5) plumbbob nv test blast-loading-and-response

7/27/2019 5) Plumbbob NV Test Blast-Loading-And-Response

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WT- 1 4 2 0OPERATION PLUMBBOB- PROJECT 3 . 1

BLASJ LOADING AND RESPONSE O f UNDERGROUNDCONCRETE- ARCH PRO7ECUVE STRUCTURES (U,. ,--- ....

W. J. Flathau, Proje ct OfficerR. A. BreckenridgeC. K. WiehleU. S. Army Engineer Waterways ExperimentCor ps of Engine ersVicksburg, Mississippiand

Station

U. S. Naval Civil Engineering LaboratoryPo rt Hueneme, Califo rnia

hibited by law.3 - 4 AL


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A0STRACTThe purpose of this project was to evaluate the effects of a kiloton-range nuclear a irbu rst onburied reinforced-concrete arc h stru ctu res located in the high overp res sur e region.were to be considered as personnel protective stru ctures, they were evaluated for their r esi st-ance to blast, radiation, and mis sile hazards.Four stru ctur es, with the top of the ar ch crown 4 feet below ground surfac e, were positionedat th re e different over pres sure ranges for the Pri sc il la Shot, a 36.6 kt, 700-foot-high bur st. Al lfour a rc he s were s emic ircu lar in cross-sect ion, with an inside span of 16 feet and an arch thick-ne ss of 8 inches. Thr ee of the s tr uc tu re s were 20 feet long and the fourth was 32 feet long. A20-foot-long st ru ct ur e was placed at each of the predic ted ground-su rface air overpr essur e levelsof 50-, l oo - , and 200-psi, while the 32-foot-long st ru ct ur e was placed at the predic ted ground-surface air ov er pr es su re level of 50 psi. It was specified that all str uct ure s be designed to with-stand a 50-psi peak blast overpressure using 3,000-psi concrete. The four st ruc tur es were in-strumented for measurements of air overpres sures, ear th pre ss ure s, deflections, accelerations,strains, radiation, and missile s.

only minor damage, all remaining structurally serviceable. The structure at the 199-psi pre s-su re level exhibited obvious crackin g of the floor s lab and minor tension cr acking of the ar chintrados; however, even though the damage was slight, the peak floor s la b acce leratio n of 13.4 gmay have been physiologically hazardous t o personnel.arch itself underwent appreciable bending.surface aided in developing the tra nsmiss ion of the compressive load.capacity of the structures at the time of the P ri sc il la Shot exceeded the specified design capacityof 50-psi ground-surface air overpressure.fo r more than tentative conclusions about the ultimate capacity of the str uctu re. A retest athigher ov er pr es su re s should furnis h the additional data needed.

The entranceway of the shel ter w as designed to exclude air ove rpr ess ure only, thereforeconsiderable radiation was admitted; however, thi s entranceway could eas ily be modified togreatly red uce the amount of radiation trans mitt ed through it to the interi or of the stru ctur e.Also, the entrance is of the emergency type, fo r economy, and would be secondary to a rapidacce ss entrance in an actual protective shelter . There were no missile and apparently no dusthazards in any of the st ruct ures .shape for res isting the effects of a kiloton-range nuclear air burst.

Since thes e

The four str uct ure s received actual air ov er pr es su re s of 56, 124, and 199 ps i and suffered

It was obser ved that the ea rt h loading around the a rc h surfa ce was not uniform and that theThe passive pr es su re exerted by the soil on the ar ch

Subsequent analysis , allowing fo r the actual concre te str engt h of 4,500 psi, showed that theConsequently, the data obtained a r e not sufficient

This test showed that an underground reinforce d-concr ete ar ch is an excellent structur al

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FORWORDThis rep ort pres ent s the res ult s of one of the 43 project s comprising the Military Effects Pro -gr am of Operation Plumbbob, which included 28 test detonations at the Nevada Test Site in 1957.

Fo r overa ll Plumbbob military-effects information, the re ad er is ref err ed to the SummaryReport of the Direc tor, DOD Te st Group (P ro gr am s 1-9), WT-1445, which includes : (1) adesc riptio n of each detonation, including yield, zero-poin t location and environment, type ofdevice, ambient atmospheric conditions, etc. ; 2) a discussion of project re sult s; (3) a summaryof the objectives and re su lt s of each projec t; and (4) a listing of project r ep or ts for the MilitaryEffects Program.

This project w a s a joint, coordinated effort between the U. S. Army Engineer W aterways Ex-per iment Station (WES), Cor ps of Engineers, Vicksburg , Mississ ippi, and the U. S. Naval CivilEngineering Laboratory (NCEL), P or t Hueneme, California. The projec t was under the generaldir ect ion of E. P. Fortson, J r . , F. R. Brown, and G. L. Arbuthnot, Jr. ;Captain R. L. Hunt,Corps of Eng ineers, was in dire ct supe rvisio n of the project, with W. J. Flathau designated asthe projec t officer. Special recognition is given to Captain E. S. Townsley who contributedvaluable technical support and assis tan ce during the prepa ration of the final repor t. NCELparticipation in the project was under the ge neral dire ction of Dr. W. M. Simpson and S. L. Bugg,with C. K. Wiehle and R. A. Breckenridge designated as co-project representatives. Other en-gineers making substantial contributions to this project were W. A. Shaw and J.0. Rotnem,NCEL, and Sp 3 J. D. L aa rman and Pfc R.A. Sager , WES.

Special credit is due Major Ja me s Irvine, Jr., USA, and Captain C. A. Robertson, USA,fo rm er ly ass igned to the Office, Chief of Engin eer s, and CAPT A. B. Chilton, USN, assignedto the Bureau of Y ards and Docks, for th ei r effor ts during the initiation of this proje ct.Massa chuse tts Institute of Technology provided valuable information in formulating the pro ject.Their advice and assistance are gratefully acknowledged.

4

Consultation with Dr. N.M. Newmark of the Univers ity of Il linois and Dr. C. H. Nor ri s of the


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APPENDIX E INTERIOR MISSILE AND DUST HAZARD - - - - - - - - - - - - - - - - - - - - - 120

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FIGURES1.1 Assumed ove rpr ess ure distributions on underground arc hes - - - - - - - - - - - - - - -1 .2 Loadings assumed by the fi rm of Holmes and Narver , Inc. - - - - - - - - - - - - - - - -2.2 P la na nd el ev at io no f typical s t r u c t u r e - - - - - - - - - - - - - - - - - - - . - - - - - - - - - - -2.1 Pro ject plot plan - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -2.32.4

Loading of model arch- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Model arch a fte r test - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

2.5 Typical backfill mat eria l of the 3.1 structu res - - - - - - - - - - - - - - - - - - - - - - - - -2.6 Compressive stren gth of concrete vers us age - - - - - - - - - - - - - - - - - - - - - - - - -2.7 Stress-strain c u r v e for concrete at shot time - - - - - - - - - - - - - - - - - - - - - - - - -2.8 Floor slab pri or to pouring concrete, Structure 3.l.c - - - - - - - - - - - - - - - - - - - -2.9 Reinforcing steel and for ms in place for arch, Structure 3.1.n - - - - - - - - - - - - -2.10 Completed str uct ure pri or to backfilling, Struc ture 3.1.a - - - - - - - - - - - - - - - -2.11 Instrumentation layout, Stru ctu res 3.l.a, b, and c - - - - - - - - - - - - - - - - - - - - -2.12 Instrumentation layout, Struc ture 3.1.n - - - - - - - - - - - - - - - - - - - - - - - - - - - -2-132.142.152-16

Interior views,Interio r views,Interior views,Interior views,

Structure 3.l.a - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - -Structure 3.l.n - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Structure 3.l.b - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Structure 3 .1 .~ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

2.17 Sample plot for double integration of accel eratio n recor d - - - - - - - - - - - - - - - -3.1 Peak transient earth pre ssu re, Structures 3.l.a, b, c , and n - - - - - - - - - - - - - -3.2 Peak transien t deflection, with res pec t to the cente r of the

floor slab, Structures 3.l.a, b, and c - - - - - - - - - - - - - - - - - - - - - - - - - -3.3 Peak transi ent deflection with res pec t to the springing3.4 Peak transie nt deflections with res pec t to the springing line,3.5 Permanent crown deflection with res pec t to the sprin ging line

of the arch, S tructu res 3.l.a, 3.l.b, an d3 .l .c . . . . . . . . . . . . . . . . . . . .3.6 Peak transient acceleration, Structu res 3.l.a, b, and c - - - - - - - - - - - - - - - - - -3.7 Adjusted double-i ntegration of Record A-3, Structure 3.1.b- - - - - - - - - - - - - - - -3.8 Adjusted double-integration of Rec ord A-4, Structure 3.1.b - - - - - - - - - - - - - - - -3.9 Adjusted double-integration of Record 1AV-10 (free -field ),3.10 Peak transi ent strai ns, Struc ture 3.1.n- - - - - - - - - - - - - - - - - - - - - - - - - - - - -3.11 Permanent concrete strains, Whittemore gages, Structure 3.1.n- - - - - - - - - - - -3.12 Total nuclear radiation dose profile, Struc ture 3.1.a - - - - - - - - - - - - - - - - - - -3.13 Total nuclear radiation dose profile, Structure 3.1.n - - - - - - - - - - - - - - - - - - -3.14 Total nuclear radiation dose profile, Structure 3.1.b - - - - - - - - - - - - - - - - - - -3.15 Total nuclear radiation dose profile, Struc ture 3.l.c - - - - - - - - - - - - - - - - - - -

line, Structu res 3.l.a, b, and c - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Structure 3.l.n - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Reference 12 - _ _ - _ _ _ _ _ - - - - - - _ - - - - _ _ - - _ _ _ - - _ _ - - _ _

