scholarly journals The influence of reinforcement temperature on stiffness of reinforced concrete beams in fire conditions

2013 ◽  
Vol 12 (1) ◽  
pp. 115-122
Author(s):  
Michał Głowacki ◽  
Marian Abramowicz ◽  
Robert Kowalski
Keyword(s):  
High Temperature ◽  
Cross Section ◽  
Static Load ◽  
Concrete Beams ◽  
Bending Moment ◽  
Reinforced Concrete Beams ◽  
Temperature Influence ◽  
Calculation Results ◽  
Tensile Zone ◽  
In Fire

This paper describes the analysis of high temperature influence on beams with heated tensile zone. High temperature experiments were preformed under the static load of 50 or 70% of the destructive force ensuring constant value of bending moment in the central part of the heated beam. Beams with 2 reinforcement ratios – 0.44 and 1.13% were examined. In total four series of beams, three in each series (12 elements) were used. This paper analyses the reduction of relative beam cross section stiffness depending on reinforcement temperature. Experimentally obtained stiffness values calculated in two ways (element maximal deflection and deflection measured in three points of analysed element) were compared to calculation results made according to Eurocode. The performed analysis shows that reduction of the stiffness of element based on Eurocode calculations is slightly bigger than the experimentally obtained one.

On the Experimental Analysis of Temperature Influence on Stiffness of Reinforced Concrete Beams

2015 ◽  
Vol 6 (1) ◽  
pp. 49-58 ◽  
Author(s):  
Robert Kowalski ◽  
Michal Glowacki ◽  
Marian Abramowicz
Keyword(s):  
Reinforced Concrete ◽  
Cross Section ◽  
Cross Sections ◽  
Concrete Beams ◽  
Rectangular Cross Section ◽  
Thermal Strain ◽  
Bending Moment ◽  
Reinforced Concrete Beams ◽  
Stiffness Reduction ◽  
Tensile Zone

The paper presents results of experimental research whose main topic was determination of stiffness reduction in bent reinforced concrete beams in two cases: when only tensioned or only compressed zone was exposed to high temperature. Twenty four reinforced concrete beams with rectangular cross-section were prepared for the experiment. Eight groups of beams were prepared in total: 2 with reinforcement ratio - 0.44 and 1.13% x 2 levels of load - 50 or 70% of destructive force ensuring the constant value of bending moment in the centre part of heated beams x 2 static schemes. Three beams were used in each group. Significant cross-section stiffness reduction was observed in beams where the tensile zone was heated. This was due to considerable elongation of the bars where the steel load elongation summed up with the free thermal strain. In beams where the compressed zone was heated the stiffness reduction was observed only after the time where the tensile zone heated cross-sections were already destroyed.

scholarly journals STRESS-STRAIN STATE OF REINFORCED CONCRETE BEAMS STRENGTHENED WITH A NEW EXTERNAL STEEL STRUCTURE

2017 ◽  
Vol 1 (48) ◽  
pp. 90-99
Author(s):  
V. P. Zhyrakhivskyi ◽  
М. G. Chekanovych ◽  
О. М. Chekanovych
Keyword(s):  
Reinforced Concrete ◽  
Cross Section ◽  
Concrete Beams ◽  
Rectangular Cross Section ◽  
Bending Moment ◽  
Steel Structure ◽  
Research Data ◽  
Reinforced Concrete Beams ◽  
Reinforced Beams ◽  
Steel Bars

The study presents a new structure for strengthening of one-span reinforced concrete beams in rectangular cross-section using external steel bars. The specific feature of the proposed strengthening is the unloading of the compressed upper zone of a beam with simultaneous compression of its lower stretched zone. The article considers some variants of making the strengthening structure with rigid and flexible reinforcement elements for faster tension of external bars, and the variant including only flexible elements. It provides a design scheme and method for such reinforced beams. The study provides experimental research data on the series of beams with different parameters of the strengthening structure in the form of «bending moment – deflection» and «bending moment - deformation of concrete» dependencies.

