Thermal behaviour of rebars and steel deck components of composite slabs under natural fire

Most of the studies involving composite slabs under fire follow the standard fire scenario described by the ISO 834 curve, disregarding the cooling-phase. However, recent studies show that this phase is equally important, as it can lead to the collapse of the structure. Therefore, the present research carried out a parametric study, using numerical models, validated through experimental tests, to evaluate the thermal behaviour of the composite slabs components under natural fire. The results showed that the maximum temperatures in the reinforcement bars occur during the cooling-phase, reaching temperatures up to 300% higher than at the heating-phase, on the steel deck occur at the end of heating, and that the concrete thickness above the steel deck influences the temperature of these components. Also, during the cooling-phase, a “heat bubble” effect is observed on the ribs of the composite slabs, where the reinforcement bars are normally placed. These results highlight the importance of considering different natural fire scenarios, in the structural performance and safety of composite slabs, since during the cooling-phase there is still heat transfer between the elements, which can lead to slab failure. New parameters are proposed to find the temperature of each component for different fire ratings

Influence of micro-textures on cutting insert heat dissipation

Metal machining is one of the most important manufacturing processes in today’s production sector. The tools used in machining have been developed over the years to improve their performance, by reducing the cutting forces, the friction coefficient, and the heat generated during the cutting process. Several cooling systems have emerged as an effective way to remove the excessive heat generated from the chip-tool contact region. In recent years, the introduction of nano and micro-textures on the surface of tools has allowed to further improve their overall performance. However, there is not sufficient scientific data to clearly show how surface texturing can contribute to the reduction of tool temperature and identify its mechanisms. Therefore, this work proposes an experimental setup to study the tool surface characteristics’ impact on the heat transfer rate from the tools’ surface to the cooling fluid. Firstly, a numerical model is developed to mimic the heat energy flow from the tool. Next, the design variables were adjusted to get a linear system response and to achieve a fast steady-state thermal condition. Finally, the experimental device was implemented based on the optimized numerical model. A good agreement was obtained between the experimental tests and numerical simulations, validating the concept and the implementation of the experimental setup. A square grid pattern of 100 μm × 100 μm with grooves depths of 50, 100, and 150 μm was introduced on cutting insert surfaces by laser ablation. The experimental results show that there is a linear increase in heat transfer rate with the depth of the grooves relatively to a standard surface, with an increase of 3.77% for the depth of 150 μm. This is associated with the increase of the contact area with the coolant, the generation of greater fluid turbulence near the surface, and the enhancement of the surface wettability.This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the grant 2020.07155.BD and by the project POCI-01-0145-FEDER-030353 (SMARTCUT). Additionally, this work was supported by FCT national funds, under the national support to R&D units grant, through the reference projects UIDB/04436/2020 and UIDP/04436/2020

The heat transfer modelling for bone metastatic lesion minimization using two different cement types

Bone tumors grow when cells divide without any control, forming a tissue mass. Bone tumors could be benign or malignant, and primary or metastatic due to systemic cancer cells dissemination. They destroy bone and lead to pathological fractures. The main objective of this work is to study the thermal effect induced by the bone cement polymerization, in the bone metastatic tumor minimization. To assess the clinical effect, it is important to test this methodology before its application and obtain sustained results. In this work, a numerical model was developed to predict the temperature distribution produced by cement polymerization. Thus, distinct tests were produced for different two cements types and amounts introduced in a cortical and spongy bone metastatic lesion, with or without an intramedullary titanium nail. The bone cement was introduced to fill in a metastatic lytic lesion area, which the main objective is playing a promising role for bone tumor necrosis due to thermal effects and biomechanical stabilization for function and pain relief.info:eu-repo/semantics/publishedVersio

Numerical thermal study in bone tumor lesion

With the evolution of science and new diagnostic technologies, it was possible to observe a continuous improvement in the treatments in general and in the aid of the patients' quality of life. Malignant tumors can be primary or secondary (metastases), with abnormal growth of cells able to invade other types of tissues and organs through systemic dissemination. Sarcomas are rare primary malignancies formed from mesenchymal tissue and often located at the extremities. In this work, the main objective is to evaluate the minimization of the evolution of bone tumor lesion through the injection of bone cement, filling in the space of the lytic tumor lesion. This methodology allows to verify at the adjacent cement – bone tissue interface, an increase in temperature that can control the local growth of bone metastasis. Different computational models, obtained by medical image processing, will be carried out for two analyses (patient younger than 70 years and older than 70 years). The computational model allows a transient thermal analysis using the finite element method. The temperature results may determine the thermal necrosis effect in the bone tumor lesion. Results will be compared using three different bone cements.info:eu-repo/semantics/publishedVersio

Advanced Calculation Model Calibrated with Experimental Test of Wooden Slabs Exposed to Fire

