Experimental Study on the Shear Behaviour of Post-Tensioned Beams without Shear Reinforcement

Assessment of the load carrying capacity of existing bridges has become a frequent task for structural engineers. Here, the shear capacity is often one of the main concerns since the amount of shear reinforcement often does not comply with the amount that is required according to design codes nowadays, e.g. for post-tensioned concrete slab bridges, the amount of shear reinforcement is often very low or non-existing.
Since the shear capacity of beams has been found to be proportional to the width, the shear capacity of one-way spanning slabs can be simulated by rectangular beams. However, in the literature, the majority of the available experimental campaigns on the shear capacity of post-tensioned concrete beams is performed on beams with I- or T-sections. The shear-failure mechanism is, however, not the same for rectangular beams as for beams with I- or T-sections.
This paper studies the shear capacity and the shear failure mechanism of post-tensioned concrete beams (slab strips) without shear reinforcement. The experimental programme comprises 10 post-tensioned beams and varies two important design parameters; the shear span and the level of prestressing. All beams had a cross-sectional height of 700mm and, outside of the anchorage zone, a width of 250mm.
The shear failure mechanism and the development of the critical shear crack are studied by use of Digital Image Correlation.
The test results are compared to existing design codes with varying accuracy.