Document Type

Thesis - Open Access

Award Date

1971

Degree Name

Master of Science (MS)

Department

Civil Engineering

Abstract

In construction of plate girder bridges, when no ground supported falsework is used, metal brackets bolted to the web of the exterior girders are used to support construction loads. The loads include the weight of the falsework, the weight of the freshly poured concrete of the overhanging portion of the bridge deck, and the weight of the finishing machine. Figure 1 shows a cross section of the bridge with the bracket mounted on the exterior girder and formwork in place. The brackets transmit to the plate girder web a vertical shear force and a couple. The couple applied to the girder web causes both significantly high stresses and deflections which, in most cases, have not been considered in designing the girder. Since the deflection allows rotation of the bracket, the overhanging portion of the deck is lowered causing a corresponding lowering of the finishing machine. The result is an undesirable decrease in deck thickness over the girders. Figure 2 shows construction brackets mounted on a bridge girder before formwork was in place. At the present time in South Dakota, it is common practice to place the brackets at a distance of six inches or less from the nearest stiffener. Since stiffener spacing cannot be standardized economically across the entire span, a bracket to be placed without regard to stiffener spacing is needed. If brackets could be placed at standard intervals, the necessary formwork could be standardized and used on different bridges. Such standardization would contribute a great deal to economy in bridge construction. The newly recommended Load Factor Method of design which-would eliminate the lateral stiffeners in areas of low shear dictates a need for a bracket that can be used without regard to stiffener spacing. Therefore stresses and deflections relative to bracket depth and distance from the nearest stiffener are being studied to determine if certain brackets could be placed without restriction to distance from the nearest stiffener.

Library of Congress Subject Headings

Strains and stresses
Brackets
Girders -- Testing
Bridges -- Design and construction

Format

application/pdf

Number of Pages

72

Publisher

South Dakota State University

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