Abstract:

The research investigates the fatigue resistance of concrete beams prestressed with carbon fibre reinforced polymer (CFRP) tendons.  The fatigue performance of the tendons have been found to be very good, however, the effect of stress concentrations at crack locations on the fatigue performance of the tendons/beams needs to be verified.  Thus the aim of the experiment was to examine the effect of stress concentrations at crack locations.

CFRP tendons have low shear strengths and stress concentrations exerted by anchorage systems have been found to cause premature failure of the tendons.  Expansive cement anchorage system was used to grip the tendons.  Using this anchorage system, a tensile test was carried out to determine the efficiency of the system and thus set a limit to the value of prestress level that could be used for the experiments.

In the main experiment, concrete beams pretensioned with CFRP tendons were cast and subjected to cyclic loading.  The maximum and minimum loads were chosen so that the beams were cycled about the crack load.  Thus as the cracks opened and closed the concrete surfaces rubbed against each other and apparently against the tendon.

A computer programme using Matlab was developed to determine the loads exerted on the beams and their corresponding stresses in the tendons.  It also predicted the cracking load and the ultimate loads pretty accurately.

It is concluded that the fatigue of CFRP tendons may not be affected when embedded in pre-cracked prestressed concrete beams subjected to cyclic loading.