Optimization of anchorage corner blisters for posttensioning tendons

Abstract

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.

Efficiency of the confinement reinforcement in anchorage zones of posttensioning tendons

“…The experimental campaign also included other five high performance concrete (HPC) specimens without reinforcement bars (P3, P4, and P5) that are out of the scope of the present paper.…”

“…So, the width of the specimen was defined considering the width of the anchorage bearing plate to which was added the concrete cover on each side. It was adopted a small amount of confinement stirrups to control cracking since the fibers of the HPFRC showed a preferential orientation …”

“…In Table , the concrete mean compressive strength ( f ccm ) is referred to 150‐mm‐width cubes and was determined by uniaxial compression tests of three specimens, according to EN 12390–3…”

“…The mean compressive strength for 150‐mm diameter and 300‐mm‐high cylinder specimens ( f cm ) was obtained using the usual relation proposed by EN 1992‐1‐1 for the ORC specimens. For the HPFRC specimens, the mean compressive strength for cylinder specimens was obtained by uniaxial compression tests of three cylinders, for specimens P6A and P6B or using the ratio f cm / f ccm obtained in a previous work for this type of concrete for specimen P6.…”

“…An experimental program to study the effectiveness of the confinement reinforcement in anchorage zones of posttensioning tendons, using both ordinary reinforced concrete (ORC) and high‐performance fiber reinforced concrete (HPFRC), and to assess both the ultimate capacity and the adequate serviceability of the local anchorage zone was carried out . The load transfer test specified in the Guideline ETAG 013 was performed.…”