STIFFNESS DAMAGE ASSEMENT OF PRESTRESSED CONCRETE BOX-GIRDER AFTER CRACKING

Cracks normally appear at supports, 1/4 span and mid span of box girders. Box girder cracking was coupled with excessive deflection of box girders,and its mechanism was complex.The difficulty to assess excessive deflection of box girder was it's stiffness distribution characteristics after cracking. In order to evaluate the box girder cracking stiffness, a large scale model of a continuous prestressed concrete box girder is made, destructive tests under repeated loading are carried out on the model. Two methods are used to research stiffness distribution characteristics of the cracking box girder. In the first method, combined with experimental data, stiffness distribution inversion of deflection at different crack degree is computed based on the Levenberg-Marquardt optimization algorithm. In the second method, the stiffness reduction evaluation parameter is directly set based on the load-deflection curve from the model test. Statistical analysis on stiffness damage distribution of box girder after cracking is done. Effectiveness of evaluation results is verified through comparing and analyzing stiffness longitudinal distribution characteristics of box girder after cracking obtained by the two methods. The results show that: the loading position is a reference point of stiffness reduction factor in box girder cracking zone. Stiffness damages on other positions are linear distribution along longitudinal direction of the box girder. The cracking box girders' stiffness damage calculation method is proposed. This study can provide theoretical reference for service performance evaluation of prestressed concrete box girders.