Currently a new Eurocode is in development where the shear capacity will be based on the Critical
Shear Crack Theory (CSCT), rather than a purely empirical model. The newly introduced formulae
provide good results overall and include the effects of bending moments on the shear capacity.
However, the formulae are known to be too conservative for prestressed continuous beams with
low amounts of shear reinforcement and severely underestimate the shear capacity. If these
formulae are applied, many existing structures would therefore no longer meet the code
requirements. New structures with prestressed continuous elements would also require more
material and it may become difficult to design efficient concrete members that meet the new code
requirements.

To prevent substantial costs, emissions and time investments, it was questioned if the design
capacity of prestressed beams near intermediate supports could be increased by changing the
location of the control section from 1d away from supports to the critical cross section. The location
of the control cross section greatly influences the shear resistance according to the CSCT calculation.
However, it is unclear how the critical cross section can be determined accurately.

In this thesis the location of the critical cross section near intermediate supports was investigated for
prestressed continuous beams with less than the minimum required shear reinforcement. A small
number of models and experiments from literature were compared. Additionally, multiple Finite
Element Analyses have been performed with a variety of settings, assuming different shear
behaviour. A plasticity approach was also investigated, where the critical cross section is found at
the location where the cracking load equals the ultimate load of a crack.

This thesis found that the reinforcement ratios, prestressing stress, shear span and effective depth
(as well as the concrete strength in lesser amount) influence the location of the critical cross section.
The experiments and models found in literature, as well as the results found using the plasticity
approach, indicate that the critical cross section for prestressed beams may be moved from 1d to
1.5d away from intermediate supports. However, due to the limitations and assumptions of the
models it would not be safe to apply this change without further validation. It is therefore
recommended that experiments are done on prestressed continuous beams with low amounts of
shear reinforcement before any changes are made to the location of the control section.