Thermal analysis of hollow tubular sections under high temperatures

This work presents a numerical model for thermal analysis of steel hollow tubular sections under high temperatures. Curved and straight pipes are structural tubular elements of essential application in the fluids transport, chemical processes or energy generation plants, eventually subjected at mechanical and thermal loading conditions. Hollow tubular sections may have internal voids filled with air (hollow columns, profile sections thermally insulated or steel pipes). The internal temperature should be calculated with some simplified formulas obtained from heat transfer equations. The results obtained in this work, using the internal void formulation, were compared with the thermal response from finite element formulation, for heat conduction with internal insulation and with corresponding results obtained using the simplified heat conduction equation, according Eurocode 3. For small values of the pipe thickness, the thermal behaviour may be determined with high accuracy using one-dimensional mesh approach, with axisymmetric boundary thermal conditions across section

Timber framed walls lined with gypsum plates under fire

Building regulations require fire rating for partition walls under standard fire exposure. New eco building solutions are becoming popular and, in particular, the light timber framed walls. The fire rating of this building element depends on fire testing. Finite element approximation can be used, when models are validated from previous experimental tests. This investigation presents the validation model from a full-scale assembly, using one gypsum board on each side and several solid timber studs. The charring rate in the wood studs is an important predictor for the fire performance of the wall and as well the temperature of the unexposed surface. This investigation also predicts the temperature field in other key points, such as the points located in interface between the studs and gypsum board, for the onset of charring. Finally, the fire resistance is also considered by means of the simplified method (improved model). This models seems to under predict and over predict the results. There is a good approximation between the numerical model (Hybrid –FEM) and the experimental test used for validation, which allowed for a parametric analysis, testing the variation of the gypsum thickness and the thickness of the cavity. The dimension increase of the wood stud does not provide almost any change on the fire resistance of the assembly (insulation), but provides significant modification on the residual area for load bearing capacity.info:eu-repo/semantics/publishedVersio

Determinação da carbonização na madeira de pinheiro quando submetida a elevadas temperaturas para diferentes direcções das fibras

A grande vulnerabilidade da madeira quando submetida a uma acção acidental, requer uma avaliação rigorosa do seu comportamento térmico e mecânico, quando utilizada para fins de construção. Com o presente trabalho, pretende-se determinar experimentalmente a espessura da camada carbonizada em perfis de madeira de pinheiro, submetidos a elevadas temperaturas. Será verificada a influência da acção térmica nos perfis de madeira atendendo às diferentes direcções das fibras. Os resultados experimentais são comparados com os resultados numéricos obtidos utilizando um programa de elementos finitos, o Ansys

Load bearing capacity of fire rated light timber frame walls

Light timer frame (LTF) walls are made of solid timber elements (studs and tracks) and are usually protected by fire insulation materials (gypsum). This investigation finds the residual load bearing capacity of LTF walls after certain fire rating periods (30, 60, 90 and 120). One LTF structure with 3 studs will be analysed with two different protection levels (one and two gypsum layers). The computational model includes the thermal analysis under standard fire and a sequential mechanical analysis with incremental load applied for each fire rated periods. The orthotropic material behaviour is considered temperature dependent, the mechanical analysis considers large displacement behaviour and the charring effect of wood. The results show that the load bearing capacity decreases with the fire exposure time. A new proposal is presented between the load bearing capacity and the fire rating.info:eu-repo/semantics/publishedVersio

Charring rate determination of wood pine profiles submitted to high temperatures

The wood material presents an increasing use for structural engineering applications in buildings and other specials engineering production. To assess safety rules, this type of elements should have sufficient mechanical resistance to guarantee the design loads. Wood is a natural material and is submitted to many constantly changing influences. The high wood vulnerability, due accidental conditions, requires rigorous thermal and mechanical assessment. The combustion and the chemical phenomena occurred in wood during an accidental situation of elevated temperature is a complex study issue. When wood structures are exposed to high temperatures, the burned wood becomes a char layer which loses all strength but insulating temperature rise in the core of material. The charring rate is more or less constant and mainly depends on the density and moisture content wood properties. Safety rules and guidelines should be useful for different wood applications. The fire safety of this type of material involves prevention, inhibition, detection and evacuation. This involves appropriate design rules, installation, construction and maintenance of the wood material applications. This paper proposes an experimental and a numerical method for charring rate determination in pine wood. Different pine sections will be tested and submitted to high temperatures using a heating power unit based on electrical resistances. The temperature results will be measured through wood profile during time heating exposure. Using appropriated material properties and boundary conditions, reasonable predictions of charring layer with a finite element analysis method, can be provided. The thermal response obtained with the finite element formulation will be compared with experimental results, in several series of wood pine profiles. Char layer thickness will be determined

