Estimation of bearing capacity and serviceability of a floor slab after high-temperature exposure

Introduction. Reinforced concrete structures of buildings have significant fire resistance, but high-temperature effects lead to changes in strength and deformation characteristics of concrete and reinforcement of structures. In addition, for prestressed reinforced concrete structures, fire impacts can be associated with partial or even complete loss of prestress. At the same time, it is the prestress of the reinforcement that makes it possible to limit the width of the crack opening and the deflection of reinforced concrete structures within acceptable limits.

Materials and methods. The paper presents and analyzes the results of analytical calculations of the bearing capacity and serviceability of a prestressed reinforced concrete ribbed floor slab before and after high-temperature fire impact on it. After fire exposure, the calculations are carried out with a complete loss of pre-stressing by the reinforcement. The heating temperature of the concrete in the compressed zone and tension reinforcement in the calculated cross section of the floor slab is taken according to the results of experimental studies.

Results. The comparison of the floor slab deflections obtained by calculation and experimentally indicates the presence of additional factors (temperature expansion of concrete and reinforcement, high-temperature creep of reinforcement) that determine the increased value of the experimental floor slab deflection compared to the calculated one. The structural solution of the floor slab is analyzed, the feasibility of increasing the area of longitudinal tensile reinforcement to increase the bearing capacity and reduce the crack opening width in the slab is considered. The effect of fire protection on the heating temperature of the concrete in the compressed zone and the tensile reinforcement of the slab is shown.

Conclusions. An analysis of the results of calculating a prestressed concrete ribbed floor slab before and after a fire showed a slight decrease in its bearing capacity after fire impact, an increase in the width of the crack opening and a significant increase in the deflection of the slab.

1. Efryushin S.V., Yuriev V.V. Numerical modeling of fire resistance of reinforced concrete plate using ansys software complex. Structural Mechanics and Structures. 2019; 4(23):86-92. EDN AQXAQL. (rus.).

2. Kudryashov V.A., Zhamoydik S.M., Kurachenko I.Yu., Nguen T.K. Results of full-scale fire tests of the monolithic reinforced concrete slab as part of a fragment of a frame building. Vestnik of the University of Civil Protection of the MES of Belarus. 2021; 5(1):49-66. DOI: 10.33408/2519-237X.2021.5-1.49. EDN EODTXX. (rus.).

3. Mkrtychev O.V., Sidorov D.S. Calculation of a reinforced concrete building for temperature effects. Vestnik MGSU [Proceedings of Moscow State University of Civil Engineering]. 2012; 5:50-55. (rus.).

4. Palevoda I., Zainudzinava N. Fire resistance of binding prestressed concrete slab with unbonded reinforcemen. Vestnik of the University of Civil Protection of the MES of Belarus. 2018; 2(2):161-167. EDN XPAXHF. (rus.).

5. Palevoda I., Zainudzinava N. Modelling of the behavior of concrete slabs with unbonded reinforcement in the ANSYS program complex. Vestnik of the University of Civil Protection of the MES of Belarus. 2017; 1(4):385-391. EDN ZRKOZD. (rus.).

6. Golovanov V.I., Pavlov V.V., Pekhotikov A.V. Experimental and analytical studies of the bearing capacity long-span reinforced concrete during fire exposure. Fire and Explosion Safety. 2015; 24(11):31-38. DOI: 10.18322/PVB.2015.24.11.31-38 (rus.).

7. Ilyin N.A., Panfilov D.A. Features of determining the fire resistance of multi-hollow prestressed reinforced concrete floor slabs of buildings. Traditions and innovations in construction and architecture. Natural sciences and technosphere safety. 2017; 231-238. EDN YQLMID. (rus.).

8. Kudryashov V.A., Kurachenko I.Yu. Analytical evaluation of the load-bearing capacity of bendable reinforced concrete structures after fire. Forensic Examination of Belarus. 2018; 1(6):56-60. EDN NVKKDR. (rus.).

9. Zaitsev A.M., Nikulin A.V. Possible exploitation of reinforced forms after fire. Fire and Explosion Safety. 2004; 13(4):66-71. (rus.).

10. Dukhov D.G., Kleschunov Ya.Ya., Kolgudaev A.N. Peculiarities of surveying buildings after a fire. Ceteris Paribus. 2015; 4:21-26. EDN UNRXYH. (rus.).

11. Plotnikov D.A., Bashevaya T.S., Novikov N.S. Character of effect of fires on reinforced concrete structures and review existing fire protection means. Bulletin of the Institute of Civil Protection of Donbass. 2016; 1(5):14-21. EDN YTLEJC. (rus.).

12. Zhuvak O.V., Rybakov V.A., Sergeeva F.A. Fire resistance of reinforced concrete structures with the use of various fireproof coatings. Problems of ensuring the functioning and development of ground infrastructure of weapon system complexes : materials of the All-Russian Scientific and Technical Conference. 2021; 51-56. EDN QSSFJG. (rus.).

13. Levashov N.F., Akulova M.V., Potemkina O.V., Sokolova Y.A. Analytical model of strength decreasing of cement composites exposed high temperatures. Building and Reconstruction. 2018; 5:104-111. (rus.).

14. Zagoruiko T.V., Ledenev A.A., Matsyurak B.K. Determination of the fire resistance of reinforced concrete structures, taking into account changes in the properties of concrete. Modern technologies for ensuring civil defense and liquidation of consequences of emergency situations. 2018; 1(9):143-145. EDN XSLVWP. (rus.).

15. Zagoruiko T.V., Ledenev A.A., Pertsev V.T. On the issue of fire resistance of reinforced concrete products and structures. Modern technologies for civil defense and liquidation of consequences of emergency situations. 2016; 1-1(7):227-230. EDN WDHLND. (rus.).

16. Danilov R.A. Corrosion as a factor of reducing the fire resistance of reinforced concrete structures. Problems of technosphere safety : materials of the international scientific-practical conference of young scientists and specialists. 2022; 11:137-141. EDN PXUPIH. (rus.).

17. Kuzneсova I.S., Surikov I.N., Vostrov M.S., Savrasov I.P. Research in physical-mechanical properties of reinforcement of modern production at high temperatures of heating and cooling. Industrial and Civil Engineering. 2016; 12:18-23. EDN XISIYX. (rus.).

18. Pristupyuk D.N., Fedorov V.Yu., Danilov R.A. The study of the loss of fire resistance of the reinforced concrete crossbars and beams in operation. Vestnik of the University of Civil Protection of the MES of Belarus. 2022; 6(3):278-293. DOI: 10.33408/2519-237X.2022.6-3.278. EDN AWIKFF. (rus.).

19. Roitman V.M., Pristupyuk D.N., Fedorov V.Yu. Method for assessing the fire resistance limits of reinforced concrete structures. Roytman Readings : collection of materials of the VII scientific and practical conference. 2019; 34-38. EDN UDGUCI. (rus.).

20. Tamrazyan A.G., Zvonov Yu.N. To assessing the reliability reinforced concrete flat slabs for punching under the action of concentrated force at high temperatures. Industrial and Civil Engineering. 2016; 7:24-28. EDN WHKJTR. (rus.).

21. Portnov F.A., Kovaleva S.A. State and prospects of development of the issue of evaluation of fire resistance of reinforced concrete structures. Proceedings of the Kyrgyz State Technical University named after I. Razzakov. 2020; 2(54):133-139. EDN BLEECI. (rus.).