Portal de Periódicos da CAPES

Prestress Losses in Continuous Composite Bridges

1986; Precast/Prestressed Concrete Institute; Volume: 31; Issue: 1 Linguagem: Inglês

10.15554/pcij.01011986.84.105

0887-9672

Mohamed H. Soliman, John B. Kennedy,

Concrete Corrosion and Durability

D uring the last 30 years composite construction of concrete slab-on-steel girders has been widely used to form the superstructure of bridges. Generally, such construction has been applied only to simple spans or to the sagging moment regions of continuous spans since transverse cracks will inevitably develop in the region of intermediate supports. Such transverse cracking, caused by the presence of large negative (hogging) moments, reduces significantly the stiffness of the bridge and leads to costly maintenance. Moreover, even in the case of simple span bridges, extensive damage to the expansion joints can occur due to seepage of deicing salt-laden water. Fig. 1 shows an example of such damage in one of the many expansion joints on the Gardiner Expressway in Toronto, Canada. Several researchers 1-3 have proposed to prestress part of the concrete deck in the vicinity of the intermediate supports of continuous bridges as shown in Fig. 2(a). A recent study2 has shown that such prestressing increases substantially the cracking load in addition to the stiffness of such bridges. For proper design it is essential to estimate accurately the anticipated losses in the prestressing force due to creep, shrinkage and steel relaxation.'`' The objective of this paper is to propose a simple method together with design aids by which these longterm losses can be reliably estimated. The results from this simple method are compared to those from an elaborate method of solution requiring the use of a computer. In this paper it is assumed that prestressing of the concrete deck is carried out on the composite sections (with the connection between the concrete and steel beams realized prior to prestressing). Previous experience' has shown that the alternative scheme of prestressing a free-to-slide con-