Strengthening prestressed beams using parafil ropes as external tendons

Abstract

Many bridges in the world are classified as deficient and in need of rehabilitation or replacement. Some of them are deficient because their load-carrying capacity is inadequate for today's increased traffic load. To improve their efficiency and increase their load capacity, several methods can be used, one of them is the external prestressing. Also, to avoid corrosion problem that faced this type of strengthening, Fibre Reinforced Plastics (FRP) can be used instead of steel tendons. Within the different types of FRP, Parafil rope was established to be well suited for prestressing system, combining the benefits of light-weight, high strength, easy handling and efficient anchorage system. Thirteen prestressed beams,one with internal prestressing steel only, and the rest strengthened externally using Parafil Ropes Type G were tested up to failure under two third point loading. Six factors were studied to investigate their effect on the behaviour of strengthened beams. These factors are the value of the external prestressing force and its eccentricity, deviator position, previous loading stage before strengthening, concrete strength and (span/depth) ratio. Also, analytical investigations were conducted to propose simple equations could be used in the analysis of this beam type, regarding its deflection and flexural strength with an acceptable accuracy. The study indicated that, external prestressing using Parafil rope is a very powerful system for strengthening or rehabilitation of prestressed concrete structures. Also, providing external prestressing force by a moderate amount improves the stiffness, and both cracking and ultimate flexural strength of prestressed concrete beams without significant reduction in ductility even for cracked beams. The modifications made to the methods used to calculate deflection and ultimate moment of bonded prestressed concrete, generalised these methods so, they can be used with beams have different types of prestressing tendons (bonded, internal unbonded, external unbonded or mixture of them). These methods, after modification, were found to give fairly accurate results. Also, the novel equation described the relation between the increase in the external prestressing force and the deflection makes the analysis of the externally strengthened beams under service loads,less complicated with a reasonable accuracy