Spilling out of condensed liquid water from needle-like holes in high-strength concrete was experimentally observed under fire attack. The presence of these holes was found to prevent explosive spalling effectively in the vicinity of the holes during fire exposure tests. This spilling out occurred at about 10 to 30 minutes after the start of high temperature heating. These needle-like holes are defined herein as local weaknesses that may act as rapid paths of water permeation to reduce the risk of explosive spalling of cover concrete. The phase change of moisture from CSH solids to condensed liquid as well as free water in micro-pores was simulated by a multi-phase chemo-physics analysis of ultra-high-strength concrete. The prediction of the high-rate phenomena was experimentally proved by using embedded moisture sensor, and the high-rate discharge of condensed water though local weaknesses was analytically simulated.

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This study shows fire resistance of slender RC columns in a plane frame. Thermal stress analyses were conducted for several frames with combination of horizontal displacement from thermal expansion of beams, decentering axial load, initial deformation, one side heating, and buckling length as parameters. The results indicate that the main factor which decreases fire resistance of slender RC columns is buckling length. When slender RC columns in a frame are designed, it is important that the buckling length is adequately evaluated as to influence of a frame.