The wooden slabs are structural elements with wide application, in particular, in building rehabilitation, interior spaces and in new building structures. The mechanical, thermal and acoustic properties make this material as an ideal solution for floor and roof slabs applications. However, when exposed to an accidental fire condition it is necessary to assess their vulnerable behaviour accurately. In this work, an advanced calculation model is presented, based on the use of finite elements, calibrated with experimental results. The experimental tests were performed on wooden slabs exposed to a fire from below the element. The slabs were instrumented with thermocouples to measure the temperature at different control points along the fire duration in a fire resistance furnace, following the standard fire curve ISO 834. The advanced calculation model also allows the obtained the transient effect and incorporates the non-linear wood properties. The physical behaviour of the wooden slab is conditioned by the char layer formation, and this phenomenon is also considered in the advanced calculation model.info:eu-repo/semantics/publishedVersio

Fire Resistance of Ultra-High-Strength Steel Columns Using Different Heating Rates

Ultra-High-Strength Steel (UHSS) offers several advantages over normal carbon steel, promoting exceptional strength, reducing self-weight, improving fire resistance, enhancing durability, and reducing material consumption. These advantages result in cost savings and sustainable engineering construction. The 3D numerical model is based on Geometrical and Materially Nonlinear Imperfection Analysis (GMNIA) and determines the fire resistance of different cross-section columns. The model is validated with experimental tests, with a maximum relative error of 11%. A parametric analysis is presented, based on 252 simulations, assuming three heating rates, two different cross-sections, two different thicknesses, three lengths, and seven load levels. The fire resistance depends on the heating rate, but the critical temperature is almost equal and independent of the heating rate, if one assumes implicit creep in the constitutive material model. The fire resistance decreases with the load level, as expected. The thickness effect of the hollow section is almost negligible in the fire resistance of UHSS columns. The fire resistance decreases more in higher load levels for slender columns. Columns with Circular Hollow Sections (CHSs) generally show higher fire resistance than hybrid columns in longer columns, but the hybrid columns are subject to much higher loads. New design formulas are presented for the critical temperature of UHSS columns, depending on the load level and slenderness of two different cross-sections

LOADBEARING CAPACITY OF LSF WALLS UNDER FIRE EXPOSURE

Light steel frame (LSF) (LSF) and prefabricated panels are widely used in loadbearing walls, with direct application to steel framed buildings. These walls are made with steel cold formed sections (studs and tracks) using gypsum plasterboard and other material layers attached to the flanges and sometimes insulation material in the cavities. The fire resistance is usually provided by one or more layer of materials and or by the cavity insulation. This investigation evaluates the fire resistance of the loadbearing walls, from the point of view of insulation (I) and loadbearing capacity (R). Experimental results obtained from partition walls were used into the numerical model to accurately preview the cracking, falling off and the ignition of combustible material. The numerical model was validated under the same fire conditions. The loadbearing capacity is determined using this hybrid model. This model is able to predict an accurate fire resistance for any load level, taking into account the brittle behaviour of gypsum panels and the ignition of combustible materials. The loadbearing decreases with the increase of the load level. A new formula is presented to determine the critical average temperature of the LSF

THREE-DIMENSIONAL NUMERICAL MODELLING OF FIRE EXPOSED COMPOSITE SLABS WITH STEEL DECK

Composite slabs with reinforced concrete and cold-formed profiled steel deck are very popular and reduce the building construction time. The steel deck acts as a permanent formwork to the concrete topping. Usually, the concrete is reinforced with individual rebars placed within the ribs for positive bending, and a steel mesh on the top for negative bending and to prevent concrete cracking. The fire rating of these building elements involves the analysis of different criteria, namely load bearing (R), integrity (E) and insulation (I). The integrity is easily verified, due to the construction method. The other two metrics require the development of experimental fire tests, the application of simplified calculation methods or the development of advanced calculation models. This investigation introduces 3-D numerical validation models for load bearing (R) and insulation (I) criteria. Parametric analyses are developed to investigate the effect of the load into the fire resistance (R) and critical temperature of the steel components (deck, rebar and mesh), as well as the effect of the concrete thickness on the fire resistance from the insulation standpoint (I). The advanced calculation model consists of a non-linear analysis for the thermal and structural behaviour. Both thermal and mechanical models consider perfect contact between materials. For the thermal model, an alternative model is used, with an air gap included between the steel deck and concrete topping to simulate debonding effects. For the mechanical model, the live load level changes from 1.0 kN/m2 to 21.0 kN/m2, and the dead load presents a constant value of 2.8 kN/m2. The fire resistance is determined according to standards, based on the maximum displacement or the rate of displacement. The critical temperature of each steel component decreases with the load level. A new proposal is presented for the critical temperature of each steel component and for the fire resistance according to the insulation criterion

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline