Modelo computacional para avaliação térmica e mecânica de estruturas em madeira

Este trabalho tem como objectivo avaliar estruturalmente duas espécies de madeira, calculando a sua resistência ao fogo para diferentes cenários de incêndio, através da redução da sua secção. Utilizando o método de elementos finitos, com recurso ao programa de cálculo Ansys®, é desenvolvido um modelo computacional térmico que permite o cálculo da camada e da velocidade de carbonização. O cálculo do perfil de temperaturas para as diferentes secções em estudo, é obtido em regime transiente, considerando as propriedades térmicas não lineares do material, obedecendo ao (EN1995-1-2, 2003). Com base ainda no programa Ansys® é efectuada uma análise numérica estrutural em vigas, solicitadas por uma carga mecânica e sob influência da redução da secção recta, função do efeito térmico, para a determinação dos estados de tensão. A resistência mecânica é obtida, considerando as propriedades mecânicas ortotrópicas da madeira e função da temperatura. Com base em equações analíticas propostas para projecto, é efectuada uma comparação com os resultados numéricos. Outro objectivo é identificar a capacidade de carga última em vigas de madeira, função da imposição de um carregamento mecânico em simultâneo com uma acção térmica, de forma a prever futuras considerações nas opções de projecto. A grande finalidade deste estudo é contribuir com regras práticas de projecto, através da apresentação de gráficos de resistência ao fogo e de uma metodologia de cálculo simplificada, para a determinação do campo de tensões e da capacidade de resistente em vigas de madeira, submetidas a acções térmicas e mecânicas. The main objective of this work is to assess the structural performance of two different timber specimens, calculating the fire resistance due different fire scenarios, through timber cross-section reduction. Using the finite element method, with Ansys® program, a computational model is developed which allows the timber charcoal thickness and the charring rate determination. The temperature evolution, in all studied timber cross-sections, is obtained using a transient thermal analysis, including the non-linear thermal properties, according (EN1995-1-2, 2003). To characterize the stress state in beam components a structural numerical analysis will be conducted with Ansys® program, where all beams are submitted to a mechanical load and with the cross-section reduction influence due thermal effect. The mechanical strength is obtained, considering the orthotropic mechanical properties of wood material, dependent of the temperature. Based on proposed analytical design equations, a comparison with numerical results will be obtained. Another objective of this work is to identify the ultimate load capacity in wooden beams, function of mechanical loading condition in simultaneous with thermal effect, in prevention to future design options. The greater purpose of this study is to contribute with design practical rules, through fire resistance charts and a simplified calculation methodology, for stresses and ultimate load capacity calculation in wooden beams submitted to thermal and mechanical loading conditions

Structural safety in wooden beams under thermal and mechanical loading conditions

The main objective of this paper is to identify different analytical methods which permit the calculation of the stress level in wooden simply supported beams, due to mechanical and thermal loading conditions. Two different wood species, with different cross-sections, will be presented. The fi reresistance, the charring depth layer and the charring rate will be determined using the fi nite element method with Ansys® program. To characterize the stress state in wooden beams, all elements are subjected to mechanical load considering the reduction of the cross-section, infl uenced by thermal action. Another purpose of this work is to identify the ultimate safe load-bearing capacity in wooden beams, subjected to uniform load simultaneously with the thermal effect. All numerical results permit the specifi cation of simple design calculation methods, simplifying the verifi cation of the fi re safety of wooden beams

Avaliação estrutural de duas espécies de madeira submetidas à acção do fogo

Um dos objectivos deste trabalho é avaliar estruturalmente duas espécies de madeira, calculando a sua resistência ao fogo para diferentes cenários de incêndio e determinando a redução da sua secção recta. Será utilizado o método dos elementos finitos através do programa ANSYS para a determinação da camada e da velocidade de carbonização, nas diferentes análises em estudo. O cálculo do perfil de temperaturas, nas diferentes secções em estudo, será obtido em regime transiente. Serão consideradas as propriedades térmicas não lineares do material, dependentes da evolução da temperatura, de acordo com as regras estabelecidas no [Eurocódigo 5, 2003]. O outro objectivo deste trabalho é a determinação de estados de tensão em elementos do tipo viga, sob influência da redução da secção recta. Neste tipo de estudo, será dada particular importância às propriedades ortotrópicas da madeira, função da temperatura, a utilizar no modelo de elementos finitos. Este trabalho será organizado de forma a contribuir com regras práticas de projecto, na utilização deste tipo de elementos estruturais, através da apresentação de gráficos da resistência ao fogo e de uma metodologia de cálculo simplificada, na determinação do campo de tensões em vigas submetidas a acções térmicas e mecânicas

