CREEP EFFECTS AND STRESS ADJUSTMENTS IN CABLE-STAYED BRIDGES WITH CONCRETE DECK

In construction stages of cable-stayed bridges with prestressed concrete deck, theinfluence of creep on stresses and strains is very important in order to foresee thefinal patterns of internal forces and displacements.In cantilever construction, the concrete deck can be considered, in each stage, as acontinuous beam resting on elastic restraints, which modify with successive additionsof new segments, until the last one has been assembled. In these stages stressrelaxation in concrete occurs as well as vertical displacements increase. Ehenstructure has been closed by inserting midspan segment, stress redistribution begins,due to creep. Deformation and internal force development in construction and servicelife modify stay stresses such as deck and pylon final profiles.It is necessary to prevent undesirable deformed shape of deck and pylon and tocontrol the final stress pattern of deck and stays. The requested final geometry of thebridge is reached by adjusting stay axial forces during construction.A study is presented in which, by taking into account creep effects, the optimization interms of deck and pylon deformed shape can be achieved through a sequence of stayforce adjustments during construction stages. The presented analysis is based on thetheory of aging linear viscoelasticity in order to give a useful tool for the conceptualdesign of cable-stayed bridges with concrete deck.The proposed procedure allows engineers to design by reducing and avoiding creepeffects instead of calculating them with refined models since the first design step.