Analysis on Deformation of Pre-Splitting Steel Reinforced Concrete Beams Strengthened by Prestressed CFRP

2011 ◽  
Vol 243-249 ◽  
pp. 929-933
Author(s):  
Na Ha ◽  
Lian Guang Wang ◽  
Shen Yuan Fu
Keyword(s):  
Reinforced Concrete ◽  
Bearing Capacity ◽  
Concrete Beams ◽  
Bending Moment ◽  
Reinforced Concrete Beams ◽  
Steel Reinforced Concrete ◽  
Cfrp Sheets ◽  
Deformation Curves ◽  
Prestressed Cfrp Sheets ◽  
Theoretical Results

In order to improve the bearing capacity of SRC which is related with deformation and stiffiness, SRC beams should be strengthened by CFRP. Based on the experiment of six pre-splitting steel reinforced concrete beams strengthened with (Prestressed) CFRP sheets, the deformation of beams are discussed. Load-deformation curves are obtained by the experiment. Considering the influence of intial bending moment on SRC beams, the calculated deformation formulas of SRC beams strengthened by (Prestressed) CFRP are deduced. The results showed that the load-deformation curves of normal and strengthened beams respectively showed three and two linear characteristics. The theoretical results which calculated by the formulas of deformation are well agreement with the experimental results.

scholarly journals Influence of stirrup spacing on shear resistance and deformation of reinforced concrete beams

2018 ◽  
Vol 7 (1) ◽  
pp. 126
Author(s):  
Latha M S ◽  
Revanasiddappa M ◽  
Naveen Kumar B M
Keyword(s):  
Concrete Beam ◽  
Concrete Beams ◽  
Bending Moment ◽  
Maximum Load ◽  
Reinforced Concrete Beams ◽  
Test Results ◽  
Cement Concrete ◽  
Simply Supported ◽  
Reinforced Cement ◽  
Flexural Reinforcement

An experimental investigation was carried out to study shear carrying capacity and ultimate flexural moment of reinforced cement concrete beam. Two series of simply supported beams were prepared by varying diameter and spacing of shear and flexural reinforcement. Beams of cross section 230 mm X 300 mm and length of 2000 mm. During testing, maximum load, first crack load, deflection of beams were recorded. Test results indicated that decreasing shear spacing and decreasing its diameter resulted in decrease in deflection of beam and increase in bending moment and shear force of beam.

scholarly journals STRAIN-STRESS ANALYSIS OF REINFORCED CONCRETE BEAMS STRENGTHENED WITHOUT UNLOADING BY EXTERIOR REINFORCEMENT/APKRAUTŲ GELŽBETONINIŲ SIJŲ, STIPRINAMŲ PAPILDOMA ARMATŪRA, ĮTEMPIŲ-DEFORMACIJŲ BŪVIO ANALIZĖ

2000 ◽  
Vol 6 (5) ◽  
pp. 307-314
Author(s):  
Arnoldas Šneideris ◽  
Gediminas Marčiukaitis
Keyword(s):  
Carrying Capacity ◽  
Concrete Beams ◽  
Reinforced Concrete Beams ◽  
Bending Stress ◽  
Reinforcing Bars ◽  
Stress Strain ◽  
Flexural Members ◽  
Concrete Members ◽  
Bending Capacity ◽  
Tensile Zone

