THERMAL RESPONSE OF REINFORCED CONCRETE STRUCTURES IN NUCLEAR POWER PLANTS

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When the temperature and sustained mechanical load are applied to the specimen simultaneously, the total thermomechanical strain will be observed. The decomposition of the total strain can be considered experimentally or numerically to estimate the effect of combined thermal and mechanical action or the influence of each strain component of the total strain.

It includes drying shrinkage due to moisture loss and expansive strains. As one can see, FTS is not the free thermal expansion we discussed earlier, because it includes drying shrinkage. LITS is composed of transient creep, basic creep, and the elastic strain that occurs during the heating process. The term basic creep is used cautiously here, because this strain strictly occurs when concrete is loaded at constant temperature and after all internal reactions have been completed Khoury b. It appears in addition to the increase in elastic strain and basic creep flow and delayed elastic components with temperature.

TTC is generally developed within a month from the start of heating Khoury a. Although it is recognized that the two components cannot be separated experimentally, one reason for the subdivision is that the two terms have different characteristics. The creep component takes place under heating and cooling and shows creep recovery, whereas the thermo-mechanical strain is only observed during first heating and not during subsequent cooling or heating cycles.

Thelandersson assumed proportionality between the thermo-mechanical strain and the thermal strain because of its simplicity. In the following, a more general formulation is adopted according to Nielsen, Pearce and Bicanic for application to transient fire scenarios. In their LITS model the dashpot associated with the viscosity is neglected, however in the case of long term load histories with mechanical and thermal loads, the temperature-dependent creep strain should be included in the total strain rate expression.

Mass losses in both concretes were also similar up to C. The highest rate of mass loss occurred in the temperature range of C to C. The rate of weight loss stabilized at temperatures above C. Lee et al. In general, the weight loss increases with increasing target temperature. However, the weight loss and the target temperature are not proportional over the entire temperature range.

The slope of the weight loss vs. In the lower temperature range, the weight loss is due mainly to the evaporation of the free water present in the voids and capillary pores. After the evaporation of all free water further weight loss comes from the removal of the adsorbed water in smaller pores, which takes more energy. Moreover, at higher temperatures, some phase transformations take place and a certain amount of chemically bound water is released and evaporated.

The amount of adsorbed water and chemically bound water released due to the phase transformation is less than This leads to the reduced slope in the weight loss curves above C. At temperatures higher than C, the slopes for both types of specimens are almost the same. This means that the evaporation of the free water in the voids and capillary pores is almost complete at C.

Therefore, regardless of the initial moisture content of concrete, after C, the rate of weight loss is similar for all specimens. The constant slope after C indicates that the weight loss of concrete is governed by the same mechanism from C up to C. The plot of the equation is shown in Figure 2. However, due to phase transformations of free and bound water in heated concrete, the specific heat exhibits a peak between C and C with a top value at C. This peak varies with the concrete properties, water content, and other parameters. K , as indicated in Figure.

One can see a large drop in the thermal diffusivity up to C, which is primarily related to the loss of free water. Beyond this temperature the thermal diffusivity shows relatively little variation with increasing temperature up to C. The table is from the recent paper by Kodur et al. Figure 3. The response behavior exhibits a drastic reduction of the proportional limit under increasing temperatures which is accompanied by a puzzling increase of the ultimate yield strength up to C at reduced ductility.

Beyond that temperature range, the ultimate the yield strength decreases rapidly with temperature while the ductility increases. The temperature dependence of hot-rolled reinforcing steel is specified in Eurocode3 ENV , in the form of Table 3. Thereby, the stiffness and strength values have been normalized by the respective values at reference temperature.

Holmes test data 1 Table. Holmes test data For reinforcing steel Table. The two th s o o recommendations are compared in Figure Thermal transport properties of Steel under high temperatures Similar to thermal transport properties of concrete, thermal transport properties of steel also include thermal conductivity, density, and specific heat also called heat capacity.

Using Eq. However, experimental evidence shows that there is a nearly linear decrease of the density with increasing temperature. As illustrated in Figure 3. Note: for simplified studies the thermal diffusivity calculated by Eq. The difference in the coefficients of thermal expansion of the two materials results in progressive damage in the interface and thus reduces the bond strength.

There are two testing methods for measuring residual bond strength and hot bond strength. The residual bond strength can be measured in a way that specimens are heated up to various target temperatures, held at the temperatures for a period of time, cooled down to ambient temperature. Then, a pull-out test is performed to pull the reinforcing steel out of the specimen. The hot bond strength can be obtained with the pull-out test carried out under the hot conditions during the holding period. Any parameters that change the coefficient of thermal expansion of concrete will have impact on the bond strength, such as mix proportion of concrete and type of aggregate.

In addition, there are several other influential parameters on the bond strenth, such as curing conditions, shape of reinforcing bar, surface conditions and type of bars, diameter of bar, shape of concrete specimen, and testing procedure. For round bars, some of the test data showed that the bond strength was increased after heating below C.

This is similar to the down-up-down trend observed for compressive strength of concrete in the same range of temperature. The bond strength reduction of round bars is more significant than the deformed bars. Therefore, the deformed bars hold better bond under high temperatures. With higher roughness, the bond strength of round bars can be improved.

For deformed bars, the rib height is an important factor for the bond strength. Some minimum height should be maintained. When a rib height of approximately 0. This is observed for both round bars and deformed bars. The type of aggregate is the main factor determining the hot bond strength. This is due to the fact that the thermal expansion of concrete depends heavily on the aggregate type; and that the lower the thermal strain of concrete, the lower the deformation mismatch between the concrete and the steel; and thus the higher the bond strength at elevated temperatures.