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3.16 Postshot crac k survey, Structure 3.1.a- - - - - - - - - - - - - - - - - - - - - - - - - - - - -3.17 Posts hot cra ck survey, Struc ture 3.1.n- - - - - - - - - - - - - - - - - - - - - - - - - - - - -3.18 Postshot crack survey, Structure 3.1.b- - - - - - - - - - - - - - - - - - - - - - - - - - - - -3.19 Postshot crac k survey, Structure 3.l.c- - - - - - - - - - - - - - - - - - - - - - - - - - - - -3.20 Interio r views, Struc ture 3. l.q postshot- - - - - - - - - - - - - - - - - - - - - - - - - - - -3.21 Northeast cor ner , Structure 3.l .q postshot - - - - - - - - - - - - - - - - - - - - - - - - -3.22 Center floor looking north, Struc ture 3.l.c, postshot - - - - - - - - - - - - - - - - - - -3.23 Hatch cove r, Struc ture 3.l.c, postshot - - - - - - - - - - - - - - - - - - - - - - - - - - - - -4.1 Per man ent downward displacement of the 3.1 str uct ure s - - - - - - - - - - - - - - - - - -4.2 Sequential plot of ea rth pre ss ur e and deflection, Stru ctur e 3.1.b- - - - - - - - - - - - -4.3 Peak trans ient and perma nent deflections of crown with resp ect

to sprihging line, Section 111, Str uctu res 3.l.a, b, and c - - - - - - - - - - - - - -4.4 Tran sien t moment and thru sts, Struct ure 3.1.n - - - - - - - - - - - - - - - - - - - - - - - -4.5 Interaction diagr am fo r measured, design, and ultimate values

of moment and thrust, St ructure 3.1.11 - - - - - - - - - - - - - - - - - - - - - - - - - -4.6 Tran sien t springing line rea ctio ns fo r Structure 3.1.n- - - - - - - - - - - - - - - - - - - -4.7 Assumed tran smis sion of gamma radiation into the 3.1 str uc tur es - - - - - - - - - - -A.1B.1

Recommended idealized loadings - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Wiancko accelerometer- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -B.2 Schematic drawing of ac cele rom eter sensing mechanism - - - - - - - - - - - - - - - - -B.3 Wiancko-Carlson soi l pr es su re gage - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -B.4 Schematic drawing of soi l pres sur e-se nsin g mechanism - - - - - - - - - - - - - - - - - -B.5 Deflection gages: self -recor ding type to left; electron ic type to right - - - - - - - - -B.6 Self-record ing deflection gage rec ord ing unit - - - - - - - - - - - - - - - - - - - - - - - - -B.7B.8B.9

Small deflection gage cal ibratio n - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Calibration of accelerometer - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Soil pressure gage calibration - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

B. 10 Soil pr es su re gage in position at crown of S tructu re 3.1.b - - - - - - - - - - - - - - - -B. 11 Transie nt records of eart h pres sure , deflection, and accelerationB.12 Transien t rec ord s of earth pres sure , deflection, acceleration, andB. 13 Transie nt records of eart h pres sure , deflection, acceleration, andC.l Completed stru ctur e with eart h-pr essu re gages and str ain gagesC.2 Installation of an SR-4 trai n gage and an eart h-pr essu re gageC.3 Typical installation of the electr oni c and the mechanicalC.4 (a) Strain ver sus time, Structure 3.1.n - - - - - - - - - - - - - - - - - - - - - - - - - - - - -C.4 (b) Strain versus time, Struct ure 3.1.n - - - - - - - - - - - - - - - - - - - - - - - - - - - - -C.4(c) Stra inver sust ime, Structure 3.1.n - - - - - - - - - - - - - - - - - - - - - - - - - - - - .C.4 (d) Strain ver sus time, Structure 3.1.n - - - - - - - - - - - - - - - - - - - - - - - - - - - - -C.5 (a) Earth pre ssu re ve rsus time, Structure 3.1.n - - - - - - - - - - - - - - - - - - - - - - -C.5 (b) Earth pre ssu re ver sus time, Structure 3.1.n - - - - - - - - - - - - - - - - - - - - - - -C.6 (a) Deflection ve rsu s time, Stru ctu re 3.1.n- - - - - - - - - - - - - - - - - - - - - - - - - - -C.6 (b) Deflection ver sus time, Struc ture 3.1.n- - - - - - - - - - - - - - - - - - - - - - - - - - -C.6 (c) Deflection ver sus time, Struc ture 3. .n- - - - - - - - - - - - - - - - - - - - - - - - - - -D.l Location of the detector coordinate sy stem in S tructur es 3.1.a and b- - - - - - - - - -D.2 Location of the detecto r coordinate syste m in Struc tur e 3.l.c - - - - - - - - - - - - - -D.3 Location of the detector coordinate sy stem in Str uctu re 3.1.n - - - - - - - - - - - - - -G.l Reinforced concrete arc h structu re, floor plan and sections - - - - - - - - - - - - - - -

for Structure 3.l .a - - - - - - - - - - - - - - - - - - - - - _ _ - - - - - - - - - - - -- - - -ai r ove rpre ssu re for Structure 3.1.b - - - - - - - - - - - - - - - - - - - - - - - - - -air overpres sure for Structure 3.l .c - - - - - - - - - -- - - - - - - - - - - - - - - -inplace _ _ _ _ _ - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _- - - - - -at the springing line - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -deflection gages - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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those se t forth in Reference 5. The analysis was performed to predict pres su re ranges fromground zero where (1)failur e of the str uct ure would not be expected (actual design level), (2 )prob able fai lur e would be expected, and (3) total fa ilu re ( colla pse) would be expected.mitted to an underground ar ch is uniform over the entire surfac e of the arch (s ee Figure 1.l.a).This type of p res sur e distribution resul ts in pure compression throughout the arch. If it is as-sumed that the overpress ure transmitted to an underground arch is not uniform, (se e Figu re1.l.b), then the arc h is subjected to combined bending and compres sion.a secondary loading is produced by the r esis tan ce of th e ea rth to the outward deflection of thearch.

The MIT design method (Reference 5) is based on the assumption that the ove rpress ure trans-

Under this assumption,The analysis made by Holmes and Narver was based on an assumption of the la tte r type.

1.3.1 Uniform Overp res sure Distribution. The following exce rpts from Section 421 (Reference5) set forth the general principles used in the design of the underground arch s tructur e for th isproject:

Page 11-7: The design of each element of the s tru ctu re for the stat ic plus dynamicearth overpressure is preceded by a preli min ary design of that element for the staticload s tre sse s to which it would normally be subjected. The stati c design should fol-low accepted design procedures and specifications.

Page 11-15: Arches, domes, and circ ular elemen ts ar e loaded practically uni-formly throughout by the earth overpressures and because of their great stiffnessunder this type loading the design is based upon a dynamic load factor of unity. .. Itis assumed f o r design purposes that the load over the ent ire surf ace of the arch , do me,or circular section is uniform and equal to the air-blast ove rpre ssu re on the groundsurface above the struct ure. The earth overpre ssure load curves on plane surface sbounding the shell su rface s, such as end walls of an arc h o r the top of a circular tank,ar e computed as for a simila rly located element of a rectangular structure.

Page 11-16: Design the main arch , dome, or cir cul ar element to support thestatic loading. . nvestigate the resistance of these elements to the static plus thedynamic load to which they a re subjected. The maximum dynamic load is handled a san additional static load and no dynamic analy sis is involved. It is assumed that thedynamic load is uniformly applied and that the element is very rigid under this typeof loading so that a dynamic load factor of unity is used.

1.3.2 Non-uniform Overp ress ure Distribution. Fo r a vertically applied dynamic overpr es-sur e, previous tes ts in Nevada indicated that the horizontal pr es su re on the vertical surface ofa relatively rigid rectangular structure is approximate ly 0.15 of the vertic al pre ss ur e (Refer-ences 6 and 7 ) .

Should the findings of Refere nce s 6 and 7 be sub stantid ed for an underground semici rculararch, then such an ar ch would be sub jected to bending, and its ultimate load-carrying capacitywould be influenced by its flexibility. A load applied to the arc h through the overlying ea rthma ss would produce a downward deflection of th e crown and an outward deflection of t he haunches.This outward deflection would be res ist ed by the s oil m as s and a passive pr ess ure would be de-veloped. The exer tion of the passive ea rth pres sur e would be beneficial, since a more favorablepr es su re distribution on the ar ch might res ult, depending on the flexibility of the str uct ure andthe compressibility of the soil. However, one requ ireme nt fo r such stru ctu ral behavior is thatthe arc h permit the deflection and still remain serviceable.

Some assumption must be made relativ e to the distribution of th e initial horizontal overp res-sure. Fo r example, it could be assumed to be a horizontal overp ressur e equal to some fractionof the vertical overpres sure, o r it could be a trapezoidal loading with the overpressure at thecrown being equal to the vertical ove rpress ure, and with the overpre ssure at the spr ing linebeing equal to some fracti on of the vertical ov erp ress ure . Holmes and Narv er made assump-tions that are shown in Figure 1.2.

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a . U n i fo r m , no d e f l e c t i o n b . N o n -u n i f o rmFigure 1.1 Assumed overpressure distributions on underground arches.

P 1 = o v e rp re s s u re a tg ro un d s u r f a c e 7

P1 ( s i n 0)

p 1 = R a d i a l o v e r p r e s s u r e d i s t r i b u t i o n P2 = R e s u l t i n g d e f l e c t i o n d e v e l o p sp a s s i v e e a r t h p r e s s u r eo l l o w i n g s i n u s o i d al v a r i a t i o n

Figure 1.2 Loadings assumed by the firm of Holmes and Narver, Inc.


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The following excerpts from the Holmes and Narver report (Reference 8) set forth the generalprinciples used in their preshot analysis of this project s underground struc ture:

In the case of semic ircular arch es, the load due to overp ress ure is assumed toact radially, following a sinuso idal variation , with a maximum intensity at the crownequal to the ove rpr ess ur e at the ground surf ace , and with zero intensity at the base.In addition to this primary pi loading which might be regard ed as being the loadpatte rn which would apply to a very rigid s tru ctu re, a secondary p2 load pattern isconsid ered, intended to approximate the load due to passive ear th pre ss ur e developedin the region of outward deflection of the arch. This is assumed as a radial sinus-oidal loading with maximum intens ity p2 at 0 =30 zero intensity at 0 =60 , andzer o intensity at the base of the ar ch where 0 =0 .ist ics and the flexibility of the a rch .

