DESIGN OF LONG INTEGRAL ROAD BRIDGES
ABSTRACT: In traditional bridges, expansion joints and supports are installed to facilitate relative displacements and prevent the occurrence of stresses induced by thermal variations. However, such devices can cause maintenance problems. On the other hand, integral bridges are structures without joints and supports where abutments, piers and deck are connected monolithically producing a complex structural and geotechnical interaction. Integral construction thus eliminates maintenance works related to the presence of connection devices. However many countries have imposed restrictive limits on the length of these structures, and this paper aims to identify the maximum length of integral bridges, in relation to the particular boundary conditions considered in the case study. The authors present a study on soil-structure interaction concerning both backfill and foundation soil, and carry out the design of some structural elements of a reinforced and prestressed concrete integral bridge, paying attention to guarantee the necessary flexibility to the structure.
KEYWORDS: integral bridge; soil-structure interaction; maintenance; thermal variation; expansion joint; support; reinforced concrete; prestressed concrete
Design of road bridges with external prestressing: 3 case studies
ABSTRACT: This paper deals with the structural design and modelling of two segmental prefabricated box-girder bridges with external prestressing only and castellated dry joints with shear keys. The construction method is by balanced cantilever. The first bridge is composed of four spans with maximum length equal to 90.4 m and longitudinal variable depth. Upper slab with constant thickness and lower slab and webs with variable thickness characterize it. The second bridge is composed by four span with maximum length equal to 47.7 m and longitudinal constant depth. Upper slab, lower slab and webs have constant thickness. The bridges are also modelled in fibre reinforced concrete. The design of prestressing system and structural elements is carried out. The authors study, with particular attention, the distorsional warping of the section due to eccentric loads and the interaction between shear, torsion and local bending moment in the design of the webs. The design of the shear keys is carried out by comparing the European and AASHTO Codes. The last section of this paper deals with the structural design of a bridge with external prestressing only. It is characterized by 45 m long spans, continuous girders, and deck made up of four post-tensioned girders with double-T section; a simple and economical solution for medium span bridges.
KEYWORDS: Segmental bridge, external prestressing, prestressed concrete, distorsional warping, torsion, shear, local bending moment, reinforced concrete, shear keys, fibre reinforced concrete, double-T secion, post-tensioning