PSI - Issue 64

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

1963

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strength is in the range of 70 to 90 % of the initial virgin strength of this rebar. If the percentage is in the defined range of the related class, this test is seen as fulfilled and a design is possible based on the characteristic or guaranteed values of the rebar. There is a huge experience in low strain applications like bridge decks, slabs on ground and barrier walls for more than 3 decades. For these applications it seems to be safe to use a percentage value from literature. Despite this huge experience there are doubts, if a correct reduction factor can be determined. As the tensile strength after ageing is compared with the virgin strength of the material the tensile tests as well the evaluation shall be done with great diligence. 3.2. Creep Rupture Approach The second approach is performance based on the creep rupture strength in alkaline concrete only as shown in figure 3. The X represents the failure points while the blue line defines the evaluation of the mean value (50 % failure probability) and the dotted line the characteristic value (5% failure probability) according least square method. The approach is used in national approvals in Germany as well in the European EAD 17-26-0023-03.01 “Carbon, glass, basalt and aramid FRP (Fibre Reinforced Polymer) bars as reinforcement of structural elements” as well as in the Annex R of the coming new Eurocode 2: FprEN 1992-1-2022. No other test is needed to get a safe long term value for tensile strength. Even short term strength is not needed to determine a safe characteristic value for tensile strength as all safety factors (load as well as material) are already included in the constant testing load. As for all common testing concepts the time temperature shifting principle is used to speed up the testing and to omit a longer extrapolation. This concept is described together with the influence of temperature and moisture in fib bulletin 40. The basics are figured out here by the following diagram.

Figure 3: typical range of creep rupture test failure point in 60°C wet concrete