New design method for PSC girder with incremental prestress

Abstract

Prestress forces in traditional PSC (prestressed concrete) girders are applied at the beginning stage of construction in order to limit extreme concrete fiber stresses within the code-specified allowable stresses under service loads. As a girder span increases, the additional increases of extreme concrete fiber stresses need to be reduced by the increase of sectional dimensions in order to limit extreme stresses. This prohibited traditional PSC girders from being economical long span bridges and it is current practice to construct them for the bridges with maximum span of 30m. In order to overcome the limitations on their spans of traditional PSC girder, a new prestressing technique is presented in this study. Its theoretical development basically follows the traditional prestressing principles but unlike traditional methods, prestressing forces are applied separately at different loading stages. It can be theoretically shown that the suggested new prestressing technique can realize the economical long span PSC girders with much shallower girder depth, and thus with much less self-weight, compared with traditional ones. The developed girders are also found to be competitive to other types of long span bridges in their structural performances and construction costs.