220 likes | 357 Views
Resistance to Accidental Explosions General principles. Outline. Classification of explosion loads Dynamic response based on SDOF analogy Dynamic response charts ISO-damage (pressure-impulse) diagram Resistance curves for beams, girders and plates Ductility limitations
E N D
Outline • Classification of explosion loads • Dynamic response based on SDOF analogy • Dynamic response charts • ISO-damage (pressure-impulse) diagram • Resistance curves for beams, girders and plates • Ductility limitations • Verification of simple design methods
Simple (SDOF) vs. advanced methods • SDOF methods – Biggs’ (1964) (Elastic-plastic/rigid plastic methods, component analysis…) • Early Design • Screening of scenarios • Codes (NORSOK, IGN(UK)… • Advanced Methods – NLFEA • Large-scale simulations feasible • Detail Engineering • Critical Scenarios • Quality of analysis? Iso-damage curve for blast loading
EXPLOSIONClassification of response • Impulsive domain - td/T< 0.3 Response independent of load magnitude • Dynamic domain - 0.3 < td/T < 3 • Quasi-static domain - 3 < td/T
EXPLOSIONImpulsive domain - td/T< 0.3 Feq(t) • Conservation of momentum Feq(t) meq Y(td) keq(y) y(t) td t R(y)= keq(y)·y • Conservation of energy
EXPLOSIONQuasi-static domain - td/T> 3 Feq(t) Feq(t) • Rise time small (1) External work Strain energy Feq(t) meq y(t) y(t) Y(td) keq(y) td trise td t trise t R(y)= keq(y)·y (2) (1) • Rise time large (2) Static solution
f(t) t ymax y(t) Load-mass transformation factor t EXPLOSIONSDOF analogy – Biggs’ method f(t) Feq(t) meq y keq(y) Dynamic equilibrium:
F(t) Rel R(y) yel t t y Development of explosion response charts • Dynamic equilibrium • Explosion load history • Solve dynamic equation – numerical integration • Determine maximum deformation ymax • Perform analysis for different duration and load amplitude Fmax
K2 K2 R R R R K2 K3 K1 K1 K1 K1 w w w w Elastic Elastic-plastic (determinate) Elastic-plastic (indeterminate) Elastic-plastic with membrane R K3 K2=0 Rel K1 Wel or yel w EXPLOSIONClassification of resistance curves
Explosion response chartmaximum displacement versus load duration • Governing parameters: • Mechanisme resistance vs. maximum load Rel/Fmax • Load duration vs. eigenperiod td/T • Membrane stiffness, if any
EXPLOSIONDynamic response chart for pressure pulse-[J.M.Biggs]Triangular load - rise time = 0.3 td
Example yallow/yel =10 Development of ISO-damage curves from dynamic response charts for a given pressure pulse
Example yallow/yel =10 Development of ISO-damage curves from dynamic response charts for a given pressure pulse Pressure = Fmax Impulse =1/2Fmaxttd
EXPLOSIONIso-damage curve for yallow/yelastic =10. [W.Baker] Inadmissible domain Admissible domain
EXPLOSIONResistance curves • Beams and girders • Tabulated values for elastic-plastic behaviour • Resistance curves based on plastic thory • Plates • Elastic and plastic theory
Transformation factors for beams with various boundary and load conditions
Transformation factors for beams with various boundary and load conditions
New Revision II: Transformation factors for clamped beam with two concentrated loads
Transformation factors for beams with various boundary and load conditions