Assessment of Effects of Aircraft Impact on Category 1 Structures Rev 00, ICN 00

000-30R-D000-00100-000

July 17,2003
 

1. INTRODUCTION - 
The September 11,2001, terrorist attacks have drawn attention. to the possibility of such 
attacks on important targets. The Yucca Mountain Repository is such an importanit facility 
and potential terrorist attacks should be considered in design (Ref. 1). This report presents 
an initia1,assessment of potential consequences of such a terrorist attack on one of the 
facilitybuildings. The structure selected for this study is the Dry Transfer Facility @TI?). 
The report addresses impact of Design Basis Threat (DBT), which is a 

airplane, on the DTF and estimates its possible effects. 


This is a qualitative look at the issue for initial assessment of the effects of the postulated 
event. The outcome is expected to help define the facility design criteria auad layout 
parameters to minimize adverse effects afsuch events. 
2. ASSUMPTIONS 
Aircraft impact is a complex problem. It involves large quantities of energy dissipation in 
a dynamic environment, nonlinear respome of both the aircraft and the target struc;ture, and 
local failure of elements in terms of yieldting and crushing. Therefore, many simplifying 
assumptions must be made in order to d v e at a reasonable solution. The ffollowinag 
assumptions/criteria will be used to evaluate the structural damage to the Yucca Mountain 
Dry Transfer Facility due to the defined DOE DBT for aircraft crash. 
0 The aircraft to be considered is a 
0 The aircraft impact speed is given ;as. 'This speed is unrealiistically 
and the maximum speed near the ground surface will be about : according to 
the manufacturer's data. Howeveq the study will address both 
aircraft speeds. 
= The body of an aircraft damage; it. 
The damaging components are the and the : as observed at 
the WTC attacks. Therefore, impat of these two components will be. addressed.in 
this report.' . 
The and the are assumed to impact the structure -. 
simultaneously. The is at the and the are separated 
by 
The other damaging element is the: However, this study will not address the 
effects of' 