Hybrid wood/steel elements under fire

The main objective of this paper is to present a computational model for the fire resistance of wood/steel hybrid elements. Different design solutions will be presented. The most important factors for fire safety in hybrid elements are the thermal effects degradation and the charring depth formation in wood materials, and also the heat conduction extremely well in steel material. Unprotected steel elements under fire condition may suffer serious damage. The use of hybrid wood/steel elements could increase both structural strength and stiffness. Wood could be considered as an insulating material, the core section could remain at low temperature, function of fire exposure time and element cross section size. All presented results will permit to evaluate different design solutions, which facilitates the fire design of wood/steel hybrid elements. The presented study was conducted in order to articulate the best constructive solution using the finite element method

Numerical model to evaluate the fire resistance in wooden slabs with cavities

The main objective of this paper is to develop a numerical model for thermal analysis of wooden slabs with cavities, when subjected to the fire action. The temperature profiles, the charring depth layer and the charring rate will be determined using the finite element method with ANSYS program. The numerical calculation of the temperature profiles will be obtained through a transient and a non-linear thermal analysis, where the material properties are temperature dependent. These properties were established in accordance with the referenced data and numerically calibrated. Two different models of wooden slabs with cavities were studied. One model characterizes a wood slab with void cavities and other with insulation material. To characterize the fire resistance in wooden slabs with insulated cavities or void cavities, different typical curves of charring depth layer will be obtained. A numerical procedure is proposed to identify the heating action into the slab cavitie

Avaliação estrutural de duas espécies de madeira submetidas à acção do fogo

Um dos objectivos deste trabalho é avaliar estruturalmente duas espécies de madeira, calculando a sua resistência ao fogo para diferentes cenários de incêndio e determinando a redução da sua secção recta. Será utilizado o método dos elementos finitos através do programa ANSYS para a determinação da camada e da velocidade de carbonização, nas diferentes análises em estudo. O cálculo do perfil de temperaturas, nas diferentes secções em estudo, será obtido em regime transiente. Serão consideradas as propriedades térmicas não lineares do material, dependentes da evolução da temperatura, de acordo com as regras estabelecidas no [Eurocódigo 5, 2003]. O outro objectivo deste trabalho é a determinação de estados de tensão em elementos do tipo viga, sob influência da redução da secção recta. Neste tipo de estudo, será dada particular importância às propriedades ortotrópicas da madeira, função da temperatura, a utilizar no modelo de elementos finitos. Este trabalho será organizado de forma a contribuir com regras práticas de projecto, na utilização deste tipo de elementos estruturais, através da apresentação de gráficos da resistência ao fogo e de uma metodologia de cálculo simplificada, na determinação do campo de tensões em vigas submetidas a acções térmicas e mecânicas

Numerical model to evaluate the fire resistance in wooden slabs with cavities

The main objective of this paper is to develop a numerical model for thermal analysis of wooden slabs with cavities, when subjected to the fire action. The temperature profiles, the charring depth layer and the charring rate will be determined using the finite element method with ANSYS program. The numerical calculation of the temperature profiles will be obtained through a transient and a non-linear thermal analysis, where the material properties are temperature dependent. These properties were established in accordance with the referenced data and numerically calibrated. Two different models of wooden slabs with cavities were studied. One model characterizes a wood slab with void cavities and other with insulation material. To characterize the fire resistance in wooden slabs with insulated cavities or void cavities, different typical curves of charring depth layer will be obtained. A numerical procedure is proposed to identify the heating action into the slab cavities. All numerical results permit the verification of the fire safety in wooden slabs with cavities

Modelo numérico para avaliação do efeito do isolamento em lajes de madeira submetidas ao fogo

O objetivo fundamental deste artigo é desenvolver um modelo numérico térmico para a análise de lajes em madeira, com e sem isolamento. Será utilizado o método de elementos finitos, através do programa ANSYS para determinar os perfis de temperaturas, a espessura e a velocidade de carbonização. O cálculo dos perfis de temperaturas será obtido em regime transiente, através de uma análise não linear em que as propriedades térmicas dependem da temperatura. Estas propriedades foram estabelecidas de acordo com dados referenciados e calibrados numericamente. Pretende-se aproximar os resultados numéricos, com os resultados experimentais obtidos por Frangi [1], obtendo-se assim um modelo numérico calibrado. Serão apresentadas conclusões relevantes sobre a utilização de diferentes isolamentos em lajes de madeira, assim como a determinação das curvas típicas de carbonização. Os resultados permitirão identificar soluções de projeto, facilitando a verificação da segurança em situação de incêndio em lajes ou pavimentos de madeira com ou sem isolamento

