TECHNICAL REPORT SL-84-13

0! EngineBLAST DOOR AND ENTRYWAYDESIGN AND EVALUATION

i by

S David W. Hyde, Sam A. Kiger

Structures Laboratory

I! 7 DEPARTMENT OF THE ARMYWaterways Experiment Station, Corps of Engineersll• .... PO Box 631

ViCksburg, Mississippi 39180

jQ4

4A if! ~July 1984 ,

Final Report

Approved For Public Release Distribution Unlimited

.fr CT I 71984D

Prepared fo, Federal Emergency Management AgencyWashington, DC 20472

ABORATORY und interagency Agreement No. EMW-E-1118

84 10 16 156

Destroy this report when no longer needed. Do notreturn it to the originator.

The findings in this report are not to be construed as anofficial Department of the Army position unless so

designated by other authorized documents.

II

The contents of this report are not to be used foradvertising, publication, or promotional purposes.Citation of trade names does not constitute anofficial endorsement or approval of the use of such

commercial products.

TECHNICAL REPORT SL-84-13

BLAST DOOR AND ENTRYWAYDESIGN AND EVALUATION

by

David W. Hyde, Sam A. KigerI, Structures Laboratory

DEPARTMENT OF THE ARMY

Waterways Experiment Station, Corps of EngineersPO Box 631

Vicksburg, Mississippi 39180

July 1984

Final Report

Approved For Public Release; Distribution Unlimited

This report has oeen reviewed in the Federal Emergency Management Agency

and approved for publication. Approval does not signify that the contentsnecessarily reflect the views and policies of the Federal Emergency ManagementAgency.

Prepared for

Federal Emergency Management AgencyWashington, DC 20472

UnclassifiedSECURITY CLASSIFICATION OF THIS PAGE ("en Date Entered)

REPORT'[DOCUMENTATION PAGE READ INSTRUCTIONSBEFORE COMPLETING FORM

1. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

Technical Report SL-84-13 /.-4(y'4 _ _ __

4. TITLE (and Subtitle) S. TYPE OF REPORT 6 PERIOD COVERED

BLAST DOOR AND ENTRYWAY DESIGN AND EVALUATION Final r4port -

6. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(s) S. CONTRACT OR GRANT NUMBER(&)

Interagency Agreement No.David W. Hyde, Sam A. KigerE--18EMW-E-1118

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT. PROJECT. TASKAREA & WORK UNIT NUMBERSUS Army Engineer Waterways Experiment Station

Structures LaboratoryPO Box 631, Vicksburg, Mississippi 39180

II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

Federal Emergency Management Agency July 1984500 C Street, SW, Room 716 I. NUMBEn OF PAGES

Washington, DC 20472 7714. MONITORING AGENCY NAME & ADDRESS(If different from Controtfine Office) IS. SECURITY CLASS. (of this report)

Unclassified

1S5. DECLASSIFICATION/DOWNGRADINGSCHEDULE

16. DISTRIBUTION STATEMENT (of this Report)

Approved for public release; distribution unlimited.

i1. DISTRIBUTION STATEMENT (of the abstract entered In Block 20, It different from Report)

II. SUPPLEMENTARY NOTES

Available from National Technical Information Service, 5285 Port Royal Road,Springfield, Virginia 22161.

19. KEY WORDS (Continue on reverse side It necessary and Identify by block number)

Blast door Protective sheltersBlast shelterCivil Defense shelterDIRECT COURSE event

X& AUSrNAcr (cin~mam - everee, sk N n~evoemy mo #~ntfly by block num~ber)

"-Objectives of this project were to design and test a walk-in, reinforcedconcrete blast shelter entryway and blast door. Two door configurations weredesigned, constructed, and tested: a commercially available standard exteriordoor with special supports, and a 3-inch-thick reinforced concrete door. Theentryway and closures were tested at the DIRECT COURSE event at White SandsMissile Range, New Mexico. The DIRECT COURSE event was a high-explosive test

(Continued)

DO i~ 1M 7 mnoo oFv mOVw IsSOL.ETE Unclassified

SECURITY CLASSIFICATION OF THIS PAr.E (When Dote Entered)

Unclassified

SECURITY CLASSIFICATION OF THIS PAOE(When DM& EafaMQm

20. ABSTRACT (Continued).

,sponsored by the Defense Nuclear Agency in October 1983. A I-KT simulatednuclear airblast and ground motion environment were provided by detonation of609 tons of an ammonium nitrate-fuel oil (ANFO) mixture at a height of burstof 166 feet. The peak recorded pressure at the opening to the entryway was69 psi and peak reflected pressure at the center of the blast door was 159 psi.

The reinforced concrete door survived the airblast effects of DIRECTCOURSE with only slight permanent deformation. The door could be easilyopened and closed again. The commerLial door was totally destroyed duringthe test. Posttest analyses indicate that the reinforced concrete blast doorwill successfully withstand the airblast effects of a 1-HT nuclear detonationat the 50-psi overpressure range.,

Unclassified

SECURITY CLASSIFICATION OF THIS PAGOE(3hen Dole Entered)

PREFACE

This investigation, sponsored by the Federal Emergency Management Agency,

under Interagency Agreement No. EMW-E-1118, was conducted by personnel of the

Structures Laboratory (SL), U. S. Army Engineer Waterways Experiment Station

(WES) during the period January 1983 through December 1983.

This study was performed under the general supervision of Messrs. Bryant

Mather, Chief, SL, and J. T. Ballard, Assistant Chief, SL, and under the di-

rect supervision of Dr. Jimmy P. Balsara, Acting Chief, Structural Mechanics

Division (SKD), SL. This report was prepared by CPT D. W. Hyde, CE, and

Dr. S. A. Kiger of the Research Group, SMD.

Commander and Director of WES during the conduct of the study and the

preparation of this report was COL Tilford C. Creel, CE. Technical Director

was Mr. F. R. Brown.

NTIS R&I

DTIC TAB AUuannouncOejustification -

WTI-_Distritu~ton/ _

AvailabilitY CodesAvail and/or

ýDist Special

CONTENTS

Page

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LIST OF FIGURES .................. ............................. 3

LIST OF TABLES ................... .............................. 3

CONVERSION FACTORS, NON-SI TO SI (METRIC) UNITS OF MEASUREMENT . . . 4

CHAPTER 1 INTRODUCTION .............. ......................... 5

1.1 Background ............................. 51.2 Objectives and Scope ................ .... ..................... 61.3 Procedure ....................... ... ........................... 6

CHAPTER 2 STRUCTURAL DETAILS AND MATERIAL PRCPERTIES ......... 7

2.1 Entryway ...................... .... ........................... 72.1.1 Shape ....................... ... ........................... 72.1.2 Airblast Prediction ................... .................... 72.1.3 Structural Details ................ ... .................... 8

2.2 Closures ...................... .... ........................... 82.2.1 Configurations Examined ................. .................. 82.2.2 Analysis of Various Configurations ........ ... ............ 92.2.3 Type 3 Door Details ................... .................... 102.2.4 Projected Cost .......................................... 122.2.5 Commercial Door and Supports ...... ............... .. 12

2.3 Models .................... ............................ 14

CtLAPTER 3 EXPERIMENTAL PROCEDURE .......... .................. .. 29

3.1 DIRECT COURSE ............................................... 293.2 Test Plan ................. ........................... .. 29

CHAPTER 4 RESULTS ................. .......................... .. 36

4.1 Data Discussion ............. ........................ .. 364.2 Structural Response ........... ...................... .. 364.3 Static Test ................................................. 37

CHAPTER 5 ANALYSIS.... ...... o... .......... ......... ... 45

5.1 Verification of Predictions................ .................... 455.1.1 Airblast ................ ......................... .. 455.1.2 Blast Door Response ......... .................... .. 45

5.2 Predicting Response to Other Weapons/Pressures ........ .. 465.3 Pass-Through Entryway ........... ..................... ... 47

CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS ..... .............. .. 53

6.1 Conclusions ................. .......................... .. 536.2 Recomuendations ............. ........................ .. 54

REFERENCES ..................... .............................. .. 56

APPENDIX A PRES,3URE DATA ............ ...................... .. 59

2

LIST OF ILLUSTRATIONS

Figure Pg

2.1 Elevation view of entryway ....... ................ .. 162.2 Plan view of entryway .......... .................. .. 162.3 Charge tower as seen from entryway interior ....... 172.4 Pretest predicted loading history for blast door ..... 182.5 Typical slab reinforcement details .... ............ .. 182.6 Concrete placement in stairs ..... ............... .. 192.7 Tying reinforcement in end wall ..... .............. ... 192.8 Reinforcement of stairwell walls; underground

chamber complete ........... .................... .. 202.9 Finishing concrete in stairwell roof ... ........... ... 202.10 Backfill placement around completed structure ...... 212.11 Blast door configuration concepts .... ............ .. 212.12 Blast door strap hinge details .... ............... .. 222.13 Blast door shell prior to concrete placement ....... 232.14 Pretest blast door response prediction ............ .. 242.15 Cross section of commercial door and supports ...... 252.16 Commercial door with support beams in place ....... 262.17 Commercial door with support plates in place ....... 272.18 1/10-scale models ............ .................... .. 283.1 DIRECT COURSE charge tower assembly ... ........... .. 303.2 Pretest photograph of site layout .... ............ .. 313.3 Surface view of full-scale entryway ... ........... .. 323.4 Reinforced concrete blast door in place .. ......... .. 333.5 Instrumentation of full-scale structure .. ......... .. 343.6 Instrumentation of dead-end tunnel 1/10-scale model . . . 353.7 Instrumentation of pass-through tunnel 1/10-scale

model ................ ......................... .. 354.1 Posttest surface view of entryway .... ............ .. 394.2 Damage to stairwell roof immediately above landing .... 404.3 Damage to stairwell roof ....... ................. .. 404.4 Closures; reinforced concrete blast door on left, open,

commercial door on right ....... ................ .. 414.5 Closures; reinforced concrete blast door on left,

commercial door on right ....... ................ .. 424.6 Damage to commercial door support plate .. ......... .. 434.7 Failure of test slab; static test .... ............ .. 445.1 Comparison of measured to calculated pressure data

for blast door loading ....... ................. .. 495.2 Calculated response of blast door to DIRECT

COURSE loading ........... ..................... .. 505.3 Calculated loading history of blast door for a I-MT,

50-psi event ..................... ............ 515.4 Calculated blast door response for 1-MT, 50-psi event 515.5 Pass-through entryway system ..... ............... .. 525.6 Comparison of incident to peak pressure on closure

in dead-end and pass-through entryway systems ..... 52

LIST OF TABLESTable

2.1 Blast door analysis results ...... ............... .. 15

3

CONVERSION FACTORS, NON-SI TO SI (METRIC) UNITS OF MEASUREMENT

Non-SI units of measurement used in this report can be converted to SI

(metric) units as follows:

Multiply By To Obtain

feet 0.3048 metres

inches 0.0254 metres

megatons (nuclear equivalent 0.004184 terajoulesof TNT)

kilotons (nuclear equivalent 4.184 terajoulesof TNT)

pounds (force) per square 0.006895 megapascalsinch (psi)

pounds (mass) 0.45359237 kilograms

pounds per cubic foot 0.1601846 grams per cubic centimetre

psi per inch 0.271447 megapascals per metre

tons (nuclear equivalent 4184.0 megajoulesof TNT)

4

BLAST DOOR AND ENTRYWAY DESIGN AND EVALUATION

CHAPTER I

INTRODUCTION

1.1 BACKGROUND

In the event of an imminent nuclear strike, current Civil Defense plan-

ning calls for the evacuation of nonessential personnel to safe host areas,

and the construction of blast shelters to protect the key workers remaining

behind. These shelters will be designed to resist blast, radiation, and asso-

ciated effects at the 50-psi* overpressure level for a 1-MT weapon. One of

the key elements to the survivability of these shelters is the vulnerability

of the shelter closure and entryway.

Several blast shelter entryways, some including blast doors, were tested

in the aboveground atomic tests at the Nevada Test Site during the 1950's. 1 - 7

The blast doors or closures tested were either massive reinforced concrete

doors, 4 ' 5 vertical shaft entryways with a submarine-type hatch, 1 ' 2 ' 3 steel

doors with beam stiffeners,6 or doors tested at less than 10 psi.7 More

recent tests have reexamined the steel door8 and the vertical shaft with a

hatch at ground level. 9

The most cost-efficient closure and entryway system, one whose surviva-

bility has clearly been demonstrated, is the vertical shaft with a hatch-type

closure. However, if a vertical entryway is used for a large shelter (100-

person capacity or larger) it may not be possible to get everyone into the

shelter in the allotted time (normally 15 minutes). Also, if the shelter is

to be a dual-use facility, the vertical entrance is not acceptable. There-

fore, a cost-efficient, walk-down entryway and blast door design is needed for

large-capacity shelters such as the deliberate 100-person-capacity key worker

blast shelter that is currently being designed for the Federal Emergency

Management Agency.

*A table of factors for converting non-SI to SI (metric) units of measurementis presented on page 4.

5

1.2 OBJECTIVES AND SCOPE

The objectives of this project were to design a walk-in, reinforced con-

crete entryway and blast door and evaluate the design in a I-KT simulated air-

blast environment in the DIRECT COURSE event at White Sands Missile Range

(WSMR), N. Mex. The DIRECT COURSE event is described in Section 3.2. Various

blast door configurations were considered and from those analyzed, a prototype

door was selected for use in the entryway. A commercially available fire-

resistant door with special supports was also tested. By using 1/10-scale

models, airblast loading data for a I-MT weapon were obtained for both a

single-tunnel dead-end entryway system and a double-tunnel pass-through entry-

way system. These data will be used for the analysis of entryways and blast

doors for the key worker blast shelter.