Assessment of Effects of Aircraft Impact on Category 1 Structures 
000-30R-D000-00 100-000-000 
Impact of aircraft on the walls of the structure is conselrvatively assumed to be 
perpendicular to the walls. 
Impact of aircraft on the is less likely and is expected to be at a small angle 
with the horizontal. Consequently, effects of impact on the ss considered to be enveloped- b-YYfhec6d.nse~~~~=~~~=6iiii=~pmn , provided that 'concrete 
thickness is at least equal to one-half the thickness. 
Concrete scabbing (ejection of pieces of concrete from the back side1 . cause 
unacceptable damage to casks and waste packages due to the small sizes of scabbed 
pieces at much lesser speeds relative to the .. Therefore, thickness 
does not control the design. 
Multiple concrete component structures (i.e , in Uhe 
path) are available to mitigate the effects of impact. 
Available generic information to characterize the damage states in comcrete 
structures due to high energy , impacts are applicable. 
Concrete design strength, f,', is 
. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . _ > ...I....... ! . . :,:: ...... .li . '-' &-i&bi.iii& .kit8 - - . . 
Two types of " h,&k V&kfi i'aenti.fld ih. &, , , , , , ; ;, .,. . ,,, , ' , : . . , 
9 . . 
a&chment to Ref. 2. These are: 
... . . . . 
between 
- . 
in diameter, at with distance 
8 diameter, at ), at 
between 
Ref. 2 states that the can be t r e ~ e d as a However, ;this 
aJssumption would be too conservative since the consists of concentric shells and is 
f& from being a The diameter is and the length is 
and the diameter towards the end. kor the purposes of 
determining an equivalent shell, the maximum diameter and two-thirds of h e total length 
may be used in evaluations. Thus, the will be idealized as a shell 
diameter and , with thicmess determined fkoni the weight, resulting in the 
fullowing equivalent shell: - 
B 
The consists of a (Ref. 2). 
Since the. vill not impact the target simultaneously with the ' , 
and since impact of the will be on a larger area, thus mitigating <he impact 
effects, the may be considered consisting of the 
housing only. The is cylinder and , and the 
housing is . cylinder, Again, the assembly is idealized as a 
F-nFForLn.1JaE-ermtY 
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Assessment of Effects of Aircraft Impact on Category I Structures 
000-30R-D000-00 100-000-000 
cylind&, with tbtal thickness of . and o~!tside diameter of. . result.ing in the 
following eauivalent shell: 
rn (the latter weight is for the and only) 
, , - 
- . -. - . .-. . -. - - . . . - - . . -.-.. :,-...:i.. .... . 
Finally, both speeds are given as Data in Ref. 2 shows that the . 
speed of the aircraft at is . and at 
Considering the height of the structures at this facility, a speed of . is more 
appropriate. Consequently, evaluations were performed for velocity as 
well as the specified velocity. 
4. STRUCTURAL RESPONSE ANALYSIS 
effects on structures are considered in bvc3 categories: local response and 
global response. In local response analysis, the fbcus is on perforation, penetration, and, 
for concrete structures, spalling and scabbing. In the global analysis, the focus is on 
, * , .-- - strength and ductility demands on ihestructural elements in the loadpath+Mlethod; of-. . a b.c\~:b . , . .. ,.. .hn,h., .r 
approach for the two types of analyses is different as described in the followring 
subsections.. 
1. Local response 
Local resmnse behavior is determined by the following parameters: 
In the 
.. case of the YMP structures, scabbing is unlikely to cause damage to the casks 
1 and waste.packages due to the anticipated small sizes of concrete pieces a t . 1 0 ~ speeds that 
, '. are generated as a result of the impact. Therefore, the controlling local behavior is 
of the wall. 
Many experiments have been performed to detennine the effects of om concrete 
targets. The , have ranged from solid cylindrical slugs to pipe sections. The 
velocities have ranged from t Based on test data, empirical equations 
have been developed to determine the target thickness required to preclude pdoration. 
Most of these formulations are for solid , but Ref. 3 provides a conversion factor 
from solid to "deformable" Aircraft associated are certainly deformable 
and therefore, a factor is applied to the solid test datta to account 
for the local damage. 
The empirical relations developed by different investigators result in a wide range of 
*. Ref. 3 recommends the equation developed im Ref. 4 be 
used for This equation is as follows: 
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Assessment of Effects of Aircraft Impact on Category 1 Structures 
' 000-30R-D000-00 100-000-000 
D= 
fCY = 
Ref. 3 recommends that the minimum thic&ess should be than that calculated 
from Eq. 1 to prevent perforation. Ref 3 also recommends that the perforation thickness for 
deformable missiles should be taken as from Eq. 1. 
Similar tests were performed in France usiing solid missiles, with velocities greater and less 
than the "critical perforation velocity." The experiments led to the following empirical 
equation: 
. ( . ,.,. I 
W =missile weight, lbs, and the other symbols are the same as before. 
.e factor for 
based od tests with 
L'." 
s also applicable here as the empirical relationship i 
~x~&&nts using were also c&ed out as part of a testing program om 
Postulated (Ref. 5). AS a iresult ofthis program, the following empirical 
relati'& were developed for estimating the distance tc (Ref. 5): 
Eq. 3 
The distance to can be conservatively taken as the required perforation 
thickness, ignoring the displacement of the target, which is presumably included in the 
distance deduced fiom the tests. .The interface force can be estimated wing the 
equivalent shell area and the yield point for steel, which can be taken as Once 
NLY' 
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Assessment of Effects of Aircraft impact on Category 1 Stmctures 
000-30R-D000-00100-000-000 
. . the interface force is known, Eq. 3 canbe used to estimate the perforation thickness. The 
assumption here is that deformation of the target structure is negligible. 
Table 1 shows the resulting estimated concrete thicknesses to prevent perforation, using the 
- . - three different equations. These three eyxtinnz vme E-lected-sincstheyrcsulti=:- 
comparable values. Calculations have been camed out for both 
velocities. The results show that the - dominates the required concrete 
thickness to preclude perforation. The table also shows the required minimum thickness 
considering the factor recommended by the previous researchers. 
2. Global Response 
~ccurate"globa1 response can only be determined from a nonlinear analysis using a specialty 
computer code that takes into account large material and geometric nonlinearities. At this 
stage on the YMP, such an analysis is not warranted since sufficient qualitative data can be 
developed to establish confidence in the..behavior of the structure. 
F, = F,A EQ. 4 
This equation shows that the interface force is independent of the velociity, provided 
that the impact energy is sufficient to cause yielding of the 
The equivalent she11'~arameters for both the were 
used to estimate the interface force due to each , as shown in Table 2. Tihe total 
maximum interface force of the'entire Arcraft impacting s building is estimated as the force 
due to impact of plus c (additional interface f ~ r c e s that 
miy be developed by other parts of the,aircraft are considered small compared tto the impact. 
forces generated by the It is'conservative to assume all the interface fforces occur 
simultaneously. It is also assumed that 'the target area of the building is sufficiently large so 
that the entire aircraft will impact the building. The maximum interface force 'tihus 
calculated is about Assuming an effective impact width of about - ' - (i.e., 
I .), the peak impact force is 
This is the estimated demand on the structure, VD,in terms of total shear. 
The capacity of the structure can be estimated considerimg the in-plane shear capacity of the 
building over the impacted area. The base shear of the structure is given by: 
. . Vc =;W,a 
where, 
Vc = the base above basemat, 
W, =.weight of the structure above the basemat 
a = average design acceleration 
Page 5 of 10 
Eq. 5 

