CCFSS Library (1939 - present)

Abstract

Shear-resistant light-gage metal diaphragms can be very effective in increasing the load carrying capacity of beams continuously braced by diaphragms, or of columns braced by girts which in turn are braced by diaphragms, if proper connections are made between the individual elements. In this thesis, behavior of diaphragm-braced I-beams, channel beams, and Z-beams under uniform moments, and the behavior of axially loaded I-section columns braced by girts which in turn are braced by diaphragms are investigated.

Load-deflection relationships of diaphragm-braced beams are obtained taking into consideration the initial imperfections of the beams and using the equilibrium method. Critical moments of diaphragm-braced beams are derived from the loaddeflection relationships by letting the initial imperfections equal zero and solving the resulting eigenvalue problem. A procedure to determine the load carrying capacities of diaphragm- braced beams is given using an assumed criteria of failure for beams and diaphragms. Using the above procedure, load carrying capacities of diaphragm-braced beams are calculated in two examples; they range from 80% to 85% of the corresponding critical moments.

A test was conducted on an assembly of four diaphragmbraced I-beams, and the moment sustained by the beams was 10% smaller than the predicted critical moment. Three tests were and the moments sustained by the beam assemblies ranged from 75% to 99.6% of the corresponding critical moments. Tests conducted on assemblies of two diaphragm-braced I-beams are also reported here. In general, the experimental and predicted load deflection relationships are in fairly good agreement for both diaphragm-braced I-beam and channel beam assemblies.

Load-deflection relationships of columns braced by girts and diaphragms are obtained taking into consideration the initial imperfections of the columns and using the energy method. The Rayleigh-Ritz technique is used to obtain an approximate solution. Similar to the case of beam assemblies, critical loads of column assemblies are derived from the load-deflection relationships. A procedure to determine the load carrying capacity of columns braced by girts and diaphragms is given using assumed criteria of failure of columns, girts, and diaphragms. Using the above procedure, load carrying capacities of two different wall columns are calculated and they.range from 68% to 83% of the corresponding critical loads.

Three tests were conducted on columns braced by two intermediate girts which in turn were braced by diaphragms, and the failure loads of the column assemblies ranged from 84% to 94% of the corresponding critical loads. Fully flexible, fully rigid, and semi-rigid girt-column connections were used in the . three tests. The experimental and theoretically predicted load-deflection relationships are in fair agreement.

Theoretical solutions for diaphragm-braced beams and for columns braced by girts and diaphragms were developed first in the elastic range and then extended to the inelastic range by suitably modifying the elastic modulii. The plastic moment of the beams or the Euler buckling load of the columns between successive girts appears to be theoretically attainable by using the diaphragm bracing.

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 Apr 1968

Document Version

Final Version

Document Type

Technical Report

File Type

text

Language(s)

English

Technical Report Number

Report No. 331

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