ANALYSIS OF THE FIRE BEHAVIOR OF COMPOSITE COLUMNS OF STEEL AND CONCRETE IN MULTI-STORY BUILDINGS

Shinasi ZEJNELI , Berat ZEJNELI

Abstract

Purpose: Unwanted fire is a destructive force that causes thousands of deaths and severe property damage each year. Fire is a spontaneous process of uncontrolled combustion with negative effects expressed through the destruction of material goods and endangering people's lives. Many of the artificial fires were caused by wars, other weather disasters, lightning, but, also by poor construction techniques used in the construction of buildings with highly flammable materials. The main factor that motivates us is to design a building that will have high fire safety with which there will be no great economic and human losses due to its premature collapse. Method: Analysis of the fire resistance of construction structures according to technical regulations: The action of high temperature on interconnected-composite structures causes a decrease in the mechanical properties of the two components of the component (concrete and steel), and thus decreases in drastically their load capacity, then they cause major damage and breakage. Fire resistance design of building structures is based on a certain fire scenario. Here are some of the types of fire scenarios that apply around the world. In most European countries, a standard fire time curve according to ISO 834 and a parametric curve are used, the standard curve is very close to the time-temperature curve used in the United States, ASTM E119. (American Society for Testing and Materials). Constructive behavior of composite elements in multi-story buildings exposed to high-fire temperatures, according to Eurocode 4, part 2. For composite columns, the control procedure: - bearing capacity of the cross section in compression and in moment (bending), - horizontal section, - the bearing capacity of the longitudinal section. Composite columns are considered, as unprotected steel elements, partially and completely concreted, in aspects of the structural scheme as freely supported or embedded elements. Nowadays, several software packages determine the fire resistance of the load-bearing elements of a composite structure. One of the most widely used software packages in most European countries is ArcelorMittal, which has been used in the analysis of fire resistance of structural elements-pillars of a multi-story building. Results: The fire resistance of the pillars is calculated for three cases/ three types of pillars with a height of H = 3.3 m/ - as an unprotected pillar made only of steel profile; - protected with partial concrete cladding and fully concreted steel pillars. Fire resistance analysis of composite columns. The room temperature is taken as the initial temperature and the heating from the induced fire is done gradually according to the standard temperature time curve (ISO 834). - Complete plasticization occurred at the critical temperature of 684 °C (degrees Celsius), a temperature that, as a result of the ignition of the burning material, is reached for a time interval of At=28 minutes, in the case of the unprotected pillar that corresponds to the resistance class R15, which is smaller than what is provided by the regulations (ISO 834). For the partially concreted column, a class of fire resistance of R 120, this is a resistance that is expected for such objects, while in the case of fire resistance for completely concrete pillars, the fire resistance is R180, which is greater than the previous one, which is R120. Conclusion: Unprotected pole - the critical temperature of collapse - collapse is Tkr = 673°C - The fire resistance of the pole in terms of time is At = 28.00min - the fire resistance class of the pole is: R 15, which is the most smaller than that provided for this type of elements Rmin120. The partially concreted column is carried out according to the rules provided by Eurocode 4 for steel and welded concrete. Constructions (Part 4). In the fire calculation, the standard temperature-time curve is used as in the previous elements. the resistance which in this case is equal to that provided for Class R 120. The fire resistance of the partially concreted pillar is R 120min and is equal to that provided for this type of element. The fully concreted pillar has a fire resistance of R 180 min and is larger than the previous one by regulation.

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