ABSTRACT

Bracing tubes of jackets are frequently loaded in compression by wave and wind forces. The members of deck trusses are often in compression. Conditions causing column failure are continually of concern to the designer. This paper summarizes 89 fabricated and solid section steel column tests. Columns with slenderness ratios over 100 followed Euler's curve. Intermediate columns with ratios from 50 to 100 followed the tangent-modulus theory. The AISC design formula always gives conservative values.

INTRODUCTION

The compression behavior of bracing members in offshore structures is of such importance as to warrant continued verification of column behavior through experimentation and comparison of test results with accepted methods of calculating buckling strength. This paper summarizes results of 89 fabricated and solid cross section structural steel column tests and discusses their behavior in comparison with the Euler-tangent modulus curves for upper limit and the AISC column formulas as lower limit of column strength.

The diagonal bracing tubes of the platform jacket are frequently loaded in compression by wave and wind forces; many of the truss members of the deck structure are loaded in compression. The conditions under which a simple compression member becomes a column are continually of concern to the designer. The purpose of this paper is to give the engineer a better appreciation of where calculated column strengths lie in comparison to experimental failures over a broad range of variables.

The solid round and solid square pin-end columns which were tested ranged from L/r of 45 to 195. There were 39 round and 42 square columns. Eight fabricated columns with pin-ends were tested, four X-shaped and welded from 3/16" plate with 1/2" square stiffeners along the outer edge of each web, and four diagonally braced rectangular lattice columns made of tubular material; the fabricated columns ranged from Llr of 47 to 118.

Electric resistance strain gages were used on the X-shaped specimens to check for torsion and to locate the buckling axis. Two transits positioned at an angle of 900 with one another were used to align the built-up tubular columns in the vertical loading frame and to determine when the columns began to buckle. Failure of the solid section columns was noted when the load indicator on the hydraulic testing machine faltered and began to recede.

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