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Of those numbers, the percentages of bridges constructed with HSC prestressed girders range from 0% to 100% among the DOTs. Nevertheless, the total number of bridges constructed per year using HSC prestressed girders is significant. HSC prestressed girders are widely used in current practice. with 85% of the responding DOTs indicating that they use f: values at service in the range of 6,000 to 8,000 psi. It was found that in some cases (in general when f’ci > 6,000 psi) mixture designs are governed by the specified concrete compressive strength at release. Thus. the specified release strength tends to be critical for HSC prestressed girder production.

Responses indicate that almost half of the DOTs have some concerns related to the use of HSC, including the following:


Maximum spin lengths are limited by transportation of the girders.


Design parameters in the AASHTO specifications do not specifically address HSC. As such, several DOTs are reluctant to specify concrete compressive strengths at service higher than 8,500 psi.


Initial cracking of girders may occur during casting and before the release stage.


There are difficulties in providing 0.6-in.-diameter strands at the proper spacing for some standard girder configurations.


In some areas suitable aggregates are not available; in some cases, there are no qualified precasters to produce HSC prestressed girders.


Research is needed to address critical issues, such as overestimation of losses and determination of creep, shrinkage, and camber for HSC.

The survey indicates that most of the DOTs have not made adjustments to the design specifications for HSC prestressed bridge girders. Seven DOTs have made in-house adjustments that include modifications to the allowable stresses and equations for modulus of elasticity, losses. creep, and camber.

It was found that the HSC prestressed girder types that are most popular among responding DOTs include the AASHTO beam, followed by the bulb beam and the box girder. Voided slabs, slabs, double T-beams, and closed box cast-in-place (CIP) beams are the structural types with less use, although the closed box CIP girder is used for long spans (typically up to 150 ft). Texas U-beams are used not only in Texas, but also in Colorado and New Mexico. Closed box CIP beams. AASHTO beams, bulb beams, and box beams are more prevalent for longer span lengths. For longer span girders, typical spans range from approximately 60 to 150 ft and the specified concrete strengths at service generally varies between 6,000 and 10.000 psi.

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