1.3 PROCEDURE

Testing was conducted during October 1983 by personnel of the Structures

Laboratory, U. S. Army Engineer Waterways Experiment Station (WES), Vicksburg,

Miss. The entryway system was tested at the DIRECT COURSE event at WSMR.

This event was a high-explosive simulation of a I-KT height-of-burst nuclear

weapon sponsored by the Defense Nuclear Agency (DNA). The entryway was con-

structed at the predicted 50-psi overpressure range. Fourteen channels of

airblast data were collected during the test. All data were recorded on mag-

netic tape and later reduced to a digital format.

6

-16:1

CHAPTER 2

STRUCTURAL DETAILS AND MATERIAL PROPERTIES

2.1 ENTRYWAY

2.1.1 Shape

Pedestrian flow-rate studies have been conducted on the movement of per-10

sonnel through protective shelter entryways. The dimensions of the proto-

type entryway were selected to provide access to approximately 100 personnel

in about 2 minutes.

The stairwell in the test entryway was 4 feet wide with a 7-foot vertical

clearance throughout. The stair risers were 7-3/4 inches high; stair treads

were 10 inches deep. The stairway had a 4- x 4-foot landing about 8 feet be-

low the surface. Both doors tested provided a clearance of 3- x 7-feet. The

ceiling height immediately in front of each door was 10 feet, which matches

the ceiling height inside the proposed key worker blast shelter. This facili-

tates building a continuous roof slab inside and outside the shelter.

Sketches of the entryway are shown in Figures 2.1 and 2.2.

2.1.2 Airblast Prediction

Prior to the design of the doors or structural elements, it was neces-

sary to obtain a pressure-time history prediction at various points inside the

entryway. A surface overpressure of 50 psi was predicted by DNA personnel at

a slant range of 503 feet, or a horizontal range of approximately 475 feet.

The prediction for pressures inside the entryway was based on the open end of

the entryway facing ground zero, which provides a worst case loading for the

closures. It will be noted from Figure 2.3 that the orientation of the entry-

way provided a nearly direct line of sight from the end of the entryway to the

charge.

Pressures at various points inside the entryway were calculated with the

ANSWER computer code, which is based on a modification of the work found in

ll References 11, 12, and 13. The ANSWER code was developed at WES in the Ex-

plosion Effects Division of the Structures Laboratory. The pressure-time his-

tory computed at the center of the blast door and used for the blast door

response analysis is shown in Figure 2.4. From Figure 2.4, the predicted peak

pressure on the blast door is about 142 psi.

7

In examining the configuration of the entryway, it is apparent that with

the given orientation of the stairway, the wall and roof slabs will be loaded

primarily from the inside. However, it is unlikely that the backfill sur-

rounding the structure would allow enough deflection in the slabs to cause

failure. Hence the worst case loading for the wall and roof slabs would be

with the open end of the entryway facing away from ground zero, so that the

slabs are initially loaded by the soil-transmitted pressures only. Since the

survival of personnel inside the protective shelter is more dependent on the

vulnerability of the closure itself, the entryway was tested for a worst case

loading on the doors, i.e., with the entryway opening facing ground zero.

Obviously, in the case of a real-world blast shelter, if the probable burst

point of a nuclear weapon can be determined with any degree of accuracy, the

shelter should be oriented in such a way that the entryway opening is facing

away from ground zero.

2.1.3 Structural Details

The entryway tested was of reinforced concrete slab-type construction

throughout. The roof and floor slabs were 6 inches thick, with 1-7/8 inches

of concrete cover to the principal steel in each face. Principal steel con-

sisted of No. 4 bars at 12 inches on center in both tension and compression,

giving a steel ratio of 0.43 percent. Temperature steel was No. 3 bars at

12 inches on center, and shear reinforcement was provided with No. 3 U-type

stirrups at 12 inches on center. Reinforcement details and dimensions are

shown in Figure 2.5. The overall length of the test structure was 29 feet

6 inches. The ground floor was approximately 15 feet 6 inches below the

surface. Photographs of the entryway under construction are shown in

Figures 2.6-2.10.

2.2 CLOSURES

2.2.1 Configurations Examined

Prior to the design of a blast door, tentative design criteria were es-

tablished. A minimum static ultimate resistance of 150 psi was selected for

the door based on the predicted peak pressure at the door opening. In order

to minimize the cost of the hinges and to facilitate handling, the weight of

the door was limited to a maximum of 1,500 pounds. The level of protection

from prompt radiation provided by the door was also taken into consideration.

8

Three concepts for a reinforced concrete door configuration were con-

sidered (Figure 2.11). In each case the clearance provided by the door

opening was taken as 3 feet wide by 7 feet high, with the door overhanging

this opening by 4 inches on all edges.

The Type 1 door (Figure 2.11) was a conventional reinforced concrete slab

with steel channels running the length of the door to provide a bearing sur-

face for the hinges and latch mechanism. The Type 2 door was of a sandwich-

type construction, with steel plates of equal thickness on each side of the

door, anchored to the concrete with welded shear studs. The Type 3 door in-

cluded a steel plate on the tension face (inside) of the door with deformed

bars across the short span near the compression face. Hooks welded to the

steel plate fix the deformed bars in place and anchor the steel plate to the

concrete. High-density concrete was examined in each configuration for its

radiation attenuation potential.

Each door configuration was examined for its flexural capacity, weight,

and radiation attenuation. Door thickness and steel ratios were varied to ob-

tain a "best case" for each door type. Equations for flexural capacity from

Reference 14 were used to calculate the maximum resistance of each door.

Results of this evaluation are given in Table 2.1. The value labeled "%

rad" indicates the percentage of the radiation level outside the door which

will be transmitted through the door. Exact figures for radiation levels

penetrating the door are not given, because this phenomenon depends not only

on weapon size and range, but also on entryway orientation and weapon type.

Reference 10 was used for radiation attenuation calculations.

2.2.2 Analysis of Various Configurations

As indicated in Table 2.1, the Type 1 door met neither the flexural

capacity requirements nor the weight restrictions. While the flexural

capacity could be raised by constructing a thicker door, this would also raise

the weight, which is already higher than the imposed limit. The Type 2 doors,

by weight, are much stronger than the Type 1 doors because of the much higher

steel ratios. However, the Type 2 doors would present a problem for concrete

placement since each outside face is covered by a steel plate. Also, since

the rebound force on the door is in the range of 25 percent of the primary

load, less steel is needed in the compression face than in the tensile face.

The Type 3 door, while not as strong as the Type 2 doors, does meet the

9

tentative flexural capacity requirement, is lighter than Type 2, and does not

present the construction problem posed by a Type 2 door. Pased on this evalu-

ation, a Type 3 door, 3 inches thick with 11-gage sheet steel in tension and

No. 4 bars at 6 inches on center in compression was selected for further

examination.

