Structural robustness assessment of precast concrete structures

All types of buildings may be subjected during their service life to extreme events such as earthquakes, tsunamis, explosions, fires or even terrorist attacks. The engineering community began to face with the structural robustness and progressive collapse topic in the last decades, after the Ronan Point apartments collapse in 1968, the Murrah Federal Building bombing in Oklahoma City in 1995 and especially after the World Trade Center terroristic attack in 2001, New York. Current codes and guidelines employ two different strategies to be considered for accidental design situations: (i) strategies based on identified accidental actions for example impacts or explosions and (ii) strategies based on unidentified accidental actions based on limiting the extent of a localized failure. For these latter, the following methods are provided to assess the structural robustness of structures against accidental action and extreme events: (i) the Tie Force, (ii) the Alternate Load Path and (iii) the Key Element methods. In the years, experimental, analytical and numerical techniques were developed, especially aimed to investigate the behaviour of reinforced concrete (RC) monolithic and steel assemblies with very scarce attention to masonry and precast concrete (PC) systems. Nowadays, experimental, numerical and analytical methods are needed to investigate the behaviour of precast concrete structures to fill the gap of the lack of knowledge on progressive collapse performance of such structural typology. To this aim, in this work, numerical techniques and an analytical method are proposed for the structural robustness assessment of PC structures based on the current experimental tests observations and current guidelines requirements available for PC systems under accidental actions. The progressive collapse phenomenon is simulated considering the resisting mechanisms which may develop in connections and members to resist accidental action (i.e. flexural and catenary stages) based on the resistance and ductility of connections. Nonlinear static and dynamic responses are investigated and a simplified analytical assessment framework is proposed. Both modelling technique and analytical method are demonstrated suitable and reasonably accurate for the assessment of structural robustness of precast concrete systems composed by beams and column members and hollow-core floor units. Design suggestions and detailing solutions are finally discussed for practical engineering purposes aimed to design and verify the structural robustness of precast concrete systems.