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Turbine Deck Load Capacity Restored

1998 ICRI Award of Excellence
Industrial Category

In 1957 the use of pre-stressed or post-tensioned concrete systems was relatively new to Southern California, and the turbine deck at Ocean Vista Power Generation Station was one of the first post-tensioned decks to be built there. This deck was originally designed and built by the Bechtel Corporation for Southern California Edison and consists of an 11" (275 mm) thick post-tensioned concrete deck supported by structural steel framing. The overall dimensions of the deck are approximately 127' x 280' (39 m x 85 m).


The pre-stressing system used 7-wire, button-headed tendons spaced at approximately 3 feet (1 m) on center parallel to the span, and 6 feet (2 m) on center perpendicular to the span. The prestressing cables appear to be located " (13 mm) below the center of the slab, with no drape. Traditional deformed reinforcing steel was omitted from the design.


In 1983, excessive cracking and localized delaminations and spalling of the deck became a concern. Because much of the original construction documentation was missing, determining the most probable root causes for the deterioration had to be based on recent data, i.e. post 1983. Three areas that were just beginning to affect the design of reinforced and pre-stressed concrete at the time were:

arrow_blue The determination of losses in the pre-stressing force which could expect to occur
arrow_blue The causes and effects of corrosion of pre-stressed systems
arrow_blue The effects of certain types of aggregate used in concrete, which have since been proven to be reactive

Although the effects of creep and shrinkage were theoretically assumed during this early era of post-tensioned construction, historical performance to verify these assumptions was limited.


Evidence of the concern over pre-stressing loss can be found in an earlier letter written by one of the engineers involved in the original construction, in which it was suggested that the deck be monitored annually to check the loss of pre-stressing as compared to the anticipated design loss. This was due, in part, to what he considered early loading of the concrete. The original design assumption for loss in the pre-stressing force was 15%. The actual force, however, is unknown.


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Ste. B
Anaheim, CA 92806
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