Improvement of the Assessment Method for Fire Resistance of Steel Structures in the Temperature Regime of Fire under Realistic Conditions

This paper proposes a method that makes it possible to study the patterns of changes in the concrete strength of reinforced concrete crossbars depending on the heating temperature under fire conditions by interpreting the results of their standard fire tests. For the implementation of this method, it is proposed to use similar data obtained using mathematical modeling based on the finite element method and given material properties, including the curve of concrete strength reduction recommended by the guidelines, as data included in the set of measurement results during fire tests depending on temperature. Such data are time dependences of temperature indicators at individual cross-section points and time dependence of the maximum deflection of the crossbar. The article proposes an interpolation method that makes it possible to set the temperature at any point of the section based on the approximation of the isotherms by parabolas with a variable indicator of their power. A method based on the mathematical interpretation of temperature indicators obtained using the proposed interpolation method and the curve of the dependence of the maximum deflection on time using a deformation model for describing the stress-strain state is proposed to identify the dependence of the concrete strength of reinforced concrete crossbars. The work also shows that the results obtained using the proposed method of identifying concrete strength reduction coefficients are adequate as their relative error is on average no more than 7 %. Based on the results, the possibility of its application to study the regularities of the decrease in the strength of reinforced concrete crossbars under fire conditions has been proven

“…This makes it possible to refine the deformation diagrams for concrete recommended in [10]. To achieve this goal, the approach described in works [13,15,16] was used.…”

Section: Results Of Data Calculation Regarding the Behavior Of A Rein...mentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Procedures For Determining the Initial Data For The Identifi...mentioning

confidence: 99%

See 1 more Smart Citation

Method for identifying the strength characteristics of concrete of a reinforced concrete crossbar during heating under conditions of fire

Pozdieiev,

Nekora,

Fedchenko

et al. 2023

“…At the same time, the cost and labor-intensiveness of these works in comparison with calculation methods are significantly exceeded and have a negative impact on the environment. The computational method using simulation involving the finite element method provides an opportunity to fully reproduce the operating conditions of the building structure during a fire [5,6]. This variant of research involves the application of various geometric parameters of structures, the application of any level of load, using various theories of the strength of various materials, which opens up the possibilities of computational experiments.…”

Section: Experimental Calculations Carried Out In the Current Work Us...mentioning

confidence: 99%

Revealing patterns in the behavior of a reinforced concrete slab in fire based on determining its stressed and deformed state

Sidnei,

Berezovskyi,

Kasiarum

et al. 2023

The object of research is the fire resistance of reinforced concrete ribbed slabs. The subject of research is the effect of the level of mechanical load on the fire resistance of the studied reinforced concrete ribbed slab under the influence of fire. Currently, the assessment of the fire resistance of such structures using the tabular method is significantly limited by certain geometric parameters of these plates. It is also not considered possible to apply the zone method, since reinforced concrete ribbed slabs consist of components that receive thermal effects according to various scenarios and geometric parameters, which is not taken into account in Eurocode 2. Experimental calculations carried out in the current work using a refined procedure involving the finite element method allow solving the actual scientific and technical problem related to the determination of the dependence of the fire resistance of these structures on the level of load applied. The calculation of the temperature spread over a reinforced concrete ribbed slab under the influence of the standard temperature regime of fire was carried out using convection and radiant heat exchange, which is recommended by Eurocode 2. The iterative implicit Newton-Raphson method was used to solve the mechanical problem. Evaluation of fire resistance of reinforced concrete ribbed slabs was carried out according to the onset of signs of the limit state of fire resistance due to the loss of load-bearing capacity. According to the results, it was established that at 100 % load level of the structure under investigation, the critical deflection of more than 268 mm and the rate of growth of deformation exceeding 18 mm/min were recorded simultaneously on minute 43.9. According to the results of the research, the regularity of the limit of fire resistance of reinforced concrete ribbed slabs from the level of the applied mechanical load was established. This will make it possible to design and build buildings and structures using the specified building structures with guaranteed fire resistance classes, which improves the level of safety for people at the facilities

“…This procedure is less laborious in comparison with the determination of the actual limit of fire resistance of building structures. The most versatile and comprehensive method for establishing fire resistance is the method of fire tests [5]. This method is applied without regard to the material of the structure and is universal for all types of structures and makes it possible to comprehensively establish the conditions for the occurrence of all three types of boundary states.…”

Section: Introductionmentioning

confidence: 99%

Determination of features of composite steel and concrete slab behavior under fire condition

Nekora

Sidnei

Shnal

et al. 2021

Self Cite

Methods for calculating the fire resistance of steel-reinforced concrete slabs made using profiled steel sheets under the influence of a standard temperature regime for more than 120 minutes are considered and analyzed. Research has been carried out to determine the heating parameters and the stress-strain state of steel-reinforced concrete slabs made using profiled steel sheets under fire conditions for more than 120 minutes. The results of this study allow to obtain indicators of temperature distribution for assessing the fire resistance of such structures for fire resistance classes above REI 120. Accordingly, the results obtained are a scientific basis for improving the existing method for calculating the fire resistance of steel-reinforced concrete slabs made using profiled steel sheets. The temperature distribution in the cross-section of structures was obtained using a general theoretical approach to solving the problem of heat conduction using the finite element method. Using the obtained temperature distributions, the parameters of the stress-strain state were determined based on the method of limiting states. To carry out the calculations, appropriate mathematical models were created that describe the effect of the standard temperature regime of a fire, to determine the temperature distribution at every minute in the sections of steel-reinforced concrete slabs with profiled steel sheets. A method is proposed for dividing the section into zones to take into account the decrease in the indicators of the mechanical properties of concrete and steel. A simplified method for the design assessment of steel-reinforced concrete slabs made using profiled steel sheets is proposed, which is consistent with the current EU standards and can be effectively used to analyze their fire resistance when establishing their compliance with the fire resistance class REI 120 and higher.