Avaliação experimental de ligações aparafusadas em pinho bravo e câmbala

No presente trabalho avaliaram-se experimentalmente ligações aparafusadas, aferindo a aplicabilidade do Eurocódigo 5 em relação às duas espécies de madeira seleccionadas, Câmbala (Milícia excelsa) e Pinho bravo (Pinus pinaster). Como ligador, utilizaram-se parafusos autoperfurantes HBS da Rotho Blaas. Para além do ensaio de ligações aparafusadas em corte simples, a campanha experimental teve como objectivo avaliar os vários mecanismos de resistência considerados pela metodologia de cálculo sugerida pelo Eurocódigo 5 para este género de ligações, nomeadamente: a) resistência ao arrancamento do parafuso do elemento que recebe a ponta; b) resistência ao atravessamento da cabeça do parafuso; c) esmagamento localizado da madeira; e d) flexão do parafuso. Os resultados experimentais demonstram a fiabilidade da metodologia de cálculo proposta pelo Eurocódigo 5 e atestam o bom comportamento garantido por ligações aparafusadas com parafusos HBS utilizando Pinho bravo e Câmbala.In the present study, screwed connections have been experimentally evaluated, checking the applicability of Eurocode 5 for the two species of wood selected, Iroko (Milícia excelsa) and Maritime pine (Pinus pinaster). As connector, self-drilling screws of HBS Roth Blaas have been used. Single shear screwed connections have been testes moreover, the experimental campaign aimed to evaluate various mechanisms of resistance considered by the calculation method suggested by Eurocode 5 for this kind of connections, including: a) axial withdrawal capacity of the screw, b) pull through parameter for screws, c) local embedment of wood, and d) yield moment of the screw. The experimental results demonstrate the reliability of the calculation methodology proposed by the Eurocode 5 and certify the good behavior guaranteed by screwed connections with HBS screws in the case of Maritime pine and Iroko

Alvenaria estrutural com elementos de madeira

Apesar da madeira e da alvenaria dialogarem constantemente no contexto construtivo, não é comum elas se fundirem nas suas funções. A madeira surge maioritariamente associada a elementos estruturais finos, formando um esqueleto, ou a elementos de revestimento, e a alvenaria associada a paredes resistentes ou simplesmente de enchimento. O que aqui se propõe, é combinar técnica e material, geralmente desassociados, procurando utilizações mais rentáveis, combinando funções estruturais e protectoras aos edifícios. Para o efeito, apresenta-se uma série de ensaios preliminares realizados no Laboratório de Ensaio de Estruturas da Universidade do Minho (LEST) que garantiram informações preciosas para o desenvolvimento de um tijolo de madeira. Os dados recolhidos nos ensaios permitem ainda a previsão da resposta global das paredes construídas utilizando estes tijolos de madeira. Realizaram-se ensaios de compressão de tijolos, avaliando quer a resposta mecânica quer o fenómeno da fluência, e ensaios de flexão de paredes, em particular, ensaios de flexão para estudo do comportamento das juntas horizontais e verticais das paredesAlthough wood and masonry constantly dialoguing in a constructive context, it is unusual to merge them in their roles. The wood comes mostly associated with slender structural elements, forming a skeleton, or cladding, and masonry as bearing walls or associated with simply filling. The aim of this work is to combine the technique and the materials, normally disassociated, looking for more profitable uses, combining structural and protective functions of the buildings. For that, a series of preliminary tests, performed at the Laboratory for Testing of Structures of the University of Minho (LEST), were performed. These tests supplied valuable information to the development of a wooden brick. Data collected from the tests also allow the prediction of the global response of the walls built using these wooden bricks. Compression tests of wooden bricks, assessing the mechanical response and the creep, and bending tests of walls studying the behaviour of bed and head joints, were performed

UT system : a structural system to build taller urban timber houses with aspired spatial flexibility

