six panel bridge truss model, Harvard Bridge
Date: 1928
Inventory Number: 5817
Classification: Bridge
Dimensions:122 x 275 x 37 cm (48 1/16 x 108 1/4 x 14 9/16 in.)
box: 85.7 × 28.9 × 16.5 cm (33 3/4 × 11 3/8 × 6 1/2 in.)
Accessories: two cylindrical black weights; two pins with silver puck stands; small booklet describing experiments to perform with the bridge model
Bibliography:New Laboratory Experiments in Practical Physics
Laboratory Equipment for Physics: Educational and Industrial
DescriptionThe bridge stands on two double A-legs, each with four cross beams connecting the two A's. There are two horizontal aluminum beams, each connecting two A-shaped legs. They form the bottom edge of the model. Each horizontal aluminum beam acts as the bottom edge of a symmetrical trapezoid. The trapezoids constitute the frame of each side of the bridge. The outermost edges of each trapezoid are constituted by mahogany beams with aluminum foil at each end. Each trapezoid contains the following crossbeams and supports: two X-shapes in the center, each made of aluminum beams and each framed by a vertical mahogany beam (with aluminum foil at each end) on either side, a V-shape made of aluminum beams on each side such that the top of the angled beam points to the outside poles of the bridge. The two parallel trapezoids and their various beams and supports are connected in various places by shorter cross beams for added support.
Two cylindrical black iron weights, each with a metal loop on the top, and two round silver pucks, each with a vertical pin emerging from the center.
Signedunsigned
FunctionThe model demonstrates the engineering principles deployed in a six panel bridge truss. The model specifically depicts the Harvard Bridge. The weights and pins are meant to test the structural integrity and tension of various components of the bridge. A small booklet containing and illustraing possible experiments accompanies the model.
A description of such an experiment with a bridge truss is described in Black's New Laboratory Experiments in Practical Physics, pp. 77 - 80. In that experiment description, the following explanation of the basic principles of bridge trusses is described as follows: "A modern bridge truss is made up of a series of triangles, and each side of the triangle, called a member, has to push or pull on the pins at the corners to keep the truss in position" (77).
Historical AttributesDesigned by Prof. Harvey N. Davis, Harvard Professor.
Primary SourcesL. E. Knott Apparatus Company, Harcourt Equipment for Physics; Standard for Education Since 1895, Catalogue 33R (Cambridge, MA: Knott, 1928), p.65.
ProvenanceFrom the attic of Lyman Lab, Department of Physics, Harvard University, 1952.
Related WorksN. Henry Black, New Laboratory Experiments in Practical Physics to accompany Black and Davis "New Practical Physics" (New York: The Macmillan Company, 1935), pp. 77 - 80.