Retrofit of CFRP Installation to Meet Current Design Standards
Metropolitan Water District of Southern California (MWD) was one of the first agencies to adopt the use of Carbon Fiber Reinforced Polymer (CFRP) as a method to repair distressed Prestressed Concrete Cylinder Pipe (PCCP) starting in the middle of the 1990’s. At that time MWD performed tests to determine the best method to bond the CFRP to the inner core of the PCCP and tested distressed PCCP repaired with CFRP to validate its ability to resist external ground load. MWD studied the other tests conducted by the industry to insure the distressed PCCP reinforced with CFRP could resist the internal pressure . MWD was one of the first agencies to adapt the use of CFRP as a method to repair distressed PCCP. However, at the time the need for the CFRP to terminate on the steel cylinder was not recognized. Over the last ten years the need for the CFRP to be terminated by attaching it to the steel cylinder has become the industry standard . Another advancement in CFRP design methodology was the need for and the quantity of longitudinal CFRP reinforcement applied in these repairs. IMWD recently upgraded all of its CFRP installations to bring them up to the requirements of the new draft code which is currently in development through AWWA. This was accomplished by removing the CFRP lining in the region adjacent to the joints, exposing the bell and spigot, which was followed by attaching new CFRP to the cylinder and overlapping the new CFRP onto the existing CFRP. In addition, more longitudinal layers were installed to resist the longitudinal stresses in the CFRP. This paper will discuss the reasons MWD decided to retrofit their existing installations, the construction challenges of installing the CFRP over the PWC, and the effect that the changes in the recent draft code had on the existing number of longitudinal and hoop layers of CFRP layers. PWC stands for potable water coating and is the final coating covering the CFRP. During construction, MWD performed adhesion pull tests to insure that the new CFRP would bond properly with the existing CFRP. Several different pull tests were performed to determine how much PWC had to be removed to insure the CFRP would bond together properly. Construction has now been completed on these projects.
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