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.
In this paper, a parametric study based on the load transfer test specified in ETAG 013 was performed with the aim of investigating the efficiency of the confining reinforcement in the local anchorage zone of post-tensioning tendons, in particular when there are two types of confining reinforcement, spiral and stirrups. The parametric study was conducted using the finite element software ATENA 3D and included 45 specimens of ordinary concrete reinforced with a combination of spirals and stirrups. The models were calibrated using the experimental results obtained in tests of similar specimens. The influence of concrete strength, cross-section dimensions, reinforcement ratio and type of anchorage device were investigated. The reinforcement strains were monitored to assess the relation between the strains of the inner and outer levels of reinforcement and the uniformity of the confinement forces along the confined length. A comparison between the bearing strength obtained by the numerical simulation and that obtained by models found in the literature is also presented. From the analysis of the strain values, it can be concluded that the spiral reinforcement is more effective. However, the results show that stirrups make an important contribution to the control of concrete cracking.
The design of anchorage corner blisters for internal continuity posttensioning tendons in bridges built using the cantilever method presents some peculiarities because they are intermediate eccentric anchorages. The simplified formulas for designing the reinforcement required to resist transverse tensile forces due to the application of point loads, as proposed by the current standards, are not sufficient because they do not cover all the effects that require reinforcement. The high density of steel reinforcement in anchorage blisters is the most common reason for problems with concrete cast in situ, resulting in zones with low concrete compactness, which may lead to concrete crushing failures under the anchor plates. The solution to this problem may involve reducing the amount of reinforcement by improving the concrete compressive and tensile strengths. An experimental program was carried out to study the transmission of prestressing force to the slab and web of the box girder, to assess the strut‐and‐tie models used in design and to investigate the feasibility of using a high‐performance fiber‐reinforced self‐compacting mix (HPFRC) in the blister only, with either in situ or precast solutions. It can be concluded that the use of HPFRC in anchorage blisters is a very interesting solution regarding the savings in materials and the reduction in the steel reinforcement density near the local anchorage zone, with obvious advantages in concrete quality.
Test setups and loading histories aim to replicate the real conditions of the building structures. However, most of the tests on beams found in literature do not include gravity loads in the cyclic loading history. An experimental campaign was carried out. Two beam specimens, named CB0 and CB1, designed to exhibit different failure modes were subjected to a loading protocol that involved the imposition of reversed cyclic loading and simultaneous gravity load. The aim was to validate the test procedure for different beam failure modes. Consequently, specimen CB1 failed by rupture of the tensile reinforcing bars while specimen CB0 failed due to concrete crushing and buckling of the compressed reinforcing bars. Results show that the presented loading protocol does not control the failure mode of the specimens. The specimens were also simulated numerically, and the results were comparable with the experimental observations in terms of load capacities, crack patterns, and failure modes.
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