The stab iliz ing effect of the p2 loading is a function of the unknown soil character-

It was further stated that:

Several types of a rch failure a re possible (see Reference 9). An upper limitingvalue of the collapsing load would be obtained on the assumption that the loading is auniform radial pressure.Failure would then occur either by elastic instability, or by a compression failure inthe material.A second type would be fail ure due to unsy mmetric al loading resulting in highbending s tre ss es accompanied by minimum thrust.lower bending st re s s in conjunction with a high thru st.collapsing pres su re that is too high. The secon d type of fai lur e is not critical becauseof its extremely transient nature.condition.oidal type previously described.reduce the stru ctu re to a mechanism at failu re. In calculation of the stati c yieldresistance, allowance is made for the effect of axial thru st and the tribu tary e art hmass on the period of vibration.. .

[The assumption made i n Section 421 of Reference 5.1

I

A third type of failure would be a sym metri cal loading condition producing a muchThe first type of failure implies complete absence of bending stresses, giving a

This leaves the third type as the cr itical loadingThe load pattern assum ed to repr esen t the critic al loading condition is the sinus-Under the loading, yield inges ar e assumed to occur in sufficient number to

These Holm es-Narver assumptions concer ning the loading were used in the ir preshot analysisand have been refined in the ir postshot an alysis. The refinements are prese nted in Appendix A.

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Chapter2PROCEDURE

2.1 TEST STRUCTURESFour reinforced-concrete arch st ruc tur es were tested during Shot Priscilla , all placed

underground with the top of the crown 4 fe et below the ground su rface.semicirc ular in cro ss section, with an inside radius of 8 feet and a thickness of 8 inches. Threeof the st ru ct ur es were 20 feet long, while the fourth was 32 feet long.w a s included to as su re an unre strain ed section of arc h essentiall y free of end-wall effects, SOthat it could be determ ined how fa r and to what extent end walls affect ar ch action. This addedlength provided a favorable length-to- span ra tio of two to one.

The 32-foot-long str uc tu re (3.1.n) and one of the 20-foot-long st ru ct ur es (3.1.a) were placedin an a re a for which a ground-surface overpressure of 50 psi was predicted; the other two struc-tu re s were placed in a re as for which ove rpre ssu res of 100 ps i (3.1.b) and 200 ps i (3.l.c) werepredicted.Figur e 2.2 shows the plan and cr os s section of a typical stru ctur e.port. Also se e Table 2.1.

The four arch es wereThe 32-foot-long st ructure

The general location and shot geometry for the st ruc tur es are shown in Figure 2.1;Fo r clarity, the following definitions pertaining to ar che s ar e presented a s used in this re -

Springing line: Form ed by the inters ectio n of the a rc h with the floor slab.Crown: The topmost pa rt of the arch.Haunch: The si de s of an ar ch between the springing line and the crown.Intrados: The inside surface of the arch.Extrados: The outside surf ace of the arch.Arch span: Horizontal distance from sp ringing line to springing line.

2.1.1 Design. The structura l design was accomplished by the fi rm of Ammann and Whitneyunder Contract No . DA-22-079-eng-195.buried so that the crown would be 4 feet below the natural ground surf ace; (2) the ar ch be semi-cir cu lar ; (3) the st ructure be designed to resist the effe cts of a 50-psi ground-surface air over-pr es su re resulting from the detonation of a 30-kt device 500 fee t aboveground; (4) the compressivest ren gth of the co ncrete be 3,000 ps i; and (5) he principles s et forth in E M 1110-345-414 to 421(Reference 5) be followed. The res ul ts of the design accomplished by Ammann and Whitney arecontained in Reference 10.orde r to provide a structu re suitable to res is t both static and transient loads, a thicker arc hwas selected. The final str uct ure was intended to be a standard-type structure that could beused by the armed services if it proved satisfactory in a full-scale test.

Although Section 421 of Refe ren ce 5, which conc erns below-ground st ruct ure s, speci fies adynamic load fac tor of one, Ammann and Whitney elec ted to use a dynamic load facto r of two,basing their decision 011 the discussion in Section 420 of Reference 5, which concern s above-ground arches.plying: design ov erpress ure tim es dynamic load factor times ar ch span.

This contract stipulated that: (1) the structure be

The procedure in the manual dictated a very thin a rch to resist the transient load, but in

Ammann and Whitney computed the ov erp ressure load per linear foot of a rc h length by multi-Total load = 50 X 2 X 144 X 16.67 = 240,000 Ib/ft

The load at each reaction would then be:

17


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- N -

A C T U A L P E A K O V E R P R E S S U R E,PREDICTED

P L A N

-/360'

P R f D I C T E D 39.5 t( A C T U A L ) 36.6K t

.CCh

E L E V A T 1ON

Figure 2.1 Project plot plan.

18


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AL

*3 EF1#3@/2:] I *6 TOP d BOTT O P d B O T SECTION A -A

SECTION B -BFigure 2. 2 Plan and elevation of typical str uct ure .

19. i . I,


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240 0002 x 12eaction =- 10,000 lb/inInasmuch as Reference 5 assumes a uni form loading, th er e would be no bending, and thus the

thickness needed to r es is t the blas t would be determined by dividing the reaction by the ultimatedynamic compres sive st rength of the concrete:

I= 3 inches, where0,0003,000 X 1.3 X 0.85equired thickness =

the ultimate static compressive strength is 0.85 X 3,000 psi , and the 30-percent strengt h in-crease is assume d for dynamic (blast) loads. However, to meet the American Concrete Insti-

TABLE 2.1 EXPECTED DEFLECTIONS

I

Crown Deflections Haunch Deflect ionsRadial Radial Tangential

Structure (inward) Tangential (outward) (downward)inches inches inches inches

0.2 to 0.4. 1 . a 0 . 5 to 0. 9 0 0.3 to 0. 63 . 1 . b 0.9 to 17.0 0 0.6 to 10.0* 0.4 to 7.0*3 . l . c t 1 7 . 0 0 10.0 7 .O

* Passive earth pressures will probably reduce the upper values noted above.t Collapse is anticipated. Maximum deflections cannot be established.tute (ACI) code re quir emen ts for th e specified 3,000-psi concrete, an arc h thickness on theor de r of 8 inches (depending upon s pecific design) was found to be the prac tica l minimum fo rstat ic loads alone. This minimum value was established by means of a cracked-section analysis.ters transversely and at 12-inch cen ter s longitudinally, placed at the cent er of the concrete -arc h section.

The final design included No. 4 rein forcing ba rs (Y2-inch diameter ), spaced at 10-inch cen-

2.1.2 Damage Prediction. Before Operat ion Plumbbob, very little was known regarding theresponse of buried ar che s to blast fo rce s from nuclear weapons. However, it was necessaryto predict the response and establi sh the locations of the s tr uc tu re s in this experiment. Thesepredictions were also to be used to establis h the range of the instrum ents involved and to setthe channel sensitivity of each electronically recorded measur ement. To this end, the fir m ofHolmes and Narver perfor med a preshot analysi s of the ar ch stru ctur e as designed by Ammannand Whitney, using methods other than those pres cri bed in Reference 5. The Holmes andNarver repo rt (Reference 8) predict ed that: (1) failure of the s tr uc tu re was not to be expectedat the 50-psi ground-surface air -ov erp res sur e level; (2) probable failure of the st ruc tur e wouldoccur at the 100-psi level; and (3) failure (collapse) of t he s tr uct ur e would occur at the 200-psi

20CONFIDENTIAL


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level.the three pressure levels is shown in Table 2.1.1.3.2. An important conclusion reached by Holmes and Narver was that:

The estimated displacement along the cent er portion of the arch es of the str uc tu res atThe general principles used in the Holmes-Narver pre shot analysis were given in Section

In the case of the arch-type structures, it is evident that soil characteristicshave an important effect on ultimate strength and that proper compaction of thebackfill around the sides of the arch is essential fo r maximum strength.To obtain a better understanding of the behavior of a buried arch in the plastic range and to

determin e the ultimate mode of failu re of the ar ch, thr ee one-eighth-scale mod els of the ar chused in this project were tested at the U.S. Naval Civil Engineering Laboratory (NCEL). Geo-me tr ic simil itude was maintained between the model and the prototype; however, because of thesma ll scale, no attempt w as made to maintain simili tude of the unit weight of the concrete.Graded sand w a s used in the concre te mix for the model, and the design streng ths of the con-crete were the same as had been specified for the prototype. Small stee l wire s were used tosimulate the reinforcing steel.a No. 10 sieve.wood box housed the model and the sand cover. Static loads were applied to the san d cover bya hydraulic jac k and steel beam, as shown in Figure 2.3. In ord er to reduce the frictional re-sis tan ce of the sand on the plywood during loading, two la ye rs of plastic- impregnated paper(well greased ) were placed on all inn er sur faces of the plywood box.pres sure gages placed at the springing line indicated that the loss of vertical pr es su re throughthe so il ma ss var ied fro m approximately 55 percent at 20-psi applied load, to 45 percen t at 50-psiload, and 30 perc ent at 130-psi load. This los s was presumably a transfer of pre ssu re to thesides of t he box through frict ion and w a s not consid ered of much importance in qualitative te st sof th is type.

Figure 2.4 shows the a rc h segment with the floor slab, after sustaifiing an applied static loadof 175 ps i. The crown of the ar ch and the floor slab cracked at 50-ps i applied load. The initialcompression failure of the concrete arc h occurred at one springin g line at about 110 psi, and atthe opposite springing line at 130 psi. Failu re of one side occu rred at 140 psi and failure of theother side at 170-psi applied load; ex trem e crack ing and spalling of the concret e accompaniedthese failures. It should be emphasized that these loads were applied to the su rfac e of the sand,and that the actual lo ads on the ar ch segment were probably less than the above-mentioned values.

