CCFSS Library (1939 - present)

Abstract

INTRODUCTION Light gage steel panels are often used as wall sheathing, roof decking or floor covering in steel framed buildings. These panels carry loads normal to their plane by virtue of their bending strength. Also, diaphragms formed by interconnecting such panels can resist shear deformation in their plane. Because of this shear resisting capacity, diaphragms can be very effective in bracing columns and beams of a steel frame against lateral buckling and, thus, increase the load carrying capacity of these members. For wall columns, such diaphragm bracing may be either directly attached or connected to girts which in turn are connected to the columns. The ribs of the panels must be perpendicular to the members to which they are attached. These diaphragms as wall, roof or floor, must be present in any event, and therefore, are available at no extra cost. If properly utilized for bracing, they can lead to economical design of beams and columns. Research has been conducted at Cornell University since 1961* (1),(2),(3) to determine the increased load carrying capacities of beams and columns due to diaphragm or diaphragmgirt bracing. Based on the results of the investigation to date, recommendations are made in this report for the design of beams and columns considering the effect of diaphragm braci~g. * Superscripts in parentheses refer to the numbers in the References. Design criteria are given in Part 2; the general design procedure in Part 3, and the specific design formulae in Part 4 are illustrated by some practical examples in Part 5. The design procedure suggested herein is based on the ultimate load capacity of the beams or columns, utilizing a conservative estimate of the strength and rigidity of the diaphragm bracing. Effectiveness of diaphragm bracing or diaphragm-girt bracing in preventing lateral buckling of beams and columns depends on its two fundamental characteristics: (1) rigidity, and (2) strength. In general, it is not economical to provide anything less than "fUll" bracing, where "full" bracing is defined as bracing such that any increase in rigidity or strength of diaphragm will not cause any substantial increase in the load carrying capacity of the braced members. Therefore, the design procedure in this report is limited to only "fullyli braced beams and columns. The procedure is based on analyses of I-section beams under uniform moment, and I-section columns under axial load. These analyses have been substantiated by tests of thirtyfive diaphragm-braced assemblies as reported in the references. Information regarding the load carrying capacities of beams and columns with less than "full" bracing can be obtained from Reference 3. The capacity of channel and Z-section beams SUbjected to uniform moment also is discussed in Reference 3. Cantilever beams and channel and Z-section beams subjected to loads in the plane of the web are currently under investigation. Light wall studs braced by wallboard on one or both faces are no different basically from columns braced by light steel diaphragms. In order to make the methods developed here applicable to such wall studs, the Appendix gives a few typical test values for diaphragm rigidity and strength of customary types of wallboard.

Department(s)

Civil, Architectural and Environmental Engineering

Sponsor(s)

American Iron and Steel Institute

Research Center/Lab(s)

Wei-Wen Yu Center for Cold-Formed Steel Structures

Publication Date

01 Oct 1968

Document Version

Final Version

Document Type

Technical Report

File Type

text

Language(s)

English

Technical Report Number

Report No. 332

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