Bond modelling of prestressed concrete during the prestressing force release

Abstract

This paper presents an analytical model for simulating the bond between steel and concrete, in precast prestressed concrete elements, during the prestressing force release. The model establishes a relationship between bond stress, steel and concrete stress and slip in such concrete structures. This relationship allows us to evaluate the bond stress in the transmission zone, where bond stress is not constant, along the whole prestressing force release process. The model is validated with the results of a series of tests and is extended to evaluate the transmission length. This capability has been checked by comparing the transmission length predicted by the model and one measured experimentally in a series of tests. Keywords:Bond, prestressed concrete, transmission length, modelling, bond strength IntroductionPrecast prestressed concrete elements are widely used for construction in Europe. A frequent problem of the precast industry is to evaluate the real transmission length in precast prestressed concrete structural elements. The semi-empirical formulae proposed by codes are usually thought for conventional concrete and usual cast conditions, but high performance concrete (high-strength, self-compacting, etc.) and non-usual cast conditions (v.gr. accelerated curing processes) are becoming more and more frequent. In these cases experimental measurement is needed, though the standardised methods are expensive and so difficult to apply by industry. Analytical and numerical models, based on parameters measured experimentally with tests being simpler than complete transmission length tests, would be welcomed. This paper presents an analytical model for steel-concrete bond when the prestressing force is transmitted by releasing the steel (wire or strand). The model is applied to evaluate the transmission length. Theoretical backgroundThe prestressing process of the precast prestressed concrete includes: a) steel wire prestressing, and b) prestressing force transmission after an accelerated curing process of concrete. Let be a prism of concrete with a single prestressed wire placed in the prism longitudinal axis (Fig. 1). Be P 0 the initial prestressing force in the wire and, for a given instant, the force at the end of the wire P 0 -∆P,

Experimental and numerical studies on the control of horizontal cracking at the ends of hollow-type pretensioned girders

“…1. Transfer length is generally defined as the bond length required to fully transfer the effective prestress from strands to the concrete [16][17][18][19]. There are various factors that can have influence in the transfer length, such as the type, number and diameter of prestressing tendons, effective prestress [20][21][22], concrete strength at the prestressing time [23][24][25], concrete cover [22,25], strand releasing method, surface condition and many more [20,26].…”

A two-stage modelling approach for the analysis of the stress distribution in anchorage zones of pre-tensioned, concrete elements

“…The resulting stress-strain relation is then used as an input for determining the bond-slip relation. This way of assessing the bond-behaviour and the confinement of the surrounding concrete was applied by Den Uijl [24], Fellinger [25], Oh et al [26] and Benitez et al [27].…”

Inference of bond slip in prestressed tendons in concrete bridge girders

“…Hence, the bond slip effectively affects the behavior and the capacity of PC structures. Thus, it has also been studied for some time by performing pullout tests , where load cells and extensometers have been used to measure the shear stress and slip, respectively. Abrishami and Mitchell (1993) performed several pullout tests introducing a simple test method to determine the bond stress versus slip response for pretensioned tendon embedded in concrete along both the transfer length and the flexure bond length for different tendon sizes (9.5, 13, and 16 mm (3/8, ½, 0.60 in)).…”