Evaluating the state of a section under bending using the location of neutral axis

Neutral axis of a composite section under loading is a line in the cross-section along which the section experiences zero strain. When a structure is under no axial load, the location of the neutral axis passes through the centroid of stiffness of the cross-section, which can be calculated based on geometric and stiffness properties of the cross-section. When the structure experiences damage, the location of the centroid of stiffness as well as the neutral axis shift in position, a phenomenon that can be used as an indication of damage. According to literature, damage in a cross-section of the concrete deck of a composite concrete-steel structure causes the neutral axis to move down. This paper attempts to explain an observation from field data that the neutral axis could move up in the presence of damage in the concrete deck of a composite structure. Preliminary results show that the use finite element model has potential to produce results that help explain the observation.