Dynamic Responses of RPC-Filled Steel Tubular Columns Post Fire Under Blast Loading
Blast-resistant capacities of 4 large scale circular Reactive Powder Concrete Filled Steel Tubular (RPC-FST) columns after exposure to fire are experimentally examined. The overpressures of shock wave, the deflections and strains of RPC-FST column specimens are recorded by advanced gauges. The influences of fire durations and scaled standoff distances of explosive charge on the dynamic behaviors and failure modes are discussed. It is shown that the RPC-FST columns remain excellent blast-resistant capacities after exposure to fire. RPC core column can be effectively confined by steel tube, but the blast-resistant capacities of RPC-FST columns are decreased as explosive charge or fire duration increased. The failure modes are transited from bending types to bendingshear types as explosive charge increased, and an obvious plastic hinge at mid-span section can be observed in the RPC-FST column with fire duration of 105min. It is also indicated that the maximum displacements of RPC-FST columns are more sensitive to fire duration than to explosive charge weight.
Mechanical and structural behaviors of ultra-high-performance fiber-reinforced concrete subjected to impact and blast
Abstract This study comprehensively investigates impact and blast resistances of ultra-high-performance fiber-reinforced concrete (UHPFRC) by considering various influential factors. At a material level, rate-dependent fiber pullout behavior, dynamic compressive behavior, and impact tensile and flexural behaviors were examined in detail, and the benefits of using UHPFRC to improve the impact resistance of ordinary concrete were discussed. It was obvious that (1) UHPFRC is able to dissipate much higher energy by impact than ordinary concrete with and without fibers, (2) the use of long straight steel fiber is effective in improving the impact resistance of UHPFRC compared to that of deformed steel fibers at high volume fractions, (3) fiber orientation significantly influences the impact resistance of UHPFRC: when more fibers are aligned in the tensile load direction, better impact resistance is achieved, and (4) size effect on the dynamic increase factor versus strain-rate relationship is insignificant. Impact and blast resistances of UHPFRC beams, slabs, columns, and composite structures were also examined at structural level, and several useful conclusions were drawn. (1) UHPFRC is favored for impact- or blast-resistant structures as compared with ordinary concrete due to its much better impact and blast resistance at identical dimensions, reinforcement configuration, and load magnitude, (2) the use of high-strength steel rebar provides the better blast resistance of UHPFRC beams or slabs as compared with that of normal-strength steel rebar, and (3) seismic detailing applied in UHPFRC columns leads to better blast resistance than is seen for columns without seismic detailing. Further research is suggested to address the remaining complicated problems or conflicts and to inspire proper design of structural UHPFRC members in an attempt to increase the use of UHPFRC.
Mechanics of deformable directed surfaces
Abstract The paper develops a simple, yet complete and consistent non-linear dynamic thermo-elastic shell theory based on the concepts of a two-dimensional directed continuum. The constitutive equations are postulated in a general form. Stress-strain relations are derived using the equation of energy balance and the two entropy production inequalities, which are rewritten in a special form. The linear theory is discussed in detail. The structure of the stress-strain relations is presented in the most general form and then specialized to concrete examples, in particular, to the classical shell theory, using their invariance properties with respective to certain symmetry groups. The elastic moduli are determined by demanding the coincidence of the frequency dispersion surfaces obtained using the two-dimensional theory with the lowest foils of the corresponding surfaces resulting from the three-dimensional theory of elasticity.