Finite element modelling of thermo-elastoplastic behaviour of hot-rolled steel profiles submitted to fire

This paper presents finite element algorithms developed to simulate the thermoelastoplastic behaviour of steel profiles under high temperatures, in particular those arising from fire conditions. Transient analyses of the temperature field and the mechanical response at each instant have been done. The thermal response obtained with the finite element formulation and the results obtained using the simplified heat conduction equation according to the Eurocode 3 have been compared for several series of hot-rolled steel profiles. The nonlinearity of the problem due to the thermal dependence of the material properties has been taken into account and an elastoplastic model has been used.This work was done within the framework of the project nº PBIC/C/CEG/2446/95 supported by FCT and entitled “Numerical Modelling of Steel Structures Behaviour Under High Temperatures”

Numerical modelling of internal voids in fire exposed structures

The study of steel structures at elevated temperatures needs the characterisation of the thermal action and the material thermal properties variation with temperature as well as the thermal conduction problem solution in a domain with well know boundary conditions. Structures may have internal voids (figure 1) filled with air (hollow columns, profile sections thermally insulated, steel pipes,…). In the presence of internal voids, the internal air temperature will be determined with some simplified formulas deduced from heat transfer equation

Evaluation of the cortical bone thickness in lumbar vertebra using CT and RP experimental techniques

The main objective of this paper was to assess the cortical bone thickness of human lumbar vertebra, through Computed Tomography (CT) images by using radiology reading software (iQ-VIEW), image processing software (ScanIP) and the rapid prototyping (RP) experimental methodology. The study here presented focus sixteen postmenopausal patients from the North of Portugal, with age between 50 and 85 years, collected from May to June 2011. All clinical data were obtained in a Medical Centre of Radiology and Imaging, in Porto. Results regarding the cortical bone thickness and the biomechanical resistance of human lumbar vertebra are presented in this work. The acquirement of accurate values, concerning cortical bone thickness, could improve the prediction of fracture risk

Análise de tensões em fémures do mesmo género e diferente faixa etária

O principal objectivo deste trabalho é avaliar a resistência biomecânica da extremidade proximal do fémur, quando submetido a carregamentos próprios da actividade quotidiana sob influência da actividade muscular. Pretende-se comparar a resistência do colo do fémur, através da distribuição de tensões, na extremidade proximal do osso, em três indivíduos do género feminino, mas faixas etárias distintas. A discussão dos resultados contempla as análises efectuadas, função da massa corporal própria de cada paciente e de um valor máximo idêntico para todos as pacientes. Nesta última análise, uma vez que a imposição de carregamento é idêntica para cada um dos modelos, pretende-se verificar a influência das alterações da espessura do osso cortical do fémur, função da idade, no resultado da distribuição de tensões. A influência da espessura cortical na resistência óssea tem vindo a ser referido por vários estudos de autores nesta área de investigação. A avaliação da compressão ou da tracção ao longo dos tecidos ósseos será também motivo da discussão dos resultados. Este trabalho permitirá ainda identificar as zonas de maior risco de fractura, para cada um dos fémures em análise

Effect of different feed-rate in bone drilling: experimental and numerical study

O comportamento do tecido ósseo durante processos de furação tem sido objeto de recentes estudos devido à sua importância. No entanto, ainda existe uma falta de informação no que diz respeito à distribuição de tensões de origem térmica e mecânica, durante a furação do osso. O presente estudo descreve uma análise sequencial termomecânica acoplada para avaliar a distribuição de tensões durante a furação óssea. Através do código de elementos finitos ANSYS/LS-DYNA foi desenvolvido um modelo termomecânico tridimensional, assumindo diferentes condições de furação. O modelo incorpora as características dinâmicas do processo de furação, bem como as propriedades térmicas e mecânicas dos materiais envolvidos. Foram também realizados testes experimentais em materiais de espuma de poliuretano. Concluiu-se que a utilização de velocidades de avanço maiores conduz a uma diminuição das tensões e deformações normais nas espumas de poliuretano. Os resultados experimentais e numéricos foram comparados e apresentaram boa concordância. O modelo numérico proposto pode ser utilizado para prever os melhores parâmetros de furação e dessa forma minimizar possíveis as lesões ósseas.info:eu-repo/semantics/acceptedVersio