It will be noted from Table 2.1 that in each case the high-density con-

crete gave lianited additional radiation protection while raising the door's

weight considerably. For this reason, high-density concrete was not con-

sidered for use in the blast door beyond this evaluation.

2.2.3 Type 3 Door Details

The welded hooks in the Type 3 door serve as shear reinforcement and pre-

vent the steel plate from separating from the concrete during loading. Shear

calculations were based on the dynamic reactions at the edges of the door

opening, obtained from Reference 15, Table 5.4. The shear reinforcement se-

lected consisted of No. 3 bars at 6 inches on center.

The door is designed to overhang the opening by 4 inches on all edges;

therefore, hinges must support the weight of the door and only some of the re-

bound force. The hinges are subjected to very little stress caused by the

primary loading of the door. The predicted rebound force was determined by

the use of Figure 9-1.4 in Reference 16 with the following input parameters:

"T = natural period of door = 5.5 ms

td = predicted duration of load = 120 ms

Assuming a ductility of 10, the ratio of rebound force to primary load

is approximately 0.15, which yields 21 psi on the door in rebound. It was

assumed that the hinges would carry about one-half of the rebound load, the

other half being carried by the latch mechanism. The hinges used were typical

heavy-duty strap hinges with 1/2-inch-diameter pins and 18-inch-long, 1/4-inch-

thick straps. The four hinges used satisfied the rebound requirements of the

L .door and gave a high factor of safety for the weight of the door alone. The

hinge straps were bent by the manufacturer to accommodate the 3-1/8-inch off-

set of the door. The hinges were fastened to the door with 3-3/8-inch-diameter

V- bolts and anchored to the door frame and supports with 3/8-inch-diameter bolts

(Figure 2.12).

The door frame was designed to prevent excessive concrete cracking in the

door supports, which are required to carry the entire load placed on the door

10

in addition to their own load. It was also considered desirable for the door

frame to provide a smooth surface which the door could close against, so that

a good seal between door and frame could be more easily attained. The door

frame was fabricated from 4- x 4-inch steel angles with a 7- x 4-inch angle on

the hinged side of the door. Shear studs were welded to the inside of the

frame every 6 inches to provide anchorage in the door supports. The door

frame was anchored in place before the door supports were formed, so that the

frame and supports were an integral unit. The frame may be seen in construc-

tion photos (Figures 2.6 and 2.7).

As stated previously, the door supports were required to withstand the

total load carried by the door plus the load placed directly on them. With

4 inches of door overhang, 4 inches taken by the hinges, and a minimum of

5 inches of clearance to the end wall from the open door, the door supports

were required to project at least 13 inches from the end wall. The dynamic

reactions around the edges of the door were obtained from Table 5.4, Refer-

ence 15. Based on design calculations, a depth of 15 inches was selected for

the support on either side of the door, and the support above the door sloped

from 15 inches deep immediately behind the door to 30 inches deep at the ceil-

ing. Principal reinforcement ratio throughout the supports was 0.36 percent.

Strips of the 11-gage sheet steel were cut 3 inches wide and welded to

the sides of the door's rear plate before concrete placement to aid in forming

the door. The hooks, made from No. 3 reinforcement bars, were cut 5-3/4 inches

long, bent through a 135-degree arc, then welded to the steel sheet. The

11-gage sheet was fixed on all edges during welding to prevent excessive warp-

ing. The No. 4 bars were fastened to the welded hooks with wire, but were not

welded to the side sheets. Prior to concrete placement, the hinges were fas-

tened to the door shell as shown in Figure 2.12.The blast door was constructed at WES and transported to WSMR prior to

construction of the entryway. All steel used in the door was ASTM

Grade 50. The concrete placed in the door had an average 28-day strength of

4,210 psi. The complete door shell, prior to concrete placement, is shown in

Figure 2.13.

The resistance function of the door was considered bilinear with a

maximum resistance of 180 psi (Table 2.1) and a stiffness given by: 1 5

201 El KK ba = 657 psi/inba 3

11

where

b = long unsupported dimension of door = 84 inches

a = short unsupported dimension of door = 36 inches

The elastic deflection is 180 psi/(657 psi/in) = 0.27 inch.

The maximum response was calculated from a single-degree-of-freedom numerical

integration. 15 Results of these calculations are shown in Figure 2.14. The

maximum predicted response of the door was 0.36 inch at 5 ms after the door

is initially loaded. Therefore, some plastic deformation was expected with a

ductility of

0.36/0.27 = 1.3

and a permanent deflection of about 0.10 inch.

After the blast door was installed in the test structure, it became evi-

dent that neither the back face of the door nor the door frame was perfectly

plane. To insure the door's airtightness, the small gaps at the door/door

frame interface were filled with a typical commercially available flexible

caulk. None of the gaps around the door exceeded 1/8 inch prior to filling.

2.2.4 Projected Cost

Given detailed construction drawings of the blast door, a private manu-

facturing firm was asked to provide an estimate of the cost of building such

a door. The figures shown include the estimated cost of all door hardware and

the steel door frame:

Individual units: $1,024 eachLots of 20 or more: $ 924 each

2.2.5 Commercial Door and Supports

A comercially available fire-resistant door was tested with specially

constructed supports with the objective of minimizing the cost of the closure

and simplifying construction. The door was constructed of a fire-retardant

"foam sandwiched between thin steel sheets. For analysis purposes the door was

considered to have negligible flexural capacity.

The three wide-flange beams shown in Figure 2.15 were designed to carry

the total load placed on the door. The beams rest in steel boxes constructed

of 1/4-inch plate and cast into the concrete door supports. In practice, the

12

beams would not be set in place until the blast shelter was occupied, at which

time they would be mounted in the boxes. The beams, W6 x 12's, weighed approx-

imately 44 pounds each.

Although the beams were capable of supporting the predicted load on the

door, there was doubt as to whether the door was capable of supporting the

load between each span (24 inches). Spreader plates were designed to transfer

the load from the door to the beams. Two different concepts for these plates

were examined. First, six separate plates would be hung, two from each beam,

to completely cover the door surface. This would in effect make the plates a

double cantilever, fixed in the center. Second, two continuous plates, each

covering one-half of the door surface, would be placed between the door and

the beams. However, if the assumption of negligible flexural capacity for the

door is correct, a 1-inch-thick plate would be needed for the smaller canti-

lever plates, or a 7/8-inch-thick plate for the continuous concept. Each

1-inch steel plate would weigh about 110 pounds, making it unmanageable in

the confines between door supports. Also, the cost of the plates would elimi-

nate any economic benefit gained by using a commercially available door. The

size of steel plate needed to insure elastic response of the door was imprac-

tical and costly. Therefore, a smaller, more manageable plate was selected

and a high level of damage was predicted. Six cantilevered plates, 3/16 inch

thick, weighing about 20 pounds each, were used to reinforce the door. The

plates were supported on the wide-flange beams with steel angles (Ll × 1 x

1/4 inch).

