factor, β. The wide range of the joints’ shear stiffness was simulated by either (i) assuming a perfect bond between glass and GFRP (i.e., neglecting the presence of the adhesive), or (ii) explicitly considering the adhesive, by means of using (ii.1) plane stress elements, or (ii.2) interface elements. For the beams analysed in this paper, the following material model for glass provided a good agreement with experimental results: Gf in the range of 3 to 300 N/m, h equal to the square root of the finite element area, fg,t = 50 MPa, linear softening diagram and β according to a power law. It was also shown that the hypothesis of perfect bond at the GFRP-glass interfaces allows for an accurate simulation of joints with high levels of interaction (epoxy), while calibrated interface elements are needed for joints with low level of interaction (polyurethane).The authors wish to acknowledge FCT, ICIST/CERIS and ISISE for funding the research, and companies SIKA, Guardian and ALTO for supplying the adhesives, the glass panes and the GFRP pultruded profiles used in the experiments. The first author also wishes to thank FCT for the financial support through his PhD scholarship SFRH/BD/80234/2011

Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi

Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies1. Although these accreted stellar populations can be forensically identified as kinematically distinct structures within the Galaxy, it is difficult in general to date precisely the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called Gaia–Enceladus1, leading to substantial pollution of the chemical and dynamical properties of the Milky Way. Here we identify the very bright, naked-eye star ν Indi as an indicator of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be 11.0 ± 0.7 (stat) ± 0.8 (sys) billion years. The star bears hallmarks consistent with having been kinematically heated by the Gaia–Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 billion years ago, at 68% and 95% confidence, respectively. Computations based on hierarchical cosmological models slightly reduce the above limits

Comprehensive genetic dissection of wood properties in a widely-grown tropical tree: Eucalyptus

Background: Eucalyptus is an important genus in industrial plantations throughout the world and is grown for use as timber, pulp, paper and charcoal. Several breeding programmes have been launched worldwide to concomitantly improve growth performance and wood properties (WPs). In this study, an interspecific cross between Eucalyptus urophylla and E. grandis was used to identify major genomic regions (Quantitative Trait Loci, QTL) controlling the variability of WPs. Results: Linkage maps were generated for both parent species. A total of 117 QTLs were detected for a series of wood and end-use related traits, including chemical, technological, physical, mechanical and anatomical properties. The QTLs were mainly clustered into five linkage groups. In terms of distribution of QTL effects, our result agrees with the typical L-shape reported in most QTL studies, i.e. most WP QTLs had limited effects and only a few (13) had major effects (phenotypic variance explained > 15%). The co-locations of QTLs for different WPs as well as QTLs and candidate genes are discussed in terms of phenotypic correlations between traits, and of the function of the candidate genes. The major wood property QTL harbours a gene encoding a Cinnamoyl CoA reductase (CCR), a structural enzyme of the monolignol-specific biosynthesis pathway. Conclusions: Given the number of traits analysed, this study provides a comprehensive understanding of the genetic architecture of wood properties in this Eucalyptus full-sib pedigree. At the dawn of Eucalyptus genome sequence, it will provide a framework to identify the nature of genes underlying these important quantitative traits. (Résumé d'auteur

Salmonella Strains Isolated from Galápagos Iguanas Show Spatial Structuring of Serovar and Genomic Diversity

It is thought that dispersal limitation primarily structures host-associated bacterial populations because host distributions inherently limit transmission opportunities. However, enteric bacteria may disperse great distances during food-borne outbreaks. It is unclear if such rapid long-distance dispersal events happen regularly in natural systems or if these events represent an anthropogenic exception. We characterized Salmonella enterica isolates from the feces of free-living Galápagos land and marine iguanas from five sites on four islands using serotyping and genomic fingerprinting. Each site hosted unique and nearly exclusive serovar assemblages. Genomic fingerprint analysis offered a more complex model of S. enterica biogeography, with evidence of both unique strain pools and of spatial population structuring along a geographic gradient. These findings suggest that even relatively generalist enteric bacteria may be strongly dispersal limited in a natural system with strong barriers, such as oceanic divides. Yet, these differing results seen on two typing methods also suggests that genomic variation is less dispersal limited, allowing for different ecological processes to shape biogeographical patterns of the core and flexible portions of this bacterial species' genome

Molecular Evolution of Regulatory Genes in Spruces from Different Species and Continents: Heterogeneous Patterns of Linkage Disequilibrium and Selection but Correlated Recent Demographic Changes

Genes involved in transcription regulation may represent valuable targets in association genetics studies because of their key roles in plant development and potential selection at the molecular level. Selection and demographic signatures at the sequence level were investigated for five regulatory genes belonging to the knox-I family (KN1, KN2, KN3, KN4) and the HD-Zip III family (HB-3) in three Picea species affected by post-glacial recolonization in North America and Europe. To disentangle neutral and selective forces and estimate linkage disequilibrium (LD) on a gene basis, complete or nearly complete gene sequences were analysed. Nucleotide variation within species, haplotype structure, LD, and neutrality tests, in addition to coalescent simulations based on Tajima’s D and Fay and Wu’s H, were estimated. Nucleotide diversity was generally low in all species (average π = 0.002–0.003) and much heterogeneity was seen in LD and selection signatures among genes and species. Most of the genes harboured an excess of both rare and frequent alleles in the three species. Simulations showed that this excess was significantly higher than that expected under neutrality and a bottleneck during the Last Glacial Maximum followed by population expansion at the Pleistocene/Holocene boundary or shortly after best explains the correlated sequence patterns. These results indicate that despite recent large demographic changes in the three boreal species from two continents, species-specific selection signatures could still be detected from the analysis of nearly complete regulatory gene sequences. Such different signatures indicate differential subfunctionalization of gene family members in the three congeneric species