Beggs deformeter gauges
Date: early 20th-mid 20th Century
Inventory Number: 1999-1-0064
Classification: Gauge
Dimensions:wooden case holding various components: 6 × 33 × 25.8 cm (2 3/8 × 13 × 10 3/16 in.)
Accessories: 6 deformeter gauges;
22 plugs;
2 cylindrical plastic boxes containing screws and metal strips for fastening the ends of the structure;
metal stylus;
2 metal pins;
2 celluloid wedges;
1 rectangular celluloid piece with a wedge coming out of one end
DescriptionInstruments in wooden case with steel hinges. In the front and rear parts of the box are six metal deformeter gauges made up of parallel metal bars. On the insides of the bars are two v-shaped notches in between which are nested white celluloid plugs. Both bars have pin holes at the midpoint toward the inside part of the bar and at the center of either half of the bar. Each bar each has a trapezoidal clamp plate fastened to it by four screws, each on one corner of the plate. One bar in each gauge has two screw holes in either side to fix it to the drawing board. The outside edges of these bars contain screws that connect the two bars. In between the heads of the screws and the bars are springs that keep the two bars pressed against each other when no plugs are inserted. The other bar has on its outside two thin rounded rectangular metal strips in stacked formation.
On both sides of the middle of the box are plastic cylindrical containers. The one on the left contains replacement parts for the gauges such as springs and small rectangular plates for clamping down other parts of the structure. Each plate has a small pinhole in the middle and larger holes on either end for screws. The larger holes are the same distance apart as the screw holes on the smaller side of the trapezoid so that they can be fastened to the gauge. The plates come in two varieties: One is thin and smooth, the other is thick with a rough-texture cross-hatch pattern on one side. The container on the right contains slotted screws of two different lengths. A substantial part of the length of the screw is not threaded.
In the middle of the box are circular slots containing cylindrical plugs made of a special hard steel with rounded celluloid caps. The caps come in five colors. The top row contains twelve plugs, all of which are clear with a red tint. Under this row are eight plugs, two of each color: yellow, maroon, black, and dark red.
The plugs of the caps are cylindrical except for one quadrant, which is flattened. On this flattened portion is a number, each number corresponding to a particular color: clear red=.32505, yellow =.30700, maroon=.34302 and .30699, black=.32231 and .32771, dark red=.34301. The maroon plugs are flattened in one quadrant; the diameter from the flat part of the circle is given as the second number. The black plugs are of different sizes. The plugs in the bottom row are flanked by two metal pins with rough-texture cylindrical heads. The pins fit into the pinholes of the gauges, so they may have been used either to pin the gauge to the drawing board rather than screwing it in or to temporarily guide the positioning of the gauge before screwing it into the board. In the center of the box is the tip of a metal stylus with a rough-texture head that could be inserted into another device such as a drill.
Also in the box are assorted celluloid pieces, one rectangular, two in the shape of a cross piece.
Signedon inside cover: GEO E. BEGGS
on left side of deformeter gauge: Pratt & Whitney Co. / Hartford, Conn. USA
on right side of deformeter gauge: GEO. E. BEGGS / PRINCETON. N.J., U.S.A.
Inscribedon inside cover: BEGGS / DEFORMETER / GAGES;
bottom line after signature: PRINCETON, N.J. U.S.Aon clear red cap of plug: .32505;
on yellow cap of plug: .30700;
on maroon cap of plug: .34302 / .30699;
on black cap of plug: .32231;
on dark red cap of plug: .34301;
on top right corner of top left gauge: 541;
on top right corner of top center gauge: 538;
on top right corner of top right gauge: 539;
on top right corner of bottom left gauge: 542;
on top right corner of bottom center gauge: 537;
on top right corner of bottom right gauge: 540
FunctionA means of predetermining the stress resistance of bridges, dams, and similar structures. This method involved making celluloid scale models and measuring the strains on them at various points. It was used to find thrust, moment, and shear stresses on a structure whose static equilibrium equations are unsolvable.
The user, normally an engineer, would cut a structure, such as an arch, out of a piece of paper or celluloid. The deformeter gauge, a set of parallel metal bars, would be attached to an end of the structure, while the other ends of the structure would be fastened to the drawing board, either with other gauges or with one of the metal strips pictured in the cylindrical box on the left. The rest of the structure would rest on steel balls on pieces of plate glass, to assure maximum freedom of motion.
The "normal" plugs would be inserted into the V-shaped notches on the inside edges of the bars in the deformeter gauge. The gauge would be fastened to the drawing board through the screw holes on either side of one of the bars. This is the fixed bar. The end of the structure would then be fastened to the movable bar by means of the trapezoidal clamp plate. A filar micrometer would then be used to measure the positions of certain points on the structure, marked with a dot or a pin prick. A micrometer allows a user to make microscopic adjustments by turning a screw and then measure it in cross hairs. The new position of the dot would be measured by adjusting the cross hairs of the micrometer to align on the new position of the dot. The horizontal and vertical motions would therefore be established. This measurement using the microscope would be performed at several points on the model.
In order to test the stresses on the structure, the normal plugs would be removed by inserting celluloid wedges into the ends of the gauge. New plugs would be inserted and the new position measured. The thrust, or the force with which the structure presses against the foundation, would be measured using large and small plugs of the same size. These are the yellow plugs (.30700 cm in diameter) and the dark red plugs (.34301 cm in diameter). The smaller plugs would be inserted, then the larger plugs. Both would be compared to the normal position. To test the moment--the tendency of the structure to bend--two plugs of different sizes are inserted into the gauge, which causes the moving bar to rotate slightly due to the difference in size of the plugs. The shear stress would be measured with plugs that are flattened on one side. This would cause the free bar to move horizontally and thereby apply a force perpendicular to the vertical axis of the structure.
The pinhole in the free-moving bar would be used in case a pivot joint had to be created in the structure. A hole would be made at the pinhole in which a ball, of slightly larger diameter than the structure, would be inserted. The ball would rotate freely in the pinhole and allow the structure to rotate but still keep it in position for measurement of thrust and shear forces.
Historical AttributesGeorge Erle Beggs, a professor of civil engineering at Princeton, used instruments of this type when working as a consultant for the Arlington Memorial Bridge, the Stevenson Creek Dam, the San Francisco-Oakland Bridge, and the towers on the Golden Gate Bridge. Beggs deformeter gauges have been used internationally by engineers.
Primary SourcesFor a full description of the function of the instrument in "Designs Concrete Arches with Microscope: Scientist Invents Method of Using Frail
Paper Models to Test Strength of Complicated Engineering Structures. Popular Science
(November 1922): 47, click here.
ProvenanceDepartment of Engineering and Applied Sciences, Harvard University.