This is shown in Figure 4. From Table 2. This may be due to the fact that moist cured specimens have higher drying shrinkage upon heating than dried specimens. The residual bond strength is lower than the bond strengths obtained from hot tests. This is due to the fact that the cooling process generates significant damage in the concrete, which was shown in earlier sections see Figure 2. The bond strength is significantly influenced by the testing procedure and the shape of specimens.

It should be noted that the absolute values of bond strengths of the specimens with conical load bearing ends obtained from Hertz's Hertz are twice as high as the values obtained from the specimens with flat load bearing ends from Diederichs et al. Diederichs, U. The properties of the materials include mechanical properties such as strength and stiffness and transport properties such as thermal diffusivity and heat capacity. There is a detailed description on long-term properties of concrete under elevated temperatures such as creep and shrinkage. The coupling effects among heating, drying, and mechanical loading the so-called thermo-hygro-mechanical coupling effects on performance of concrete are discussed.

Several aspects are covered for each material property of concrete, including damage mechanisms, available test results, code requirements, and prediction models. The bond between concrete and steel under elevated temperatures is also reviewed. American Concrete Institute. American Concrete Institute Bazant, Z. Blundell, R.

Browne, R. Concrete for Loading Ages up to Dissertation, TU Braunschweig. ENV , Design of concrete structures-part General rules-structural fire design, European Committee for Standardization, Brussels. Design of steel structures-part General rules-structural fire design, European Committee for Standardization, Brussels. Furumura, F. Convention, Boston April Gvozdev, A. Harmathy, T. Hertz, K. The effects of elevated temperatures on the strength properties of reinforcing and prestressing steels, Structural Engineer, March, 60B 1 , Jennings, H.

Skalny, The Amer. Kodur, V. A, Sullivan, P. Radial temperature distributions within solid concrete cylinders under transient thermal states, Magazine of Concrete Research, 36 , Khoury, G. Transient thermal strain of concrete: literature review, conditions within specimen and individual constituent behavior, Magazine of Concrete Research, 37 , Khoury, G. Ulm, Z. Bazant and F. Wittmann, Elsevier Science, Ltd.

Lee, J. Concrete Inst. Residual mechanical properties of high strength concrete members exposed to high temperature-part 1. Nasser, K. Neville, A. Nielsen, C. Improved phenomenological modeling of transient thermal strains for concrete at high temperature, Computers and Concrete, March, 1 2 , Noumowe, A. Phan, L. Rigberth, J. Sager, H. Theoretical considerations about spalling in tunnels at high temperatures, Technical Report, Technical University Vienna, Austria.

Schneider, U. Verlag W. Thelandersson, S. Modelling of combined thermal and mechanical action in concrete, J. Willam, K. Johann i. In this chapter, we will first review the test results on structural components like beams and columns, and then on structural systems such as floor slabs.

Their study investigated the influence of a number of factors including beam continuity, moment redistribution and aggregate type on the behavior of RC beams under standard fire conditions. One of the tested beams was simply supported at both ends, while the remaining beams were overhanging at one or both ends.

The applied loading on the cantilever was chosen to reflect the continuity effect in RC beams. With the exception of the beam with simply supported at both end, B, all specimens were tested in manner to simulate continuous beams. Six tests were conducted to simulate interior-span conditions, and four to simulated end spans. This was accomplished by maintaining one or both end of the beam at constant elevation by varying load P 2 or loads P 1 and P 2. These cantilever loads generally increased sharply during the first 15 minutes of the fire test, reached a maximum value 30 to 45 minutes after start of test, and more or less remained constant for the reminder of the test.

Initial, maximum, and end-of-test values of the P 1 and P 2 cantilever loads are listed in Table 7. Table 7. Midspan 0 hr Max. Generally, thin hairline cracks were observed on top surface of the continuous specimens near supports, after the full superimposed loads were Moisture oozed from cracks for different lengths of time. From the result of simply supported beam, it appears that fire endurance would have been significantly longer if the cutoff bars had been longer. Nevertheless, it is apparent that for simply supported members, fire endurance is the duration of test until moment capacity is reduced to the applied moment.

From the results of continuous beams, Except B, the mode of failure was flexural. Failure was imminent when three hinges formed. Specimen B failed in shear, possibly because the shear capacity was less than that required by American Concrete Institute ACI This study concluded that the fire resistance of continuous beams in much higher than that of simply supported beams due to the occurrence of redistribution of bending moment and shear forces in fire conditions. The loading and heating systems are presented in Fig The beam is loaded and heated symmetrically.

The thermal program is applied according to ISO R The dimensions of the cross-section and the reinforcement arrangement are indicated in Fig Fig. In a reinforced concrete beam submitted to a fire test there is a steep thermal gradient on the cross-section producing large deflection even at the beginning of the test when the stiffness properties of materials remain unchanged. The main objective of this fire resistance test was to assess the fire resistance rating of an RC beam. The objectives of the test program were: a To examine flexural and shear behavior of beams exposed to fire, and b To generate experimental data for validating computer programs developed for calculating thermal and structural behavior of beams exposed to fire.

Test specimens included five in. All beams measured approximately 27ft 8. They were fabricated with normal-weight concrete. And Table 7. As the test progressed, shear cracks remained essentially unchanged, but flexural cracks rapidly worsened and surpassed the shear cracks in magnitude during the third hour of the test. All beams formed flexural failure mechanisms that caused the termination of tests. The length of the fire tests were: 3 hr 40 min for Beam No.

Applied loads, furnace atmosphere, concrete and steel temperatures, deflections, expansions, and slopes were measured in each test. These data were needed to validate the computer program developed in the Center for Building Technology of the National Bureau of Standards. This investigation has shown that thermo-mechanical structural analysis, coupled with appropriate material constants, can predict the behavior of reinforced concrete structural elements exposed to different fire exposures, at least within the limits of accuracy required for states limit states design.

