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 curvature