Effect of grout properties on shear strength of column base connections: FEA and analytical approach

Concrete grout is used in most column base connections to facilitate the construction process and to ensure that full contact is achieved between the steel plate and the concrete pedestal. However, insignificant attention has been given to its use and performance while there is a lack of clear understanding towards its contribution to the shear strength of column base connections. A comprehensive finite element (FE) study is presented herein investigating the shear capacity of the column base connection on the grout thickness and strength. 3D FE models incorporate important behavioural aspects including the surface interaction and multi-axial constitutive models of the assemblages. The results of the investigation indicated that the introduction of grout improves the behaviour and strength of the column base connections significantly by developing a different load path system consisted of the grout strut, the friction between the base plate and grout, and the tension in the anchor rod due to second order effects. It is found that the current design codes of practice do not consider the positive influence of grout and lead to very conservative shear strengths. Furthermore, the paper proposes a mathematical equation to account for the lateral displacement which is overlooked in the current international regulations.