The resaerch objective of this project is to use actual data on excessive creep deflections to find a realistic multi-decade concrete creep law. The fatal collapse of KB Bridge in Palau, a segmental box-girder bridge of world record span, called attention to the preceding creep deflections, which attained 1.61m, nearly 5-times the design deflection. Forced unsealing of the technical data on this bridge allowed Northwestern University researchers to conclude that the standard design recommendations were obsolete. This motivated a broad search which has so far led to a collection of 64 large-span bridges deflecting excessively within 20 to 40 years, while supposed to serve >100 years. The main cause of this obsoleteness is that most laboratory creep data have durations <6 years. The bridge deflection data are combined in one aggregate database, and an inverse three-dimensional finite-element creep analysis of box-girder deflections is combined with the lab database to calibrate an improved material law for creep of concrete. Sophisticated statistical concepts and a genetic algorithm are used to predict the parameters of material creep law from the concrete composition characteristics and strength. The results will be proposed for standard design recommendations of engineering societies.

Although the societal costs of retrofits or closings of numerous excessive deflecting bridges are enormous, their data represent a gold mine for progress. The research will clarify how to avoid repetitions, which causes serviceability losses and cracking with corrosion. An improved creep model will also be important for design against differential shortening of columns in modern super-tall buildings.

Project Start
Project End
Budget Start
2011-09-01
Budget End
2014-08-31
Support Year
Fiscal Year
2011
Total Cost
$347,061
Indirect Cost
Name
Northwestern University at Chicago
Department
Type
DUNS #
City
Evanston
State
IL
Country
United States
Zip Code
60201