FATIGUE STRENGTH OF CABLE COUPLERS IN PRESTRESSED CONCRETE BEAMS

During the erection of prestressed concrete bridges cable couplers are often used in the construction joints. Observed damage in many coupled construction joints of prestressed bridges in the Federal Republic of Germany has led the Swedish National Road Administration to look into the problem. An investigation was initiated at Lulea University of Technology with the main purpose to examine in which degree a coupled joint reduce the fatigue strength of a prestressed concrete structure. Fatigue tests have thus been carried out on twenty prestressed concrete beams. Fourteen of the beams were furnished with a cable coupler in the mid-span and six beams had no cable coupler. The coupled beams showed in some cases a fatigue strength which was only 12-14 per cent of the fatigue strength of the uncoupled beams. Some probable causes to the coupled beams lower fatigue life are discussed in the paper and tests on beams with modified coupler show that is possible to improve the fatigue strengths of coupled beams. The actual test conditions in the investigation do not always represent the situation of large bridge girders. However, it is believed that general tendencies with regard to the test results are representative for bridge structures as well as other jointed prestressed structures. (Author/TRRL)