The ability of the analysis to predict structural behavior is limited by the quality of data available on the structural materials at elevated temperatures, and to a lesser extent by the analytical model which neglects the effect of localized cracks and spalling of concrete. The most important factor affecting predicted beam behavior is the calculated temperature history in the reinforcement. The computation of these temperatures directly from temperatures in the concrete obtained from a two-dimensional thermal analysis tends to be conservative because the capacity of the reinforcement to conduct heat longitudinally is not taken into account.

In contrast, accuracy in predicting temperature distribution in the concrete is not as important in predicting load-carrying capacity of reinforced concrete beams. A total of nine specimens were tested. All specimens were of the same size and contained the same reinforcement. The specimens were beams with cross-sections mm wide and mm deep. The yield strength of the main and transverse bars was MPa. The specified design strength of the concrete was 24 MPa.

A core specimen is shown in Fig Each core cylinder was mm in diameter and mm long.

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A total of nine specimens as shown in Table 7. To examine the core strength, a total of nine plain concrete specimens were cast corresponding to the RC beams and exposed to the same heating conditions Table 7. For the specimens heated to 90 C, the maximum load decreased with increasing heating period. The stiffness after cracking of specimens M and H-1 degraded compared with the unheated specimen.

The normalized shear strength ratios of ultimate shear strength of heated specimens divided by that of the unheated specimen were calculated. For 65 C heating, no deterioration was observed. The strength of the core cylinder compared with the shear test under the same heating conditions is discussed. From the Figure, the degradation ratio of core strength was greater than that of shear strength in all portions.

However, the core strength ratio of the upper portion approximately corresponded to the shear strength ratio. For the specimen heated at 65 C Fig.


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The tendency for young s modulus to deteriorate was approximately the same as for the compressive strength ratio. Fig Young s modulus vs. These paths are expressed simply by two basic paths: the path of constant forces but subjected to elevated temperature FT path , and the path of constant temperature but subjected to applying forces TF path. A total of 13 beam specimens subjected to two such basic paths were tested.

Fig and Table 7. This is T T because the value of M u is mainly dependent on the yield strength of tensile reinforcement f y, and the temperature of the tensile reinforcement approaches T 0 after T 0 exceeds C regardless of the FT or TF path. Form comparison of curvatures for specimens subjected to the FT and TF paths, it can be seen that specimen curvatures for different force-temperature paths will experience very different variations.

Twelve tied, reinforced concrete columns were fabricated and tested. Ten of the columns had a cross-section of 12 12in mm , one of 8 8in mm and one of 16 16in mm. All columns were 12ft 6in mm long. Three specimens were made with carbonate aggregate and nine with siliceous. The tests were carried out by exposing the columns to heat in a furnace specially built for this purpose. The heat input into. Several of the columns were tested under a load, which was concentric. The loads were applied about one hour prior to the test.

Of the variables studied in this report, load, cross-section size and type of aggregate have the largest influence on the fire resistance of reinforced concrete columns. Particularly the use of carbonate aggregate instead of siliceous aggregate will substantially increase the fire resistance of the column. The influence of concrete moisture content on fire resistance is in the practical range, insignificant. The fire resistance of the columns studied is considerably higher than those assigned to them in the National Building Code and in the ACI They also enable the In this study, each fire tests carried according to test purpose and major characteristics as follows: a standards, b carbonate aggregate, c lightweight aggregate, d high-strength concrete, e restraint, f doubled reinforcement, g size and extra steel, h shape, i end conditions, j other than standard fire, k eccentric load, and l eccentric load with constraints.

Columns were 12ft 6in 3. They were fabricated with either siliceous, carbonate, or lightweight aggregate concrete. Specimens included columns with 8 8, 12 12, 16 16, 12 18, 8 36in , , , , mm cross sections and circular columns with 14in mm diameter. Furthermore, it showed that increasing the cross section size even in only one direction or utilizing a carbonate aggregate concrete rather than a siliceous aggregate concrete would significantly increase fire resistance.

The test results also indicated that full restraint on a column did not significantly decrease its fire resistance. Since eccentrically-loaded columns will fail in excessive lateral deflection rather than in compression, additional factor must be considered in developing rational-design methods for these columns. These calculations would have to account for end conditions as well as reduction in material strength and reduction in effective cross-section size due to high temperatures. The three columns tested by Diederichs et al. Mixture I had specified cube strength of MPa and contained fibers not clearly specified.

Mixture II had specified cube strength of MPa and contained no fibers. The two columns with fibers experienced minor spalling mixture I and no spalling mixture III during fire tests. Fire tests on these columns were terminated at minutes after the start of the tests. The mixture II column without fibers experienced spalling at about 6 minutes into the fire test.

Spalling continued until 30 minutes into the test when it reached the longitudinal reinforcement at the edges of the column. The test was terminated at 45 minutes, which is significantly less than the time of minutes for specimens with fibers. In the VTT fire tests, the ten HSC specimens were made of three different concrete mixtures, all contained variable fiber contents. None of the columns experienced spalling. All columns were reported to have failed due to loss of compressive strength at high temperature.

In the full scale column test, the specimen was made of concrete with a specified cube compressive strength of MPa and contained fibers. The column was eccentrically loaded Shallow spalling occurred at about 10 minutes after starting the test and stopped after 30 minutes. At minutes, the column collapsed due to compressive failure of the concrete near the maximum stressed cross section. This study indicated that the use of capillary forming fibers help reduce the potential for spalling in HSC columns and suggested that further studies be conducted on the effects of variations in fiber contents.