Rebound forces acting on the door were anticipated to be about 25 percent

of the primary load, assuming the door survived. To prevent the door from

opening during rebound, it was necessary to anchor it to the support beams.

L-shaped anchor bolts served this purpose with the small leg of the "L" hookedi' • to the back sides of the support beams. Three 3/8-inch bolts were used at

each beam. Photographs of the commercial door and its supports are shown int

Figures 2.16 and 2.17.

Approximate cost of the commercial door and its supports is given below:

ApproximateMaterials Cost

Steel fire door, fire rating B $200

Door frame 67

(Continued)

13

ApproximateMaterials Cost

Hinges 17

W6 v 12 beam, 11 feet 108

3/16-inch steel plate & angles 120

1/4-inch plate 45Total Materials $557

Labor (Fabrication only;

does not include installation costs) $200

Total Cost $757

2.3 MODELS

The prototype entryway and closures were to be subjected to a l-KT simu-

lated 50-psi airblast environment. Test results were intended to verify the

vulnerability of the entryway system to this environment. However, I-MT load-

ing data were required to determine whether the design of the entryway and

blast door would be appropriate for future use in protective shelters. One-

tenth-scale models were fabricated to obtain loading data, which could then be

scaled, using cube-root scaling, to a I-MT event and used for design calcula-

tions of a full-scale entryway.

Two nonresponding models, one single entrance similar to the full-scale

structure and one pass-through tunnel, were constructed. The models were

fabricated from 1/4-inch steel plate with all joints welded for strength and

airtightness. Each model was instrumented with airblast gages and tested with

the entrances facing ground zero. A photograph of the 1/10-scale models is

shown in Figure 2.18.

14

cii

00 co

E-4-4

-*4 -0C4 L,

Ndii

A* 00 00 -

-44

cc N - 4.i

0 .0 CCu '-44 -4 (

41. 4Jto UV V

U) 0-

C.) P4 cn \s0o 0

" "4 Vn WLn

rii

v-a Cu 0 C 04J (n..'i, ~ic 00 .0 00 r-4

r-4 ,0-41 En \0 N4 ON V)

$4 r- N' -

F- I -44

5- '4 N 0 0

00 C n00-r4

- r

-4 -u

0) .- 4 .,4t

N -~ N 5

,BLAST

Figure 2.1. Elevation view of entryway.

i6

16

Fiur 2..Cag-oera enfo

enrwyineir

I1

PEAK PRESSURE =142.38 (PSI)

-100usc-

C0.50

0-0 20 40 60 80 100 120 140 160

TIME, MSEC

Figure 2.4. Pretest predicted loading historyfor blast door.

#3 U -STIRRUPS @ 1?" OFFSET

#3 TEMPERA TURE STEEL #4 12" EACH FACE-,',

Figure 2.5. Typical slab reinforcement details.

18

41

0I~'4.4GJ'

1.4

.9-4

0-@

41 o

0 4)

G00

19 .

Figure 2.8. Reinforcement of stairwell walls;underground chamber complete.

Figure 2.9. Finishing concrete in stairwell roof.

20

Figure 2.10. Backfill placement around completed structure.

STEEL CHANNEL>

TYPE 1 ,

p = p = 0.5%

TYPE 2 [." *I STEEL PLATE

TYPE 3 ,STEEL PLA TE

Figure 2.11. Blast door configuration concepts.

21

'AMM.

* �

q * -.1* .9 . L&J

* *.. 14J

I'. � * (4.b.'. h

I-.uJ

'4 �**�'*�* * C')* .A .

.4.'.. c�

C') ..- .d*--. g�. -

U)14: * ** -4

A

0*

4.. 4A* . * * 00

A '':...,.-A ' . * ** S.i

V St k '.5* 4 -.5 U)

'-40

A 0

6

b *� �*?�* .. :�..' .4�5U)

A" ***''.�.* Z� * .b.' * . ,.. * * CJ

* £4 * (4 e.J

I-.. -J 4)

A. 0 � * 1-4

IJj & ?a"��'-Ma. . 00

4

b .1IL. .4.1 1�

44 * 9.*.9..

Jr

22

Li

C

0-

C

*

*

V23 V.

0.4

Y (MAX) 0.36"

ImI.-

95• 0.24

0.1 " Y (MAXm) a 0.36

0

0 00.3

0

0. YPRM=0.0

TIME, SEC

Figure 2.14. Pretest blast door response prediction.

24

•; • 3/16" STEEL PLA TE

COMMERCIALDOOR

W 6x 12

"38" ANCOR L T

RIC COL UMN

Figure 2.15. Cross section of commercial door and supports.

25-

25

II

W O O N.v.. .

v Figure 2.16. Commercial door (on left, open)with support beams in place.

26

- " ". - : . .- , - ""X• ; ' -• - •'aL"., ' is•

,.A , '. sA '• : -" • ' , •. .. .. , • ,,

IfI

I Figure 2.17. Commercial door (on left, open) with

I support plates in place.

if 27

,j- ,

'9.

~Uri I

"dl~

71N

* 28

CHAPTER 3

EXPERIMENTAL PROCEDURE

3.1 DIRECT COURSE

The DIRECT COURSE event was a high-explosive (HE) test sponsored by the

DNA in October 1983. A simulated nuclear weapon airblast and ground motion

environment were provided by the detonation of 609 tons of an ammoniun nitrate-

fuel oil (ANFO) mixture at a height-of-burst of 166 feet. The airblast ef-

fects from the detonation of 609 tons of ANFO are approximately equivalent to

the airblast effects from the detonation of a I-KT nuclear device or the deto-

nation of 500 tons of TNT.

The explosive charge was placed in a spherical fiberglass container,

35 feet in diameter, and suspended from a rigid steel column. A photograph of

the charge tower assembly is shown in Figure 3.1.

3.2 TEST PLAN

The entryway test structure was constructed and instrumented during June-

August 1983. After construction and instrumentation were completed, backfill

was placed in 1-foot lifts around the structure up to the existing ground

level. Backfill material consisted of a sandy clay. A photograph of the

entryway and models in place prior to thL test is shown in Figure 3.2. The

closures are shown ia Figures 3.3 and 3.4.

Figures 3.5-3.7 are instrumentation plans showing all airblast gages used

in the test. The airblast gage behind the commercial door, No. P-8, was ren-dered inoperable prior to the test when its cable was severed during construc-

tion. Hence no airblast data are available for the area behind the commercial

door. The airblast gages were Kulite V5 92 pressure gages with a maximum

range of 200 psi.

29

3:t ý

-4-

30

.-4

C

a

4W

-u

Cd)

C

'4 0-

C�

c-c-C-Cd)

C

-C

CC C-4 0

'�1 -'04 -C

.4 vi 4 C

N

Cc4' I

j� t�;

31C.4

-t

A

A

Figure 3.3. SurfaCe view4 of full-scale entryway

(closures

on left arnd right at bottom Of tunnel).

