PSI - Issue 64

André Weber et al. / Procedia Structural Integrity 64 (2024) 1959–1966 A. Weber/ Structural Integrity Procedia 00 (2019) 000 – 000

1962

4

In the last two decades this testing protocol has been slightly modified, While the first tests were just an ageing in the alkaline solution, a further development added a small strain of 0.2 % to the test setup, while in recent developments the strain has been increased to a value of 0.3% (3000 microstrain). Real strains of the reinforcement in structural application are generally in a comparable range, although no limit has been introduced for that value. In contrast to this tested strain, a general factor of 0.2 of the strength has been introduced as limit for the sustained load based on a literature review. Especially for bars with a higher failure strain which can reach more than 2% there may be a theoretical safety gap. Example: A recently developed material has a characteristic failure strain of more than 2% (strength higher than 1200 MPa). The stress limitation check allows 20% of this stress for sustained loads in serviceability limit state. This results in a strain of 0.2 x 2% = 0.4% strain in serviceability state. Is this allowable strain of 0.4% in serviceability state seen as safe, if 0.3% strain only are tested according the common test protocol? In contrast to this safety issue, the percentage of the allowable load is now increased from 0,2. 3. Common safety concepts for FRP rebars 3.1. Residual Strength concept This international prevalent concept deals with a standard specification of rebars. A defined list of tests has to be fulfilled and minimum values have to be shown. A compliance for all properties is assumed for this safety concept. If all tests regarding durability and creep are fulfilled, factors from experience, literature fixed in guidelines can be applied.

Fig. 2: test diagram for a standard test according international testing guidelines In figure 2 we see a logarithmic chart representing an ageing under load with a subsequent residual strength testing. It has been assumed, that the bar has a failure strain of around 2 % leading to a test load of 15% of the strength if 0,3 % strain is applied. Generally, for common tested bars the characteristic or guaranteed residual