Effects of Fire on the Strength of Reinforced Concrete Structural Members (original) (raw)
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The Effect of Fire on the Strength of Concrete Material
2021
Structural members exposed to fire may damage considerably, lose their durability, and even collapse due to the failure of the members. This work presents the results of an experimental investigation of the effect of fire on the strength of concrete. Cylindrical and beam specimens were prepared and burnt in the fire for one hour. In both cases, two systems were followed for cooling the samples, (i) natural cooling in the air (ii) forced cooling in the water. Afterwards, the compressive and flexural strength of the specimens were determined. The result shows that the strength of concrete was considerably reduced due to burning in fire. The compressive strength of cylindrical specimens was decreased by 44% and 60%, respectively, for the natural and forced cooling of the specimens. In the case of beam samples, the flexural strength was decreased60% and 69%, respectively, for the natural and forced cooled specimens. This research also reveals that the specimen cooled in air showed bette...
2015
Concrete is a composite construction material consisting basically of a binder, aggregates, water and with or without admixture to modify either or both its physical and chemical properties. The rate at which concrete structures especially buildings are gutted by fire hazards is on the increase and this has adverse effect on the strength, hence, the need to assess the post fire structural strengths of Normal Strength Concrete(NSC). NSC of grade 50 was produced and cast into specimens of sizes 150mm cubes and 100mm x 100mm x 500mm reinforced concrete beams. The concrete cubes and beams were subjected to elevated cyclic thermal loadings after 7, 14 and 28 days of curing, while the rate of heating was maintained at 1 o C/min until the target temperature of (100, 130, 160, 200 and 250) o C where attained and this was maintained for one hour and then allowed to cool at 1 o C/min to room temperature of 32 o C. Unstressed Residual Uniaxial Compressive Test (URUCT and Flexural Stre...
Experimental Investigation on Effect of Fire on Properties of Concrete with the Use of Admixture
Damage due to fire can cause in terms of loss of life, homes and livelihoods. One of the advantages of concrete over other building materials is its inherent fireresistive properties. However, concrete structures must still be designed for fire effects. Structural components must still be able to withstand dead & imposed loads without collapse even though the rise in temperature causes a decrease in the strength & modulus of elasticity for concrete. Fire resistance is measured in terms of structural stability, structural integrity and insulation. This Experimentation involve the study of residual strength in concrete after exposure to elevated temperatures for concrete in which coarse aggregate replace with (20%, 40% and 60%) blast furnace slag and additional 1% steel fiber is added to increase the tensile strength of concrete. The effect of elevated temperature at 200, 400, 600, 800, 1000 and 1200 for the exposure of 1hours are studied. Compressive strength, split tensile strength and flexural strength are obtained after exposure to elevated temperature. Also investigated colour change, area of colour spot, width of crack, types of crack, of samples when exposed to fire at different temperatures and exposure times.
Forensic Investigation of Fire-affected Reinforced Concrete Buildings
This study focused on forensic investigation of fire-affected reinforced concrete buildings. Post-fire investigation was conducted on structural elements in three selected fire-affected concrete buildings, in order to ascertain their in situ residual strengths and also to provide data for use in future assessment of fire-affected buildings. The selected sites for investigation include a five-storey building at Alagbaka and a bungalow at Adegbola in Akure, and a ten-storey building in Benin, Nigeria. Rebound hammer and ultrasonic pulse velocity are two non-destructive tests apparatus used for this investigation. Average values of pulse velocity were fitted into an established model in order to estimate the probable temperature, which the buildings were subjected to. Tests were conducted on beams, columns and slabs in both the affected and the unaffected parts of the buildings. From the results, visual examination of the fire-affected buildings revealed changes in the colour of the concrete, delamination of plaster of slab and exposure of reinforcement for severe cases at various locations on the concrete members. In addition, there was notable reduction in the in situ strengths of the fire-affected structural members when compared with the unaffected members. It was deduced that concrete members subjected to temperatures above 600 0 C lost about 70 % of its strength.
