Stress concentration factors in CFRP-reinforced KT-joints under multiplanar bending loads: experimental and numerical investigation

Composite materials are widely utilised for rehabilitating critical load-bearing members, including the joints of circular hollow section (CHS) structures, due to their enhanced performance and durability. The accurate prediction of stress concentration factors (SCFs) in CHS joints is challenging because of the complex stress distribution, especially under multiplanar loading conditions. Traditional empirical models predict SCFs only at specific locations, such as the saddle and crown, which are insufficient under multiplanar loading as the maximum SCF can occur elsewhere, potentially leading to inaccuracies in fatigue life estimations. This study aims to address these limitations by developing new empirical models for SCF prediction across the weld toe at the chord-brace interface. A comprehensive finite element analysis was conducted on 10,858 CFRP-reinforced KT-joints with varying configurations under uniplanar, biplanar, and multiplanar bending loads. Artificial neural networks (ANNs) were employed to create empirical models capable of predicting SCFs across diverse load scenarios. The proposed models were validated experimentally on a typical KT-joint, demonstrating a maximum error of less than 15 % at the location of peak SCF. These findings highlight the critical influence of reinforcement properties, such as thickness, orientation and elastic modulus, on SCFs and fatigue life. Future research should focus on enhancing the generalisability of these models to other CHS joints and considering practical factors, including residual stresses from welding and environmental effects like temperature and humidity.