Transfer length of high performance pretensioned concrete elements

摘要

The scope of this research was to study the feasibility of producing high strength lightweight concrete pretensioned beams, with the same design criteria as normalweight high strength concrete, with 15.2 mm diameter strand. This paper reports an experimental program conducted to measure bond properties of two lightweight concrete dosages compared to those of a reference normal weight high strength concrete, used in a prestressing plant to produce great pretensioned beams. As a part of the research, eight specimens (prisms) were pretensioned with a 15.2 mm diameter strand centered in the cross section, without confinement reinforcement. Experimental results show that none of the prisms cracked right after transfer, which seems to guarantee that adopted strand cover, 45 mm, is enough for lightweight concrete prisms. However, some time after transfer deferred longitudinal cracking was observed in all the lightweight concrete prisms, and a considerable increase of transfer length was detected. Also a new objective method has been developed to determine transfer length from longitudinal concrete strains at strand depth.