Arul Jayachandran S

Uprights act as a column member in the rack system. In pallet racking systems, all upright sections are perforated to accept the hooks of the beam end connector and are the heart of the structural system. The perforations not only play an important role in the rack industry (for holding component in place), but are prone to more problems compared to any other form of structural member without perforation. The present study focuses on the behavior of perforated uprights under axial concentric loading. For better understanding, experiments were conducted on four specimens of steel rack uprights, by varying the thickness of sections as 1.6 and 1.8 mm with limitation on the slenderness ratio 10 and 18. Experimental investigations on the cold formed upright sections were studied for different type of configuration and their results are presented. Stress distribution across the specimen is also presented.

This paper presents the application of constrained spline finite strip method (cSFSM) for cold-formed steel members with complex edge stiffeners. In this method, the principles of GBT are used to develop restraint matrices corresponding to local, distortional and global buckling. These matrices are applied in generalized eigen value equation by using transformation technique. The critical buckling stresses were calculated separately for pure local, distortional and global buckling. Based on the formulation, cross sectional geometries having complex lips are analysed to study the variations in buckling stresses developed. The increase in complexity of lip stiffeners increases the local buckling capacity of the cross section. However, for distortional buckling, the cross sections with inward lip stiffener offer higher buckling capacity than those with outward lips. The influence of lip stiffeners on global buckling was observed to be marginal from the present study.

In this paper, a mode identification technique in the context of spline finite strip method (SFSM) is presented to compute the contribution of primary (global, distortional and local) and secondary (shear/transverse extension) buckling modes. The base vectors corresponding to individual buckling modes are developed based on the principles of generalized beam theory. The buckling mode shape in SFSM is approximated as a linear combination of these orthonormal base vectors to evaluate the participation of individual buckling mode. The proposed mode identification technique is able to successfully quantify the participation of different buckling modes and the mode participation is comparable with mode identification using finite strip method (FSM) and generalized beam theory (GBT). Illustrative examples are presented to calculate the participation of individual modes in cold-formed steel sections under different loading and boundary conditions. Also the specific application of mode identification in SFSM is demonstrated.

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.

This paper presents a brief review of previous research work done on uniaxial compressive behavior of concrete filled steel tubular (CFT) columns and the resultsof experimental study conducted on twenty four number of cold-formed steel square sections filled with conventional concretes of grade M30 and M60 tested under uniaxial compression. The effect of length to breadth (L/B) ratio of square steel tubes and concrete core strength of CFTs on axial compressive strength and behavior of CFT columnswas studied. The experimental strength values were compared with predictions using Eurocode 4-1994, ACI 1999, AS 3600-1994, AISC-LRFD-1999, AISC 2005, GJB 4142-2000 an BS5400-1979 and from equation suggested by previous researcher. The effect of breadthtothickness (B/t) ratio, % steel area contribution and constraining factor on axial compressive strength was also examined. The results showed that the axial compressiv strength of CFTs increases due to confinement effect of concrete core on steel tubes andthe estimation of axial compressive strength using all methods is conservative. modified equation is also suggested.

In this paper, an analysis procedure has been presented for cold-formed steel sections, for decomposing the buckling modes obtained using spline finite strip method (SFSM) into their primary and independent buckling modes such as local, distortional and global buckling. This procedure utilizes principles of generalized beam theory (GBT) to evaluate the restraint matrices corresponding to different modes. The restraint matrices are integrated in to spline stiffness matrices using transformation technique to extract pure modes corresponding to local, distortional and global modes. The proposed analysis technique termed as constrained spline finite strip method (cSFSM) has been validated for cold-formed steel open cross-sections subjected to axial compression and bending under various boundary conditions. The results are in agreement with buckling stresses evaluated using constrained finite strip method (cFSM) and GBT.