The mostly used method for strengthening flexural concrete members is mounting exterior reinforcing bars. When applying the strengthening by exterior reinforcing, the problem of assessing the remaining carrying capacity of the member being strengthened and estimating the actual stress in the reinforcement placed in the tensile zone of the member is to be solved. In the paper a method for the analysis of the flexural concrete members strengthened by exterior reinforcing bars is proposed. The method allows to design the exterior reinforcement by taking account of the remaining carrying capacity of the member being strengthened. Moreover, the method proposed enables one to assess a redistribution of stress between the originally placed reinforcement and the exterior reinforcement used to strengthen the member. The redistribution of stress has a considerable influence on the carrying capacity of the member as well as on its bending stiffness. The stress-strain relationships of the both reinforcements are necessary for assessing the redistribution of stress between them, and these relationships are input for the analysis method proposed in this paper. In opposite to other methods suggested in the literature and used for the analysis of the flexural members strengthened in the way described above, the method proposed in the present paper allows one to take account of the pastiche deformations of concrete and steel in the member being strengthened. In addition, the proposed method is less complicated to apply when compared to methods suggested to date. The method proposed is represented by the formula (9), which expresses the bending capacity of the flexural member after its strengthening. The main idea of the proposed method is to replace the design strengths of the reinforcement cast in concrete and mounted outside the member, R s , by the reduced strength σ s, redwhich is assigned to the both reinforcements. The reduced strength σs, red was introduced in order to take account of the plastic deformations of reinforcing steel. The proposed method was verified by a series of experiments with simple reinforced concrete beams. The aim of the experiments was an investigation of the redistribution of stress inside the normal section of the member analysed and the assessment of the influence of the stress-strain state in the member before strengthening on the characteristics of its tensile zone after the member is strengthened. The results of the experiments are shown in Fig 7. In this figure, the experimental relationship between the deflection of the beams being investigated, f, and the reduced bending stress M/M u is depicted, where M is the stress applied and M u is the carrying capacity of the beam. One can see from the polygons shown in Fig 7 that the exceedance of the yield stress in the reinforcement cast in concrete has a considerable influence on the carrying capacity and the bending stiffness of the beams under investigation. Another results obtained from the experiments with the beams strengthened by the exterior reinforcement is shown in Fig 10. This figure demonstrates the dependence of the strain in the reinforcement cast in concrete and the exterior reinforcement, ϵ, on the reduced bending stress M/M u . From Fig 10, one can conclude that the strain in both reinforcements is influenced by the stress-strain state available in the member before strengthening. In Table 1, the bending capacities measured in the experiments just mentioned are compared with the ones calculated by applying the formula (9), which utilises the reduced strength σ s, red , and also the formula (1), which expresses the bending capacity through the design strengths R s . The formula (1) represents one of the methods suggested to date for the prediction of the bending carrying after strengthening of flexural members by exterior reinforcement. The comparison of the experimental results with the ones obtained from formulas (1) and (9) demonstrates that the method represented by the formula (1) has the unconservative difference in bending capacity of 11 %, whereas the proposed method represented by the formula (9) yields a conservative difference of only 2%. The results of experiments may be applied to predict the redistribution of stress in the statically indetermined structures.

Reliability of reinforced concrete beams in serviceability limit state via microprestress-solidification theory, a structural health monitoring strategy

2022 ◽  
pp. 146442072110690
Author(s):  
Mohsen Ghabdian ◽  
Seyed BB Aval ◽  
Mohammad Noori ◽  
Wael A Altabey
Keyword(s):  
Reinforced Concrete ◽  
High Temperature ◽  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Concrete Beams ◽  
Limit State ◽  
Reinforced Concrete Beams ◽  
Nonlinear Creep ◽  
Structural Health ◽  
Serviceability Limit State

An important and critical area within the broad domain of structural health monitoring, as related to reinforced civil and mechanical structures, is the assessment of creep, shrinkage, and high-temperature effects on reliability and serviceability. Unfortunately, the monitoring and impact of these inherent mechanical characteristics and behaviors, and subsequent impact on serviceability, have rarely been considered in the literature in structural health monitoring. In this paper, the microprestress-solidification creep theory for beams is generalized for the simultaneous effect of linear/nonlinear creep, shrinkage, and high temperature in a reliability framework. This study conducts a systematic time-dependent procedure for the reliability analysis of structures using a powerful nanoscale method. It must be noted that this paper aims to extend the previously developed microprestress-solidification method in a health monitoring reliability-based framework with a close look at a nonlinear creep, parameters affecting creep, and long-time high temperature. A finite element approach is proposed where creep, shrinkage, temperature, and cracking are considered using strain splitting theory. First, the model performance was evaluated by comparing the results with the experimental test available in the literature in the case of creep and shrinkage. Then, the simultaneous effect of creep, shrinkage, and temperature was compared with experimental results obtained by the authors. Reliability analysis was applied to reinforced concrete beams subjected to sustained gravity loading and uniform temperature history in order to calculate exceedance probability in the serviceability limit state. It was found that the exceedance probability of reinforced concrete beams was dependent on the shear span-to-depth ratio. In the serviceability limit state, exceedance probabilities of 0.012 and 0.157 were calculated for the span-to-depth ratios of 1 and 5, respectively. In addition, it was shown that temperature plays an important role in the reliability of reinforced concrete beams. A 4.27-fold increase was observed in the case of moderate to high temperature. Finally, for three different load levels of 40%, 70%, and 80%, the exceedance probabilities were 0.156, 0.328, and 0.527, respectively, suggesting that load level is another key parameter affecting the reliability of reinforced concrete beams. It is thus concluded these fundamental phenomenological studies should be further considered as part of the broad field of structural health monitoring.

