Web crippling of stainless steel built-up sections subjected to interior-two-flange loading

A built-up section is a composite section assembled from at least two component sections using screws, welds or bolts, providing good load-carrying capacity, optimised cross-section properties and high material efficiency. This paper focuses on the web crippling behaviour and resistances of stainless steel built-up I-sections and box-sections under Interior-Two-Flange (ITF) concentrated transverse loading. An experimental programme was firstly conducted on 23 stainless steel built-up section specimens subjected to ITF loading, including fourteen specimens with I-sections and nine specimens with box-sections. A numerical modelling programme was also performed to investigate the web crippling behaviour of stainless steel built-up sections with wide ranges of screw arrangements, cross-section dimensions and bearing lengths. Finite element (FE) models were validated against the experimental data, confirming the capability of the FE models to accurately replicate the ITF loading test results. After validation of the FE models, parametric studies were conducted to generate additional numerical data. The experimental and numerical data were then used to assess the current American specification and European code for designing stainless steel built-up sections under ITF loading. The assessment results revealed that the American specification offered overall accurate failure load predictions though some were unsafe, while the European code provided excessively conservative and scattered failure load predictions. Hence, an improved design approach was proposed and considered the effects of the screw arrangements and material properties of stainless steel, offering accurate, consistent and safe failure load predictions of stainless steel built-up sections under ITF loading.