Center for Sustainable Engineering of Geological and Infrastructure Materials

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Model B4 for concrete creep, drying shrinkage and autogenous shrinkage

A new model for concrete creep, labeled B4, has been developed, which can overcome some of the shortcomings of the CEB-fib, ACI, JSCE and GL prediction models for concrete creep and shrinkage. The B4 model represents an extension and systematic recalibration of the theoretically founded model B3, a 1995 RILEM recommendation. In addition to introducing the so far missing separation of autogenous and drying shrinkage, model B4 takes into account the cement type and admixture parameters, as well as the effects of various types of aggregate. The new predictors for the creep compliance function more accurately, capture the composition information, and are recalibrated to match the multi-decade behavior. This behavior has recently been documented by observed deflection records of many bridges, which is evidence that has so far been systematically underestimated. The improved model was calibrated through a joint optimization of a new, significantly enlarged database of laboratory creep and shrinkage tests and a new database of bridge deflection records.

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The Koror-Babeldaob Bridge was completed in 1977, to connect the two main islands of the Palau archipelago. Its main span of 241 meters (790 ft) was the longest span post-tensioned concrete box girder bridge structure in the world at the time. Its two lane single cell box girder superstructure was built using cast-in-place segments and a permanent mid-span hinge. The bridge collapsed in September 1996, shortly after completion of construction contracts to replace its pavement and correct the increasing deflections of its main span.


References:

R. Wendner, M. H. Hubler, and Z. P. Bažant (2013) The B4 Model for Multi-decade Creep and Shrinkage Prediction. Mechanics and Physics of Creep, Shrinkage, and Durability of Concrete: pp. 429-436.