Analytical Modelling of the Transmission Length in Prestressed-Concrete Members

Adequate transmission of prestressing forces into the concrete in prestressed-concrete (PC) members requires a careful detailing, especially in the end regions. Most of the existing design Codes introduce only few parameters concerning strand diameter and prestressing force value, to evaluate the transmission length. Experimental evidence demonstrates that further variables have a remarkable influence on the transmission length, such as concrete strength and cover. In this work, the bond mechanism controlling the transmission of the prestressing force from the pretensioned steel to the concrete is modelled using an analytical approach based on the theory of thick-walled cylinders (TWC), adopting for the concrete an anisotropic behavior. The model has been calibrated on the basis of an extended number of experimental tests on beam specimens available in the literature. Such dataset spans over a variety of influencing parameters related to geometry, materials and prestressing-force release method. After the calibration of the model, a parametric study has been carried out to investigate the roles of such parameters as concrete compressive strength, concrete cover, steel-strand diameter and spacing.