Th e arch deflection at maximum load w as approximately y4inch; permanent se t after removalof the load was Y2 inch.Based on a static analysis of the stru ctu re (assuming a nonuniform p re ss ur e distribution) and

on re su lt s of the model tests , the NCEL prediction of s tru ctu ra l behavior of the a rc h section upto th e desig n load (50 psi) was as follows:

At a dynamic ov er pr es su re of approx imately 10 to 15 psi, the moment-ca rrying capacity ofthe a rch will be exceeded at the springing line. Since the reinforc ing steel will be stre ss ed be-yond the yield point, th er e will, in effect, be plastic hinges formed at the springing line. Duringthe next phase the stru ctu re will act as a two-hinged arch, and because of the sti ffne ss of thear ch the deflection will be small. At approximately 25- to 35-psi over pres sure , assumin g asymm etric al loading, additional plas tic hinges will form at the crown and at the haunches, re-sulting in a 5-hinged ar ch mechanism. Fail ure of the st ru ct ur e is prevented by the buttressi ngeff ect of the soi l agains t the outward deflection of th e haunches. At the 50-psi design overpres-sur e level the arch will show evidence of perm anent deflection due to the plas tic deformatio n atthe criti cal sections. On the intrados of the arch, tension cr ac ks will be apparent at the crown,and compression failure will be apparent at a point on the a rc h about 25 deg ree s up from thespringing line. Although the arc h will be serviceable after receiving a blast load of 50 psi ,Plastic hinges will have form ed at the five critical sections. It is evident that considerable plas-

Soil cover was prov ided by sand which had been passed throughFo r convenience, the width of the a rc h segment was limited to 4 y2 nches. A reinforc ed ply-

Three a rch segments were tested , one with floor sla b and two without floor slab. Soil-

2 1CONF BE N T l A L


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tic deformation will occur befo re a uniform pr es su re distribution can be realized.met ric al loading of any gre at magnitude on the arch, considerable struct ura l damage could occurduring this te st because of the smal l stee l rat io of one-half of one percent.

With an asym-

2.2 CONSTRUCTION AND MATERIALSThe four st ru ctu res were constructed by the general contracting firm of Lembke, Clough, and

King of La s Vegas, Nevada. Holmes and Narve r acted as the architect-engineer for the AtomicEnergy Commission and provided construction-inspection se rv ic es for all projects. The entireconstruction time fo r this project was about th re e months. The excavation for the four struc-tur es was completed early in March 1957, the st ruc tur es were completed by 12 April 1957, andthe backfill operation was completed by 4 June 1957. (See Appendix G or specifications and as-sociated design drawings used in conjunction with the construction program. )

2.2.1 Soil Properties. Pr io r to the field operation, laboratory tes ts were performed as apart of Project 3.8, Soils Survey, on both undisturbed and remolded samples of soil obtainedf ro m the gene ral vicinity of the site where the structu res were to be located. The soil in th earea had a uniform appearance and texture, and can be generally classified as clayey-silt. There su lts of compaction test s, Atterberg limit s tests , and mechanical analyse s on the natural soilat various depths are shown in Figure 2.5.

In an attempt to duplicate the compressibility characteristics of th e natural soil, a ser ies oftests were performe d on samples of remolded s oil of v arious water contents, using th re e dif-fere nt compaction efforts. Test specime ns were prepare d from the mold samples, and a con-fined compression test was performed in a consolidometer apparatus. A tangent modulus ofdeformation was established fr om the test data; based on analysis of the data, the backfill ma-ter ial was recommended to be placed at 100 perc ent s tand ard AASHO density, with a water con-tent 3 percent less than optimum. The resu lting recommended and as-plac ed values of drydensity and water content fo r the backfilled soil ne cessary to duplicate the modulus of compress-ibility a re given in Table 2.2 along with values for the undisturbed natural soil located adjacentto the backfill a rea s.

Shortly after the backfilling operation was completed, undisturbed soil s ampl es were obtainedfro m both the backfill and th e adjacent natural soil at depths of 4 and 10 feet at the four stations.Samples were obtained in the backfill after the shot also, but no strength tes ts were made sincethe re su lts f ro m the preshot and postshot density and water-content t es ts showed no significantchange and thus no change in the postshot strength cha racte risti cs of the mate rial ( see Table 2.2).The comp ress ibil ity of the compacted backfill was about equal to that of the natu ral undisturbedsoil when compared by means of s imilar tests, i. e., consolidation tests , constant ratio of applieds t r e s s triaxial tests, and soniscope tests, as shown in Table 2.3. The compre ssive modulus forthe compacted backfill as determined by the soniscope test is lower than that for th e natural soil,which may be due to test conditions. The natural soi l samp les were encased in 3-inch-diameterstee l tubes when subjected to soniscope tests whereas th e undisturbed rec ord s amples were en-cased in 6-inch-diameter cardboa rd tubes. The difference in tubes may have had a marked ef-fect on the transmi ssio n charact eris tics of the samples.various soil properties and associated tests, see the repo rt of Plumbbob Proj ect 3.8, Refer-ence 11.)

(F or a detailed description of the

2.2.2 Construction-Material Properties. Type I1portland cement was used in the constructionof the concrete arches. The aggregate was pit run, screened, and stockpiled at the FrenchmanFlat area; the maximum size of co ar se aggregate was approximately 2 inches. A mechanicalanalysis of the sand indicated that the grain s ize s ranged from a No. 4 to a No. 200 U.S. standardsiev e size. A summ ary of the proportions used in the concrete mix design fo r th e four structuresis shown in Table 2.4.(flexural strength specimens) were obtained from each str uct ure for laboratory tests which es-Thirty standard concrete cylinders (compressive strength specimens) and ten concrete beams


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0WATER CONTENT. PERCENT OF DRY WEIGHT

N o t e : S t a n d a r d A A S H O C o m p a c t i o n

U, . STANDARD SIEVE SIZE

i . 1 0 0 10 1.0 01 0.01GRAIN SIZE IN MILLIMETERSG LL

A v er ag e C l a y e y - S i l t ( C L - M L ) 2.72 29 2Sample No. Elev or oepth Classification

I 1 I I ISample No.Optimum Water Content % 23.3

L b s K u F t 97 7ax Dry DensityOptimum Water Content Con fw + xMa x Density Con fW + Lbs/Cu Ft

N o t e : G = S p e c i f i c G r a v i t yrojectL L = L i q u i d L i m i tP L = P l a s t i c L i m i t

A r m F r e n c h m a n F l a tSample No.oring No.

Elev or Depth DateCOMPACTION TEST REPORT

Figure 2. 5 Typical backfill m ateri al of the 3.1 st ruc tures .


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TABLE 2.2 DENSITY AND WATER CONTENT OF SOILWater Content, pct Dry Density, pcf

Ranged RangedFro m To Average From To Average

Undisturbed Natural Soil 9.4 15.1 12.8 73.5 86.3 79 ORecommended for Backfill 20 .o 23.0 21.5 94.7 99.4 97.1Control Tes ts during Backfill* 17.5 24.0 20.7 88.0 107.0 96.7Preshot, 4 ft below 16.3 22.1 19.2 90.4 104.2 99.9Postshot, 4 ft below 16.8 20.8 18.5 90.2 106 .1 99.2

Surface of Backfill

Surface of Backfill

* Average of 40 samples per s tructure.

TABLE 2.3 COMPARISON OF COMPRESSIBILITY CHARACTERISTIC OFNATURAL SOIL WITH COMPACTED BACKFILL

Natural Soil (psi)Ranged Ranged

Compacted Backfill (psi)Fro m To Average From To Average

Modulus of deforma-tion (consolidatedtests at appliedstress = 50 psi) 2,410 6,080 4,130 3,200 6,950 5,300

Modulus of compres-sion (triaxialtests) 1,500 12,000 6,450 3,850 14,000 7,600

Compressive modulus(soniscope test s) 223,580 734,050 506,000 130,440 146,340 135,800

TABLE 2.4 CONCRETE DESIGN MIX PER CUBIC YARDStandard mix prescribed for all structures

AbsoluteMate rial Weight Volume

GravelSand, 1,188 Ib (dry)Free Water in Sand, 4.35 pct or 52 IbWater Added, 28.5 ga lCement, 5.5 sacks

Totals:

lb2,0001,188

ft312.03.7.70

52 0.84237 3.80517-3,994 2.6327.00-

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tablis hed 7-day, 28-day, and shot- time st reng ths . The tops of the cylinder specimens werecovered immediately afte r they wer e prepared. A ll the exposed surfa ces of the spe cimens andst ru ct ur es were spr ayed with Hunt's curing compound. The various specimens were placed onthe ground surface near the appropriate structure.

Shortly after the fo rm s were s tripped fro m the various st ruct ures , half of the specimens tobe tested at shot time were removed from the molds and allowed to cure in the open. When thest ru ct ur es were backfilled, the specim ens that had been removed fro m the molds were coveredwith the s ame backfill materia l in an attempt to s imulate the curing condition experienced bythe various struct ures . The remaining specim ens ("-day, 28-day, and the remaining shot-timespecimens) were removed from the molds in the testing laboratory. All of the shot-time speci-mens were sent to the testing laboratory one month prior to the P ris cil la event.

The labora tory tes ts , conducted by the Nevada Testi ng Laboratory, Ltd., Las Vegas, Nevada,consisted of determining the compr essive stre ngths, flexura l strengths, and stati c moduli ofelasticity of the conc rete specimens at various tim es after the st ru ct ur es were poured. In addi-tion to the se tes ts , values of the dynamic modulus of ela sti city at shot time were determined forse ve ra l of the specim ens by personnel of the Concre te Division of the Waterways Expe rimen tStation (WES). Te st s to determine the stati c modulus of elasticity were perf ormed on the cylinderspecimens, while the dynamic te st s (nondestructive) were perfor med on the beam specim ens inor de r to take advantage of the additional length-thus increas ing the reliability of the resu lts.Dynamic modulus of elast icity was calcu lated by using proced ure s outlined by the American So-ciety for Tes ting Materi als (ASTM Designation C215-55T). Several specimens were teste d atthe end of seven days to deter mine if the c oncrete had attained sufficient streng th to allow theremoval of forms.event. The re su lt s of all tes ts indicating the compressive strength values with respect to agefor each struc ture ar e shown in Figure 2.6. Four curves of ave rage stress versus s train forthe concrete specimens obtained from the various arc h sections and tested at shot time areshown in Figure 2.7. The re su lt s of the concrete strength te st s at the time of the Pri sc il laevent ar e shown in Table 2.5.flexura l stren gth specim ens fro m both the base slab and the arc h of Structu re 3.1.n.specimens were removed from the molds when the forms were stripped from Structure 3.1.11,stored on the floor slab for curing purposes, and tested at shot time. The re su lt s of these NCELtests ar e included with the strengt h res ul ts shown in Figures 2.6 and 2.7.

