A LIMIT ANALYSIS APPROACH TO THE STABILITY ASSESSMENT OF REINFORCED CONCRETE PANELS IN FIRE CONDITIONS

Abstract

REINFORCED CONCRETE STRUCTURES (RCE) CAN BE CONSIDERABLY AFFECTED WHEN EXPOSED TO HIGH TEMPERATURES, ESPECIALLY IN CASES OF FIRE. THE MAIN PROBLEMS THAT OCCUR WHEN RCE ARE EXPOSED TO HIGH TEMPERATURES INCLUDE DEGRADATION OF ITS CONSTITUENTS (CONCRETE AND STEEL) MECHANICAL PROPERTIES, DAMAGE INDUCED BY EXCESSIVE THERMAL DEFORMATION AND SPALLING. THE PRESENT STUDY INVESTIGATES THE STABILITY CONDITIONS OF REINFORCED CONCRETE PANELS SUBJECTED TO FIRE LOADING. THE STABILITY ANALYSIS OF THESE STRUCTURAL ELEMENTS, USUALLY USED IN INDUSTRIAL AND STORAGE BUILDINGS, IS ADDRESSED WITHIN THE FRAMEWORK OF LIMIT ANALYSIS THEORY (LAT). THE METHOD RELIES IN A FIRST STEP UPON THE PRELIMINARY DETERMINATION OF THE TEMPERATURE DEPENDENT INTERACTION DIAGRAMS OF THE STRUCTURAL ELEMENT THAT IS VIEWED AS A BEAM ELEMENT. INTERACTION DIAGRAMS DERIVED FROM THE STATIC APPROACH OF LAT ARE SHOWN TO DEPEND ON THE GEOMETRY OF PANEL CROSS-SECTION AS WELL AS ON THE CONSTITUENTS (STEEL AND CONCRETE) STRENGTH PROPERTIES, WHICH DEGRADE CONTINUOUSLY WITH THE TEMPERATURE INCREASE AS FIRE PROCEEDS. THE SECOND STEP OF THE METHOD CONSISTS IN DETERMINING THE DEFORMED CONFIGURATION OF PANEL AND ASSOCIATED DISTRIBUTION OF AXIAL AND BENDING MOMENT EFFORTS. THIS IS ACHIEVED BY ANALYZING THE THERMO-ELASTIC EQUILIBRIUM OF THE PANEL UNDER THE COMBINED ACTION OF THERMAL GRADIENT INDUCED BY FIRE AND SELF-WEIGHT LOADING. IN THAT RESPECT, APPROXIMATE ANALYTICAL SOLUTIONS ARE DERIVED FOR BOTH DEFORMED CONFIGURATION AND EFFORTS DISTRIBUTIONS ALONG THE PAINED. THE STABILITY ANALYSIS AND DESIGN OF THE PANEL IN ITS DEFORMED GEOMETRY IS THEN CARRIED OUT BY COMPARING THE DISTRIBUTION OF INTERNAL EFFORTS TO ITS REDUCED STRENGTH CAPACITIES EXPRESSED BY MEANS OF THE ASSOCIATED INTERACTION DIAGRAMS EVALUATED IN THE FIRST STEP. SEVERAL NUMERICAL EXAMPLES ARE PRESENTED TO ASSESS THE EFFECT OF RELEVANT PARAMETERS ON THE OVERALL FIRE SAFETY OF THE STRUCTURE, EMPHASIZING THE EFFECTIVENESS OF THE APPROACH FOR DESIGN PURPOSES.