The use of externally bonded CFRP sheets for shear strengthening of I-shaped prestressed concrete bridge girders.

摘要

The repair and rehabilitation of civil engineering structures is a rapidly expanding industry. Worldwide, structures that have deteriorated with exposure and tune are being subjected to increasing modern load levels. The demand for increasingly heavier truck loads is forcing bridge owners to upgrade existing structures.; The City of Winnipeg, Manitoba, Canada is considering upgrading the Maryland Bridge using CFRP sheets, since analysis conducted using current codes indicates that the shear strength of the bridge girders is not sufficient to withstand increased modern truck loads.; The use of externally bonded Fibre Reinforced Polymer (FRP) sheets provides an excellent solution for the repair and rehabilitation of civil engineering structures. Since the strength to weight ratio of FRP materials is extremely high in comparison with traditional materials, the installation of continuous light-weight FRP sheets or strips is remarkably simple in comparison with conventional strengthening techniques.; While the use of FRP sheets or strips for flexural strengthening of concrete structures has been studied extensively, the study of externally bonded FRP sheets for shear strengthening has been limited. Due to a lack of information on the use of CFRP sheets for shear strengthening of I-shaped prestressed concrete AASHTO girders, an experimental program has been undertaken at the University of Manitoba, to test scaled models of I-shaped concrete bridge girders strengthened with CFRP sheets.; Seven prestressed concrete beams were strengthened using three different types of CFRP sheets and ten different CFRP sheet configurations. The beams were tested to failure at each end to determine the most efficient strengthening scheme. The contribution of the CFRP sheets to the enhanced shear capacity of the girder is examined, with emphasis on the effect of this particular girder shape.; Design guidelines. and recommendations for the use of externally bonded CFRP sheets for shear strengthening of I-shaped prestressed concrete girders are developed, and are intended to contribute to the current state-of-the-art and the development of design codes.; A rational model is introduced, to predict the shear resistance provided by FRP sheets externally bonded to I-shaped concrete girders. For I-shaped sections, the concrete substrate is subjected to both peeling and shear stresses and failure is initiated by straightening of the CFRP sheets.; Depending upon the configuration of the FRP sheets and the corresponding mode of failure, the internal steel stirrups may not reach yield prior to the initiation of failure. The stirrup contribution to shear resistance is therefore based on the load sharing relationship between the FRP sheets and the steel stirrups, and the predicted mode of failure.; The versatility of the proposed rational model is demonstrated, by applying the model to the traditional ACI approach to shear design, the modified sectional-truss model, the compression field theory and the modified compression field theory. The shear capacity of each beam tested in this experimental program is predicted using the shear prediction models listed above in combination with the proposed rational model, and the predictions are compared with the test results. (Abstract shortened by UMI.)