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Dongxiao Wu P. Eng. (Alberta, Canada)

 

Home  >> Tutorial >>  Single Angle Factored Compression Resistance As Per CSA S16-09        ? Buy This Document

 

 

1.0 INTRODUCTION

 

Although single-angle compression members, attached by one leg, appear to be very simple structural elements, they are amongst the most complex of structural elements to analyze and design. This is due to the end eccentricities and the fact that the principal axes of the angle do not coincide with the axis of the structure. The design of single-angle compression members, according to the Canadian standards, is not as straightforward as might be expected. There are numerous clauses to be considered in two standards. In some cases, all failure modes are not covered explicitly. The Canadian standards are examined and applied to the two generally accepted design approaches used in Canada and the United States. These approaches are

(i) to ignore the end eccentricities and to treat the angle as a concentrically loaded member and

(ii) to account for the end eccentricities by treating the angle as a beam-column.

A flow chart is presented which will guide the designer through the many clauses that have to be considered in the two standards. Some suggestions are made which should help a practicing engineer design single-angle compression members

that are attached by one leg.

 

Above is the abstract from Design of single-angle compression members according to the Canadian standards by Murray C. Temple published in Canadian Journal of Civil Engineering 23: 632-638 1996

 

In CSA S16-2009 Clause 13.3.3, Canadian steel code eventually provides an explicit guideline on single angle compression member design, following the exact same provision as AISC 360-05 Specification for Structural Steel Buildings Section E5.

The new approach uses modified slenderness ratios indirectly to account for bending in the angles due to the eccentricity of loading and for the effects of end restraint from the truss chords.

In CSA S16-2009 Clause 13.3.3.1, it specifies that the effects of eccentricity on single angle members are permitted to be neglected when the members are evaluated as axially loaded compression members using one of the effective slenderness ratios specified in Clause 13.3.3.2 or 13.3.3.3, provided that:

(a) members are loaded at the ends in compression through the same one leg

(b) members are attached by welding or by minimum two-bolt connections; and

(c) there are no intermediate transverse loads.

 

This guideline is to provide the single-angle capacity design chart, as per new provisions in CSA S16-2009, to facilitate the daily routine design.

 

Design Basis & Assumption:

1.       Angle design yield strength 300 MPa

2.       Neglect the effects of eccentricity with the use of modified slenderness ratio as per CSA S16-09 Cl 13.3.3.2 & Cl 13.3.3.3

3.       Assume single angle member and connection complies to conditions (a) (b) (c) as specified in CSA S16-09 Cl 13.3.3.1

4.       For class 4 angle section, effective yield stress Fye is used to calculate compressive resistance Cr as per

CSA S16-09 Cl 13.3.5 (b)

5.       Single angle is a member of planar truss

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2.0 DESIGN CHARTS

 

 

 

 

 


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