A finite element (FE)-based numerical model is developed in ABAQUS®, to evaluate the response of steel fiber reinforced concrete (SFRC) columns under combined effects of fire and structural loading. The model utilizes a sequentially coupled thermo-mechanical analysis procedure to trace the fire response of concrete columns. The FE model accounts for temperature dependent properties of the SFRC and reinforcing steel as well as the material and geometrical nonlinearities. Predictions from the numerical model including temperature and axial deflection are compared with the data measured in fire tests to establish the validity of the model in predicting overall fire response of the SFRC columns.
One of the important issues about concrete of-late is its behaviour during fire. The mechanical properties of concrete decrease on exposure to a temperature above 300ºC. In order to circumvent this problem, hybridization of two or more types of fibres in concrete is gaining importance. A high modulus fibre helps in preventing thermal cracks, whereas low modulus fibre (polypropylene, nylon) helps in preventing spalling by reducing pore pressure. An experimental study was conducted to explore the use of basalt fibres. The aim of this study was to develop a concrete that shall be able to retain strength and prevent spalling even after exposure to 800ºC. It has been found that hybrid fibre reinforced concrete with polypropylene (Vf=0.25%)+basalt (Vf=0.50%) fibres retained upto 70% strength when exposed to elevated temperature of 800ºC, whereas control specimens retained only 52% of their original strength. In addition, no spalling was observed for both basalt fibre reinforced concrete (BFRC) and hybrid fibre reinforced concrete (HyFRC) even when exposed to 1000ºC temperature for all mixes. A relationship between residual properties and fibre dosage was developed to optimize fibre dosage for a temperature range of 25ºC ? t ? 1000ºC.
This paper aims to present the study conducted on steel fiber reinforced concrete columns that were exposed to temperatures up to 800ºC and cooled by two methods. The study was carried out on 34 columns of length 1200 mm and cross section of 150 mm X 150 mm, out of which 17 were RC columns with steel fibers, while the remaining 17 were made of just reinforced concrete. The columns are heated at temperatures of 100, 200, 300, 400, 500, 600, 700 and 800ºC for a duration of 3 hours at each temperature, and later cooled by two methods, namely, natural air cooling and water quenching. The samples were tested for first crack load, ultimate load and toughness, and the results are discussed
Natural river sand is becoming scarce day by day due to rapid growth in construction sector. There is need for alternatives to be used in place of river sand. The performance of alternatives to river sand at elevated temperatures is also important in the likely event of fire accidents. In this study, the effect of elevated temperatures on the compressive strength of mortars containing Crushed Rock Fines (CRF) and Lateritic Sand (LS) is investigated. Cement mortar cubes were cast for varied proportion of lateritic soil and quarry dust as fine aggregate. Lateritic content was varied from 25%-100%, and 50% quarry dust was adopted. After 28 days of water curing, specimens were exposed to temperatures of 200, 400, 600, and 800ºC. At room temperature, the compressive strength decreases with increase in level of lateritic fine aggregate. The lateritic mortar mixes (50, 75, and 100%) have exhibited superior elevated temperature endurance characteristics at 400, 600, and 800ºC when compared to control mix. Even the 25% laterized mortar has performed equally well as that of control mix. At elevated temperatures, CRF blended mix has performed very poorly. Mortar containing lateritic sand has potential for utilization in buildings and other structures, for better fire endurance in the likely event of fire accidents.
As per the Indian codal guidelines, the ties in reinforced concrete columns are provided either as rectangular or circular depending on the shape of column. In addition to perimeter ties, single or multi-legged crossties are also provided for larger sections. At ambient temperatures, it has been observed that decrease in tie spacing is beneficial as it increases moment capacity of the section leading to better confinement. However, in case of fire the positive effects of decrease in tie spacing beyond 100 mm have not been observed. Considering that the transverse and circumferential cracks are observed in columns due to thermal gradients as known from literature review, the diamond tie configuration was adopted in reinforced concrete columns. Three reinforced concrete columns of full-scale size, 3.15 m each, (two control and other with diamond configuration) are loaded at service load with maximum expected load eccentricity. They are subjected to ISO-834 standard fire curve in a furnace. It is observed that there is an improvement in fire resistance by 150% for column with diamond configuration as compared to rectangular tie configuration with crossties. Further, it is observed that there was no appreciable variation in the amount of spalling for columns with diamond configuration. This indicated better confinement during fire for columns with diamond configuration. It also indicates that diamond configuration of ties reduces the effect of thermal gradient cracks in limiting the fire resistance of RC columns particularly at decreased tie spacing
Petrographic examination technique is one of the well established methods for determining the depth of fire damage in reinforced concrete structure. This paper demonstrates the use of petrography to assess the behavior of concrete structures affected by fire using optical microscopy. Two different types of fire affected buildings were studied by extracting concrete cores and preparing concrete thin samples to study the changes in cement paste, coarse aggregate, fine aggregate, microcracking and other microscopic features to understand the depth of fire penetration inside the concrete. The petrography study revealed that degree of fire damage varies inside the concrete. Findings of the petrographic examination for concrete sample were confirmed with non-destructive test results (mainly with ultrasonic pulse velocity test); loss in the compressive strength and quality of concrete.
This study investigates the residual strength and microstructural identification of slurry infiltrated fibrous concrete at elevated temperature. The mechanical properties of slurry infiltrated fibrous concrete specimen are found by replacing cement by fly ash and metakaolin in the proportions of 5, 7.5 and 10% by weight of cement. The influence of raised temperature, up to 600°C, on the compressive strength and microstructure of metakaolin and fly ash blended slurry infiltrated fibrous concrete (SIFCON) has been investigated in this study. Two hundred twenty-eight cube specimens of slurry infiltrated fibrous concrete were tested at 20°C and 200-600°C. In this investigation, control specimen, residual compressive strength for 200°C, 400°C and 600°C elevated temperatures as 77, 55 and 20%, respectively, and metakaolin blended slurry infiltrated fibrous concrete residual compressive strength shows 95, 88 and 74%, respectively. Based on the experimental results, this study provides an aid to estimate the mechanical properties of slurry infiltrated fibrous concrete exposed to high temperature.
CSIR-Central Building Research Institute, Roorkee, a constituent laboratory of the Council of Scientific and Industrial Research (CSIR), is the only institute that is continuously pursuing research and providing solutions to the problems of building materials, health monitoring and rehabilitation of structures including disaster mitigation, fire safety and energy efficient housing. Since its inception in 1947, the institute has been assisting the building construction and building material industries with its state of the art facility and through path-breaking innovations in fire engineering.
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