The parameters used were the load level, the dimension of the cross section, the length of columns, the main reinforcement, the concrete cover and the eccentricity of the axial load. The fire resistance tests were performed according to the Belgian Standard NBN and the columns were exposed to fire on four sides. The support conditions of the columns were hinges at both ends. The dimensions of the cross section were: mm, mm, and mm. The column lengths were 3. Concrete covers of 25mm, 35mm, and mm were used. Eccentricities of mm, 20mm , 20mm, 20mm , and 0.

Longitudinal reinforcing bars of 12mm, 16mm, and 25mm in diameter were used. Although the type and arrangement of stirrups was not a parameter buckling of some individual longitudinal reinforcements may occur between two stirrups at column failure. Therefore, decreasing the spacing between stirrups might improve the behavior of the column under fire conditions, however theoretical and experimental research should be performed in order to quantify this effect. A summary of the test results follows: 1 In all problems involving fire resistance, the load level column stress is the most important factor.

The fire resistance decreases when load increases. The fire resistance of mm sections was between 1 hour and 2 hours, while in most of the mm sections the fire resistance was greater than 2 hours. However the applied load must be limited and reinforcement with large diameters rebars should be avoided. For one of the columns, the fire resistance time was shorter than 1 hour, and for the other, the fire resistance time was between 1 hour and 2 hours. These inconsistent results may be partly explained by the existence of reinforcement with large diameters in one case, and by the use of a section with large dimensions and small concrete cover in both cases.

The test results showed that the increase of concrete cover had a positive effect on the fire resistance. But, additional tests on columns involving reinforcing with large diameter bars are still required to clarify the effect of the bar diameters of longitudinal reinforcement. On the contrary, the use of eccentricities 20mm, 20mm exhibited a decrease of the load capacity levels.

Test specimens, four columns with circular cross section diameter mm and a length of mm, have been tested. The material qualities are C60 siliceous for concrete and S for the steel reinforcing bars. The test results are summarized in Table 7. The following conclusions were drawn from this study: 1 Observations made during experiments show that surface spalling was noticed between 20 and 60 minutes of fire test.

The circular shape of the cross-section does not prevent the occurrence of this phenomenon. In order to take account of the short length of the specimens, a new formulation has been proposed for the buckling coefficient used in the second method. Qty-size Tie-conf. Typ Factored Resistance kn Comp. Load Fire End. The elevation and cross-sectional details of the columns together with the locations of the ties are given in Fig And Full details on fabrication of these columns, including rebar arrangement, concrete placement, curing, and instrumentation is given by Kodur et al.

Effect of Concrete Strength Data from these experimental studies indicate that good fire endurance can be obtained for HSC columns. However, a comparison of the fire endurance in Table 7. While for NSC columns a fire endurance of about six hours was obtained in Lie s Report , for HSC columns, with similar confinement, fire endurance of about four hours was obtained.

Data from the Table shows that high fire endurance three hours or more can be obtained for HSC columns even under full service loads. Effect of Lateral Reinforcement Results from experimental studies can be used to study the influence of confinement on the fire performance of HSC columns. The higher fire endurance in columns HSC4 to HSC6, as compared to columns HSC1 to HSC3, can be attributed to the closer spacing, and better detailing of the column ties ties were bent back into the core of the column and increased lateral reinforcement.

Also, despite the It should be noted that for column HSC5, where additional confinement was provided, fire endurance as high as minutes was obtained even under full service load. Further, Column HSC6 has attained a high fire resistance of minutes under an increased load level, as a result of enhanced confinement provided by the provision of cross-ties. The fire endurance of a column increases with decreasing load.

The fire endurance of Column HSC6, with a load intensity of 1. While there are other differences in the configuration of these two columns, such as the concrete strength and load level, one of the major variables is the type of aggregate. This occurs mainly because carbonate aggregate has a substantially higher heat capacity specific heat than siliceous aggregate, due to an endothermic reaction that takes place in carbonate aggregate at about C Lie, The aggregate type also influences the spalling phenomenon.

This could be partly attributed to the effect of aggregate type used in the concrete mix. Of the two concrete types, carbonate aggregate concrete provides better spalling resistance than siliceous aggregate concrete. The higher specific heat and lower thermal expansion of carbonate aggregate concrete at higher temperatures, contributes to this spalling resistance. The specific heat of carbonate aggregate concrete, above C temperature, is generally much higher than that of siliceous aggregate concrete. This specific heat is approximately ten times the heat needed to produce the same temperature rise in siliceous aggregate concrete.

The increase in specific heat is likely caused by the dissociation of the dolomite in the carbonate concrete, and is beneficial in preventing the spalling of the concrete. It is important to emphasize that 3 specimens were tested in each case factor combination. The final part of program included an experimental investigation of methods designed to prevent explosive spalling of 6 columns Fig Experimental research program Ali et al. Always minor spalling took place first followed by major and severe spalling. Low heating rate reduced the risk of explosive spalling.

And the generated Normal strength concrete columns showed higher spalling degrees when tested under restraint. Increasing the loads imposed on the column reduces the maximum value of the generated restraint forces. And unloaded columns generated restraint forces that reached 0. There are two extremes of natural fires to be used in this experimental work.

The first curve represents the BS, defined as the high heating rate HH with high energy, high temperatures and short duration, likely to induce high surface gradients, promoting spalling. The other curve represents the ISO standard heating, defined as low heating rate LH , producing lower peak temperatures but is of longer duration sufficient to permit significant heat conduction, which may produce a large build up of vapor pressure and also create significant thermal expansion producing restraint force. The load ratio LR is defined as the ratio of the applied load to the BS design load.

