Fire-resistance tests on composite rebars

ABSTRACT

The strength-temperature correlation of a material can be determined by tensile tests on the material itself at different temperatures. This was done for a glass fibre reinforced polymer rebar in a series of tensile tests at temperatures ranging from 200 to 550°C. The rebar presented herein contains parallel, linearly oriented ECR glass fibres and a vinyl ester hybrid resin. From the results of the tensile tests a limit temperature in the range of 400°C - 450°C was determined for the bar. In a second series of tests the bond between the bar and concrete was tested at temperatures in the range between 150 and 400°C. The results show a decrease of the bond strength with increasing temperature. In the range of the glass transition temperature (Tg) the bond strength decreases substantially. At lower temperatures, on the other hand, the bond strength depends mostly on the properties of the concrete.

In a full-scale lap splice test a 5 by 2m concrete slab reinforced with GFRP bars was subjected to a predetermined service load (SLS). The load of 116,8kN was applied by four load equally spaced load beams. In combination with the dead load of the slab this load caused a stress in the rebar of 300 N/mm². The longitudinal rebars were all lap spliced in the middle of the slab. The length of the lap splices was 1060mm, which corresponds with 66 times the diameter of the 16mm bar. After applying the load, the fire exposure according to DIN EN 1363 was started. The slab withstood this exposure for 90 minutes. The temperature at the centerlineof the bars reached approximately 230°C before bond failure occurred.