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.
Mechanics of damage in reinforced concrete member under post-blast fire scenario
Abstract Recent terrorist activities in the form of blast and its cascading effects in the form of fire have had devastating impacts in structures, posing serious safety issues in structural members. In this context, a numerical study is conducted here to investigate the mechanics of damage in a reinforced concrete (RC) wall panel exposed to post-blast fire. The study involves developing a three-dimensional (3-D) nonlinear finite element (FE) model considering material nonlinearity as well as geometric nonlinearity. The developed FE model of the RC wall panel is first exposed to blast scenario, where the dynamic effect of blast loading is incorporated using strain-rate-dependent models of concrete and steel. The subsequent transient thermo-mechanical analysis, considering pre-damaging effects of the RC wall panel, is carried out by duly incorporating the temperature variation in thermal and mechanical properties of concrete and steel reinforcing bars. Responses are compared in terms of out-of-plane deflection, variation in stresses and strains at exposed and unexposed faces, damage pattern, and nodal temperatures of the wall panel. It is concluded that the responses obtained under the cascaded extreme loading scenario demonstrate significant damage caused to the RC wall panel as compared to the damage induced when it is exposed to either of the particular hazards. Moreover, fire resistance rating of the wall panel decreases considerably under the extreme cascading effects. Hence, current design standards may be required to incorporate the pre-damaging effects of cascading hazard to safeguard civil infrastructures from such extreme accidental/ manmade threats.
Broadcasting Freedom: Radio, War, and the Politics of Race, 1938-1948
The World War II era represented the golden age of radio as a broadcast medium in the United States; it also witnessed a rise in African-American activism against racial segregation and discrimination, especially as they were practised by the federal government itself. In this study, the author links these cultural and political forces by showing how African-American activists, public officials, intellectuals, and artists sought to access and use radio to influence a national debate about racial inequality. Drawing on a body of national public affairs programming about African-Americans and race relations, the author uses these radio shows to demonstrate the emergence of a new national discourse about race and ethnicity, racial hatred and injustice, and the contribution of racial and immigrant populations to the development of the United States. These programmes, Savage contends, challenged the nation to reconcile its professed egalitarian ideals with its unjust treatment of black Americans and other minorities. This examination of radio's treatment of race as a national political issue also provides important evidence that the campaigns for racial justice in the 1940s served as an essential, and still overlooked, precursor to the civil rights campaigns of the 1950s and 1960s, Savage argues. The next battleground would be in the South, and on television.