The restraint ratio RR is defined as the ratio of the column k c to the restraint stiffness provided by the structure k c. Twelve high strength concrete columns were tested at load ratio LR of 0. All specimens failed by axial deflection, no buckling took place. The additional generated forces depend on the load ratio but are independent on the restraint ratio.

The temperature gradients within the concrete columns exposed to both high and low heating rates is shown in Fig The main conclusions that can be drawn from this experimental research are as follows: 1 All specimens failed by axial deflection, no buckling took place. There has been no premature failure. An increase of restraint against axial column expansion generated less additional forces. The maximum value of axial displacement is independent of the rate of heating and it is dependent on the load that has been applied during the test.

Evaporation of moisture occurred when the temperature within the concrete centre reaches approximately the value C. The water was boiling and evaporating through these points releasing by that the internal pressure and causing explosive spalling. Corner columns are usually under high biaxial eccentricity. Furthermore, during a fire, only the interior two faces of corner columns may be exposed to fire in contrast to interior columns of which all four faces are exposed.

The material asymmetry of concrete after fire further complicated the behavior of corner columns. Six RC corner columns were manufactured for this research under high temperatures. RC columns with dimensions of mm were cast for this study. Two rebar sizes, No. The design follows the ACI code. Column size is commonly used for 3- storey buildings. The eccentricity was a constant in this experiment.

The temperature changes and appearance of the columns were observed and recorded during fire loading. The longitudinal and lateral displacements were measured during the strength tests, which were performed after the columns were exposed to high temperatures. Based on the result of the experimental studies, the following conclusions can be drawn: 1 The dimensions of the core of the column are very important for the residual strength. For the same fire duration, the larger core area gives a higher residual strength.

The thicker the cover, the earlier the cover tends to fall off. The column strength depends mainly on the core of concrete. Therefore, if the core area is increased, the RC column will have a higher residual strength after high temperature exposure. This statement also holds for columns not affected by high temperature. However, the existence and the characteristics of surface cracking after fire are not directly related to strength loss.

That is, the temperature of the exterior part of the specimen was decreasing while the temperature of the interior was increasing. This difference may cause secondary damage to the column and further complicates analysis. This study only focused on lowrise buildings, which have a lower axial load. High-rise building is a different issue. It involves high strength material, slender columns, and high axial forces. Their behavior is more complex and they were not included in this study. The findings of this study of residual strengths can be used for future evaluation, repairs and strengthening.

The 14 18ft specimens were made with carbonate-aggregate concrete. Joists were 6in. Specimens were supported at the four corners. Fig shows the important features of the two specimens. The main difference between them was in the thickness of the deck slab. Specimen S had a 5in. Because the specimen size was fixed by the dimensions of the floor furnace, three sizes of domes were necessary to obtain the desired joist configuration. Twelve domes were in. In addition, 14 partial domes were used around the perimeter of each specimen.

All domes were 8in, deep. Age at test, days Concrete compressive strength at test, psi Average relative humidity at slab middepth, persent Equivalent live laod, psf Live load deflection at mid point, in Fire exposure duration, hr: min Adjusted time for avg. The greater deflection for S was probably a result of the higher load and lower concrete modulus of elasticity.

During the fire tests, the deflection increased to about an inch during the first hour of test, and then either remained constant or gradually diminished, as shown in Fig. Specimens were permitted to expand certain amounts and then further expansion was stopped. Most of the allowed expansion occurred within the first half hour of test, as shown in Fig Thermal thrusts that developed because the specimens were not entirely free to expand are shown in Fig Thrusts were greater for S than for S because S was not permitted to expand as much as S Fire endurances were determined by the criteria for temperature rise of the unexposed surface.

In both tests, the fire endurances were longer than results of 3 3ft fire tests had indicated, probably because of the heat sink effect of the joists. The 14 18ft specimens were made with carbonate, siliceous, or expanded shale aggregates. Specimens were approximately ft in plan, with the joists spanning the 18ft direction, as shown in Fig Metal pans, 30 in.

Joists were 5 in. A transverse beam, 6 in. The fire endurance of each of the eight full-scale pan-joist floor specimens was determined by the rise of the unexposed surface temperature, rather than by structural considerations. Fire endurances of the full-scale specimens temperature rise of unexposed surface correlated well with results of similar 3 3ft slab specimens, as shown in Fig Specimens supported the design loads during the standard fire tests from 1 to 4 hours even though the temperature of the reinforcing steel reached 1, to 1, deg.

A wide range of restraint of thermal expansion was used in various tests, with expansions ranging between 0. Fig Specimen details and instrumentation locations Abrams et al. The tests were designed to show the effect of varying the slab thickness, type of concrete, imposed load, soffit protection and nature of fire exposure on the mid-span flexural deflection and axial movements of the slab ends.

For the slab specimens of BRE Building Research Establishment , the following parameters were varied: slab thickness and mm , type of concrete normal weight and light weight , live load zero and two different gypsum board systems and severity of standard of fire exposure ISO and the Norwegian Petroleum Directorate NPD temperature-time curves.


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  8. Based on the result of the experimental studies, the following conclusions can be drawn: 1 Mid-span deflections were dominated by thermal bowing during the 90 min design period of fire exposure; the effect on deflections of imposing the design live load of 1. Fig Effect of imposed load Cooke, 2 The higher rate of heating associated with the NPD hydrocarbon fire exposure caused almost a doubling of mid-span deflection obtained using the ISO fire exposure in the first 20 min, Fig. Fig Effect of slab thickness and concrete type Cooke, 4 The effect of soffit protection is, as one might expect, to reduce the mid-span deflection.

    The test allowed a direct comparison between the modes of failure observed at ambient and elevated temperatures. Both mild steel and stainless-steel welded smooth wire meshes, with varying bar diameters and spacing, were used as reinforcement. The test program comprised four series of slabs as follows: 1 M-series: 14 slabs with mild steel mesh reinforcement at ambient temperature.

