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.
Stress-Strain Model for Reactive Powder Concrete Confined by Steel Tube
The reliable prediction using nonlinear methods for reactive powder concrete (RPC)-filled steel tube columns relies on the use of an accurate model for core RPC. However, the existing stress-strain model for core concrete has some disadvantages, such as a complicated form, excessive unknown parameters, and inapplicability to RPC. To establish a stress-strain model for RPC confined by a steel tube in finite element analysis (FEA), compressive experiments were carried out on RPC-filled steel tube columns. Calculation formulas of the theory-character parameters (peak stress and peak strain) for RPC-filled circular steel tube were also presented, and a multiparameter stress-strain model for RPC confined by steel tube was proposed based on the existing constitutive model for concrete-filled steel tube. Several nonlinear finite element models were established with ABAQUS, applying the proposed stress-strain model for RPC confined by a steel tube, and the calculating results were compared with the test results of six groups of RPC-filled steel tube stub columns. Experimental results demonstrate that the confining pressure varies from 14.43 MPa to 32.85 MPa; hence, the core RPC is in a low confining pressure state. The peak strength of core RPC increases with the increasing material strength and hoop coefficient. Thus, hoop coefficient and material strength are key parameters that affect the peak strength of the core RPC. The load-strain curves of the specimens obtained by experiments and finite element simulation are in good agreement, thereby verifying the reliability of the proposed model in this study. This study provides a theoretical reference for FEA and calculation of an RPC-filled steel tube structure.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.