Short-term effects of post-fire salvage logging on runoff and soil erosion

Research has been undertaken on the hydrological and erosional impact of forest fires, but remarkably little work has been conducted on salvage logging operations that often follow them. We assessed the effects of mechanical salvage logging following wildfire on soil physical properties, ground cover, and runoff and erosion response on a eucalypt stand in Portugal. We compared two levels of mechanical disturbance, skid trails by a wheeled forwarder tractor (“skid_low”) and skid trails by the same tractor followed by a tracked feller-buncher (“skid_high”) with control conditions (no mechanical disturbance). Three plots (16 m2) by level of soil disturbance were installed after a moderate intensity fire and subsequent logging operations, and monitored during the first post-fire year. In two control and two skid_low plots runoff was also measured. Soil bulk density was higher with increasing mechanical disturbance. Soil compaction reduced porosity 7–16%, but as the control porosity was 70%, the reduced porosity still was 60–65%. Soil resistance to penetration significantly increased for the most disturbed area, whereas soil shear strength was significantly reduced in the intermediate disturbance level. Mechanical disturbance did not induce significant effects on soil moisture or ground cover. Initial greater coverage by bare soil in the disturbed plots compared to the control was compensated by a more rapid vegetation recovery in those plots. Annual runoff amount was not higher at the skid-low than at control plots. Absence of runoff difference was due to high soil porosity of 65%, even after tractor trafficking, and a greater surface roughness on the skid_low plots compared to the control. Sediment production increased with increasing soil disturbance. The mean sediment rate was 1.6–3 times greater for the disturbed than the control plots. This increase could be explained by the higher soil compaction and reduced soil shear strength on the mechanically disturbed plots and initial differences in ground cover. Organic matter content of the eroded sediments was higher on the control than the disturbed plots, due to initial higher ash cover on the control plots. Overall, sediment production was significantly related to rainfall intensity and reduced by vegetation regrowth. Sediment rates tend to decrease with time since the initial fire and logging disturbance, highlighting the importance of a rapid implementation of erosion control measures. Specific management practices are needed to minimize the impacts of logging in burnt soils which are already subject to greater erosion risk and soil degradation.publishe

Brazilian Flora 2020: Leveraging the power of a collaborative scientific network

International audienceThe shortage of reliable primary taxonomic data limits the description of biological taxa and the understanding of biodiversity patterns and processes, complicating biogeographical, ecological, and evolutionary studies. This deficit creates a significant taxonomic impediment to biodiversity research and conservation planning. The taxonomic impediment and the biodiversity crisis are widely recognized, highlighting the urgent need for reliable taxonomic data. Over the past decade, numerous countries worldwide have devoted considerable effort to Target 1 of the Global Strategy for Plant Conservation (GSPC), which called for the preparation of a working list of all known plant species by 2010 and an online world Flora by 2020. Brazil is a megadiverse country, home to more of the world's known plant species than any other country. Despite that, Flora Brasiliensis, concluded in 1906, was the last comprehensive treatment of the Brazilian flora. The lack of accurate estimates of the number of species of algae, fungi, and plants occurring in Brazil contributes to the prevailing taxonomic impediment and delays progress towards the GSPC targets. Over the past 12 years, a legion of taxonomists motivated to meet Target 1 of the GSPC, worked together to gather and integrate knowledge on the algal, plant, and fungal diversity of Brazil. Overall, a team of about 980 taxonomists joined efforts in a highly collaborative project that used cybertaxonomy to prepare an updated Flora of Brazil, showing the power of scientific collaboration to reach ambitious goals. This paper presents an overview of the Brazilian Flora 2020 and provides taxonomic and spatial updates on the algae, fungi, and plants found in one of the world's most biodiverse countries. We further identify collection gaps and summarize future goals that extend beyond 2020. Our results show that Brazil is home to 46,975 native species of algae, fungi, and plants, of which 19,669 are endemic to the country. The data compiled to date suggests that the Atlantic Rainforest might be the most diverse Brazilian domain for all plant groups except gymnosperms, which are most diverse in the Amazon. However, scientific knowledge of Brazilian diversity is still unequally distributed, with the Atlantic Rainforest and the Cerrado being the most intensively sampled and studied biomes in the country. In times of “scientific reductionism”, with botanical and mycological sciences suffering pervasive depreciation in recent decades, the first online Flora of Brazil 2020 significantly enhanced the quality and quantity of taxonomic data available for algae, fungi, and plants from Brazil. This project also made all the information freely available online, providing a firm foundation for future research and for the management, conservation, and sustainable use of the Brazilian funga and flora