Intermediate-grade billet steel was used exclusively as the reinforcing material in the variousstr uctu res . Ten sample reinforcing bar s of 18-inch length were taken fo r each of the th re e siz esused (Nos. 3, 4, and 6). A ll bar s fr om each group were tested for ultimate strength, percentageof elongation, and st re s s ve rs us str ai n into the plasti c range.specimens were performed at NCEL; r esu lts of t hese te st s a re shown in Table 2.6.

The other specimens were tested at 28 days and at th e t ime of th e Priscil la

In addition to the above specimens, NCEL person nel prepa red thr ee com pressi ve and thr eeThese

The tests on the reinforcing-bar

2.2.3 Construction Methods. A backhoe was used to excava te the four areas. The soil prop-er ti es were such that the contractor could utilize vertic al excavations, thereby necessitating aminimum of excavation effort. The sid es of the excavation were approximately 2 feet fr om theside s of the base sla bs of the various st ruct ures , and the floor of the excavation w a s level towithin *v4 inch.

Concrete materials were combined in a portable, cent ral batching plant adjacent to WaterWell 5b (Frenchman Flat), 2 '/z miles f rom the construction area. Bulk cemen t was used andwas stored in a portable hopper that weighed the amount of cement required pe r batch of con-crete. A portab le batching plant (T rav el Batche r) was used to hold and weigh the cemen t, sand,and gravel . The cement, aggregate, and water we re poured into the mixing truck s (5-cubic-yard capacity) simultaneously.

The stee l in the base sl ab wasplaced according to plan, except that the top reinforcing ba rs were inadvertently placed oneinch lower than was specified. (See Figure 2.8 for typical placement of reinforcing st eel in a

The base slabs for all of the s truct ures were poured first.

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i

6000

5000

4000

3000

2000

1000

0

E c

I -30 I L

0 S t r u c t u r e 3.1. aV S t r u c t u r e 3.1. bEl S t r u c t u r e 3.1. cA S t r u c t u r e 3.1. n

A g e , Days1 I

Figure 2 .6 Compressive strength of concrete vers us age.


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2

:L

80

9


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base slab. ) Concrete was placed by a hydrau lic cra ne with a drop-bottom bucket (%-cubic- yardcapacity) and was compacted by elec trical v ibrato rs. After the concrete had attained it s initialset , the exposed sur fac es were sprayed with Hunt's curin g compound.

The upper portion of the s tr uc tu re s (the arch, end walls, and the entranc e shaft) was pouredmonolithically and placed in the manner descr ibed previously.str uct ure s were formed by placing Universal-type for ms (1 by 4 feet) on semicircular wood sup-po rt s fixed on 4-foot c ent ers along the floor sla bs.

The intrados of the variousThe extrados forms, seven rows on 1-foot

TABLE 2.5 CONCRETE STRENGTH CHARACTERISTICSSpecimens tested at the time of the Pri scil la eventCompressive Modulus Modulus of Elas ticity ModulusStructure Strength,

UltimatePsi

3.1.a 4,270 (83 days)3.1.b 4,610 (88 days)3.l .c 4,780 (94 days)3.1.n 4,210 (76 days)Average 4,470-

ofRupturePsi539524548490525-

EStatic* Dynamicl o 6 psi l o 6 psi

A t B t C t3.44 4.65 4.40 5.303.74 4.65 4.49 5.223.82 4.42 4.54 5.243.44 5.01 4.73 5.473.61 4.68 4.54 5.31

of Poisson's Ratio, rRigidity, Gl o 6 psi Dimensionless

Dt E t F t1.93 0.21 0.141.94 0.20 0.161.94 0.20 0.172.01 0.23 0.161.95 0.21 0.16- - -

* Values obtained from 6- by 12-inch cylinders; all other values obtained from 6- by 6- by 24-inch beams.tA. Obtained from flexural resonant frequency by vibrating transverse ly in the horizontal plane.B. Same as above by vibrating transversely in a vertical plane.C. Obtained from longitudinal resonant frequency.D. Obtained from torsional resonant frequency.E. Poisson's ratio, r =E/(2G) - 1, using E value from Column A .F. Same a s above, using E value from Column B.

centers, were placed on the bottom half of the arch, leaving the remaining sur fac e adjacent tothe crown to be screeded.the concrete had attained its initial set.in the arch section of the structu res; a completed structure is shown in Figu re 2.10.)with the backfill material in order to establish the desired water content.

The exposed concrete was sprayed with Hunt's curing compound after(See Figure 2.9 fo r details of fo rm and ste el placement

Pr io r to the placement of the backfill, controlled amounts of wate r were thoroughly mixedThe material was

TABLE 2.6 REINFORCING STEEL PROPERTIESBar Size Yield Ultim ate Elongation Modulus ofNumber Point Strength in 8 inches Elasticity

ps i psi percent l o 6 psi3 52,200 73,400 21.3 294 47,500 73,200 21.3 316 47,100 75,600 22.3 30

then s pre ad in 4-inch lifts and compacted with mechanical and pneumatic tampe rs. The soilimmediately around the ear th pr es su re cell s located on the various st ruc tur es was carefullyhand tamped to attain the sam e deg ree of compaction as the surrounding backfill material.sonnel from Proje ct 3 .8 took samples during the backfill operation to ensure that proper com-paction was obtained. (See Section 2.2.1 fo r soil properties.)cracking pattern, the cr ack s penetrating the top lift of t he compac ted backfill.

Pe r -

Shortly aft er the backfill opera tion was completed, the top layer of soi l developed a polygonalTo prevent fur-

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ther crack s in the soil and the subsequent loss of moisture, the backfill a re as were spr ayed withwater and covered with a loose lay er of d ry s oil over which tarpaulins were placed.

2.3 MEASUREMENTSDetermination of the load applied to a str uct ure is a requisi te in proper design. However,

up to the pres ent t ime, no reli able experimental information has been available concerning theload distribution on an underground ar ch s truc ture subjected to a nuclear blast.true pi cture of the pressu re-t ime distribution for an underground arc h under these conditionsis complicated by various fact ors , such as the flexibility of the a rc h and the compressibi lity of

Obtaining a

Figure 2.8 Floor slab prio r to pouring concrete, Structu re 3.l.c.

the soil.age la te ra l pr es su re on a vertical wall of an underground rectangul ar s truc ture subjected to anuclear blast is approximately 15 percent as great in magnitude as the pr ess ure applied at thetop sur fac e of the soi l for depths of ea rt h cover of up to 8 feet.applicable to arc h stru ctur es, however, since the ar ch deflection affects the soil pr ess ure .Therefore, attempts wer e made in this investigation to determine the load distribution on thearch.an understanding of it s struct ura l behavior under the applied loads.respons e of an underground arch s tr uc tu re subjected to blast loading is meager, responsemeasurements were also obtained for these structures.

Previous reports (References 6 and 7) indicate that for Nevada Test Site soil the aver-

This information is not directly

In addition to a knowledge of the loading conditions, proper design of a s tr uc tu re depends onSince informat ion on the

2.3.1 Instrumentation. Instrumentat ion of the four st ru ct ur es of this projec t included bothelectronic (remote- recordin g) and mechanical (self- recordin g) systems . Electronic measure-ments were made of transient air overpressu res, deflections, accelerations, earth pre ssu res ,and st ra in s; mechanical measurement s were made of a ir o ver pr es su re s and deflections.Ballistic Researc h Labo ratories ( Proj ect 3.7) accomplished the instrumentation for St ruct ures3.l.a, b, and c; for a detailed description of th is work ref er to Appendix B.

TheThe NCEL accom-

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Figure 2.9 Reinforcing s teel and for ms in d a c e for arch, Structure 3.1.n.

Figure 2.10 Completed st ruc tur e pri or to backfilling, Structu re 3.1.a.31


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plished the instrumentation for Structure 3.1.n; for a detailed description of this work refe r toAppendix C. The gene ral instrumentation layout, including gage identification for the fourstructures, is shown in Figures 2.11 and 2.12.

In ord er to det ermine the degree of radiatio n protection afforded, all four structu res wereinstrumented with gamma film badges and neutron chemical do sime ters by the Chemical W a r -far e Laboratory (Project 2.4). A descrip tion of this work is presented in Appendix D.A possibility existed that the severe ground shock would spall the inside surfaces of thestructure, thereby creating missile (chips o r fragments of concrete) hazards. To determinethe quantity and siz e of thes e miss iles , Styrofoam miss ile tr ap s were installed in all of thestructures by the Lovelace Foundation (Project 33.2). In addition, dust collec tors were placedin the four stru cture s to determine if the ground shock would cause dust on and within the con-crete walls to spill into the structure. A descrip tion of th is work can b e found in Appendix E.all layout of the record ing instrument s in the four str uct ure s, as well as a view of the interiorof the struct ures .

T o det ermine the effect of irr ad iat ion on different types of photographic paper and fi lm usedin electr oni c recording, four types of r ecording pap er and one type of film were exposed tovariou s intensities of radiation. Results a r e presen ted in Appendix F.

The instrumentation utilized is listed in Table 2.7. Fig ures 2.13 through 2.16 show the over-

2.3.2 Damage Survey. The damage survey consisted of level and tr an si t surveys, photo-A level and trans it survey w a s performed aft er the stru cture s were completed, and prior tographs, and

a visual inspection.the backfilling.to determine the relative permanent deflections and movements caused by the ground-surfaceair overpressure.record visible damage and also to aid in the interpret ation of instrumentation res ults .

Identical surveys were also performed both prior to and after the shot in order

Photographs and visual inspections of the st ruc tur es were made before and after the shot to

2.3.3 Methods of Data Analysis. The methods of reducing the rec or ds obtained from thevarious gages are presented in Appendices B and C. Presente d below are two methods in whichthe final records shown in Appendices B and C were used to determine: (1) ransient deflectionby means of double-integration of acce lera tion reco rd s; and (2) tra ns ien t moment and th ru stfrom strain records.

