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Each pair was isolated from the others so that a failure of one pair would not relieve the blast loading on adjacent pairs. Blast seals were placed around the periphery of each slab to prevent pressure leakage

to the inside of the chamber.

The intent was to have blast loading on only one side of the slab. Actually some pressure did exist on the underside, because the deflection of the slab compressed the air inside the chamber. The chamber was constructed with the slabs at ground level so that the blast loading would be free from the uncertainties of diffraction, that is, the blast loading on the slabs was the same as that measured by a pressure gage placed at the ground surface.

The physical results of the experiment are shown in figure 2.

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FIGURE 2.-Table 3.1. Station 8-34.2-8017.01 postshot.

The forward pair was designed for the expected yield; the remaining pairs, to cover uncertainties in yield.

Mr. HOLIFIELD. How thick were those slabs?

Mr. VORTMAN. They were 10 inches thick.

Mr. HOLIFIELD. Were they reinforced with steel?

Mr. VORTMAN. Yes. In each pair one of the slabs was reinforced with rail steel and the other reinforced with intermediate grade steel. Mr. HOLIFIELD. What was the pressure per square inch?

Mr. VORTMAN. Somewhere on the order of 7 pounds per square inch. Mr. HOLIFIELD. Could you tell us offhand what that pressure was in relation to the size of the weapon and the distance from the weapon or do you have that information?

Mr. VORTMAN. I do not have that. The yield has been announced, however, as 43 kilotons.

Mr. HOLIFIELD. Could you give an approximation of the distance? Mr. CORSBIE. I do not recall the distance. We can get that for you. Mr. HOLIFIELD. Was that an air shot?

Mr. VORTMAN. It was a tower shot.

Mr. CORSBIE. It was on a 700-foot tower. It was the so-called Smoky shot. It was announced as 43 kilotons.

Mr. HOLIFIELD. Just about twice the size of the Hiroshima-Nagaski bomb?

Mr. CORSBIE. Yes, sir.

Mr. HOLIFIELD. If you will furnish the distance on that it will give us some idea of what it means.

Mr. VORTMAN. We will provide you with the distances.

(The following information was subsequently received:)

The distance at which the Plumbbob project 34.2 was located at 7 pounds per square inch was 4,200 feet.

Mr. HOLIFIELD. Three feet of dirt over that would have increased the protection from a blast standpoint? I know it would from radioactivity.

Mr. VORTMAN. Three feet of earth certainly would have. However, it would have decreased the accuracy with which we could have predicted the deflection of the slabs. We were trying in this experiment to achieve maximum deflections because we wanted to better understand the behavior of the two types of slabs.

Mr. HOLIFIELD. Now, let me ask you, if that had been in the form of an arch, would you have had a stronger surface there and more resistance than as constructed?

Mr. VORTMAN. I am sure an arch shape would have been stronger. However, it would not have been compatible with the purposes of this particular experiment.

Mr. HOLIFIELD. All right. Proceed.

Mr. VORTMAN. This slide illustrates the deflection of the slabs in the particular experiment.

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Preshot predictions based on assumed material properties and pressure loading.
Deflection exceeded gage capacity. The 25.0 is the permanent deflection measured with a steel tape

Mr. HOLIFIELD. What is the meaning of those figures? What does that register? Pounds per square inch?

Mr. VORTMAN. In the first column are the maximum centerline deflections in inches. In the second column the permanent centerline deflections in inches-that is, after it had gone through the maximum and recovered to an amount which was permanent deflection; and the last column is the maximum centerline deflection predicted prior to the shot, also in inches.

The slabs were designed for a predicted yield of 45 kilotons, with a spread between 40 and 50 kilotons.

The actual yield, 43 kilotons, was 5 percent less than the yield designed for. Consequently, the actual blast loading, as indicated by the impulse was 7.5 percent less than the computed for the predicted yield. These uncertainties being taken into account, the average actual deflection of all slabs was within 15 percent of that calculated for the pressure wave anticipated from the predicted yield.

Mr. HOLIFIELD. In making your testimony, try to identify for the record, in place of using such terms as "this column to that column," use "first column to third," and so forth, and also identify each one of these slides by your identification number, because we will ask you to supply us typed copies of these slides to place in our permanent record.

Mr. VORTMAN. Copies of the slides have been furnished with the statement.

Mr. HOLIFIELD. Then identify them in your testimony by whatever identification you have.

Mr. VORTMAN. Very well. The average maximum centerline deflections predicted prior to the shot, for the third column, are within 15 percent of the maximum centerline deflections in inches, measured after the shot, shown in the first column.

Two major points emerge from this experiment:

1. The blast loading produced on a structure by a device of known yield can be estimated quite accurately if the uncertainties of blast diffraction are eliminated, as they were in this experiment by using a ground-level structure.

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2. If the blast loading is known accurately, the response of simple structures can often be calculated with a precision which is surprising to the layman.

It is now appropriate to go from ground-level structures to aboveground structures on which blast loading is complicated by the diffraction of the blast wave around the structure.

Aboveground structures-Operation Greenhouse, project 3.1.1: During Operation Greenhouse, the Office, Chief of Engineers, sponsored a three-story, aboveground structure with reinforced concrete, shear-wall sections, steel-framed sections, and reinforced-concreteframed sections, figure 4.

The displacements of the roof, third, and second floors of the steelframed building were calculated before the test by estimating blast loads, measured during the test, and were calculated after the test from measured blast loads.

Results can be summarized as below, the measured displacements being taken as unity:

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Section 2 was the structural-steel building. No. 3 was identical, but with reinforced-concrete columns and beams.

I have here the roof, third floor, and second floor, and have normalized the deflections or displacements of those floor levels. The preshot calculations for the roof deflection were 1.11 larger than the measured deflection. The postshot calculations, that is, calculated from the blast pressures measured during the shot, were three-fourths of the deflections measured. Results for the other two floors are as shown.

Thus, for a relatively complex structure, the calculated response with within 50 percent of the measured response. Calculations for the other six sections were in some cases better and in some cases worse than in the steel-framed sections.

Mr. HOLIFIELD. I think this shows clearly the difference between laboratory calculations and actual results. It shows, without doubt, if you wish to have accurate knowledge or information on a subject, that you must go through the actual test to put into proper perspective the validity of your calculations.

Mr. VORTMAN. Operation Teapot, project 34.1: At Operation Teapot, a series of aboveground, utility-type, personnel shelters were tested. Insofar as these were planned as dual-purpose structures, the concept was a step in the right direction.

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