In past few years, in consequence to the continuous increase of urban densities and seeking for a more sustainable profile for construction, some new proposals for tall timber city housing have emerged. The development of new wood-based materials, like cross laminated timber (CLT), has made possible to believe to build high with timber. Demonstration buildings located in different locations around the world contribute to the development of this new concept of urban housing. With the exception of few recent proposals based on hybrid systems, majority of buildings so far built are fully based in the monolithic construction system offered by CLT panels. Despite all the advantages related with this monolithic system, two main important weaknesses related with architectural freedom have been pointed out: the excessive compartmentalization of inner spaces and the external expression of an extruded box with reduced openings. Inspired on new CLT/steel and CLT/concrete hybrid proposals and their advantages in comparison to the CLT monolithic system, a CLT/glulam hybrid construction system, named UT system (urban timber system), has been developed. CLT remains the main structural material in the UT system but, glulam linear elements are used to reduce the CLT walls both inside and in the building perimeter. Further, based in the bundled tube concept, UT system looks into the possibility of overcome eccentricity problems caused by non-symmetrical location of vertical cores and consequently, offers more design freedom. UT system is described and illustrated, considering concerns related with structural system, tall building specificities, construction sequences, architectural design possibilities, moisture effects, durability, fire resistance, acoustic performance and joints between timber elements.Fundação para a Ciência e a Tecnologia (FCT

MLCC na construção em altura

Na última década tem-se observado o aumento da procura por novas soluções estruturais em madeira para a construção em altura. Esta temática possui vários fatores de motivação, sendo o de maior importância o perfil sustentável associado à madeira. A madeira lamelada colada cruzada (MLCC) é o material de eleição uma vez que os sistemas construtivos em painéis mostram maior adequabilidade para este tipo de construção. O presente artigo apresenta um enquadramento desta recente temática, descrevendo os fatores motivadores e as principais barreiras ao seu desenvolvimento. Descrevem-se as principais características da MLCC analisando as suas potencialidades na construção de edifícios em altura apresentando e discutindo exemplos que recorrem a este novo material. É realizada uma breve descrição de quatro edifícios, nomeadamente o Stadthaus e o Bridport em Londres, o Forté em Melbourne’s Docklands, e o Via Cenni em Milão, de modo a desvendar os pontos fortes e as principais fragilidades deste sistema construtivo. Por fim, são apresentados dois casos de projetos em desenvolvimento, o Barents House e o FFTT system, os quais prometem, através de sistemas híbridos, serem capazes de conceber estruturas mais arrojadas.Fundação para a Ciência e a Tecnologia (FCT

A project contribution to the development of sustainable multi-storey timber buildings

Wood is a natural material, renewable, easily recyclable, and able to store carbon-dioxide, which makes tall timber buildings a solution with potential to answer the main sustainability targets. Cross laminated timber (CLT) has been pointed out as the best wood-based material to make this ambition a real thing. In order to understand why, this paper introduces the material and describe some demonstration buildings recently built. Based on diagnosed weaknesses of CLT buildings, it is presented an initial propose for a new CLT/glulam hybrid construction system, called Urban Timber (UT) system, which aims be able to support taller timber buildings. The main motivation was the development of a wood-based structural solution that provides more spatial flexibility and wider versatility for visual architectural expressions. The system is described and illustrated, considering concerns related with structural behavior, architectural value, structural connections and wood shrinkage.Fundação para a Ciência e a Tecnologia (FCT

Visual assessment and diagnosis of a timber railway station warehouse in Foz do Tua

Aiming at the rehabilitation of a timber warehouse in the Tua train station for a new use, it was necessary to assess the level of conservation of the building’s elements and determine whether intervention measures were required. This work summarizes the assessment made of the timber elements by means visual inspection and non-destructive testing. The main results, obtained in the diagnostic survey, were the conservation level of the timber warehouse, the visual strength grading of the timber elements and damage maps indicating the main pathologies and its probable causes.The drawings of the Tua station warehouse (artmetro, arquitetos associados 2011) were provided by the Architecture School Study Centre of University of Minho and their reproduction is acknowledged. The support of FEDER through COMPETE and of FCT within the scope of project POCI-01-0145-FEDER-007633 are acknowledged. The financial support of COST FP1101 – Assessment, Reinforcement and Monitoring of Timber Structures is gratefully acknowledged.info:eu-repo/semantics/publishedVersio