-32

MW m 0-M 0 m : -i

Cad

li

1All

Figure 3.4. Reinforced concrete blast door in place.

33

6'

P2

23'-6"

Figure 3.5. Instrumentation of full-scale structure.

-r

34

IPll

GZ

Figure 3.6. Instrumentation of dead-end tunnel1/10-scale model.

P13

IP15 I P14 IP12GZ

Figure 3.7. Instrumentation of pass-through tunnel1/10-scale model.

35

CHAPTER 4

RESULTS

4.1 DATA DISCUSSION

All airblast data were recorded on magnetic tape and later reduced to

digital format. A "sample and hold" technique was used to digitize the data.

For digitizing, data records were started at the time of detonation. Each of

the pressure record3 was divided into 200,000 uniform time steps per second

and sampled at the end of each step.

The location of the test structure was at a higher-than-predicted pres-

sure level. Two surface-flush gages at ground level, P1 and P2, recorded an

average maximum overpressure of 69 psi. Hence the pressures recorded inside

the entryway were also higher than those predicted. The maximum pressures

recorded on the entryway end wall and on the blast door were 180 psi and

159 psi, respectively.

Complete pressure records for each of the airblast gages are shown in

Appendix A. Gage P8 was inoperable prior to the test. Zero time on each of

the records is the time of detonation.

4.2 STRUCTURAL RESPONSE

Although the roof and walls of the entryway suffered cracking and some

permanent deflections, there was no structural failure. The stairwell walls

had large cracks along the roof and floor joints, and smaller vertical cracks

along their height. The end wall, which received the most severe loading,

suffered the most damage. Large cracks formed from the floor to the roof

along each wall/door support joint. The end wall was displaced a maximum of

about 2 inches on the east edge and 1-1/2 inches on the west edge. The roof

exhibited minor cracking along its entire length but was largely undamaged. A

posttest surface view of the entryway is shown in Figure 4.1. Wall and roof

. ,damage are shown in Figures 4.2 and 4.3.

Upon examination, the blast door showed no signs of damage. The exterior

concrete face of the door was intact and had no cracks. The seal surrounding

the door's edges was slightly deformed but was not torn. The pressure record

from gage P7, immediately behind the door, indicates that there were no pres-

sure leaks at the door's edges. The door's hinges were undamaged and the door

36_

could be easily opened and closed again, as shown in Figure 4.4. The center

of the door had a permanent deflection of about 0.18 inch (the door was

checked for distortion prior to the test).

The commercial door was completely destroyed during the test. The door

and each of the steel plates supporting it were bent around the wide-flange

beams, so that large gaps were left between door and frame at either end of

the door. As shown in Figure 4.5, the door was obviously inoperable. One of

the steel support plates is shown in Figure 4.6. The pressure records for

gages P5 and P6 should have been nearly identical, had the commercial door

survived. However, comparison of the pressure records for these gages seems

to indicate that the commercial door failed very early (about 10 ms after

initial loading).

The 1/10-scale models were intact after the test and showed no signs of

displacoment or rotation. The amount of dust and dirt that accumulated in the

J ;•models during the test was insignificant.

4.3 STATIC TEST

Static loading of a typical blast door section was conducted at WES to

examine the mode of failure of the blast door when loaded to failure. The

test specimen was a typical 18-inch-wide section taken from the door's width0$ and was tested as a one-way slab, simply supported, subjected to a two-point

loading.

A longitudinal crack formed from the left edge of the test section to the

left load point on the top surface of the test specimen very early in the

test. When loaded to approximately 24,000 pounds, a diagonal crack formed on

the left end of the test section, and •he slab abruptly failed (Figure 4.7).

As seen in Figure 4.7, the slab failed in diagonal tension, an undesir-

able mode of failure. The static test indicated that additional shear rein-

forcement near the door supports would be needed to insure ductile behavior at

high overpressures.

The equivalent uniform load necessary to cause the same moment at the

center of the test section due to a two-point load of 24,000 pounds is approx-

imately 49.4 psi. The equivalent uniform load necessary to cause that same

moment at the center of the full-scale door, simply supported on all four

sides, is only 57 psi. The calculations are obviously not in agreement with

37

the measured results of the DIRECT COURSE event, where the door survived a

pressure of 159 psi.

The initial concrete cracking in the test slab was probably due to a lack

of confinement at the edges of the slab, which is not a problem in the full-

scale door. How much influence, if any, this initial crack had on the final

results of the static test is hard to determine. The conclusion drawn from

this test is that the shear reinforcement should be modified in the full-scale

door to insure a ductile mode of failure.

38

38

Figure 4.1. Posttest surface view of entryway.

39

Figure 4.2. Damage to stairwell roof immediately above landing.

Figure 4.3. Damage to stairwell roof.

40

.4 ..... ....-. ~ !

0

-4 0

41.

.1Z4

4 -0

14 .J

0

u- 0

~c3

WWI~

42

Fiur 4..Dmg ocmecaldo upr.pae

44

771.

Figure 4.7. Failure of test slab; static test.

44

AA

lii

"CHAPTER 5

ANALYSIS

5.1 VERIFICATION OF PREDICTIONS

5.1.1 Airblast

Since the pressures recorded at the tunnel entrance were higher than

those predicted, the measured internal entryway pressures were also higher

than the initial predictions. Revised internal pressures were calculated

based on the measured pressure data at the tunnel entrance with the following

input parameters:

Peak pressure = 69 psi

Positive phase duration = 107 ms

Impulse = 1.48 psi-s

Comparisons of posttest pressure calculations with actual recorded data

are tabulated below:

Airblast Actual Peak Calculated PeakGage Pressure, psi Pressure, psi

P4 180 166P5 159 158PlO 185 235PI1 153 235P13 65 75

The results of these calculations show close agreement between measured and

calculated pressures for the full-scale structure and the pass-through 1/10-

scale model, while the calculated pressures for the closed-end model were

overpredicted. Calculated positive durations were also reasonably close to

the measured values (Figure 5.1).

A• Comparison of calculated and measured pressures inside the entryway gave

assurance that input parameters for the design event (1 MT, 50 psi) would

yield a reasonable estimate of the airblast record inside the entryway during

that event.

5.1.2 Blast Door Response

Since the peak pressure on the blast door wou higher than that predicted,

the response of the blast door would be expected to be slightly more severe

than pretest calculations indicated. A single-degree-of-freedom response

45

15analysis was again performed for the blast door with the airblast record

from the center of the door input as the loading function. For this analysis,

the door was considered lightly damped (3 percent of critical damping). Re-

sults of this analysis are shown in Figure 5.2. The calculated maximum re-

sponse of the door was 0.45 inch at 8 ms after the door was initially loaded,

resulting in a ductility of about 1.7 and a permanent deflection of about

0.18 inch. Recall that the measured permanent deflection in the door was also

about 0.18 inch.

Since both the internal pressure calculations and the blast door response

predictions compare favorably with the measured data, response predictions due

to other weapons and/or pressures should approximate the response with little

error.

