Studies on shear strengthening with TRC under non predominantly static loading
Table of contents
Project data
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Report in the yearbook 2012
TRC – an Alternative Means of Strengthening under Cyclic Loading?
Damage pattern after failure
In a feasibility study, ten large scale T-beams were tested with regard to their shear resistance under exposure to static and cyclic loading. It was the aim to determine the influence of cyclic loading on the load carrying capacity of reinforced concrete beam, on a strengthening layer made of textile reinforced concrete and on the bond between old structural member and strengthening. Toward this aim, threshold stress with two million load cycles was introduced. The sustained load quota amounts to 80 %, the working stroke 30 % of the service load.
All of the cyclic loaded components resisted the scheduled two million load cycles. While the threshold stress was introduced, the crack pattern was regularly checked for changes and documented photographically. In the course of the load application, a fine crack, which eventually developed into the shear crack which led to failure, formed between the upper web area and the underside of the slab.
The textile strengthening as well as the higher degree of reinforcement of the T-beams helped to increase the strain stiffness of the web. This, in turn, leads to a higher shear resistance. When the remaining load carrying capacity was tested at the end of the cyclic loading, the beams achieved even higher load carrying capacities than the reference T-beams tested under static loading. According to the current state of knowledge, this result was due to its higher concrete strength at the beginning of cyclic testing. Failure was indicated by a clearly visible shear crack. The centre deflection was approximately the same for all test samples independent of the load. Apparently, the threshold stress did not have a negative influence in the tests.
The failure loads measured in the tests were afterwards compared with calculated values. The predictions were based on a modified truss model which is similar to that of the steel stirrup reinforcement. All of the tested load bearing capacities were underestimated by the model. However, the deviation between the calculation and the test seems to be systematic. It is almost identical for all beams. Thus, it could be shown that the increase of the load carrying capacity caused by the textile reinforced concrete layer was idealized quite accurately. The deviations probably can be put down to a load carrying property which cannot be captured by the usual models based on parallel chord trusses.