STRUCTURAL RESPONSE OF AN EARTH COVERED MAGAZINE TO A

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UNCLASSIFIED,BRIEFING OUTLINE B 18 63,1 Background and Analytical Model Overview. 1 Geometry,2 Material Models,3 Boundary Conditions. 4 Model Features,a Reinforcing Steel Mesh,b Column Capital Mesh. 5 Load Application,2 Analytical Model Results,1 Partial Strip Model and Material Sensitivity. 2 Half Symmetry Model and Boundary Condition Effects. 3 Half Symmetry Partial Strip Model Comparison,3 Summary Conclusions.
UNCLASSIFIED,1 0 BACKGROUND MOTIVATION B 18 63, Earth Covered Magazines ECM are used for storing ammunition and explosive materials. Intended purpose is to mitigate sympathetic detonation risk. Need to meet loading criteria of DoD 6055 09 M, Some ECM designs may have been validated with field tests while others may need additional analysis. Older ECM designs may need additional modern analysis to demonstrate their roof can withstand loads from external. explosions, The project this work was a part of was an effort to better understand the response of a. representative ECM to a roof applied air blast load. Previous SDOF calculations gave failure capacity of columns and roof slab. Desire to predict roof slab or debris velocity in the event of failure. This presentation covers a portion of the modeling effort. Challenges of modeling this problem with FEA,Material strength effects. Boundary condition effects,UNCLASSIFIED,1 1 ANALYTICAL MODEL GEOMETRY B 18 63.
Typical Element Size,Soil 4 x4 x4,Concrete Roof Slab Column 1 x1 x1. Partial Strip 690k elements Half Symmetry 4 5M elements. Identify load at which ECM collapses assess sensitivity of Assess ECM response for critical load and material property. ECM response to material properties combinations identified by partial strip model. UNCLASSIFIED,1 2 MATERIAL MODEL INFORMATION B 18 63. Target Material Strength Notes,Soil LS DYNA MAT 072R3. K C Concrete Release 3 Fit 6,f c 2 500 psi,Principal strain failure 0 8. K C Concrete Release 3 Fit 6,f c 8 000 psi,Principal strain failure 0 8.
ASTM A36 steel basis for material,ASTM A572 Gr 50 steel basis for. material model fit,K C Concrete Release 3 fit based. on characterization tests for soil,Soil classified as silty sand with some. gravel average dry bulk density of, Concrete upper bound strength based on in situ testing. performed by NAVFAC, Concrete lower bound strength is specified unconfined.
compressive strength from drawings, Concrete Basis of design drawings indicate reinforcing steel permissible. LS DYNA MAT 072R3 tensile stress is 20 ksi which per Section A 3 2 of ACI 318 89. correlates to either Grade 40 or Grade 50 reinforcement. Previous studies done with MAT 072R3, Reinforcing Steel MAT CONCRETE DAMAGE REL3 used to validate material. LS DYNA MAT 024 Piecewise Linear Plasticity fit for both soil and concrete models. UNCLASSIFIED,1 3 ANALYTICAL MODEL BOUNDARY CONDITIONS B 18 63. Rigid wall plane,placed at edge of,Symmetry constraints X RY. model to constrain,RZ applied to only mid line of,soil by compression.
half symmetry model,only no tension,Symmetry constraints X RY. RZ applied to both sides of,partial strip model,Retain Wall. Constrained,Rigid wall plane placed at bottom of, Fixed constraints X Y Z RX RY model to simulate ground level and. RZ applied to all nodes at base prevent any debris from moving past this. UNCLASSIFIED,1 4 1 REBAR DETAILS B 18 63,Details from floor plan used to. determine spacing and,Rebar beam elements dimensions of roof slab rebar.
merged with concrete solid Length of rebar as detailed on. element nodes,plans was explicitly modeled,Rebar at lap splices was not. merged offset by one element,for all lap splices,UNCLASSIFIED. 1 4 2 COLUMN CAPITAL MESHING B 18 63, Nodes typically merged except drop panel connection used tied contact due to geometry. UNCLASSIFIED,1 5 LOAD APPLICATION B 18 63,Blast load was applied to. top of soil,Simplified blast load,allows comparison to.
previous SDOF studies,and is required for design,of magazines This. simplified load increases,overall impulse seen,during loading. Gravity load was applied to all bodies ramped up to The structure dynamic response was given 100ms to. 386 1 in s 2 during the first 400ms of simulation and settle after the gravity load was ramped up and then at. then held steady 500ms the blast load was applied,UNCLASSIFIED. 2 1 PARTIAL STRIP MODEL RESULTS SENSITIVITY TO MATERIAL. PROPERTIES B 18 63,Load 1 Load 2, For Load 1 case column crushing For some Load 2 cases structure collapse. leads to structure collapse in partial occurred at late time following rotation of. strip model column wall,2 5 ksi concrete,column failure.
instability, Load 1 Cases w 2 5 ksi concrete exhibit column crushing and subsequent structure collapse early in simulation time. Load 2 Both cases w 2 5ksi concrete rack at late time and ultimately collapse indicating insufficient lateral. resistance of structure i e artifice of partial strip model boundary conditions. Structure response shows greater sensitivity to concrete unconfined compressive strength than rebar yield strength. UNCLASSIFIED, 2 2 HALF SYMMETRY MODEL RESULTS BOUNDARY CONDITION EFFECTS B 18 63. Load 2 2 5 ksi concrete 50 ksi reinforcement,This material configuration. with the partial strip model,showed late time instability. and failure but here with the,half symmetry model there.
was stability and no failure A B C D E,Nodes A B C D E in the. plots below correspond to Roof slab nodal velocity settles at 0 in s. nodes in image to the right w o roof slab being thrown in. Z DISPLACEMENT Z VELOCITY,UNCLASSIFIED, LOAD 1 2 5 KSI CONCRETE 50KSI REBAR ROOF SLAB DISPLACEMENT. VELOCITY B 18 63,Z DISPLACEMENT Z VELOCITY,UNCLASSIFIED. HALF SYMMETRY MODEL ROOF SLAB VELOCITY SUMMARY B 18 63. These cases showed,instability and failure with,the partial strip model. but with the half,symmetry model showed,stability and no roof.
UNCLASSIFIED,2 3 HALF SYMMETRY PARTIAL STRIP MODEL COMPARISON. DEMONSTRATE LATE TIME INSTABILITY OF PARTIAL STRIP COMPARED TO STABILITY OF HALF SYMMETRY B 18 63. Load 1 8 0 ksi concrete 50 ksi rebar,The presence of the side wall in. half symmetry model serves to,preclude the late time racking. failure observed in partial strip,Boundary instability. at column base, Bending of rear and front walls in partial strip model.
UNCLASSIFIED, FAILURE MECHANISM DIFFERENCES BETWEEN HALF SYMMETRY AND PARTIAL STRIP B 18 63. Load 1 2 5 ksi concrete 50 ksi rebar,Half Symmetry. Partial strip model exhibited column,crushing failure as governing failure mode. while half symmetry model exhibited,punching shear failure in roof slab. Both models led to complete structure,Partial Strip.
A Partial Strip A Partial Strip,B Half Sym B Half Sym. Structure response shows greater sensitivity to concrete unconfined compressive strength than rebar yield strength Load 2 Both cases w 2 5ksi concrete rack at late time and ultimately collapse indicating insufficient lateral resistance of structure i e artifice of partial strip model boundary conditions

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