Application of Fibre Optical Sensors in Push‐out Tests on Composite Steel Truss and Concrete Beams

Abstract

Experimental push‐out tests have been playing an essential role for the evaluation of the structural behaviour of shear connectors in steel‐concrete composite beams along with the development of analytical design guidelines for predicting the respective longitudinal shear capacity. Although standard push‐out tests allow to quantify the global response of the specimen in terms of load‐slip behaviour, numerical simulations are usually needed to broaden the mechanical insight with a special focus to the areas involved in the mechanical failure. This holds in particular for composite steel truss and concrete beams, where a dedicated shear connection does not exist. The shear connection relies instead on a mechanical interlock between the steel parts and the concrete. Modern measurement devices allow expanding the experimental insight to internal mechanisms of combined concrete‐steel failure. This paper reports on the instrumentation of push‐out tests on composite steel truss and concrete (CSTC) beams with the support of a distributed fibre optical sensing (DFOS) system and evaluates the experimental results. The content presents different concepts of fibre installation and discusses the respective rate of success and the measurement ranges along the global load‐slip curves of the push‐out specimens. The results from the DFOS system provide the strain field histories along essential structural elements embedded in concrete within a crucial range of the load‐slip curves. Hereby it was possible to gain more insight into the load‐bearing mechanisms and identify the material component most likely involved in the stiffness degradation of the push‐out specimens.

On the load‐carrying behaviour of CSTC slim‐floor beams

“…However, the whole strain field in the embedded steel diagonals during the tests remained unknown and more advanced measurement techniques are required to overcome this issue. Hence, additional push-out test specimens were fabricated and instrumented with a distributed fibre optical sensing (DFOS) system [6]. This enabled to successfully measure strains along the whole sinusoidal bar in a continuous manner over time giving a deeper insight into the actual resistance mechanisms.…”

“…The peculiar geometry of the NPS beams described in the previous section allows refraining from dedicated shear connectors as the sinusoidal structural steel bars are responsible for transferring the vertical shear forces (as in a typical truss system) and the longitudinal shear forces into the surrounding concrete simultaneously. Whilst the potential issues arising from the interaction between vertical and longitudinal shear forces have been numerically tackled in [4], the longitudinal shear transfer was investigated experimentally by means of a wide push-out test campaign consisting of a total of 43 push-out tests [5,6]. It is worth mentioning that past experimental and numerical studies focused mostly on CSTC beams using reinforcement steel bars [7,8,9], in some cases with relatively small diameters (lower than 18 mm) [10,11], rather than structural steel bars.…”

“…Based on the promising results obtained by applying fibreoptic sensors in push-out test specimens [6], DFOS system was also employed in the current work to narrow the gap between the push-out and beam tests in terms of load-slip behaviour. It could be argued that the former may not always be representative of the actual behaviour observed in the beam due to the different boundary, as already discussed in past studies for typical composite beams [15].…”

“…All steel trusses had 3 parallel upper chords. The length of the specimens varies in a small range because of the geometry of the sinusoidal truss but it is approximately 6.4 m while the span length is 6 m. The samples were designed in close agreement with the samples tested in the push-outs earlier [6]. In particular, the chosen diameter of the steel truss section is identical to a subset of the push-out specimens in order to design the shear connection of the beam samples, but also in order to have the load-slip curves of the shear connectors for computational analyses at a later stage.…”