08-16-2017, 08:52 PM
fire damaged rcc structures
ABSTRACT:
The assessment of concrete structures affected by the fire should allow understanding what
happened during fire and developing rational criteria for the evaluation of the security of the structure. The
result of the assessment should be used to take the decision on further repair, partial or total demolition of the
structure. Two main goals to be answered during the assessment analysis are: 1) The determination of the depth
of concrete exposed to temperatures that produce irreversible alteration of concrete components, and 2) the
mechanical strength decay of concrete that can affect the load bearing capacity of the element or the structure
itself. The assessment of the integrity of a concrete structure in the post fire situation involves addressing the
damaged of each component. To differentiate between concrete chemically affected by the fire or physically
damaged is an important issue. In this paper the depth of concrete of a structure exposed 48 h in fire and a tall
building, >100 m (Windsor Tower) 18 h exposed to fire are used as examples of real fires. In-situ inspection
and laboratory tests of concrete components have been performed. The heterogeneity in the distribution of the
damage is identified and the depth of concrete affected by the fire is determined.
INTRODUCTION
This article summarizes an engineering evaluation of the extent of fire damage to a concrete structure under construction. The fire occurred in a portion of the reinforced concrete structure and visibly damaged a load bearing exterior foundation wall. The purpose of the assessment was to promptly evaluate the in situ condition of the wall and recommend necessary repair or replacement options prior to commencement of backfilling and the concrete construction to be supported by the subject wall. The engineering assessment of the damaged wall included a nondestructive evaluation phase consisting of ultrasonic pulse velocity testing and a laboratory testing phase on the concrete cores removed from the damaged wall. Dynamic Young s modulus of elasticity and an air permeability index of 25 mm (1 in.) thick disks sawed from the cores were determined. Analysis of properties of 25 mm (1 in.) concrete specimens permitted assessment of the presence and degree of any damage in smaller depth increments compared to the size of a compressive strength core. Significant differences were not indicated by compressive strength of cores, however, the in situ nondestructive testing and laboratory testing of the disks were effective in determining the depth of damage, as a result of the fire. The results of the nondestructive and laboratory evaluation indicated that the distressed zone of the concrete was limited to a near-surface layer. Repair recommendations were based on removal and replacement of the affected concrete sections identified by the testing program.