Experimental and Analytical Investigation of the Shear Strength of Unstiffened Tapered Steel Members

Abstract

Tapered beams and columns are often used in single story gable framed steel buildings for reasons of economy. By varying the resistance to bending in similar proportion to the bending moments, more economical structures can be obtained. The beam and column connection, or knee area, is generally subject to the greatest bending moments. It is therefore comprised of the deepest sections of the tapered members, which also possess the least resistance to shear buckling.

The web element's stress distribution in this region of relatively complicated geometry is unknown. For this reason, web stiffening plates are commonly used to brace the slender web elements against elastic shear buckling. The design and proper installation of these relatively small elements, while proven to be effective, is also costly. Because it is desirable to remove the stiffeners, the shear behavior of unstiffened tapered members near the moment connection was the primary focus of this study. Four knee area specimens were tested to failure under simulated gravity load conditions.

The specimens were analyzed according to the AISC shear provisions for prismatic members. The appropriateness of a modified shear force, which accounts for the influence of inclined flanges, and the role of initial web imperfections were examined as well. Finally an analysis method which most consistently produces conservative results is proposed.