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Canadian Long Span Earth Covered Magazine
(CLSECM)
Design Challenges
2018 – International Explosives Safety Symposium & Exhibition
PLACE L2 HERE (DG LEVEL)
ASSISTANT DEPUTY MINISTER (INFRASTRUCTURE AND ENVIRONMENT)
H. (Vaidy) Vaidyanathan, Department of National Defence, Canada
David Bogosian, Baker Engineering and Risk Consultants, Inc., California, USA
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Outline of presentation
• Unique features/requirements of CLSECM
• Design issues/challenges– Original design (early 1990s)
– Design verification (2016/17)
– ECM Bar-Rating classification
• Remedial action for design inadequacy
• Impact of earth fill overlap between ECMs
• Conclusions
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CLSECM structure requirements
• Column free large clear span for easy warehousing
• Retain clear span but accept minimal change to other
structural dimensions to accommodate varying quantities
of ammunition and explosives
• Large door opening to permit entry/exit of Flat-Bed trucks
loaded with ammunition pallets + Fork Lift Trucks
• Electrical/Mechanical Annex separate from storage area
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CLSECM Anatomy
4
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CLSECM – Design features• Two types were developed in early 1990s by department engineers
– Large variant (17.1m wide x 28.75m long x 5.7m high)houses 250,000 kg of Equiv. TNT of HD 1.1
– Small variant (17.1m wide x 18m long x 4.2m high)houses 40,000 kg of Equiv. TNT of HD 1.1
• Design standard – AC 258, predecessor to the current AASTP – 1, NATO document on Explosives Safety Storage and Operations
• AC 258 required design of ECM to 7 bar (103 psi) blast load on roof and head wall/door assembly at separation scaled distance (m) of a) side-side at 0.5 Q 1/3 and b) front/rear or rear/front at 0.8 Q 1/3, where Q is the maximum Net Explosives Quantity (NEQ) in kg.
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CLSECM – Design features (Cont’d)
• Resistant to 7 bar blast load on the large span roof of CLSECM did not seem efficient and cost-effective; hence, idea was to increase separation distances to reduce the blast load on the roof.
• No standard or guidance was available for determination of blast loads on varying Inter-Magazine-Distance (IMD) between ECMs.
• Late Dr. Wifred Baker, well known US Blast Physicist, assisted in the determination of ECM blast loads from varying IMDs, based on the data available from ESKIMO field and Lab tests –BRL 2680 steel arch ECMs. Developed Pressure/Impulse and Scaled distance curves.
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ECM Blast LoadsPressure Impulse
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CLSECM – Separation Scaled Distance (m)
Small variant Large variant 7-bar ECM
standard
Side-to-side 0.6 Q1/3 0.6 Q1/3 0.5 Q1/3
Rear-to-front 1.1 Q1/3 1.4 Q1/3 0.8 Q1/3
Q 40-45,000 kg 250,000 kg —
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CLSECM – Analysis/ Design
Large Variant CLSECM (max.loads)
Roof – 5.5 bar & 35 msec
(Incident pressure)
Head wall/Door assembly – 4.2 bar & 38 msec
(Reflected pressure)
Dynamic Design using SDOF analysis using
decoupled components and component
response, based on TM 5-1300, predecessor to
UFC 3-340-02
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Small Variant
11 – 40,000 kg
11 – 45,000 kg
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Large Variant
18 – 250,000 kg
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Interior View
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CLSECM design verification in 2016/17- Why
• Original design was completed in early 1990s
• Possible advancements in ECM design procedures, blast
evaluation methods, and sophisticated analytical tools
• Lack of Bar Rating classification - required for licensing
purposes of ECMs, based on QD criteria.
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CLSECM design verification – Loads/Analysis
• Conduct state-of the art literature study on ECM design and select the most appropriate procedure; consulted standards/publications on ECMs from US, UK, UN, NATO, Canada
• Self-weight of soil and concrete
– Accounted for in FE model (LS-DYNA) by applying global acceleration to entire model
• Snow loads 3.2 kpa
• Dynamic Blast loads determined using BEC 7.0 tool(Studied adjustments to blast loads due to the impact of CLSECM features (Explosives density Q/V ratio, flat RC roof versus arched roof, thicker concrete skin etc.) on the data set used in the derivation of BEC curve fit; no adjustments were finally considered to be of significance)
• Non Linear dynamic analysis using LS-DYNA software and component design verification using UFC 3-340-02-Protection Category Level 3.
