CCFSS Library (1939 - present)

Abstract

Introduction Roofing materials that combine shelter, fire safety, durability, and strength have largely replaced such historic types of roofing covering as straw, leaves, tile, bark and various wooden coverings. Thus, we have such modern roof coverings as asphalt composition, cement-asbestos, and metal. Of these, metal roofing is used more than any other on farm service buildings. Approximately 40 per cent of present day farm service buildings in the United States are roofed with metal. This proportion continues to increase as more and more metal roofing materials are made available for rural construction. The wide use of metal roofing is due primarily to its many advantages. Flat sheets of copper, zinc, aluminum, and galvanized iron have been used as roofing for more than half a century, offering not only shelter but added fire resistance and weathering ability. Even aluminum, considered a modern building material was used as early as 1895 to roof a building in Sidney, Australia. Most farm building roofs of steel or aluminum are made in various shapes and forms of corrugations which afford structural strength due to shape. Corrugated metal roofing materials require only “open slat” or “skip deck” roofing systems for support. In the stronger corrugations they require only “purlin” type backing. With such design the metal roofing provides both strength and economy. Metal sheet shapes such as 3V crimp, 5V crimp and standing seam requires either solid deck or “skip deck” backing since they do not use corrugations for structural strength. Metal sheets have long been used for forming into corrugated shapes to obtain desired properties for specific purposes. One early use for corrugated sections was for internal subdivisions in marine construction to resist lateral hydraulic pressures. In recent years the aircraft industry has developed many sizes and shapes of corrugations for the fabrication of airplanes. Common practice in multi-storied buildings is use of corrugated floor sections to support masonry floors. These are only a few of the fields of use; many special sizes and shapes are found in each. Usually, a sheet is corrugated and designed to provide greater stiffness and rigidity per pound of material used, as compared to flat sheets. Corrugated sheets give greater resistance than flat sheets to loads which tend to bend the sheet across the corrugations. Loads that exert this bending force are exemplified by wind and snow loads on corrugated metal roofs having purlin supports. This type loading is commonly referred to as “flexural loading.” Most corrugated shapes now in use have been established mainly through practical experience and trends toward standardization of design. Relatively little research data and theoretical evaluations have been used. With the general acceptance of corrugated sheets and the wide range of patterns available, it is desirable to have a common basis for comparing flexural strengths for design purposes. In the manufacture or design it would be desirable to compare the efficiency of use of given corrugated shapes; that is, which section will support the greatest flexural load per pound of material used. Such comparisons are not presently available. Commercial claims are being made that are not based upon controlled test conditions. A standard test procedure which could be used by all manufacturers would be valuable in that claims would be based on tests made under comparable conditions. Present formulas used in evaluating flexural properties of corrugated metal sheets are inadequate. Corrugations are designed principally by hit and miss methods. Proper evaluation of flexural strength would allow more accurate and economical corrugation designs. The flexural load which a corrugated sheet can support depends upon (1) size and shape of the corrugation, (2) width of the corrugated sheet, and (3) the material of which it is made. These characteristics are the flexural properties of the sheet. They determine the comparative strength and efficiency of one sheet as compared with another. Flexural strength, given major emphasis in this report, is of course, only one of several qualities that may be desired in a farm building roof.

Department(s)

Civil, Architectural and Environmental Engineering

Research Center/Lab(s)

Wei-Wen Yu Center for Cold-Formed Steel Structures

Publication Date

01 Aug 1954

Document Version

Final Version

Document Type

Technical Report

File Type

text

Language(s)

English

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