M e t h o d U s i n g A c c e l e r a t i o n R e c o r d s . Since t ra ns ie nt deflection re co rd s f or thebase slab were not available, the accele ration rec ord s for Struct ure s 3.1.4 b, and c weredouble-integrated by the /3 method, originated by Professor N. M.Newmark, to yield the tran-sient deflections. This method is a numerical integration process in which various values of /3can be selected to represe nt vari ations of acc eleratio ns in the time interval, h. It is particularlyadaptable to computer solution.

Equation of motion: The equations of velocity and displacement take the following form:

and

Where: X = deflectionV = velocity(Y = accelerationh = time intervalp = variable

When p is assigned a value of y6, the variation of accele ration is line ar in the time interval h,


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I

SECTION C-C

GradeEIO. EI0. I

SECT I ON B-B

GradeI

I

3 . 1 . A 3.1.B 3.1.C

KEY PLANLEGEND

ELECTRONIC RECORDING- ( E ) Earth Pressure/Time0 (D ) Deflect ion/Time (Radial)A (A ) Acce le rat ion (Ver t ica l )SELF RECORDING7 ( P ) Air Pressure(D) Def lect ion

0 Radial9 AngularA (SI Scratch Gage

SECT I ON A -A

Figure 2.11 Instrumenta tion layout, Str uct ures 3. l .a , b, and c .

3 3

1 .


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Ed iFd S E C T I O N D-D

S E C T I O N E- E

3.1.A 3.1.8 3. CK E Y PLAN

L E G E N D

S E L F RECORDING(D) Deflection

HorizontoVert ica

A

ELECTRONIC RECORDING( E ) Eorth Pressure/Timea P ) A ir Pressure/Time(D) Deflectton/Tirne

*@ HorizontalVertical? ( A ) Acceleration (Vertical)- (SI Strain

SIO. II. 12 I

S E C T I O N F-F

Figu re 2.12 Instrumenta tion layout, S truc tur e 3.1.n.

34


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TABLE 2.7 INSTRUMENTATION SUMMARYType Quantity Type Quantity

Electronic-recording Gages:Earth pressure/timeDisplacement/timeAcceleration/timeAir pressure/timeStrain/time

TotalSelf-recording Gages:

Scratch type @e& deflection only)Deflection/timeAir pressure/time

Total

2617721668

4246

34

Radiation Measuring Devices:Gamma film badges 20Neutron chemical dosimeters 20Neutron threshold de vices 2

Total 4 2Missile Measuring Devices 4

Mechanical Strain Gage Stations 39Electrical Strain Gages (static readings only) 9

Figure 2.13 Interio r views, Structu re 3.1.a.35


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Figure 2.14 Inte rio r views, Structure 3.1.n.

and the deflection equation becomesXn+ , = Xn +Vnh + '/,(unh2i / 6 ( ~ ~ + ~2

Since reco rds fr om accelerom eters a re subject to baseline shifts, the rec ord s shown in Ap-pendix B were corr ected using a method s uggested by D. C. Sachs of Stanford Researc h Institute.This method assum es that no acceleration for underground stru ctu res occurs after td (td is timeat which the positive air pre ssu re phase ends) and therefore that the velocity remains constantthereaft er. Since the accel erom eter was found stationary, this constant velocity must have been

36

@


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Figure 2.15 Interio r views, Structu re 3.1.b.

Figure 2.16 Interio r views, Struct ure 3.l. c.3 7


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w- VI- i wa aJ 'a Z Pa > n4 o aa w

L OO ' La 4

4 ::u >

zwSECOND BA SE LIN E SHIFT---\ --

SECOND B AS E L I N E S H I F T 7-4-- - 2 -- ---I R ST BA SE LI NE SHIFT-- ----

{ SECOND BASE L INE SHIFT-- _ _ --F I R ST B A S E L I N E S H I FT -\

1A

Figure 2 .17 Sample plot for double integration of acceleration record.38. . ,., , . i / ... ,


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zero.axis of the accelera tion re cor d was shifted to obtain the desi red z er o velocity (see Figur e 2.17).fr o m the above discussion both the acceleration and velocity ar e ze ro after td, it follows thatthe displacemen t at td must be the permanen t displacement. Accordingly, a second shift of theacceleration recor d axis was made s o that the computed displacem ents at td were equal to thesurveyed permanent displacement (see Figu re 2.17).of displacement time data.

The major purpo se of instrumenting Struc ture 3.1.nwith str ain gages w a s to determ ine the moment and thrust at various points throughout the arch,and how this moment and thrust varied with time. In particular, it was desired to ascertain thesereactions at the springing line.

With this purpos e in mind, st ra in gages were placed on the outside surfa ce, inside surface,and the steel reinforcing (neutral axis of uncracked section) at seve n different points around thearch. Th er e were, however, insufficient channels to rec ord all of these gages during the blast .It w a s theref ore decided to record the strains at both springing lines, at the crown, and at the30- and 60-degree poin ts of the ground-z ero side. In addition, the measu rements at the threela tt er points could be record ed only for two of the three gages. Since concre te crack s at tensilest ra in s of about 100 o 200 microinches pe r inch, gages on the tensio n side would not give worth-while data at stra ins grea ter than this. Therefore, the gage on the steel and the gage thoughtmost likely to be on the compression side were the two gages used for recording purposes.

In or de r to simplify the reduction of s tr ai n to moment and thrus t, it was assumed that: (1)the variation of s tr ai n acro ss a given section was line ar; (2 ) as long as the structure remainedelasti c, a constant value could be used fo r the modulus of e lastic ity; ( 3 ) the concrete was crackedat tensile st rai ns gre ate r than approximately 100 microinches per inch; and (4) he effect of theste el in the ar ch could be neglected.due to moment and the s tr ai n due to thrust. The st ra in due to moment would be equal to one halfthe algebraic difference of the s tra ins in the extreme uncracked fibers. The st rai n due to thrustwould be equal to one half the algebraic sum of the str ain s in the extreme uncracked fibers.

The thr ust would then be determined by multiplying the st ra in due to thrus t by the modulus ofelasticity and area of the concre te. The moment would be determin ed by multiplying the st ra indue to moment by the modulus of e lasti city and the s ection modulus of the conc rete.

One st ra in gage was placed on the top reinforcing ste el of the floor slab near each springingline. To deter mine the horizontal react ion at the springing line, it was neces sary to make theassumption that the moment in the floor sla b at this point was equal to the moment in the a rc hat the springing l ine. A moment that placed the intrados i n compression at thi s point would alsoproduce a com pressive s tra in in the subject gage. An outward movement of the a rc h would pro-duce a tensile s tra in in the gage. Therefore, to determine the stra in due to the horizontal thrust ,the bending str ain had to be algebraically subtracted from the recorded strain.to horizontal thrust was then used in the manner described previously to calculate the horizontalthrust in the base slab.the springing line.

If the first integration of the acc elerat ion rec ord did not give a ze ro velocity at td, theThis revised acceleration record was then double-integrated to obtain displacement. Since

This twice-revised acceleration record w a s then considered valid, and was used as the sour ceM e t h o d U s i n g S t r a i n R e c o r d s .

With the above assumptions, the strains at any given section could be se parat ed into the st ra in

The str ain dueThis was assumed to be equal to the horizontal reaction of the ar ch at

39I" Y ""


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Chopfer3RSUL TS

All four of the s tr uc tu re s withstood the effects of the Pr is ci ll a Shot and remained in usable con-dition.the test.a nuclear weapon.variations of ear th pr es su re , deflection, accelerat ion, etc., with time a re presente d in AppendicesB and C.

Even though none of the 3.1 st ru ct ur es failed, valuable information was obtained fromThe buried concrete arc he s proved very effective in resi sti ng the blast effects from

This chapter pr esen ts only the peak values of transie nt and permanent measurements. The

3.1 AIR OVERPRESSUREThe actual air overpr essur es received at the thr ee ranges were 56, 124, and 199 ps i com-

pa red to the predic ted values of 50, 100, and 200 psi . The project plot plan (Figure 2.1) showsthat Structures 3.1.a and 3.1.n received the lowest loading of 56 psi, Structure 3.1.b next with 124psi, and Structu re 3.l.c r eceived 199 psi, the highest loading. The clos enes s of the predic tedvalues to the recorded values indicated that load-input conditions in this test were satisfactory.appear reliable, since these values comp are favorably with the blast-line data. The blast linewas located approximately 250 feet from the above gages.

Measure ments showed no increas e in air pr es su re within any of the four str uc tu re s duringthe test.

The ground-surface air-over pressure values measured by the self-recording pre ss ure gages

3.2 EARTH PRESSUREThe peak transie nt ea rt h pr es su re s on Structure 3.1.b (s ee Figure 3.1) show that in several

instances the earth pr ess ure exceeded the ground-surface air over pres sur e. Even though thevalues of pr es su re were recorde d to the nearest one psi, some of the values could not be ac-cura tely determined because ei ther the rang e of the calibr ation o r the range of the amplifyingequipment was exceeded. This was especia lly true for gages E10 and E1O.l, at the crown ofStructu re 3.1.b. These gages were placed next to each other in ord er to determine what effectthe method of mounting had on ear th -pr ess ure meas urem ents (see Appendix B). Only the peakear th- pre ssu re values for the pr ecur sor phase could be compared since the peak values for themain shock phase were beyond the cal ibra ted range of th e gages.

