Optimization of anchorage corner blisters for posttensioning tendons

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.