In the past decades, there has been an increasing effort to describe the local bond behavior with
a bond stress-slip model. Such bond models are often used in studies of long bond lengths,
numerical calculations and crack width determination. Local bond behavior is usually
investigated experimentally in pull-out tests with short bond lengths equal to or less than 5 times
the bar diameter ds, recording the pull-out force and bar slip. Therefore, existing bond models,
like the approach of fib Model Code 2010, are mainly based on data determined outside the
bond zone. Distributed optical fiber sensing opens up the possibility to get an insight of the
processes within the bond zone during testing.
Current investigations at Technische Universität Dresden focus on the bond behavior and the
bond stress distribution for ribbed bars with bond lengths from 1·ds up to 60·ds under various
loading conditions. The test program includes systematic investigations of the influence of the
bond length on the ultimate bond stress testing pull-out, beam-end and tensile tie specimens as
well as the targeted use of distributed optical fiber sensing. Therefore, the hair thin sensors are
applied directly on the pull-out bar and enable quasi-continuously strain reading along the bond
length. Based on the local resolution of the strain, conclusions about the local force transmission
between reinforcement and concrete at different load levels or after a certain load duration can
be drawn. Hence, already with a bond length of 2·ds, non-linear distributions of the bond
stresses and local peaks in front of the ribs could be observed.
This article deals with the experimental and instrumental setup, test results and the procedure
of evaluation. Furthermore, it will be discussed how distributed optical fiber sensing can help
to derive a local bond stress-slip model.