Assessment of Effects of Aircraft Impact on Category 1 Structures 
000-30R-D000-00 100-000-000 
Initial design shows that, the weight above grade will be about : 
The plan,dimensions of the building will be about .. considering the longer 
dimension, the design base shear per unit length will be: 
.. '.' -. ~ . . ~ ~ q ~ - > - ~ b ~ ~ ~ ~ ~ ; = . : :.: ..-z- :. - .. , Eq. 5a , . " c - . ; A 
.. - 
Tkdemand-capacity ratio is then established as: 
Eq. 6 
Eq. 6 is plotted in Figure 1. When the D/C ratio is less than unity, the structure remains 
elastic, excluding the local crushing a spalling that may take place. Research on shear walls 
indicate that these walls have limited ductility. DOE-STD-1020 permits a ductility factor of 
for in-plane shear. It is estimated that this allowable has a factor of safety of 
Therefore, Figure 1 can be divided into three regions: if the base shear coefficient is 
the structural response remains within allowable limits. When the base shear 
-__. -. --. -_ coefficientis between ,&e structure is. still-expectednoLt~,c~llapse,but xpay,,;,,,. , .-,. 
suffer significant deformations. Finally, if the base shear coefficient is , the 
structure may not survive a DBT and therefore such a design is unacceptable. 
Considering the preliminary design spectra Eor this sight, the base shear coefficient is 
expected to be :' Therefore, it is comcluded that the DTF will withstand an impact 
from' a DBT without suffering unacceptable damage. 
5. DISCUSSION OF RESULTS 
he evaluations summ+zed above show that the perforation thickness for the concrete 
walls will be controlled by the impact of the and will have an upper bomd value of 
about For the , a thickness aqua1 to one-half the wall thickness is 
considered adequate. 
so'far as the global response is concerned, &he structure is expected,to survive the DBT 
withqut unacceptable damage. This is due do the fact that the structure will be designed for 
large seismic forces. In fact, at this site, the structure resulting from, the seisnnic design is 
expected to remain essentially elastic, excluding the spalling (near face) and scabbing (far 
face) . . of c~ncrete. .. . . 
~hese conclusions are consistent with Ref 6, which has been concluded recently. This 
report has concluded that containment and fie1 buildings at existing,cornrnerciial nuclear 
power plants will survive a large aircraft irnlpact without conseqnences. The 
containments generally are .shells and the he1 buildings are ractangular 
concrete structures with approximately dimension and wall thickness. 
Unfortunately, details of this report are mot ;available publicly and therefore a direct 
comparison is not possible. 
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Assessment of Effects of Aircraft Impact on Category I Styctures 
000-30R-D000-00 100-000-000 
Nevertheless, both DTF and typical nuclear power plant fucl buildings are reinforced 
concrete structures with similar span-to-thickness ratios for concrete walls. In a fuel 
building there are no intermediate walls whereas in the DTF there will be numerous walls 
at spacing of Consequently, it may be stated on a qualitative basis that the DTF 
. would have lztersl load capacity than a typical fuel building, giver, tkz z ~ t x a - & ~ q . ma -- -I*- 
basis. Therefore, the conclusions reached in Ref. 6 should be considered applicable to tl-le 
DTF. 
' The above. conclusions are arrived at using a conservative approach. This discussion will 
not be complete without'addressing some of the conservatism associated with this 
qualitative study. These include: 
1. Dynamic concrete strength is typically higher than the static strength by about ' 
This strength increase is due to the high rate of loading and is ignored in the 
cal&lations. 
2. The impact is assumed to be "perpendicular" to the surface. This is conservative as 
any deviation from perpendicular condition will tend to reduce the impact energy. 
3. The global response evaluation assumes that all three components impact the 
-----.--- A-L-> - - - - - -- ---bhilding simuit~eously~whieh~ish-i.~ly-u~likely~-60nsidering.the~fact- that- the-.-.. +~.-i+jr., .- 
impact force duration is measured in milliseconds, any difference in timing of the 
different components will reduce the maximum impact force. 
4. In all these evaluations soil-structure interaction is ignored. Since the buildings are 
located at a soil site, the impact forces will be reduced with "yielding" of the soilstructure 
interface. 
5. This evaluation has also ignored the fact that the interface force due to impact is 
duration, in the order of Even though the structure is 
rather rigid, the hndamental frequency wilU be in the order of thus resulting 
in a force duration-period ratio that will be about Dynamic amplification at 
these low ratios is relatively 
6. The design will be based on the ACI 349 code. The in-plane shear provisions in 
this code are known to be conservative. Capacity of the shear walls designed in 
accordance with ACI 349 is cdculated. This provides 
margin in design which is not taken into account. 
6. CONCLUSIONS AND RECOMMENDATIONS 
The following conclusions are reached from this study: 
1. The cnntrolling aircraft associated are the and the 
2. The controlling mode is the penetration of the walls and s6riking a 
cask or a waste package. 
3. Scabbing of concrete (i.e., ejection of concrete pieces from the side opposite to the 
impact area) will not result in damage. 
4. DBT aircraft impact will not result in damage so long as the 
exterior wall thickness is about 