5.2 PREDICTING RESPONSE TO OTHER WEAPONS/PRESSURES

The DIRECT COURSE event provided a I-KT simulated nuclear airblast en-

vironment from which response and pressure predictions could be verified.

However, survival of structural elements in a l-KT environment does not guar-

antee survival in a 1-MT environment at the same overpressure level. Airblast

predictions for a I-MT, 50-psi event were necessary to verify the surviva-

bility of the blast door in that environment.

Internal tunnel pressures were calculated for a 1-NT, 50-psi event with

the following input:

Peak pressure = 50.0 psi

Positive phase duration = 964 ms

Impulse = 12.4 psi-s

The predicted loading history for the blast door is shown in Figure 5.3. The

calculated peak pressure on the door is 165 psi. Note that this peak pressure

is substantially higher than the peak pressure of 142 psi predicted for the

I-KT, 50-psi overpressure level at the DIRECT COURSE event. This is because

the airblast associated with a 1-KT event decays much more rapidly than the

airblast from a 1-MT event at the same overpressure level. Hence, the inci-

dent pressure at the closed end of the entryway will be higher for a 1-MT

event than for a I-KT event, and the reflected pressures at the same point

will be higher by an even larger margin.

Response calculations for the blast door were performed with input from

Figure 5.3, with the following results:

46

IMaximum deflection = 0.55 inch

Ductility, p = 2.0 (see Figure 5.4)

Permanent deflection = 0.28 inch

These calculations indicate that the blast door will sustain very light damage

and should remain completely serviceable when subjected to a I-MT, 50-psi air-

blase environment. (Recall that the calculated ductility from the DIRECT

COURSE event was about 1.7.)

Although the blast door will survive the airblast effects of a 1-MT,

50-psi event, a slightly higher surface overpressure with a worst case orien-

tation will cause substantially greater damage. For example, a 1-MT event

with a surface overpressure of 60 psi will result in a peak pressure of

204 psi at the blast door with a duration of about 900 ms. As the ultimate

resistance of the door is about 180 psi, this load would very probably result

in the complete collapse of the door.

When a shock wave strikes the end wall of the dead-end entryway, a re-

flected pressure is instantly developed on that surface. The magnitude of the

reflected pressure varies from about double the applied pressure to greater

than a factor of 8 times the applied pressure, depending on the magnitude of

the incident pressure. Since the peak reflected pressure acting on the door

in a dead-end tunnel is so sensitive to changes in the surface overpressure,

it may be desirable to consider a pass-through tunnel system, in which the

shock wave is allowed to flow through the tunnel past the closure.

5.3 PASS-THROUGH ENTRYWAY

A pass-through entryway system (Figure 5.5) similar to the 1/10-scale

model tested at DIRECT COURSE was evaluated to determine its survivability and

cost relative to a dead-end entryway. The ANSWER computer code was used to

determine the airblast inside the tunnel.

Airblast calculations indicate that the worst case orientation for a pass-

through entryway is with one opening facing ground zero. Comparison of inci-

dent to peak pressures for dead-end and pass-through entryways is shown in

Figure 5.6.

Response calculations for the blast door in a pass-through entryway were

performed for various overpressure levels with the following results:

47

Calculated Maximum Response of BlastP psi Peak Pressure Door in a Pass-Through Tunnel,so, on Closure, psi in.

50 77 0.15

100 142 0.29

130 180 0.44

135 186 1.2

140 192 4.5

150 204 14.5 (probable collapse)

These calculations show that the blast door, when placed in a pass-through

entryway, should survive the airblast effects of a peak surface overpressure

(P so) of about 135 psi. Survivability of the shelter closure at 135 psi

yields a decrease in the lethal radius from ground zero of about 35 percent,

or about 1,500 feet. While this difference may seem insignificant, inclusion

of a pass-through entryway would obviously provide a beneficial factor of

safety for a 50-psi-rated shelter.

A rough cost analysis of the two entryway systems examined indicates that

the pass-through entryway could be constructed for an additional 60 percent

above the cost of the dead-end entryway. This figure would approach 50 per-

cent if the stairwell formwork is reused on the mirror-image second stairwell.

4

4.5 180 -

4.0 160 --2

3.5 140 -

3.0 - 120 -

U 2.5 -,100

xIJ

' 2.0 -I 80-J

- \ -CA L CULA TED DATA

• 1.5 60 -II

1.0 40 -

0.5 20 - \

. 0 0- • _-.-

-0.5 -20 I I I I I I I I I

100 120 140 160 180 200 220 240 260 280 300

TIME, MSEC

* Figure 5.1. Comparison of measured to calculated pressuredata for blast door loading.

49

0.5

Y (MAX) 0. 45"

0.4

-0.3

z

0.

0~

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10TIME, SEC

Figure 5.2. Calculated response of blast dooi to DIRECT COURSE loading.

50

200

PEAK PRESSURE = 164.90 (PSI)

IS0

wD 100

w

50

50

_,0 -II I I I

0 100 200 300 400 500 600 700 800

TIME, MSEC

Figure 5.3. Calculated loading history of blastdoor for I-lT, 50-psi event.

0.8

0.6 Y (MAX) = 0.55"

z

2

•'. • 0.4LU

04

Y (PERM) =0. 28"

0.2

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10TIME, SEC

Figure 5.4. Calculated blast door responsefor 1-MT, 50-psi event.

51

Figure 5.5. Pass-through entryway sYstem.

400

DEAODE,cVD

300000

wj20K 0.

20 406100002 1 0 1 0 8 0

SURFACE OVERPRESSURE, PSIFig re .6. Co m ari 0~ Of incident to peak pressure on Closurein dead-end and pass-through entrrway sYstems.

5n

CHAPTER 6

CONCLUSIONS AND RECOMMENDATIONS

6.1 CONCLUSIONS

The blast door evaluated will successfully withstand peak pressures of

about 160 psi, as demonstrated in the DIRECT COURSE event. Since the duration

of the airblast from a 1-KT event at the 50- to 150-psi overpressure level is

very long relative to the natural period of vibration of the door (about

5.5 ms), the response of the door to a peak pressure of 160 psi should be

roughly equivalent to that measured at DIRECT COURSE, regardless of the dura-

tion. Hence, the blast door is an adequate design for a I-MT, 50-psi e~ent

when placed in a dead-end tunnel. The blast door evaluated would provide ade-

quate protection from much higher overpressures if used in a pass-through tun-

nel system, which would allow the blast wave to flow through the tunnel past

the closure without striking any large reflecting surfaces. For example, a

1-MT, 135-psi event would result in a peak pressure on the closure of about

186 psi and a maximum door deflection of about 1.2 inches in a pass-through

_innel (compared to 520 psi and collapse in a dead-end tonnel). Existing

commercially available doors capable of withstanding 50 to 150 psi range in

price from about $5,000 to $51,000 each, while reinforced concrete blast doors

could be built for about $1,000 each, or $900 each if purchased in lots of 20

7/ or more.