Strategies to avoid humidity causing damages in tall timber buildings

The number of tall housing buildings using cross laminated timber (CLT) as the main structural material has been growing all around the world but especially in Europe. This kind of construction has already proven to be a solution with a sustainable profile and despite the conflicts with some building codes and some countries legislation, this construction material is able to shape safe structures. However, to get the full confidence of the public, several researches focused on main CLT restrictions are still under development, such as fire safety, strength of connections, structural behavior, acoustics and durability. This last point is of huge importance considering timber’s propensity for rotting and its known hygroscopic behavior. If humidity effects are not considered during the building design as well as the structure’s integrity the people’s wellbeing can be compromised. The content of the present paper aims to outline important recommendations concerning the reduction of humidity causing damages in tall timber buildings. For that, CLT/glulam hybrid construction system (Urban Timber system) is used to illustrate and describe suggested construction details of a timber building, from the foundations to the roof: the most cautious solution for foundations is to resort to reinforced concrete, in case of biological attacks or unexpected hazards; facades have to ensure the protection of timber structural elements from contact with moisture either through insulation materials or by glazed walls; windows in contact with timber ends should be able to prevent water to reach them; connection between timber elements must predict swelling/shrinkage movements of timber; at least an efficient rain water drainage has to be guaranteed by the balconies and the roof design

Exploring the Effects of bolA in Biofilm Formation and Current Generation by Shewanella oneidensis MR-1

Microbial electrochemical technologies (METs) have emerged in recent years as a promising alternative green source of energy, with microbes consuming organic matter to produce energy or valuable byproducts. It is the ability of performing extracellular electron transfer that allows these microbes to exchange electrons with an electrode in these systems. The low levels of current achieved have been the limiting factor for the large-scale application of METs. Shewanella oneidensis MR-1 is one of the most studied electroactive organisms regarding extracellular electron transfer, and it has been shown that biofilm formation is a key factor for current generation. The transcription factor bolA has been identified as a central player in biofilm formation in other organisms, with ist overexpression leading to increased biofilm. In this work we explore the effect of this gene in biofilm formation and current production by S. oneidensis MR-1. Our results demonstrate that an increased biofilm formation and consequent current generation was achieved by the overexpression of this gene. This information is crucial to optimize electroactive organisms toward their practical application in METs

The influence of moisture content variation on the withdrawal capacity of self-tapping screws

Due to high axial load-bearing capacity and economical application without pre-drilling, self-tapping screws are widely used in modern timber constructions nowadays. Their withdrawal behaviour, as one mechanism to be verified according to EN 1995-1-1 (2004), is discernibly influenced by the timber member and its moisture content. In case of increase of moisture content above 12 %, test results indicate a significant decrease in withdrawal capacity, which is actually not considered in design procedure. In our paper, we thus concentrate on these experimental studies, carried out in the frame of two research projects. Furthermore, we discuss two models developed for design procedure as well as for data assessment covering a large bandwidth of moisture content and compare them with results from previous investigations

Influence of moisture content and gaps on the withdrawal resistance of self tapping screws in CLT

Self-tapping screws (STS) have been proclaimed as the easiest solution for structural timber connections, in special for cross laminated timber (CLT) constructions. In order to understand deeply the composite model “CLT-STS”, an experimental campaign which comprised 270 withdrawal tests was carried out. Maximum withdrawal load capacity of self-tapping screws inserted in plane side of a three layered CLT panel was evaluated considering three main parameters: moisture levels of CLT (i), number of gaps (ii) and the width of gaps (iii). Regarding (i), connections were tested with CLT at 8%, 12% and 18% of moisture content. Concerning (ii) and (iii), different test configurations with 1, 2 and 3 gaps, with 0 or 4mm, were tested. The influences of moisture content and number of gaps were modeled. Further a correlation between test results and a prediction model developed by Uibel and Blaß (2007) has been proposed