A BASIC STUDY ON ESTIMATION OF FIRE-DAMAGED DEPTH OF DEFORMATION SINGULARITY BY COMPRESSIVE STRESS-VOLUME STRAIN CURVE OF CORE SAMPLED FROM FIRE DAMAGE CONCRETE MEMBER

Abstract

 Fire damage determination of buildings in Japan is often carried out based on the "Recommendation for diagnosis and repair method of fire-damaged buildings" edited by the Architectural Institute of Japan. According to the guideline, when a reinforced concrete member is subjected to fire, the fire test is carried out by performing a compression test using concrete cores sampled from the fire damaged part and the non-damaged part respectively, then comparing the compressive strength results of the two. Although the fire damage grade of the concrete of the department has been decided, currently there are not many methods to estimate the damage depth.

 Concrete exposed to fire is cracked when the heated surface is exposed to high temperature. It is known that the cracks grow as the temperature rises from the shrinkage of cement paste and the expansion behavior of aggregate, and propagate inside concrete.

 Damage caused by cracking of concrete after heating and cooling is the most severe on the heated surface side, and the less on the inside. When a core taken from the heated surface of the concrete is subjected to a compressive strength test, it is considered that the breakage occurs from the heated surface side and does not reach the inner side of the core.

 However, due to the mechanism of the compression tester, the core under pressure is restrained at both ends by the end face friction of the pressure plate, and exhibits uniform failure over the entire core, including the damaged portion.

 In this basic study, focusing on the compressive strength test of the core sampled from the fire-damaged concrete, the compressive strength test is carried out with the end face friction between the pressure plate and the core end reduced, and we tested whether the damage depth could be estimated.

 As a result, the following conclusions were reached.

 ・ The fracture pattern of the compressive splitting type is obtained by reducing the friction between the pressure plate of the tester and the upper and lower ends of the core during the compressive strength test of the core, and it gradually deforms inwardly from the upper end of the core (heated surface side) It was confirmed that the singularity was reached.

 ・ In the compressive strength test with reduced friction between the pressure plate of the tester and the upper and lower ends of the core, the damage depth of the fire damage zone can be estimated from the deformation singular point and critical stress degree of each depth in the core axial direction .