A static test of an 18-inch-wide typical section from the blast door sub-

jected to a two-point loading indicates a brittle mode of failure. What in-

fluence, if any, the lack of confinement at the longitudinal edges of the test

specimen had on the failure mode is hard to determine. Additional shear rein-

forcement should be added to insure ductile behavior of the door at relatively

large deflections. If the 3/8-inch bars used as shear reinforcement are re-

placed by 1/4-inch welded studs with smaller spacings, the shear reinforcement

requirements can be met without significantly altering the cost of the door.

The fire-rated door with special supports which was evaluated was a typi-

cal commercially available exterior door. Though this door was heavily rein-

forced with wide-flange beams and steel plates, it was completely destroyed

during the DIRECT COURSE event, apparently failing about 10 ms after initial

loading. The support beams survived the blast, but the door and steel plates

53

were unable to support the load between each beam span. A much thicker, and

thus heavier and more expensive, steel plate would be required to insure sur-

vival of this closure concept. Placement of the supports prior to the test

was a cumbersome process and required an undesirable amount of time, espec-

ially when considered in the context of an imminent nuclear strike. The cost

of the commercial door, door frame, and fabrication of the supports was about

$750. With thicker, more expensive, steel plates the door might be made to

survive, but the problem of placing the supports would be much worse. At the

pressure levels examined in this test, standard commercial doors are not a

practical alternative for blastproof shelters.

The entryway wall and roof slabs survived the DIRECT COURSE event with

only minor cracking, and the structure remained completely intact. As ex-

pected, the greatest damage occurred at the slab joints, since the net effect

of the interior and exterior loads was to punch out each corner of the tunnel.

In no case was the damage extensive enough to warrant changes in the slab de-

sign. The slab design tested, which was 6 inches thick with principal rein-

forcement consisting of 1/2-inch bars spaced at 12 inches on center, is ade-

quate for a 1-NT, 50-psi event. Higher overpressures would require slightly

thicker walls, but this parameter is not as sensitive to changes in peak pres-

sure as might be expected because of the additional strength provided by the

soil backfill.

Calculations of airblast in the tunnel were performed with the ANSWER

computer code, which was developed in the Explosion Effects Division of the

Structures Laboratory at WES. Predicted peak pressures inside the full-scale

structure were remarkably close to those measured at the DIRECT COURSE event,

and predicted durations and impulses were equally accurate. The ANSWER code

has proven to be a valuable tool for predicting airblast characteristics in-

side a tunnel.

6.2 RECOMMENDATIONS

Based on the results of this project, the following recommendations are

made:

1. Given the uncertainties of predicting the airblast associated with nu-

clear detonations, a pass-through entryway system is recommended over a dead-

end tunnel to insure a factor ol safety for the shelter closure.

2. Concepts such as the commercial door evaluated in this project should not

54

be used when the design overpressure is greater than about 25 psi. The cost

of upgrading a standard door can be larger than the cost of a reinforced con-

crete door.

3. Additional static tests of the blast door should be conducted to deter-

miae the minimum amount and spacing of sheai reinforcement needed to insure

ductile behavior.

4. The blast door evaluated is recommended for use in a 50-psi shelter with

modifications to the shear reinforcement. For reasons of economy, welded

shear studs should be used in place of bent reinforcing steel. These shear

studs should be spaced at ne> more than 1-1/2 inches on center near the door

supports to insure ductile behavior at higher overpressures.

5. Shear stirrups may be safely omitted from the entryway walls, but should

be included in the roof slabs. A minimal number of stirrups should be used in

the walls to keep the principal reinforcement properly aligned during concrete

placement.

6. Backfill placement around the entryway should be tightly controlled to

prevent excessive outward wall mcvement.

55

REFERENCES

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2. G. H. Albright, J. C. LeDoux, and R. A. Mitchell; "Evaluation ofBuried Conduits as Personnel Shelters"; Technical Report No. WT-1421, Opera-tion Plumbob, Project 3.2, July 1960, U. S. Naval Civil Engineering Labora-tory, Port Hueneme, Calif.

3. G. H. Albright and others; "Evaluation of Buried Corrugated-SteelArch Structures and Associated Components"; Technical Report No. WT-1422,Operation Plumbob, Project 3.3, February 1961, Bureau of Yards and Docks,U. S. Navy Department, Washington, D.C., and U. S. Naval Civil EngineeringLaboratory, Port Hueneme, Calif.

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7. N. Fitzsimons; "Evaluation of Industrial Doors Subjected to BlastLoading"; Technical Report No. ITR-1459, Operation Plumbob, Project 31.4,August 1958, Federal Civil Defense Administration, Washington, D.C.

8. R. S. Cummins, Jr.; "Blast Door Tests for the Federal Republic ofGermany"; Miscellaneous Paper N-76-13, September 1976, U. S. Army EngineerWaterways Experiment Station, CE, Vicksburg, Miss.

9. J. L. Petras and others; "Test of the Donn Corporation Blast Shel-ters, A Condensed Version of the Final Report, Structures Tested in the MisersBluff Event, November 1978"; Donn Incorporated Staff.

10. J. D. Stevenson and J. A. Havers; "Entranceways and Exits for Blast-Resistant Fully-Buried Personnel Shelters"; IITRI Project No. M6064(3), Sep-tember 1965; Illinois Institute of Technology Research Institute, Chicago,

11. G. A. Coulter; "Attenuation of Peaked Air Shock Waves in Smooth Tun-nels"; BRL Report No. 1809, November 1966; Ballistics Research Laboratories,U. S. Army Research and Development Center, Aberdeen Proving Ground, Md.

12. S. Hikida and C. E. Needham; "Low Altitude Multiple Burst (LAMB)Model, Volume 1: Shock Description"; Report No. S-CUBED-R-81-5067, DNA #58632,June 1981; Systems, Science, and Software, Albuquerque, N. Mex.

A

.56

13. G. A. Coulter; "Blast Loading in Existing Structures-BasementModels"; Memorandum Report No. 2208, August 1972; Ballistic Research Labora-

tories, U. S. Army Research and Development Center, Aberdeen Proving Ground,Md.

14. Civil Nuclear Systems Corporation; "The Air Force Manual for Designand Analysis of Hardened Structures"; Technical Report AFWL-TR-74-102, October1974; Air Force Weapons Laboratory, Kirtland Air Force Base, N. Mex.

15. J. M. Biggs; "Introduction to Structural Dynamics"; 1964, McGraw-Hill Book Company, New York, N. Y.

16. Committee on Structural Dynamics, Engineering Mechanics Division,American Society of Civil Engineers; "Design of Structures to Resist NuclearWeapons Effects"; Manuals of Engineering Practice No. 42, 1961; AmericanSociety of Civil Engineers, Now York, N. Y.

I

57

APPENDIX A: PRESSURE DATA

5,

59..

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