A comparison of p re ss ur e values from gages E9 and E l l shows that the loading was asym-metrical.higher than for gage E l l , located on the lee side of the ar ch.sulting from ground-surface air overpress ure and that the static earth pre ss ur es (dead load)existing at the time of the shot are not included. Negative values would indicate reductions inthe existing static earth pres sur es.The geometry of the eart h-p res sur e gage mounting at the 30- and 60-degree positions on Struc-tu re 3.1.n (see Figure C.l) adversely affected the measuremen ts. The pro ject ion of the mountsinto the soil apparently caused an incr ease of pr es su re on the gages measur ing vertical pr es su re sand, possib ly because of arching, a decrease on the gages measuring horizontal pressure. The

The peak pr es su re for gage E9, located on the ground-zero side, was 60 percentIt should be pointed out that the earth pre ss ur es being discussed ar e transient pre ss ur es re -


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I

STRUCTURE 3 . 1 . A

K EY PLAN

=-0. 42 IN.AT 4 26 M S

ISTRUCTURE 3.1.8

AT 2 4 5 MS

STRUCTURE 3.1.C

D -E L E C T R ON C D E F L E C T lON GAGENOTE ZERO TIME IS T A K E N A S THE TIME OF DETONATION OF THE DEVICE

Figure 3.2 Peak trans ient deflection, with res pec t to the center ofthe floor slab, S t r u $ y r $ { ~ ~ ~ ; ~ ~ ~ - ~ ~ d.I_ %.

4 2 - -U^..-LIIU-. *..,I.I


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gages at the crown and springing line, however, wer e flush-mounted and gave what appear to bereliab le mea surem ents, which a r e included in Figur e 3.1.

3.3 DEFLECTIONThe peak transie nt radia l deflections of the a rc h with respe ct to the cente r of the floor slabThese values ar e the actual recorded

However, the floor sla b itself underwentfor Struct ures 3.l.a, b, and c ar e shown in Figure 3.2.maxima, as read f rom the deflection-gage records.differential deflection a s indicated by comparing the integrated acceleration reco rds (see Figures3.7 and 3.8). Therefore , the plots of peak transi ent radia l deflections of the ar ch wer e adjusted ,

NOTES:1. ACCURACY 15 f O2. V = V E R T I C A L

H = HO RI ZO NTALD D E F L E C T I O N

\r PRINGING LINE

.Ol IN.

GAGE

I \I/ uSECTION A-A

Figure 3.4 Peak ransi ent deflections with res pec t to the springing line, Struc ture 3.1.n.taking into considerati on the movement of the floor s lab.Figu re 3.3, which shows the peak trans ient rad ial deflections of the ar ch and center of the floorslab with resp ect to the springing line.

The record from the accele romete r located at the cen ter of the floor slab for Stru cture 3.1.awas not suita ble for double integration and could not be used in determinin g deflections of theslab.that the re was no differential deflection in the floor slab. However, by comparing the combinedtransient deflection of 0.42 inch fo r Struct ure 3.1.a with the crown deflection of 0.23 inch fo rStruc ture 3.1.n (Figure 3.4), it might be assum ed that the peak trans ient downward deflection forStr ucture 3.1.a ranged fr om 0.20 to 0.30 inch and that the upward deflection of the cen ter of thebase slab was approximately 0.20 inch, all values being relativ e to the springing line.

The corre cte d plot s (F igure 3.3) show the outward movement of the haunch, which was notevident in Figure 3.2.only one gage was locate d at eac h of the t hr ee points on the ar che s, even though it requir es twogages to descri be the e xcursion of a point.

These corrected values a re used in

Therefore, since the acceleration of the slab was small, it was assumed for F igure 3.3

\

Since electronic instrumentation channels in the field were at a premium,It was hoped that the two self -recor din g (backup) gages


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would desc ribe both the horizontal and ve rt ic al movement of the crown; however, none of the self-recording deflection gages functioned.

The peak tran sien t deflections of the 3.1.n ar ch with resp ect t o the springing lines ar e shownin Figure 3.4. In this stru ctur e two gages were used at each point to tr ac e both the horizontaland vert ical movements. Section A-A of Figure 3.4 shows the maximum excursion of three pointson the intrad os near th e cent er of the stru ctur e. These deflections show that the st ruc tur e under-went bending with the crown moving downward and the haunches outward. It can also be observedthat the bending was slightly asym met ri cal with some movement away fr om ground zero. Theelevation view shows the defl ections of t he crown along the longitudinal center line of the arch.The deflections of t his str uct ure wer e not la rge enough to definitely estab lish the distance towhich the end walls affected arc h action. Th is was indicated, however, by the pat te rn of thecra cks disc uss ed in Section 3.8.

The permanent deflection of the crown with resp ect to the sp ringing line for S tru ctur e 3.l.a,b, and c is compared in Figure 3.5, again showing the influence of the end walls in res tra ini ng

f LEGEND---- 9.1.0- .1.b- - s.1.c

Figure 3.5 Permanent crown deflection with res pec t to th e springing l ineof the arch , Stru ctur es 3.l.a, 3.l.b, and 3.l.c.ar ch deflection.Stru ctur e 3.1.n meas ured less than 0.05 inch.level survey are given in Tables 3.1, 3.2, 3.3, and 3.4.

The permanent deflection of the crown with re spe ct to the springing line forThe permanent deflections determined fro m a

3.4 ACCELERATIONThe peak transie nt ac celer atio ns of the floor slabs are shown in Figure 3.6. The la rg es t

acceleratio n was a 13.4 g at the springing line of Str uctu re 3.l.c. This acceleration had adurat ion of approximately 25 milli seconds. It is interesting to compare this peak floor-s labaccele ration of 13.4 g with the peak free- field acc ele rat ion of the soil. The top of t he floorslab was 12y4feet below the ground surf ace. At a depth of 10 feet and at the sam e range asStru ctur e 3.l.c, References 1 2 and 19 show free- field acc ele rat ion s of 16.5 g and 17.1 g,respectively. It is also interes ting to obse rve how the acceleration in creas es as the overpres-su re increases . The same refer ences indicate that by increas ing the ground-surface air over-pr es su re fr om 200 to 300 psi the peak acceleration at a depth of 10 feet would be increased from

45


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TABLE 3.1 PERMANENT DEFLECTION, STRUCTURE 3.1.a

-0.2.

r ~ ~ m n r xx aI4Points M, D, and D' moved 0-47 inch dawn.V e r t i c a l deflections are actua l residual movement.The horizontal movement of th e arck relat ive to the floor slab wa sThese m?asurements were taken v i th l eve l and plwnbbob and are accuratewithin th e h a a t reading of tais survey.t o w i t h i n 0.06 inch.

Set- V e r t i c a l Deflection (inches)t i on C C' C t o C' B B' B t o B' A A ' A t o A'I 0.60+ 0.48t 0.12 o.a+ 0.484 0.12 o.a+ 0.481 0.12I1 0.601 0.481 0.12 0.60j 0.484 0.12 0.601 0.421 0.18111 0.481 0.481 0 0.66 t O.h.24 0.24 0.661 0.481 0.18IV 0.541 0.481 0.06 0.661 0.U I 0.18 0.541 0.481 0.c6V 0.541 0.421 0.12 0.60). 0.404 0.12 0 . 9 1 0.541 0VI 0.54f 0.481 0.06 0.54+ 0.481 0.06 0.541 0.48j 0.06V I 1 0.54+ 0.481 0.06 0.604 0.484 0.12 0.601 0.484 0.12

TABLE 3 .2 PERMANENT DEFLECTION, STRUCTURE 3.1.11k -t

FooiSts M, D, and D* moved 0.34 inch m.Vertical deflections are actual real-1 mo-nt.These measurements were taken with level and plwnbbob and afe accThe horizontal movement of the arch relat ive to the floor slab watc within 0.06 inch.within th e least rea- of t h i s survey.

V e r t i d Deflection (inches)C t C t o C' B B' B t o B' A A t A t oectionI 0.34t 0.2e1 0.06 0.341 0.151 0.19 0.34) 0.284 0.0611 0.344 0.28) 0.06 0.341 0.151 O.i.9 0.341 0.154 0.1I11 0.341 0.281 0.06 0.341 0.151 0.19 0.341 0.221 0.12Iv 0.34t 0.224 0.12 0.341 0.221 0.12 0.341 0.281 0.06V 0.34) 0.281 0.06 0.344 0.221 0.12 0.341 0.224 O LVI 0.341 0.281 0.06 0.341 0.31 0 0.341 0.281 0.06


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Figure 3.7 Adjusted double-integration of Record A- 3, Structure 3.1.b.


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UIO

@Figure 3.9 Adjusted double-integration of Record 1AV- 10 (free-field), Reference 12.52


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G Z

STRAIN, STRUCTURE 3 .1 .h , MICROINCHES PER INCH

NOTfS :1) I) ASSUMED MAXIMUM CONCRETE TENSION OF APPROX-

IMATELY 100 MICROINCHES PER INCH2) T =TENSI O N AND C- CO M PRESSI O N3) ABOVE STRA INS OCCURRED APPROXIMATELY I5 0

MILLISECONDS AFTER BLAST WAVE FIRS T REACHEDSTRUCTURE 3.1.n

4) GAGES S4, 7, 12.13, 14,15, 16.17, 18, USED FOR STATICREADINGS ONLY

5) GAGES 521 AN D S 2 4 - N O TRANSIENT RECORDS

Figure 3.10 Peak transient strains, Structure 3.1.n.

C =CompressionT =Tension

\4I

SECTION A -ANote: 1. Al l stations are located on arch intrados

at 10-inch centers.2. Readings are in microin ches per inch.

Figure 3.11 Permanent concrete strains, Whittemore Structure 3.1.n.


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10'

~ - -.. . .. . ' = .- . .. I

* .. .. ... .. I-e: s' *. ...

K EY PLAN

. . . . . .. . ..........4 . * .

F R E .E F I E L D R A D I A T I O N D OS EGAMMA: 1.05 x io5 RNEUTRON: 0.75 x io5 RE P

TOTAL: 1.80 x io5 REP

. . . . . . . . . . . . . . . . . .. a ; 1.. . . . . . . . . . . . . -~'.:o:: :. , . . .. . . . . . . . . . . . . . . v . . *. . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . .., . _ .1 : . . q : .... . . . e :.: . . . ...&.'.*.*. . .......... . . . .? . ' . .*. ..........

- O T A L DO SE-- AMMA DOSEN E U T R O N DO S E.-

Figure 3.12 Total nucle ar radiation dose profile, Structure 3.1.a.

54

........ - ................ ...... .............. . . . . . . . . . . . . . . . . . . . . . . . . . ............ ..... ........... ... ...


