Blast behaviour of precast segmental vs monolithic concrete beams prestressed with unbonded tendons: A numerical investigation

This study aims to numerically investigate the response of precast/prefabricated segmental concrete girders/ beams (PSCBs) under detonations of high explosives. A new and effective method of applying prestressing force in tendons in LS-DYNA is explored and used. The working mechanisms of PSCBs vs conventional monolithic beams in resisting blast loads are comprehensively examined and discussed. The numerical results show that blast-induced damage to the beams is primarily caused by three different mechanisms, namely the propagations of blast-induced stress waves and plastic hinges, and the beam free-vibration deflection (global response). There are similar stress wave propagation and the resultant damage in the monolithic and segmental beams at the early stage when the joints are closed. The different damage patterns in these two beams are mainly due to the propagation of plastic hinges and the beam's free-vibration deflection. Damage is more severe and well distributed in the monolithic beam whereas damage to PSCB mainly concentrates in the segment next to the explosive and around the joints. The energy absorption mechanism provided by the relative movement between the segments is the main reason for the reduced damage in the PSCB. Although having larger displacement, the PSCB shows better blast resistance compared to the monolithic beam. Either increasing the prestressing rein-forcement ratio or effective prestressing stress reduces the peak and residual displacement of the beam but in-creases concrete damage. Increasing the number of segments leads to a larger beam displacement response but reduces concrete damage. Energy dissipation (ED) bars are found to effectively unite the segments and hence result in the segmental beam having a similar blast behaviour as the monolithic counterpart.