Fatigue Testing of Galvanized-Strand Stay Cable

The proposed Bridge 9 is an asymmetric cable-stayed box girder bridge with a 75° forward-inclined pylon 96 m high. The bridge spans a 168.5-m-wide manmade body of water in Malaysia. The length of the bridge between the two abutments is 240 m. The bridge deck consists of a 3.5-m-deep prestressed concrete box girder spine with two prestressed concrete ribbed wings, and two 1.5-m-deep edge beams to accommodate the cable stay anchorages. Freyssinet International sought preconstruction testing to confirm the suitability of the stay cable design.

Freyssinet International hired CTLGroup to conduct fatigue and static ultimate tests of a 109-strand stay cable specimen. Each 15.7-mm-nominal-diameter strand was composed of 7 galvanized wires, and had a characteristic breaking load of 265 kN. The test was conducted in accordance with the Post-Tensioning Institute (PTI) "Recommendations for Stay Cable Design, Testing, and Installation," 1993.

The stay cable specimen was subjected to 2,000,000 cycles of fatigue loading between 36% and 45% of the specimens' guaranteed ultimate tensile strength (GUTS), providing a stress range of 158 Mpa. Static tests verified the ultimate tensile strength of the specimens; they were performed after every 500,000 load cycles during the fatigue test.

One of CTLGroup's custom-designed stay cable test fixtures was used for the test. This testing setup has a nominal dynamic load capacity of 4.8 million lbs and a nominal static load capacity of 9.6 million lbs at 8,000- psi oil pressure.

PTI criteria allowed the fracture of no more than 2% of the total wires during the fatigue test. Accelerometers, combined with an automated electronic data acquisition system, monitored wire breaks, providing data on the date and the time of each trigger.