    In each series, half of the slabs had a size of 1. Twenty-six small-scale slabs have been tested at ambient temperature, with a further 22 similar small-scale slabs tested at elevated temperatures. The slabs were reinforced with either mild-steel or stainless-steel welded mesh. The ambient temperature tests highlighted two modes of failure comprising fracture of the reinforcement across the shorter span of the rectangular slabs or one of the spans of the square slabs or crushing of the concrete in the corners of the slab.

    The mode of failure, together with the magnitude of enhancement, which provides an indication of the magnitude of membrane action and is defined as the maximum sustained load divided by the theoretical yield load, seemed to depend on the reinforcement ratio. Provided the mode of failure was by fracture of the reinforcement, an increase in reinforcement ratio resulted in an increase in enhancement.

    However, continually increasing the reinforcement ratio finally led to compressive failure where a further increase in reinforcement ratio led to a decrease in enhancement. The ambient tests also highlighted that the square slabs had a higher enhancement compared to rectangular slabs for a given vertical displacement. The square slabs were shown to fail at a This was due to the strains of the reinforcement in the shorter span of the rectangular slab being relieved as the longer span edges of the slab are pulled inwards as the slab deflects vertically.

    The enhancement, considering all the tests, ranged from 1. Due to the similar geometry and mesh reinforcement a direct comparison of the failure mode could be made between the twenty-two elevated temperature tests and the ambient temperature tests. For the elevated temperature tests all failure modes comprised fracture of the reinforcement, due to the reinforcement s high temperatures which reduced its strength. For compressive failure to occur at elevated temperature the reinforcement ratio, based on the elevated temperature strength of the reinforcement and concrete, would have to be of similar magnitude to the ratio, based on normal room temperature values, of the slabs which failed by crushing at ambient temperature.

    In the fire tests presented in this paper, the reinforcement lost greater strength compared to the concrete in the corners of the slab where crushing was observed in the ambient tests resulting in reinforcement fracture being the critical failure mode. The theoretical yield-line load of the slabs at the failure temperature was calculated using the reduction factors given in EN and EN The slabs tested had to support a static load between 2. In this chapter, we will first review the analysis results on structural components like beams and columns, and then on structural systems such as floor slabs.

    Particular interest was the load carrying capacity, the thermal forces, and the deformation capacity. The effects on these properties due to variation in strength with temperature, the temperature level and its distribution across the section, the amount of reinforcing steel 0. Stress-strain relationships for the concrete based on the lower and upper bound relations in these Figures are presented in Fig Stress-strain relationships at various temperatures used for the Grade 60 reinforcing bars are presented in Fig a Lower bound b Upper bound Fig. They are based on the finite element method using beam elements with subdivision of the cross-section in a rectangular mesh.

    The structure submitted to increasing temperatures is analyzed step-by-step using the Newton- Raphson procedure.


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    To validate this method, a comparison between theoretical and experimental results is made for a reinforced concrete and a composite beam. It must also be pointed out that the analysis of the failure mode is more complicated for composite structures. The temperature distribution in the section of concrete member is calculated by Hertz s simplified method, which is then input into the FE program for doing the time-dependent thermal stress analysis. The rectangular cross-section members are defined by depth d and width w, and have a length L.

    The two ends were assumed to be simply supported and are subjected to equal compressed loads for column and pure bending loads for beam. Because of the symmetry of the problem, only one quarter of the members is analyzed. The load is applied to the plate which is only allowed to move longitudinally and rotate about symmetric axis.

    Extreme Reactors Turbine Explosion

    It can be seen that the lateral displacement of the midsection of the beam increases with the time and the maximum failure time of fire resistance decreases with the proportion of bending load to the beam. The various lateral displacements show that the collapse of a beam is caused mostly by excessive deflection. Since the load is pure moment, a beam bends at the beginning of load. During the fire the temperature-induced expansion at the lower part is larger than the temperature induced expansion at the upper part of the concrete section which leads to additional directional bending and deflection.

    The collapse of beam is caused by reduction of material strength and excessive displacement at high temperature. As is expected, an increase in the concrete cover results in an increase of fire resistance. It can be seen that the increase of beam dimension results in a significant increase of fire resistance, which means the fire resistance of beams is proportional to their size. It gives the evidence for recent codes and recommendations to present a tabulation of data for beams related to the minimum width of the member.

    The results obtained from the two different fire cases have shown that three sides fire exposures is much worse than the one-side fire exposure, not only with respect to fire resistance but also with respect to deformation and deflection. The example demonstrates that the results of the method provided in this paper agree well with the current standards. The method can take into account holonomic hardening or perfectly plastic constitutive models of generic shape. The proposed method is implemented in a computer program permitting the analysis of the effect of the non-linear thermal loads owing to daily and seasonal changes in shade air temperature, solar radiation, re-radiation, etc.

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    The outcome of this investigation is that the non-linear thermal load does not significantly affect the load carrying capacity of the sections both when dealing with steel reinforcement and when adopting FRP reinforcement. The tensile stress in the reinforcement does not markedly change either, both under service loads and at failure.

    On the contrary, the stress and strain distribution in concrete under service loads markedly varies because of the non-linear thermal load, but this effect becomes feasible at ultimate load. This analysis program includes two steps: the first step is the calculation of the transient temperature field in cross-sections exposed to fire and the second step is the determination of the mechanical response due to the effect of thermal and mechanical load.

    A nonlinear finite-element procedure is proposed to predict the temperature field history. In this thermal analysis, the effect of moisture has been taken into account by introducing a water vapor fraction function to define the variation of enthalpy. A mechanical nonlinear analysis of the cross-sections is performed for each temperature distribution and for the applied exterior load using an algorithm of arc-length control.

