Fire reaction of concrete with and without PP fibres: experimental analysis and numerical simulation
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abstract
Structural elements of reinforced concrete, in general, present good performance in case of fire. However, more recent structures have adapted new types of concrete (high strength, self-compacting, etc.) presenting different thermo mechanical behaviour, acquiring special importance the study of spalling. One of the most common procedures to minimize this events is the addition of polypropylene fibres (PP) to natural components, reducing the internal void pressure of the material through the channels created by the fusion of the fibres.
The experimental study of concrete under fire conditions and the development of new numerical models has allowed the assessment of more or less complex phenomena to determine temperature evolution and other state variables, enabling different levels of approaches, using coupled or uncoupled field interaction (thermal, mechanical, hydrodynamic, chemical). This investigation studies the thermal performance of a two dimensional model, using nonlinear and transient finite element analysis.
The fire resistance of partially encased sections (HEB and IPE) depends on the temperature evolution during fire exposure. Eurocode 4, part 1.2 [1], proposes the assessment of the cross section using the method of the four components (flanges, web, reinforcement and concrete) to determine the resistance and stiffness under fire (R30, R60, R90, R120). This study aims to assess the balanced summation model of Eurocode (informative annex G). New formulae will be proposed to evaluate the plastic resistance to axial compression and effective flexural stiffness around the weak axis, based on new simple formulas to determine the flange average temperature, the residual height and average temperature of the web, the residual cross section and average temperature of concrete, the reduced stiffness and strength of reinforcement. The advance calculation method was used to validate new and safe formulae, based on the analysis of the cross section totally engulfed in fire (fire in four sides).
