Luísa Barreira

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 calcula- tion 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 re resistance, 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 per- mit the specifi cation of simple design calculation methods, simplifying the verifi cation of the fi re safety of wooden beams. Wood is a renewable resource, recently attracting public attention, as an environmentally friendly material. This product is a building material with attractive attributes such as archi- tectural and structural characteristics. Wood is classifi ed in two different botanical terms. The botanical terms, softwoods and hardwoods, indicate the basic structure and cell type of mois- ture within the tree. Softwoods generally come from the coniferous species (pines, fi rs and spruces, for example) and are generally fi ne textured. Hardwoods (eucalypts and oaks, for example) have broad leaves and the texture ranges from fi ne to coarse. The types of wood include softwoods, hardwoods and glued laminated woods, in the forms of solid wood, ply- wood and wood-based panels. Due to large variation, type and wood quality, a system of strength classes was established. Each grade of classifi cation is a function of the physical and wood properties. The wood when exposed to accidental actions, such as ficonditions, pre- sents a surrounding charring layer. However, this layer can delay the heating process from the exposed side to the wood core section, acting as an insulating layer. The wood core section may remain at low temperatures, depending on the fi re exposure and element size therefore. It is important to calculate the value of charring rate and determine the thickness of char layer formation through the section. These parameters are important in fisafety design because they determine the residual load-bearing cross-section, due to critical external conditions. Safety rules and guidelines should be useful for different wooden structures. The high vulner- ability of wood, with respect to firequires a rigorous thermal and mechanical analysis. The study of fi re resistance of wood structures is therefore a topic of great interest. Several researchers have presented experimental and numerical models for the study of wood in the presence of high temperatures (1-3). The charring rate of softwood or hardwood material, exposed to fi conditions, has been studied in different countries, (4-11). Some empirical models for charring rate calculation have been developed by other researchers (4-6). The wood species considered in this work are the Fir subalpine and Redwood, from Northern Europe. These conifer species are widely used in construction, textile, paper- making, resin

Charring rate determination of wood pine profiles submitted to high temperatures

Wood material is being used increasingly for structural engineering applications in buildings and other special engineering productions. To assess safety rules, this type of element should have sufficient mechanical resistance to guarantee the design loads. Wood is a natural material and is subject to many constantly changing influences. High wood vulnerability, due to accidental conditions, requires rigorous thermal and mechanical assessment. The combustion and the chemical phenomena occurring in the 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 the insulating temperature rises in the core of the material. The charring rate is more or less constant and mainly depends on the density and moisture content of the wood. 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 a wood profile during time heating exposure. Using appropriated material properties and boundary conditions, reasonable predictions of the 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. The char layer thickness will be determined.

The measuring of the cortical bone thickness in L4 vertebra and comparison with bone mass density

The aim of this work is to identify the cortical bone thickness in L4 vertebra, through a digital methodology using computed tomography and an experimental methodology with the rapid prototyping, and to compare with the body mass density for each vertebra in analysis. The study presents clinic results of 16 women from the Northwest of Portugal, with age between 52 and 83 years, collected from May to June 2011. The patients underwent a dual energy X-ray densitometry scan system (Lunar, DPX Pro, daily calibrated) at L4 vertebra for body mass density determination, and simultaneous a lumbar spine computed tomography scan (Lightspeed Plus, GE Medical System) was performed. All clinical data were obtained in a Medical Imaging Centre of Radiology. Discussions of results regarding the measuring of the cortical bone thickness and the relation with body mass density in L4 vertebra are presented in this work. The L4 vertebra is one of the most common spinal sites that lead to chronic lower back pain. The goal of this study is to acquire accurate values, concerning cortical bone thickness, which could improve the prediction of vertebral fractures.

High temperatures in parallel or perpendicular wood grain direction: a numerical and experimental study

The high vulnerability of wood due to accidental conditions requires a rigorous thermal and mechanical assessment. In this work, an experimental and numerical study will be presented to determine the char-layer evolution in pine wood crosssection, submitted at high temperatures due to an anaerobic process. A non-linear thermal and transient analysis will be conducted using the numerical program. A thermal unit and electro ceramic resistances will be used during the experimental program. The evolution of a char-layer by the orientation of different fibres will be determined. The experimental results obtained with several wood samples will be compared using a numerical program with a finite element formulation.

Experimental and numerical method for determining wood char-layer at high temperatures due to an anaerobic heating

This work proposes an experimental and numerical method to determine char-layer and temperature in pine wood at high temperatures. The elevated temperature in the wood is due to an anaerobic heating process. A thermal unit and electro-ceramic resistance are used during experimental tests to simulate elevated temperatures in wood profi les. Wood samples have been manufactured for experimental tests. To ensure greater efficiency in the heating process, it is necessary to insulate the wood samples. A numerical method that predicts the thermal degradation of wood exposed to high temperatures is used. A non-linear thermal and transient analysis is conducted using the finite element method. Numerical results are obtained to determine temperature fi elds and char-layer in wood profi les under same con-ditions. The char-layer is calculated for pine wood profi les (Pinus pinaster) through this study. This parameter is important in safety design because it determines how cross-section size decreases to criti-cal external conditions. These methodologies could be used to assess the performance time of wood material, during exposure to high temperatures or in fi re conditions. Keywords char-layer, heating process, high temperatures, pine wood Language: en

Cortical bone thickness and bone mass density in L2 vertebra, a comparison study with L3 and L4 measurements

The main goal of this study is to acquire values in spinal vertebrae, related with the cortical bone thickness, the body mass density and T–score in L2 vertebra. The study presents clinic results of sixteen women from the northwest of Portugal. For this study, a digital methodology using computed tomography and an experimental methodology with the rapid prototyping will be used for each vertebra in analysis. Discussions of results regarding the measuring of the cortical bone thickness, the body mass density, and T–score values in L2 are presented and compared with all values obtained in L3 and L4 vertebrae.