    Eurocode 2, design of concrete structures, part general rules - structural fire design ENV , Fig Simply supported beam with cantilever ends Capua and Mari, Fig shows geometric, material and loading data of the beam. The flange is considered laterally insulated, and the upper side is exposed to ambient temperature 20 C.

    The thermal properties of concrete and steel are assumed to take into account the European Standard ENV It is important to note that the cross-section over the support is able to resist for a longer time than the section in the midspan. And it is observed that when the reinforcing steel reaches the critical temperature the moment capacity drops dramatically.

    The heating and the cooling phases are considered. Standard planar, four-node quadrilateral finite elements are employed in the non-linear time-dependent thermal analysis of cross-sections, while the recently proposed strain-based planar beam finite elements are used in the non-linear mechanical analysis of the frame. The formulation includes both exact geometric and material nonlinearities, and considers the temperature dependence of thermal and material parameters, the plastic, creep and thermal strains in concrete and steel, the transient strain in concrete and the strain localization as a consequence of softening of material at high temperatures.

    A so called constant strain element is introduced to resolve numerically the loss of uniqueness of strain measures at the point of localization. The formulation is validated by comparing some of the present numerically predicted results with the data, measured in experiments. The numerical example is a simply supported concrete beam with overhangs. This beam has been extensively tested by Lin et al. In what follows three variants of this beam will be analyzed and marked as B 1, B 3 and B 5.

    Geometric, material and loading data are given in Fig and in Table 8. Table 8. Bratina et al. In case B, The result is that w increased somewhat see Fig. The fire resistance time is greater than min. This indicates that the creep of concrete is not essential for the loss of stability of the simply supported beam in fire. The fire resistance time is still The analysis of case D considers all kinds of strain contributions. It clearly shows a decisive effect of the viscosity of steel at temperatures above C.

    Williams-Leir provided the data for steel with different creep characteristics. If we consider the steel with mild creep characteristics steel Austen 50 , the agreement between measured and predicted response curves is sufficient see Fig. Fig Comparison of the variation of the predicted and measured vertical deflection with time.

    This program controls a Big Reactors nuclear reactor in Minecraft with a Computercraft computer, using Computercraft's own wired modem connected to the reactors computer control port. On April 26, , the Number Four RBMK reactor at the nuclear power plant at Chernobyl, Ukraine, went out of control during a test at low-power, leading to an explosion and fire that demolished the reactor building and released large amounts of radiation into the atmosphere.

    Reactor unit No. The best way to avoid the possibility of a prompt supercritical condition is to not build that "very special kind" of. PCTran to validate extreme. Russia will launch the world's first floating nuclear reactor and send it on an epic journey across the Arctic on Friday, despite environmentalists warning of serious risks to the region. The new reactor is designed for basic research on fusion and also as a potential prototype power plant that could produce significant power.

    The shutdown was designed to test the ability of the plant to function at low power, although other tests of similar plants and other reactors had suggested that powering down the plant was unsafe. This thread is mainly aimed at the devs. A fourth explosion has rocked the Fukushima nuclear plant on Tuesday at Unit 4 at the facility, the Japanese Kyodo news agency reports.

    Three over-heating nuclear reactors at the Fukushima nuclear plant hit by the tsunami went into 'meltdown' today, as officials in Japan admitted that fuel rods appear to be melting. The aim is for the tokamak reactor to heat plasma up to million degrees Celsius. The main usage for hydrogen on a power station nuclear or conventional is turbine stator cooling. The automatic shutdown system was disabled to allow the reactor to continue working under low power conditions.

    The Independent. Steam explosions are thought to have occurred in the SL1 and Chernobyl accidents and possibly in the Fukushima accident in rector unit number 3. Increasingly poor air quality in Texas has sparked a statewide drive for clean energy production. Details of Bushehr nuclear power plant phase one. An explosion early Saturday damaged the building housing.

    Petersburg, Russia, where it was built. Mid-level GE engineers expressed concerns, relayed to Tepco, that this left them vulnerable to flooding. An empty reactor will have a radius of 10 blocks, with each Uranium Cell increasing the radius by 3 blocks and each Integrated Reactor Plating reducing the radius by 1 block. When the operators cut power and switched to the energy from turbine inertia, the coolant pump system failed, causing heat and extreme steam pressure to build inside the reactor core.

    It should generate about the same amount of power as turbines of 1, RPM designs mentioned above, due to platinum and Enderium blocks having the same efficiency. But even more than that, the vast quantity of fallout produced and other factors show that the explosions were not produced by ordinary atomic bombs. Before powering on the reactor, some additional safety features are probably a good idea. That's the major difficulty: obtaining a significant amount of antimatter to sustain a reactor. Clean, cheap nuclear energy is often touted as a means to battle climate change. The force of the blasts blew the reinforced steel and concrete lid off the reactor and exposed its deadly contents to the world.

    I could not find any info about how to setup this reactors self-sustaining if possible or how the waste is produced. The radioactive cloud drifted over Europe and as far as North. A small nuclear reactor was involved in the failed missile test last week in Russia that ended in an explosion that killed five scientists, Bloomberg News reported Monday.

    In , nuclear. The project was, however, abandoned due to extreme diplomatic pressure from the US, and the onset of the Iranian revolution and the Iran-Iraq. The Reactor utilized in Reactor Incremental produces your money through power. Can a Big Reactor blow up? GF is going to making her first big reactor in Infinity and we are curious if they can detonate.