• Response criteria; Roof & Walls < 6 deg; Steel door < 12 deg, allowing for clearances for the stacked ammunition pallets to prevent impact from deforming components
For more details on the design verification, refer to Report on Structural response evaluation of CLSECMs, March 2017, Baker Engineering and Risk Consultants Inc.,California, USA
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FE model - Roof
Model overview
Rebar
Cross-section
Roller
boundary
Snow, dead, & blast load
Soil
Concrete
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Roof dynamic response
Load: 7-bar QD, p = 745 kPa, I = 170 kPa-ms/kg1/3
Time [ms]
Dis
pla
cem
en
t [m
m]
Borden - Roof Response
0 25 50 75 100 125 150 175 200-350
-300
-250
-200
-150
-100
-50
0
Deformations exaggerated 6x
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Model overview
Roller
boundary
Symm.
Soil
Concrete
Slab-on-grade
Rebar
Cross Section
Snow, dead, &
blast load
FE model - Sidewall
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Sidewall Response
Time [ms]
Dis
pla
ce
me
nt
[mm
]
0 15 30 45 60-40
-30
-20
-10
0
10
Load: 7-bar QD, p = 745 kPa, I = 170 kPa-ms/kg1/3
A
A
Deformations exaggerated 6x
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FE model - Headwall
Model overview Bla
st lo
ad
Door Detail
Soil
Concrete
Slab-on-grade
Snow, dead, & blast load
(with multiplier)
SectionO
penin
g
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Headwall Response
Time [ms]D
isp
lac
em
en
t [m
m]
0 20 40 60 80-10
0
10
20
30
40
Deformations exaggerated 6x
Load: 7-bar QD, p = 700 kPa, I = 200 kPa-ms/kg1/3
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Door Response
Deformations not exaggerated
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0
1
2
3
4
5
6
Roof slab Headwall Door
Sup
po
rt R
ota
tio
n [
°]
SDOF FEA
Comparison of Analytical Methods
• Responses
compared using
the same (old)
loads
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Incident Impulse [kPa-ms]
Incid
en
t P
res
su
re [
kP
a]
200 300 500 7001,000 2,000 5,000 10,000 20,000 50,000 100,000 200,000200,0005050
70
100
200
300
400
500
700
1,000
2,000
3,000
4,000
5,000
7,000
10,000
20,000
30,000
40,000
50,00050,000
RoofHeadwallDoor
Door controls capacity
Pressure-Impulse Curves
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CLSECM – Bar Rating classification - 3 bar, 7 bar or ….???
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Satisfaction of QD Design
Requirements
• Thus, large variant in its current configuration
can only be treated as a 3-bar magazine
• Small variant can be treated as 7-bar
Design NEQ Rating
[kg TNT]
Design
Separations QD 3 bar QD 7 bar
Borden – Large Variant 250,000 OK OK NG
Bedford – Small Variant 45,000 OK OK OK
() – failure of door
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Remedial measure for door upgrade of large variant
Attach precast concrete
blocks to the pilaster
to reduce the door opening
to avoid shear failure
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Effect of earth-fill overlap between CLSECMs located side-sideAccording to Canadian standard, based on
NATO, amount of earth fill overlap impacts
on the allowable NEQ as follows, based on
the Q-D standard
- If overlap is < 0.5 H, no change in QD (D3)
- If overlap is >0.5 < 0.75 H, increase QD (D4)
- if overlap is > o.75 H, increase QD (D5),
where H is the height of structure;
D3 = 0.5 Q 1/3 (m/kg1/3); D4= 0.8; D5 =1.1
The above requirement is in conflict with the
ECM design standard that only requires D3.
Such requirement is not stipulated in the
US DoD 4145.26 M-Contractor Safety Manual
for Ammunition and Explosives, which permits
solid backfill without restrictions.
Engineering study is to be commenced soon to
assess the impact of earth fill overlap on the
structural integrity of CLSECM.
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Conclusions
• CLSECMs, as designed/constructed in early 1990s at specific separation distances, meet current day ECM standards and best practice
• The original design, based on decoupled components using SDOF analysis, is conservative and overdesigned as determined by recent assessment (2016/17) by LS DYNA using FEM models with coupled components.
• BEC 7.0 tool appears to be the best tool available to determine the blast loads from ECMs.
• Use of P-I curves for CLSECM should enable siting and licensing at various IMDs and NEQs, without the need for QD Table currently used.
• Suggest Standard writing authorities revisit the demand for designing ECMs for Bar Rating Loads. Instead, consider what is specified in the NATO document – Nationally Approved Structures for Explosives,
“when design environment criteria are available as continuous functions of NEQ and IMD, there is complete freedom to choose both the distance and the type of construction in order to obtain the most economical solution. Design and Construction are based on analytical calculations supported by model or full scale tests”.
• Impact of earth fill overlap between CLSECMs is yet to be evaluated.