Second-order analysis of prestressed concrete columns

The use of prestressed concrete columns has been quite rare in Finland, mainly for reason of a lack of national design regulations and guidelines. To promote their use, the Confederation of Finnish Construction Industries initiated a research project on precast prestressed concrete columns, in connection with an extensive research programme at Tampere University examining slender concrete structures. A displacement-based calculation model developed earlier in the programme for reinforced concrete columns and piles was developed further for evaluating the buckling of slender prestressed columns. The researchers applied this model to compare structural behaviour between prestressed and reinforced columns of the same dimensions and concrete strength and to evaluate the structure’s suitability for test specimens for a later, experimental stage of research. The prestressed cross section cracked only after quite considerable bending. With simultaneous compressive force to the top of the column, there was even less cracking. The mathematical calculations took into account the normal force dependent bending stiffness. The results reveal a significant reduction in the amount of steel material necessary when prestressing is applied.