Assessment of Effects of Aircraft Impact on Category 1 Structures 
,000-30R-D000-00 100-000-000 
5.;:; Full. impact on the rs not considered a credible event. Consequently, a 
. .: minimum -thickness equal to one-half the thickness. is considered 
':. :: adequate. 
6; Design of the superstructure for the expected seismic forces will result in a 
.... __ ._._......... . - ._ ...-.z.L-c..=: _.. ..x.L:-. I . structure with ample capacity to resist the.imysst. .$fcsts.-...:. ~2:~:7bz-m.:~...-~p:'.r.L.:,zrt =.,: .: , , ,, . . . . . . .. . 
Based on these conclusions, the following acfions are recommended: 
1. Design the facility buildings with a minimum of thickness and of 
thickness. These thicknesses can be if it can be shown that there will be 
another concrete barrier before a penetrating reaches a cask or waste 
package. 
2. This qualitative conclusion is robust so that further, more detailed 
aircraft impact study is not warranted. 
The above conclusions and recommendatiorns may be further refined with a more detailed 
study aimed at providing a more vigorous basis for some of the assumptions involved. 
.However, such. a study is not considered hi& priority and may be undertaken following the ' 
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : : . . . . . . . . . .~A,,-appl~ca~i~n;:I : :-;..;::- . . . . . . . . . . _ . : . . . . . .... .: .................. . . . . . . . . . . . . . : . . ' . : : , : j : , , , ; . . . . ,,. 1 , .i.. :, .'..i 
I . . . . . 
Orhan Gurbuz 
Bechtel Fellow and Senior Principal Engineer 
July 14,2003 . \ 
7. REFERENCES 
1. Letter No. 03-028, from Birdie V. Hamilton-Ray to J.T. Mitchell, Jr. 
2. Aircraft data faxed from R. Pernisi to 0. Gurbuz, dated June 24,2003. 
3. "Accident Analysis for Aircraft Crash into Hazardous Facilities," DOE-STD-3014-1996, 
U.S. Department of Energy, Washington, DC 
4. Chang, W.S., "Impact of Solid Missiles on Concrete Barriers," The Journal of Structural 
Division, American Society of Civil Engineers, Vol. 1 07, No. ST2, February 1 98 1. 
5. Rotz, J.V., "Results of Missile Impact Tests on Reinforced Concrete Panels," Vol. 1A, pp. 
720-738, Second specialty Conference on Structural Design of Nuclear Power Plant 
Facilities, New Orleans, LA, December 1975. 
6. "Deterring Terrorism: Aircraft Crash Impact Analyses Demonstrate Nuclear Power Plant's 
Structural Strength," posted at website wwv.nei.org. 
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Assessment of Effects of Aircraft Impact on Category 1 Structures 
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Notes: 
1. See,text for the equations. 
2. ' landing calculations are based on 
Table 1. Concrete Thickness to Preclude Perforation aqd Spalling 
Table 2. Peak Interface Force Calculation 
Type 
. .- 
Type I Equivalent Shell ( Weight I Equivalent I . Cross- I Interface 1 
Velocity 
mph 
I 1. I . . (a) assumed to be same as the vdue given in the specification, 
(b) assumed to be two-thirds of the value given in the specification, 
(c) Equivalent h is based on - diameter, total thickness of. 
and , ana volume of a d ' 
(d) Equivalent cyllnaer is based on higher weight of the equivalent cylinder iin (c) 
- - 
- 
Page 9 of JO 
Design 
Thickness 
t,,,xl.2 
26 
40 
28 
35 
Perforation Thickness, inches -' Max. 
Diameter & 
Length 
in x in 
94 x 161 
94 x 107 
10 x 58.5 
10 x 83.5 
Thickness 
- 1 7 ~ ~ . ~ - 7 ~ w ~ ~ e ~ 
22 
33 
23 
2 9 
~ q . 1 -.I p4.2 
lbs 
Calc 
9 
12 
10 
12 
Maximum possible interface force of the entire aircraft with and a 
-- Thickness - 
in. 
-- .--- 1.10 
2.00 
2.00 
325 
50 
5 0 
Calc 
Sectional! .. 
Area 
in2 
6 
8 
7 
8 
22 
27 
23 
29 
.- . , Force : 
Ibs 
0.73 
3 1 
38 
3 3 
41 
18 
33 
14 
26 
215 

Assessment of Effects of Aircraft Impact on Category 1 Structures 
000-30R-D000-00 100-000-000 
.. . - b 
Fig. 1 Behavior under Aircraft Impact Effects