Degradation of structural safety levels in prototype balanced beam systems

Abstract

Post-tensioned balanced beam structures are very sensitive to natural deterioration and excessive environmental attacks, which can lead to relatively rapid drops in safety levels. Since partial failure or corrosion of pre-stressing tendons can be difficult to detect, the strategy of last resort to ensure that safety levels are acceptable remains to perform a mechanical load test, with the risks that this entails. In the case of some iconic balanced beam systems, destructive investigations are further limited by the need to comply with the deontological standards valid for cultural heritage structures. The capacity and robustness of balanced beam systems can therefore be estimated by relying primarily on accurate mechanical models and sensitivity analyses against scenarios that may degrade safety. To this end, reference models can be corroborated by information from various sources, including experimental campaigns and archives. This study, in particular, focuses on the evaluation of the residual capacity offered by Morandi's prototype balanced beam scheme, to aid prognosis, and possibly support “decision-making” for possible reuse. Finally, an experimental and numerical application to the most complex post-tensioned concrete balanced beam system ever designed by Riccardo Morandi is presented, i.e. the roofing system of Pavilion V of Torino Esposizioni dating back to the late 1950 s.