Experimental investigation and evaluation of Direct Strength Method on beam-column behavior of uprights

• Experiments on concentrically/eccentrically loaded cold formed steel uprights.
• Direct Strength Method (DSM) is briefed in general for beam-column.
• Need for choosing appropriate yield moment has been detailed with examples for DSM.
• Linear and Non-Linear Interaction of DSM equations for beam-column strength check are compared.

Uprights in storage racks being predominantly subjected to axial compression are also subjected to bending moments, hence acting as beam-columns by nature. The design of uprights is currently based on experimental or high-end computational methods, but analysis based-design involves lesser design office effort enabling development of innovative and optimized sections. The major challenges in this design are perforation, buckling interaction and combined loading. Although recent attempts use Direct Strength Method (DSM) to determine the nominal strength of uprights, experimental evidence on beam-column behavior of uprights that validate analytical equations are scarce. With this background, 16 experiments were carried out on uprights subjected to axial or biaxial compression, considering biaxial compression for constant and linearly varying moments. Interaction of distortional mode with global modes is evident from the experiments, which is generally ignored in DSM. In this paper, DSM is briefly explained and the choice of appropriate yielding moment is exemplified. The experimental results are presented in terms of DSM for both Linear Interaction (LI – from current code of practice) and Nonlinear Interaction (NLI – from literature). The results show that NLI may lead to unconservative design for eccentrically loaded specimens with linearly varying moments.