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enen

1o3

1o2

10'

f

4 F R E E F I E L D R A D I A T IO N D O SEGA M M A : 1.05 i o 5 RNEUTRON: 0.75 105 REPTOTAL: 1.80 x i o 5 REP

KEY PLAN- O T A L D O SEG A M M A D O S E--- E U T R O N D O SE--100%L E T H A L D O SE

G A G E L O C A T I O N

Figure 3 .13 Total nuclear radiation dose profile, Struc ture 3 .1 .n .


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1o 4

Z0

10'

KE Y P L A N

F R E E F I E L D R A D I A T IO N D O S EGAMMA: 2.0 x i o 5 RNEUTRON: 1.6 x i o 5 REP

TOTAL : 3 .6 x i o 5 REP- O T A L D O S E-- A M M A DOSE- 0 - N E U T R O N D O SE

100%L E T H A L D OS E

I . I I I

G A G E L O C A T I O N

Figure 3.14 Total nuclear radiation dose profile, Structu re 3.1.b.

66


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i o 4

a i o 3a

10

KE Y PLAN

- O T A L D O S E-- A M M A D O S E-*- N E U T R O N D O SE

F R E E F I E L D R A D I A TI O N D OS EGAM M A: 3.0 x i o 5 RNEUTRON: 2.5 x i o 5 REP

T OT AL : 5.5 x i o 5 REP

1

G A G E LOCATION

Figure 3.15 Total nuclear radiation dose profile, Structure 3.l.c.


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A C

Scab - Fm1mNOTE: Al l Crock& shan Ar e Less Thmh Inch Wldello CvookY In RW End W o l l .

KEY PLAN

Iz

I I

1/RCH INTRA S,DEVELOPEDFigure 3.16 Postshot crack survey, Structure 3.1.a.

02__cKEY PLANI

i-iI - INOTE No Cracks In Rear End Wall.

Figure 3.17 Postshot crack survey, Structure 3.1.n.


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END 'WALLrh

FLOOR ISLAB

K EY PLANGZ I

ARCH INTRAD0 5

Scale - Fee?S, DEVELOPED

1NOTE: A l l Crack Widths Not Noted A re Less Thon 64 Inch Wide.

END WALLIFigure 3.18 Postshot crack survey, Structure 3.1.b.

in the intrados varied from hairline to 1/32 inch.bending, with the top of the floor s lab in tension.above the plane of the spring ing line s on the ground-ze ro side of the intrados show that the a rchalso underwent bending.structure.

It is apparent that the floor slab underwentHorizontal hairline cr ack s located 7 feet

Figure 3.18 shows the re su lt s of the postshot crack's urvey of t his

Structure 3.l.c. A lar ge number of cr ac ks developed in the floor slab, intrad os, and endw a l l s of this struc ture . The width of the cr ac ks in the floor slab varied fr om hairl ine to Yl6nch,59


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Figure 3.20 Interior views, Structure 3.l .c , postshot.

Figure 3.21 Northeast corner, Structure 3. l.c , postshot. Figure 3.22 Center floor looking north, Structure 3. l. c, pos


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Figure 3.23 Hatch cover, Structu re 3.l.c, postshot.springing line. Horizontal cr ac ks 7 feet up fr om the plane of the springing lines on the in tradosof both the ground-zero and leeward side of the ar ch indicated that the a rch was subjec ted tobending.of the st ru ct ur e ar e shown in Figure 3.23.ground- zero side. The entranceway had been moved away fr om the ear th on the ground-zeroside, creat ing a vertical crack between the concrete surfa ce of the entranceway and the earthbackfill.

The entranceway hatch cover and the surrounding ground surface p ri or to the initial re- entrySome scouring of the ear th was observed on the


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4.1 CONSTRUCTION

Chapter 4DIscusslo~f RSUL7sMATERIALS

In a field test in which theload is generated by an atomic weapon, it is just as important thatthe actual st reng th of the mate ri als involved (i .e., the concrete, reinforcing steel, and soil)closely approximate their design strength values a s it is for the actual blast pres sur e to closelyapprox imate the design bla st pre ss ur e. The degree of proximity of the actual values of m ater ialstreng th and blast pre ss ur e to the predicted values dictates the degree of succ ess of the experi-ment.

4.1.1 Concrete Strength. The average concrete compre ssive streng th of the four st ru ct ur esat ,the tim e of the P ri sc il la Shot was approximately 4,500 psi, o r 50 percent grea ter than thedesign streng th of 3,000 psi. Theref ore, the structur al capacity of the ar ch structures to res is toverpress ure loadings was accordingly greater. The average concrete strength for Structure3.l.c (199-psi air-ov erpr ess ure level) at shot time was 4,800 psi, which was 60 percent greaterthan the design strength.cr et e strength, then the ultimate load (ground- sur face over pres sur e that would cause collapse)fo r the 4,800-psi concret e would be appreciably gre ater than that f or the 3,000-psi concrete.

If a unifor m rad ial loading (Figu re A.l, Loading A) is used and 3,000-psi and 4,800-psi con-cre te strengths a re assumed, the calculated collapsing air overpressures for Structure 3.l.cfor thes e two str eng ths would be 280 ps i and 450 psi, respec tively .

If it is assumed that res ista nce to failu re depends on ultimate con-

4.1.2 Backfill Mater ial. In te st s of buried stru ctu re s, knowledge of backfill materia l isimportant since it is through this medium that the air-induced ground shock must pas s in or de rto act upon the structures.

difficult quantity to evaluate and no attempt is made in this report to determine the archingc h a r a c t e r i s t i c s of t h e s o i l s u r r o u n d i n g t h e t e s t s t r u c t u r e s .and controlled s o that the modulus of compressib ility would be the same a s that of the adjacentnatural soil; thus, a given overpressure would cause equal deflections in the backfill and in thenatural soil. (See Table 2.2 for a compari son of moduli of compres sibil ity. ) In order to attainthi s duplication of the moduli of compressib ility , it was necess ary that the density and the watercontent of the backfill mater ial be great er than that of the natural so il. Because of the duplica-tion of the co mpress ive moduli, the tes t st ru ct ur es were surrounded by soil having nearly thesa me load-carr ying capacity as that of the natural soil.found that no change in water content or density of the backfilled soil occurr ed at depths of 4feet below the ground surface at the three press ure levels.

measured depth of ea rt h cover over the crown of Str uct ure s 3.l.a, b, c, and n was 4.3, 4.1,4.1, and 4.2 feet, respec tively .The s tr ai ns and deflections measured on Structure 3.1.n during backfilling were small.

proximately 250 st ra in readings were taken, none of which were g reat er than 50 microinchespe r inch.of the crown was about 0.01 inch and the maximum inward deflection of the haunch midway be-

The degree to which the load is diverted fro m the s truc ture (the arching action of soil) is aHowever , the backf i l l was p laced

By comparing the density and water-content samp les pri or t o and afte r the shot, it was

The depth of the backfill ove r the a rc he s was not changed by the effects of the shot. The

Ap-The deflection readings showed that during backfilling the maximum upward deflection


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tween the spr inging line and crown was about 0.01 inch. At the comple tion of the backfilling,the crown was defl ected downward about 0.02 inches and the haunch was deflected outward about0.01 inch.

4.2 ARCH RESPONSEThe crack pattern of the model arc h (Fi gure 2.4) tested by the U. S. Naval Civil Engineering

Laboratory (NCEL) was geometrically si mil ar to the crack patterns (Fi gure s 3.16 through 3.19)that developed in all four prototype str uctu res . The compres sive spalling of concrete observedin Structur e 3.l.c occu rred 2 feet above the springing line, which corre sponds closely to thegeomet rical ly equivalent location of compr ess ive failu re in- the model arch. On the ba si s ofgeometric s imilitude only, the predicted load to produce failure f or Str ucture 3.l.c by usingthe values obtained fr om the model arc h is calculated as follows:

Pm X f ppP = f m

Where: pp = Fail ure load, pro totype. (Assume that the dynamic load is carrieda s a stat ic load and that the concrete strength, fc, is increased fordynamic capacity, Reference 5).Stati c fai lure load, model.occu rred at 140 ps i and the other at 170 psi ; however, the effectiveload on th e arch must be computed by reducing the pressures by 28and 25 percen t, respectively, to account fo r the load loss to thewalls of the tes t container. The effective loads are therefore 101and 128 psi, respectively, the averag e being 115 ps i. )by a dynamic incr eas e factor of 0.85 X 1.30 equals 5,300 psi. )

pm = (Section 2.1.2: Fai lure on one side

fp = Concrete strength, prototype. (4,780 ps i fro m Table 2.5 multipliedf m = Concre te strength , model (3,000 psi).

Then:115 ps i x 5,300 psi = 203 psiPP = 3,000 psi

If a value of plus or minus 10 percent is assum ed for the variance of co ncrete strength, then thepr es su re to cause failure would range fro m approximately 180 to 220 psi. The effect that theend walls of the prototype str uctu re had in supporting pa rt of th e ove rpre ssu re load is not in-cluded nor is the magnitude of that load known.dence of compres sive spalli ng indicate that the arch may have been very close to fail ure.displacement, as well as relativ e deflections of the ar ch and floor sla b with resp ect t o thespringing lines of the arches . The total permanent downward displacemen ts of the four tes tstr uctu res, referen ced to a survey point located on the top of the entranceway of each struct ure,is presented in Figure 4.1, showing that the displacement caused by the bla st increas ed li nearlywith air over pres sur e up to the 200-psi level.

These crude calculations coupled with the evi-It was found that the four st ru ct ur es underwent a gr os s transient and permanent downward

4.2.1 Transient Response to Earth Press ure . To represent graphically the transient responseof the ar ch to the eart h pr es su re o r ground shock, sequential plots of e ar th pr es su re and de-flections (Structure 3.1.b) with resp ect to time, along with the respect ive ground-surface ai roverpressures, ar e shown in Figure 4.2. In the sequential plots, the base (line AB) has beenremoved from the arc h proper, thus giving two distinct plots (i . e. , ar ch and base slab) of ea rthpr es su re and deflection. The radial arch deflections a r e plotted with respec t to the springingline, whereas the base s lab not only shows the rel ativ e deflection of the center of the base slab

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5) plumbbob nv test blast-loading-and-response

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