The effect of the bolt spacing on the performance of the steel-aluminum composite mullions of curtain wall

The main purpose of this study was to investigate the effect of the spacing of through bolts on the performance of the steel-aluminum composite mullions (SACM) using finite element analysis, and the equations for the stress and composite stiffness at the midspan of the SACM considering the coefficient of shear resistance η were proposed. The results shown that the ultimate bearing capacity of the SACM with a full composite action is increased by 18% and 65% as compared with that of the SACM with no composite action and the pure aluminum alloy mullion. The deflection at the midspan of the SACM decreases with the bolt spacing decreases, indicating that the stiffness of SACM increase with the bolt spacing decreases, because SACM can enhance the material utilization of aluminum alloy and the capability of cooperative work of steel and aluminum alloy, in addition, the bolt spacing that equals a third of the span is sufficient to allow the steel and aluminum to have a desired composite action. The equations for the stress and composite stiffness at the midspan of the SACM under the condition of partial shear connection are derived, and the results calculated from these equations agree well with that obtained by the finite element method.