Abstract: Rectangular hollow tubes can be inserted horizontally into unstiffened steel plate shear walls. This arrangement reduces the wall’s vertical stiffness， thereby mitigating vertical stress and enabling the wall to primarily resist shear stress. This paper introduces vertical stiffness reduction factors for such walls. A numerical example shows that using two tubes per story with a flange width-to-thickness ratio of approximately 14 can reduce the vertical stiffness to about 0.3 times the original. The steel plate shear wall ultimately develops a diagonal tension field. The flexural stiffness and strength of the hollow steel tube walls provide anchorage for this tension field. Formulas for determining the required tube thickness in relation to the strength of the tension field are derived. Furthermore， 26 numerical examples are presented， calculating the tension field development factor and the vertical stiffness reduction factor. The range of parameters and results from these examples validates the feasibility of this approach.