One of the main problems in assessing the structural response of RC elements during fire is the non-linear temperature profiles through the depth of exposed elements, leading to a non-linear distribution of strains which violates the principle 'plane cross-sections remain plane'. To fulfil the planeity of cross-sections under fire conditions, self-generating self equilibrating stresses are developed, arising from the
self-restraint of the cross-sections. As a consequence, and disregarding the side-effects of possible internal microcracking, an 'effective' temperature profile should be determined, resulting in a reduced effective imposed curvature and a reduced axial deformation of the element.
T.P. Tassios and M.P. Chronopoulos