Development and validation of a model to calculate full-range response of bolted angle cleats in bending

Abstract

This study investigates the full-range behaviour of bolted angle steel cleats, commonly used in beam-column connections of steel structural frameworks. Eight experiments were conducted on bolted angle cleats in bending with four different configurations. Complementary finite element simulation models were developed, incorporating a ductile fracture model, termed Lode angle modified void growth model (LMVGM). The proposed finite element model effectively captures cracking in the angle cleats under multi-axial stresses and plastic strains. Test and finite element analysis results showed that the bolt gauge dimensions of the legs of the angle connected to the column and beam flanges (referred to as the column leg and beam leg, respectively) affect the fracture location, which tends to initiate within the plastic hinge line that forms in the column or beam leg with the larger bolt gauge. Specifically, the bolt gauge dimension refers to the distance between the angle heel and bolt hole centre on either column or beam leg. Additionally, a measurable reduction in the angle plate thickness (up to 14 % reduction) was observed in the plastic hinges due to the presence of high tensile stresses resulting from the tensile membrane action developed in the transverse direction of each leg under large deformations. Based on observations from the tests and finite element simulations, a theoretical model is proposed to predict the full-range behaviour of angle cleats. The theoretical model incorporates the gradual formation of a plastic bending mechanism, nonlinear response due to material yielding and large-deformation response (membrane action), reductions in plate thickness and bending strength due to local plastic flow in the plate hinges, and bolt slippage. The proposed model was validated using the angle cleat tests presented herein, showing substantially better accuracy than the model codified in EN 1993-1-8. The proposed model was incorporated in the Generalised Component Method to simulate the moment-rotational responses of published bolted angle connection tests. The proposed model is shown to provide more accurate response curves compared to Generalised Component Method analyses that employ existing angle cleat models.