BEHAVIOR OF RC WALL COLUMNS SUBJECTED TO ONE SIDE HEATING AND ECCENTRIC AXIAL LOAD IN FIRE: Study on fire resistance of slender RC columns Part 3

Reinforced concrete columns formed with high-strength concrete have been developed with a smaller cross section than conventional “short” columns as axial load carrying members. Known as “slender” columns, they can enlarge building space and provide good visibility in architectural space. RC wall columns whose shape of cross-section are flat and the smallest diameter are small on an equality with slender RC columns are used as earthquake resisting elements for enhancing horizontal stiffness of structural frame. They have been also developed as quake-absorbing system and vibration control system known as damage-controlled system. These RC wall columns belong in the “slender RC columns” defined by authors in case the ratio of column height to cross sectional smallest diameter is large. RC wall columns are possibly heated with one side when RC walls are used as outer wall. In these one side heating situations, RC wall columns are displaced toward a horizontal direction due to non-uniform thermal degradation of the cross-section. And furthermore, axial load generates additional moment. Bending stiffness decreases considerably due to thermal degradation of the heated surface in fire. It is anticipated that RC wall columns subjected to one side heating would fail earlier than ones subjected to all circumferences heating because of this additional moment. Moreover, it is similarly anticipated that additional moment generated by an eccentric joint of beams would lower the fire-resistance performance of RC wall columns. This paper presents the results from an experimental and analytical studies of RC wall columns subjected to one side heating and decentering axial load in fire and leads to a discussion of fire performance which includes deformation behavior, failure mode and fire resistance time. All specimens consist of concrete with a compressive strength of approximately 120N/mm2 and have rectangular cross-section with sides 250mm and 600mm in length and 4500mm in height. Comparing the experimental and analytical results, the analysis method using a fiber model based on the mechanical properties of the materials in high temperature offers a good approximation of deformation behavior, failure mode and fire resistance time. In addition, the results confirm that the centrally loaded specimens subjected to one side heating fail earlier than ones subjected to all circumferences heating under conditions that axial load ratio is about 0.3 or over.