Abstract
Material-efficient, highly load-bearing members made of high-performance compressive concretes are often exposed to cyclical loads because of their slender construction, which can be relevant to the design. When investigating the fatigue behaviour of high-performance concretes in pressure swell tests, however, the specimen temperature rises strongly owing to the elevated loading rate at frequencies higher than 3 Hz. This leads to a negative influence on the achieved number of load cycles compared to tests carried out at slow speeds and calculated values, for example, according to fib Model Code 2010. This phenomenon, which was already observed, must be considered when generating design formulae or Wöhler lines for component design, as the test conditions with high constant load frequencies as well as sample storage in a climate chamber at constant conditions are prerequisites that cannot be expected in real material applications. Therefore, laboratory testing influences must be eliminated in order to avoid underestimating the material. Instead of adjusting the test conditions to prevent or control temperature development, as was the case in previous approaches, this article shows how the temperature effects can be corrected when analysing the results, considering both the applied stress and the maximum temperature reached. For this purpose, a calculation method was developed that was validated on the basis of a large number of fatigue tests. Thus, in the future, the application of one temperature sensor to the test specimen can effectively advance the extraction of values for Wöhler curves, even with high test frequencies.
Highlights
By developing an optimised packing density and achieving a low water–cement ratio through the use of very fine-grained admixtures like silica fume and high-performance superplasticisers, it is possible to achieve concretes with compressive strengths of up to 200 MPa, see, e.g., [1,2].In general, greater slimness can be achieved, for example, in long-span bridges or wind turbines with increasing material strength
A temperature increase in the sample was measured during testing [3,4,5,6,7,8,9], which usually resulted in an earlier failure, compared to the expected values according to fib Model Code 2010 [10] or to slowly cycled attempts [7,9,11,12,13,14,15]
Comparing the modified test results with the Wöhler curve according to fib Model Code 2010 [10], one can see that the corrected tested maximum stress level was everywhere so high that the number of load cycles lay above it
Summary
By developing an optimised packing density and achieving a low water–cement ratio through the use of very fine-grained admixtures like silica fume and high-performance superplasticisers, it is possible to achieve concretes with compressive strengths of up to 200 MPa, see, e.g., [1,2]. Greater slimness can be achieved, for example, in long-span bridges or wind turbines with increasing material strength Such constructions are exposed to very high numbers of load cycles and are susceptible to vibration because of the increasing slenderness. It was evident that the observed effect was strong for specimens stored in a typical laboratory climate chamber (20 ◦C and 65% RH) until testing This reduction was found to be a test-related influence that cannot be expected in the real building construction. Heating during cyclic tests can be prevented as far as possible by greatly reducing the test frequency This would disproportionately increase the duration for cyclic tests for standardising the fatigue strength of UHPC. In contrast to [15], the test procedure does not have to be adapted in order to eliminate the temperature effect
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
