Title: Effect of deck cracking on prestress
Date Published: May - June 2019
Volume: 64
Issue: 3
Page Numbers: 66 -75
Authors: Soumya Vadlamani, Richard A. Miller, and Gian A. Rassati
https://doi.org/10.15554/pcij64.3-04
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Abstract
The American Association of State Highway and
Transportation Officials' AASHTO LRFD Bridge
Design Specifications have a refined method for the
calculation of time-dependent losses in prestressing
force. This method estimates a gain in the prestressing
force due to differential shrinkage between the precast
concrete girder and the cast-in-place deck; however,
it does not consider the possibility of cracking in the
deck. Some state departments of transportation believe
that after the deck cracks, the gain in the prestressing
force is lost, and they do not include it in the prestress loss calculations. Some other state departments
of transportation believe that not all of the prestress
gain is lost and allow some percentage of the gain to
be retained. This study focuses on the effect of deck
cracking on the long-term loss of prestressing force.
A finite element software model was used to simulate three different girder lengths with varying deck
concrete strengths, differential shrinkage parameters,
and girder ages at the time the deck was placed. When
the girder age at the time of deck placement is more
than 60 days, there is a high probability that the deck
will crack, though a deck placed on a girder of any age
may crack, depending on the properties of the deck and
girder. When the deck cracks, some of the gain of prestressing force is lost, but the percentage lost depends
on the extent of cracking in the deck. The older the
girder is when the deck is placed, the greater the cracking. The cracked deck still provides some restraint, and
even in cracked decks, nearly 50% of the prestress gain
due to differential shrinkage was retained.