Efficiency of the confinement reinforcement in anchorage zones of posttensioning tendons

Abstract

In order to study the efficiency of the confinement reinforcement in anchorage zones of posttensioning tendons, using both ordinary reinforced concrete (ORC) and high‐performance fiber reinforced concrete (HPFRC), an experimental research has been performed on the bearing strength of concrete prismatic specimens. This research also intended to assess both ultimate capacity and adequate serviceability of the local anchorage zone when reducing the concrete cross section and the confining reinforcement, both specified by the anchorage device supplier, by using an HPFRC. The experimental program included ORC prismatic specimens with 305 mm × 305 mm × 650 mm reinforced with spirals and a combination of spirals and stirrups, and HPFRC specimens with 210 mm × 210 mm × 420 mm reinforced with stirrups. The reinforcement steel strains were measured to monitor the steel yielding, to assess the relation between the strains of the inner (spiral) and outer (stirrups) levels of reinforcement and the uniformity of the confinement forces along the confined length. A comparison between the bearing strength obtained by experimental tests and by models found in the literature is also presented. From the strain measurements, it can be concluded that in the case where there are, simultaneously, two types of confinement reinforcement, the outer reinforcement is not as effective as the inner one. Therefore, when computing the bearing strength, the linear superposition of contributions of both spiral and stirrups for confinement can be nonconservative, leading to too high estimated load capacity.

Performance Assessment of the Post-Tensioned Anchorage Zone Using High-Strength Concrete Considering Confinement Effect

“…Compared to other studies, the reinforcing level of this study was lower [ 11 , 12 , 14 , 16 , 19 , 20 ]. In particular, Marchão et al [ 16 ] installed lateral reinforcements with 60 mm spacing, and the size of specimens was similar to this study. Yang et al [ 19 ] installed lateral reinforcements with 65 mm spacing and specimen sizes almost 2 times more greater than this study.…”

“…It brings 1.5 to 2 times of increasing of compressive force resistance [ 15 ]. Although secondary confining by lateral reinforcements is relatively small than the spiral reinforcement, it increases the jacking forces’ load resistance [ 16 ]. The mechanism of confining is indicated in Figure 6 .…”

“…The mechanism of confining is indicated in Figure 6 . The confinement effect is hard to calculate, but it can be confirmed by checking the strain of lateral reinforcements in the loading condition [ 16 ].…”

“…With the confinement effect, the load-bearing tolerance increases and this effect can be found easily. Marchão et al [ 16 ] clearly showed the confinement effect in load transfer tests of the ETAG method. Marchão et al [ 16 ] compared the performance of NC and high-performance fiber-reinforced concrete (HPFRC).…”

“…Marchão et al [ 16 ] clearly showed the confinement effect in load transfer tests of the ETAG method. Marchão et al [ 16 ] compared the performance of NC and high-performance fiber-reinforced concrete (HPFRC). From the results, HPFRC showed a much larger load-bearing tolerance than NC.…”