19 research outputs found
IL METODO DEGLI SCHEMI ELASTICI PARZIALI NELLA COSTRUZIONE A SBALZO DEI PONTI AD ARCO
In questo lavoro viene presentato uno studio sulle sequenze di tesatura degli
stralli nei ponti ad arco costruiti per sbalzi successivi con l’ausilio di tiranti provvisori. In
particolare viene presentato il metodo degli schemi elastici parziali, proposto per la
determinazione degli sforzi iniziali nei cavi. Tale metodologia è stata dapprima applicata sui
ponti strallati e viene estesa in questo studio al caso dei ponti ad arco costruiti per sbalzi
successivi. La trattazione teorica è seguita da un’applicazione numerica su un caso studio di
un ponte ad arco in calcestruzzo
CREEP EFFECTS AND STRESS ADJUSTMENTS IN CABLE-STAYED BRIDGES WITH CONCRETE DECK
In construction stages of cable-stayed bridges with prestressed concrete deck, the
influence of creep on stresses and strains is very important in order to foresee the
final patterns of internal forces and displacements.
In cantilever construction, the concrete deck can be considered, in each stage, as a
continuous beam resting on elastic restraints, which modify with successive additions
of new segments, until the last one has been assembled. In these stages stress
relaxation in concrete occurs as well as vertical displacements increase. Ehen
structure has been closed by inserting midspan segment, stress redistribution begins,
due to creep. Deformation and internal force development in construction and service
life modify stay stresses such as deck and pylon final profiles.
It is necessary to prevent undesirable deformed shape of deck and pylon and to
control the final stress pattern of deck and stays. The requested final geometry of the
bridge is reached by adjusting stay axial forces during construction.
A study is presented in which, by taking into account creep effects, the optimization in
terms of deck and pylon deformed shape can be achieved through a sequence of stay
force adjustments during construction stages. The presented analysis is based on the
theory of aging linear viscoelasticity in order to give a useful tool for the conceptual
design of cable-stayed bridges with concrete deck.
The proposed procedure allows engineers to design by reducing and avoiding creep
effects instead of calculating them with refined models since the first design step
Hamiltonian structural analysis of curved beams with or without generalized two-parameter foundation
A parametric study of curved incrementally launched bridges
The structural behaviour of incrementally launched bridges in the construction stages depends on different parameters involving deck, nose, supports and guide devices, because static schemes vary continuously with the advance of the deck above the piers. For this reason temporary stresses in the deck, during launching, are rather different from those occurring in service life. Horizontally curved launched bridges also present the effects of torsion induced by geometric curvature. A parametric study is presented in order to analyse the influence of design parameters on the construction of these bridges. Analyses were carried out by extending to curved beams a procedure based on the Transfer Matrix Method, already known for straight continuous decks. Effects of curvature, nose–deck ratios of length and load, bending and torsional stiffness ratio were taken into account. The results show that maximum torsion values increase with the decrease in the curvature radius R and with the decrease in the ratio between bending and torsional stiffness. Moreover, with variation in the nose length ratio, the value ln/l = 0.60 with respect to the span length, is confirmed as the optimal value, as happens for straight bridges. With variation in the nose weight, a significant increase in bending moment and torsion can only be appreciated in the cantilever stages of launching. Dimensionless diagrams and related expressions are given for numerical evaluation of the maximum values of bending moment and torsion in the construction stages, with variation in the stiffness ratio and the radius of curvatur