    The explosion released times more radiation than the atomic bomb that exploded over Hiroshima, affecting parts or all of Ukraine, Belarus, Russia, Poland and the Baltic nations. The result was a power excursion of between and times full power as the rods were inserted into the reactor. Explosion at Japanese nuclear power plant that is hoped to reach Extreme Green people who'd the reactor that explosion blew in the air and caused air to enter.

    They added more absorbers so that reactions would remain stable at low power, they increased the number of control rods in the core, and increased the fuel enrichment of uranium required at power plants. If cooling is insufficient, the reactor will gradually overheat and eventually explode. Seven people earlier reported as missing have been accounted for, a company official told reporters. But the Redstone Flux port says its at 0 RF and no energy is being output. Here's what you need to know to. The Big Reactors mod adds multi-block power systems capable of providing large amounts of RF power to Minecraft.

    Follow their code on GitHub. At the time, investigation and analysis concluded that a steam explosion was the cause, and that's been the accepted explanation ever since. But seconds later, power levels suddenly surged to dangerous levels. The energy released by nuclear reaction heats water in the reactor vessel, causing convection current that circulates the water through the vessel. Five scientists in Russia were killed last week after a failed missile test involving a small nuclear reactor exploded, Time Magazine reported, …. The explosion would have been between three and five megatons.

    They range from 1 kilowatt, which they say is only enough to power a. Thirty years after an explosion ripped apart the Chernobyl power plant and spewed radioactive. It occurred on April 26, , when a sudden surge in power during a reactor systems test resulted in an explosion and fire that destroyed Unit 4.

    The last section of the chapter is dedicated to experiments in the generation and study of extreme states of matter with the use of intense shock waves driven by a nuclear explosion. This will create an unstable reactor, and eventually an explosion. Nuclear reactors the size of wastebaskets could power our Martian settlements is set to be the first nuclear fission reactor to reach space since the Popular Science may receive financial. A fusion reactor is exactly the opposite of a Fission Reactor.

    The Chernobyl accident in was the result of a flawed reactor design that was operated with inadequately trained personnel. This aerial view of the Chernobyl shows damage from an explosion and fire in reactor four on April 26, Something like this happened during the Chernobyl meltdown: water around the reactor core got hot and turned to steam fast enough to blow the very large, heavy lid off the containment vessel into the air. This can be examined by analysis of isotope ratios.

    Of course, the accidents led to release of radioactivity due to probable melt down of reactor core and hydro-gen explosion in the containment; however, there were no casualties in the accident since the. Heat may be removed by several different cooling methods. This program was tested on and designed to work with the mod versions and configurations installed on Flawedspirit's Mental Instability Pack no longer available , though as the.

    You might already know this, either because you're a history buff or just a fan of HBO's hit miniseries Chernobyl, which ended. So it is recommended to place all reactor parts and cooling system at the same chunk, or if you can't, using a Dimensional Anchor is another option. The reactor may have super-heated a "liquid-propellant" in the form of highly explosive hydrogen. While the residual effects of the accident were limited due to the remote location and relatively small scale of the reactor, it remains today the only such incident to ever result in immediate deaths.

    An Enantiomorphic Reactor Core can take the extreme energy of nether stars and draw continual power by destabilizing them. A nuclear weapon is a device that uses a nuclear reaction to create an explosion. If you want to see what a fission reactor explosion looks like, look at Chernobly. Chernobyl reactor entombed in giant steel shield 30 years after worst nuclear disaster in history. This is a port of the 1. Particularly, the Nuclear Thermal Rocket NTR is a leading candidate for near-term human missions to Mars and beyond due to its relatively high thrust and efficiency.

    The reactor's emergency shutdown which should have halted a chain reaction failed. Indeed, the explosion that occurred on 26 April in one of the reactors of the nuclear power plant, and the consequent fires that lasted for 10 days, led to huge amounts of radioactive materials being released into the environment and a radioactive cloud spreading over much of Europe.

    So use glass in your reactor : - added support for Modularity fluids to replaces the ones from Thermal Expansion please keep in mind that Modularity is still being worked on the the fluids may not yet be available in the public release and a bunch of metals from TiC to be used in the Turbine. The sarcophagus that encased Unit 4 of the Chernobyl Nuclear Power Plant is a giant metal concrete and structure quickly constructed as an emergency measure in to halt the release of radiation into the atmosphere following the explosion.

    Nothing more, nothing less. A sudden power output surge took place, and when an attempt was made for emergency shutdown, a more extreme spike in power output occurred which led to a reactor vessel rupture and a series of explosions. I am a fission reactor designer from Los Alamos National Laboratory. The engineers continued to raise rods. An extensive testing program kept the reactor at very low power levels—too low to make electricity—until December 29, In this blog, I will acquaint you with Detuned Reactors and analyse their usage and benefits.

    In my guide, I have used a 6 x 6 base.

    THERMAL RESPONSE OF REINFORCED CONCRETE STRUCTURES IN NUCLEAR POWER PLANTS

    A transformer exploded and a fire erupted at a a nuclear power plant north of New York City, leading to an emergency shut down of one of the reactors. So for years afterwards people would come to work in the same plant that had irradiated much of Europe.

    According to Rossi and a handful of others who have observed the system in operation, it is producing 1 MWatt continuous net output power, in the form of heat, from a few grams of "fuel" in each of a set of modest-sized reactors in a network. On April 26, a nuclear reactor exploded in the Soviet Union. The web version is at 1. Nuclear power is the fifth-largest source of electricity in India after coal, gas, hydroelectricity and wind power. On April 26, at an explosion in reactor 4 of the Chernobyl Nuclear Power Plant released a nuclear fallout times that of the atomic bomb explosion in Hiroshima.

    For example, when the reactor showed a temperature rise, there was no cooling water and no agitation after the power failure, so the operator had to open the manhole of the reactor and inject cold water into the reactor.


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