Preliminary study on the behaviour of the SFT Qiandao prototype against explosions and impacts

This paper dealswith the behavior of theQiandao prototype of submerged floating tunnel (SFT) against exceptional loads due to explosions and impacts. A preliminary study is carried out on a singlemodule of the prototype, 100mlong, with a cross-section conceived as a layered circular steel concrete composite cross-section, with the external lattice layer made of aluminum. A refined three-dimensional structuralmodel is set up through the softwareABAQUS for performing the dynamic analyses. The explosions are assumed to be generated by a TNT charge. Three possible locations of explosions are assumed: Inside the tunnel, at the water bottom and at the water surface. The mechanical model of materials accounts for the strain rate effect, it being calibrated on literature experimental tests. Impacts of two sinking boats, differing in shape (ellipsoidal and V shaped), material (wood and resin) and sinking position (transverse or longitudinal)with respect to the tunnel are considered. Results of the preliminary analyses are given in terms of stress and strain states and displacements over time. Also the density variation of the fluid (water or air) hit by the explosion is examined. Themain outputs showthat when the explosion is internal, the tunnel undergoes greater stress and strains, although the ultimate strength is not reached, except at the concrete layer; besides in case of the longitudinal impact of a wooden boat, which is the most severe, the aluminum and concrete layers reach the ultimate strength, while the internal steel layer protects the tunnel roadway.