FINITE ELEMENT ANALYSIS OF POST-TENSIONED CONCRETE BOX GIRDERS

الملخص

The behavior of prestressed concrete box-girder bridges has been studied under short term loading.
The 20-noded isoparametric three-dimensional brick elements have been used to model the concrete
in the box-girder with its two cantilever flanges. The reinforcing bars are idealized as axial
members embedded within the brick elements. The behavior of concrete in compression was
simulated by an elastic-plastic work hardening model followed by a perfectly plastic response,
which is terminated at the onset of crushing. In tension, a smeared crack model with fixed
orthogonal cracks is used with the inclusion of models for the retained post-cracking stress and
reduced shear modulus. The prestressing forces in the tendons are transformed into equivalent nodal
forces and by Lin's method. The contribution of the prestressing tendon stiffness to the global
stiffness matrix is considered by treating the tendon as axial member embedded within the brick
element. Two types of short-term prestress losses are considered in this study. The bond-slip
phenomenon at concrete-tendon is considered by reducing the tendon axial stiffness. Several
examples of prestressed concrete box girders are analyzed and compared with available
experimental and theoretical studies in order to demonstrate the validity and efficiency of the
proposed method. Good agreements between the results are obtained.