THE ANALYSIS OF SHEAR STRENGTH OF FLEXURAL RC ELEMENTS ACCORDING TO EC2 AND STR / LENKIAMŲJŲ GELŽBETONINIŲ ELEMENTŲ ĮSTRIŽOJO PJŪVIO STIPRUMO PAGAL STR IR EC2 ANALIZĖ

2013 ◽  
Vol 4 (4) ◽  
pp. 133-144 ◽  
Author(s):  
Šarūnas Kelpša ◽  
Mindaugas Augonis
Keyword(s):  
Shear Strength ◽  
Reinforced Concrete ◽  
Cross Section ◽  
Shear Force ◽  
Bending Moment ◽  
Intersection Point ◽  
Shear Reinforcement ◽  
Truss Model ◽  
Calculation Results ◽  
The Difference

When the various reinforced concrete structures are designed according to EC2 and STR, the difference of calculation results, is quite significant. In this article the calculations of shear strength of bending reinforced concrete elements are investigated according to these standards. The comparison of such calculations is also significant in the sense that the shear strength calculations are carried out according to different principles. The STR regulations are based on work of the shear reinforcement crossing the oblique section and the compressed concrete at the end of the section. In this case, at the supporting zone, the external bending moment and shear force should be in equilibrium with the internal forces in reinforcement and compressed concrete, i.e., the cross section must be checked not only from the external shear force, but also from bending moment. In EC2 standard, the shear strengths are calculated according to simplified truss model, which consists of the tension shear reinforcement bars and compressed concrete struts. The bending moment is not estimated. After calculation analysis of these two methods the relationships between shear strength and various element parameters are presented. The elements reinforced with stirrups and bends are investigated additionally because in EC2 this case is not presented. According to EC2 the simplified truss model solution depends on the compression strut angle value θ, which is limited in certain interval. Since the component of tension reinforcement bar directly depends on the angle θ and the component of compression strut depends on it conversely, then exists some value θ when the both components are equal. So the angle θ can be found when such two components will be equated. However, such calculation of angle θ became complicated if the load is uniform, because then the components of tension bar are estimated not in support cross section but in cross section that are displaced by distance d. So, the cube equation should be solved. For simplification of such solution the graphical method to find out the angle θ and the shear strength are presented. In these graphics the intersection point of two components (shear reinforcement and concrete) curves describes the shear strength of element. Santrauka Straipsnyje apžvelgtos ir palygintos STR ir EC2 įstrižojo pjūvio stiprumo skaičiavimo metodikos stačiakampio skerspjūvio elementams. Normatyve neapibrėžtas EC2 metodikos santvaros modelio spyrių posvyrio kampo skaičiavimas, lemiantis galutinį įstrižojo pjūvio stiprumą. Straipsnyje pateikiamos kampo θ apskaičiavimo lygtys, atsižvelgiant į apkrovimo pobūdį. Norint supaprastinti pateiktų lygčių sprendimą siūlomas grafoanalitinis sprendimo būdas, pritaikant papildomus koeficientus. EC2 neapibrėžia skaičiavimo išraiškų, kai skersinis armavimas yra apkabos ir atlankos. Minėtos išraiškos suformuluotos ir pateiktos straipsnyje. Nustačius EC2 metodikos dėsningumus siūlomas alternatyvus apytikslis skaičiavimo būdas atlankomis ir apkabomis armuotiems elementams. Straipsnyje apžvelgtos abi – STR ir EC2 – metodikos, išskiriant pagrindinius skirtumus ir dėsningumus.

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