Strength Studies on Different Grades of Concrete Considering Fire Exposure
American Journal of Civil Engineering
Concrete is generally strong in compression and weak in tension also it resist against fire. Cement concrete is a complex mixture of different materials, for which the properties may alter in different environmental conditions. The behavior of concrete is depends on difference in temperatures and its mix proportions. The principle effects in the concrete due to elevated temperatures are loss in compressive strength, loss in weight or mass, change in color and spalling of concrete. The objective of this research attempt was to prove experimentally the effects on the behavior of concrete under elevated temperatures of different grades (M20, M40 and M60) of concrete. The compressive strength was determined at different temperatures, thus providing scope of determining loss in strength. In addition, effects on strength under cooling for different grades of concrete were studied. The specimens were kept in oven at certain temperatures (200°C, 400°C, 600°C, and 800°C) for 1 hour at constant temperatures. Non-destructive testing (NDT) methods, i.e. Rebound hammer test was adopted to study the changes in surface hardness of concrete specimens subjected to elevated temperatures.
Fire Behaviour of Reinforced Concrete Beams
2016
Increasing fire accidents in buildings and structures are of major concern these days. The extensive use of concrete in buildings as a structural material has led us to study the effect of fire on concrete. Concrete is proven to have a high degree of fire resistance. It is non-combustible and has a high thermal emissivity and low conductivity which significantly slows down the penetration of heat through concrete elements. In most fires, the outer layer of concrete with a thickness of 3-5 cm is damaged. Therefore, many concrete buildings that experienced fire can be simply restored and reused. However concrete remains a complex material, made up of several constituents which show different behaviour when exposed to fire. Several physico-chemical transformations take place in concrete resulting in a decrease of strength and stiffness. Therefore, the fire resistance of concrete structures should not be taken for granted. This can be done by studying the behaviour of different structur...
Evaluation of Effect of Fire on Frame Members of Structure
Journal of emerging technologies and innovative research, 2020
The study of ingredient and properties of concrete for M20 grade. The study is carried out experimentally using Compressive testing machine is for testing of concrete cube and Universal testing machine is for testing of concrete beam. To calculate the compressive strength of concrete cube and flexural strength of concrete beam experimentally with and without effect of fire at different fire duration like F30, F60, F90, F120 etc. All category concrete specimens are tested for with and without effect of fire at different fire duration. These samples are also tested for properties of Hardened concrete i.e. Compressive Strength, Flexural strength. All concrete beams are tested for M20 grade with and without effect of fire at different fire duration. IndexTerms – Mix Design, Concrete Specimens, Effect of Fire at Different Fire Duration, Compressive Strength, Flexural Strength.
Concrete under Fire: Damage Mechanisms and Residual Properties
The paper firstly presents the basic damage mechanisms of concrete under fire attacks, and then the experimental study of the residual compressive strength and durability properties of normal and high strength concretes made of materials available in Hong Kong after exposure to high temperatures up to 800°C. The effects of post-fire-curing on the strength and durability recovery of fire-damaged concrete were also investigated. It was found that concretes containing fly ash and blast furnace slag gave the best performance particularly at temperatures below 600°C as compared to the pure cement concretes. Explosive spalling occurred in most high strength concretes containing silica fume. The high-strength pozzolanic concretes showed a severe loss permeability-related durability than the compressive strength loss. The post-fire-curing resulted in substantial strength and durability recovery and its extent depended upon the types of concrete, exposure temperature, method and the duration of recuring.
Behaviour of Reinforcement in Reinforced Concrete Beam Subjected To Fire on Tensile Strength
ABSTRACT: Fire is an extreme event, the occurrence of which affects the behavior of the structures significantly in terms of both serviceability and strength criteria; hence, provision of appropriate fire safety measures for structural members is an important aspect of structural design. However, the impact of fire on steel reinforcement at elevated temperature is analyzed by exposing the concrete beam to fire at an interval of time, the reduced in strength of the steel reinforcement for the 10mm and 12mm in diameter was found.
Fire: Structural and Material Consequences
Zbornik radova Građevinskog fakulteta
In addition to the mechanical properties, behaviourstructural materials at elevated temperatures is also of high importance. Present paper deals with the effects of fire attack on concrete or concrete structures in Hungary. Residual compressive strength of concrete exposed to high temperatures is influenced by the following factors: water to cement ratio, cement to aggregate ratio, type of aggregate, water content of concrete before exposing it to high temperatures and the fire process. Therefore, mix design and composition of concrete are of high importance.Material and structural behavior are analyzed at high temperatures, which, based on practical observations, could reach even 1100°C in some cases. Relationship of concrete mix design and structural behaviour arediscussed with test results on prestressed concrete beams. By the analysis of earlier fire attacks, important information can be obtained for future fire design.The fire cases of the Budapest Sports Hall (1999) and of the Athletic Hall of the University of Physical Education in Budapest, Hungary (2015) are also summarized in our paper.