The span-wise coherence function of the aerodynamic lifting force in the
buffeting response of bridges is analyzed by using the lifting-surface theory of airfoils.
Result shows that the values of the coherence function are larger than those of the on-
coming span-wise wind velocity fluctuation, and the strip assumption has limitation in
some instances. Because the joint acceptance function based on the strip assumption
underestimates the response of structures to the wind force, a coherence function for the
aerodynamic lifting force along the span-wise direction is proposed , which is fit to be
used in the calculation of the joint acceptance function for the buffeting response of
bridges.